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Sample records for catalyzing ester bond

  1. Energy-efficient green catalysis: supported gold nanoparticle-catalyzed aminolysis of esters with inert tertiary amines by C-O and C-N bond activations.

    Science.gov (United States)

    Bao, Yong-Sheng; Baiyin, Menghe; Agula, Bao; Jia, Meilin; Zhaorigetu, Bao

    2014-07-18

    Catalyzed by supported gold nanoparticles, an aminolysis reaction between various aryl esters and inert tertiary amines by C-O and C-N bond activations has been developed for the selective synthesis of tertiary amides. Comparison studies indicated that the gold nanoparticles could perform energy-efficient green catalysis at room temperature, whereas Pd(OAc)2 could not.

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

    Science.gov (United States)

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

    2014-05-16

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

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

    Science.gov (United States)

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

    2015-10-12

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

  4. Lipase catalyzed ester synthesis for food processing industries

    Directory of Open Access Journals (Sweden)

    Aravindan Rajendran

    2009-02-01

    Full Text Available Lipases are one of the most important industrial biocatalyst which catalyzes the hydrolysis of lipids. It can also reverse the reaction at minimum water activity. Because of this pliable nature, it is widely exploited to catalyze the diverse bioconversion reactions, such as hydrolysis, esterification, interesterification, alcoholysis, acidolysis and aminolysis. The property to synthesize the esters from the fatty acids and glycerol promotes its use in various ester synthesis. The esters synthesized by lipase finds applications in numerous fields such as biodiesel production, resolution of the recemic drugs, fat and lipid modification, flavour synthesis, synthesis of enantiopure pharmaceuticals and nutraceuticals. It plays a crucial role in the food processing industries since the process is unaffected by the unwanted side products. Lipase modifications such as the surfactant coating, molecular imprinting to suit for the non-aqueous ester synthesis have also been reported. This review deals with lipase catalyzed ester synthesis, esterification strategies, optimum conditions and their applications in food processing industries.Lipases são catalizadores industriais dos mais importantes, os quais catalizam a hidrólise de lipídeos. Também podem reverter a reação a um mínimo de atividade de água. Devido sua natureza flexível, é amplamente explorada para catalizar uma diversidade de reações de bioconversão como hidrólise, esterificação, interesterificação, alcoólise, acidólise e aminólise. A propriedade de síntese de esteres a partir de ácidos graxos e glicerol promoveu seu uso em várias sínteses de esteres. Os esteres sintetizados por lipases encontram aplicação em numerosos campos como a produção de biodiesel, resolução de drogas racêmicas, modificação de gorduras e lipídios, sintese de aromas, síntese de produtos farmacêuticos enantiopuro e nutracêuticos. As lipases possuem um papel crucial nas indústrias de

  5. Preparing (Multi)Fluoroarenes as Building Blocks for Synthesis: Nickel-Catalyzed Borylation of Polyfluoroarenes via C-F Bond Cleavage.

    Science.gov (United States)

    Zhou, Jing; Kuntze-Fechner, Maximilian W; Bertermann, Rüdiger; Paul, Ursula S D; Berthel, Johannes H J; Friedrich, Alexandra; Du, Zhenting; Marder, Todd B; Radius, Udo

    2016-04-27

    The [Ni(IMes)2]-catalyzed transformation of fluoroarenes into arylboronic acid pinacol esters via C-F bond activation and transmetalation with bis(pinacolato)diboron (B2pin2) is reported. Various partially fluorinated arenes with different degrees of fluorination were converted into their corresponding boronate esters.

  6. Gold-catalyzed reactions of propargylic esters with vinylazides for the synthesis of Z- or E-configured buta-1,3-dien-2-yl esters.

    Science.gov (United States)

    Wagh, Sachin Bhausaheb; Liu, Rai-Shung

    2015-10-28

    Gold-catalyzed synthesis of buta-1,3-dien-2-yl esters by the reaction of propargyl esters with vinylazides is described; the reaction mechanism is postulated to involve a vinyl attack of vinylazides at alkenyl gold carbenes.

  7. Solvent effects on hydrogen bonding between primary alcohols and esters

    Institute of Scientific and Technical Information of China (English)

    DHARMALINGAM K.; RAMACHANDRAN K.; SIVAGURUNATHAN P.

    2006-01-01

    The interaction by hydrogen bond formation of some primary alcohols (1-heptanol, 1-octanol and 1-decanol) with esters (methyl methacrylate, ethyl methacrylate and butyl methacrylate) was investigated in non-polar solvents viz., n-heptane,CCh and benzene by means of FTIR spectroscopy. Formation constants and free energy changes of complex formation were determined. The dependence of the equilibrium constants and free energy changes of complex formation on the alkyl chain length of both the alcohols and esters are discussed. The solvent effect on the hydrogen bond formation is discussed in terms of specific interaction between the solute and solvent.

  8. Saliva-catalyzed hydrolysis of a ketobemidone ester prodrug

    DEFF Research Database (Denmark)

    Hansen, L.B.; Christrup, Lona Louring; Bundgaard, H.

    1992-01-01

    Saliva enzyme-catalysed hydrolysis of ester prodrugs or drugs containing sensitive ester groups may be a limiting factor for the buccal absorption of such compounds. Using the isopropyl carbonate ester of ketobemidone as a model substance of a hydrolysis-sensitive prodrug the esterase activity...

  9. Kinetically controlled synthesis of monoglyceryl esters from chiral and prochiral acids methyl esters catalyzed by immobilized Rhizomucor miehei lipase.

    Science.gov (United States)

    Acosta, Andreina; Filice, Marco; Fernandez-Lorente, Gloria; Palomo, Jose M; Guisan, Jose M

    2011-01-01

    Partial acylation of only one primary hydroxyl group of glycerol generates a chiral center at position 2. Rhizomucor miehei lipase (RML) catalyzes the kinetically controlled transesterification of different aromatic carboxylic acids methyl esters with glycerol. High synthetic yields of glyceryl esters (around 70-80%) were obtained even in the presence of significant concentrations of water (from 5% to 20%). After a long incubation of the reaction mixture in the presence of the biocatalyst only pure free acid was obtained. Other lipases (from Geobacillus thermocatenulatus and from Thermomyces lanuginose) also catalyzed similar kinetically controlled transesterifications although less efficiently. RML immobilized on Sepharose-Q showed a high activity and specificity, compared to the immobilization by other techniques, only producing monoglyceryl esters with all substrates. In particular, monoglyceryl-phenylmalonate product was synthesized in 82% overall yield and >99% diastereomeric excess at pH 7.0 and 37°C and 90% glycerol.

  10. Rhodium-catalyzed acyloxy migration of propargylic esters in cycloadditions, inspiration from the recent "gold rush".

    Science.gov (United States)

    Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M; Tang, Weiping

    2012-12-07

    Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most π-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed.

  11. Synthesis of Fluoroalkoxy Substituted Arylboronic Esters by Iridium-Catalyzed Aromatic C–H Borylation

    KAUST Repository

    Batool, Farhat

    2015-08-17

    The preparation of fluoroalkoxy arylboronic esters by iridium-catalyzed aromatic C–H borylation is described. The fluoroalkoxy groups employed include trifluoromethoxy, difluoromethoxy, 1,1,2,2-tetrafluoroethoxy, and 2,2-difluoro-1,3-benzodioxole. The borylation reactions were carried out neat without the use of a glovebox or Schlenk line. The regioselectivities available through the iridium-catalyzed C–H borylation are complementary to those obtained by the electrophilic aromatic substitution reactions of fluoroalkoxy arenes. Fluoroalkoxy arylboronic esters can serve as versatile building blocks.

  12. Lipase-catalyzed syntheses of sugar esters in non-aqueous media.

    Science.gov (United States)

    Kobayashi, Takashi

    2011-10-01

    The lipase-catalyzed reaction is useful to obtain sugar esters with chemically defined structures and will contribute to the synthesis of sugar-based compounds by a chemo-enzymatic pathway. The synthesis of sugar esters in nonaqueous media has been attempted for a quarter century. To facilitate the reactions, they have been performed either in an organic solvent with/without a polar adjuvant or in an ionic liquid, or by using a hydrophobic sugar derivative. In this review, the following points are discussed: (1) various synthetic methods of sugar esters; (2) role of the solvents or adjuvants; and (3) improvement in the productivity.

  13. Palladium-catalyzed α-arylation of zinc enolates of esters: reaction conditions and substrate scope.

    Science.gov (United States)

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

    2013-09-06

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

  14. Lipase catalyzed synthesis of aromatic esters of sugar alcohols

    NARCIS (Netherlands)

    Croitoru, R.; Broek, van den L.A.M.; Frissen, A.E.; Davidescu, C.M.; Peter, F.; Boeriu, C.G.

    2011-01-01

    Commercially available lipases (Candida antarctica lipase B, Novozyme 435, Thermomyces lanuginosus lipase, and Lipozyme TL IM), as well as sol-gel immobilized lipases, have been screened for their ability to acylate regioselectively xylitol, sorbitol, and mannitol with a phenolic ester in a binary m

  15. Transition-Metal-Catalyzed C-H Bond Addition to Carbonyls, Imines, and Related Polarized π Bonds.

    Science.gov (United States)

    Hummel, Joshua R; Boerth, Jeffrey A; Ellman, Jonathan A

    2016-12-12

    The transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds has emerged as a particularly efficient and powerful approach for the construction of an incredibly diverse array of heteroatom-substituted products. Readily available and stable inputs are typically employed, and reactions often proceed with very high functional group compatibility and without the production of waste byproducts. Additionally, many transition-metal-catalyzed C-H bond additions to polarized π bonds occur within cascade reaction sequences to provide rapid access to a diverse array of different heterocyclic as well as carbocyclic products. This review highlights the diversity of transformations that have been achieved, catalysts that have been used, and types of products that have been prepared through the transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds.

  16. PtCl2-catalyzed tandem enyne cyclization/1,2 ester migration reaction controlled by substituent effects of all-carbon 1,6-enynyl esters.

    Science.gov (United States)

    Huo, Xing; Zhao, Changgui; Zhao, Gaoyuan; Tang, Shouchu; Li, Huilin; Xie, Xingang; She, Xuegong

    2013-05-01

    On the move: A novel PtCl2-catalyzed tandem 1,6-enyne cyclization/1,2-acyloxy migration reaction was developed, which was shown to be controlled by substitution effects. Using this method, a series of substituted enol esters containing the cyclopentenyl motif were prepared in moderate to high yields.

  17. Accurate bond energies of biodiesel methyl esters from multireference averaged coupled-pair functional calculations.

    Science.gov (United States)

    Oyeyemi, Victor B; Keith, John A; Carter, Emily A

    2014-09-04

    Accurate bond dissociation energies (BDEs) are important for characterizing combustion chemistry, particularly the initial stages of pyrolysis. Here we contribute to evaluating the thermochemistry of biodiesel methyl ester molecules using ab initio BDEs derived from a multireference averaged coupled-pair functional (MRACPF2)-based scheme. Having previously validated this approach for hydrocarbons and a variety of oxygenates, herein we provide further validation for bonds within carboxylic acids and methyl esters, finding our scheme predicts BDEs within chemical accuracy (i.e., within 1 kcal/mol) for these molecules. Insights into BDE trends with ester size are then analyzed for methyl formate through methyl crotonate. We find that the carbonyl group in the ester moiety has only a local effect on BDEs. C═C double bonds in ester alkyl chains are found to increase the strengths of bonds adjacent to the double bond. An important exception are bonds beta to C═C or C═O bonds, which produce allylic-like radicals upon dissociation. The observed trends arise from different degrees of geometric relaxation and resonance stabilization in the radicals produced. We also compute BDEs in various small alkanes and alkenes as models for the long hydrocarbon chain of actual biodiesel methyl esters. We again show that allylic bonds in the alkenes are much weaker than those in the small methyl esters, indicating that hydrogen abstractions are more likely at the allylic site and even more likely at bis-allylic sites of alkyl chains due to more electrons involved in π-resonance in the latter. Lastly, we use the BDEs in small surrogates to estimate heretofore unknown BDEs in large methyl esters of biodiesel fuels.

  18. Rhodium-Catalyzed Acyloxy Migration of Propargylic Esters in Cycloadditions, Inspiration from Recent “Gold Rush”

    OpenAIRE

    Shu, Xing-Zhong; Shu, Dongxu; Schienebeck, Casi M.; Tang, Weiping

    2012-01-01

    Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most π-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative a...

  19. Enantioselective α-Hydroxylation by Modified Salen-Zirconium(IV)-Catalyzed Oxidation of β-Keto Esters.

    Science.gov (United States)

    Yang, Fan; Zhao, Jingnan; Tang, Xiaofei; Zhou, Guangli; Song, Wangze; Meng, Qingwei

    2017-02-03

    The highly enantioselective α-hydroxylation of β-keto esters using cumene hydroperoxide (CHP) as the oxidant was realized by a chiral (1S,2S)-cyclohexanediamine backbone salen-zirconium(IV) complex as the catalyst. A variety of corresponding chiral α-hydroxy β-keto esters were obtained in excellent yields (up to 99%) and enantioselectivities (up to 98% ee). The zirconium-catalyzed enantioselective α-hydroxylation of β-keto esters was scalable, and the zirconium catalyst was recyclable. The reaction can be performed in gram scale, and corresponding chiral products were acquired in 95% yield and 99% ee.

  20. Chiral Borated Esters in Asymmetric Synthesis:1.The First Asymmetric Reaction Catalyzed by Chiral Spiroborated Esters with an O3BN Framework

    Institute of Scientific and Technical Information of China (English)

    LIU, De-Jun(刘德军); SHAN, Zi-Xing(单自兴); QIN, Jin-Gui(秦金贵)

    2004-01-01

    The first asymmetric reaction catalyzed by chiral spiroborated esters with an O3BN framework was reported. In the presence of 0.1 equivalent of (R,S)-1 or (S,S)-1, acetophenone was reduced by 0.6 equivalent of borane in THF at 0-5 ℃ for 2 h to give (R)-1-phenylethanol of up to 76% ee and 73% isolated yield. Influence of reaction conditions on the stereoselectivity of the reduction was investigated and a possible catalytic mechanism of the chiral spiroborated esters toward the reduction was also suggested.

  1. Dehydrogenative Coupling of Primary Alcohols To Form Esters Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex

    DEFF Research Database (Denmark)

    Sølvhøj, Amanda Birgitte; Madsen, Robert

    2011-01-01

    The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the c...

  2. Enzyme-Catalyzed Polymerization of Beta-alanine Esters, A Sustainable Route Towards the Formation of Poly-Beta-alanine

    NARCIS (Netherlands)

    Steunenberg, P.; Uiterweerd, M.; Sijm, M.; Scott, E.L.; Zuilhof, H.; Sanders, J.P.M.; Franssen, M.C.R.

    2013-01-01

    The synthesis of poly-ß-alanine by a lipase catalyzed polycondensation reaction between ß-alanine esters is reported. The effect of different solvents, reaction temperatures and substrate/enzyme concentrations on polymer yield and degree of polymerization (DP) was determined. Also the effect of meth

  3. Rhodium(III)-catalyzed C-H activation/annulation with vinyl esters as an acetylene equivalent.

    Science.gov (United States)

    Webb, Nicola J; Marsden, Stephen P; Raw, Steven A

    2014-09-19

    The behavior of electron-rich alkenes in rhodium-catalyzed C-H activation/annulation reactions is investigated. Vinyl acetate emerges as a convenient acetylene equivalent, facilitating the synthesis of sixteen 3,4-unsubstituted isoquinolones, as well as select heteroaryl-fused pyridones. The complementary regiochemical preferences of enol ethers versus enol esters/enamides is discussed.

  4. Tandem beta-enamino ester formation and cyclization with o-alkynyl anilines catalyzed by InBr3: efficient synthesis of beta-(N-indolyl)-alpha,beta-unsaturated esters.

    Science.gov (United States)

    Murai, Kenichi; Hayashi, Shoko; Takaichi, Nobuhiro; Kita, Yasuyuki; Fujioka, Hiromichi

    2009-02-06

    A tandem reaction providing beta-(N-indolyl)-alpha,beta-unsaturated esters from beta-keto esters and o-alkynyl anilines was developed. Z-Alkenes were selectively formed due to the stability of the beta-enamino ester as an intermediate of the reaction. This reaction includes the intermolecular beta-enamino ester formation and intramolecular cyclization catalyzed by InBr(3).

  5. Recent advances in the gold-catalyzed additions to C–C multiple bonds

    Directory of Open Access Journals (Sweden)

    He Huang

    2011-07-01

    Full Text Available C–O, C–N and C–C bonds are the most widespread types of bonds in nature, and are the cornerstone of most organic compounds, ranging from pharmaceuticals and agrochemicals to advanced materials and polymers. Cationic gold acts as a soft and carbophilic Lewis acid and is considered one of the most powerful activators of C–C multiple bonds. Consequently, gold-catalysis plays an important role in the development of new strategies to form these bonds in more convenient ways. In this review, we highlight recent advances in the gold-catalyzed chemistry of addition of X–H (X = O, N, C bonds to C–C multiple bonds, tandem reactions, and asymmetric additions. This review covers gold-catalyzed organic reactions published from 2008 to the present.

  6. Copper-catalyzed Suzuki-Miyaura coupling of arylboronate esters: transmetalation with (PN)CuF and identification of intermediates.

    Science.gov (United States)

    Gurung, Santosh K; Thapa, Surendra; Kafle, Arjun; Dickie, Diane A; Giri, Ramesh

    2014-02-21

    An efficient Cu(I)-catalyzed Suzuki-Miyaura reaction was developed for the coupling of aryl- and heteroarylboronate esters with aryl and heteroaryl iodides at low catalyst loadings (2 mol %). The reaction proceeds under ligand-free conditions for aryl-heteroaryl and heteroaryl-heteroaryl couplings. We also conducted the first detailed mechanistic studies by synthesizing [(PN-2)CuI]2, [(PN-2)CuF]2, and (PN-2)CuPh (PN-2 = o-(di-tert-butylphosphino)-N,N-dimethylaniline) and demonstrated that [(PN-2)CuF]2 is the species that undergoes transmetalation with arylboronate esters.

  7. N-Heterocyclic Carbene-Catalyzed Vinylogous Mukaiyama Aldol Reaction of α-Keto Esters and α-Trifluoromethyl Ketones

    KAUST Repository

    Du, Guang-Fen

    2015-11-05

    © Georg Thieme Verlag Stuttgart · New York · Synthesis 2016. N-Heterocyclic carbene (NHC)-catalyzed vinylogous Mukaiyama aldol reaction of ketones was developed. Under the catalysis of 5 mol% NHC, α-keto esters and α-trifluoromethyl ketones reacted with 2-(trimethysilyloxy)furan efficiently to produce γ-substituted butenolides containing adjacent quaternary and tertiary carbon centers in high yields with good diastereoselectivities.

  8. Rh-Catalyzed Asymmetric Hydrogenation of a-Enol Ester Phosphonates with 1-Phenylethylamine-Derived Phosphine- Phosphoramidite Ligands

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    HU Juan, WANG Dao-yong, ZHENG Zhuo, HU Xiang-ping J. Mol. Catal. (China) 2012, 26(6), 487 ~492 Chiral phosphine-phosphoramidite ligand, ( So, S,, )-2b, was found to be highly efficient in the Rh-catalyzed asymmetric hydrogenation of various α-enol ester phosphonates, in which excellent enantioselectivities (up to 〉99% ee) and high catalyticactivity ( S/C up to 5000) were achieved.

  9. Mechanism of the cobalt oxazoline palladacycle (COP)-catalyzed asymmetric synthesis of allylic esters.

    Science.gov (United States)

    Cannon, Jeffrey S; Kirsch, Stefan F; Overman, Larry E; Sneddon, Helen F

    2010-11-03

    The catalytic enantioselective S(N)2' displacement of (Z)-allylic trichloroacetimidates catalyzed by the palladium(II) complex [COP-OAc](2) is a broadly useful method for the asymmetric synthesis of chiral branched allylic esters. A variety of experiments aimed at elucidating the nature of the catalytic mechanism and its rate- and enantiodetermining steps are reported. Key findings include the following: (a) the demonstration that a variety of bridged-dipalladium complexes are present and constitute resting states of the COP catalyst (however, monomeric palladium(II) complexes are likely involved in the catalytic cycle); (b) labeling experiments establishing that the reaction proceeds in an overall antarafacial fashion; (c) secondary deuterium kinetic isotope effects that suggest substantial rehybridization at both C1 and C3 in the rate-limiting step; and (d) DFT computational studies (B3-LYP/def2-TZVP) that provide evidence for bidentate substrate-bound intermediates and an anti-oxypalladation/syn-deoxypalladation pathway. These results are consistent with a novel mechanism in which chelation of the imidate nitrogen to form a cationic palladium(II) intermediate activates the alkene for attack by external carboxylate in the enantiodetermining step. Computational modeling of the transition-state structure for the acyloxy palladation step provides a model for enantioinduction.

  10. Photoresponsive Liquid Crystalline Epoxy Networks with Shape Memory Behavior and Dynamic Ester Bonds.

    Science.gov (United States)

    Li, Yuzhan; Rios, Orlando; Keum, Jong K; Chen, Jihua; Kessler, Michael R

    2016-06-22

    Functional polymers are intelligent materials that can respond to a variety of external stimuli. However, these materials have not yet found widespread real world applications because of the difficulties in fabrication and the limited number of functional building blocks that can be incorporated into a material. Here, we demonstrate a simple route to incorporate three functional building blocks (azobenzene chromophores, liquid crystals, and dynamic covalent bonds) into an epoxy-based liquid crystalline network (LCN), in which an azobenzene-based epoxy monomer is polymerized with an aliphatic dicarboxylic acid to create exchangeable ester bonds that can be thermally activated. All three functional building blocks exhibited good compatibility, and the resulting materials exhibits various photomechanical, shape memory, and self-healing properties because of the azobenzene molecules, liquid crystals, and dynamic ester bonds, respectively.

  11. Investigating the role of a backbone to substrate hydrogen bond in OMP decarboxylase using a site-specific amide to ester substitution.

    Science.gov (United States)

    Desai, Bijoy J; Goto, Yuki; Cembran, Alessandro; Fedorov, Alexander A; Almo, Steven C; Gao, Jiali; Suga, Hiroaki; Gerlt, John A

    2014-10-21

    Hydrogen bonds between backbone amide groups of enzymes and their substrates are often observed, but their importance in substrate binding and/or catalysis is not easy to investigate experimentally. We describe the generation and kinetic characterization of a backbone amide to ester substitution in the orotidine 5'-monophosphate (OMP) decarboxylase from Methanobacter thermoautotrophicum (MtOMPDC) to determine the importance of a backbone amide-substrate hydrogen bond. The MtOMPDC-catalyzed reaction is characterized by a rate enhancement (∼10(17)) that is among the largest for enzyme-catalyzed reactions. The reaction proceeds through a vinyl anion intermediate that may be stabilized by hydrogen bonding interaction between the backbone amide of a conserved active site serine residue (Ser-127) and oxygen (O4) of the pyrimidine moiety and/or electrostatic interactions with the conserved general acidic lysine (Lys-72). In vitro translation in conjunction with amber suppression using an orthogonal amber tRNA charged with L-glycerate ((HO)S) was used to generate the ester backbone substitution (S127(HO)S). With 5-fluoro OMP (FOMP) as substrate, the amide to ester substitution increased the value of Km by ∼1.5-fold and decreased the value of kcat by ∼50-fold. We conclude that (i) the hydrogen bond between the backbone amide of Ser-127 and O4 of the pyrimidine moiety contributes a modest factor (∼10(2)) to the 10(17) rate enhancement and (ii) the stabilization of the anionic intermediate is accomplished by electrostatic interactions, including its proximity of Lys-72. These conclusions are in good agreement with predictions obtained from hybrid quantum mechanical/molecular mechanical calculations.

  12. FTIR study of hydrogen bonding between substituted benzyl alcohols and acrylic esters

    Directory of Open Access Journals (Sweden)

    P. Sivagurunathan

    2016-11-01

    Full Text Available Hydrogen bonding between substituted benzyl alcohols (benzyl alcohol, o-aminobenzyl alcohol, o-chlorobenzyl alcohol and o-nitrobenzyl alcohol and acrylic esters (methyl methacrylate, ethyl methacrylate is studied in carbon tetrachloride by using the FTIR spectroscopic method. Utilizing the Nash method, the formation constant (K of the 1:1 complexes is calculated. Using the K value, the Gibbs free energy change (ΔG0 is also calculated. The calculated formation constant and Gibbs free energy change values vary with the substituent of benzyl alcohol and ester chain length, which suggests that the proton donating ability of substituted benzyl alcohols is in the order: o-aminobenzyl alcohol < benzyl alcohol < o-chlorobenzyl alcohol < o-nitrobenzyl alcohol, and proton accepting ability of acrylic esters is in the order: methyl methacrylate < ethyl methacrylate.

  13. Rh(III-catalyzed directed C–H bond amidation of ferrocenes with isocyanates

    Directory of Open Access Journals (Sweden)

    Satoshi Takebayashi

    2012-10-01

    Full Text Available [RhCp*(OAc2(H2O] [Cp* = pentamethylcyclopentadienyl] catalyzed the C–H bond amidation of ferrocenes possessing directing groups with isocyanates in the presence of 2 equiv/Rh of HBF4·OEt2. A variety of disubstituted ferrocenes were prepared in high yields, or excellent diastereoselectivities.

  14. Direct 2-acetoxylation of quinoline N-oxides via copper catalyzed C-H bond activation.

    Science.gov (United States)

    Chen, Xuan; Zhu, Chongwei; Cui, Xiuling; Wu, Yangjie

    2013-08-07

    An efficient and direct 2-acetoxylation of quinoline N-oxides via copper(I) catalyzed C-H bond activation has been developed. This transformation was achieved using TBHP as an oxidant in the cross-dehydrogenative coupling (CDC) reaction of quinoline N-oxides with aldehydes, and provided a practical pathway to 2-acyloxyl quinolines.

  15. Palladium-catalyzed Suzuki-Miyaura coupling of amides by carbon-nitrogen cleavage: general strategy for amide N-C bond activation.

    Science.gov (United States)

    Meng, Guangrong; Szostak, Michal

    2016-06-15

    The first palladium-catalyzed Suzuki-Miyaura cross-coupling of amides with boronic acids for the synthesis of ketones by sterically-controlled N-C bond activation is reported. The transformation is characterized by operational simplicity using bench-stable, commercial reagents and catalysts, and a broad substrate scope, including substrates with electron-donating and withdrawing groups on both coupling partners, steric-hindrance, heterocycles, halides, esters and ketones. The scope and limitations are presented in the synthesis of >60 functionalized ketones. Mechanistic studies provide insight into the catalytic cycle of the cross-coupling, including the first experimental evidence for Pd insertion into the amide N-C bond. The synthetic utility is showcased by a gram-scale cross-coupling and cross-coupling at room temperature. Most importantly, this process provides a blueprint for the development of a plethora of metal catalyzed reactions of typically inert amide bonds via acyl-metal intermediates. A unified strategy for amide bond activation to enable metal insertion into N-C amide bond is outlined ().

  16. Dipentaerythritol penta-acrylate phosphate - an alternative phosphate ester monomer for bonding of methacrylates to zirconia

    Science.gov (United States)

    Chen, Ying; Tay, Franklin R.; Lu, Zhicen; Chen, Chen; Qian, Mengke; Zhang, Huaiqin; Tian, Fucong; Xie, Haifeng

    2016-12-01

    The present work examined the effects of dipentaerythritol penta-acrylate phosphate (PENTA) as an alternative phosphate ester monomer for bonding of methacrylate-based resins to yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and further investigated the potential bonding mechanism involved. Shear bond strength testing was performed to evaluate the efficacy of experimental PENTA-containing primers (5, 10, 15, 20 or 30 wt% PENTA in acetone) in improving resin-Y-TZP bond strength. Bonding without the use of a PENTA-containing served as the negative control, and a Methacryloyloxidecyl dihydrogenphosphate(MDP)-containing primer was used as the positive control. Inductively coupled plasma-mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) were used to investigate the potential existence of chemical affinity between PENTA and Y-TZP. Shear bond strengths were significant higher in the 15 and 20 wt% PENTA groups. The ICP-MS, XPS and FTIR data indicated that the P content on the Y-TZP surface increased as the concentration of PENTA increased in the experimental primers, via the formation of Zr–O–P bond. Taken together, the results attest that PENTA improves resin bonding of Y-TZP through chemical reaction with Y-TZP. Increasing the concentration of PENTA augments its binding affinity but not its bonding efficacy with zirconia.

  17. Characterization of Wax Esters by Electrospray Ionization Tandem Mass Spectrometry: Double Bond Effect and Unusual Product Ions.

    Science.gov (United States)

    Chen, Jianzhong; Green, Kari B; Nichols, Kelly K

    2015-08-01

    A series of different types of wax esters (represented by RCOOR') were systematically studied by using electrospray ionization (ESI) collision-induced dissociation tandem mass spectrometry (MS/MS) along with pseudo MS(3) (in-source dissociation combined with MS/MS) on a quadrupole time-of-flight (Q-TOF) mass spectrometer. The tandem mass spectra patterns resulting from dissociation of ammonium/proton adducts of these wax esters were influenced by the wax ester type and the collision energy applied. The product ions [RCOOH2](+), [RCO](+) and [RCO-H2O](+) that have been reported previously were detected; however, different primary product ions were demonstrated for the three wax ester types including: (1) [RCOOH2](+) for saturated wax esters, (2) [RCOOH2](+), [RCO](+) and [RCO-H2O](+) for unsaturated wax esters containing only one double bond in the fatty acid moiety or with one additional double bond in the fatty alcohol moiety, and (3) [RCOOH2](+) and [RCO](+) for unsaturated wax esters containing a double bond in the fatty alcohol moiety alone. Other fragments included [R'](+) and several series of product ions for all types of wax esters. Interestingly, unusual product ions were detected, such as neutral molecule (including water, methanol and ammonia) adducts of [RCOOH2](+) ions for all types of wax esters and [R'-2H](+) ions for unsaturated fatty acyl-containing wax esters. The patterns of tandem mass spectra for different types of wax esters will inform future identification and quantification approaches of wax esters in biological samples as supported by a preliminary study of quantification of isomeric wax esters in human meibomian gland secretions.

  18. Novel hot-melting hyperbranched poly(ester-amine) bearing self-complementary quadruple hydrogen bonding units

    Institute of Scientific and Technical Information of China (English)

    Yi Peng Qiu; Li Ming Tang; Yu Wang; Shi You Guan

    2008-01-01

    Hyperbranched poly(amine-ester)s bearing serf-complementary quadruple hydrogen bonding units display excellent mechanical and temperature-dependent melt rheological properties,which make them suitable as novel hot-melting materials.

  19. Lipase-catalyzed Synthesis of Caffeic Acid Phenethyl Ester in Ionic Liquids:Effect of Specific Ions and Reaction Parameters

    Institute of Scientific and Technical Information of China (English)

    王俊; 李晶; 张磊霞; 顾双双; 吴福安

    2013-01-01

    Caffeic acid phenethyl ester (CAPE) is a rare, naturally occurring phenolic food additive. This work systematically reported fundamental data on conversion of caffeic acid (CA), yield of CAPE, and reactive selectiv-ity during the lipase-catalyzed esterification process of CA and phenylethanol (PE) in ionic liquids (ILs). Sixteen ILs were selected as the reaction media, and the relative lipase-catalyzed synthesis properties of CAPE were meas-ured in an effort to enhance the yield of CAPE with high selectivity. The results indicated that ILs containing weakly coordinating anions and cations with adequate alkyl chain length improved the synthesis of CAPE. [Emim][Tf2N] was selected as the optimal reaction media. The optimal parameters were as follows by response surface methodology (RSM):reaction temperature, 84.0 °C;mass ratio of Novozym 435 to CA, 14︰1;and molar ratio of PE to CA, 16︰1. The highest reactive selectivity of CAPE catalyzed by Novozym 435 in [Emim][Tf2N] reached 64.55%(CA conversion 98.76%and CAPE yield 63.75%, respectively). Thus, lipase-catalyzed esterifica-tion in ILs is a promising method suitable for CAPE production.

  20. PLE CATALYZED HYDROLYZES OF ALPHA-SUBSTITUTED ALPHA-HYDROXY ESTERS - THE INFLUENCE OF THE SUBSTITUENTS

    NARCIS (Netherlands)

    MOORLAG, H; KELLOGG, RM

    1991-01-01

    The enzymatic hydrolyses of a variety of alpha-substituted mandelic and lactic esters using pig liver esterase (PLE) have been investigated. High to moderate enantioselectivity was found for various alpha-substituted mandelic esters, whereas PLE showed low to no enantioselectivity for alpha-substitu

  1. Thermodynamically leveraged Tandem catalysis for ester RC(O)O-R' bond hydrogenolysis. scope and mechanism.

    Energy Technology Data Exchange (ETDEWEB)

    Lohr, Tracy L.; Li, Zhi; Assary, Rajeev S.; Curtiss, Larry A.; Marks, Tobin J.

    2015-06-01

    Rapid and selective formal hydrogenolysis of aliphatic ester RC(O)O-R' linkages is achieved by a tandem homogeneous metal triflate + supported palladium catalytic system. The triflate catalyzes the mildly exothermic, turnover-limiting O-R' cleavage process, whereas the exothermic hydrogenation of the intermediate alkene further drives the overall reaction to completion.

  2. Chelation-assisted palladium-catalyzed direct cyanation of 2-arylpyridine C-H bonds.

    Science.gov (United States)

    Jia, Xiaofei; Yang, Dongpeng; Zhang, Shouhui; Cheng, Jiang

    2009-10-15

    A chelation-assisted palladium-catalyzed ortho-cyanation of the sp2 C-H bond by CuCN provided aromatic nitriles in moderate to good yields. Notably, the reaction could be conducted on a 10 mmol scale. The key intermediate of the natural product of Menispermum dauricum DC was concisely synthesized by the procedure. This new approach represents an exceedingly practical method for the synthesis of aromatic nitriles and offers an attractive alternative to the traditional Sandmeyer reaction.

  3. Ordered cleavage of myeloperoxidase ester bonds releases active site heme leading to inactivation of myeloperoxidase by benzoic acid hydrazide analogs.

    Science.gov (United States)

    Huang, Jiansheng; Smith, Forrest; Panizzi, Peter

    2014-04-15

    Myeloperoxidase (MPO) catalyzes the breakdown of hydrogen peroxide and the formation of the potent oxidant hypochlorous acid. We present the application of the fluorogenic peroxidase substrate 10-acetyl-3,7-dihydroxyphenoxazine (ADHP) in steady-state and transient kinetic studies of MPO function. Using initial kinetic parameters for the MPO system, we characterized under the same conditions a number of gold standards for MPO inhibition, namely 4-amino benzoic acid hydrazide (4-ABAH), isoniazid and NaN3 before expanding our focus to isomers of 4-ABAH and benzoic acid hydrazide analogs. We determined that in the presence of hydrogen peroxide that 4-ABAH and its isomer 2-ABAH are both slow-tight binding inhibitors of MPO requiring at least two steps, whereas NaN3 and isoniazid-based inhibition has a single observable step. We also determined that MPO inhibition by benzoic acid hydrazide and 4-(trifluoromethyl) benzoic acid hydrazide was due to hydrolysis of the ester bond between MPO heavy chain Glu 242 residue and the heme pyrrole A ring, freeing the light chain and heme b fragment from the larger remaining MPO heavy chain. This new mechanism would essentially indicate that the benzoic acid hydrazide analogs impart inhibition through initial ejection of the heme catalytic moiety without prior loss of the active site iron.

  4. Unsaturated Fatty Acid Esters Metathesis Catalyzed by Silica Supported WMe5

    KAUST Repository

    Riache, Nassima

    2015-11-14

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

  5. A Synthesis of 1H-Indazoles via a Cu(OAc)2-Catalyzed N-N Bond Formation.

    Science.gov (United States)

    Chen, Cheng-yi; Tang, Guangrong; He, Fengxian; Wang, Zhaobin; Jing, Hailin; Faessler, Roger

    2016-04-01

    A facile synthesis of 1H-indazoles featuring a Cu(OAc)2-catalyzed N-N bond formation using oxygen as the terminal oxidant is described. The reaction of readily available 2-aminobenzonitriles with various organometallic reagents led to o-aminoaryl N-H ketimine species. The subsequent Cu(OAc)2-catalyzed N-N bond formation in DMSO under oxygen afforded a wide variety of 1H-indazoles in good to excellent yields.

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

    Energy Technology Data Exchange (ETDEWEB)

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach

  7. Enantioselective epoxidation and carbon-carbon bond cleavage catalyzed by Coprinus cinereus peroxidase and myeloperoxidase.

    Science.gov (United States)

    Tuynman, A; Spelberg, J L; Kooter, I M; Schoemaker, H E; Wever, R

    2000-02-01

    We demonstrate that myeloperoxidase (MPO) and Coprinus cinereus peroxidase (CiP) catalyze the enantioselective epoxidation of styrene and a number of substituted derivatives with a reasonable enantiomeric excess (up to 80%) and in a moderate yield. Three major differences with respect to the chloroperoxidase from Caldariomyces fumago (CPO) are observed in the reactivity of MPO and CiP toward styrene derivatives. First, in contrast to CPO, MPO and CiP produced the (S)-isomers of the epoxides in enantiomeric excess. Second, for MPO and CiP the H(2)O(2) had to be added very slowly (10 eq in 16 h) to prevent accumulation of catalytically inactive enzyme intermediates. Under these conditions, CPO hardly showed any epoxidizing activity; only with a high influx of H(2)O(2) (300 eq in 1.6 h) was epoxidation observed. Third, both MPO and CiP formed significant amounts of (substituted) benzaldehydes as side products as a consequence of C-alpha-C-beta bond cleavage of the styrene derivatives, whereas for CPO and cytochrome c peroxidase this activity is not observed. C-alpha-C-beta cleavage was the most prominent reaction catalyzed by CiP, whereas with MPO the relative amount of epoxide formed was higher. This is the first report of peroxidases catalyzing both epoxidation reactions and carbon-carbon bond cleavage. The results are discussed in terms of mechanisms involving ferryl oxygen transfer and electron transfer, respectively.

  8. Lewis acid promoted ruthenium(II)-catalyzed etherifications by selective hydrogenation of carboxylic acids/esters.

    Science.gov (United States)

    Li, Yuehui; Topf, Christoph; Cui, Xinjiang; Junge, Kathrin; Beller, Matthias

    2015-04-20

    Ethers are of fundamental importance in organic chemistry and they are an integral part of valuable flavors, fragrances, and numerous bioactive compounds. In general, the reduction of esters constitutes the most straightforward preparation of ethers. Unfortunately, this transformation requires large amounts of metal hydrides. Presented herein is a bifunctional catalyst system, consisting of Ru/phosphine complex and aluminum triflate, which allows selective synthesis of ethers by hydrogenation of esters or carboxylic acids. Different lactones were reduced in good yields to the desired products. Even challenging aromatic and aliphatic esters were reduced to the desired products. Notably, the in situ formed catalyst can be reused several times without any significant loss of activity.

  9. Regioselective Synthesis of Polymerizable Vinyl Guaifenesin Esters Catalyzed by an Alkaline Protease of Bacillus subtilis

    Institute of Scientific and Technical Information of China (English)

    Na WANG; Qi WU; Jian Ming XU; Xiu Ming JIANG; Xian Fu LIN

    2004-01-01

    Three polymerizable vinyl guaifenesin esters with different acyl donor carbon chain lengths (C4,C6,C10) were regioselectivly synthesized by an alkaline protease from Bacillus subtilis in pyridine at 50°C for 1, 3, 5 days respectively.

  10. Direct aerobic oxidation of primary alcohols to methyl esters catalyzed by a heterogeneous gold catalyst

    DEFF Research Database (Denmark)

    Nielsen, Inger Staunstrup; Taarning, Esben; Egeblad, Kresten

    2007-01-01

    Methyl esters can be produced in high yield by oxidising methanolic solutions of primary alcohols with dioxygen over a heterogeneous gold catalyst. The versatility of this new methodology is demonstrated by the fact that alkylic, benzylic and allylic alcohols, as well as alcohols containing...

  11. Rhodium(I)-Catalyzed Benzannulation of Heteroaryl Propargylic Esters: Synthesis of Indoles and Related Heterocycles.

    Science.gov (United States)

    Li, Xiaoxun; Xie, Haibo; Fu, Xiaoning; Liu, Ji-Tian; Wang, Hao-Yuan; Xi, Bao-Min; Liu, Peng; Xu, Xiufang; Tang, Weiping

    2016-07-18

    A de novo synthesis of a benzene ring allows for the preparation of a diverse range of heterocycles including indoles, benzofurans, benzothiophenes, carbazoles, and dibenzofurans from simple heteroaryl propargylic esters using a unified carbonylative benzannulation strategy. Multiple substituents can be easily introduced to the C4-C7 positions of indoles and related heterocycles.

  12. ESTIMATION OF PHOSPHATE ESTER HYDROLYSIS RATE CONSTANTS. II. ACID AND GENERAL BASE CATALYZED HYDROLYSIS

    Science.gov (United States)

    SPARC (SPARC Performs Automated Reasoning in Chemistry) chemical reactivity models were extended to calculate acid and neutral hydrolysis rate constants of phosphate esters in water. The rate is calculated from the energy difference between the initial and transition states of a ...

  13. Hydrogenation of esters catalyzed by ruthenium PN3-Pincer complexes containing an aminophosphine arm

    KAUST Repository

    Chen, Tao

    2014-08-11

    Hydrogenation of esters under mild conditions was achieved using air-stable ruthenium PN3-pincer complexes containing an aminophosphine arm. High efficiency was achieved even in the presence of water. DFT studies suggest a bimolecular proton shuttle mechanism which allows H2 to be activated by the relatively stable catalyst with a reasonably low transition state barrier. © 2014 American Chemical Society.

  14. Probing the role of backbone hydrogen bonds in protein-peptide interactions by amide-to-ester mutations

    DEFF Research Database (Denmark)

    Eildal, Jonas N N; Hultqvist, Greta; Balle, Thomas;

    2013-01-01

    -protein interactions, those of the PDZ domain family involve formation of intermolecular hydrogen bonds: C-termini or internal linear motifs of proteins bind as β-strands to form an extended antiparallel β-sheet with the PDZ domain. Whereas extensive work has focused on the importance of the amino acid side chains...... of the protein ligand, the role of the backbone hydrogen bonds in the binding reaction is not known. Using amide-to-ester substitutions to perturb the backbone hydrogen-bonding pattern, we have systematically probed putative backbone hydrogen bonds between four different PDZ domains and peptides corresponding...... to natural protein ligands. Amide-to-ester mutations of the three C-terminal amides of the peptide ligand severely affected the affinity with the PDZ domain, demonstrating that hydrogen bonds contribute significantly to ligand binding (apparent changes in binding energy, ΔΔG = 1.3 to >3.8 kcal mol(-1...

  15. Theoretical Study of the Iodine-catalyzed Nucleophilic Addition by Halogen Bond

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The iodine-catalyzed nucleophilic addition of pyrrole to acetone has been studied by density functional theory at the level of Lanl2DZ*. It has been shown that the first iodine molecule appears to have a remarkable catalytic effect on this reaction by halogen bond between carbonyl oxygen and iodine molecule, but the second one does not improve the reaction largely. In general, the nucleophilic addition at the C(2) site of pyrrole is more favorable than that at the C(3)site;however, this trend is not prominent or even changed in acetronitrile solvent for the indole system, which is consistent with the experimental result by Bandgar.

  16. Rhodium(III)-catalyzed indazole synthesis by C-H bond functionalization and cyclative capture.

    Science.gov (United States)

    Lian, Yajing; Bergman, Robert G; Lavis, Luke D; Ellman, Jonathan A

    2013-05-15

    An efficient, one-step, and highly functional group-compatible synthesis of substituted N-aryl-2H-indazoles is reported via the rhodium(III)-catalyzed C-H bond addition of azobenzenes to aldehydes. The regioselective coupling of unsymmetrical azobenzenes was further demonstrated and led to the development of a new removable aryl group that allows for the preparation of indazoles without N-substitution. The 2-aryl-2H-indazole products also represent a new class of readily prepared fluorophores for which initial spectroscopic characterization has been performed.

  17. Synthesis of Wax Esters by Lipase-catalyzed Esterification with Immobilized Lipase from Candida sp. 99-125

    Institute of Scientific and Technical Information of China (English)

    邓利; 王晓静; 聂开立; 王芳; 刘军峰; 王璞; 谭天伟

    2011-01-01

    Wax esters were synthesized in a solvent free system catalyzed by immobilized lipase from Candida sp. 99-125, with oleic acid and cetyl alcohol. The effects of substrate molar ratio, lipase dosage and water removal were investigated in a 50 ml flask incubated in a thermostatic cultivation cabinet. The optimized conditions were: temperature 40 ℃, shaking at 170 r·min-1, acid/alcohol molar ratio 1:0.9, lipase dosage in 10% (by mass) of oleic acid, and open reaction for water removal. As a result, the conversion rate reached 98% for reaction of 8 h. The volume of reactor was scaled up to 1 L three-neck flask. The optimized parameters were: 200 r·min-1 agitation speed, 2.5% (by mass) lipase dosage, others were the same as the parameters described above. The conversion rate reached 95% for reaction of 24 h. The lipase retained 46% conversion rate after reuse for 6, 7 batches. The products were purified by removing remained cetyl alcohol and fatty acids with ethanol and saturated sodium carbonate so-lution, respectively. The purity of the wax ester, cetyl oleate, was 96%. The physical and chemical properties of cetyl oleate were tested and compared with those of jojoba oil. The results show that the product cetyl oleate has great potential to use as the substitute of natural jojoba oil.

  18. Metal-catalyzed double migratory cascade reactions of propargylic esters and phosphates.

    Science.gov (United States)

    Kazem Shiroodi, Roohollah; Gevorgyan, Vladimir

    2013-06-21

    Propargylic esters and phosphates are easily accessible substrates, which exhibit rich and tunable reactivities in the presence of transition metal catalysts. π-Acidic metals, mostly gold and platinum salts, activate these substrates for an initial 1,2- or 1,3-acyloxy and phosphatyloxy migration process to form reactive intermediates. These intermediates are able to undergo further cascade reactions leading to a variety of diverse structures. This tutorial review systematically introduces the double migratory reactions of propargylic esters and phosphates as a novel synthetic method, in which further cascade reaction of the reactive intermediate is accompanied by a second migration of a different group, thus offering a rapid route to a wide range of functionalized products. The serendipitous observations, as well as designed approaches involving the double migratory cascade reactions, will be discussed with emphasis placed on the mechanistic aspects and the synthetic utilities of the obtained products.

  19. Effect of Alcohol Structure on the Optimum Condition for Novozym 435-Catalyzed Synthesis of Adipate Esters

    Directory of Open Access Journals (Sweden)

    Mohd Basyaruddin Abdul Rahman

    2011-01-01

    Full Text Available Immobilized Candida antarctica lipase B, Novozym 435, was used as the biocatalyst in the esterification of adipic acid with four different isomers of butanol (n-butanol, sec-butanol, iso-butanol, and tert-butanol. Optimum conditions for the synthesis of adipate esters were obtained using response surface methodology approach with a four-factor-five-level central composite design concerning important reaction parameters which include time, temperature, substrate molar ratio, and amount of enzyme. Reactions under optimized conditions has yielded a high percentage of esterification (>96% for n-butanol, iso-butanol, and sec-butanol, indicating that extent of esterification is independent of the alcohol structure for primary and secondary alcohols at the optimum conditions. Minimum reaction time (135 min for achieving maximum ester yield was obtained for iso-butanol. The required time for attaining maximum yield and also the initial rates in the synthesis of di-n-butyl and di-sec-butyl adipate were nearly the same. Immobilized Candida antarctica lipase B was also capable of esterifying tert-butanol with a maximum yield of 39.1%. The enzyme is highly efficient biocatalyst for the synthesis of adipate esters by offering a simple production process and a high esterification yield.

  20. Rh(III)-Catalyzed C-H Bond Addition/Amine-Mediated Cyclization of Bis-Michael Acceptors.

    Science.gov (United States)

    Potter, Tyler J; Ellman, Jonathan A

    2016-08-01

    A Rh(III)-catalyzed C-H bond addition/primary amine-promoted cyclization of bis-Michael acceptors is reported. The C-H bond addition step occurs with high chemoselectivity, and the subsequent intramolecular Michael addition, mediated by a primary amine catalyst, sets three contiguous stereocenters with high diastereoselectivity. A broad range of directing groups and both aromatic and alkenyl C-H bonds were shown to be effective in this transformation, affording functionalized piperidines, tetrahydropyrans, and cyclohexanes.

  1. Reaction Pathways and Energetics of Etheric C–O Bond Cleavage Catalyzed by Lanthanide Triflates

    Energy Technology Data Exchange (ETDEWEB)

    Assary, Rajeev S.; Atesin, Abdurrahman C.; Li, Zhi; Curtiss, Larry A.; Marks, Tobin J.

    2013-09-06

    Efficient and selective cleavage of etheric C-O bonds is crucial for converting biomass into platform chemicals and liquid transportation fuels. In this contribution, computational methods at the DFT B3LYP level of theory are employed to understand the efficacy of lanthanide triflate catalysts (Ln(OTf)3, Ln = La, Ce, Sm, Gd, Yb, and Lu) in cleaving etheric C-O bonds. In agreement with experiment, the calculations indicate that the reaction pathway for C-O cleavage occurs via a C-H → O-H proton transfer in concert with weakening of the C-O bond of the coordinated ether substrate to ultimately yield a coordinated alkenol. The activation energy for this process falls as the lanthanide ionic radius decreases, reflecting enhanced metal ion electrophilicity. Details of the reaction mechanism for Yb(OTf)3-catalyzed ring opening are explored in depth, and for 1-methyl-d3-butyl phenyl ether, the computed primary kinetic isotope effect of 2.4 is in excellent agreement with experiment (2.7), confirming that etheric ring-opening pathway involves proton transfer from the methyl group alpha to the etheric oxygen atom, which is activated by the electrophilic lanthanide ion. Calculations of the catalytic pathway using eight different ether substrates indicate that the more rapid cleavage of acyclic versus cyclic ethers is largely due to entropic effects, with the former C-O bond scission processes increasing the degrees of freedom/particles as the transition state is approached.

  2. Hydrolysis of Surfactants Containing Ester Bonds: Modulation of Reaction Kinetics and Important Aspects of Surfactant Self-Assembly

    Science.gov (United States)

    Lundberg, Dan; Stjerndahl, Maria

    2011-01-01

    The effects of self-assembly on the hydrolysis kinetics of surfactants that contain ester bonds are discussed. A number of examples on how reaction rates and apparent reaction orders can be modulated by changes in the conditions, including an instance of apparent zero-order kinetics, are presented. Furthermore, it is shown that the examples on…

  3. Lipase catalyzed synthesis of organic acid esters of lactic acid in non-aqueous media.

    Science.gov (United States)

    Kiran, K R; Divakar, S

    2001-05-04

    Lipases from Rhizomucor miehei (Lipozyme IM20) and porcine pancreas (PPL) were employed as catalysts for the esterification reaction between the hydroxyl group of lactic acid and the carboxyl group of organic acids. Reactions were carried out at both shake-flask and bench-scale levels. Various parameters, such as solvent, temperature, substrate and enzyme concentrations, effect of buffer volume, buffer pH and water volume, were investigated for optimization of yields. While ethylmethyl ketone (EMK) was found to be the best solvent for shake-flask reactions, chloroform gave higher yields at bench-scale level. Detailed studies were carried out with respect to the synthesis of palmitoyl and stearoyl lactic acids. At shake-flask level, maximum yields of 37.5 and 40% were observed in case of palmitoyl and stearoyl lactic acids, respectively, with Lipozyme IM20; at bench-scale level, the maximum yields were 85.1 and 99% respectively, when PPL was employed. Of all the organic acids employed (C(2)--C(18)), only lauric, palmitic and stearic acids gave yields above 50%. At bench-scale level, PPL could be reused for up to three cycles with yields above 40%. Esters prepared were found to conform to Food Chemical Codex (FCC) specifications in terms of acid value, ester value, sodium and lactic acid contents.

  4. On the nature of ionic liquids and their effects on lipases that catalyze ester synthesis.

    Science.gov (United States)

    De Diego, Teresa; Lozano, Pedro; Abad, Miguel A; Steffensky, Katharina; Vaultier, Michel; Iborra, José L

    2009-03-25

    Free and immobilized lipases from Candida antarctica (CALA and CALB), Thermomyces lanuginosus (TLL) and Rhizomucor miehei (RML) were used as catalysts in the synthesis of butyl propionate by transesterification in reaction media consisting in nine different ionic liquids. Enzyme activities were clearly dependent on the nature of the ions, the results being improving as the alkyl chain length of the imidazolium cation increased, and as a function of the type of anion ([PF(6)], [BF(4)] or [ethylsulphate]). The best synthetic activity (655.5U/mg protein at 40 degrees C) was obtained when free CALB were assayed in the water-miscible IL cocosalkyl pentaethoxy methyl ammonium methosulfate ([CPMA][MS]), and was clearly related with the water content of the medium. The synthetic activity of free CALB in [CPMA][MS] was enhanced with the increase in temperature, while practically no effect was obtained for TLL. The ability of free CALB to synthesize aliphatic esters of different alkyl chain lengths, using different alkyl vinyl esters and 1-alkanols as substrates, was also studied in [CPMA][MS], the best results (4500U/mg protein) being obtained for the synthesis of hexyl butyrate.

  5. Hydrodeoxygenation of fatty acid esters catalyzed by Ni on nano-sized MFI type zeolites

    Energy Technology Data Exchange (ETDEWEB)

    Schreiber, Moritz W.; Rodriguez-Niño, Daniella; Gutiérrez, Oliver Y.; Lercher, Johannes A.

    2016-01-01

    The impact of support morphology and composition on the intrinsic activity of Ni supported on MFI-type zeolite was explored in the hydrodeoxygenation of methyl stearate, tristearate, and algae oil (mixture of triglycerides). The nano-sized structure of the support (self-pillared nanosheets) is beneficial for the activity of the catalysts. Higher Ni dispersion and concomitant higher reaction rates were obtained on nano-structured supports than on zeolite with conventional morphology. Rates normalized to accessible Ni atoms (TOF), however, varied little with support morphology. Acidity of the support increases the rate of Ni-catalyzed C-O hydrogenolysis per surface metal site.

  6. Hydrolysis of carboxylate ester catalyzed by a new artificial abzyme based on molecularly imprinted polymer

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new kind of artificial abzyme MIP-3, which contains N-phenyl benzonic amide group and “nanochannel” formed by embedded ZnO nano materials, and is imprinted by a transition-state analogue of p-nitrophenyl methyphosphonate in the hydrolysis of p-nitrophenyl acetate, was prepared by radical co-polymerization. Hydrolytic kinetics of p-nitrophenyl carboxylate catalyzed by MIP-3 was investigated. The results showed that the artificial abzyme exhibited notable substructure selectivity and strong catalytic ability in hydrolysis of p-nitrophenyl acetate

  7. Carbon-Oxygen Bond Cleavage by Bis(imino)pyridine Iron Compounds : Catalyst Deactivation Pathways and Observation of Acyl C-O Bond Cleavage in Esters

    NARCIS (Netherlands)

    Trovitch, Ryan J.; Lobkovsky, Emil; Bouwkamp, Marco W.; Chirik, Paul J.

    2008-01-01

    Investigations into the substrate scope of bis(imino)pyridine iron-catalyzed hydrogenation and [2 pi + 2 pi]. diene cyclization reactions identified C-O bond cleavage as a principal deactivation pathway. Addition of diallyl or allyl ethyl ether to the bis(imino)pyridine iron dinitrogen complex, ((iP

  8. Palladium(II)-Catalyzed C-H Bond Activation/C-C and C-O Bond Formation Reaction Cascade: Direct Synthesis of Coumestans.

    Science.gov (United States)

    Neog, Kashmiri; Borah, Ashwini; Gogoi, Pranjal

    2016-12-02

    A palladium catalyzed cascade reaction of 4-hydroxycoumarins and in situ generated arynes has been developed for the direct synthesis of coumestans. This cascade strategy proceeds via C-H bond activation/C-O and C-C bond formations in a single reaction vessel. This methodology affords moderate to good yields of coumestans and is tolerant of a variety of functional groups including halide. The methodology was applied to the synthesis of natural product flemichapparin C.

  9. Solvent-Free Lipase-Catalyzed Synthesis of Technical-Grade Sugar Esters and Evaluation of Their Physicochemical and Bioactive Properties

    Directory of Open Access Journals (Sweden)

    Ran Ye

    2016-05-01

    Full Text Available Technical-grade oleic acid esters of sucrose and fructose were prepared using solvent-free biocatalysis at 65 °C, without any downstream purification applied, and their physicochemical and bioactivity-related properties were evaluated and compared to a commercially available sucrose laurate emulsifier. To increase the conversion of sucrose and fructose oleate, prepared previously using solvent-free lipase-catalyzed esterification catalyzed by Rhizomucor miehei lipase (81% and 83% ester, respectively, the enzymatic reaction conditions was continued using CaSO4 to control the reactor’s air headspace and a lipase (from Candida antarctica B with a hydrophobic immobilization matrix to provide an ultralow water activity, and high-pressure homogenation, to form metastable suspensions of 2.0–3.3 micron sized saccharide particles in liquid-phase reaction media. These measures led to increased ester content of 89% and 96% for reactions involving sucrose and fructose, respectively. The monoester content among the esters decreased from 90% to <70% due to differences in regioselectivity between the lipases. The resultant technical-grade sucrose and fructose lowered the surface tension to <30 mN/m, and possessed excellent emulsification capability and stability over 36 h using hexadecane and dodecane as oils, comparable to that of sucrose laurate and Tween® 80. The technical-grade sugar esters, particularly fructose oleate, more effectively inhibited gram-positive foodborne pathogens (Lactobacillus plantarum, Pediococcus pentosaceus and Bacillus subtilis. Furthermore, all three sugar esters displayed antitumor activity, particularly the two sucrose esters. This study demonstrates the importance of controlling the biocatalysts’ water activity to achieve high conversion, the impact of a lipase’s regioselectivity in dictating product distribution, and the use of solvent-free biocatalysis to important biobased surfactants useful in foods, cosmetics

  10. Efficient Synthesis of Functionalized Benzimidazoles and Perimidines: Ytterbium Chloride Catalyzed CmC Bond Cleavage%Efficient Synthesis of Functionalized Benzimidazoles and Perimidines: Ytterbium Chloride Catalyzed CmC Bond Cleavage

    Institute of Scientific and Technical Information of China (English)

    Cai, Lijian; Ji, Xiaofeng; Yao, Zhigang; Xu, Fan; Shen, Qi

    2011-01-01

    An efficient method is developed for the synthesis of functionalized benzimidazoles and perimidines by the condensation of aryl diamines with β-carbonyl compounds catalyzed by ytterbium chloride. The reactions give good yields under mild conditions. A mechanism involving a lanthanide activated C--C bond cleavage is proposed.

  11. Nickel-Catalyzed C sp2 –C sp3 Cross-Coupling via C–O Bond Activation

    KAUST Repository

    Guo, Lin

    2016-06-13

    A new and efficient nickel-catalyzed alkylation of CAr-O electrophiles with B-alkyl-9-BBNs is described. The transformation is characterized by its functional group tolerance and provides a practical and versatile access to various Csp2-Csp3 bonds through Csp2-O substitution, without the restriction of β-hydride elimination. Moreover, the advantage of the newly developed method was demonstrated in a selective and sequential C-O bond activation process. © 2016 American Chemical Society.

  12. Two-step synthesis of fatty acid ethyl ester from soybean oil catalyzed by Yarrowia lipolytica lipase

    Directory of Open Access Journals (Sweden)

    Chen Jinnan

    2011-03-01

    Full Text Available Abstract Background Enzymatic biodiesel production by transesterification in solvent media has been investigated intensively, but glycerol, as a by-product, could block the immobilized enzyme and excess n-hexane, as a solution aid, would reduce the productivity of the enzyme. Esterification, a solvent-free and no-glycerol-release system for biodiesel production, has been developed, and two-step catalysis of soybean oil, hydrolysis followed by esterification, with Yarrowia lipolytica lipase is reported in this paper. Results First, soybean oil was hydrolyzed at 40°C by 100 U of lipase broth per 1 g of oil with approximately 30% to 60% (vol/vol water. The free fatty acid (FFA distilled from this hydrolysis mixture was used for the esterification of FFA to fatty acid ethyl ester by immobilized lipase. A mixture of 2.82 g of FFA and equimolar ethanol (addition in three steps were shaken at 30°C with 18 U of lipase per 1 gram of FFA. The degree of esterification reached 85% after 3 hours. The lipase membranes were taken out, dehydrated and subjected to fresh esterification so that over 82% of esterification was maintained, even though the esterification was repeated every 3 hours for 25 batches. Conclusion The two-step enzymatic process without glycerol released and solvent-free demonstrated higher efficiency and safety than enzymatic transesterification, which seems very promising for lipase-catalyzed, large-scale production of biodiesel, especially from high acid value waste oil.

  13. Enhancement of Lipase-catalyzed Synthesis of Caffeic Acid Phenethyl Ester in Ionic Liquid with DMSO Co-solvent☆

    Institute of Scientific and Technical Information of China (English)

    Shuangshuang Gu; Jun Wang; Xianbin Wei; Hongsheng Cui; Xiangyang Wu; Fuan Wu

    2014-01-01

    Caffeic acid phenethyl ester (CAPE) is a natural and rare ingredient with several biological activities, but its indus-trial production using lipase-catalyzed esterification of caffeic acid (CA) and 2-phenylethanol (PE) in ionic liquids (ILs) is hindered by low substrate concentrations and long reaction time. To set up a high-efficiency bioprocess for production of CAPE, a novel dimethyl sulfoxide (DMSO)–IL co-solvent system was established in this study. The 2%(by volume) DMSO–[Bmim][Tf2N] system was found to be the best medium with higher substrate solu-bility and conversion of CA. Under the optimum conditions, the substrate concentration of CA was raised 8-fold, the reaction time was reduced by half, and the conversion reached 96.23%. The kinetics follows a ping-pong bi-bi mechanism with inhibition by PE, with kinetic parameters as follows:Vmax=0.89 mmol · min−1 · g−1, Km,CA=42.9 mmol · L−1, Km,PE=165.7 mmol · L−1, and Ki,PE=146.2 mmol · L−1. The results suggest that the DMSO co-solvent effect has great potential to enhance the enzymatic synthesis efficiency of CAPE in ILs.

  14. Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

    Science.gov (United States)

    Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

    2015-01-01

    Succinimide formation from aspartic acid (Asp) residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe) as a model compound, we propose the possibility that acetic acid (AA), which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition) to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds) occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism. PMID:25588215

  15. Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

    Directory of Open Access Journals (Sweden)

    Ohgi Takahashi

    2015-01-01

    Full Text Available Succinimide formation from aspartic acid (Asp residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe as a model compound, we propose the possibility that acetic acid (AA, which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

  16. Exploiting the pressure effect on lipase-catalyzed wax ester synthesis in dense carbon dioxide.

    Science.gov (United States)

    Knez, Zeljko; Laudani, Chiara Giulia; Habulin, Maja; Reverchon, Ernesto

    2007-08-15

    The present work focuses on the thermodynamic interpretation of the lauryl oleate biosynthesis in high-pressure carbon dioxide. Lipase-catalyzed lauryl oleate production by oleic acid esterification with 1-dodecanol over immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) was successfully performed in a sapphire window batch stirred tank reactor (BSTR) using dense CO(2) as reaction medium. The experiments were planned to elucidate the pressure effect on the reaction performance. With increasing the pressure up to 10 MPa, the catalytic efficiency of the studied enzyme improved rising up to a maximum and decreased at higher pressure values. Kinetic observations, exhibiting that dense CO(2) expanded reaction mixture in subcritical conditions led to higher performance than when diluted in a single supercritical phase, were elucidated by phase-equilibrium arguments. The experimental results were justified with emphasis on thermodynamic interpretation of the studied system. Particularly, the different reaction performances obtained were related to the position of the operating point with respect to the location of liquid-vapor phase boundaries of the reactant fatty acid/alcohol/CO(2) ternary system. The outlook for exploitation of CO(2) expanded phase at lower pressure compared to supercritical phase, with heterogeneous system in which the solid catalyst particles are exposed to dense CO(2) expanded reaction mixture, in developing new biotransformation schemes is promising.

  17. Optimization of oligoglycerol fatty acid esters preparation catalyzed by Lipozyme 435

    Directory of Open Access Journals (Sweden)

    Wan, F. L.

    2015-09-01

    Full Text Available Oli goglycerol fatty acid esters (OGEs are an important kind of polyglycerol fatty acid esters (PGEs which have been widely used as emulsifiers in food, medicine and cosmetic industries. The aim of this study was to investigate the preparation of OGEs by the esterification of olig oglycerol with linoleic acid in a solvent- free system using Lipozyme 435 as the catalyst. The effects of substrate molar ratio, reaction time, reaction temperature, enzyme dosage, and water addition on the efficiency of esterification (EE were studied. Single factor experiments and response surface methodology (RSM were employed to optimize the reaction parameters. The optimum conditions were obtained as follows: reaction time 4.52 h, reaction temperature 90 °C, enzyme dosage 2 wt% (based on the total substrate mass, the molar ratio of oligoglycerol to linoleic acid 1.59:1 and no water addition. Under these conditions, the experimental EE (95.82±0.22% fitted well with that predicted by RSM (96.15%. Similar results were obtained when the process was scaled up to a production of 500 g in a pilot bubble column reactor (BCR. The enzyme maintained 98.2% of the relative activity after 10 batches of reaction in the BCR. Electro spray ionization mass spectrum was employed to rapidly analyze the esterification products, and most species of OGEs have been identified.Los ésteres grasos de oligoglicerol (OGEs son una clase importante de ésteres de ácidos grasos de poliglicerol (PGE que han sido ampliamente utilizados como emulsionantes en alimentación, medicina y en la industria cosmética. El objetivo de este estudio fue investigar la preparación de OGEs mediante la esterificación de oligoglicerol con ácido linoleico en un sistema libre de disolvente utilizando Lipozyme 435 como catalizador. Se estudiaron los efectos en la eficiencia de esterificación (EE de la relación molar de sustratos, de los tiempos de reacción, las temperaturas de reacción, la dosis de la

  18. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  19. Palladium-catalyzed picolinamide-directed iodination of remote ortho-C−H bonds of arenes: Synthesis of tetrahydroquinolines

    Science.gov (United States)

    Nack, William A; Wang, Xinmou; Wang, Bo

    2016-01-01

    Summary A new palladium-catalyzed picolinamide (PA)-directed ortho-iodination reaction of ε-C(sp2)−H bonds of γ-arylpropylamine substrates is reported. This reaction proceeds selectively with a variety of γ-arylpropylamines bearing strongly electron-donating or withdrawing substituents, complementing our previously reported PA-directed electrophilic aromatic substitution approach to this transformation. As demonstrated herein, a three step sequence of Pd-catalyzed γ-C(sp3)−H arylation, Pd-catalyzed ε-C(sp2)−H iodination, and Cu-catalyzed C−N cyclization enables a streamlined synthesis of tetrahydroquinolines bearing diverse substitution patterns. PMID:27559375

  20. NMR-spectroscopic characterization of phosphodiester bond cleavage catalyzed by the minimal hammerhead ribozyme.

    Science.gov (United States)

    Fürtig, Boris; Richter, Christian; Schell, Peter; Wenter, Philipp; Pitsch, Stefan; Schwalbe, Harald

    2008-01-01

    In order to relate the conformational dynamics of the hammerhead ribozyme to its biological function the cleavage reaction catalyzed by the hammerhead ribozyme was monitored by time-resolved nuclear magnetic resonance (NMR) spectroscopy. For this purpose, the two nucleosides around the scissile phosphodiester bond were selectively (13)C labelled in multi-step organic syntheses starting from uniformly (13)C-labelled glucose. The phosphoamidites were incorporated using phosphoamidite chemistry in the hammerhead substrate strand. In addition, the 2'-OH group on the 5'-side of the hammerhead substrate strand was labelled with a photolabile protecting group. This labelling strategy enabled a detailed characterisation of the nucleotides around the scissile phosphodiester bond in the ground state conformation of the hammerhead ribozyme in the absence and presence of Mg(2+) ions as well as of the product state. Photochemical induction of the reaction in situ was further characterized by time-resolved NMR spectroscopy. The detailed structural and dynamic investigations revealed that the conformation of the hammerhead ribozyme is significantly affected by addition of Mg(2+) leading to an ensemble of conformations where dynamic transitions between energetically similar conformations occur on the ms-timescale in the presence of Mg(2+). The dynamic transitions are localized around the catalytic core. Cleavage from this ensemble cannot be described by mono-exponential kinetics but follows bi-exponential kinetics. A model is described to take into account these experimental data.

  1. Cu(I)-catalyzed (11)C carboxylation of boronic acid esters: a rapid and convenient entry to (11)C-labeled carboxylic acids, esters, and amides.

    Science.gov (United States)

    Riss, Patrick J; Lu, Shuiyu; Telu, Sanjay; Aigbirhio, Franklin I; Pike, Victor W

    2012-03-12

    Rapid and direct: the carboxylation of boronic acid esters with (11)CO(2) provides [(11)C]carboxylic acids as a convenient entry into [(11)C]esters and [(11)C]amides. This conversion of boronates is tolerant to diverse functional groups (e.g., halo, nitro, or carbonyl).

  2. Stereocontrolled Synthesis of (E)-β, γ-Unsaturated Esters via Palladium-Catalyzed Cross-Coupling of (E)-Alkenylboronic Acids with a-Bromoacetic Esters

    Institute of Scientific and Technical Information of China (English)

    DUAN Yazhen; ZHANG Jianshe; YANG Jun; DENG Minzhi

    2009-01-01

    The cross-coupling reaction of trans-alkenylboronic acids with α-bromoacetic esters was firstly studied. It was found that using Pd(OAc)2 as catalyst, a bulky electron-rich phospine, (2-dicyclohexylphospino-biphenyl) as ligand, the reaction can be readily accomplished to give specific (E)-β,γ-unsaturated esters in high yields.

  3. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of

  4. Direct functionalization of nitrogen heterocycles via Rh-catalyzed C-H bond activation.

    Science.gov (United States)

    Lewis, Jared C; Bergman, Robert G; Ellman, Jonathan A

    2008-08-01

    [Reaction: see text]. Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2 alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh- N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy 3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy 3) 2 fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid cocatalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of

  5. Rh-Catalyzed, Regioselective, C-H Bond Functionalization: Access to Quinoline-Branched Amines and Dimers.

    Science.gov (United States)

    Reddy, M Damoder; Fronczek, Frank R; Watkins, E Blake

    2016-11-04

    Rh-catalyzed, chelation-induced, C-5 regioselective C-H functionalization of 8-amidoquinolines with a range of N-Boc aminals is reported for the first time. The addition of in situ generated imines to C(sp(2))-H bonds afforded branched amines in good to excellent yields. Moreover, this transformation features good functional group compatibility, broad substrate scope, and mild reaction conditions and is suitable for gram-scale synthesis. In addition, an unprecedented, chelation-induced, site-selective, remote dimerization of quinolines led to the formation of dimer frameworks in moderate yields under Rh-catalyzed conditions.

  6. Synthesis of ethoxy dibenzooxaphosphorin oxides through palladium-catalyzed C(sp2–H activation/C–O formation

    Directory of Open Access Journals (Sweden)

    Seohyun Shin

    2014-05-01

    Full Text Available We report an efficient Pd-catalyzed C(sp2–H activation/C–O bond formation for the synthesis of ethoxy dibenzooxaphosphorin oxides from 2-(arylarylphosphonic acid monoethyl esters under aerobic conditions.

  7. Fe-Catalyzed C–C Bond Construction from Olefins via Radicals

    Science.gov (United States)

    2017-01-01

    This Article details the development of the iron-catalyzed conversion of olefins to radicals and their subsequent use in the construction of C–C bonds. Optimization of a reductive diene cyclization led to the development of an intermolecular cross-coupling of electronically-differentiated donor and acceptor olefins. Although the substitution on the donor olefins was initially limited to alkyl and aryl groups, additional efforts culminated in the expansion of the scope of the substitution to various heteroatom-based functionalities, providing a unified olefin reactivity. A vinyl sulfone acceptor olefin was developed, which allowed for the efficient synthesis of sulfone adducts that could be used as branch points for further diversification. Moreover, this reactivity was extended into an olefin-based Minisci reaction to functionalize heterocyclic scaffolds. Finally, mechanistic studies resulted in a more thorough understanding of the reaction, giving rise to the development of a more efficient second-generation set of olefin cross-coupling conditions. PMID:28094980

  8. Local bonding and atomic environments in Ni-catalyzed complex hydrides.

    Science.gov (United States)

    Graetz, J; Chaudhuri, S; Salguero, T T; Vajo, J J; Meyer, M S; Pinkerton, F E

    2009-05-20

    The local bonding and atomic environments in the Ni-catalyzed destabilized system LiBH4/MgH2 and the quaternary borohydride-amide phase Li3BN2H8, were studied by x-ray absorption spectroscopy. In both cases the Ni catalyst was introduced as NiCl2 and a qualitative comparison of the Ni K-edge near-edge structure suggests the Ni2+ is reduced to primarily Ni0 after ball milling. The extended fine structure of the Ni K edge indicates that the Ni is coordinated by approximately 3 boron atoms with an interatomic distance of approximately 2.1 A and approximately 11 Ni atoms in a split shell at around 2.5 and 2.8 A. These results, and the lack of long-range order, suggest that the Ni is present as a disordered nanocluster with a local structure similar to that of Ni3B. In the fully hydrogenated phase of LiBH4/MgH2 a small amount Mg2NiHx was also present. Surface calculations performed using density functional theory suggest that the lowest kinetic barrier for H2 chemisorption occurs on the Ni3B(100) surface.

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

    Science.gov (United States)

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

    2015-08-06

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

  10. Gold-Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2-Migration of an Endocyclic Carbon-Heteroatom Bond.

    Science.gov (United States)

    Chen, Ming; Sun, Ning; Xu, Wei; Zhao, Jidong; Wang, Gaonan; Liu, Yuanhong

    2015-12-14

    A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/Nazarov cyclization reaction sequence.

  11. Cobalt(III)-catalyzed synthesis of indazoles and furans by C-H bond functionalization/addition/cyclization cascades.

    Science.gov (United States)

    Hummel, Joshua R; Ellman, Jonathan A

    2015-01-14

    The development of operationally straightforward and cost-effective routes for the assembly of heterocycles from simple inputs is important for many scientific endeavors, including pharmaceutical, agrochemical, and materials research. In this article we describe the development of a new air-stable cationic Co(III) catalyst for convergent, one-step benchtop syntheses of N-aryl-2H-indazoles and furans by C-H bond additions to aldehydes followed by in situ cyclization and aromatization. Only a substoichiometric amount of AcOH is required as an additive that is both low-cost and convenient to handle. The syntheses of these heterocycles are the first examples of Co(III)-catalyzed additions to aldehydes, and reactions are demonstrated for a variety of aromatic, heteroaromatic, and aliphatic derivatives. The syntheses of both N-aryl-2H-indazoles and furans have been performed on 20 mmol scales and should be readily applicable to larger scales. The reported heterocycle syntheses also demonstrate the use of directing groups that have not previously been applied to Co(III)-catalyzed C-H bond functionalizations. Additionally, the synthesis of furans demonstrates the first example of Co(III)-catalyzed functionalization of alkenyl C-H bonds.

  12. Synthesis, Anti-HCV, Antioxidant and Reduction of Intracellular Reactive Oxygen Species Generation of a Chlorogenic Acid Analogue with an Amide Bond Replacing the Ester Bond

    OpenAIRE

    2016-01-01

    Chlorogenic acid is a well known natural product with important bioactivities. It contains an ester bond formed between the COOH of caffeic acid and the 3-OH of quinic acid. We synthesized a chlorogenic acid analogue, 3α-caffeoylquinic acid amide, using caffeic and quinic acids as starting materials. The caffeoylquinc acid amide was found to be much more stable than chlorogenic acid and showed anti-Hepatitis C virus (anti-HCV) activity with a potency similar to chlorogenic acid. The caffeoylq...

  13. Synthesis, Anti-HCV, Antioxidant and Reduction of Intracellular Reactive Oxygen Species Generation of a Chlorogenic Acid Analogue with an Amide Bond Replacing the Ester Bond

    Directory of Open Access Journals (Sweden)

    Ling-Na Wang

    2016-06-01

    Full Text Available Chlorogenic acid is a well known natural product with important bioactivities. It contains an ester bond formed between the COOH of caffeic acid and the 3-OH of quinic acid. We synthesized a chlorogenic acid analogue, 3α-caffeoylquinic acid amide, using caffeic and quinic acids as starting materials. The caffeoylquinc acid amide was found to be much more stable than chlorogenic acid and showed anti-Hepatitis C virus (anti-HCV activity with a potency similar to chlorogenic acid. The caffeoylquinc acid amide potently protected HepG2 cells against oxidative stress induced by tert-butyl hydroperoxide.

  14. Mechanisms and origins of switchable chemoselectivity of Ni-catalyzed C(aryl)-O and C(acyl)-O activation of aryl esters with phosphine ligands.

    Science.gov (United States)

    Hong, Xin; Liang, Yong; Houk, K N

    2014-02-05

    Many experiments have shown that nickel with monodentate phosphine ligands favors the C(aryl)-O activation over the C(acyl)-O activation for aryl esters. However, Itami and co-workers recently discovered that nickel with bidentate phosphine ligands can selectively activate the C(acyl)-O bond of aryl esters of aromatic carboxylic acids. The chemoselectivity with bidentate phosphine ligands can be switched back to C(aryl)-O activation when aryl pivalates are employed. To understand the mechanisms and origins of this switchable chemoselectivity, density functional theory (DFT) calculations have been conducted. For aryl esters, nickel with bidentate phosphine ligands cleaves C(acyl)-O and C(aryl)-O bonds via three-centered transition states. The C(acyl)-O activation is more favorable due to the lower bond dissociation energy (BDE) of C(acyl)-O bond, which translates into a lower transition-state distortion energy. However, when monodentate phosphine ligands are used, a vacant coordination site on nickel creates an extra Ni-O bond in the five-centered C(aryl)-O cleavage transition state. The additional interaction energy between the catalyst and substrate makes C(aryl)-O activation favorable. In the case of aryl pivalates, nickel with bidentate phosphine ligands still favors the C(acyl)-O activation over the C(aryl)-O activation at the cleavage step. However, the subsequent decarbonylation generates a very unstable tBu-Ni(II) intermediate, and this unfavorable step greatly increases the overall barrier for generating the C(acyl)-O activation products. Instead, the subsequent C-H activation of azoles and C-C coupling in the C(aryl)-O activation pathway are much easier, leading to the observed C(aryl)-O activation products.

  15. NHC Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling Reactions of Aryl Boronate Esters with Perfluorobenzenes.

    Science.gov (United States)

    Zhou, Jing; Berthel, Johannes H J; Kuntze-Fechner, Maximilian W; Friedrich, Alexandra; Marder, Todd B; Radius, Udo

    2016-07-01

    An efficient Suzuki-Miyaura cross-coupling reaction of perfluorinated arenes with aryl boronate esters using NHC nickel complexes as catalysts is described. The efficiencies of different boronate esters (p-tolyl-Beg, p-tolyl-Bneop, p-tolyl-Bpin, p-tolyl-Bcat) and the corresponding boronic acid (p-tolyl-B(OH)2) in this type of cross-coupling reaction were evaluated (eg, ethyleneglycolato; neop, neopentylglycolato; pin, pinacolato; cat, catecholato). Aryl-Beg was shown to be the most reactive boronate ester among those studied. The use of CsF as an additive is essential for an efficient reaction of hexafluorobenzene with aryl neopentylglycolboronates.

  16. Reusable ionic liquid-catalyzed oxidative coupling of azoles and benzylic compounds via sp(3) C-N bond formation under metal-free conditions.

    Science.gov (United States)

    Liu, Wenbo; Liu, Chenjiang; Zhang, Yonghong; Sun, Yadong; Abdukadera, Ablimit; Wang, Bin; Li, He; Ma, Xuecheng; Zhang, Zengpeng

    2015-07-14

    The heterocyclic ionic liquid-catalyzed direct oxidative amination of benzylic sp(3) C-H bonds via intermolecular sp(3) C-N bond formation for the synthesis of N-alkylated azoles under metal-free conditions is reported for the first time. The catalyst 1-butylpyridinium iodide can be recycled and reused with similar efficacies for at least eight cycles.

  17. Production of flavor esters catalyzed by CALB-displaying Pichia pastoris whole-cells in a batch reactor.

    Science.gov (United States)

    Jin, Zi; Ntwali, Janvier; Han, Shuang-Yan; Zheng, Sui-Ping; Lin, Ying

    2012-05-31

    Candida antarctica lipase B (CALB) has been employed as an efficient catalyst in the preparation of many flavor esters. A CALB-displaying yeast whole-cell biocatalyst could be an attractive alternative to commercial immobilized CALB because of its low-cost preparation and high enzymatic activity. We investigated the potential application of CALB-displaying Pichia pastoris cells for the production of flavor esters. The optimal conditions for flavor esters synthesis by this biocatalyst were determined in 50-ml shake flasks. Under optimized conditions, the synthesis of 12 kinds flavor esters were scaled up in a 5-l batch stirred reactor. Among these, the mole conversions of 10 exceeded 95% after reactions for 4h. In addition, this biocatalyst showed good tolerance for high substrates concentration and excellent operational stability. Repeated use of the cells in 10 batches resulted in an activity loss of less than 10%. Thus, CALB-displaying P. pastoris whole cells are robust biocatalysts with potential commercial application in the large-scale production of flavor esters in non-aqueous media.

  18. Immobilized Rhizopus oryzae lipase catalyzed synthesis of palm stearin and cetyl alcohol wax esters: Optimization by Response Surface Methodology

    Directory of Open Access Journals (Sweden)

    Gargouri Youssef

    2011-06-01

    Full Text Available Abstract Background Waxes are esters of long-chain fatty acids and long-chain alcohols. Their principal natural sources are animals (sperm whale oil and vegetables (jojoba which are expensive and not easily available. Wax esters synthesized by enzymatic transesterification, using palm stearin as raw material, can be considered as an alternative to natural ones. Results Palm stearin is a solid fraction obtained by fractionation of palm oil. Palm stearin was esterified with cetyl alcohol to produce a mixture of wax esters. A non-commercial immobilized lipase from Rhizopus oryzae was used as biocatalyst. Response surface methodology was employed to determine the effects of the temperature (30-50°C, the enzyme concentration (33.34-300 IU/mL, the alcohol/palm stearin molar ratio (3-7 mol/mol and the substrate concentration (0.06-0.34 g/mL on the conversion yield of palm stearin. Under optimal conditions (temperature, 30°C; enzyme concentration, 300 IU/mL; molar ratio 3 and substrate concentration 0.21 g/mL a high conversion yield of 98.52% was reached within a reaction time of 2 h. Conclusions Response surface methodology was successfully applied to determine the optimum operational conditions for synthesis of palm stearin based wax esters. This study may provide useful tools to develop economical and efficient processes for the synthesis of wax esters.

  19. Mechanism and Stereoselectivity in an Asymmetric N-Heterocyclic Carbene-Catalyzed Carbon-Carbon Bond Activation Reaction.

    Science.gov (United States)

    Pareek, Monika; Sunoj, Raghavan B

    2016-11-18

    The mechanism and origin of stereoinduction in a chiral N-heterocyclic carbene (NHC) catalyzed C-C bond activation of cyclobutenone has been established using B3LYP-D3 density functional theory computations. The activation of cyclobutenone as an NHC-bound vinyl enolate and subsequent reaction with the electrophilic sulfonyl imine leads to the lactam product. The most preferred stereocontrolling transition state exhibits a number of noncovalent interactions rendering additional stabilization. The computed enantio- and diastereoselectivities are in good agreement with the previous experimental observations.

  20. An Iron-Catalyzed Bond-Making/Bond-Breaking Cascade Merges Cycloisomerization and Cross-Coupling Chemistry.

    Science.gov (United States)

    Echeverria, Pierre-Georges; Fürstner, Alois

    2016-09-05

    Treatment of readily available enynes with alkyl-Grignard reagents in the presence of catalytic amounts of Fe(acac)3 engenders a remarkably facile and efficient reaction cascade that results in the net formation of two new C-C bonds while a C-Z bond in the substrate backbone is broken. Not only does this new manifold lend itself to the extrusion of heteroelements (Z=O, NR), but it can even be used for the cleavage of activated C-C bonds. The reaction likely proceeds via metallacyclic intermediates, the iron center of which gains ate character before reductive elimination occurs. The overall transformation represents a previously unknown merger of cycloisomerization and cross-coupling chemistry. It provides ready access to highly functionalized 1,3-dienes comprising a stereodefined tetrasubstituted alkene unit, which are difficult to make by conventional means.

  1. The unexpected mechanism of carbonyl hydrosilylation catalyzed by (Cp)(ArN[double bond, length as m-dash])Mo(H)(PMe(3)).

    Science.gov (United States)

    Shirobokov, Oleg G; Gorelsky, Serge I; Simionescu, Razvan; Kuzmina, Lyudmila G; Nikonov, Georgii I

    2010-11-07

    Complex (Cp)(ArN[double bond, length as m-dash])Mo(H)(PMe(3)) (2, Ar = 2,6-diisopropylphenyl) catalyzes the hydrosilylation of carbonyls by an unexpected associative mechanism. Complex 2 also reacts with PhSiH(3) by a σ-bond metathesis mechanism to give the silyl derivative (Cp)(ArN[double bond, length as m-dash])Mo(SiH(2)Ph)(PMe(3)).

  2. Transition Metal Catalyzed Reactions for Forming Carbon–Oxygen and Carbon–Carbon Bonds

    DEFF Research Database (Denmark)

    Sølvhøj, Amanda Birgitte

    of hydrogen per formed mol of ester as assumed. Furthermore a disproportionation mechanism (Tishchenko) could be ruled out due to the fact that free aldehydes did not enter the catalytic cycle. Fast deuterium/hydrogen exchange in the reaction with benzyl alcohol points towards a ruthenium dihydride species...... eliminates a bromo radical and forms the product....

  3. Atmospheric Hydrogenation of Esters Catalyzed by PNP-Ruthenium Complexes with an N-Heterocyclic Carbene Ligand.

    Science.gov (United States)

    Ogata, Osamu; Nakayama, Yuji; Nara, Hideki; Fujiwhara, Mitsuhiko; Kayaki, Yoshihito

    2016-08-01

    New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup.

  4. A Facile Construction of Eudesmanolide Denebutenolide via SmI2-catalyzed Rearrangement of an Enol Ester Epoxide

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A very convenient construction procedure of the a, b-unsaturated lactone has been carried out in 98% yield. SmI2 (10%) was used as catalyst for rearrangement of an enol ester epoxide of eudesmanolide sesquiterpene. The possible mechanism was also discussed.

  5. A Facile Construction of Eudesmanolide Denebutenolide via SmI2—catalyzed Rearrangement of an Enol Ester Epoxide

    Institute of Scientific and Technical Information of China (English)

    WuJiongXIA; AoChengCAO; 等

    2002-01-01

    A very convenient construction procedure of the α,β-unsaturated lactone has been carried out in 98% yield. SmI2 (10%) was used as catalyst for rearrangement of an enol ester exoxide of eudesmanolide sesquiterpene. The possible mechanism was also discussed.

  6. Lipase-catalyzed Regioselective Synthesis of Vinyl Ester Derivatives of Thiamphenicol: Novel Thiamphenicol Monomers for Preparation of Macromolecular Antibiotic

    Institute of Scientific and Technical Information of China (English)

    Yu Zhen SHI; Zhi Chun CHEN; Na WANG; Qi WU; Xian Fu LIN

    2005-01-01

    Three polymerizable vinyl thiamphenicol esters with different acyl donor carbon chain length (C4, C6, C10) were regioselectivly synthesized by Lipozyme(R) (immobilized from mucor miehei) in acetone at 50 ℃ for 12 h to give 73%, 81%, 63% yield, respectively. The products were valuable monomers for preparation of macromolecular antibiotic.

  7. Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

    Directory of Open Access Journals (Sweden)

    Axel G. Griesbeck

    2014-05-01

    Full Text Available The homogeneous titanium- and dye-catalyzed as well as the heterogeneous semiconductor particle-catalyzed photohydroxymethylation of ketones by methanol were investigated in order to evaluate the most active photocatalyst system. Dialkoxytitanium dichlorides are the most efficient species for chemoselective hydroxymethylation of acetophenone as well as other aromatic and aliphatic ketones. Pinacol coupling is the dominant process for semiconductor catalysis and ketone reduction dominates the Ti(OiPr4/methanol or isopropanol systems. Application of dilution effects on the TiO2 catalysis leads to an increase in hydroxymethylation at the expense of the pinacol coupling.

  8. Long-chain ethers as solvents can amplify the enantioselectivity of the Carica papaya lipase-catalyzed transesterification of 2-(substituted phenoxy)propanoic acid esters.

    Science.gov (United States)

    Miyazawa, Toshifumi; Iguchi, Wakana

    2013-10-01

    The enantioselectivity of the transesterification of the 2,2,2-trifluoroethyl esters of 2-(substituted phenoxy)propanoic acids, as catalyzed by the lipase from Carica papaya, was greatly improved by using long-chain ethers, such as di-n-hexyl ether, as solvents instead of the conventional diisopropyl ether. Thus, for example, the E value was enhanced from 21 [in diisopropyl ether (0.8 ml)] to 57 [in di-n-hexyl ether (0.8 ml)] in the reaction of 2,2,2-trifluoroethyl(RS)-2-phenoxypropanoate (0.1 mmol) with methanol (0.4 mmol) in the presence of the plant lipase preparation (10 mg); it was also improved from 13 (in diisopropyl ether) to 44 (in di-n-hexyl ether) in the reaction of 2,2,2-trifluoroethyl(RS)-2-(2-chlorophenoxy)propanoate with methanol under the same reaction conditions.

  9. Enantioselective epoxidation and carbon-carbon bond cleavage catalyzed by Coprinus cinereus peroxidase and myeloperoxidase

    NARCIS (Netherlands)

    Tuynman, A; Lutje Spelberg, Jeffrey; Kooter, IM; Schoemaker, HE; Wever, R

    2000-01-01

    We demonstrate that myeloperoxidase (MPO) and Coprinus cinereus peroxidase (CiP) catalyze the enantioselective epoxidation of styrene and a number of substituted derivatives with a reasonable enantiomeric excess (up to 80%) and in a moderate yield. Three major differences with respect to the chlorop

  10. Evidence for porphyrins bound, via ester bonds, to the Messel oil shale kerogen by selective chemical degradation experiments

    Science.gov (United States)

    Huseby, B.; Ocampo, R.

    1997-09-01

    High amounts of nickel mono- and di-acid porphyrins were released from Messel oil shale kerogen (Eocene, Germany) by selective chemical degradation (acid and base hydrolysis). The released porphyrin fractions were quantified (UV-vis) and their constituents isolated and characterized at the molecular level (UV-vis, MS, NMR). The mono-acid porphyrin fraction released contained four compounds of similar abundance which arise from an obvious chlorophyll or bacteriochlorophyll precursor. The di-acid porphyrin fraction was, however, dominated by far by one compound, mesoporphyrin IX, which must have originated from heme-like precursors (heme, cytochromes, etc.). These results show unambigously that the released mono- and di-acid porphyrins were linked to the macromolecular kerogen network via ester bonds and suggest that precursor heme-like pigments could be selectively and/or more readily incorporated into the macromolecular kerogen network than precursor chlorophylls and bacteriochlorophylls.

  11. Cross-linked PEG via degradable phosphate ester bond: synthesis, water-swelling, and application as drug carrier.

    Science.gov (United States)

    Liu, Zhaoxing; Wang, Lei; Bao, Chunyan; Li, Xinxin; Cao, Lei; Dai, Kerong; Zhu, Linyong

    2011-06-13

    A new series of degradable and water-swellable cross-linked PEG phosphoester polymers (CPPs) based on a facile cross-linked reaction between diphosphoesters of polyethylene glycol (P-PEG-P) and diglycidyl ether of polyethylene glycol (E-PEG-E) has been prepared and characterized. The molecular weights and ratios of the prepolymers played an important role for the properties of CPPs polymers, such as mechanical property, swelling, and degradation rates. In the curing process, the glycidyl ether was consumed by both hydroxyl of the phosphoester (P-OH) and hydroxyl generated from the opened glycidyl ethers (C-OH) with the presence of acid, which generated degradable phosphate esters as cross-linked points and ether bonds as the short branches, respectively. Drug entrapment and release test and biological cytotoxicity studies in vitro suggested that the polymers and generated hydrogels have great potential applications in drug delivery system and biological materials.

  12. Localization of double bonds in wax esters by high-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry utilizing the fragmentation of acetonitrile-related adducts.

    Science.gov (United States)

    Vrkoslav, Vladimír; Háková, Martina; Pecková, Karolina; Urbanová, Klára; Cvačka, Josef

    2011-04-15

    Unsaturated wax esters (WEs) provided molecular adducts with C(3)H(5)N ([M + 55](+•)) in APCI sources in the presence of acetonitrile. CID MS/MS of [M + 55](+•) yielded fragments allowing the localization of double bond(s) in the hydrocarbon chains of the WEs. These fragments were formed by a cleavage on each side of the double bond. In methylene-interrupted polyunsaturated WEs, diagnostic fragments related to each double bond were detected; the most abundant were those corresponding to the cleavage of the C-C bond next to the first and the last double bond. To differentiate between those fragments differing in their structure or origin, a simple nomenclature based on α and ω ions has been introduced. Fragmentation of the α-type ions (fragments containing an ester bond) provided information on the occurrence of a double bond in the acid or alcohol part of the WEs. While no significant differences between the spectra of the WEs differing by cis/trans isomerism were found, the isomers were separated chromatographically. A data-dependent HPLC/APCI-MS(2) method for the comprehensive characterization of WEs in their complex mixtures has been developed and applied to natural mixtures of WEs isolated from jojoba oil and beeswax. More than 50 WE molecular species were completely identified, including the information on the acid and alcohol chain length and the position of the double bonds.

  13. Gold-catalyzed cycloisomerization of 1,7-enyne esters to structurally diverse cis-1,2,3,6-tetrahydropyridin-4-yl ketones.

    Science.gov (United States)

    Rao, Weidong; Sally; Koh, Ming Joo; Chan, Philip Wai Hong

    2013-04-05

    A synthetic method that relies on gold(I)-catalyzed cycloisomerization of 1,7-enyne esters to prepare highly functionalized cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivatives in good to excellent yields and as a single regio-, diastereo-, and enantiomer is described. By taking advantage of the distinctive differences in the electronic and steric properties between an NHC (NHC = N-heterocyclic carbene) and phosphine ligand in the respective gold(I) complexes, a divergence in product selectivity was observed. In the presence of [PhCNAuIPr](+)SbF6(-) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) as the catalyst, tandem 1,3-acyloxy migration/6-exo-trig cyclization/1,5-acyl migration of the substrate was found to selectively occur to give the δ-diketone-substituted 1,2,3,6-tetrahydropyridine adduct. In contrast, reactions with the gold(I) phosphine complex [MeCNAu(JohnPhos)](+)SbF6(-) (JohnPhos = (1,1'-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst was discovered to result in preferential 1,3-acyloxy migration/6-exo-trig cyclization/hydrolysis of the 1,7-enyne ester and formation of the cis-1,2,3,6-tetrahydropyridin-4-yl ketone derivative. The utility of this piperidine forming strategy as a synthetic tool that makes use of 1,7-enyne esters was exemplified by its application to the synthesis of an enantiopure analogue of the bioactive 2,3,4,4a,5,9b-hexahydroindeno[1,2-c]pyridine family of compounds.

  14. Scaling-up the synthesis of myristate glucose ester catalyzed by a CALB-displaying Pichia pastoris whole-cell biocatalyst.

    Science.gov (United States)

    Guo, DongHeng; Jin, Zi; Xu, YanShan; Wang, Ping; Lin, Ying; Han, ShuangYan; Zheng, SuiPing

    2015-01-01

    The novel whole-cell biocatalyst Candida antarctica lipase B displaying-Pichia pastoris (Pp-CALB) is characterized by its low preparation cost and could be an alternative to the commercial immobilized Candida antarctica lipase B (CALB). This study addresses the feasibility of using Pp-CALB in large scale glucose fatty acid esters production. 1,2-O-Isopropylidene-α-D-glucofuranose (IpGlc) was used as the acyl acceptor to overcome the low solubility of glucose in an organic solvent and to avoid the addition of toxic co-solvents. IpGlc significantly improved the Pp-CALB catalyzing esterification efficiency when using long chain fatty acids as the acyl donor. Under the preferred operating conditions (50 °C, 40 g/L molecular sieve dosage and 200 rpm mixing intensity), 60.5% of IpGlc converted to 6-O-myristate-1, 2-O-isopropylidene-α-D-glucofuranose (C14-IpGlc) after a 96-h reaction in a 2-L stirred reactor. In a 5-L pilot scale test, Pp-CALB also showed a similar substrate conversion rate of 55.4% and excellent operational stability. After C14-IpGlc was collected, 70% trifluoroacetic acid was adopted to hydrolyze C14-IpGlc to myristate glucose ester (C14-Glc) with a high yield of 95.3%. In conclusion, Pp-CALB is a powerful biocatalyst available for industrial synthesis, and this study describes an applicable and economical process for the large scale production of myristate glucose ester.

  15. Kinetics and stereochemistry of hydrolysis of an N-(phenylacetyl)-α-hydroxyglycine ester catalyzed by serine β-lactamases and DD-peptidases.

    Science.gov (United States)

    Pelto, Ryan B; Pratt, R F

    2012-09-28

    The α-hydroxydepsipeptide 3-carboxyphenyl N-(phenylacetyl)-α-hydroxyglycinate (5) is a quite effective substrate of serine β-lactamases and low molecular mass DD-peptidases. The class C P99 and ampC β-lactamases catalyze the hydrolysis of both enantiomers of 5, although they show a strong preference for one of them. The class A TEM-2 and class D OXA-1 β-lactamases and the Streptomyces R61 and Actinomadura R39 DD-peptidases catalyze hydrolysis of only one enantiomer of at any significant rate. Experiments show that all of the above enzymes strongly prefer the same enantiomer, a surprising result since β-lactamases usually prefer L(S) enantiomers and DD-peptidases D(R). Product analysis, employing peptidylglycine α-amidating lyase, showed that the preferred enantiomer is D(R). Thus, it is the β-lactamases that have switched preference rather than the DD-peptidases. Molecular modeling of the P99 β-lactamase active site suggests that the α-hydroxyl 5 of may interact with conserved Asn and Lys residues. Both α-hydroxy and α-amido substituents on a glycine ester substrate can therefore enhance its productive interaction with the β-lactamase active site, although their effects are not additive; this may also be true for inhibitors.

  16. A kinetic study on the Novozyme 435-catalyzed esterification of free fatty acids with octanol to produce octyl esters.

    Science.gov (United States)

    Chowdhury, Avisha; Mitra, Debarati

    2015-01-01

    Octyl esters can serve as an important class of biolubricant components replacing their mineral oil counterparts. The purpose of the current work was to investigate the enzymatic esterification reaction of free fatty acids (FFA, from waste cooking oil) with octanol in a solvent-free system using a commercial lipase Novozyme 435. It was found that the esterificaton reaction followed the Ping-pong bi-bi kinetics with no inhibition by substrates or products within the studied concentration range. The maximum reaction rate was estimated to be 0.041 mol L(-1) g(-1) h(-1) . Additionally, the stability of Novozyme 435 in the current reaction system was studied by determining its activity and final conversion of FFA to esters after 12 successive utilizations. Novozyme 435 exhibited almost 100% enzyme activity up to 7 cycles of reaction and gradually decreased (by 5%) thereafter. The kinetic parameters evaluated from the study shall assist in the design of reactors for large-scale production of octyl esters from a cheap biomass source. The enzyme reusability data can further facilitate mass production by curtailing the cost of expensive enzyme consumption.

  17. Efficient synthesis of π-conjugated molecules incorporating fluorinated phenylene units through palladium-catalyzed iterative C(sp2–H bond arylations

    Directory of Open Access Journals (Sweden)

    Fatiha Abdelmalek

    2015-10-01

    Full Text Available We report herein a two or three step synthesis of fluorinated π-conjugated oligomers through iterative C–H bond arylations. Palladium-catalyzed desulfitative arylation of heteroarenes allowed in a first step the synthesis of fluoroaryl-heteroarene units in high yields. Then, the next steps involve direct arylation with aryl bromides catalyzed by PdCl(C3H5(dppb to afford triad or tetrad heteroaromatic compounds via regioselective activation of C(sp2–H bonds.

  18. Borane-catalyzed cracking of C-C bonds in coal; Boran-katalysierte C-C-Bindungungsspaltung in Steinkohle

    Energy Technology Data Exchange (ETDEWEB)

    Narangerel, J.; Haenel, M.W. [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany)

    1998-09-01

    Coal, especially coking coal, was reacted with hydrogen at comparatively mild reaction conditions (150-280 degrees centigrade, 20 MPa hydrogen pressure) in the presence of catalysts consisting of borange reagents and certain transition metal halides to obtaine more than 80 percent of pyridine-soluble products. The influence of the degree of coalification, catalyst and temperature on the borane-catalyzed hydrogenolysis of C-C bonds in coal was investigated. (orig.) [Deutsch] Steinkohlen, insbesondere im Inkohlungsbereich der Fettkohlen (Kokskohlen), werden in Gegenwart von Katalysatoren aus Boran-Reagentien und bestimmten Uebergangsmetallhalogeniden mit Wasserstoff bei vergleichsweise milden Reaktionsbedingungen (250-280 C, 20 MPa Wasserstoffdruck) in zu ueber 80% pyridinloesliche Produkte umgewandelt. Der Einfluss von Inkohlungsgrad, Katalysator und Temperatur auf die Boran-katalysierte C-C-Bindungshydrogenolyse in Kohle wurde untersucht. (orig.)

  19. Kinetics of T3-DNA Ligase-Catalyzed Phosphodiester Bond Formation Measured Using the α-Hemolysin Nanopore.

    Science.gov (United States)

    Tan, Cherie S; Riedl, Jan; Fleming, Aaron M; Burrows, Cynthia J; White, Henry S

    2016-12-27

    The latch region of the wild-type α-hemolysin (α-HL) protein channel can be used to distinguish single base modifications in double-stranded DNA (dsDNA) via ion channel measurements upon electrophoretic capture of dsDNA in the vestibule of α-HL. Herein, we investigated the use of the latch region to detect a nick in the phosphodiester DNA backbone. The presence of a nick in the phosphodiester backbone of one strand of the duplex results in a significant increase in both the blockade current and noise level relative to the intact duplex. Differentiation between the nicked and intact duplexes based on blockade current or noise, with near baseline resolution, allows real-time monitoring of the rate of T3-DNA ligase-catalyzed phosphodiester bond formation. Under low ionic strength conditions containing divalent cations and a molecular crowding agent (75 mg mL(-1) PEG), the rate of enzyme-catalyzed reaction in the bulk solution was continuously monitored by electrophoretically capturing reaction substrate or product dsDNA in the α-HL protein channel vestibule. Enzyme kinetic results obtained from the nanopore experiments match those from gel electrophoresis under the same reaction conditions, indicating the α-HL nanopore measurement provides a viable approach for monitoring enzymatic DNA repair activity.

  20. Preparation of stearoyl lactic acid ester catalyzed by lipases from Rhizomucor miehei and porcine pancreas optimization using response surface methodology.

    Science.gov (United States)

    Kiran, K R; Karanth, N G; Divakar, S

    1999-10-01

    The esterification reaction between stearic acid and lactic acid using Rhizomucor miehei lipase and porcine pancreas lipase was optimized for maximum esterification using response surface methodology. The formation of the ester was found to depend on three parameters namely enzyme/substrate ratio, lactic acid (stearic acid) concentration and incubation period. The maximum esterification predicted by theoretical equations for both lipases matched well with the observed experimental values. In the case of R. miehei lipase, stearoyl lactic acid ester formation was found to increase with incubation period and lactic acid (stearic acid) concentrations with maximum esterification of 26.9% at an enzyme/substrate (E/S) ratio of 125 g mol-1. In the case of porcine pancreas lipase, esterification showed a steady increase with increase in incubation period and lactic acid (stearic acid) concentration independent of the E/S ratios employed. In the case of PPL, a maximum esterification of 18.9% was observed at an E/S ratio of 25 g mol-1 at a lactic acid (stearic acid) concentration of 0.09 M after an incubation period of 72 h.

  1. Copper-Catalyzed Redox-Triggered Remote C-H Functionalization: Highly Selective Formation of C-CF3 and C-O Bonds

    Institute of Scientific and Technical Information of China (English)

    Taotao Li; Peng Yu; Jin-Shun Lin; Yonggang Zhi; Xin-Yuan Liu

    2016-01-01

    A Cu-catalyzed remote sp3 C-H/unactivated alkenes functionalization reaction for the concomitant construction ofC-CF3 and C-O bonds was described.An 1,5-H radical transfer involving an sp3 C-H bond adjacent to a nitrogen atom and an α-CF3-alkyl radical intermediate derived from unactivated alkenes was observed and demonstrated to proceed via the radical process.

  2. Directing Group in Decarboxylative Cross-Coupling: Copper-Catalyzed Site-Selective C-N Bond Formation from Nonactivated Aliphatic Carboxylic Acids.

    Science.gov (United States)

    Liu, Zhao-Jing; Lu, Xi; Wang, Guan; Li, Lei; Jiang, Wei-Tao; Wang, Yu-Dong; Xiao, Bin; Fu, Yao

    2016-08-03

    Copper-catalyzed directed decarboxylative amination of nonactivated aliphatic carboxylic acids is described. This intramolecular C-N bond formation reaction provides efficient access to the synthesis of pyrrolidine and piperidine derivatives as well as the modification of complex natural products. Moreover, this reaction presents excellent site-selectivity in the C-N bond formation step through the use of directing group. Our work can be considered as a big step toward controllable radical decarboxylative carbon-heteroatom cross-coupling.

  3. Esterification and Chemoselective Synthesis of R-Tetrahydrothiazo-2- thione-4-carboxylic Esters Catalyzed by TiCl4

    Institute of Scientific and Technical Information of China (English)

    SHANG Yan-mei; LI Jing; SONG Zhi-guang; LI Ye-zhi; HUANG Hua-min

    2007-01-01

    A series of esters of R-tetrahydrothiazo-2-thione-4-carboxylic acid[ R-TTCA] was synthesized by direct esterification of R-TTCA with alcohols(CH3OH, C2H5OH, n-C3H7OH, i-C3H7OH, n-C4H9OH, sec-C4H9OH) in the presence of TiCl4 as the catalyst at room temperature without using any other solvent or dehydrant in high yields,91.6%-99.1% for primary alcohols and 55%- 80% for secondary alcohols. The catalyst has a strong chemoselecfive activity for the esterification of primary alcohols with R-TTCA in the presence of secondary alcohols. Owing to high yield, high chemoselectivity, and mild conditions used, this is an efficient method for the esterification of primary alcohols with R-TTCA.

  4. Lipase-Catalyzed Production of 6-O-cinnamoyl-sorbitol from D-sorbitol and Cinnamic Acid Esters.

    Science.gov (United States)

    Kim, Jung-Ho; Bhatia, Shashi Kant; Yoo, Dongwon; Seo, Hyung Min; Yi, Da-Hye; Kim, Hyun Joong; Lee, Ju Hee; Choi, Kwon-Young; Kim, Kwang Jin; Lee, Yoo Kyung; Yang, Yung-Hun

    2015-05-01

    To overcome the poor properties of solubility and stability of cinnamic acid, cinnamate derivatives with sugar alcohols were produced using the immobilized Candida antarctica lipase with vinyl cinnamate and D-sorbitol as substrate at 45 °C. Immobilized C. antarctica lipase was found to synthesize 6-O-cinnamoyl-sorbitol and confirmed by HPLC and (1)H-NMR and had a preference for vinyl cinnamate over other esters such as allyl-, ethyl-, and isobutyl cinnamate as co-substrate with D-sorbitol. Contrary to D-sorbitol, vinyl cinnamate, and cinnamic acid, the final product 6-O-cinnamoyl-sorbitol was found to have radical scavenging activity. This would be the first report on the biosynthesis of 6-O-cinnamoyl-sorbitol with immobilized enzyme from C. antarctica.

  5. Consecutive condensation, C-N and N-N bond formations: a copper- catalyzed one-pot three-component synthesis of 2H-indazole.

    Science.gov (United States)

    Kumar, Manian Rajesh; Park, Ahbyeol; Park, Namjin; Lee, Sunwoo

    2011-07-01

    2H-Indazoles are synthesized using copper-catalyzed, one-pot, three-component reactions of 2-bromobenzaldehydes, primary amines, and sodium azide. A copper catalyst plays the key role in the formation of C-N and N-N bonds. This method has a broad substrate scope with a high tolerance for a variety of functional groups.

  6. Theoretical studies on N-O or N-N bond formation from aryl azide catalyzed by iron(II) bromide complex.

    Science.gov (United States)

    Li, Juan; Zhang, Qi; Zhou, Lixin

    2012-03-02

    DFT calculations have been carried out to study the reaction mechanism on N-O or N-N bond formation from aryl azide catalyzed by iron(II) bromide complex. A favorable reaction pathway is proposed to account for the construction of the core structure of 2H-indazoles or 2,1-benzisoxazoles.

  7. Rh-Catalyzed C–C Bond Cleavage by Transfer Hydroformylation

    Science.gov (United States)

    Murphy, Stephen K.; Park, Jung-Woo; Cruz, Faben A.; Dong, Vy M.

    2015-01-01

    The dehydroformylation of aldehydes to generate olefins occurs during the biosynthesis of various sterols, including cholesterol in humans. Here, we implement a synthetic version that features the transfer of a formyl group and hydride from an aldehyde substrate to a strained olefin acceptor. A Rh(Xantphos)(benzoate) catalyst activates aldehyde C–H bonds with high chemoselectivity to trigger C–C bond cleavage and generate olefins at low loadings (0.3 to 2 mol%) and temperatures (22 to 80 °C). This mild protocol can be applied to various natural products and was used to achieve a three step synthesis of (+)-yohimbenone. A study of the mechanism reveals that the benzoate counterion acts as a proton-shuttle to enable transfer hydroformylation. PMID:25554782

  8. Computational study of alkynes insertion into metal-hydride bonds catalyzed by bimetallic complexes.

    Science.gov (United States)

    Di Tommaso, Stefania; Tognetti, Vincent; Sicilia, Emilia; Adamo, Carlo; Russo, Nino

    2010-11-01

    Density Functional Theory investigations on the insertion mechanism of phenylacetylene into metal-hydride bonds in bimetallic (Pt,Os) catalysts have been carried out. The results obtained have been also compared with the non-reactive monometallic (Os-based) system, to elucidate the cooperative effects and to explain the observed absence of reactivity. The identified reaction path involves phenylacetylene coordination followed by the insertion into the metal-hydride bond, leading to the formation of the experimentally observed products. Both steps do not require large energies compatible with the experimental conditions. The comparison with the reaction path for the monometallic species gives some hints on the cooperative effects due to the presence of the second metal which is related to its role in the CO release for creating a coordination site for phenylacetylene and not in the insertion energetics. The calculations provide a detailed analysis of the reaction complexity and provide a rationale for the efficiency of the process.

  9. DFT Studies on the Isomerization of Butene Double Bond Catalyzed by 1-Butyl-3-methyl-imidazolium in Ionic Liquid

    Institute of Scientific and Technical Information of China (English)

    LI Ying-Xia; PU Min; CHEN Biao-Hua; LI Hui-Ying; LIU Kun-Hui; WANG Wen-Xing

    2005-01-01

    The geometries of reactant, product and transition state of the title reaction have been optimized by using density functional theory (DFT) at the B3LYP/6-31G(d,p) and B3LYP/6- 311++G(d,p) levels.The variations of the bond parameters in the course of reaction were analyzed.The zero point energy corrections were performed by vibrational analysis.The equilibrium states and the transition state were verified according to the number of virtue frequency of geometry.The intrinsic reaction coordinates (IRC) were calculated from the transition state.The calculated results show that the double bond rearrangement of butene catalyzed by 1-butyl-3-methyl-imidazolium cation is a one-step reaction.The forward energy barrier of isomerization from 1-butene to 2- butene is about 193 kJmol-1 and the reverse energy barrier about 209 kJmol-1 at the B3LYP/6- 31G(d,p) level, which means that the reaction is easy to proceed at or above room temperature.

  10. Nickel-catalyzed Csp2-Csp3 bond formation by carbon-fluorine activation.

    Science.gov (United States)

    Sun, Alex D; Leung, Kaylyn; Restivo, Anita D; LaBerge, Nicole A; Takasaki, Harumi; Love, Jennifer A

    2014-03-10

    We report herein a general catalytic method for Csp(2)-Csp(3) bond formation through C-F activation. The process uses an inexpensive nickel complex with either diorganozinc or alkylzinc halide reagents, including those with β-hydrogen atoms. A variety of fluorine substitution patterns and functional groups can be readily incorporated. Sequential reactions involving different precatalysts and coupling partners permit the synthesis of densely functionalized fluorinated building blocks.

  11. Silicon-Carbon Bond Formation via Nickel-Catalyzed Cross-Coupling of Silicon Nucleophiles with Unactivated Secondary and Tertiary Alkyl Electrophiles

    OpenAIRE

    Chu, Crystal K.; Liang, Yufan; Fu, Gregory C.

    2016-01-01

    A wide array of cross-coupling methods for the formation of C–C bonds from unactivated alkyl electrophiles have been described in recent years. In contrast, progress in the development of methods for the construction of C–heteroatom bonds has lagged; for example, there have been no reports of metal-catalyzed cross-couplings of unactivated secondary or tertiary alkyl halides with silicon nucleophiles to form C–Si bonds. In this study, we address this challenge, establishing that a simple, comm...

  12. Ampicillin-Ester Bonded Branched Polymers: Characterization, Cyto-, Genotoxicity and Controlled Drug-Release Behaviour

    Directory of Open Access Journals (Sweden)

    Ewa Oledzka

    2014-06-01

    Full Text Available The development and characterization of novel macromolecular conjugates of ampicillin using branched biodegradable polymers has been described in this study. The conjugates have been prepared coupling the β-lactam antibiotic with branched polymer matrices based on the natural oligopeptide core. The cyto- and genotoxicity of the synthesized polymers were evaluated with a bacterial luminescence test, two protozoan assays and Salmonella typhimurium TA1535. The presence of a newly formed covalent bond between the drug and the polymer matrices was confirmed by 1H-NMR and FTIR studies. A drug content (15.6 and 10.2 mole % in the macromolecular conjugates has been determined. The obtained macromolecular products have been subjected to further in vitro release studies. The total percentage of ampicillin released after 21 days of incubation was nearly 60% and 14% and this resulted from the different physicochemical properties of the polymeric matrices. This is the first report on the application of branched biodegradable polymeric matrices for the covalent conjugation of ampicillin. The obtained results showed that the synthesized macromolecular drug-conjugates might slowly release the active drug molecule and improve the pharmacokinetics of ampicillin.

  13. Synthesis of α-methylene-δ-oxo-γ-amino esters via Rh(ii)-catalyzed coupling of 1-sulfonyl-1,2,3-triazoles with Morita-Baylis-Hillman adducts.

    Science.gov (United States)

    Jeon, Hyun Ji; Kwak, Mi Soo; Jung, Da Jung; Bouffard, Jean; Lee, Sang-Gi

    2016-11-29

    A rhodium(ii)-catalyzed coupling of 1-sulfonyl-1,2,3-triazoles, prepared from 1-alkynes and sulfonyl azides, with Morita-Baylis-Hillman (MBH) adducts afforded highly functionalized α-methylene-δ-oxo-γ-amino esters in excellent yields with broad functional group tolerance. This transformation can also be successfully accomplished as a multicomponent all-in-one-pot reaction of 1-alkynes, sulfonyl azides and MBH adducts in the presence of Cu(i) and Rh(ii) catalysts.

  14. Gene cloning and molecular characterization of the Talaromyces thermophilus lipase catalyzed efficient hydrolysis and synthesis of esters.

    Science.gov (United States)

    Romdhane, Ines Belhaj-Ben; Frikha, Fakher; Maalej-Achouri, Inès; Gargouri, Ali; Belghith, Hafedh

    2012-02-15

    A genomic bank from Talaromyces thermophilus fungus was constructed and screened using a previously isolated fragment lipase gene as probe. From several clones isolated, the nucleotide sequence of the lipase gene (TTL gene) was completed and sequenced. The TTL coding gene consists of an open reading frame (ORF) of 1083bp encoding a protein of 269 Aa with an estimated molecular mass of 30kDa. The TTL belongs to the same gene family as Thermomyces lanuginosus lipase (TLL, Lipolase®), a well known lipase with multiple applications. The promoter sequence of the TTL gene showed the conservation of known consensus sequences PacC, CreA, Hap2-3-4 and the existence of a particular sequence like the binding sites of Oleate Response Element (ORE) and Fatty acids Responsis Element (FARE) which are similar to that already found to be specific of lipolytic genes in Candida and Fusarium, respectively. Northern blot analysis showed that the TTL expression was much higher on wheat bran than on olive oil as sole carbon source. Compared to the Lipolase®, this enzyme was found to be more efficient for the hydrolysis and the synthesis of esters; and its synthetic efficiency even reached 91.6% from Waste Cooking Oil triglycerides.

  15. Enantioselective Palladium-Catalyzed Carbene Insertion into the N-H Bonds of Aromatic Heterocycles.

    Science.gov (United States)

    Arredondo, Vanessa; Hiew, Stanley C; Gutman, Eugene S; Premachandra, Ilandari Dewage Udara Anulal; Van Vranken, David L

    2017-03-15

    C3-substituted indoles and carbazoles react with α-aryl-α-diazoesters under palladium catalysis to form α-(N-indolyl)-α-arylesters and α-(N-carbazolyl)-α-arylesters. The products result from insertion of a palladium-carbene ligand into the N-H bond of the aromatic N-heterocycles. Enantioselection was achieved using a chiral bis(oxazoline) ligand, in many cases with high enantioselectivity (up to 99 % ee). The method was applied to synthesize the core of a bioactive carbazole derivative in a concise manner.

  16. Enzymatic synthesis of phytosterol esters catalyzed by Candida rugosa lipase in water-in-[Bmim]PF6 microemulsion.

    Science.gov (United States)

    Zeng, Chaoxi; Qi, Suijian; Li, Zhigang; Luo, Riming; Yang, Bo; Wang, Yonghua

    2015-05-01

    A water-in-ionic liquid microemulsion ([Bmim]PF6/Tween20/H2O) was applied as reusable reaction medium to esterify phytosterols with fatty acid by Candida rugosa lipase (CRL) successfully. Two kinds of commercial CRLs, AY30 and AYS which cannot effectively catalyze esterification in conventional reaction system were found effective in the microemulsion system. Effects of reaction parameters on esterification were investigated; results showed that the conversion rate of 87.9 and 95.1 % was obtained in 24 and 48 h of reaction, respectively, under the optimized condition: the molar ratio of water to Tween 20 (w 0 value) at 5.4, Tween 20 at a concentration of 305 mM, 50 °C,pH 7.4, 10 % of enzyme loading (w/w, with respect to total reactants), and phytosterols/lauric acid molar ratio of 1:2. Moreover, by using n-hexane as the extraction agent, the lipase-encapsulated microemulsion could be reused at least seven times (>168 h) without significant changes in the conversion rate, while achieving a purpose of simple separation and purification.

  17. Engineered DsbC chimeras catalyze both protein oxidation and disulfide-bond isomerization in Escherichia coli: Reconciling two competing pathways

    OpenAIRE

    Segatori, Laura; Paukstelis, Paul J.; Gilbert, Hiram F.; Georgiou, George

    2004-01-01

    In the Escherichia coli periplasm, the formation of protein disulfide bonds is catalyzed by DsbA and DsbC. DsbA is a monomer that is maintained in a fully oxidized state by the membrane enzyme DsbB, whereas DsbC is a dimer that is kept reduced by a second membrane protein, DsbD. Although the catalytic regions of DsbA and DsbC are composed of structurally homologous thioredoxin motif domains, DsbA serves only as an oxidase in vivo, whereas DsbC catalyzes disulfide reduction and isomerization a...

  18. 氨基磺酸催化合成脂肪酸丁酯的研究%Synthesis of fatty acid butyl ester catalyzed by amino sulfonic acid

    Institute of Scientific and Technical Information of China (English)

    程正载; 龚凯; 张卫星; 高松; 雷锐; 颜晓潮; 从野

    2014-01-01

    The fatty acid butyl ester was respectively synthesized by the esterification of oleic acid with bu-tanol and the transesterification of rapeseed oil with butanol catalyzed by amino sulfonic acid. The fatty acid butyl ester product was analyzed by GC and its structure was characterized by FT-IR. The effects of molar ratio of butanol to oil ( oleic acid or rapeseed oil) , catalyst dosage, reaction temperature and reac-tion time on the conversion rates of oleic acid and rapeseed oil were investigated. The results showed that the optimal esterification conditions were obtained as follows: molar ratio of butanol to oleic acid 3∶1 , catalyst dosage 0. 8% (based on the mass of oleic acid), reaction temperature 110℃and reaction time 1. 5 h. Under these conditions, the conversion rate of oleic acid and the yield of fatty acid butyl ester reached 88. 6% and 83. 5%, respectively. The optimal transesterification conditions were obtained as follows:molar ratio of butanol to rapeseed oil 10∶1, catalyst dosage 1. 0% (based on the mass of rapeseed oil), reaction temperature 115℃ and reaction time 2. 0 h. Under the optimal conditions, the conversion rate of rapeseed oil and the yield of fatty acid butyl ester achieved 85. 6% and 80. 1%, respectively.%以氨基磺酸为催化剂,油酸及菜籽油与正丁醇分别进行酯化反应与酯交换反应制备脂肪酸丁酯。并利用气相色谱及红外光谱对产物进行分析及结构表征。考察了醇(正丁醇)油(油酸及菜籽油)摩尔比、催化剂用量、反应温度和反应时间对油酸及菜籽油转化率的影响。结果表明,油酸酯化反应的最佳工艺条件为:醇油摩尔比3∶1,催化剂用量为油酸质量的0.8%,反应温度110℃,反应时间1.5 h,此时油酸转化率达到88.6%,产品收率为83.5%;菜籽油酯交换反应的最佳工艺条件为:醇油摩尔比10∶1,催化剂用量为菜籽油质量的1.0%,反应温度115℃,反应时间2.0 h,

  19. Graphene Oxide Catalyzed C-H Bond Activation: The Importance Oxygen Functional Groups for Biaryl Construction

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Yongjun; Tang, Pei; Zhou, Hu; Zhang, Wei; Yang, Hanjun; Yan, Ning; Hu, Gang; Mei, Donghai; Wang, Jianguo; Ma, Ding

    2016-02-24

    A heterogeneous, inexpensive and environment-friendly carbon catalytic system was developed for the C-H bond arylation of benzene resulting in the subsequent formation of biaryl compounds. The oxygen-containing groups on these graphene oxide sheets play an essential role in the observed catalytic activity. The catalytic results of model compounds and DFT calculations show that these functional groups promote this reaction by stabilization and activation of K ions at the same time of facilitating the leaving of I. And further mechanisms studies show that it is the charge induced capabilities of oxygen groups connected to specific carbon skeleton together with the giant π-reaction platform provided by the π-domain of graphene that played the vital roles in the observed excellent catalytic activity. D. Mei acknowledges the support from the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory.

  20. Iron-Carbonyl-Catalyzed Redox-Neutral [4+2] Annulation of N-H Imines and Internal Alkynes by C-H Bond Activation.

    Science.gov (United States)

    Jia, Teng; Zhao, Chongyang; He, Ruoyu; Chen, Hui; Wang, Congyang

    2016-04-18

    Stoichiometric C-H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C-H transformations have not been developed. Herein, an iron-catalyzed annulation of N-H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C-H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C-H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C-H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step.

  1. Non-innocent additives in a palladium(II)-catalyzed C-H bond activation reaction: insights into multimetallic active catalysts.

    Science.gov (United States)

    Anand, Megha; Sunoj, Raghavan B; Schaefer, Henry F

    2014-04-16

    The role of a widely employed additive (AgOAc) in a palladium acetate-catalyzed ortho-C-H bond activation reaction has been examined using the M06 density functional theory. A new hetero-bimetallic Pd-(μ-OAc)3-Ag is identified as the most likely active species. This finding could have far-reaching implications with respect to the notion of the active species in palladium catalysis in the presence of other metal salt additives.

  2. Transition Metal Catalyzed Hydroarylation of Multiple Bonds: Exploration of Second Generation Ruthenium Catalysts and Extension to Copper Systems

    Energy Technology Data Exchange (ETDEWEB)

    T. Brent Gunnoe

    2011-02-17

    Catalysts provide foundational technology for the development of new materials and can enhance the efficiency of routes to known materials. New catalyst technologies offer the possibility of reducing energy and raw material consumption as well as enabling chemical processes with a lower environmental impact. The rising demand and expense of fossil resources has strained national and global economies and has increased the importance of accessing more efficient catalytic processes for the conversion of hydrocarbons to useful products. The goals of the research are to develop and understand single-site homogeneous catalysts for the conversion of readily available hydrocarbons into useful materials. A detailed understanding of these catalytic reactions could lead to the development of catalysts with improved activity, longevity and selectivity. Such transformations could reduce the environmental impact of hydrocarbon functionalization, conserve energy and valuable fossil resources and provide new technologies for the production of liquid fuels. This project is a collaborative effort that incorporates both experimental and computational studies to understand the details of transition metal catalyzed C-H activation and C-C bond forming reactions with olefins. Accomplishments of the current funding period include: (1) We have completed and published studies of C-H activation and catalytic olefin hydroarylation by TpRu{l_brace}P(pyr){sub 3}{r_brace}(NCMe)R (pyr = N-pyrrolyl) complexes. While these systems efficiently initiate stoichiometric benzene C-H activation, catalytic olefin hydroarylation is hindered by inhibition of olefin coordination, which is a result of the steric bulk of the P(pyr){sub 3} ligand. (2) We have extended our studies of catalytic olefin hydroarylation by TpRu(L)(NCMe)Ph systems to L = P(OCH{sub 2}){sub 3}CEt. Thus, we have now completed detailed mechanistic studies of four systems with L = CO, PMe{sub 3}, P(pyr){sub 3} and P(OCH{sub 2}){sub 3}CEt

  3. Purification, molecular cloning, and expression of 2-hydroxyphytanoyl- CoA lyase, a peroxisomal thiamine pyrophosphate-dependent enzyme that catalyzes the carbon-carbon bond cleavage during à-oxidation of 3- methyl-branched fatty acids

    CERN Document Server

    Foulon, V; Croes, K; Waelkens, E

    1999-01-01

    Purification, molecular cloning, and expression of 2-hydroxyphytanoyl- CoA lyase, a peroxisomal thiamine pyrophosphate-dependent enzyme that catalyzes the carbon-carbon bond cleavage during à-oxidation of 3- methyl-branched fatty acids

  4. Pyridine N-Oxide vs Pyridine Substrates for Rh(III)-Catalyzed Oxidative C-H Bond Functionalization.

    Science.gov (United States)

    Neufeldt, Sharon R; Jiménez-Osés, Gonzalo; Huckins, John R; Thiel, Oliver R; Houk, K N

    2015-08-12

    The origin of the high reactivity and site selectivity of pyridine N-oxide substrates in O-pivaloyl hydroxamic acid-directed Rh(III)-catalyzed (4+2) annulation reactions with alkynes was investigated computationally. The reactions of the analogous pyridine derivatives were previously reported to be slower and to display poor site selectivity for functionalization of the C(2)-H vs the C(4)-H bonds of the pyridine ring. The N-oxide substrates are found to be more reactive overall because the directing group interacts more strongly with Rh. For N-oxide substrates, alkyne insertion is rate-limiting and selectivity-determining in the reaction with a dialkyl alkyne, but C-H activation can be selectivity-determining with other coupling partners such as terminal alkynes. The rates of reaction with a dialkyl alkyne at the two sites of a pyridine substrate are limited by two different steps: C-H activation is limiting for C(2)-functionalization, while alkyne insertion is limiting for C(4)-functionalization. Consistent with the observed poor site selectivity in the reaction of a pyridine substrate, the overall energy barriers for functionalization of the two positions are nearly identical. High C(2)-selectivity in the C-H activation step of the reaction of the N-oxide is due to a cooperative effect of the C-H Brønsted acidity, the strength of the forming C-Rh bond, and intramolecular electrostatic interactions between the [Rh]Cp* and the heteroaryl moieties. On the other hand, some of these forces are in opposition in the case of the pyridine substrate, and C(4)-H activation is moderately favored overall. The alkyne insertion step is favored at C(2) over C(4) for both substrates, and this preference is largely influenced by electrostatic interactions between the alkyne and the heteroarene. Experimental results that support these calculations, including kinetic isotope effect studies, H/D exchange studies, and results using a substituted pyridine, are also described.

  5. A hydrogen-bonding network is important for oxidation and isomerization in the reaction catalyzed by cholesterol oxidase

    Energy Technology Data Exchange (ETDEWEB)

    Lyubimov, Artem Y. [Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Sinsheimer Laboratories, 1156 High Street, Santa Cruz, CA 95064 (United States); Chen, Lin; Sampson, Nicole S. [Department of Chemistry, Stony Brook University, Stony Brook, NY 11794-3400 (United States); Vrielink, Alice, E-mail: alice.vrielink@uwa.edu.au [School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Department of Molecular, Cell and Developmental Biology, University of California, Santa Cruz, Sinsheimer Laboratories, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2009-11-01

    The importance of active-site electrostatics for oxidative and reductive half-reactions in a redox flavoenzyme (cholesterol oxidase) have been investigated by a combination of biochemistry and atomic resolution crystallography. A detailed examination of active-site dynamics demonstrates that the oxidation of substrate and the re-oxidation of the flavin cofactor by molecular oxygen are linked by a single active-site asparagine. Cholesterol oxidase is a flavoenzyme that catalyzes the oxidation and isomerization of 3β-hydroxysteroids. Structural and mutagenesis studies have shown that Asn485 plays a key role in substrate oxidation. The side chain makes an NH⋯π interaction with the reduced form of the flavin cofactor. A N485D mutant was constructed to further test the role of the amide group in catalysis. The mutation resulted in a 1800-fold drop in the overall k{sub cat}. Atomic resolution structures were determined for both the N485L and N485D mutants. The structure of the N485D mutant enzyme (at 1.0 Å resolution) reveals significant perturbations in the active site. As predicted, Asp485 is oriented away from the flavin moiety, such that any stabilizing interaction with the reduced flavin is abolished. Met122 and Glu361 form unusual hydrogen bonds to the functional group of Asp485 and are displaced from the positions they occupy in the wild-type active site. The overall effect is to disrupt the stabilization of the reduced FAD cofactor during catalysis. Furthermore, a narrow transient channel that is shown to form when the wild-type Asn485 forms the NH⋯π interaction with FAD and that has been proposed to function as an access route of molecular oxygen, is not observed in either of the mutant structures, suggesting that the dynamics of the active site are altered.

  6. Transition-metal-catalyzed C-N bond forming reactions using organic azides as the nitrogen source: a journey for the mild and versatile C-H amination.

    Science.gov (United States)

    Shin, Kwangmin; Kim, Hyunwoo; Chang, Sukbok

    2015-04-21

    Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions. This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp(2))-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new

  7. Production of oleic acid ethyl ester catalyzed by crude rice bran (Oryza sativa lipase in a modified fed-batch system: problem and its solution

    Directory of Open Access Journals (Sweden)

    Indro Prastowo

    2015-01-01

    Full Text Available A fed-batch system was modified for the enzymatic production of Oleic Acid Ethyl Ester (OAEE using rice bran (Oryza sativa lipase by retaining the substrate molar ratio (ethanol/oleic acid at 2.05: 1 during the reaction. It resulted in an increase in the ester conversion up to 76.8% in the first 6 h of the reaction, and then followed by a decrease from 76.8% to 22.9% in 6 h later. Meanwhile, the production of water in the reaction system also showed a similar trend to the trend of ester production. The water was hypothesized to lead lipase to reverse the reaction which resulted in a decrease in both (water and esters in the last 6 h of the reaction. In order to overcome the problem, zeolite powders (25 and 50 mg/ml were added into the reaction system at 5 h of the reaction. As the result, final ester conversions increased drastically up to 90 - 95.7% (1.17 – 1.24 times. The addition also proved a hypothesis that the water was involved in reducing the ester conversion in the last 6 h of the reaction. Thus, the combination was effective to produce the high final ester conversion.

  8. Lipase catalyzed synthesis of L-alanyl, L-leucyl and L-phenylalanyl esters of D-glucose using unprotected amino acids.

    Science.gov (United States)

    Vijayakumar, Giriyapura R; Lohith, Kenchaiah; Somashekar, Bhandya R; Divakar, Soundar

    2004-09-01

    Enzymatic synthesis of l-alanyl, l-leucyl and l-phenylalanyl esters of D-glucose was carried out in a non-polar solvent using lipases from Rhizomucor miehei and porcine pancreas. The unprotected amino acids at millimolar concentrations were used in presence of 10 to 50% (w/w) glucose of the lipases to give ester yields up to >99%. The reaction mixture on analysis by 2-D NMR showed that the product is a mixture of 6-O-, 3-O- and 2-O-monoesters and 2,6-di-O- and 3,6- di-O-esters.

  9. Copper-Catalyzed Carbenoid Insertion Reactions of α-Diazoesters and α-Diazoketones into Si-H and S-H Bonds.

    Science.gov (United States)

    Keipour, Hoda; Jalba, Angela; Delage-Laurin, Léo; Ollevier, Thierry

    2017-01-28

    An efficient copper-catalyzed carbenoid insertion reaction of α-diazo carbonyl compounds into Si-H and S-H bonds was developed. A wide range of α-silylesters and α-thioesters was obtained in high yields (up to 98%) from α-diazoesters using 5 mol % of a simple copper(I) salt as catalyst. Using 0.05 mol % of the same catalyst, α-diazoketones led to α-silylketones in low to good yields (up to 70%).

  10. Pd-catalyzed autotandem C-C/C-C bond-forming reactions with tosylhydrazones: synthesis of spirocycles with extended π-conjugation.

    Science.gov (United States)

    Barroso, Raquel; Valencia, Rocío A; Cabal, María-Paz; Valdés, Carlos

    2014-04-18

    A new Pd-catalyzed autotandem process is presented by the reaction of tosylhydrazones of cyclic ketones and 2,2'-dibromobiphenyls and related systems. The process involves cross-coupling with tosylhydrazone followed by an intramolecular Heck reaction and gives rise to spirocyclic structures. Noteworthy, two C-CAr bonds are formed on the hydrazonic carbon during the process. Depending on the starting dibromide, an array of spirofluorenes, spirodibenzofluorenes, spiroacridines, and spiroanthracenes have been prepared. Thus, this methodology may be applied for the preparation of interesting structures useful in the development of optoelectronic materials.

  11. Lipase-catalyzed polyester synthesis – A green polymer chemistry

    Science.gov (United States)

    Kobayashi, Shiro

    2010-01-01

    This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’. PMID:20431260

  12. Lipase-catalyzed polyester synthesis--a green polymer chemistry.

    Science.gov (United States)

    Kobayashi, Shiro

    2010-01-01

    This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemoenzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting 'green polymer chemistry'.

  13. Initial Stages in the Rhodium(III)-Catalyzed C-H Bond Activation of Primary Alcohols in Aqueous Solution

    DEFF Research Database (Denmark)

    Eriksen, J.; Monsted, L.; Monsted, O.

    2010-01-01

    ,4,8,11-tetraazacyclotetradecane) cation. The hydride complex is stable for extended periods of time in acidic solution in the absence of oxidants. In basic solutions a series of base-catalyzed reactions take place to yield ultimately the same mixture of [Rh(cycb)(OH)(2)](+) isomers as produced by base hydrolysis of the trans...

  14. The C-Cl bonds in trichloroethylidene trichlorolactic ester, Cl3CCHOCOCHOCCl3. A 35Cl-NQR single crystal study

    Science.gov (United States)

    Hashimoto, M.; Nagarajan, V.; Weiden, Norbert; Weiss, Alarich

    1983-01-01

    By single crystal 35Cl-NQR with a 4π Zeeman spectrometer, the six independent 35Cl-nuclear quadrupole coupling tensors in trichloroethylidene trichlorolactic ester (chloralide) Cl3CCHOCOCHOCC13 have been studied at T=21 °C. The directions of the electric field gradient (EFG) tensor components have been determined. The main axes φzz are within ±0.5° parallel to the C-Cl bound directions. Very small asymmetry parameters in the range 0.005≤η≤0.053 are characteristic for the EFG tensors of Cl bond to carbon in aliphatic systems, and the six nuclear quadrupole coupling constants are found in the range 76.053≤e2qQh-1/MHz≤78.790. The orientations of the principal axes φxx and φyy is explained as due to intramolecular interactions likely of through space origin.

  15. A domino palladium-catalyzed C-C and C-O bonds formation via dual O-H bond activation: synthesis of 6,6-dialkyl-6H-benzo[c]chromenes.

    Science.gov (United States)

    Mahendar, Lodi; Krishna, Jonnada; Reddy, Alavala Gopi Krishna; Ramulu, Bokka Venkat; Satyanarayana, Gedu

    2012-01-20

    An efficient Pd-catalyzed domino reaction of α,α-dialkyl-(2-bromoaryl)methanols to 6,6-dialkyl-6H-benzo[c]chromenes is presented. Their formation can be explained via a five membered Pd(II)-cycle that efficiently involves a domino homocoupling with the second molecule, β-carbon cleavage, and finally intramolecular Buchwald-Hartwig cyclization. This domino process effectively involves breaking of five σ-bonds (2C-Br, 2O-H, and a C-C) and formation of two new σ-bonds (C-C and C-O). This mechanistic pathway is unprecedented and further illustrates the power of transition metal catalysis.

  16. Recent developments in lipase-catalyzed synthesis of polyesters.

    Science.gov (United States)

    Kobayashi, Shiro

    2009-02-18

    Polyester synthesis by lipase catalyst involves two major polymerization modes: i) ring-opening polymerization of lactones, and, ii) polycondensation. Ring-opening polymerization includes the finding of lipase catalyst; scope of reactions; polymerization mechanism; ring-opening polymerization reactivity of lactones; enantio-, chemo- and regio-selective polymerizations; and, chemoenzymatic polymerizations. Polycondensation includes polymerizations involving condensation reactions between carboxylic acid and alcohol functional groups to form an ester bond. In most cases, a carboxylic acid group is activated as an ester form, such as a vinyl ester. Many recently developed polymerizations demonstrate lipase catalysis specific to enzymatic polymerization and appear very useful. Also, since lipase-catalyzed polyester synthesis provides a good opportunity for conducting "green polymer chemistry", the importance of this is described.

  17. SEPARATION OF CHOLESTEROL ESTERS BY SILVER ION CHROMATOGRAPHY USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OR SOLID-PHASE EXTRACTION COLUMNS PACKED WITH A BONDED SULFONIC-ACID PHASE

    NARCIS (Netherlands)

    HOVING, EB; MUSKIET, FAJ; CHRISTIE, WW

    1991-01-01

    Two methods for the separation of cholesterol esters, based on the number of double bonds in their fatty acid moieties, are presented. Silver ion chromatography, usually performed on thin-layer chromatographic plates, was made suitable for high-performance liquid chromatography (HPLC) and solid-phas

  18. Copper-catalyzed direct amination of quinoline N-oxides via C-H bond activation under mild conditions.

    Science.gov (United States)

    Zhu, Chongwei; Yi, Meiling; Wei, Donghui; Chen, Xuan; Wu, Yangjie; Cui, Xiuling

    2014-04-04

    A highly efficient and concise one-pot strategy for the direct amination of quinoline N-oxides via copper-catalyzed dehydrogenative C-N coupling has been developed. The desired products were obtained in good to excellent yields for 22 examples starting from the parent aliphatic amines. This methodology provides a practical pathway to 2-aminoquinolines and features a simple system, high efficiency, environmental friendliness, low reaction temperature, and ligand, additives, base, and external oxidant free conditions.

  19. Mono-thioesters and di-thioesters by lipase-catalyzed reactions of alpha,omega-alkanedithiols with palmitic acid or its methyl ester.

    Science.gov (United States)

    Weber, N; Klein, E; Vosmann, K; Mukherjee, K D

    2004-06-01

    1- S-Mono-palmitoyl-hexanedithiol and 1- S-mono-palmitoyl-octanedithiol were prepared in high yield (80-90%) by solvent-free lipase-catalyzed thioesterification of palmitic acid with the corresponding alpha,omega-alkanedithiols in vacuo. Similarly, 1,6-di- S-palmitoyl-hexanedithiol and 1,8-di- S-palmitoyl-octanedithiol were prepared in moderate yield (50-60%) by solvent-free lipase-catalyzed thioesterification of palmitic acid with 1- S-Mono-palmitoyl-hexanedithiol and 1- S-mono-palmitoyl-octanedithiol, respectively. An immobilized lipase preparation from Rhizomucor miehei (Lipozyme RM IM) was more effective than a lipase B preparation from Candida antarctica (Novozym 435) or a lipase preparation from Thermomyces lanuginosus (Lipozyme TL IM). Lipase-catalyzed transthioesterifications of methyl palmitate with alpha,omega-alkanedithiols using the same enzymes were less effective than thioesterification for the preparation of the corresponding 1- S-mono-palmitoyl thioesters.

  20. High-yield preparation of wax esters via lipase-catalyzed esterification using fatty acids and alcohols from crambe and camelina oils.

    Science.gov (United States)

    Steinke, G; Weitkamp, P; Klein, E; Mukherjee, K D

    2001-02-01

    Fatty acids obtained from seed oils of crambe (Crambe abyssinica) and camelina (Camelina sativa) via alkaline saponification or steam splitting were esterified using lipases as biocatalysts with oleyl alcohol and the alcohols derived from crambe and camelina oils via hydrogenolysis of their methyl esters. Long-chain wax esters were thus obtained in high yields when Novozym 435 (immobilized lipase B from Candida antarctica) and papaya (Carica papaya) latex lipase were used as biocatalysts and vacuum was applied to remove the water formed. The highest conversions to wax esters were obtained with Novozym 435 (> or =95%) after 4-6 h of reaction, whereas with papaya latex lipase such a high degree of conversion was attained after 24 h. Products obtained from stoichiometric amounts of substrates were almost exclusively (>95%) composed of wax esters having compositions approaching that of jojoba (Simmondsia chinensis) oil, especially when crambe fatty acids in combination with camelina alcohols or camelina fatty acids in combination with crambe alcohols were used as substrates.

  1. Uniform Free-Energy Profiles of the P-O Bond Formation and Cleavage Reactions Catalyzed by DNA Polymerases β and λ.

    Science.gov (United States)

    Klvaňa, Martin; Bren, Urban; Florián, Jan

    2016-12-29

    Human X-family DNA polymerases β (Polβ) and λ (Polλ) catalyze the nucleotidyl-transfer reaction in the base excision repair pathway of the cellular DNA damage response. Using empirical valence bond and free-energy perturbation simulations, we explore the feasibility of various mechanisms for the deprotonation of the 3'-OH group of the primer DNA strand, and the subsequent formation and cleavage of P-O bonds in four Polβ, two truncated Polλ (tPolλ), and two tPolλ Loop1 mutant (tPolλΔL1) systems differing in the initial X-ray crystal structure and nascent base pair. The average calculated activation free energies of 14, 18, and 22 kcal mol(-1) for Polβ, tPolλ, and tPolλΔL1, respectively, reproduce the trend in the observed catalytic rate constants. The most feasible reaction pathway consists of two successive steps: specific base (SB) proton transfer followed by rate-limiting concerted formation and cleavage of the P-O bonds. We identify linear free-energy relationships (LFERs) which show that the differences in the overall activation and reaction free energies among the eight studied systems are determined by the reaction free energy of the SB proton transfer. We discuss the implications of the LFERs and suggest pKa of the 3'-OH group as a predictor of the catalytic rate of X-family DNA polymerases.

  2. 逆相转移催化合成葵花籽油蔗糖酯%Synthesis of sunflower oil sucrose ester catalyzed by inverse phase - transfer catalyst

    Institute of Scientific and Technical Information of China (English)

    樊国栋; 康丽; 林振宇

    2012-01-01

    Using water solvent method, sunflower oil sucrose ester was synthesized by inverse phase -transfer catalyst DMAP with sucrose and fatty acid methyl ester prepared by ester - exchange method in the presence of basic catalyst from sunflower oil and methanol. The effects of molar ratio of fatty acids methyl ester to sucrose, catalyst dosage, reaction temperature and reaction time were studied. The results showed that the optimal conditions were as follows; molar ratio of fatty acids methyl ester to sucrose 2.5:1, catalyst dosage 4% , reaction temperature 85 °C and reaction time 7 h. Under the optimal conditions, the conversion rate of sunflower oil fatty acid methyl ester could reach 65. 32%. The final product had good surface activity, the critical micelle concentration(CMC) was 6. 5 g/L, surface tension was 27.41 mN/ m, emulsifying power was 79s, water count was 7. 2 mL, HLB was 10. 1 and iodine value was 126. 9 gI/ 100 g.%先由食用葵花籽油和甲醇在碱性催化剂条件下酯交换反应制得脂肪酸甲酯,然后脂肪酸甲酯与蔗糖通过水溶剂法,以逆相转移催化剂DMAP催化制备蔗糖脂肪酸酯.通过对酯糖摩尔比、催化剂用量、反应温度、反应时间进行考察,确定最佳合成条件为:酯糖摩尔比2.5∶1,催化剂用量4%,反应温度 85℃,反应时间7h.在最佳合成条件下,葵花籽油脂肪酸甲酯的转化率高达65.32%,所得产品具有良好的表面活性,其临界胶束质量浓度(CMC)为6.5 g/L,表面张力为27.41 mN/m,乳化力为79 s,浊点指数为7.2 mL,HLB值为10.1,碘值(Ⅰ)为126.9 g/100 g.

  3. Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step.

    Science.gov (United States)

    Jayakumar, Jayachandran; Cheng, Chien-Hong

    2016-01-26

    A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant.

  4. Water as a green solvent for efficient synthesis of isocoumarins through microwave-accelerated and Rh/Cu-catalyzed C-H/O-H bond functionalization

    Energy Technology Data Exchange (ETDEWEB)

    Li, Qiu; Yan, Yunnan; Wang, Xiaowei; Gong, Binwei; Tang, Xiaobo; Shi, JingJing; Xu, H. Eric; Yi, Wei [Shenyang; (Gannan); (Van Andel); (UST - China); (Chinese Aca. Sci.)

    2014-08-14

    Green chemistry that uses water as a solvent has recently received great attention in organic synthesis. Here we report an efficient synthesis of biologically important isocoumarins through direct cleavage of C–H/O–H bonds by microwave-accelerated and Rh/Cu-catalyzed oxidative annulation of various substituted benzoic acids, where water is used as the only solvent in the reactions. The remarkable features of this “green” methodology include high product yields, wide tolerance of various functional groups as substrates, and excellent region-/site-specificities, thus rendering this methodology a highly versatile and eco-friendly alternative to the existing methods for synthesizing isocoumarins and other biologically important derivatives such as isoquinolones.

  5. Synthesis of Bioactive 2-(Arylaminothiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation

    Directory of Open Access Journals (Sweden)

    Damien Hédou

    2016-06-01

    Full Text Available A library of thirty eight novel thiazolo[5,4-f]quinazolin-9(8H-one derivatives (series 8, 10, 14 and 17 was prepared via the Hügershoff reaction and a Cu catalyzed intramolecular C-S bond formation, helped by microwave-assisted technology when required. The efficient multistep synthesis of the key 6-amino-3-cyclopropylquinazolin-4(3H-one (3 has been reinvestigated and performed on a multigram scale from the starting 5-nitroanthranilic acid. The inhibitory potency of the final products was evaluated against five kinases involved in Alzheimer’s disease and showed that some molecules of the 17 series described in this paper are particularly promising for the development of novel multi-target inhibitors of kinases.

  6. Comparison of estimation capabilities of response surface methodology (RSM with artificial neural network (ANN in lipase-catalyzed synthesis of palm-based wax ester

    Directory of Open Access Journals (Sweden)

    Salleh Abu

    2007-08-01

    Full Text Available Abstract Background Wax esters are important ingredients in cosmetics, pharmaceuticals, lubricants and other chemical industries due to their excellent wetting property. Since the naturally occurring wax esters are expensive and scarce, these esters can be produced by enzymatic alcoholysis of vegetable oils. In an enzymatic reaction, study on modeling and optimization of the reaction system to increase the efficiency of the process is very important. The classical method of optimization involves varying one parameter at a time that ignores the combined interactions between physicochemical parameters. RSM is one of the most popular techniques used for optimization of chemical and biochemical processes and ANNs are powerful and flexible tools that are well suited to modeling biochemical processes. Results The coefficient of determination (R2 and absolute average deviation (AAD values between the actual and estimated responses were determined as 1 and 0.002844 for ANN training set, 0.994122 and 1.289405 for ANN test set, and 0.999619 and 0.0256 for RSM training set respectively. The predicted optimum condition was: reaction time 7.38 h, temperature 53.9°C, amount of enzyme 0.149 g, and substrate molar ratio 1:3.41. The actual experimental percentage yield was 84.6% at optimum condition, which compared well to the maximum predicted value by ANN (83.9% and RSM (85.4%. The order of effective parameters on wax ester percentage yield were; respectively, time with 33.69%, temperature with 30.68%, amount of enzyme with 18.78% and substrate molar ratio with 16.85%, whereas R2 and AAD were determined as 0.99998696 and 1.377 for ANN, and 0.99991515 and 3.131 for RSM respectively. Conclusion Though both models provided good quality predictions in this study, yet the ANN showed a clear superiority over RSM for both data fitting and estimation capabilities.

  7. Iodine Catalyzed One-pot Synthesis of 3,4-Dihydroquinazolin-4-ones from Anthranilic Acids, Ortho Esters and Amines under Solvent-free Conditions

    Institute of Scientific and Technical Information of China (English)

    WANG,Hong-She; ZENG,Jun-E

    2008-01-01

    A simple and efficient procedure has been developed for the one-pot synthesis of 3,4-dihydroquinazolin-4-ones from anthranilic acids, ortho esters and amines using a catalytic amount of iodine under solvent-free conditions to afford the corresponding products in excellent yields. The direct use of commercially available catalyst, mild and solvent-free reaction conditions, short reaction time, easy workup and excellent yields are the advantages of the present protocol.

  8. A Convenient Hydrogenation Method for the Synthesis of Metallo-mesoporphyrin IX Dimethyl Esters via Self-catalyzed CoCI2-NaBH4 Reagent System

    Institute of Scientific and Technical Information of China (English)

    徐士超; 胡炳成; 胡田菁; 王欢; 黄修有; 娄兴焜; 刘祖亮

    2012-01-01

    A convenient protocol has been developed for the hydrogenation of metallo-protoporphyrin IX dimethyl esters (MPPDMEs) to their mesoporphyrin analogues using CoC12-NaBH4 reagent system. Metallo-porphyrin complexes were found to perform as self-catalysts in this procedure. This method provides several advantages such as safe and simple procedure, short reaction time, high yields and low cost.

  9. Transition metal-catalyzed oxidative double bond cleavage of simple and bio-derived alkenes and unsaturated fatty acids

    NARCIS (Netherlands)

    Spannring, Peter; Bruijnincx, Pieter C. A.; Weckhuysen, Bert. M.; Klein Gebbink, Bert

    2014-01-01

    The oxidative cleavage of the C=C double bond in unsaturated fatty acids into aldehydes or carboxylic acids is a reaction of current interest in biomass valorization. The products of this reaction, which is currently being performed on an industrial scale by means of ozonolysis, can be applied for t

  10. New Initiation Modes for Directed Carbonylative C–C Bond Activation: Rhodium-Catalyzed (3 + 1 + 2) Cycloadditions of Aminomethylcyclopropanes

    Science.gov (United States)

    2016-01-01

    Under carbonylative conditions, neutral Rh(I)-systems modified with weak donor ligands (AsPh3 or 1,4-oxathiane) undergo N-Cbz, N-benzoyl, or N-Ts directed insertion into the proximal C–C bond of aminomethylcyclopropanes to generate rhodacyclopentanone intermediates. These are trapped by N-tethered alkenes to provide complex perhydroisoindoles. PMID:27709913

  11. Thiol-functionalized copolymeric polyesters by lipase-catalyzed esterification and transesterification of 1,12-dodecanedioic acid and its diethyl ester, respectively, with 1-thioglycerol

    OpenAIRE

    Fehling, Eberhard; Bergander, Klaus; Klein, Erika; Weber, Nikolaus; Vosmann, Klaus

    2010-01-01

    Abstract Copolymeric polyoxoesters containing branched-chain methylenethiol functions, i.e., poly(1,12-dodecanedioic acid-co-1-thioglycerol) and poly(diethyl 1,12-dodecanedioate-co-1-thioglycerol), were formed by lipase-catalyzed polyesterification and polytransesterification of 1,12-dodecanedioic acid and diethyl 1,12-dodecanedioate, respectively, with 1-thioglycerol (3-mercaptopropane-1,2-diol) using immobilized lipase B from Candida antarctica (Novozym 435) in vacuo without dryi...

  12. Transfer Hydrogenation of C= C Double Bonds Catalyzed by Ruthenium Amido-Complexes:Scopes, Limitation and Enantioselectivity

    Institute of Scientific and Technical Information of China (English)

    XUE,Dong; CHENG,Ying-Chun; CUI,Xin; WANG,Qi-Wei; ZHU,Jin; DENG,Jin-Gen

    2004-01-01

    @@ The reduction of C = C double bonds is one of the most fundamental synthetic transformations and plays a key role in the manufacturing of a wide variety of bulk and fine chemicals. Hydrogenation of olefinic substrates can be achieved readily with molecular hydrogen in many cases, but transfer hydrogenation methods using suitable donor molecules such as formic acid or alcohols are receiving increasing attention as possible synthetic alternatives because it requires no special equipment and avoids the handling of potentially hazardous gaseous hydrogen.

  13. Rhodotorulaglutinis phenylalanine/tyrosine ammonia lyase enzyme catalyzed synthesis of the methyl ester of para-hydroxycinnamic acid and its potential antibacterial activity

    Directory of Open Access Journals (Sweden)

    Marybeth C MacDonald

    2016-03-01

    Full Text Available Biotransformation of L-tyrosine methyl ester (L-TM to the methyl ester of para- hydroxycinnamic acid (p-HCAM using Rhodotorula glutinis yeast phenylalanine/tyrosine ammonia lyase (PTAL; EC 4.3.1.26 enzyme was successfully demonstrated for the first time; progress of the reaction was followed by spectrophotometric determination at 315 nm. The following conditions were optimized for maximal formation of p-HCAM: pH (8.5, temperature (37 C, speed of agitation (50 rpm, enzyme concentration (0.080 µM, and substrate concentration (0.50 mM. Under these conditions, the yield of the reaction was ~15% in 1 h incubation period and ~63% after an overnight (~18 h incubation period. The product (p-HCAM of the reaction of PTAL with L-TM was confirmed using Nuclear Magnetic Resonance spectroscopy (NMR. Fourier Transform Infra-Red spectroscopy (FTIR was carried out to rule out potential hydrolysis of p-HCAM during overnight incubation. Potential antibacterial activity of p-HCAM was tested against several strains of Gram positive and Gram negative bacteria. This study describes a synthetically useful transformation, and could have future clinical and industrial applications.

  14. Rhodotorula glutinis Phenylalanine/Tyrosine Ammonia Lyase Enzyme Catalyzed Synthesis of the Methyl Ester of para-Hydroxycinnamic Acid and its Potential Antibacterial Activity.

    Science.gov (United States)

    MacDonald, Marybeth C; Arivalagan, Pugazhendhi; Barre, Douglas E; MacInnis, Judith A; D'Cunha, Godwin B

    2016-01-01

    Biotransformation of L-tyrosine methyl ester (L-TM) to the methyl ester of para- hydroxycinnamic acid (p-HCAM) using Rhodotorula glutinis yeast phenylalanine/tyrosine ammonia lyase (PTAL; EC 4.3.1.26) enzyme was successfully demonstrated for the first time; progress of the reaction was followed by spectrophotometric determination at 315 nm. The following conditions were optimized for maximal formation of p-HCAM: pH (8.5), temperature (37°C), speed of agitation (50 rpm), enzyme concentration (0.080 μM), and substrate concentration (0.50 mM). Under these conditions, the yield of the reaction was ∼15% in 1 h incubation period and ∼63% after an overnight (∼18 h) incubation period. The product (p-HCAM) of the reaction of PTAL with L-TM was confirmed using Nuclear Magnetic Resonance spectroscopy (NMR). Fourier Transform Infra-Red spectroscopy (FTIR) was carried out to rule out potential hydrolysis of p-HCAM during overnight incubation. Potential antibacterial activity of p-HCAM was tested against several strains of Gram-positive and Gram-negative bacteria. This study describes a synthetically useful transformation, and could have future clinical and industrial applications.

  15. Un-catalyzed peptide bond formation between two monomers of glycine, alanine, serine, threonine, and aspartic acid in gas phase: a density functional theory study

    Science.gov (United States)

    Bhunia, Snehasis; Singh, Ajeet; Ojha, Animesh K.

    2016-05-01

    In the present report, un-catalyzed peptide bond formation between two monomers of glycine (Gly), alanine (Ala), serine (Ser), threonine (Thr), and aspartic acid (Asp) has been investigated in gas phase via two steps reaction mechanism and concerted mechanism at B3LYP/6-31G(d,p) and M062X/6-31G(d,p) level of theories. The peptide bond is formed through a nucleophilic reaction via transition states, TS1 and TS2 in stepwise mechanism. The TS1 reveals formation of a new C-N bond while TS2 illustrate the formation of C=O bond. In case of concerted mechanism, C-N bond is formed by a single four-centre transition state (TS3). The energy barrier is used to explain the involvement of energy at each step of the reaction. The energy barrier (20-48 kcal/mol) is required for the transformation of reactant state R1 to TS1 state and intermediate state I1 to TS2 state. The large value of energy barrier is explained in terms of distortion and interaction energies for stepwise mechanism. The energy barrier of TS3 in concerted mechanism is very close to the energy barrier of the first transition state (TS1) of the stepwise mechanism for the formation of Gly-Gly and Ala-Ala di- peptide. However, in case of Ser-Ser, Thr-Thr and Asp-Asp di-peptide, the energy barrier of TS3 is relatively high than that of the energy barrier of TS1 calculated at B3LYP/6-31G(d,p) and M062X/6-31G(d,p) level of theories. In both the mechanisms, the value of energy barrier calculated at B3LYP/6-31G(d,p) level of theory is greater than that of the value calculated at M062X/6-31G(d,p) level of theory.

  16. The amide C-N bond of isatins as the directing group and the internal oxidant in Ru-catalyzed C-H activation and annulation reactions: access to 8-amido isocoumarins.

    Science.gov (United States)

    Kaishap, Partha Pratim; Sarma, Bipul; Gogoi, Sanjib

    2016-07-28

    The N-O, N-N and O-O bonds are the frequently used internally oxidative directing groups used in various redox-neutral coupling reactions. The sole use of the C-N bond as the oxidizing directing group was reported recently by Li X. and co-workers for the Rh(iii)-catalyzed C-H activation of phenacyl ammonium salts. Herein, we report the use of the amide C-N bond of isatins as the oxidizing directing group for the Ru(ii)-catalyzed redox-neutral C-H activation and annulation reactions with alkynes which afford 8-amido isocoumarins. The reaction also features excellent regioselectivity with alkyl aryl substituted alkynes.

  17. Functional-Group-Tolerant, Silver-Catalyzed N-N Bond Formation by Nitrene Transfer to Amines.

    Science.gov (United States)

    Maestre, Lourdes; Dorel, Ruth; Pablo, Óscar; Escofet, Imma; Sameera, W M C; Álvarez, Eleuterio; Maseras, Feliu; Díaz-Requejo, M Mar; Echavarren, Antonio M; Pérez, Pedro J

    2017-02-15

    Silver(I) promotes the highly chemoselective N-amidation of tertiary amines under catalytic conditions to form aminimides by nitrene transfer from PhI═NTs. Remarkably, this transformation proceeds in a selective manner in the presence of olefins and other functional groups without formation of the commonly observed aziridines or C-H insertion products. The methodology can be applied not only to rather simple tertiary amines but also to complex natural molecules such as brucine or quinine, where the products derived from N-N bond formation were exclusively formed. Theoretical mechanistic studies have shown that this selective N-amidation reaction proceeds through triplet silver nitrenes.

  18. Enantio- and periselective nitroalkene Diels-Alder reactions catalyzed by helical-chiral hydrogen bond donor catalysts.

    Science.gov (United States)

    Peng, Zhili; Narcis, Maurice J; Takenaka, Norito

    2013-08-19

    Helical-chiral double hydrogen bond donor catalysts promote the nitroalkene Diels-Alder reaction in an enantio- and periselective manner. This represents the first asymmetric catalytic nitroalkene Diels-Alder reaction via LUMO-lowering catalysis. To gain an insight into this new process, the substrate scope of our catalyst was investigated by exploiting readily available 5-substituted pentamethylcyclopentadienes. The catalyst was found to tolerate dienes with different steric demands as well as dienes substituted with heteroatoms. The synthetic utility of 5-substituted pentamethylcyclopentadienes is rather limited, and thus we have developed a three-step route to 1,4,5,5-tetrasubstituted cyclopentadienes from commercially available ketones.

  19. Enantio- and Periselective Nitroalkene Diels-Alder Reactions Catalyzed by Helical-Chiral Hydrogen Bond Donor Catalysts

    Directory of Open Access Journals (Sweden)

    Zhili Peng

    2013-08-01

    Full Text Available Helical-chiral double hydrogen bond donor catalysts promote the nitroalkene Diels-Alder reaction in an enantio- and periselective manner. This represents the first asymmetric catalytic nitroalkene Diels-Alder reaction via LUMO-lowering catalysis. To gain an insight into this new process, the substrate scope of our catalyst was investigated by exploiting readily available 5-substituted pentamethylcyclopentadienes. The catalyst was found to tolerate dienes with different steric demands as well as dienes substituted with heteroatoms. The synthetic utility of 5-substituted pentamethylcyclopentadienes is rather limited, and thus we have developed a three-step route to 1,4,5,5-tetrasubstituted cyclopentadienes from commercially available ketones.

  20. Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, Jared; Berman, Ashley; Bergman, Robert; Ellman, Jonathan

    2007-07-18

    A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.

  1. Thiol-functionalized copolymeric polyesters by lipase-catalyzed esterification and transesterification of 1,12-dodecanedioic acid and its diethyl ester, respectively, with 1-thioglycerol.

    Science.gov (United States)

    Fehling, Eberhard; Bergander, Klaus; Klein, Erika; Weber, Nikolaus; Vosmann, Klaus

    2010-10-01

    Copolymeric polyoxoesters containing branched-chain methylenethiol functions, i.e., poly(1,12-dodecanedioic acid-co-1-thioglycerol) and poly(diethyl 1,12-dodecanedioate-co-1-thioglycerol), were formed by lipase-catalyzed polyesterification and polytransesterification of 1,12-dodecanedioic acid and diethyl 1,12-dodecanedioate, respectively, with 1-thioglycerol (3-mercaptopropane-1,2-diol) using immobilized lipase B from Candida antarctica (Novozym 435) in vacuo without drying agent in the reaction mixture. After 360-480 h, both polyoxoesters were purified by extraction from the reaction mixtures followed by solvent fractionation. The precipitate of poly(1,12-dodecanedioic acid-co-1-thioglycerol) demonstrated a M(W) of ~170,000 Da, whereas a M(W) of ~7,100 Da only was found for poly(diethyl 1,12-dodecanedioate-co-1-thioglycerol). Both polycondensates were analyzed by GPC/SEC, alkali-catalyzed transmethylation, NMR- and FTIR-spectrometry.

  2. Cinchona Alkaloid Derivative-Catalyzed Enantioselective Synthesis via a Mannich-Type Reaction and Antifungal Activity of β-Amino Esters Bearing Benzoheterocycle Moieties

    Directory of Open Access Journals (Sweden)

    Han Xiao

    2014-04-01

    Full Text Available An efficient synthesis of highly functionalized chiral β-amino ester derivatives containing benzothiophene and benzothiazole moieties is developed by a Mannich-type reaction using a cinchona alkaloid-derived thiourea catalyst. The desired products were obtained in good yields and high enantioselectivities (~86% yield, >99% ee using to the optimized reaction conditions. The synthesized compounds were characterized by 1H-NMR, 13C-NMR, IR, and HREI-MS analyses. The bioassays identified that compound 5dr has excellent antifungal activity, with a 60.53% inhibition rate against F. oxysporum, higher than that of the commercial agricultural fungicide hymexazol, whose inhibition rate was 56.12%.

  3. Optimization of lipase-catalyzed synthesis of fatty acid ethyl ester from corn oil%脂肪酶催化玉米油合成脂肪酸乙酯工艺研究

    Institute of Scientific and Technical Information of China (English)

    康建波; 胡士恒; 王亚男; 周亚军

    2012-01-01

    为研制食药两用的功能性原料亚油酸乙酯,以玉米油和乙醇为原料,经固定化脂肪酶催化合成脂肪酸乙酯.通过单因素试验和响应面分析法(RSM)研究醇油摩尔比、脂肪酶用量、反应温度、反应时间对玉米油脂肪酸乙酯合成的影响.研究结果表明,玉米油脂肪酸乙酯合成的最佳工艺条件为醇油摩尔比为4∶1,脂肪酶质量分数为30.82%,反应温度为50.39℃,反应时间为24.15 h,在此工艺条件下脂肪酸乙酯转化率为90.20%.%In order to develop the functional raw material linoleic acid ethylester which can be used as both food and medicine, the fatty acid ethyl esters are synthesized by immobilized lipase-catalyzed reaction with corn oil and alcohol as raw material in this study. Based on the single factor experiments and response surface methodology ( RSM ) , the influences of molar ratio ethanol and corn oil, the amount of enzyme, the reaction temperature and reaction time on the synthesis of fatty acid ethyl ester from corn oil are investigated. The obtained optimal parameters are shown as follows -A-1 molar ratio of ethanol to oil,30 % of amount of enzyme,50. 39℃ of reaction temperature and 24 hours of reaction time. The rate of conversion of corn oil can reach 90. 20% .

  4. Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

    Energy Technology Data Exchange (ETDEWEB)

    Klobukowski, Erik [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and

  5. Lewis酸性离子液体催化合成丁二酸二异丙酯%Synthesis of succinic acid diisopropyl ester catalyzed by Lewis acid ionic liquids

    Institute of Scientific and Technical Information of China (English)

    赵地顺; 葛京京; 翟建华; 张娟; 刘猛帅; 李俊盼

    2014-01-01

    采用两步法制备了9种不同的Lewis酸性离子液体,采用1H NMR、FT-IR对离子液体的结构进行了表征,并系统地考察了其对丁二酸和异丙醇酯化反应的催化性能。结果表明,离子液体随着卤化物用量增加表现出更强的酸性。其中[Bmim]Br-Fe2Cl6催化合成丁二酸二异丙酯效果良好,催化剂用量为丁二酸质量的10.0%,反应温度100℃,反应时间4 h,酸醇摩尔比为1:5,丁二酸二异丙酯收率为88.9%,酯化率达92.7%。离子液体重复使用6次后,产品收率下降1.7%。%Nine kinds of different Lewis acid ionic liquids were synthesized by two-step process and their structures were characterized with 1H NMR and FT-IR. Lewis acid ionic liquids prepared were used to catalyze the esterification reaction of succinic acid and isopropyl alcohol. With the increase of dosage of halide, the ionic liquids showed stronger acidity. [Bmim]Br-Fe2Cl6 had the best catalytic performance, and optimal conditions for the synthesis of succinic acid diisopropyl ester were obtained as follows, amount of catalyst 10.0%(g/g)of succinic acid, reaction temperature 100℃ and reaction time 4 h, succinic acid and isopropyl alcohol ratio 1:5. Under the optimal conditions, the yield of succinic acid diisopropyl ester was up to 88.9%, esterification rate was 92.7%.The catalyst was recycled 6 times, and the yield of succinic acid diisopropyl ester only decreased by 1.7%.

  6. 氮杂冠醚化双Schiff碱配合物催化羧酸酯水解的研究%Study on aza crown ether substituted bis-Schiff base complexes catalyze carboxylic acid esters hydrolysis

    Institute of Scientific and Technical Information of China (English)

    程杰; 李建章; 何锡阳; 曾俊; 肖正华; 胡伟

    2012-01-01

    将4种氮杂冠醚取代的双Schiff碱钴(H)、锰(m)配合物作为仿水解酶模型催化羧酸酯(PNPP)水解.考察了Schiff碱配合物中氮杂冠醚取代的位置、氮杂冠醚的数目对其仿水解酶性能的影响;探讨了Schiff配合物催化PNPP水解的动力学和机理;提出了配合物催化PNPP水解的动力学模型.结果表明,在25℃条件下随着缓冲溶液pH值的增大,配合物催化PNPP水解速率提高;四种氮杂冠醚取代的双Schiff碱配合物在催化PNPP水解反应中表现出良好的催化活性;氮杂冠醚3-取代的Schiff碱配合物CoL2的催化活性高于5-取代的Schiff碱配合物CoL1,含有2个氮杂冠醚的配合物CoL3的催化活性高于含有1个氮杂冠醚的配合物CoL2.%Four aza crown ether substituted bis-Schiff base transition-mental complexes have been used as mimic hydrolytic enzyme model catalyzing carboxylic acid esters ( PNPP) hydrolysis. The effects of substituted position of aza-crown and amount of aza-crown of Schiff base complexes were studied. The kinetics on PNPP hydrolysis catalyzed by these complexes was investigated. The kinetic mathematical model of PNPP cleavage catalyzed by these complexes was proposed. The results showed that the rate for the catalytic PNPP hydrolysis was increased following the increase of pH of the buffer solution; four complexes exhibited high activity in the catalytic PNPP hydrolysis, The catalytic activity of unsymmetrical Schiff base complexes of 3-substitute benzo-10-aza-crown groups ( CoL2 ) is larger than that of 5 -substitute benzo-10-aza-crown groups ( CoL1) , and the catalytic activity of Schiff base complexes with two benzo-10-aza-crown ether pendants (CoL3) is larger than that of Schiff base complexes with one benzo-10-aza-crown ether pendants (CoL2).

  7. Sonolytic and Silent Polymerization of Methacrlyic Acid Butyl Ester Catalyzed by a New Onium Salt with bis-Active Sites in a Biphasic System — A Comparative Investigation

    Directory of Open Access Journals (Sweden)

    Perumberkandgai A. Vivekanand

    2013-02-01

    Full Text Available Currently, ingenious new analytical and process experimental techniques which are environmentally benign techniques, viz., ultrasound irradiation, have become immensely popular in promoting various reactions. In this work, a novel soluble multi-site phase transfer catalyst (PTC viz., 1,4-bis-(propylmethyleneammounium chloridebenzene (BPMACB was synthesized and its catalytic efficiency was assessed by observing the kinetics of sonolytic polymerization of methacrylic acid butyl ester (MABE using potassium persulphate (PPS as an initiator. The ultrasound–multi-site phase transfer catalysis (US-MPTC-assisted polymerization reaction was compared with the silent (non-ultrasonic polymerization reaction. The effects of the catalyst and various reaction parameters on the catalytic performance were in detail investigated by following the kinetics of polymerization of MABE in an ethyl acetate-water biphasic system. From the detailed kinetic investigation we propose a plausible mechanism. Further the kinetic results demonstrate clearly that ultrasound-assisted phase-transfer catalysis significantly increased the reaction rate when compared to silent reactions. Notably, this environmentally benign and cost-effective process has great potential to be applied in various polymer industries.

  8. A pinoresinol-lariciresinol reductase homologue from the creosote bush (Larrea tridentata) catalyzes the efficient in vitro conversion of p-coumaryl/coniferyl alcohol esters into the allylphenols chavicol/eugenol, but not the propenylphenols p-anol/isoeugenol.

    Science.gov (United States)

    Vassão, Daniel G; Kim, Sung-Jin; Milhollan, Jessica K; Eichinger, Dietmar; Davin, Laurence B; Lewis, Norman G

    2007-09-01

    The creosote bush (Larrea tridentata) accumulates a complex mixture of 8-8' regiospecifically linked lignans, of which the potent antioxidant nordihydroguaiaretic acid (NDGA) is the most abundant. Its tetra-O-methyl derivative (M4N) is showing considerable promise in the treatment of refractory (hard-to-treat) brain and central nervous system tumors. NDGA and related 9,9'-deoxygenated lignans are thought to be formed by dimerization of allyl/propenyl phenols, phenylpropanoid compounds that lack C-9 oxygenation, thus differentiating them from the more common monolignol-derived lignans. In our ongoing studies dedicated towards elucidating the biochemical pathway to NDGA and its congeners, a pinoresinol-lariciresinol reductase homologue was isolated from L. tridentata, with the protein obtained in functional recombinant form. This protein efficiently catalyzes the conversion of p-coumaryl and coniferyl alcohol esters into the corresponding allylphenols, chavicol and eugenol; neither of their propenylphenol regioisomers, p-anol and isoeugenol, are formed during this enzyme reaction.

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

    Science.gov (United States)

    Meng, Xiangtao; Edgar, Kevin J

    2015-11-05

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

  10. Degradation of phthalate esters and acetaminophen in river sediments using the electrokinetic process integrated with a novel Fenton-like process catalyzed by nanoscale schwertmannite.

    Science.gov (United States)

    Yang, Gordon C C; Huang, Sheng-Chih; Wang, Chih-Lung; Jen, Yu-Sheng

    2016-09-01

    The main objective of this study was to develop and establish an in situ remediation technology coupling nano-schwertmannite/H2O2 process and electrokinetic (EK) process for the removal of phthalates (PAEs) and acetaminophen in river sediments. Test results are given as follows: (1) injection of nano-schwertmannite slurry and H2O2 (collectively, "novel oxidant") into the anode reservoir would yield ·OH radicals that then will be diffused into the sediment compartment and further transported by the electroosmotic flow and/or electrophoresis from the anode end toward the cathode to degrade PAEs and pharmaceuticals in the sediment if any; (2) an electric potential gradient of 1.5 V cm(-1) would help the removal of PAEs and acetaminophen in the blank test, which no "novel oxidants" was added to the remediation system; (3) the practice of electrode polarity reversal would maintain neutral pH for sediment after remediation; (4) injection of equally divided dose of 10 mL novel oxidant into the anode reservoir and four injection ports on the top of sediment chamber would further enhance the removal efficiency; and (5) an extension of treatment time from 14 d to 28 d is beneficial to the removal efficiency as expected. In comparison, the remediation performance obtained by the EK-assisted nano-SHM/H2O2 oxidation process is superior to that of the batch degradation test, but is comparable with other EK integrated technologies for the treatment of same contaminants. Thus, it is expected that the EK-assisted nano-SHM/H2O2 oxidation process is a viable technology for the removal of phthalate esters and pharmaceuticals from river sediments in large-scale operations.

  11. InX3(X=F,Br)催化N-甲基吲哚与酮酸酯不对称合成机理的研究%Investigation on the Mechanism for N-Methylindole and Keto Ester Catalyzed by InX3(X=F,Br)

    Institute of Scientific and Technical Information of China (English)

    王薇; 毛双; 彭丹; 李来才

    2016-01-01

    The reaction mechanism for N-methylindole and keto ester catalyzed by InX3 (X=F,Br) was studied by the density functional theory (DFT).The geometries and the frequencies of reactants,intermediates,transition states,and products have been calculated at the B3LYP/6-31 +G(d,p) level,dichloroethane (DCE) is used as a solvent and the LanL2DZ basis has been used for In atom.Transition states have been confirmed by the corresponding vibration analysis and intrinsic reaction coordinate (IRC).In addition,nature bond orbital (NBO) and atoms in molecules (AIM) theories have been used to analyze orbital interactions and bond natures.The results showed that the activation energies of rate-determining steps in which N-methylindole reacted with keto ester to form 1,2-adduct and 1,4-adduct were 25.62 and 12.52 kcal/mol catalyzed by InF3 while those were 26.87 and 13.95 kcal/mol when the reaction was catalyzed by InBr3 under the same conditions.Comparing the results of our research,InF3 can effectively catalyze the reaction,and the 1,4-adduct was more likely to be produced.The final result of our theory study agreed with the experimental data,meanwhile,self-consistent reaction field (SCRF) was carried out using the polarized continuum model (PCM) at the same theoretical level for geometry optimizations and frequency calculations in five different salvations.We predicted that the productivity to form 1,4-adduct was more higher catalyzed by InF3 in the solvent of dimethyl sulfoxide (DMSO).%采用密度泛函理论(DFT)中的B3LYP方法,在B3LYP/6-31+ G(d,p)基组水平上(In采用赝势基组LanL2DZ),二氯乙烷(DCE)作为溶剂,研究了InX3 (X=F,Br)催化N-甲基吲哚与酮酸酯不对称合成微观反应机理,对反应通道上反应物、中间体、过渡态和产物进行了结构优化,通过能量和振动频率分析以及内禀反应坐标(IRC)计算证实了过渡态和中间体的合理性,并且在相同基组水平上,通过自然键轨道(NBO)理论和原子理论

  12. Synthesis of trimethylolpropane esters by powdered lipase-catalyzed esterification%脂肪酶粉催化酯化合成三羟甲基丙烷酯

    Institute of Scientific and Technical Information of China (English)

    王娟; 陈必强; 谭天伟

    2011-01-01

    以辛酸、癸酸和三羟甲基丙烷作为反应底物,利用Candida sp.99-125脂肪酶粉催化反应,研究了反应条件对酶法合成三羟甲基丙烷三辛癸酸酯的影响,并在实验中找到一种可以提高酶粉稳定性的添加剂β-环糊精.结果表明,加入0.01 mol三羟甲基丙烷(TMP) (1.34g),n三羟甲基丙烷/n(癸酸+辛酸)=1∶4,其中n癸酸∶n辛酸=1∶1,添加水的质量分数为0.05%(以底物总质量为基准)、脂肪酶粉的质量分数为12%(以底物总质量为基准)、β-环糊精的质量为酶粉质量的1.5倍,40℃下在恒温摇床中,振荡反应130h,转速130 r/min.在此条件下,反应产物三羟甲基丙烷三辛癸酸酯(三羟基酯)的质量分数可达到80%左右,酸与酯分离后收率可达96%;连续使用6批添加了β-环糊精的脂肪酶粉,三羟基酯的质量分数可保持在60%以上,与固定化酶的使用寿命相当.%The enzymatic production of trimethylolpropane (TMP) esters from the reaction of octanoic acid and de-canoic acid with TMP in the presence of powdered lipase Candida sp. 99-125 in a solvent-free system has been studied. The effects of varying the experimental conditions were studied in order to optimize the process. A maximum mass fraction of 80% of triesters was obtained after 130 h under the following optimized conditions; 0. 01 mol TMP, nTMP/n(octanoic acid +decanoic acid) =1: 4, noctanoic acid /ndecanoic acid = 1: 1, 0.05% (mass fraction) of added water (based on the weight of total substrate) , 12% (mass fraction) of powdered lipase (based on the weight of total substrate) , with added β-cyclodextrin (1.5 times the mass of powdered lipase) , at 40 ℃. After separating the products, the yield of triester reached 96% . Moreover, the powdered lipase with added β-cyclodextrin could be used continuously in six batches with the final mass fraction of triester remaining over 60% .

  13. Analyzing site selectivity in Rh2(esp)2-catalyzed intermolecular C-H amination reactions.

    Science.gov (United States)

    Bess, Elizabeth N; DeLuca, Ryan J; Tindall, Daniel J; Oderinde, Martins S; Roizen, Jennifer L; Du Bois, J; Sigman, Matthew S

    2014-04-16

    Predicting site selectivity in C-H bond oxidation reactions involving heteroatom transfer is challenged by the small energetic differences between disparate bond types and the subtle interplay of steric and electronic effects that influence reactivity. Herein, the factors governing selective Rh2(esp)2-catalyzed C-H amination of isoamylbenzene derivatives are investigated, where modification to both the nitrogen source, a sulfamate ester, and substrate are shown to impact isomeric product ratios. Linear regression mathematical modeling is used to define a relationship that equates both IR stretching parameters and Hammett σ(+) values to the differential free energy of benzylic versus tertiary C-H amination. This model has informed the development of a novel sulfamate ester, which affords the highest benzylic-to-tertiary site selectivity (9.5:1) observed for this system.

  14. Synthesis and Characteristics of an Aspartame Analogue, L-Asparaginyl L-3-Phenyllactic Acid Methyl Ester

    Institute of Scientific and Technical Information of China (English)

    Hu TAO; Da-Fu CUI; You-Shang ZHANG

    2004-01-01

    An aspartame analogue,L-asparaginyl L-3-phenyllactic acid methyl ester was synthesized with aspartic acid replaced by asparagine and peptide bond replaced by ester bond.The aspartic acid of aspartame could be replaced by asparagine as reported in the literature.In this analogue,the hydrogen ofamide group could still form a hydrogen bond with the oxygen of ester bond and the ester bond was isosteric with peptide bond.However,the product was not sweet,showing that the peptide bond could not be replaced by ester bond.The peptide C-N bond behaves as a double bond that is not free to rotate and the C,O,N and H atoms are in the same plane.The replacement of peptide bond by ester bond destroyed the unique conformation of peptide bond,resulting in the loss of sweet taste.

  15. Ester Formation

    NARCIS (Netherlands)

    Lopez Garzon, C.S.; Straathof, A.J.J.

    2014-01-01

    The present invention is in the field of a process for producing an ester, such as a biobased ester, from an aqueous biomass comprising solution, batch wise or continuously, wherein use of raw material is limited and if possible re-used. The present invention is in the field of green technology.

  16. Gold-Catalyzed Synthesis of Heterocycles

    Science.gov (United States)

    Arcadi, Antonio

    2014-04-01

    The following sections are included: * Introduction * Synthesis of Heterocycles via Gold-Catalyzed Heteroatom Addition to Unsaturated C-C Bonds * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Cyclization of Polyunsaturated Compounds * Synthesis of Heterocyclic Compounds via α-Oxo Gold Carbenoid * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Cycloaddition Reactions * Synthesis of Heterocyclic Derivatives through Gold-Catalyzed Activation of Carbonyl Groups and Alcohols * Synthesis of Heterocyclic Compounds through Gold-Mediated C-H Bond Functionalization * Gold-Catalyzed Domino Cyclization/Oxidative Coupling Reactions * Conclusions * References

  17. Recent Progress in the Research of Transition-Metal-Catalyzed C-CN Bond Cleavage%过渡金属催化的C—CN键断裂的研究进展

    Institute of Scientific and Technical Information of China (English)

    寇学振; 范佳骏; 童晓峰; 沈增明

    2013-01-01

    有机氰化物是一种重要的合成中间体,在药物、农药、染料和活性物质中都有应用.使用廉价、简单、低毒的氰基化合物在过渡金属的催化下通过C-CN键断裂生成复杂的氰化物是合成有机氰化物的重要手段之一.综述了不同过渡金属(如Ni,Pd,Rh,Cu,Ru,Fe,Mo,Co等)催化不同种类的氰基化合物C-CN键断裂的最新研究进展,如含C(sp1)-CN键化合物、C(sp2)-CN键化合物以及C(sp3)-CN键化合物,并对有关的反应机理及C-CN键断裂机理的进展进行了探讨.%Nitriles are an important class of organic compounds which can be found in pharmaceuticals,agrochemicals,dyes,and bioactive compounds.Transition-metal-catalyzed C-CN bond cleavage using inexpensive,simple and less toxic nitriles is one of the most attractive modem methods for the synthesis of complicated organic cyanides.Research progress of transition-metal-catalyzed (Ni,Pd,Rh,Cu,Ru,Fe,Mo,Co) different types of C-CN bond cleavage is reviewed,which includes some organic cyanides containing C(sp1)—CN bond,C(sp2)—CN bond and C(sp3)—CN bond.The C-CN cleavage mechanisms are also discussed in this review.

  18. Transition metal-catalyzed functionalization of pyrazines

    NARCIS (Netherlands)

    Nikishkin, Nicolai I.; Huskens, Jurriaan; Verboom, Willem

    2013-01-01

    Transition metal-catalyzed reactions are generally used for carbon–carbon bond formation on pyrazines and include, but are not limited to, classical palladium-catalyzed reactions like Sonogashira, Heck, Suzuki, and Stille reactions. Also a few examples of carbon–heteroatom bond formation in pyrazine

  19. Ester Exchange Polymerization of 3-Hydroxyl Propionic Acid Methyl Ester Catalyzed by SO3 H-functionalized Ionic Liquids%磺酸功能化离子液体催化3-羟基丙酸甲酯酯交换聚合反应

    Institute of Scientific and Technical Information of China (English)

    徐国荣; 刘建华; 宋大勇; 陈静; 夏春谷

    2012-01-01

    Employing SO3 H-functionalized ionic liquids as catalysts, the biodegradable poly [ 3-hydroxypropionic acid] (PHP) was obtained by ester exchange polymerization of 3-Hydroxyl propionie acid methyl ester(3-HPM). The effects of various ionic liquids, reaction temperature and reaction time on the polymerization performance were discussed in detail. Meanwhile, the FFIR, NMR and TG-DSC were applied to characterize the products. The PHP with Mw above 1.0×104 and yield above 82% could be obtained when catalyzed by [ BsMIm] [ OTf] under the opti- mal reaction conditions. In addition, the catalyst in the polymer could be removed completely after washing with water, efficiently avoiding the pollution of the product.%以磺酸功能化咪唑离子液体为催化剂,以3-羟基丙酸甲酯为原料,采用自身酯交换法合成了具有生物可降解性能的聚羟基脂肪酸酯.系统考察了离子液体种类、反应温度以及聚合反应时间对反应性能的影响,同时采用红外、核磁、热分析等手段对产物进行表征.研究结果表明:阴离子为CF3SO-3的磺酸功能化离子液体在120℃的低温下催化聚合反应所得聚酯Mw可达10 159,收率82.1%;通过水洗方法可有效去除产物中的离子液体催化剂,从而避免催化剂污染产物.

  20. Rhizopus arrhizus Lipase Catalyzed Syntheses of Three Esters in Nonaqueous Solvents%非水溶剂中Rhizopus arrhizus脂肪酶催化合成三种酯的最佳条件

    Institute of Scientific and Technical Information of China (English)

    杨本宏; 吴克; 刘斌; 郑敏; 蔡敬民; 潘仁瑞

    2003-01-01

    以少根根霉(Rhizopus arrhizus)脂肪酶为催化剂,有机溶剂为反应介质,合成了3种短链脂肪酸酯.研究了反应温度、溶剂、底物浓度、底物摩尔比、吸水剂用量等因素对酯化反应的影响.确定了3种酯的最佳合成条件:(1)己酸乙酯:反应温度为40℃,环己烷为溶剂,0.25 mol/L底物浓度,酸醇摩尔比为1∶1.2;(2)乙酸异丙酯:50℃,环己烷为溶剂,0.15 mol/L底物浓度,摩尔比为1∶1;(3)乙酸异戊酯:50℃,异辛烷为溶剂,0.20 mol/L底物浓度,摩尔比为1∶1. 三种酯合成时均需0.125 g/ml的0.5 nm分子筛为吸水剂,在8 h后,合成酯转化率达到97%~99%.%The Rhizopus arrhizus lipase catalyzed syntheses of three short-chain esters in organic solvents were studied. The optimum conditions for each esterification were determined as follows: (1)ethyl caproate: synthesized in cyclohexane at 40℃ with 0.25 mol/L substrate and 1∶1.2 acid-alcohol molar ratio; (2)isopropyl acetate: reacted in cyclohexane at 50℃ with 0.15 mol/L substrate and 1∶1 molar ratio; (3)isoamyl acetate: in isooctane at 50℃ with 0.20 mol/L substrate, and 1∶1 molar ratio. 0.125 g per ml of 0.5 nm molecular sieve was required as adsorbent for water in the reactions. Under the optimal conditions, the yields reached 97%-99% after incubation for 8 hours.

  1. Homologation of α-aryl amino acids through quinone-catalyzed decarboxylation/Mukaiyama-Mannich addition.

    Science.gov (United States)

    Haugeberg, Benjamin J; Phan, Johnny H; Liu, Xinyun; O'Connor, Thomas J; Clift, Michael D

    2017-03-09

    A new method for amino acid homologation by way of formal C-C bond functionalization is reported. This method utilizes a 2-step/1-pot protocol to convert α-amino acids to their corresponding N-protected β-amino esters through quinone-catalyzed oxidative decarboxylation/in situ Mukaiyama-Mannich addition. The scope and limitations of this chemistry are presented. This methodology provides an alternative to the classical Arndt-Eistert homologation for accessing β-amino acid derivatives. The resulting N-protected amine products can be easily deprotected to afford the corresponding free amines.

  2. Copper-catalyzed aerobic C(sp2)-H functionalization for C-N bond formation: synthesis of pyrazoles and indazoles.

    Science.gov (United States)

    Li, Xianwei; He, Li; Chen, Huoji; Wu, Wanqing; Jiang, Huanfeng

    2013-04-19

    A simple, practical, and highly efficient synthesis of pyrazoles and indazoles via copper-catalyzed direct aerobic oxidative C(sp(2))-H amination has been reported herein. This process tolerated a variety of functional groups under mild conditions. Further diversification of pyrazoles was also investigated, which provided its potential for drug discovery.

  3. A general and efficient approach to 2H-indazoles and 1H-pyrazoles through copper-catalyzed intramolecular N-N bond formation under mild conditions.

    Science.gov (United States)

    Hu, Jiantao; Cheng, Yongfeng; Yang, Yiqing; Rao, Yu

    2011-09-28

    A new efficient copper-catalyzed intramolecular amination reaction has been developed to readily synthesise a wide variety of multi-substituted 2H-indazole and 1H-pyrazole derivatives from easily accessible starting materials under mild conditions. A highly selective ligand for estrogen receptor β was prepared in three steps by employing this method.

  4. Ruthenium-Catalyzed Transformations of Alcohols: Mechanistic Investigations and Methodology Development

    DEFF Research Database (Denmark)

    Makarov, Ilya; Madsen, Robert; Fristrup, Peter

    in the transition state of the turnover-determining step. The value of the kinetic isotope effect of 2.290.15 indicated that the C–H bond breakage is not the rate-determining step, but that it is one of several slow steps in the catalytic cycle. Experiments with deuterium-labeled alcohols and amines revealed......The mechanism of the ruthenium-catalyzed dehydrogenative synthesis of amides from alcohols and amines was studied in detail by employing the combination of experimental and theoretical techniques. The Hammett study revealed that a small positive charge is formed at the benzylic position...... alcohols to give esters. Addition of 16.7 mol% of Mg3N2 to the reaction mixture gave esters from aliphatic alcohols in similar yields but at lower temperature as compared with previously a reported catalytic system. This additive also suppressed the decarbonylation of aromatic alcohols. A previously...

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

    KAUST Repository

    Elshewy, Ahmed M.

    2013-12-01

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

  6. Carbon kinetic isotope effects at natural abundances during iron-catalyzed photolytic cleavage of Csbnd C bonds in aqueous phase α,ω-dicarboxylic acids

    Science.gov (United States)

    Irei, Satoshi

    2016-09-01

    Carbon kinetic isotope effects (KIEs) at natural abundances during photolysis of Fe3+-oxalato, malonato, and succinato complexes in aqueous solution were studied to identify the Csbnd C bond cleaving mechanism of Fe3+-oxalato complexes under sunlight irradiation. Observed overall KIEs were 5.9‰, 11.5‰, and 8.4‰, respectively. This variation is inconsistent with secondary carbon KIEs for the Fesbnd O bond cleavage, but consistent with primary carbon KIEs for sequential cleavage of Fesbnd O and Csbnd C bonds. Position-specific probability of 13C content estimated KIEs of 5.9‰, 17.2‰, and 17‰ for 12Csbnd 13C bond cleavage, respectively, indicating the different KIEs for carboxyl-carboxyl and methyl-carboxyl cleavage.

  7. Mechanism of papain-catalyzed synthesis of oligo-tyrosine peptides.

    Science.gov (United States)

    Mitsuhashi, Jun; Nakayama, Tsutomu; Narai-Kanayama, Asako

    2015-01-01

    Di-, tri-, and tetra-tyrosine peptides with angiotensin I-converting enzyme inhibitory activity were synthesized by papain-catalyzed polymerization of L-tyrosine ethyl ester in aqueous media at 30 °C. Varying the reaction pH from 6.0 to 7.5 and the initial concentration of the ester substrate from 25 to 100 mM, the highest yield of oligo-tyrosine peptides (79% on a substrate basis) was produced at pH 6.5 and 75 mM, respectively. In the reaction initiated with 100 mM of the substrate, approx. 50% yield of insoluble, highly polymerized peptides accumulated. At less than 15 mM, the reaction proceeded poorly; however, from 30 mM to 120 mM a dose-dependent increase in the consumption rate of the substrate was observed with a sigmoidal curve. Meanwhile, each of the tri- and tetra-tyrosine peptides, even at approx. 5mM, was consumed effectively by papain but was not elongated to insoluble polymers. For deacylation of the acyl-papain intermediate through which a new peptide bond is made, L-tyrosine ethyl ester, even at 5mM, showed higher nucleophilic activity than di- and tri-tyrosine. These results indicate that the mechanism through which papain polymerizes L-tyrosine ethyl ester is as follows: the first interaction between papain and the ester substrate is a rate-limiting step; oligo-tyrosine peptides produced early in the reaction period are preferentially used as acyl donors, while the initial ester substrate strongly contributes as a nucleophile to the elongation of the peptide product; and the balance between hydrolytic fragmentation and further elongation of oligo-tyrosine peptides is dependent on the surrounding concentration of the ester substrate.

  8. Metal-catalyzed C-C bond cleavage in alkanes: effects of methyl substitution on transition-state structures and stability.

    Science.gov (United States)

    Flaherty, David W; Hibbitts, David D; Iglesia, Enrique

    2014-07-01

    Methyl substituents at C-C bonds influence hydrogenolysis rates and selectivities of acyclic and cyclic C2-C8 alkanes on Ir, Rh, Ru, and Pt catalysts. C-C cleavage transition states form via equilibrated dehydrogenation steps that replace several C-H bonds with C-metal bonds, desorb H atoms (H*) from saturated surfaces, and form λ H2(g) molecules. Activation enthalpies (ΔH(‡)) and entropies (ΔS(‡)) and λ values for (3)C-(x)C cleavage are larger than for (2)C-(2)C or (2)C-(1)C bonds, irrespective of the composition of metal clusters or the cyclic/acyclic structure of the reactants. (3)C-(x)C bonds cleave through α,β,γ- or α,β,γ,δ-bound transition states, as indicated by the agreement between measured activation entropies and those estimated for such structures using statistical mechanics. In contrast, less substituted C-C bonds involve α,β-bound species with each C atom bound to several surface atoms. These α,β configurations weaken C-C bonds through back-donation to antibonding orbitals, but such configurations cannot form with (3)C atoms, which have one C-H bond and thus can form only one C-M bond. (3)C-(x)C cleavage involves attachment of other C atoms, which requires endothermic C-H activation and H* desorption steps that lead to larger ΔH(‡) values but also larger ΔS(‡) values (by forming more H2(g)) than for (2)C-(2)C and (2)C-(1)C bonds, irrespective of alkane size (C2-C8) or cyclic/acyclic structure. These data and their mechanistic interpretation indicate that low temperatures and high H2 pressures favor cleavage of less substituted C-C bonds and form more highly branched products from cyclic and acyclic alkanes. Such interpretations and catalytic consequences of substitution seem also relevant to C-X cleavage (X = S, N, O) in desulfurization, denitrogenation, and deoxygenation reactions.

  9. Papain-Catalyzed Synthesis of Polyglutamate Containing a Nylon Monomer Unit

    Directory of Open Access Journals (Sweden)

    Kenjiro Yazawa

    2016-05-01

    Full Text Available Peptides have the potential to serve as an alternative for petroleum-based polymers to support a sustainable society. However, they lack thermoplasticity, owing to their strong intermolecular interactions. In contrast, nylon is famous for its thermoplasticity and chemical resistance. Here, we synthesized peptides containing a nylon unit to modify their thermal properties by using papain-catalyzed chemoenzymatic polymerization. We used l-glutamic acid alkyl ester as the amino acid monomer and nylon 1, 3, 4, and 6 alkyl esters as the nylon unit. Papain catalyzed the copolymerization of glutamic acid with nylon 3, 4, and 6 alkyl esters, whereas the nylon 1 unit could not be copolymerized. Other proteases used in this study, namely, bromelain, proteinase K, and Candida antarctica lipase (CALB, were not able to copolymerize with any nylon units. The broad substrate specificity of papain enabled the copolymerization of l-glutamic acid with a nylon unit. The peptides with nylon units demonstrated different thermal profiles from that of oligo(l-glutamic acid. Therefore, the resultant peptides with various nylon units are expected to form fewer intermolecular hydrogen bonds, thus altering their thermal properties. This finding is expected to broaden the applications of peptide materials and chemoenzymatic polymerization.

  10. Synthesis of Free Amino Acid Esters Co-catalyzed by Ionic Liquid%离子液体协同催化合成游离氨基酸酯

    Institute of Scientific and Technical Information of China (English)

    尚岩; 贾俊英; 高海鹏; 裴蕾; 仲昭琪

    2011-01-01

    以L-氨基酸和醇为原料,酸性离子液体辅以少量强酸性阳离子交换树脂作催化剂,直接酯化合成了8种游离的L-氨基酸酯,并用1HNMR对产物进行了表征.通过L-苯丙氨酸正丁酯的合成对离子液体的活性进行了考察,结果表明,所选用的11种离子液体在反应过程中均起到了一定的催化作用和助溶作用.其中,[Hmim][HSO4]效果较好,在重复使用后,显示了较好的稳定性,是氨基酸酯化反应理想的催化剂和助溶剂.%Eight kinds of free L-amino acid esters including L-phenylalanine ethyl ester, L-phenylalanine n-butyl ester, L-phenylalanine i-butyl ester, L-tyrosine n-butyl ester, L-tyrosine i-butyl ester, L-tyrosine i-amyl ester, L-aspartic n-butyl diester and L-aspartic i-butyl diester were synthesized by direct esterification of L-amino acid and alcohol with acidic ionic liquid assisted by strong acidic cation resin as catalyst. The structures of free L-amino acid esters were characterized by 1HNMR.Optimal reaction conditions were obtained when synthesizing L-phenylalanine n-butyl ester. Among eleven kinds of the acidic ionic liquids used in this case, [Hmim] [ HSO4 ] indicated excellent activity and the catalyst is easily regenerated and reused. By this token, it exhibits its potential application as catalyst and co-solvent in the esterification of amino acid.

  11. Synthesis of Palm Acide Polyol Esters Catalyzed by Acidic Ionic Liquid%酸性离子液体催化合成棕榈油酸多元醇酯

    Institute of Scientific and Technical Information of China (English)

    牛玉莲; 邢宝妹; 陆杨; 李在均; 刘俊康; 黄路

    2011-01-01

    将5种酸性离子液体分别应用于棕榈油酸多元醇酯的合成反应,结果发现硫酸三乙基铵离子液体催化活性最大.利用硫酸三乙基铵盐的温控特点,设计出一种“高温反应”和“低温分离”相结合的棕榈油酸多元醇酯的合成方法,得到了合成棕榈油酸季戊四醇酯的最佳反应条件:油酸与季戊四醇的物质的量比为6:1,离子液体质量分数为5%,210℃的反应温度和3.5h的反应时间.在相应的最佳条件下,棕榈油酸季戊四醇酯、棕榈油酸三羟甲基丙烷酯、棕榈油酸二羟甲基新戊烷酯、棕榈油酸山梨醇酯和棕榈油酸1,3-丁二醇酯的转化率分别达94.6%,94.5%,97.0%,98.5%和99.2%.反应完成后,离子液体沉淀析出,可直接用于下一次的合成反应.对5种酯化产品理化性质的研究结果表明,棕榈油酸多元醇酯具有良好的流动及低温特性,其黏度指数和倾点范围分别在184~388和- 23~-40℃之间,可作为生物润滑剂基础油.%Five acidic ionic liquids were investigated to synthesize palm acide polyol esters, the results indicated triethylammonium sulfate offers best catalytic activity. Based on temperature-controlled characteristics of triethylammonium sulfate, we designed a novel method for preparation of palm acide polyol esters, in which the reaction under relatively high temperature combined with the separation of the ionic liquid under relatively low temperature. The optimal conditions to produce palm acide pentaerythritol esters were obtained, these include a6'l of palm acide/pentaerythritol, 5% of the ionic liquid, 210 ℃ of the reaction temperature and 3.5 h of reaction time. Under corresponding optimal conditions, five palm acide pentaerythritol esters, which includes palm acide pentaerythritol ester, palm acide trimethylolpropane ester, palm acide dihydroxymethylneopentane ester, palm acide sorbitol ester and palm acide 1,3-butanediol ester, were synthesized in the

  12. Magnesium-induced copper-catalyzed synthesis of unsymmetrical diaryl chalcogenide compounds from aryl iodide via cleavage of the Se-Se or S-S bond.

    Science.gov (United States)

    Taniguchi, Nobukazu; Onami, Tetsuo

    2004-02-06

    The methodology for a copper-catalyzed preparation of diaryl chalcogenide compounds from aryl iodides and diphenyl dichalcogenide molecules is reported. Unsymmetrical diaryl sulfide or diaryl selenide can be synthesized from aryl iodide and PhYYPh (Y = S, Se) with a copper catalyst (CuI or Cu(2)O) and magnesium metal in one pot. This reaction can be carried out under neutral conditions according to an addition of magnesium metal as the reductive reagent. Furthermore, it is efficiently available for two monophenylchalcogenide groups generated from diphenyl dichalcogenide.

  13. 离子液体中6-O-(11-十二烯酸)葡萄糖酯的脂肪酶催化合成及其表征%Lipase-catalyzed synthesis and characterization of 6-O-(11-dodecenoic)-glucose ester in ionic liquids

    Institute of Scientific and Technical Information of China (English)

    黄广君; 韦超; 姚评佳; 魏远安

    2012-01-01

    In order to investigate the lipase-catalyzed selective transesterification of glucose with 11-dodecenoic ethyl ester in ionic liquids, the single-factor method was used to optimize the reaction conditions and determined various factors on the yield such as ionic liquids, temperature, molar rati-o, water content and enzyme concentration. The synthetic product structure was characterized by FT-IR, HPLC, MS and NMR. The results showed that the highest yield of sugar ester was obtained in 1-butyl-3-methyl imidazolium tetrailuoroborate [Bmitn] [BF4] under such conditions as the reaction temperature at 55 ℃, the enzyme concentration at 20 mg/mL, the mole ratio of glucose over 11 -dodecenoic ethyl ester at 1:2, and the water content of the system at 2% . Lipase Novozym-435 can be used 7 times repeatedly. The catalyzed product by Novozym-435 lipase in selective transesterification in [Bmim]BF4 was 6-O-(11-dodecenoic)-glucose ester.%为了探索脂肪酶在离子液体中选择性地催化葡萄糖与11-十二烯酸乙酯的转酯化反应,通过不同脂肪酶在不同离子液体中进行转酯化反应,并用单因素法研究离子液体种类、温度、底物的比例、体系含水量和脂肪酶含量对反应产率的影响,优化反应条件.反应产物的结构通过红外光谱、高效液相色谱、质谱和核磁共振等表征.结果表明:脂肪酶Novozym - 435在离子液体1-正丁基-3-甲基咪唑氟硼酸盐[BMIM][BF4]中,当反应温度为55℃、酶浓度20mgnmL、葡萄糖/11 -十二烯酸乙酯的摩尔比1∶2、体系的水含量为2%时,获得糖酯的产率最高,Novozym - 435可以重复使用7次.脂肪酶Novozym - 435在离子液体[BMIM][BF4]中选择性转酯化反应的产物为6-O-(11-十二烯酸)葡萄糖单酯.

  14. Synthetic Catalysts that Hydrolyze Phosphate and Carboxylate Esters

    Science.gov (United States)

    1992-09-18

    side hydroxylamine ýderivative of 0-cyclodextrin demonstrates base - catalyzed transesterification from pH 6.5-9.5, ,while the primary-side derivative does...hydroxylamine derivative of 0-cyclodextrin demonstrates base - catalyzed transesterification from pH 6.5-9.5, while the primary-side derivative does not...Chem. Soc. 1988, 110, 8553. 2) B. F. Duerr and A. W. Czarnik, "Cu(II) Catalyzed Hydrolysis of an Unactivated Ester Based on Reversible Conjugate

  15. 麦芽糊精硬脂酸酯的酶法合成及其乳化性的研究%Lipase-Catalyzed Synthesis and Emulsification of Dextrin Ester

    Institute of Scientific and Technical Information of China (English)

    孙平; 杨惠娟; 王雅琦; 刘可志; 徐雅雯

    2013-01-01

    研究了麦芽糊精硬脂酸酯的酶法合成工艺及其性能,对该工艺的影响因素进行单因素及正交试验.所确定的较佳工艺条件为:硬脂酸与糊精质量比为4∶1,酶添加量为7g/L,反应温度65℃,反应时间60 h,并研究了其结构与乳化性能.结果表明:乳液的乳化性随糖酯的质量分数增加而增加.在相同质量分数下,麦芽糊精硬脂酸酯乳化性最好,高于麦芽糖脂肪酸酯以及淀粉脂肪酸酯.%In this paper,the process of enzymatic catalysis for the synthesis of dextrin ester was investigated. The single factor and the orthogonal experiments for the affecting factors of this technology were carried out. Under the optimum conditions of 7 g/L lipase from Novozym 435, and acid/dextrin molar ratio of 4:1 at 65 t for 60 h,the optimum process was achieved. The results showed that:the emulsification increased with the concentration of dextrin esters. At the same concentration, the emulsification of the dextrin ester is higher than that of maltose ester and starch ester.

  16. Mechanistic Insights on C-O and C-C Bond Activation and Hydrogen Insertion during Acetic Acid Hydrogenation Catalyzed by Ruthenium Clusters in Aqueous Medium

    Energy Technology Data Exchange (ETDEWEB)

    Shangguan, Junnan; Olarte, Mariefel V.; Chin, Ya-Huei [Cathy

    2016-06-07

    Catalytic pathways for acetic acid (CH3COOH) and hydrogen (H2) reactions on dispersed Ru clusters in the aqueous medium and the associated kinetic requirements for C-O and C-C bond cleavages and hydrogen insertion are established from rate and isotopic assessments. CH3COOH reacts with H2 in steps that either retain its carbon backbone and lead to ethanol, ethyl acetate, and ethane (47-95 %, 1-23 %, and 2-17 % carbon selectivities, respectively) or break its C-C bond and form methane (1-43 % carbon selectivities) at moderate temperatures (413-523 K) and H2 pressures (10-60 bar, 298 K). Initial CH3COOH activation is the kinetically relevant step, during which CH3C(O)-OH bond cleaves on a metal site pair at Ru cluster surfaces nearly saturated with adsorbed hydroxyl (OH*) and acetate (CH3COO*) intermediates, forming an adsorbed acetyl (CH3CO*) and hydroxyl (OH*) species. Acetic acid turnover rates increase proportionally with both H2 (10-60 bar) and CH3COOH concentrations at low CH3COOH concentrations (<0.83 M), but decrease from first to zero order as the CH3COOH concentration and the CH3COO* coverages increase and the vacant Ru sites concomitantly decrease. Beyond the initial CH3C(O)-OH bond activation, sequential H-insertions on the surface acetyl species (CH3CO*) lead to C2 products and their derivative (ethanol, ethane, and ethyl acetate) and the competitive C-C bond cleavage of CH3CO* causes the eventual methane formation. The instantaneous carbon selectivities towards C2 species (ethanol, ethane, and ethyl acetate) increase linearly with the concentration of proton-type Hδ+ (derived from carboxylic acid dissociation) and chemisorbed H*. The selectivities towards C2 products decrease with increasing temperature, because of higher observed barriers for C-C bond cleavage than H-insertion. This study offers an interpretation of mechanism and energetics and provides kinetic evidence of carboxylic acid assisted proton-type hydrogen (Hδ+) shuffling during H

  17. Research progress of lipase-catalyzed synthesis of carbohydrate esters as food additives in non-aqueous phase%非水相中脂肪酶催化合成糖酯类食品添加剂的研究进展

    Institute of Scientific and Technical Information of China (English)

    戴清源; 朱秀灵

    2012-01-01

    糖酯类食品添加剂是同时含有亲水和疏水基团、HLB值为1~16的一种非离子型表面活性剂,具有无臭、无味、无毒及优良的表面性能等特点,在食品工业中具有诱人的应用前景。脂肪酶非水相催化合成糖酯有着化学合成法无可比拟的优点,已引起众多研究者的广泛关注。本文就非水相中催化合成糖酯所用脂肪酶的来源、非水相体系、酶的催化活性、糖酯类食品添加剂的检测方法及其在食品工业中的应用进行了综述,并展望其发展前景。%Carbohydrate fatty acid esters are non-ionic surfactants containing both hydrophilic and hydrophobic groups and having a wide range of hydrophilic-lipophilic balance(HLB)value from 1 to 16.These esters,which have several characteristics,such as odorless,tasteless,non-toxic and surface-active,have been applied to food industry with attractive prospects.Compared with chemical synthesis,lipase-catalyzed synthesis of carbohydrate fatty acid esters in non-aqueous has a lot of unexampled advantages,as a result,it has attracted many researchers' attention.In this paper,the source of lipase,non-aqueous system,catalytic activity of lipase in non-aqueous system,detection and application of carbohydrate fatty acid esters as food additive in food industry were summarized briefly.The prospects for future development of carbohydrate fatty acid esters were also introduced.

  18. Density functional study of electronic, charge density, and chemical bonding properties of 9-methyl-3-Thiophen-2-YI-Thieno [3,2-e] [1, 2, 4] Thriazolo [4,3-c] pyrimidine-8-Carboxylic acid ethyl ester crystals

    Energy Technology Data Exchange (ETDEWEB)

    Reshak, A.H., E-mail: maalidph@yahoo.co.uk [New Technologies – Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kamarudin, H. [Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Auluck, S. [CSIR-National Physical Laboratory, Dr. K S Krishnan Marg, New Delhi 110012 (India); Chyský, Jan [Department of Instrumentation and Control Engineering, Faculty of Mechanical Engineering, CTU in Prague, Technicka 4, 166 07 Prague 6 (Czech Republic)

    2014-06-01

    A comprehensive theoretical density functional investigation of the electronic crystal structure, chemical bonding, and the electron charge densities of 9-Methyl-3-Thiophen-2-YI-Thieno [3, 2-e] [1, 2, 4] Thriazolo [4,3-c] Pyrimidine-8-Carboxylic Acid Ethyl Ester (C{sub 15}H{sub 12}N{sub 4}O{sub 2}S{sub 2}) is performed. The density of states at Fermi level equal to 5.50 (3.45) states/Ry cell, and the calculated bare electronic specific heat coefficient is found to be 0.95 (0.59) mJ/mole-K{sup 2} for the local density approximation (Engel–Vosko generalized gradient approximation). The electronic charge density space distribution contours in (1 0 0) and (1 1 0) planes were calculated. We find that there are two independent molecules (A and B) in the asymmetric unit exhibit intramolecular C–H…O, C–H…N interactions. This intramolecular interaction is different in molecules A and B, where A molecule show C–H…O interaction while B molecule exhibit C–H…N interaction. We should emphasis that there is π–π interaction between the pyrimidine rings of the two neighbors B molecules gives extra strengths and stabilizations to the superamolecular structure. The calculated distance between the two neighbors pyrimidine rings found to be 3.345 Å, in good agreement with the measured one (3.424(1) Å). - Highlights: • Electronic structure, chemical bonding, and electron charge density were studied. • Density of states at Fermi level is 5.50 (3.45) states/Ry cell, for LDA (EVGGA). • Bare electronic specific heat coefficient is 0.95 (0.59) mJ/mole-K{sup 2} for LDA(EVGGA). • There are two independent molecules (A and B) in the asymmetric unit.

  19. Rh-Catalyzed Decarbonylation of Conjugated Ynones via Carbon–Alkyne Bond Activation: Reaction Scope and Mechanistic Exploration via DFT Calculations

    Science.gov (United States)

    Dermenci, Alpay; Whittaker, Rachel E.; Gao, Yang; Cruz, Faben A.; Yu, Zhi-Xiang; Dong, Guangbin

    2015-01-01

    In this full article, detailed development of a catalytic decarbonylation of conjugated monoynones to synthesize disubstituted alkynes is described. The reaction scope and limitation has been thoroughly investigated, and a broad range of functional groups including heterocycles were compatible under the catalytic conditions. Mechanistic exploration via DFT calculations has also been executed. Through the computational study, a proposed catalytic mechanism has been carefully evaluated. These efforts are expected to serve as an important exploratory study for developing catalytic alkyne-transfer reactions via carbon−alkyne bond activation. PMID:26229587

  20. Chiral Pd aqua complex-catalyzed asymmetric C-C bond-forming reactions: a Brønsted acid-base cooperative system.

    Science.gov (United States)

    Sodeoka, Mikiko; Hamashima, Yoshitaka

    2009-10-21

    Chiral cationic Pd aqua complexes can function as acid-base catalysts, effectively activating active methylene and methine compounds to give chiral Pd enolates. It is noteworthy that such enolate formation occurs with concomitant formation of a strong protic acid. Although the reactivity of the Pd enolate itself is not sufficient for reactions with carbon-based electrophiles, its cooperative action with the protic acid to activate the electrophiles allows the desired C-C bond-forming reactions to proceed smoothly in a highly enantioselective manner. Based on this mechanistic feature, reactions with acetals have been developed; these are difficult to achieve using conventional basic enolate chemistry.

  1. Recent Progress in Visible-Light Photoredox-Catalyzed Intermolecular 1,2-Difunctionalization of Double Bonds via an ATRA-Type Mechanism.

    Science.gov (United States)

    Courant, Thibaut; Masson, Géraldine

    2016-08-19

    Radical difunctionalizations of alkenes constitute an efficient method for the construction of complex organic molecules. This synopsis focuses on visible-light catalysis, a recent and very promising technological refinement of this class of transformations. Examples taken from the literature illustrate the use of a variety of (metallic or nonmetallic) systems, which allow us to leverage the energy of readily available visible-light radiation to efficiently create some of the most commonly looked for types of bonds (C-X, C-O, C-N, and C-C) under mild conditions and starting from unsaturated substrates.

  2. The origin of enantioselectivity in the l-threonine-derived phosphine-sulfonamide catalyzed aza-Morita-Baylis-Hillman reaction: Effects of the intramolecular hydrogen bonding

    KAUST Repository

    Lee, Richmond

    2013-01-01

    l-Threonine-derived phosphine-sulfonamide 4 was identified as the most efficient catalyst to promote enantioselective aza-Morita-Baylis-Hillman (MBH) reactions, affording the desired aza-MBH adducts with excellent enantioselectivities. Density functional theory (DFT) studies were carried out to elucidate the origin of the observed enantioselectivity. The importance of the intramolecular N-H⋯O hydrogen-bonding interaction between the sulfonamide and enolate groups was identified to be crucial in inducing a high degree of stereochemical control in both the enolate addition to imine and the subsequent proton transfer step, affording aza-MBH reactions with excellent enantioselectivity. © 2013 The Royal Society of Chemistry.

  3. FINAL TECHNICAL REPORT for grant DE-FG02-93ER14353 "Carbon-Hydrogen Bond Functionalization Catalyzed by Transition Metal Systems"

    Energy Technology Data Exchange (ETDEWEB)

    Goldman, Alan S

    2012-05-21

    Alkanes are our most abundant organic resource but are highly resistant to selective chemical transformations. Alkenes (olefins) by contrast are the single most versatile class of molecules for selective transformations, and are intermediates in virtually every petrochemical process as well as a vast range of commodity and fine chemical processes. Over the course of this project we have developed the most efficient catalysts to date for the selective conversion of alkanes to give olefins, and have applied these catalysts to other dehydrogenation reactions. We have also developed some of the first efficient catalysts for carbonylation of alkanes and arenes to give aldehydes. The development of these catalysts has been accompanied by elucidation of the mechanism of their operation and the factors controlling the kinetics and thermodynamics of C-H bond activation and other individual steps of the catalytic cycles. This fundamental understanding will allow the further improvement of these catalysts, as well as the development of the next generation of catalysts for the functionalization of alkanes and other molecules containing C-H bonds.

  4. Task-Specific Ionic Liquids Catalyzed Carbon-Heteroatom Bond Formation Reactions%功能化离子液体催化碳-杂键形成反应

    Institute of Scientific and Technical Information of China (English)

    李满; 杨磊; 韩峰; 陈静; 夏春谷

    2013-01-01

    离子液体独特的溶剂性能使它在合成和催化领域得到了广泛的应用.然而,离子液体的经济问题和可能的环境友好性问题使得人们逐渐把目光投向了离子液体自身的催化性能.人们通过对离子液体结构的修饰设计出了各种具有特定催化性能的功能化离子液体.近年来功能化离子液体在催化碳-杂键形成反应方面有了相当多的应用.本文以形成的碳-杂原子键类型为主线,综述了功能化离子液体在催化碳-杂键形成反应方面的最新研究进展,涉及到了酸性离子液体、碱性离子液体、金属有机功能化离子液体、酸碱双功能离子液体、手性离子液体等多种类型的功能化离子液体.%Ionic liquids have emerged as excellent solvents for synthesis and catalysis in the past decades due to their special properties.However,their relatively high cost and potential risks to human health and environment make their function as catalysts rather than solvents more popular.Incorporating specific functional group(s) into one or both ions of ionic liquids to make them catalytic is highly important.Numerous so-called task-specific or functionalized ionic liquids are designed and successfully applied in catalyzing various reactions.In this review,we present the latest achievements in the carbon-heteroatom bond formation reactions catalyzed by task-specific ionic liquids.The contents are arranged according to the specific types of carbon-heteroatom bond formation reactions.As for the type of task-specific ionic liquids,this review focuses on acidic ionic liquids,basic ionic liquids,organometallic ionic liquids,acid-base bifunctional ionic liquids and chiral ionic liquids.

  5. One-Pot Synthesis of Pyrrolo[1,2-a]indoles by Chiral N-Triflyl Phosphoramide Catalyzed Friedel-Crafts Alkylation of 4,7-Dihydroindole with ②, y-Unsaturated a-Keto Esters

    Institute of Scientific and Technical Information of China (English)

    曾蜜; 张玮; 游书力

    2012-01-01

    Chiral N-triflyl phosphoramide was found an efficient catalyst for the enantioselective Friedel-Crafts alkylation reaction of 4,7-dihydroindole with β, γ-unsaturated a-keto esters. In the presence of 5 tool% of the optimized catalyst, various pyrrolo[1,2-a]indoles were obtained in excellent enantioselectivity, moderate yields and up to 3 : 1 di- astereoselectivity based on the one-pot synthesis including the Friedel-Crafts alkylation reaction and the subsequent p-benzoquinone oxidation.

  6. SELECTIVITY OF LIPASE CATALYZED HYDROLYSIS OF SAFLOWER OIL%脂肪酶催化红花油水解的选择性研究

    Institute of Scientific and Technical Information of China (English)

    冯瑞军

    2011-01-01

    在无溶剂体系中用脂肪酶Lipase LVK、Lipase AY 30G及LipaseF-AP15催化红花油水解,测试了水解产物中脂肪酸与酯的碘值及酯中单甘酯的含量,研究了脂肪酶对脂肪酸种类的选择性以及对甘油酯键位置的选择性.结果表明,脂肪酶Lipase LVK、Lipase AY30G没有位置选择性和脂肪酸选择性,而Lipase F-AP15无脂肪酸选择性,但有一定的位置选择性.%Enzymatic hydrolysis of safflower oil catalyzed by Lipase LVK 、 Lipase AY 30G and Lipase F-AP15 was investigated in a solvent-free system. The selectivity of the lipase was also examined by testing the monoglycerides content in the ester and the iodine values (IV) of the fatty acid and the ester. The experiment showed that Lipase LVK and Lipase AY 30G has no selectivity on either the fatty acid or the site of the ester bond on the acylg-lycerol,while Lipase F-AP15 has some selectivity on the site of the ester bond on the acylg-lycerol but it has no selectivity on the fatty acid either.

  7. Formation of Chiral a-Monofluorinated-.8-amino Esters through Organocatalytic Asymmetric Reduction of a-Fluoro-j3-enamino Esters by Trichlorosilane

    Institute of Scientific and Technical Information of China (English)

    张鹏; 王超; 周莉; 孙健

    2012-01-01

    A concise method was developed to prepare chiral a-monofluorinated-β-amino esters through N-sulfinyl urea catalyzed asymmetric hydrosilylation of a-fluoro-β-enamino esters, which affords high yields, good to high di- astereoselectivities (up to〉99/1), and moderate to good enantioselectivities (up to 83% ee).

  8. Iron-Catalyzed Ortho C-H Methylation of Aromatics Bearing a Simple Carbonyl Group with Methylaluminum and Tridentate Phosphine Ligand.

    Science.gov (United States)

    Shang, Rui; Ilies, Laurean; Nakamura, Eiichi

    2016-08-17

    Iron-catalyzed C-H functionalization of aromatics has attracted widespread attention from chemists in recent years, while the requirement of an elaborate directing group on the substrate has so far hampered the use of simple aromatic carbonyl compounds such as benzoic acid and ketones, much reducing its synthetic utility. We describe here a combination of a mildly reactive methylaluminum reagent and a new tridentate phosphine ligand for metal catalysis, 4-(bis(2-(diphenylphosphanyl)phenyl)phosphanyl)-N,N-dimethylaniline (Me2N-TP), that allows us to convert an ortho C-H bond to a C-CH3 bond in aromatics and heteroaromatics bearing simple carbonyl groups under mild oxidative conditions. The reaction is powerful enough to methylate all four ortho C-H bonds in benzophenone. The reaction tolerates a variety of functional groups, such as boronic ester, halide, sulfide, heterocycles, and enolizable ketones.

  9. 油包水微乳液中抗体酶催化布洛芬酯选择性水解的酶学特性%Enzymological Characteristics of Catalytic Antibody-catalyzed enantioselective Hydrolysis of Ibuprofen Ester in Water-in-oil microemulsion

    Institute of Scientific and Technical Information of China (English)

    杨根生; 戚映丹; 欧志敏; 姚善泾

    2009-01-01

    The asymmetric hydrolyzation of racemic ibuprofen ester is one of the most important methods for chiral separation of ibuprofen. A catalytic antibody that accelerates the rate of enantioselective hydrolysis of ibuprofen methyl ester was successfully elicited against an immunogen consisting of tetrahedral sulfate hapten attached to bovine serum albumin (BSA). The rate constant enhancement factor Kcat/Kuncat was about 1.6x104. The catalytic activity of the catalytic antibody in a reverse micelle reaction system based on sodium b/s (2-ethylhexyl) sodium sulfosuccinate (AOT) in isooctane was studied. Kinetic analysis of the catalytic antibody-catalyzed reaction was found to be possible in this system. Kinetic studies showed that hydrolysis in the microemulsion system follow Michaelis-Menten kinetics. The catalytic antibody can also accelerate catalysis of S-ibuprofen methyl ester in the microemulsion system. Temperature effects, the pH profile, Km,app and Kcat were determined. The dependence of the catalytic antibody hydrolytic activity on the Wo (molar ratio of water to surfactant) showed a bell-shaped curve, presenting a maximum at about wo = 21.%根据过渡态理论设计和合成了能诱导产生催化选择性水解布洛芬甲酯的催化抗体的四面体硫酸盐半抗原,并与牛血清白蛋白(BSA)偶联制备成免疫源,通过免疫手段成功筛选出具有加速选择性水解生成S-布洛芬的特异性催化抗体.其Kcat,app/Kuncat,app达1.6x104.进一步地将催化抗体运用到W/O微乳体系(反胶束)中进行布洛芬酯的选择性水解研究,其动力学研究证明其催化过程同样遵循Michaelis.Menten方程.考察了pH值和温度对催化初速度影响,Wo(体系中水和琥珀酸二辛酯磺酸钠(AOT)的摩尔比)对催化初速度影响呈现为钟罩型,最适的Wo.为21.

  10. 微波辐射硫酸氢钠催化合成对氨基苯甲酸苄酯%Synthesis of 4-aminobenzoic acid benzyl ester catalyzed by sodium bisulfate under microwave radiation

    Institute of Scientific and Technical Information of China (English)

    杨晓军; 李西安

    2011-01-01

    在微波辐射下,以一水合硫酸氢钠为催化剂,对氨基苯甲酸和苯甲醇为原料,合成对氨基苯甲酸苄酯.结果表明,当微波辐射功率为500W,0.05mol对氨基苯甲酸为基准,催化剂的用量为1.6 g,酸醇的摩尔比为1∶1.2,反应时间14 min时,醋化率达93.8%.%The 4-aminobcnzoic acid benzyl ester was synthesized under microwave radiacion from 4-aminobenzoic acid and benzyl alcohol using sodium bisulfate as catalyst. When the power of microwave radiation was 500 W, amount of catalyst was 1. 6 g, the molar ratio of acid to alcohol was 1∶ 1.2( using 0. 05 mol of 4-aminobenzoic acid ) and reaction time was 14 min, the yield reached 93. 8% .

  11. Dimethyl carbonate-mediated lipid extraction and lipase-catalyzed in situ transesterification for simultaneous preparation of fatty acid methyl esters and glycerol carbonate from Chlorella sp. KR-1 biomass.

    Science.gov (United States)

    Jo, Yoon Ju; Lee, Ok Kyung; Lee, Eun Yeol

    2014-04-01

    Fatty acid methyl esters (FAMEs) and glycerol carbonate were simultaneously prepared from Chlorella sp. KR-1 containing 40.9% (w/w) lipid using a reactive extraction method with dimethyl carbonate (DMC). DMC was used as lipid extraction agent, acyl acceptor for transesterification of the extracted triglycerides, substrate for glycerol carbonate synthesis from glycerol, and reaction medium for the solvent-free reaction system. For 1g of biomass, 367.31 mg of FAMEs and 16.73 mg of glycerol carbonate were obtained under the optimized conditions: DMC to biomass ratio of 10:1 (v/w), water content of 0.5% (v/v), and Novozyme 435 to biomass ratio of 20% (w/w) at 70°C for 24h. The amount of residual glycerol was only in the range of 1-2.5mg. Compared to conventional method, the cost of FAME production with the proposed technique could be reduced by combining lipid extraction with transesterification and omitting the extraction solvent recovery process.

  12. 苯乙胺衍生的手性膦-亚磷酰胺酯配体在Rh-催化α-烯醇酯膦酸酯的不对称氢化反应中的应用%Rh-Catalyzed Asymmetric Hydrogenation of α-Enol Ester Phosphonates with 1-Phenylethylamine-Derived Phosphine-Phosphoramidite Ligands

    Institute of Scientific and Technical Information of China (English)

    胡娟; 王道永; 郑卓; 胡向平

    2012-01-01

    A series of phosphine-phosphoramidite ligands derived from commercially available,inexpensive chiral 1-phenylethylamine were employed in the Rh-catalyzed asymmetric hydrogenation of various α-enol ester phosphonates.The results indicated that the ligand(Sc,Sa)-2b bearing a Me-group on amino moiety exhibited similar enantioselectivity but superior catalytic activity to(Rc,Ra)-THNAPhos.Excellent enantioselectivities(up to 99% ee) and high catalytic activity(S/C up to 5 000) have been achieved in the hydrogenation of various β-alkyl and β-aryl substituted substrates,demonstrating the high potential of this phosphine-phosphoramidite ligand in the preparation of optically active α-hydroxyphosphonates%将苯乙胺衍生的手性膦-亚磷酰胺酯配体应用在Rh-催化α-烯醇酯膦酸酯的不对称氢化反应中,考察了配体结构及反应条件对反应结果的影响,并在优化的条件下研究了各种底物的适用范围,产物的对映选择性最高〉99%ee.

  13. A Convenient, General Synthesis of 1,1-Dimethylallyl Esters as Protecting Groups for Carboxylic Acids

    Science.gov (United States)

    Sedighi, Minoo; Lipton, Mark A.

    2006-01-01

    Carboxylic acids were converted in high yield to their 1,1-dimethylallyl (DMA) esters in two steps. Palladium-catalyzed deprotection of DMA esters was shown to be compatible with tert-butyl, benzyl and Fmoc protecting groups, and Fmoc deprotection could be carried out selectively in the presence of DMA esters. DMA esters were also shown to be resistant to nucleophilic attack, suggesting that they will serve as alternatives to tert-butyl esters when acidic deprotection conditions need to be avoided. PMID:15816730

  14. A convenient, general synthesis of 1,1-dimethylallyl esters as protecting groups for carboxylic acids.

    Science.gov (United States)

    Sedighi, Minoo; Lipton, Mark A

    2005-04-14

    [reaction: see text] Carboxylic acids were converted in high yield to their 1,1-dimethylallyl (DMA) esters in two steps. Palladium-catalyzed deprotection of DMA esters was shown to be compatible with tert-butyl, benzyl, and Fmoc protecting groups, and Fmoc deprotection could be carried out selectively in the presence of DMA esters. DMA esters were also shown to be resistant to nucleophilic attack, suggesting that they will serve as alternatives to tert-butyl esters when acidic deprotection conditions need to be avoided.

  15. Short-chain aliphatic ester synthesis using Thermobifida fusca cutinase.

    Science.gov (United States)

    Su, Lingqia; Hong, Ruoyu; Guo, Xiaojie; Wu, Jing; Xia, Yongmei

    2016-09-01

    Short-chain aliphatic esters are commonly used as fruit flavorings in the food industry. In this study, Thermobifida fusca (T. fusca) cutinase was used for the synthesis of aliphatic esters, and the maximum yield of ethyl caproate reached 99.2% at a cutinase concentration of 50U/ml, 40°C, and water content of 0.5%, representing the highest ester yield to date. The cutinase-catalyzed esterification displayed strong tolerance for water content (up to 8%) and acid concentration (up to 0.8M). At substrate concentrations ⩽0.8M, the ester yield remained above 80%. Moreover, ester yields of more than 98% and 95% were achieved for acids of C3-C8 and alcohols of C1-C6, respectively, indicating extensive chain length selectivity of the cutinase. These results demonstrate the superior ability of T. fusca cutinase to catalyze the synthesis of short-chain esters. This study provides the basis for industrial production of short-chain esters using T. fusca cutinase.

  16. Efficient hydrogenation of biomass-derived cyclic di-esters to 1,2-diols.

    Science.gov (United States)

    Balaraman, Ekambaram; Fogler, Eran; Milstein, David

    2012-01-28

    The unprecedented homogeneous hydrogenation of cyclic di-esters, in particular biomass-derived glycolide and lactide, to the corresponding 1,2-diols is catalyzed by Ru(II) PNN (1) and Ru(II) CNN (2) pincer complexes under mild hydrogen pressure and (in the case of 1) neutral conditions. No racemization was observed when a chiral di-ester was used.

  17. Can laccases catalyze bond cleavage in lignin?

    DEFF Research Database (Denmark)

    Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand

    2015-01-01

    Modification of lignin is recognized as an important aspect of the successful refining of lignocellulosic biomass, and enzyme-assisted processing and upcycling of lignin is receiving significant attention in the literature. Laccases (EC 1.103.2) are taking the centerstage of this attention, since...... is proposed. (C) 2015 Elsevier Inc. All rights reserved....

  18. 酶法催化乙酯甘油酯酯交换制备富含EPA和DHA的甘油酯%Preparation of glycerides rich in EPA and DHA by lipase-catalyzed transesterification between ethyl esters and triglycerides

    Institute of Scientific and Technical Information of China (English)

    郭正霞; 孙兆敏; 张芹; 王静凤; 薛长湖

    2012-01-01

    The immobilized Candida sp. lipase was used as the catalyst of transesterification to prepare glycerides which contained 45% DHA and EPA totally. Transesterification was carried out with fish oil ethyl esters and triglycerides as substrates. The effect on transesterification of temperature,reaction time,enzyme dosage,substrate weight ratio and water dosage were investigated with 5g glycerides as one of the substrates. The favorable conditions obtained were., reaction temperature 60℃, reaction time 24h,the substrate weight ratio 5:4,enzyme dosage 80U,without adding water to the reaction system. Under these conditions,the glycerides obtained contained 33.40% EPA and 13.10% DHA,and the immobilized enzyme could be used for seven times.%采用国产固定化假丝酵母脂肪酶,催化乙酯型和甘油酯型鱼油酯交换制备富舍EPA和DHA的甘油酯型鱼油,得到EPA和DHA总量超过45%的甘油酯。以5g甘油酯型鱼油为反应底物之一,考察了反应温度、时间、酶加量、底物质量比及加水量五个因素对酯交换反应的影响,利用正交实验优化,得到最佳反应条件为:反应温度60℃,反应时间24h,底物质量比为5:4,加酶量为80U,不向反应体系中加入水分。在该条件下得到的甘油酯中EPA和DHA的含量分别为33-40%和13.10%.并且脂肪酶重复利用7次仍能达到工艺目标。

  19. Advances in lipase-catalyzed esterification reactions.

    Science.gov (United States)

    Stergiou, Panagiota-Yiolanda; Foukis, Athanasios; Filippou, Michalis; Koukouritaki, Maria; Parapouli, Maria; Theodorou, Leonidas G; Hatziloukas, Efstathios; Afendra, Amalia; Pandey, Ashok; Papamichael, Emmanuel M

    2013-12-01

    Lipase-catalyzed esterification reactions are among the most significant chemical and biochemical processes of industrial relevance. Lipases catalyze hydrolysis as well as esterification reactions. Enzyme-catalyzed esterification has acquired increasing attention in many applications, due to the significance of the derived products. More specifically, the lipase-catalyzed esterification reactions attracted research interest during the past decade, due to an increased use of organic esters in biotechnology and the chemical industry. Lipases, as hydrolyzing agents are active in environments, which contain a minimum of two distinct phases, where all reactants are partitioned between these phases, although their distribution is not fixed and changes as the reaction proceeds. The kinetics of the lipase-catalyzed reactions is governed by a number of factors. This article presents a thorough and descriptive evaluation of the applied trends and perspectives concerning the enzymatic esterification, mainly for biofuel production; an emphasis is given on essential factors, which affect the lipase-catalyzed esterification reaction. Moreover, the art of using bacterial and/or fungal strains for whole cell biocatalysis purposes, as well as carrying out catalysis by various forms of purified lipases from bacterial and fungal sources is also reviewed.

  20. Highly efficient synthesis of β-amino esters via Mannich-type reaction under solvent-free conditions using ZnCl2 catalyst

    Institute of Scientific and Technical Information of China (English)

    Xue Ming Chen; Xing Shu Li; Albert S.C. Chan

    2009-01-01

    β-Amino esters were synthesized via ZnCl2-catalyzed Mannich-type reaction of imines and malonate esters under solvent-free conditions in 6 min.The β-amino ester was converted into the corresponding aspartic acid derivatives.

  1. Synthesis and physical properties of pennycress estolides and esters

    Science.gov (United States)

    A new series of pennycress (Thlasphi arvense L.) based free-acid estolides was synthesized by an acid-catalyzed condensation reaction, followed by an esterification reaction to produce the 2-ethylhexyl (2-EH) esters of the initial estolides. The physical properties of the estolides are highly affect...

  2. Synthesis and physical properties of petroselinic based estolide esters

    Science.gov (United States)

    A new series of petroselinic (Coriandrum sativum L.)-based estolide 2-ethylhexyl (2-EH) esters were synthesized, as the capping material varied in length and in degrees of unsaturation, in a perchloric acid catalyzed one-pot process with the esterification process incorporated into an in situ second...

  3. Thermodynamic Strategies for C-O Bond Formation and Cleavage via Tandem Catalysis.

    Science.gov (United States)

    Lohr, Tracy L; Li, Zhi; Marks, Tobin J

    2016-05-17

    To reduce global reliance on fossil fuels, new renewable sources of energy that can be used with the current infrastructure are required. Biomass represents a major source of renewable carbon based fuel; however, the high oxygen content (∼40%) limits its use as a conventional fuel. To utilize biomass as an energy source, not only with current infrastructure, but for maximum energy return, the oxygen content must be reduced. One method to achieve this is to develop selective catalytic methods to cleave C-O bonds commonly found in biomass (aliphatic and aromatic ethers and esters) for the eventual removal of oxygen in the form of volatile H2O or carboxylic acids. Once selective methods of C-O cleavage are understood and perfected, application to processing real biomass feedstocks such as lignin can be undertaken. This Laboratory previously reported that recyclable "green" lanthanide triflates are excellent catalysts for C-O bond-forming hydroalkoxylation reactions. Based on the virtues of microscopic reversibility, the same lanthanide triflate catalyst should catalyze the reverse C-O cleavage process, retrohydroalkoxylation, to yield an alcohol and an alkene. However, ether C-O bond-forming (retrohydroalkoxylation) to form an alcohol and alkene is endothermic. Guided by quantum chemical analysis, our strategy is to couple endothermic, in tandem, ether C-O bond cleavage with exothermic alkene hydrogenation, thereby leveraging the combined catalytic cycles thermodynamically to form an overall energetically favorable C-O cleavage reaction. This Account reviews recent developments on thermodynamically leveraged tandem catalysis for ether and more recently, ester C-O bond cleavage undertaken at Northwestern University. First, the fundamentals of lanthanide-catalyzed hydroelementation are reviewed, with particular focus on ether C-O bond formation (hydroalkoxylation). Next, the reverse C-O cleavage/retrohydroalkoxylation processes enabled by tandem catalysis are

  4. Using the biomarker bonded on the asphaltenes for biodegraded oil-source correlation

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Ruthenium-ion-catalyzed oxidation (RICO) has been used to investigate asphaltenes from three oils with the same origin in the Juquan Basin and three oils with the same origin but with different degree of biodegradation in the Turpan Basin, Northwest China. The preliminary results showed that the biomarkers bonded on the asphaltenes with the same origin is similar and is correlated with the free biomarker in saturates. The bonded biomarkers have no relationship with the biodegradation. An application on the severely biodegraded oils is reported here. The biomarker and benzenecarboxylic methyl esters reflecting the structure of the asphaltenes after RICO should provide a new way for oil-source correlation and it should be specially useful for severely biodegraded oil-source correlation.

  5. Lipase catalyzed synthesis of epoxy-fatty acids

    Institute of Scientific and Technical Information of China (English)

    CHEN, Qian; LI, Zu-Yi

    2000-01-01

    Lipase catalyzed synthesis of epoxy-fatty acidas from unsaturated carboxylic acids was investigated.Under mild conditions unsaturated arboxylic acids were convcveed to peroxide,then the unsaturated peroxycarboxylic acids epoxidised the C=C bond of themselves

  6. 超声波辅助下K2O/C催化制备纤维低聚糖脂肪酸酯表面活性剂%Ultrasonic-assisted Synthesis of Cellulosic Oligosaccharide Esters Surfactant Catalyzed by K2 O/C

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    The solid base catalyst K2 O/C was prepared by the vacuum impregnation method. The orthogonal experiment was employed to optimize the preparation condition. The results indicated that the optimal reaction parameters were carbon carrier with average pore size 2. 87 nm, K2 CO3/C mass ratio 0. 5, catalyst calcination temperature 450 ℃, and calcination time 2 h. The prepared catalyst K2 O/C was adopted to catalyze the transesterification reaction of cellulosic oligosaccharide esters from cellulosic oligosaccharide and methyl oleate under ultrasonic assistance. The optimum conditions were obtained as follows: the ultrasonic frequency 20 kHz, the ultrasonic power 150 W, treatment time 15 min, the mole ratio of methyl oleate to cellulosic oligosaccharide esters 2∶1, the mass fraction of K2 O/C 5%, the reaction temperature 125 ℃, and the reaction time 2 h. Under these conditions, the yield of cellulosic oligosaccharide esters reached 85. 6%. The synthesized product has esterification degree 18. 8%, HLB 9. 89, surface tension 32. 1 mN/m, and the emulsifying ability 28. 1%. The product showed good performance on surface tension, emulsion and stability in hard water.%采用真空浸渍法制备炭基固体碱催化剂 K2 O/C,并在超声波辅助条件下,利用制备的K2 O/C催化纤维低聚糖与油酸甲酯制备纤维低聚糖脂肪酸酯表面活性剂。选取L9(34)正交试验确定制备K2 O/C催化剂的最佳条件为:炭基载体平均孔径为2.87 nm,K2 CO3与炭基载体的质量比值为0.5,真空浸渍后,450℃下煅烧2 h。考察了超声波辅助下超声波时间、超声波频率、反应温度、反应时间和催化剂用量对产品得率的影响。研究发现:在20 kHz,150 W超声功率下,将物质的量之比为2∶1的油酸甲酯和纤维低聚糖(水溶液)超声波作用15 min,形成均一稳定的乳化体系,真空条件下,移除体系中的水分后,加入占总物料量5%的K2 O/C催化剂,125℃下反应2 h,纤维低聚糖

  7. Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp2 C–H and sp3 C–H bonds

    Science.gov (United States)

    Bhunia, Subhajit

    2016-01-01

    Summary The synthesis of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudo benzylic position has been achieved via a ‘transition-metal-free’ intramolecular dehydrogenative coupling (IDC). The construction of 2-oxindole moieties was carried out through formation of carbon–carbon bonds using KOt-Bu-catalyzed one pot C-alkylation of β-N-arylamido esters with alkyl halides followed by a dehydrogenative coupling. Experimental evidences indicated toward a radical-mediated path for this reaction. PMID:27559367

  8. Hydroboration-oxidation: A chemoselective route to cellulose ω-hydroxyalkanoate esters.

    Science.gov (United States)

    Meng, Xiangtao; York, Emily A; Liu, Shu; Edgar, Kevin J

    2015-11-20

    We describe the first synthesis of hydroxy-functionalized polysaccharide esters via chemoselective olefin hydroboration-oxidation in the presence of ester groups. Cellulose esters with terminally olefinic side chains were first synthesized by esterification of commercially available cellulose esters (e.g., cellulose acetate) with undec-10-enoyl chloride or pent-4-enoyl chloride. Subsequent two-step, one-pot hydroboration-oxidation reactions of the cellulose esters were performed, using 9-borabicyclo[3.3.1]nonane as hydroboration agent, followed by oxidizing the intermediate borane to a hydroxyl group using mildly alkaline H2O2. Sodium acetate was used as a weak base to catalyze the oxidation, thereby minimizing undesired ester hydrolysis. Characterization methods including FTIR, (1)H, and (13)C NMR proved the selectivity of the hydroboration-oxidation pathway, providing a family of novel cellulose ω-hydroxyalkanoyl esters that were previously difficult to access.

  9. Rhodium-catalyzed restructuring of carbon frameworks.

    Science.gov (United States)

    Murakami, Masahiro

    2010-10-01

    Metal-catalyzed reactions involving an elementary step which cleaves a carbon-carbon bond provide unique organic transformations. Restructuring reactions recently developed in our laboratory, through which the carbon framework of a starting substance is restructured into a totally different carbon framework, are discussed, with the possibility of applying such methods to the synthesis of natural products.

  10. Chemoenzymatic Synthesis and Chemical Recycling of Poly(ester-urethanes

    Directory of Open Access Journals (Sweden)

    Hiroto Hayashi

    2011-08-01

    Full Text Available Novel poly(ester-urethanes were prepared by a synthetic route using a lipase that avoids the use of hazardous diisocyanate. The urethane linkage was formed by the reaction of phenyl carbonate with amino acids and amino alcohols that produced urethane-containing diacids and hydroxy acids, respectively. The urethane diacid underwent polymerization with polyethylene glycol and a,w-alkanediols and also the urethane-containing hydroxy acid monomer was polymerized by the lipase to produce high-molecular-weight poly(ester-urethanes. The periodic introduction of ester linkages into the polyurethane chain by the lipase-catalyzed polymerization afforded chemically recyclable points. They were readily depolymerized in the presence of lipase into cyclic oligomers, which were readily repolymerized in the presence of the same enzyme. Due to the symmetrical structure of the polymers, poly(ester-urethanes synthesized in this study showed higher Tm, Young’s modulus and tensile strength values.

  11. Polyhydroxyester films obtained by non-catalyzed melt-polycondensation of natural occurring fatty polyhydroxyacids.

    Directory of Open Access Journals (Sweden)

    Jose Jesus Benitez

    2015-08-01

    Full Text Available Free-standing polyesters films from mono and polyhydroxylated fatty acids (C16 and C18 have been obtained by non-catalyzed melt-condensation polymerization in air at 150°C. Chemical characterization by Fourier Transform Infrared Spectroscopy (FTIR and 13C Magic Angle Spinning Nuclear Magnetic Resonance (13C MAS-NMR has confirmed the formation of the corresponding esters and the occurrence of hydroxyl partial oxidation which extent depends on the type of hydroxylation of the monomer (primary or secondary. Generally, polyester films obtained are hydrophobic, insoluble in common solvents, amorphous and infusible as revealed by X-ray Diffraction (XRD and Differential Scanning Calorimetry (DSC. In -polyhydroxy acids, esterification reaction with primary hydroxyls is preferential and, therefore, the structure can be defined as linear with variable branching depending on the amount of esterified secondary hydroxyls. The occurrence side oxidative reactions like the diol cleavage are responsible for chain cross-linking. Films are thermally stable up to 200-250°C though this limit can be extended up to 300°C in the absence of ester bonds involving secondary hydroxyls. By analogy with natural occurring fatty polyesters (i.e. cutin in higher plants these polymers are proposed as biodegradable and non-toxic barrier films or coatings to be used, for instance, in food packing

  12. Polyhydroxyester films obtained by non-catalyzed melt-polycondensation of natural occurring fatty polyhydroxyacids.

    Science.gov (United States)

    Benitez, Jose; Heredia-Guerrero, José; Guzman-Puyol, Susana; Barthel, Markus; Dominguez, Eva; Heredia, Antonio

    2015-08-01

    Free-standing polyesters films from mono and polyhydroxylated fatty acids (C16 and C18) have been obtained by non-catalyzed melt-condensation polymerization in air at 150°C. Chemical characterization by Fourier Transform Infrared Spectroscopy (FTIR) and 13C Magic Angle Spinning Nuclear Magnetic Resonance (13C MAS-NMR) has confirmed the formation of the corresponding esters and the occurrence of hydroxyl partial oxidation which extent depends on the type of hydroxylation of the monomer (primary or secondary). Generally, polyester films obtained are hydrophobic, insoluble in common solvents, amorphous and infusible as revealed by X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). In ?-polyhydroxy acids, esterification reaction with primary hydroxyls is preferential and, therefore, the structure can be defined as linear with variable branching depending on the amount of esterified secondary hydroxyls. The occurrence side oxidative reactions like the diol cleavage are responsible for chain cross-linking. Films are thermally stable up to 200-250°C though this limit can be extended up to 300°C in the absence of ester bonds involving secondary hydroxyls. By analogy with natural occurring fatty polyesters (i.e. cutin in higher plants) these polymers are proposed as biodegradable and non-toxic barrier films or coatings to be used, for instance, in food packing

  13. Iridium-Catalyzed Allylic Substitution

    Science.gov (United States)

    Hartwig, John F.; Pouy, Mark J.

    Iridium-catalyzed asymmetric allylic substitution has become a valuable method to prepare products from the addition of nucleophiles at the more substituted carbon of an allyl unit. The most active and selective catalysts contain a phosphoramidite ligand possessing at least one arylethyl substituent on the nitrogen atom of the ligand. In these systems, the active catalyst is generated by a base-induced cyclometalation at the methyl group of this substituent to generate an iridium metalacycle bound by the COD ligand of the [Ir(COD)Cl]2 precursor and one additional labile dative ligand. Such complexes catalyze the reactions of linear allylic esters with alkylamines, arylamines, phenols, alcohols, imides, carbamates, ammonia, enolates and enolate equivalents, as well as typical stabilized carbon nucleophiles generated from malonates and cyanoesters. Iridium catalysts for enantioselective allylic substitution have also been generated from phosphorus ligands with substituents bound by heteroatoms, and an account of the studies of such systems, along with a description of the development of iridium catalysts is included.

  14. Selective conversion of polyenes to monoenes by RuCl(3) -catalyzed transfer hydrogenation: the case of cashew nutshell liquid.

    Science.gov (United States)

    Perdriau, Sébastien; Harder, Sjoerd; Heeres, Hero J; de Vries, Johannes G

    2012-12-01

    Cardanol, a constituent of cashew nutshell liquid (CNSL), was subjected to transfer hydrogenation catalyzed by RuCl(3) using isopropanol as a reductant. The side chain of cardanol, which is a mixture of a triene, a diene, and a monoene, was selectively reduced to the monoene. Surprisingly, it is the C8-C9 double bond that is retained with high selectivity. A similar transfer hydrogenation of linoleic acid derivatives succeeded only if the substrate contained an aromatic ring, such as a benzyl ester. TEM and a negative mercury test showed that the catalyst was homogeneous. By using ESI-MS, ruthenium complexes were identified that contained one, two, or even three molecules of substrate, most likely as allyl complexes. The interaction between ruthenium and the aromatic ring determines selectivity in the hydrogenation reaction.

  15. Reaction Mechanism for Cocaine Esterase-Catalyzed Hydrolyses of (+)- and (−)-Cocaine: Unexpected Common Rate-Determining Step

    OpenAIRE

    Liu, Junjun; Zhao, Xinyun; Yang, Wenchao; Zhan, Chang-Guo

    2011-01-01

    First-principles quantum mechanical/molecular mechanical (QM/MM)-free energy (FE) calculations have been performed to examine catalytic mechanism for cocaine esterase (CocE)-catalyzed hydrolysis of (+)-cocaine in comparison with CocE-catalyzed hydrolysis of (−)-cocaine. It has been shown that the acylation of (+)-cocaine consists of nucleophilic attack of hydroxyl group of Ser117 on carbonyl carbon of (+)-cocaine benzoyl ester and the dissociation of (+)-cocaine benzoyl ester. The first react...

  16. Linear and cyclic ester Oligomers of succinic acid and 1,4-butanediol: Biocatalytic synthesis and characterization

    NARCIS (Netherlands)

    Habeych Narvaez, D.I.; Eggink, G.; Boeriu, C.G.

    2011-01-01

    The lipase-catalyzed synthesis of cyclic ester oligomers from non-activated succinic acid (A) and 1,4-butanediol (B) in the presence of immobilized Candida antarctica lipase B was investigated. Batch and pulse fed-batch systems were implemented to increase the formation of cyclic ester products. The

  17. Regulatory link between steryl ester formation and hydrolysis in the yeast Saccharomyces cerevisiae.

    Science.gov (United States)

    Ploier, Birgit; Korber, Martina; Schmidt, Claudia; Koch, Barbara; Leitner, Erich; Daum, Günther

    2015-07-01

    Steryl esters and triacylglycerols are the major storage lipids of the yeast Saccharomyces cerevisiae. Steryl esters are formed in the endoplasmic reticulum by the two acyl-CoA:sterol acyltransferases Are1p and Are2p, whereas steryl ester hydrolysis is catalyzed by the three steryl ester hydrolases Yeh1p, Yeh2p and Tgl1p. To shed light on the regulatory link between steryl ester formation and hydrolysis in the maintenance of cellular sterol and free fatty acid levels we employed yeast mutants which lacked the enzymes catalyzing the degradation of steryl esters. These studies revealed feedback regulation of steryl ester formation by steryl ester hydrolysis although in a Δtgl1Δyeh1Δyeh2 triple mutant the gene expression levels of ARE1 and ARE2 as well as protein levels and stability of Are1p and Are2p were not altered. Nevertheless, the capacity of the triple mutant to synthesize steryl esters was significantly reduced as shown by in vitro and in vivo labeling of lipids with [(14)C]oleic acid and [(14)C]acetate. Enzymatic analysis revealed that inhibition of steryl ester formation occurred at the enzyme level. As the amounts and the formation of sterols and fatty acids were also decreased in the triple mutant we concluded that defects in steryl ester hydrolysis also caused feedback inhibition on the formation of sterols and fatty acids which serve as precursors for steryl ester formation. In summary, this study demonstrates a regulatory link within the steryl ester metabolic network which contributes to non-polar lipid homeostasis in yeast cells.

  18. Crystal structure and characterization of esterase Est25 mutants reveal improved enantioselectivity toward (S)-ketoprofen ethyl ester.

    Science.gov (United States)

    Kim, Jinyeong; Seok, Seung-Hyeon; Hong, Eunsoo; Yoo, Tae Hyeon; Seo, Min-Duk; Ryu, Yeonwoo

    2017-03-01

    Esterases comprise a group of enzymes that catalyze the cleavage and synthesis of ester bonds. They are important in biotechnological applications owing to their enantioselectivity, regioselectivity, broad substrate specificity, and the fact that they do not require cofactors. In a previous study, we isolated the esterase Est25 from a metagenomic library. Est25 showed catalytic activity toward the (R,S)-ketoprofen ethyl ester but had low enantioselectivity toward the (S)-ketoprofen ethyl ester. Because (S)-ketoprofen has stronger anti-inflammatory effects and fewer side effects than (R)-ketoprofen, enantioselectivity of this esterase is important. In this study, we generated Est25 mutants with improved enantioselectivity toward the (S)-ketoprofen ethyl ester; improved enantioselectivity of mutants was established by analysis of their crystal structures. The enantioselectivity of mutants was influenced by substitution of Phe72 and Leu255. Substituting these residues changed the size of the binding pocket and the entrance hole that leads to the active site. The enantioselectivity of Est25 (E = 1.1 ± 0.0) was improved in the mutants F72G (E = 1.9 ± 0.2), L255W (E = 16.1 ± 1.1), and F72G/L255W (E = 60.1 ± 0.5). Finally, characterization of Est25 mutants was performed by determining the optimum reaction conditions, thermostability, effect of additives, and substrate specificity after substituting Phe72 and Leu255.

  19. Recent advances in osmium-catalyzed hydrogenation and dehydrogenation reactions.

    Science.gov (United States)

    Chelucci, Giorgio; Baldino, Salvatore; Baratta, Walter

    2015-02-17

    CONSPECTUS: A current issue in metal-catalyzed reactions is the search for highly efficient transition-metal complexes affording high productivity and selectivity in a variety of processes. Moreover, there is also a great interest in multitasking catalysts that are able to efficiently promote different organic transformations by careful switching of the reaction parameters, such as temperature, solvent, and cocatalyst. In this context, osmium complexes have shown the ability to catalyze efficiently different types of reactions involving hydrogen, proving at the same time high thermal stability and simple synthesis. In the catalytic reduction of C═X (X = O, N) bonds by both hydrogenation (HY) and transfer hydrogenation (TH) reactions, the most interest has been focused on homogeneous systems based on rhodium, iridium, and in particular ruthenium catalysts, which have proved to catalyze chemo- and stereoselective hydrogenations with remarkable efficiency. By contrast, osmium catalysts have received much less attention because they are considered less active on account of their slower ligand exchange kinetics. Thus, this area remained almost neglected until recent studies refuted these prejudices. The aim of this Account is to highlight the impressive developments achieved over the past few years by our and other groups on the design of new classes of osmium complexes and their applications in homogeneous catalytic reactions involving the hydrogenation of carbon-oxygen and carbon-nitrogen bonds by both HY and TH reactions as well as in alcohol deydrogenation (DHY) reactions. The work described in this Account demonstrates that osmium complexes are emerging as powerful catalysts for asymmetric and non-asymmetric syntheses, showing a remarkably high catalytic activity in HY and TH reactions of ketones, aldehydes, imines, and esters as well in DHY reactions of alcohols. Thus, for instance, the introduction of ligands with an NH function, possibly in combination with a

  20. Ester Tuiksoo / Ester Tuiksoo ; interv. Piret Tali

    Index Scriptorium Estoniae

    Tuiksoo, Ester, 1965-

    2007-01-01

    Juhan Partsi valitsuse (05.04.2004-13.04.2005) ja Andrus Ansipi valitsuse (13.04.2005-) põllumajandusminister Ester Tuiksoo oma lapsepõlvest ja elukutsevalikust, poliitilise karjääri algusest ja erakonna valikust, ministritöö kogemustest, naistest poliitikas

  1. A computational study on the N-heterocyclic carbene-catalyzed Csp(2)-Csp(3) bond activation/[4+2] cycloaddition cascade reaction of cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry.

    Science.gov (United States)

    Wang, Yang; Wu, Bohua; Zhang, Haoyang; Wei, Donghui; Tang, Mingsheng

    2016-07-20

    A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp(2)-Csp(3) single bond activation of cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to cyclobutenone, C-C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the C[double bond, length as m-dash]N bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the C[double bond, length as m-dash]O bond to a dienolate intermediate. Moreover, the Re face addition of the C[double bond, length as m-dash]N bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C-C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.

  2. Biodiesel production by enzyme-catalyzed transesterification

    Directory of Open Access Journals (Sweden)

    Stamenković Olivera S.

    2005-01-01

    Full Text Available The principles and kinetics of biodiesel production from vegetable oils using lipase-catalyzed transesterification are reviewed. The most important operating factors affecting the reaction and the yield of alkyl esters, such as: the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol are discussed. In order to estimate the prospects of lipase-catalyzed transesterification for industrial application, the factors which influence the kinetics of chemically-catalysed transesterification are also considered. The advantages of lipase-catalyzed transesterification compared to the chemically-catalysed reaction, are pointed out. The cost of down-processing and ecological problems are significantly reduced by applying lipases. It was also emphasized that lipase-catalysed transesterification should be greatly improved in order to make it commercially applicable. The further optimization of lipase-catalyzed transesterification should include studies on the development of new reactor systems with immobilized biocatalysts and the addition of alcohol in several portions, and the use of extra cellular lipases tolerant to organic solvents, intracellular lipases (i.e. whole microbial cells and genetically-modified microorganisms ("intelligent" yeasts.

  3. Cooperative catalysis of metal and O-H···O/sp3-C-H···O two-point hydrogen bonds in alcoholic solvents: Cu-catalyzed enantioselective direct alkynylation of aldehydes with terminal alkynes.

    Science.gov (United States)

    Ishii, Takaoki; Watanabe, Ryo; Moriya, Toshimitsu; Ohmiya, Hirohisa; Mori, Seiji; Sawamura, Masaya

    2013-09-27

    Catalyst-substrate hydrogen bonds in artificial catalysts usually occur in aprotic solvents, but not in protic solvents, in contrast to enzymatic catalysis. We report a case in which ligand-substrate hydrogen-bonding interactions cooperate with a transition-metal center in alcoholic solvents for enantioselective catalysis. Copper(I) complexes with prolinol-based hydroxy amino phosphane chiral ligands catalytically promoted the direct alkynylation of aldehydes with terminal alkynes in alcoholic solvents to afford nonracemic secondary propargylic alcohols with high enantioselectivities. Quantum-mechanical calculations of enantiodiscriminating transition states show the occurrence of a nonclassical sp(3)-C-H···O hydrogen bond as a secondary interaction between the ligand and substrate, which results in highly directional catalyst-substrate two-point hydrogen bonding.

  4. Enzymatic synthesis of polyol esters in aqueous-organic two-phase systems.

    OpenAIRE

    Janssen, A.E.M.

    1993-01-01

    The last decade increasingly attention is paid to lipases as catalysts for synthesis of components, such as fatty acid-based surfactants, flavors, edible oil equivalents, monomers and polymers, and amides. In this thesis, the lipase-catalyzed esterification of polyols and fatty acids is described. These esters consist of a nonpolar part (fatty acid) and a polar part (polyol). Therefore, polyol esters have surface-active properties and are used as emulsifier in food, pharmaceutics; and cosmeti...

  5. Functional Group Interconversion: Decarbonylative Borylation of Esters for the Synthesis of Organoboronates

    KAUST Repository

    Guo, Lin

    2016-09-26

    A new and efficient nickel-catalyzed decarbonylative borylation reaction of carboxylic acid esters with bis(pinacolato)-diboron has been developed. This transformation allows access to structurally diverse aryl as well as alkenyl and alkyl boronate esters with high reactivity, broad substrate scope, and excellent functional-group tolerance. Further experiments show that this protocol can be carried out on a gram scale and applied to orthogonal synthetic strategies.

  6. Esterification of phenolic acids catalyzed by lipases immobilized in organogels.

    Science.gov (United States)

    Zoumpanioti, M; Merianou, E; Karandreas, T; Stamatis, H; Xenakis, A

    2010-10-01

    Lipases from Rhizomucor miehei and Candida antarctica B were immobilized in hydroxypropylmethyl cellulose organogels based on surfactant-free microemulsions consisting of n-hexane, 1-propanol and water. Both lipases kept their catalytic activity, catalyzing the esterification reactions of various phenolic acids including cinnamic acid derivatives. High reaction rates and yields (up to 94%) were obtained when lipase from C. antarctica was used. Kinetic studies have been performed and apparent kinetic constants were determined showing that ester synthesis catalyzed by immobilized lipases occurs via the Michaelis-Menten mechanism.

  7. Azobenzene dye-coupled quadruply hydrogen-bonding modules as colorimetric indicators for supramolecular interactions

    Directory of Open Access Journals (Sweden)

    Yagang Zhang

    2012-04-01

    Full Text Available The facile coupling of azobenzene dyes to the quadruply hydrogen-bonding modules 2,7-diamido-1,8-naphthyridine (DAN and 7-deazaguanine urea (DeUG is described. The coupling of azobenzene dye 2 to mono-amido DAN units 4, 7, and 9 was effected by classic 4-(dimethylaminopyridine (DMAP-catalyzed peptide synthesis with N-(3-dimethylaminopropyl-N’-ethyl carbodiimide hydrochloride (EDC as activating agent, affording the respective amide products 5, 8, and 10 in 60–71% yield. The amide linkage was formed through either the aliphatic or aromatic ester group of 2, allowing both the flexibility and absorption maximum to be tuned. Azobenzene dye 1 was coupled to the DeUG unit 11 by Steglich esterification to afford the product amide 12 in 35% yield. Alternatively, azobenzene dye 16 underwent a room-temperature copper-catalyzed azide–alkyne Huisgen cycloaddition with DeUG alkyne 17 to give triazole 18 in 71% yield. Azobenzene coupled DAN modules 5, 8, and 10 are bright orange–red in color, and azobenzene coupled DeUG modules 12 and 18 are orange–yellow in color. Azobenzene coupled DAN and DeUG modules were successfully used as colorimetric indicators for specific DAN–DeUG and DAN–UPy (2-ureido-4(1H-pyrimidone quadruply hydrogen-bonding interactions.

  8. Oxidation of Disulfides to Thiolsulfinates with Hydrogen Peroxide and a Cyclic Seleninate Ester Catalyst.

    Science.gov (United States)

    McNeil, Nicole M R; McDonnell, Ciara; Hambrook, Miranda; Back, Thomas G

    2015-06-11

    Cyclic seleninate esters function as mimetics of the antioxidant selenoenzyme glutathione peroxidase. They catalyze the reduction of harmful peroxides with thiols, which are converted to disulfides in the process. The possibility that the seleninate esters could also catalyze the further oxidation of disulfides to thiolsulfinates and other overoxidation products under these conditions was investigated. This has ramifications in potential medicinal applications of seleninate esters because of the possibility of catalyzing the unwanted oxidation of disulfide-containing spectator peptides and proteins. A variety of aryl and alkyl disulfides underwent facile oxidation with hydrogen peroxide in the presence of catalytic benzo-1,2-oxaselenolane Se-oxide affording the corresponding thiolsulfinates as the principal products. Unsymmetrical disulfides typically afforded mixtures of regioisomers. Lipoic acid and N,N'-dibenzoylcystine dimethyl ester were oxidized readily under similar conditions. Although isolated yields of the product thiolsulfinates were generally modest, these experiments demonstrate that the method nevertheless has preparative value because of its mild conditions. The results also confirm the possibility that cyclic seleninate esters could catalyze the further undesired oxidation of disulfides in vivo.

  9. Naturally Occurring Cinnamic Acid Sugar Ester Derivatives

    Directory of Open Access Journals (Sweden)

    Yuxin Tian

    2016-10-01

    Full Text Available Cinnamic acid sugar ester derivatives (CASEDs are a class of natural product with one or several phenylacrylic moieties linked with the non-anomeric carbon of a glycosyl skeleton part through ester bonds. Their notable anti-depressant and brains protective activities have made them a topic of great interest over the past several decades. In particular the compound 3′,6-disinapoylsucrose, the index component of Yuanzhi (a well-known Traditional Chinese Medicine or TCM, presents antidepressant effects at a molecular level, and has become a hotspot of research on new lead drug compounds. Several other similar cinnamic acid sugar ester derivatives are reported in traditional medicine as compounds to calm the nerves and display anti-depression and neuroprotective activity. Interestingly, more than one third of CASEDs are distributed in the family Polygalaceae. This overview discusses the isolation of cinnamic acid sugar ester derivatives from plants, together with a systematic discussion of their distribution, chemical structures and properties and pharmacological activities, with the hope of providing references for natural product researchers and draw attention to these interesting compounds.

  10. Neutral lipid biosynthesis in engineered Escherichia coli: jojoba oil-like wax esters and fatty acid butyl esters.

    Science.gov (United States)

    Kalscheuer, Rainer; Stöveken, Tim; Luftmann, Heinrich; Malkus, Ursula; Reichelt, Rudolf; Steinbüchel, Alexander

    2006-02-01

    Wax esters are esters of long-chain fatty acids and long-chain fatty alcohols which are of considerable commercial importance and are produced on a scale of 3 million tons per year. The oil from the jojoba plant (Simmondsia chinensis) is the main biological source of wax esters. Although it has a multitude of potential applications, the use of jojoba oil is restricted, due to its high price. In this study, we describe the establishment of heterologous wax ester biosynthesis in a recombinant Escherichia coli strain by coexpression of a fatty alcohol-producing bifunctional acyl-coenzyme A reductase from the jojoba plant and a bacterial wax ester synthase from Acinetobacter baylyi strain ADP1, catalyzing the esterification of fatty alcohols and coenzyme A thioesters of fatty acids. In the presence of oleate, jojoba oil-like wax esters such as palmityl oleate, palmityl palmitoleate, and oleyl oleate were produced, amounting to up to ca. 1% of the cellular dry weight. In addition to wax esters, fatty acid butyl esters were unexpectedly observed in the presence of oleate. The latter could be attributed to solvent residues of 1-butanol present in the medium component, Bacto tryptone. Neutral lipids produced in recombinant E. coli were accumulated as intracytoplasmic inclusions, demonstrating that the formation and structural integrity of bacterial lipid bodies do not require specific structural proteins. This is the first report on substantial biosynthesis and accumulation of neutral lipids in E. coli, which might open new perspectives for the biotechnological production of cheap jojoba oil equivalents from inexpensive resources employing recombinant microorganisms.

  11. Apomorphine and its esters

    DEFF Research Database (Denmark)

    Borkar, Nrupa; Chen, Zhizhong; Saaby, Lasse

    2016-01-01

    Oral delivery of apomorphine via prodrug principle may be a potential treatment for Parkinson's disease. The purpose of this study was to investigate the transport and stability of apomorphine and its esters across Caco-2 cell monolayer and their affinity towards chylomicrons. Apomorphine...... cells. Molecular dynamics (MD) simulations were performed to understand the stability of the esters on a molecular level. The affinity of the compounds towards plasma derived chylomicrons was assessed. The A-B transport of intact DLA was about 150 times lower than the transport of apomorphine...

  12. Metal-catalyzed simultaneous chain- and step-growth radical polymerization: marriage of vinyl polymers and polyesters.

    Science.gov (United States)

    Mizutani, Masato; Satoh, Kotaro; Kamigaito, Masami

    2010-06-02

    All polymerization reactions are categorized into two large different families, chain- and step-growth polymerizations, which are typically incompatible. Here, we report the simultaneous chain- and step-growth polymerization via the metal-catalyzed radical copolymerization of conjugated vinyl monomers and designed monomers possessing unconjugated C horizontal lineC and active C-Cl bonds. Especially, almost ideal linear random copolymers containing both vinyl polymer and polyester units in a single polymer chain were formed by the CuCl/1,1,4,7,10,10-hexamethyltriethylenetetramine- or RuCp*Cl(PPh(3))(2)-catalyzed copolymerization of methyl acrylate (MA) for the chain-growth polymerization and 3-butenyl 2-chloropropionate (1) for the step-growth polymerization. In contrast, other transition metal catalysts, such as CuCl with tris[2-(dimethylamino)ethyl]amine or N,N,N',N'',N''-pentamethyldiethylenetriamine and FeCl(2)/PnBu(3), resulted in branched structures via the concomitant chain-growth copolymerization of 1 with MA. The polymerization mechanism was studied in detail by NMR and MALDI-TOF-MS analyses of the polymerizations as well as the model reactions. Furthermore, a series of copolymers changing from random to multiblock polymer structures were obtained by varying the feed ratios of the two monomers. These copolymers can be easily degraded into lower molecular weight oligomers or polymers via methanolysis of the ester-linkages in the main chain using sodium carbonate.

  13. Cyclization strategies to polyenes using Pd(II)-catalyzed couplings of pinacol vinylboronates.

    Science.gov (United States)

    Iafe, Robert G; Chan, Daniel G; Kuo, Jonathan L; Boon, Byron A; Faizi, Darius J; Saga, Tomomi; Turner, Jonathan W; Merlic, Craig A

    2012-08-17

    As a complement to Pd(0)-catalyzed cyclizations, seven Pd(II)-catalyzed cyclization strategies are reported. α,ω-Diynes are selectively hydroborated to bis(boronate esters), which cyclize under Pd(II)-catalysis producing a diverse array of small, medium, and macrocyclic polyenes with controlled E,E, Z,Z, or E,Z stereochemistry. Various functional groups are tolerated including aryl bromides, and applications are illustrated.

  14. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    Science.gov (United States)

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized.

  15. The effect of ethanol on the kinetics of lipase-mediated enantioselective esterification of 4-methyloctanoic acid and the hydrolysis of its ethyl ester

    NARCIS (Netherlands)

    Heinsman, N.W.J.T.; Valente, A.M.; Schmienk, H.G.F.; Padt, van der A.; Franssen, M.C.R.; Groot, de Æ.; Riet, van 't K.

    2001-01-01

    The Novozym 435? catalyzed esterification and hydrolysis reactions of 4-methyloctanoic acid (ethyl ester) were investigated. In both the hydrolysis and esterification reactions, the increase of ethanol concentration led to an increase in enantiomeric ratio (E). For hydrolysis of the ethyl ester, the

  16. Synthesis of some glucose-fatty acid esters by lipase from Candida antarctica and their emulsion functions.

    Science.gov (United States)

    Ren, Kangzi; Lamsal, Buddhi P

    2017-01-01

    The synthesis of glucose esters with palmitic acid, lauric acid and hexanoic acid using lipase enzyme was studied and their emulsion functionality in oil-in-water system were compared. Reactions at 3:1M ratio of fatty acids-to-glucose had the highest conversion percentages (over 90% for each of the fatty acid). Initial conversion rate increased as substrate solubility increased. Ester bond formation was confirmed by nuclear magnetic resonance technique that the chemical shifts of glucose H-6 and α-carbon protons of fatty acids in the ester molecules shifted to the higher fields. Contact angle of water on esters' pelleted surface increased as the hydrophobicity increased. Glucose esters' and commercial sucrose esters' functionality as emulsifiers were compared. Glucose esters delayed, but did not prevent coalescence, because the oil droplets diameter doubled during 7days. Sucrose esters prevented coalescence during 7days since the droplets diameter did not have significant change.

  17. Cobalt catalyzed hydroesterification of a wide range of olefins

    Energy Technology Data Exchange (ETDEWEB)

    Van Rensburg, H.; Hanton, M.; Tooze, R.P.; Foster, D.F. [Sasol Technology UK, St Andrews (United Kingdom)

    2011-07-01

    Petrochemical raw materials are an essential raw material for the production of detergents with a substantial portion of synthetic fatty alcohols being produced via hydroformylation of oil or coal derived olefins. Carbonylation processes other than hydroformylation have to date not been commercially employed for the production of fatty esters or alcohols. In this document we highlight the opportunities of converting olefins to esters using cobalt catalyzed alkoxycarbonylation. This process is highly versatile and applicable to a wide range of olefins, linear or branched, alpha or internal in combination with virtually any chain length primary or secondary alcohol allowing the synthesis of a diverse array of compounds such as ester ethoxylated surfactants, methyl branched detergents, lubricants and alkyl propanoates. Furthermore, alkoxycarbonylation of a broad olefin/paraffin hydrocarbon range could be used to produce the corresponding broad cut detergent alcohols. (orig.)

  18. Microwave-Assisted Olefination Reaction of Alkylzinc with Aromatic Aldehyde Catalyzed by Nickel Complex

    Institute of Scientific and Technical Information of China (English)

    MEN Xiu-Qin; WANG Jin-Xian; SHI Xiao-Ning; WANG Ke-Hu

    2003-01-01

    @@ Carbon-carbon double bond-forming reactions have always been great importance in organic synthesis. Manymethods have been described for C =C bond formation. We[1] have reported the new method of C =C bond formation of nickel catalyzed organozinc with aromatic aldehydes in the presence of Me3SiC1.

  19. Recent advances in copper-catalyzed asymmetric coupling reactions

    Directory of Open Access Journals (Sweden)

    Fengtao Zhou

    2015-12-01

    Full Text Available Copper-catalyzed (or -mediated asymmetric coupling reactions have received significant attention over the past few years. Especially the coupling reactions of aryl or alkyl halides with nucleophiles became a very powerful tool for the formation of C–C, C–N, C–O and other carbon–heteroatom bonds as well as for the construction of heteroatom-containing ring systems. This review summarizes the recent progress in copper-catalyzed asymmetric coupling reactions for the formation of C–C and carbon–heteroatom bonds.

  20. Phosphate Esters, Thiophosphate Esters and Metal Thiophosphates as Lubricant Additives

    Directory of Open Access Journals (Sweden)

    David W. Johnson

    2013-12-01

    Full Text Available Phosphate esters, thiophosphate esters and metal thiophosphates have been used as lubricant additives for over 50 years. While their use has been extensive, a detailed knowledge of how they work has been a much more recent development. In this paper, the use of phosphate esters and thiophosphate esters as anti-wear or extreme pressure additives is reviewed with an emphasis on their mechanism of action. The review includes the use of alkyl phosphates, triaryl phosphates and metal containing thiophosphate esters. The mechanisms of these materials interacting with a range of iron and steel based bearing material are examined.

  1. Catalyzing RE Project Development

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Kate; Elgqvist, Emma; Walker, Andy; Cutler, Dylan; Olis, Dan; DiOrio, Nick; Simpkins, Travis

    2016-09-01

    This poster details how screenings done with REopt - NREL's software modeling platform for energy systems integration and optimization - are helping to catalyze the development of hundreds of megawatts of renewable energy.

  2. Muon Catalyzed Fusion

    Science.gov (United States)

    Armour, Edward A.G.

    2007-01-01

    Muon catalyzed fusion is a process in which a negatively charged muon combines with two nuclei of isotopes of hydrogen, e.g, a proton and a deuteron or a deuteron and a triton, to form a muonic molecular ion in which the binding is so tight that nuclear fusion occurs. The muon is normally released after fusion has taken place and so can catalyze further fusions. As the muon has a mean lifetime of 2.2 microseconds, this is the maximum period over which a muon can participate in this process. This article gives an outline of the history of muon catalyzed fusion from 1947, when it was first realised that such a process might occur, to the present day. It includes a description of the contribution that Drachrnan has made to the theory of muon catalyzed fusion and the influence this has had on the author's research.

  3. Cleavage of an RNA model catalyzed by dinuclear Zn(II) complexes containing rate-accelerating pendants. Comparison of the catalytic benefits of H-bonding and hydrophobic substituents.

    Science.gov (United States)

    Mohamed, Mark F; Brown, R Stan

    2010-12-17

    The transesterification of a simple RNA model, 2-hydroxypropyl p-nitrophenyl phosphate (2, HpNPP) promoted by seven dinuclear Zn(II) catalysts (3,4,5,6,7,8,9:Zn(II)2:(-OCH3)) based on the bis[bis(2-substituted-pyridinyl-6-methyl)]amine ligand system was investigated in methanol under sspH-controlled conditions at 25.0 ± 0.1 °C. The two metal complexing ligands were joined together via the amino N connected to a m-xylyl linker (3, 4, 5, 6, 7) where the 2-pyridinyl substituent = H, CH3, (CH)4, NH2, and NH(C═O)CH3, respectively, and a propyl linker (8, 9) where the ring substituent = H and CH3. All of the dinuclear complexes except 8:Zn(II)2 exhibit saturation kinetics for the kobs versus [catalyst] plots from which one can determine catalyst:substrate binding constants (KM), the catalytic rate constants for their decomposition (kcat), and the second order catalytic rate constants (k2cat = kcat/KM). In the case of 8:Zn(II)2, the plots of kobs versus [catalyst] as a function of sspH are linear, and the catalytic rate constants (k2cat) are defined as the gradients of the plots. Analysis of all of the data at the sspH optimum for each reaction indicates that the presence of the amino and acetamido H-bonding groups and the CH3 group provides similar increases of the kcat terms of 25−50 times that exhibited by the parent complex 3:Zn(II)2. However, in terms of substrate catalyst binding (KM), there is no clear trend that H-bonding groups or the CH3 group provides stronger binding than the parent complex. In terms of the overall second order catalytic rate constant, the CH3, amino, and NH(C═O)CH3 groups provide 20, 10, and 68 times the k2cat observed for the parent complex. In the case of 9:Zn(II)2, the presence of the methyl groups provides a 1000-fold increase in activity (judged by k2cat) over the parent complex 8:Zn(II)2. The results are interpreted to indicate that H-bonding effects may be important for catalysis and less so for substrate binding, but the

  4. A Conformational Model for MTPA Esters of Chiral N-(2-Hydroxyalkylacrylamides

    Directory of Open Access Journals (Sweden)

    Eduardo M. Rustoy

    2014-01-01

    Full Text Available The absolute stereochemistry of novel chiral N-(2-hydroxylalkylacrylamides prepared by a lipase-catalyzed resolution was successfully determined by 1H NMR of their MTPA esters. The method was validated for this particular case by computational experiments.

  5. Low-temperature side-chain cleavage and decarboxylation of polythiophene esters by acid catalysis

    DEFF Research Database (Denmark)

    Søndergaard, Roar; Norrman, Kion; Krebs, Frederik C

    2012-01-01

    Solubility switching of polymers is very useful in thin layer processing of conjugated polymers, as it allows for multilayer processing and increases the stability of the polymer. Acid catalyzed thermocleavage of ester groups from thiophene polymers carrying primary, secondary, and tertiary subst...

  6. Synthesis of the Fatty Esters of Solketal and Glycerol-Formal: Biobased Specialty Chemicals

    Directory of Open Access Journals (Sweden)

    Alvise Perosa

    2016-01-01

    Full Text Available The caprylic, lauric, palmitic and stearic esters of solketal and glycerol formal were synthesized with high selectivity and in good yields by a solvent-free acid catalyzed procedure. No acetal hydrolysis was observed, notwithstanding the acidic reaction conditions.

  7. Synthesis of Versatile Building Blocks through Asymmetric Hydrogenation of Functionalized Itaconic Acid Mono-Esters

    NARCIS (Netherlands)

    Hekking, Koen F.W.; Lefort, Laurent; Vries, André H.M. de; Delft, Floris L. van; Schoemaker, Hans E.; Vries, Johannes G. de; Rutjes, Floris P.J.T.

    2008-01-01

    The rhodium-catalyzed asymmetric hydrogenation of several β-substituted itaconic acid mono-esters, using a library of monodentate phosphoramidite and phosphite ligands is described. Two β-alkyl-substituted substrates were readily hydrogenated by the rhodium complex Rh(COD)2BF4 in combination with (S

  8. Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters

    Science.gov (United States)

    Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

    2015-01-01

    N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ɛ-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

  9. Switchable Surface Wettability by Using Boronic Ester Chemistry.

    Science.gov (United States)

    Taleb, Sabri; Noyer, Elisabeth; Godeau, Guilhem; Darmanin, Thierry; Guittard, Frédéric

    2016-01-18

    Here, we report for the first time the use of a boronic ester as an efficient tool for reversible surface post-functionalization. The boronic ester bond allows surfaces to be reversibly switched from hydrophilic to hydrophobic. Based on the well-known boronic acid/glycol affinity, this strategy offers the opportunity to play with surface hydrophobic properties by adding various boronic acids onto substrates bearing glycol groups. The post-functionalization can then be reversed to regenerate the starting glycol surface. This pathway allows for the preparation of various switchable surfaces for a large range of applications in biosensors, liquid transportation, and separation membranes.

  10. Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Mader, Mary M.; Vitale, Maxime

    2003-01-01

    Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjecte...

  11. Iridium‐Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols with the Liberation of Syngas

    DEFF Research Database (Denmark)

    Olsen, Esben Paul Krogh; Madsen, Robert

    2012-01-01

    to excellent yields. Ethers, esters, imides, and aryl halides are stable under the reaction conditions, whereas olefins are partially saturated. The reaction is believed to proceed by two consecutive organometallic transformations that are catalyzed by the same iridium(I)–BINAP species. First, dehydrogenation...

  12. Preparation of fluorinated biaryls through direct palladium-catalyzed coupling of polyfluoroarenes with aryltrifluoroborates

    KAUST Repository

    Fang, Xin

    2013-07-01

    The direct palladium-catalyzed coupling of polyfluoroarenes with aryltrifluoroborates gave the desired products of fluorinated biaryls in good to excellent yields. A diverse set of important functional groups including methoxy, aldehyde, ester, nitro and halide can be well tolerated in the protocol. © 2013 Elsevier B.V. All rights reserved.

  13. Preparation of polyfunctional zinc organometallics using an Fe- or Co-catalyzed Cl/Zn-exchange.

    Science.gov (United States)

    Melzig, Laurin; Diène, Coura R; Rohbogner, Christoph J; Knochel, Paul

    2011-06-17

    A new Fe- or Co-catalyzed Cl/Zn-exchange reaction allows the direct transformation of aryl, heteroaryl, and also alkyl chlorides into the corresponding zinc reagents. The method tolerates functional groups such as a nitrile or an ester. Remarkably, secondary and tertiary alkyl chlorides are suitable substrates for the Cl/Zn exchange.

  14. Efficient Synthesis of β-Acetamido Ketones and Esters Using Aluminum Chloride as an Inexpensive and Green Catalyst%Efficient Synthesis of β-Acetamido Ketones and Esters Using Aluminum Chloride as an Inexpensive and Green Catalyst

    Institute of Scientific and Technical Information of China (English)

    Mohammad Ali, Zolfigol; Ardeshir, Khazaei; Mohammad, Mokhlesi; Abdolkarim, Zare; Maliheh, Safaiee; Fatemeh, Derakhshan-Panah; Hassan, Keypour; Ahmad, Ali Dehghani-Firouzabadi; Maria, Merajoddin

    2012-01-01

    Aluminum chloride (AlCl3) efficiently catalyzes one-pot multicomponent condensation of enolizable ketones or alkyl acetoacetates with aldehydes, acetonitrile and acetyl chloride to afford β-acetamido ketone or ester derivatives in high to excellent yields and in relatively short reaction times. Moreover, by this synthetic method, some novel β-acetamido ketones and esters (i.e. one complex structure) are prepared.

  15. Cyanate Ester Graphene Composites

    Science.gov (United States)

    2012-03-29

    weight Cu(II) acetylacetonate : nonylphenol • Mixture degassed at 300 mm/Hg 30 minutes at 90 °C and prior to pouring into silicone molds • Cure ...resin and well-understood; enables development of superior predictive models for failure; readily catalyzed to cure at reasonable temperatures BADCy Δ...Typical DSC Trace of CEs DISTRIBUTION A: Approved for public release. Distribution is unlimited. AFRL Public Affairs Clearance Number

  16. Method of making alkyl esters

    Science.gov (United States)

    Elliott, Brian

    2010-09-14

    Methods of making alkyl esters are described herein. The methods are capable of using raw, unprocessed, low-cost feedstocks and waste grease. Generally, the method involves converting a glyceride source to a fatty acid composition and esterifying the fatty acid composition to make alkyl esters. In an embodiment, a method of making alkyl esters comprises providing a glyceride source. The method further comprises converting the glyceride source to a fatty acid composition comprising free fatty acids and less than about 1% glyceride by mass. Moreover, the method comprises esterifying the fatty acid composition in the presence of a solid acid catalyst at a temperature ranging firm about 70.degree. C. to about 120.degree. C. to produce alkyl esters, such that at least 85% of the free fatty acids are converted to alkyl esters. The method also incorporates the use of packed bed reactors for glyceride conversion and/or fatty acid esterification to make alkyl esters.

  17. Bond Issues.

    Science.gov (United States)

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

  18. Muon catalyzed fusion

    Energy Technology Data Exchange (ETDEWEB)

    Ishida, K. [Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Nagamine, K. [Muon Science Laboratory, IMSS-KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Matsuzaki, T. [Advanced Meson Science Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Kawamura, N. [Muon Science Laboratory, IMSS-KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

    2005-12-15

    The latest progress of muon catalyzed fusion study at the RIKEN-RAL muon facility (and partly at TRIUMF) is reported. The topics covered are magnetic field effect, muon transfer to {sup 3}He in solid D/T and ortho-para effect in dd{mu} formation.

  19. LIPASE-CATALYZED TRANSESTERIFICATION OF PALM KERNEL OIL WITH DIALKYLCARBONATES

    Directory of Open Access Journals (Sweden)

    Tjahjono Herawan

    2014-01-01

    Full Text Available Lipase-catalyzed transesterifications-especially in a solvent-free medium-are important for industrial applications because such systems would have an enormous advantage by avoiding the problem of separation, toxicity and flammability of organic solvents. However, the organic solvent-free alcoholysis, especially methanolysis, does not give high conversions. The same problem also occurs when ethyl or methyl acetate are used as acyl acceptors. The main problems of lipase-catalyzed organic solvent-free alcoholysis are first, the solubility of the plant oil in the substrate or solvent and second, the fact that transesterification is an equilibrium reaction. Dialkyl carbonates, versatile compounds due to their chemical reactivity and physical properties, may provide an alternative to solve both problems. Using dialkyl carbonates transesterification is not an equilibrium reaction, because the intermediate compound immediately decomposes to carbon dioxide and an alcohol. Moreover, dialkyl carbonates (especially dimethyl carbonate are cheap and widely available. For single step lipase-catalyzed transesterification of palm kernel oil, diakyl carbonates (in this case dimethyl and diethyl carbonate gave better yields compared to those of short chain alcohols. The rate of ester formation with dialkyl carbonates as substrate was about 6-7 times higher than that obtained with short chain alcohols. The formation of esters was gradually increased by a higher enzyme amount from 5-20% (w/w of oil for 8 h reaction time. However from the economic point of view, an enzyme amount of 10% on the weight base of oil was proposed for further reaction. Generally, the highest ester formation was observed when a temperature of 60°C was used. However, in the case of dimethyl carbonate little difference was observed at reaction temperatures of 60 and 70oC and the reactions proceeded nearly identically. The esters formation increased drastically up to more than 70% when water

  20. Enzymatic synthesis and application of fatty acid ascorbyl esters

    Directory of Open Access Journals (Sweden)

    Stojanović Marija M.

    2013-01-01

    Full Text Available Fatty acid ascorbyl esters are liposoluble substances that possess good antioxidative properties. These compounds could be synthesized by using various acyl donors for acylation of vitamin C in reaction catalyzed by chemical means or lipases. Enzymatic process is preferred since it is regioselective, performed under mild reaction conditions, with the obtained product being environmentally friendly. Polar organic solvents, ionic liquids, and supercritical fluids has been successfully used as a reaction medium, since commonly used solvents with high Log P values are inapplicable due to ascorbic acid high polarity. Acylation of vitamin C using fatty acids, their methyl-, ethyl-, and vinyl esters, as well as triglycerides has been performed, whereas application of the activated acyl donors enabled higher molar conversions. In each case, majority of authors reported that using excessive amount of the acyl donor had positive effect on yield of product. Furthermore, several strategies have been employed for shifting the equilibrium towards the product by water content control. These include adjusting the initial water activity by pre-equilibration of reaction mixture, enzyme preparation with water vapor of saturated salt solutions, and the removal of formed water by the addition of molecular sieves or salt hydrate pairs. The aim of this article is to provide a brief overview of the procedures described so far for the lipase-catalyzed synthesis of fatty acid ascorbyl esters with emphasis on the potential application in food, cosmetics, and pharmaceutics. Furthermore, it has been pointed out that the main obstacles for process commercialization are long reaction times, lack of adequate purification methods, and high costs of lipases. Thus, future challenges in this area are testing new catalysts, developing continuous processes for esters production, finding cheaper acyl donors and reaction mediums, as well as identifying standard procedures for

  1. Phosphine-directed C-H borylation reactions: facile and selective access to ambiphilic phosphine boronate esters.

    Science.gov (United States)

    Crawford, Kristina M; Ramseyer, Timothy R; Daley, Christopher J A; Clark, Timothy B

    2014-07-14

    Ambiphilic ligands have received considerable attention over the last two decades due to their unique reactivity as organocatalysts and ligands. The iridium-catalyzed C-H borylation of phosphines is described in which the phosphine is used as a directing group to provide selective formation of arylboronate esters with unique scaffolds of ambiphilic compounds. A variety of aryl and benzylic phosphines were subjected to the reaction conditions, selectively providing stable, isolable boronate esters upon protection of the phosphine as the borane complex. After purification, the phosphine-substituted boronate esters could be deprotected and isolated in pure form.

  2. Synthesis and Suzuki Cross-Coupling Reactions of 2,6-Bis(trifluoromethyl)pyridine-4-boronic Acid Pinacol Ester

    KAUST Repository

    Batool, Farhat

    2016-11-18

    Iridium-catalyzed aromatic borylation provides quick one-step access to 2,6-bis(trifluoromethyl)pyridine-4-boronic acid pinacol ester. Suzuki couplings of this highly electron-deficient pyridine-4-boronic ester with various (hetero)aryl bromides was successfully carried out and the coupled products were obtained in 46–95% isolated yields. Double and triple Suzuki couplings, with dibromo- and tribromoarenes, respectively, were also achieved. Thus demonstrating that this pyridine-4-boronic ester can be a useful source for the installation of one of the strongest electron-withdrawing aromatic group in organic compounds. Copyright © 2016, Georg Thieme Verlag. All rights reserved.

  3. First Palladium-Catalyzed Addition of Organoboronic Acids to Allenes: A Magic Regioselectivity Switch by Using a Base or an Acid

    Institute of Scientific and Technical Information of China (English)

    MA Sheng-Ming; JIAO Ning

    2003-01-01

    @@ Organoboronic acids enjoy high prestige in the metal-catalyzed C-C bond formations. The most notable progress is the rhodium- and nickel-catalyzed conjugate addition with unsaturated carbon-carbon bond, aldehydes, N-sulfonyl imines reported by Miyaura, Hayashi and Shirakawa.[1

  4. Specificity of Mucor miehei lipase on methyl ester substrates

    Directory of Open Access Journals (Sweden)

    Pina, M.

    1993-12-01

    Full Text Available Fatty acid methyl esters constitute a good substrate for the characterization of lipase typospecificity. In the present work, the hydrolytic action of lipase from Mucor miehei was studied. It was demonstrated that this lipase preferentially catalyses the hydrolysis of fatty acid methyl esters with small number of double bonds. It was also found that this lipase shows a specificity in the hydrolysis of fatty acid methyl esters with short aliphatic chain.Los esteres metílicos de ácidos grasos constituyen un buen sustrato para la caracterización de tipos de especificidad de lipasa. En el presente trabajo, se estudió la acción hidrolítica de lipasa de Mucor miehei. Se demostró que esta lipasa cataliza preferencialmente la hidrólisis de esteres metílicos de ácidos grasos con número pequeño de dobles enlaces. Se encontró también que esta lipasa muestra una especificidad en la hidrólisis de ásteres metílicos de ácidos grasos con cadena alifática corta.

  5. Mechanism of Imidazole-Promoted Ligation of Peptide Phenyl Esters

    Institute of Scientific and Technical Information of China (English)

    王晨; 刘磊

    2012-01-01

    Imidazole-promoted ligation of peptide phenyl esters was recently found to be a complementary method for protein chemical synthesis. Theoretical calculations have been carried out to understand the detailed mechanism of this particular ligation process. It is found that both the reaction of the phenyl ester with imidazole and the reaction of the acyl imidazole intermediate with cysteine proceed through an addition-elimination mechanism. The cleavage of the C--O bond in the reaction between the phenyl ester and imidazole is the rate-limiting step of the overall liga- tion process. Interestingly, although the imidazole-promoted phenyl ester ligation has a higher free energy barrier than the conventional thiophenol-promoted native chemical ligation for a sterically less hindered C-terminal amino acid (e.g. gylcine), for a sterically hindered C-terminal amino acid (e.g. proline) the imidazole-promoted phenyl ester ligation is calculated to be more favorable than the conventional thiophenol-promoted native chemical ligation.

  6. Altering small and medium alcohol selectivity in the wax ester synthase.

    Science.gov (United States)

    Barney, Brett M; Ohlert, Janet M; Timler, Jacobe G; Lijewski, Amelia M

    2015-11-01

    The bifunctional wax ester synthase/acyl-coenzyme A:diacylglycerol acyltransferase (WS/DGAT or wax ester synthase) catalyzes the terminal reaction in the bacterial wax ester biosynthetic pathway, utilizing a range of alcohols and fatty acyl-CoAs to synthesize the corresponding wax ester. The wild-type wax ester synthase Maqu_0168 from Marinobacter aquaeolei VT8 exhibits a preference for longer fatty alcohols, while applications with smaller alcohols would yield products with desired biotechnological properties. Small and medium chain length alcohol substrates are much poorer substrates for the native enzyme, which may hinder broad application of the wax ester synthase in many proposed biosynthetic schemes. Developing approaches to improve enzyme activity toward specific smaller alcohol substrates first requires a clear understanding of which amino acids of the primary sequences of these enzymes contribute to substrate specificity in the native enzyme. In this report, we surveyed a range of potential residues and identified the leucine at position 356 and methionine at position 405 in Maqu_0168 as residues that affected selectivity toward small, branched, and aromatic alcohols when substituted with different amino acids. This analysis provides evidence of residues that line the binding site for wax ester synthase, which will aid rational approaches to improve this enzyme with specific substrates.

  7. Adipocyte protein modification by Krebs cycle intermediates and fumarate ester-derived succination.

    Science.gov (United States)

    Manuel, Allison M; Frizzell, Norma

    2013-11-01

    Protein succination, the non-enzymatic modification of cysteine residues by fumarate, is distinguishable from succinylation, an enzymatic reaction forming an amide bond between lysine residues and succinyl-CoA. Treatment of adipocytes with 30 mM glucose significantly increases protein succination with only a small change in succinylation. Protein succination may be significantly increased intracellularly after treatment with fumaric acid esters, however, the ester must be removed by saponification to permit 2SC-antibody detection of the fumarate adduct.

  8. New lipophilic tyrosyl esters. Comparative antioxidant evaluation with hydroxytyrosyl esters.

    Science.gov (United States)

    Mateos, Raquel; Trujillo, Mariana; Pereira-Caro, Gema; Madrona, Andrés; Cert, Arturo; Espartero, José Luis

    2008-11-26

    New lipophilic esters of tyrosol, a naturally occurring phenol with interesting biological properties, have been synthesized in good yields by a chemoselective procedure, using lipase from Candida antarctica or p-toluenesulfonic acid as catalysts. Their antioxidant activities have been evaluated by the Rancimat test in lipophilic food matrices, as well as by FRAP and ABTS assays in methanolic solutions, and compared with those of previously synthesized hydroxytyrosyl esters. Free tyrosol, hydroxytyrosol, butylhydroxytoluene, and alpha-tocopherol were used as standards. All methods used for the antioxidant activity evaluation emphasized the high influence of the ortho-diphenolic structure on the antioxidant capacity, tyrosol and its derivatives being less active than hydroxytyrosol and its analogues and even less than BHT and alpha-tocopherol. In addition, the Rancimat test revealed a lower activity for ester derivatives than for their respective reference compounds (HTy or Ty), in agreement with the polar paradox. On the other hand, FRAP and ABTS methods reported an opposite behavior between the synthetic esters and their respective references. Thus, hydroxytyrosyl esters were more active than HTy, whereas tyrosyl esters were less active than Ty. The length and nature of the acyl side chain did not seem to play an important role in the antioxidant activity of either the hydroxytyrosyl or tyrosyl ester series, since no significant differences were observed among them.

  9. Parental Bonding

    Directory of Open Access Journals (Sweden)

    T. Paul de Cock

    2014-08-01

    Full Text Available Estimating the early parent–child bonding relationship can be valuable in research and practice. Retrospective dimensional measures of parental bonding provide a means for assessing the experience of the early parent–child relationship. However, combinations of dimensional scores may provide information that is not readily captured with a dimensional approach. This study was designed to assess the presence of homogeneous groups in the population with similar profiles on parental bonding dimensions. Using a short version of the Parental Bonding Instrument (PBI, three parental bonding dimensions (care, authoritarianism, and overprotection were used to assess the presence of unobserved groups in the population using latent profile analysis. The class solutions were regressed on 23 covariates (demographics, parental psychopathology, loss events, and childhood contextual factors to assess the validity of the class solution. The results indicated four distinct profiles of parental bonding for fathers as well as mothers. Parental bonding profiles were significantly associated with a broad range of covariates. This person-centered approach to parental bonding has broad utility in future research which takes into account the effect of parent–child bonding, especially with regard to “affectionless control” style parenting.

  10. Intramolecular interactions in ortho-methoxyalkylphenylboronic acids and their catechol esters

    Science.gov (United States)

    Adamczyk-Woźniak, Agnieszka; Borys, Krzysztof M.; Czerwińska, Karolina; Gierczyk, Błażej; Jakubczyk, Michał; Madura, Izabela D.; Sporzyński, Andrzej; Tomecka, Ewelina

    2013-12-01

    Catechol esters of ortho-methoxyalkylphenylboronic acids have been synthesized and characterized by 17O NMR spectroscopy. The results were compared with the data for the parent acids. The influence of intramolecular and intermolecular hydrogen bonds on the properties of the boronic acids has been discussed. The 17O NMR data for the boronic esters proved that there are no O → B interactions in the investigated compounds. This fact is connected with weak Lewis acidity of the parent acids and their low sugars' receptors activity. Crystal structure of ortho-methoxyphenylboronic acid catechol ester was determined.

  11. New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Qinhua [Iowa State Univ., Ames, IA (United States)

    2004-12-19

    The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I2, ICl, PhSeCl, PhSCl and p-O2NC6H4SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement

  12. New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

    Energy Technology Data Exchange (ETDEWEB)

    Qinhua Huang

    2004-12-19

    The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I{sub 2}, ICl, PhSeCl, PhSCl and p-O{sub 2}NC{sub 6}H{sub 4}SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that

  13. Origin of Kinetic Resolution of Hydroxy Esters through Catalytic Enantioselective Lactonization by Chiral Phosphoric Acids.

    Science.gov (United States)

    Changotra, Avtar; Sunoj, Raghavan B

    2016-08-05

    Kinetic resolution is a widely used strategy for separation and enrichment of enantiomers. Using density functional theory computations, the origin of how a chiral BINOL-phosphoric acid catalyzes the selective lactonization of one of the enantiomers of α-methyl γ-hydroxy ester is identified. In a stepwise mechanism, the stereocontrolling transition state for the addition of the hydroxyl group to the si face of the ester carbonyl in the case of the S isomer exhibits a network of more effective noncovalent interactions between the substrate and the chiral catalyst.

  14. Synthesis of thermoplastic poly(ester-olefin elastomers

    Directory of Open Access Journals (Sweden)

    Tanasijević Branka

    2004-01-01

    Full Text Available A series of thermoplastic poly(ester-olefin elastomers, based on poly(ethylene-stat-butylene, HO-PEB-OH, as the soft segment and poly (butylene terephthalate, PBT, as the hard segment, were synthesized by a catalyzed transesterification reaction in solution. The incorporation of soft hydrogenated poly(butadiene segments into the copolyester backbone was accomplished by the polycondensation of α, ω-dihydroxyl telechelic HO-PEB-OH, (PEB Mn = 3092 g/mol with 1,4-butanediol (BD and dimethyl terephthalate (DMT in the presence of a 50 wt-% high boiling solvent i.e., 1,2,4-trichlorobenzene. The molar ratio of the starting comonomers was selected to result in a constant hard to soft weight ratio of 60:40. The synthesis was optimized in terms of both the concentration of catalyst, tetra-n-butyl-titanate (Ti(OBu4, and stabilizer, N,N'-diphenyl-p-phenylenediamine (DPPD, as well as the reaction time. It was found that the optimal catalyst concentration (Ti(OBu4 for the synthesis of these thermoplastic elastomers was 1.0 mmol/mol ester and the optimal DPPD concentration was 1.0 wt-%. The extent of the reaction was followed by measuring the inherent viscosity of the reaction mixture. The effectiveness of the incorporation of the soft segments into the copolymer chains was proved by Soxhlet extraction with chloroform. The molecular structures, composition and the size of the synthesized poly(ester-butylenes were verified by 1H NMR spectroscopy, viscometry of dilute solutions and the complex dynamic melt viscosity. The thermal properties of poly(ester-olefins were investigated by differential scanning calorimetry (DSC. The degree of crystallinity was also determined by DSC. The thermal and thermo-oxidative stability were investigated by thermogravimetric analysis (TGA. The rheological properties of poly(ester-olefins were investigated by dynamic mechanical spectroscopy in the melt and solid state.

  15. Optimization of reaction parameters for enzymatic glyceride synthesis from fish oil: Ethyl esters versus free fatty acids

    DEFF Research Database (Denmark)

    Ravn, Helle Christine; Damstrup, Marianne L.; Meyer, Anne S.

    2012-01-01

    Enzymatic conversion of fish oil free fatty acids (FFA) or fatty acid ethyl esters (FAE) into glycerides via esterification or transesterification was examined. The reactions catalyzed by Lipozyme™ 435, a Candida antarctica lipase, were optimized. Influence on conversion yields of fatty acid chain...

  16. Influence of extended storage on fuel properties of methyl esters prepared from canola, palm, soybean, and sunflower oils

    Science.gov (United States)

    Fatty acid methyl esters prepared from canola, palm, soybean, and sunflower oils by homogenous base-catalyzed methanolysis were stored for 12 months at three constant temperatures (-15, 22, and 40 deg C) and properties such as oxidative stability, acid value, kinematic viscosity, low temperature ope...

  17. Enzymatic Synthesis of Palm Alkyl Ester Using Dialkyl Carbonate as an Alkyl Donors

    Directory of Open Access Journals (Sweden)

    Roila Awang

    2010-01-01

    Full Text Available Problem statement: Though efficient in terms of reaction yield and time, the chemical approach to synthesizing alkyl ester has drawback such as difficulties in the recovery of glycerol and the need for removal of salt residue. On the other hand, biocatalyst allow for synthesis of specific alkyl esters and easy recovery of glycerol. However, the solvent-free alcoholysis, does not give high conversion. The same problem was also found when ethyl or methyl acetate was used as acyl acceptors. Approach: Lipase catalyzed transesterification of oil and dialkyl carbonate was predicted to give higher conversion in solvent free reaction system. Results: Alkyl esters were synthesized enzymatically to overcome the problems associated with chemical processes. In this study, dialkyl carbonates were used as an alkyl donor for the production of alkyl ester. Nine commercial lipases were tested for their suitability for the reaction system. Among the lipase tested, Novozym 435 was chosen for optimization study because of their higher activity. In a solvent-free reaction system, the ester formation using dialkyl carbonate was 6 times higher than using ethanol and methanol. The effect of various reaction parameters such as temperature, amount of enzyme, organic solvent and structure of substrates were studied to determine optimal condition. The optimal conditions of ester formation were reaction temperature at 60°C, reaction time at 8 h, enzyme amount of 10% (w/w of oil and 0.2% wt added water. Conclusion: Solvent-free lipase catalyzed transesterification of palm kernel oil and dialkyl carbonates gave higher conversion of ester compared to the reaction using short chain alcohol as an alkyl donors.

  18. Catalyzed Ceramic Burner Material

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Amy S., Dr.

    2012-06-29

    Catalyzed combustion offers the advantages of increased fuel efficiency, decreased emissions (both NOx and CO), and an expanded operating range. These performance improvements are related to the ability of the catalyst to stabilize a flame at or within the burner media and to combust fuel at much lower temperatures. This technology has a diverse set of applications in industrial and commercial heating, including boilers for the paper, food and chemical industries. However, wide spread adoption of catalyzed combustion has been limited by the high cost of precious metals needed for the catalyst materials. The primary objective of this project was the development of an innovative catalyzed burner media for commercial and small industrial boiler applications that drastically reduce the unit cost of the catalyzed media without sacrificing the benefits associated with catalyzed combustion. The scope of this program was to identify both the optimum substrate material as well as the best performing catalyst construction to meet or exceed industry standards for durability, cost, energy efficiency, and emissions. It was anticipated that commercial implementation of this technology would result in significant energy savings and reduced emissions. Based on demonstrated achievements, there is a potential to reduce NOx emissions by 40,000 TPY and natural gas consumption by 8.9 TBtu in industries that heavily utilize natural gas for process heating. These industries include food manufacturing, polymer processing, and pulp and paper manufacturing. Initial evaluation of commercial solutions and upcoming EPA regulations suggests that small to midsized boilers in industrial and commercial markets could possibly see the greatest benefit from this technology. While out of scope for the current program, an extension of this technology could also be applied to catalytic oxidation for volatile organic compounds (VOCs). Considerable progress has been made over the course of the grant

  19. PREPARATION AND PROPERTIES OF FUMED SILICA/CYANATE ESTER NANOCOMPOSITES

    Institute of Scientific and Technical Information of China (English)

    Elhussein A.Taha; Jun-tao Wu; Kai Gao; Lin Guo

    2012-01-01

    Fumed silica/bisphenol A dicyanate ester (BADCy) nanocomposites were prepared by introducing different contents of nano-sized fumed SiO2 into the BADCy matrix.Two different average primary particle diameters of 12 and 40 nm were chosen.Dibutyltindilaurate (DBTDL) catalyst was chosen to catalyze the cyanate ester group into triazine group via cyclotrimerization reaction.The SEM micrographs indicated that the fumed SiO2 particles were homogeneously dispersed in the poly(bisphenol A dicyanate) matrix by means of ultrasonic treatment and the addition of a coupling agent.The FTIR spectroscopy shows that,not only DBTDL catalyzes the polymerization reaction but also-OH groups of the SiO2 particles surface help the catalyst for the complete polymerization of BADCy monomer.The thermal stability of the cured BADCy can be improved by adequate addition of fumed SiO2.A slight increase in the dielectric constant and dielectric loss values were identified by testing the dielectric properties of the prepared nanocomposite samples.By increasing the SiO2 content,there was a slight increasing in the thermal conductivity values of the tested samples.The obtained results proved that the fumed silica/BADCy nanocomposites had good thermal and dielectrical properties and can be used in many applications such as in the thermal insulation field.

  20. A kinetic study of lipase-catalyzed alcoholysis of palm kernel oil.

    Science.gov (United States)

    de Oliveira, D; Alves, T L

    2000-01-01

    The use of lipases as biocatalysts in interesterification reactions has been the object of growing interest, owing to the importance of esters as emulsifiers, intermediates to produce oleochemicals, and fuel alternatives. We consider in this article a kinetic study of lipase-catalyzed alcoholysis of palm kernel oil, using n-hexane as the solvent. In a first step the ester production was maximized by using a Taguchi design, and then an empirical model was built to determine the influence of the process variables. Taking into account the results obtained in the first step, we performed a kinetic study and developed a simple model for this system.

  1. Liquid Crystalline Esters of Dibenzophenazines

    Directory of Open Access Journals (Sweden)

    Kevin John Anthony Bozek

    2015-01-01

    Full Text Available A series of esters of 2,3,6,7-tetrakis(hexyloxydibenzo[a,c]phenazine-11-carboxylic acid was prepared in order to probe the effects of the ester groups on the liquid crystalline behavior. These compounds exhibit columnar hexagonal phases over broad temperature ranges. Variations in chain length, branching, terminal groups, and the presence of cyclic groups were found to modify transition temperatures without substantially destabilizing the mesophase range.

  2. Ru/Me-BIPAM-Catalyzed Asymmetric Addition of Arylboronic Acids to Aliphatic Aldehydes and α-Ketoesters

    Directory of Open Access Journals (Sweden)

    Momoko Watanabe

    2011-06-01

    Full Text Available A ruthenium-catalyzed asymmetric arylation of aliphatic aldehydes and α-ketoesters with arylboronic acids has been developed, giving chiral alkyl(arylmethanols and α-hydroxy esters in good yields. The use of a chiral bidentate phosphoramidite ligand (Me-BIPAM achieved excellent enantioselectivities.

  3. Ru/Me-BIPAM-catalyzed asymmetric addition of arylboronic acids to aliphatic aldehydes and α-ketoesters.

    Science.gov (United States)

    Yamamoto, Yasunori; Shirai, Tomohiko; Watanabe, Momoko; Kurihara, Kazunori; Miyaura, Norio

    2011-06-17

    A ruthenium-catalyzed asymmetric arylation of aliphatic aldehydes and α-ketoesters with arylboronic acids has been developed, giving chiral alkyl(aryl)methanols and α-hydroxy esters in good yields. The use of a chiral bidentate phosphoramidite ligand (Me-BIPAM) achieved excellent enantioselectivities.

  4. Palladium-Catalyzed Modification of Unprotected Nucleosides, Nucleotides, and Oligonucleotides

    Directory of Open Access Journals (Sweden)

    Kevin H. Shaughnessy

    2015-05-01

    Full Text Available Synthetic modification of nucleoside structures provides access to molecules of interest as pharmaceuticals, biochemical probes, and models to study diseases. Covalent modification of the purine and pyrimidine bases is an important strategy for the synthesis of these adducts. Palladium-catalyzed cross-coupling is a powerful method to attach groups to the base heterocycles through the formation of new carbon-carbon and carbon-heteroatom bonds. In this review, approaches to palladium-catalyzed modification of unprotected nucleosides, nucleotides, and oligonucleotides are reviewed. Polar reaction media, such as water or polar aprotic solvents, allow reactions to be performed directly on the hydrophilic nucleosides and nucleotides without the need to use protecting groups. Homogeneous aqueous-phase coupling reactions catalyzed by palladium complexes of water-soluble ligands provide a general approach to the synthesis of modified nucleosides, nucleotides, and oligonucleotides.

  5. The Structural Basis of Ribozyme-Catalyzed RNA Assembly

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, M.P.; Scott, W.G.; /UC, Santa Cruz

    2007-07-12

    Life originated, according to the RNA World hypothesis, from self-replicating ribozymes that catalyzed ligation of RNA fragments. We have solved the 2.6 angstrom crystal structure of a ligase ribozyme that catalyzes regiospecific formation of a 5' to 3' phosphodiester bond between the 5'-triphosphate and the 3'-hydroxyl termini of two RNA fragments. Invariant residues form tertiary contacts that stabilize a flexible stem of the ribozyme at the ligation site, where an essential magnesium ion coordinates three phosphates. The structure of the active site permits us to suggest how transition-state stabilization and a general base may catalyze the ligation reaction required for prebiotic RNA assembly.

  6. Fatty acid methyl ester profiles of bat wing surface lipids.

    Science.gov (United States)

    Pannkuk, Evan L; Fuller, Nathan W; Moore, Patrick R; Gilmore, David F; Savary, Brett J; Risch, Thomas S

    2014-11-01

    Sebocytes are specialized epithelial cells that rupture to secrete sebaceous lipids (sebum) across the mammalian integument. Sebum protects the integument from UV radiation, and maintains host microbial communities among other functions. Native glandular sebum is composed primarily of triacylglycerides (TAG) and wax esters (WE). Upon secretion (mature sebum), these lipids combine with minor cellular membrane components comprising total surface lipids. TAG and WE are further cleaved to smaller molecules through oxidation or host enzymatic digestion, resulting in a complex mixture of glycerolipids (e.g., TAG), sterols, unesterified fatty acids (FFA), WE, cholesteryl esters, and squalene comprising surface lipid. We are interested if fatty acid methyl ester (FAME) profiling of bat surface lipid could predict species specificity to the cutaneous fungal disease, white nose syndrome (WNS). We collected sebaceous secretions from 13 bat spp. using Sebutape(®) and converted them to FAME with an acid catalyzed transesterification. We found that Sebutape(®) adhesive patches removed ~6× more total lipid than Sebutape(®) indicator strips. Juvenile eastern red bats (Lasiurus borealis) had significantly higher 18:1 than adults, but 14:0, 16:1, and 20:0 were higher in adults. FAME profiles among several bat species were similar. We concluded that bat surface lipid FAME profiling does not provide a robust model predicting species susceptibility to WNS. However, these results provide baseline data that can be used for lipid roles in future ecological studies, such as life history, diet, or migration.

  7. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen,and Zhejiang and Guangdong provinces to issue bonds for the first time.How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the Shanghai Securities Journal.Edited excerpts follow.

  8. Bond Boom

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The Ministry of Finance recently kick-started a pilot program allowing local governments of Shanghai and Shenzhen, and Zhejiang and Guangdong provinces to issue bonds for the first time. How will the new policy affect fiscal capacities of local governments and the broader economy? What else should the country do to build a healthy bond market? Economists and experts discussed these issues in an interview with the ShanghaiSecuritiesJournal. Edited excerpts follow:

  9. Enzymatic synthesis of lipophilic rutin and vanillyl esters from fish byproducts.

    Science.gov (United States)

    Mbatia, Betty; Kaki, Shiva Shanker; Mattiasson, Bo; Mulaa, Francis; Adlercreutz, Patrick

    2011-07-13

    Lipase-catalyzed synthesis of lipophilic phenolic antioxidants was carried out with a concentrate of n-3 polyunsaturated fatty acids (PUFAs), recovered from oil extracted from salmon ( Salmon salar ) byproduct. Vanillyl alcohol and rutin were selected for the esterification reaction, and obtained esters yields were 60 and 30%, respectively. The antioxidant activities of the esters were compared with those of commercial butylated hydroxytoluene (BHT) and α-tocopherol using DPPH radical scavenging and thiobarbituric acid assays. In the DPPH assay, rutin esters showed better activity than vanillyl esters, and on the contrary in lipophilic medium, vanillyl esters were found to be superior to rutin esters. In bulk oil system, the antioxidant activities of rutin and vanillyl derivatives were lower than that of BHT and α-tocopherol, but in emulsion, they showed better activity than α-tocopherol. By attaching to natural phenolics, the PUFAs are protected against oxidation, and PUFA improves the hydrophobicity of the phenolic, which could enhance its function in lipid systems.

  10. One-pot stereoselective synthesis of α,β-differentiated diamino esters via the sequence of aminochlorination, aziridination and intermolecular SN2 reaction.

    Science.gov (United States)

    Xiong, Yiwen; Qian, Ping; Cao, Chenhui; Mei, Haibo; Han, Jianlin; Li, Guigen; Pan, Yi

    2014-01-01

    We report here an efficient one-pot method for the synthesis of α,β-differentiated diamino esters directly from cinnamate esters using N,N-dichloro-p-toluenesulfonamide and benzylamine as nitrogen sources. The key transformations include a Cu-catalyzed aminohalogenation and aziridination, followed by an intermolecular SN2 nucleophilic ring opening by benzylamine. The reactions feature a wide scope of substrates and proceed with excellent stereo- and regioselectivity (anti:syn >99:1) .

  11. Identification and characterization of a cold-active phthalate esters hydrolase by screening a metagenomic library derived from biofilms of a wastewater treatment plant.

    Directory of Open Access Journals (Sweden)

    Yiying Jiao

    Full Text Available A cold-active phthalate esters hydrolase gene (designated dphB was identified through functional screening of a metagenomic library derived from biofilms of a wastewater treatment plant. The enzyme specifically catalyzed the hydrolysis of dipropyl phthalate, dibutyl phthalate, and dipentyl phthalate to the corresponding monoalkyl phthalate esters at low temperatures. The catalytic triad residues of DphB were proposed to be Ser159, Asp251, and His281.

  12. Identification and Characterization of a Cold-Active Phthalate Esters Hydrolase by Screening a Metagenomic Library Derived from Biofilms of a Wastewater Treatment Plant

    OpenAIRE

    Jiao, Yiying; CHEN Xu; Wang, Xin; Liao, Xuewei; Xiao, Lin; Miao, Aijun; Wu, Jun; Yang, Liuyan

    2013-01-01

    A cold-active phthalate esters hydrolase gene (designated dphB) was identified through functional screening of a metagenomic library derived from biofilms of a wastewater treatment plant. The enzyme specifically catalyzed the hydrolysis of dipropyl phthalate, dibutyl phthalate, and dipentyl phthalate to the corresponding monoalkyl phthalate esters at low temperatures. The catalytic triad residues of DphB were proposed to be Ser159, Asp251, and His281.

  13. The hydrolysis kinetics of monobasic and dibasic aminoalkyl esters of ketorolac.

    Science.gov (United States)

    Qandil, Amjad M; Jamhawi, Noor M; Tashtoush, Bassam M; Al-Ajlouni, Ahmad M; Idkaidek, Nasir M; Obaidat, Aiman A

    2013-09-01

    Six aminoethyl and aminobutyl esters of ketorolac containing 1-methylpiperazine (MPE and MPB), N-acetylpiperazine (APE and APB) or morpholine (ME and MB), were synthesized and their hydrolysis kinetics were studied. The hydrolysis was studied at pH 1 to 9 (for MPE, APE and ME) and pH 1 to 8 (for MPB, APB and MB) in aqueous phosphate buffer (0.16 M) with ionic strength (0.5 M) at 37°C. Calculation of k(obs), construction of the pH-rate profiles and determination of the rate equations were performed using KaleidaGraph® 4.1. The hydrolysis displays pseudo-first order kinetics and the pH-rate profiles shows that the aminobutyl esters, MPE, APB and MB, are the most stable. The hydrolysis of the ethyl esters MPE, APE and ME, depending on the pH, is either fast and catalyzed by the hydroxide anion or slow and uncatalyzed for the diprotonated, monoprotonated and nonprotonated forms. The hydrolysis of the butyl esters showed a similar profile, albeit it was also catalyzed by hydronium cation. In addition, the hydroxide anion is 105 more effective in catalyzing the hydrolysis than the hydronium cation. The hydrolysis pattern of the aminoethyl esters is affected by the number and pKa of its basic nitrogen atoms. The monobasic APE and ME, show a similar hydrolysis pattern that is different than the dibasic MPE. The length of the side chain and the pKa of the basic nitrogen atoms in the aminoethyl moiety affect the mechanism of hydrolysis as the extent of protonation at a given pH is directly related to the pKa.

  14. SO4^2-/TiO2-Al2O3催化合成双季戊四醇六脂肪酸酯%Synthesis of dipentaerythritol hexa-esters catalyzed by SO4^2-/TiO2-Al2O3

    Institute of Scientific and Technical Information of China (English)

    万庆梅; 金一丰; 王胜利

    2011-01-01

    With self-prepared SO42-/TiO2-Al2O3 solid super-acid as the catalyst,dipentaerythritol and fatty acid were esterified to dipentaerythritol hexa-esters.Effects of factors,such as molar ratio of fatty acid to dipentaerythritol,the dosage of catalyst,reaction temperature and reaction time on the results of esterification were investigated.The optimal condition was determined as n(fatty acid)∶n(dipentaerythritol)=6.5∶1,the dosage of the catalyst w=0.060% of total mass of the reactants,reaction time 6 h and reaction temperature 210 ℃.SO42-/TiO2-Al2O3 solid superacid shows good catalytic activity and high reaction selectivity in the process of dipentaerythritol hexa-esters synthesis.The esterifying conversion is above 98%,and the catalyst can be repeatedly used for eight times without significant declining of its catalytic activity.The reaction products were characterized by the FTIR.%以自制SO42-/TiO2-Al2O3固体超强酸为催化剂,进行双季戊四醇和脂肪酸的酯化反应,合成了双季戊四醇六脂肪酸酯,考察了酸醇摩尔比、催化剂用量、反应温度、反应时间等条件对酯化反应的影响。确定了较优的合成条件:n(脂肪酸)﹕n(双季戊四醇)=6.5﹕1,催化剂用量为总反应物质量的0.060%,210℃回流反应6 h。用红外光谱对反应产物进行了表征,结果表明,SO42-/TiO2-Al2O3固体超强酸在双季戊四醇六脂肪酸酯合成反应中有较高的催化活性和高的反应选择性,酯化率达98%以上,且催化剂重复使用8次仍保持较高活性。双季戊四醇六脂肪酸酯产品结构经FTIR表征确认。

  15. Adsorption of diethyl phthalate ester to clay minerals.

    Science.gov (United States)

    Wu, Yanhua; Si, Youbin; Zhou, Dongmei; Gao, Juan

    2015-01-01

    Phthalate esters are a group of plasticizers, which have been widely detected in China's agricultural and industrial soils. In this study, batch adsorption experiments were conducted to investigate the environmental effects on the adsorption of diethyl phthalate ester (DEP) to clay minerals. The results showed that DEP adsorption isotherms were well fitted with the Freundlich model; the interlayer spacing of K(+) saturated montmorillonite (K-mont) was the most important adsorption area for DEP, and di-n-butyl ester (DnBP) was limited to intercalate into the interlayer of K-mont due to the bigger molecular size; there was no significant effect of pH and ionic strength on DEP adsorption to K-mont/Ca-mont, but to Na-mont clay. The adsorption to kaolinite was very limited. Data of X-ray diffraction and FTIR spectra further proved that DEP molecules could intercalate into K-/Ca-mont interlayer, and might interact with clay through H-bonding between carbonyl groups and clay adsorbed water. Coated humic acid on clay surface would enhance DEP adsorption at low concentration, but not at high concentration (eg. Ce>0.26 mM). The calculated adsorption enthalpy (ΔHobs) and adsorption isotherms at varied temperatures showed that DEP could be adsorbed easier as more adsorbed. This study implied that clay type, compound structure, exchangeable cation, soil organic matter and temperature played important roles in phthalate ester's transport in soil.

  16. Silver-Catalyzed C(sp(3))-H Chlorination.

    Science.gov (United States)

    Ozawa, Jun; Kanai, Motomu

    2017-03-17

    A silver-catalyzed chlorination of benzylic, tertiary, and secondary C(sp(3))-H bonds was developed. The reaction proceeded with as low as 0.2 mol % catalyst loading at room temperature under air atmosphere with synthetically useful functional group compatibility. The regioselectivity and reactivity tendencies suggest that the chlorination proceeded through a radical pathway, but an intermediate alkylsilver species cannot be ruled out.

  17. Catalyzing alignment processes

    DEFF Research Database (Denmark)

    Lauridsen, Erik Hagelskjær; Jørgensen, Ulrik

    2004-01-01

    This paper describes how environmental management systems (EMS) spur the circulation of processes that support the constitution of environmental issues as specific environ¬mental objects and objectives. EMS catalyzes alignmentprocesses that produce coherence among the different elements involved......, the networks of environmental professionals that work in the environmental organisation, in consulting and regulatory enforcement, and dominating business cultures. These have previously been identified in the literature as individually significant in relation to the evolving environmental agendas....... They are here used to describe the context in which environmental management is implemented. Based on findings from contributions to a research program studying the implementation and impact of EMS in different settings, we highlight the diverse roles that these systems play in the Thai context. EMS may over...

  18. NMR spectroscopic investigations on copper-catalyzed reactions and zintl anions

    OpenAIRE

    Koch, Carina

    2016-01-01

    The copper-catalyzed asymmetric conjugated 1,4-addition reaction of organozinc reagents to a,b-unsaturated compounds is a very effective and widely used method for the enantioselective carbon-carbon bond formation. By the use of phosphoramidite ligands it is possible to reach ee-values and conversion up to > 99 %. Furthermore, this outstanding reaction provides lower costs in comparison to other transition-metal catalyzed reactions and compatibility to many functional groups. Despite the grea...

  19. Palladium-Catalyzed Nucleophilic Substitution of Alcohols : Mechanistic Studies and Synthetic Applications

    OpenAIRE

    Sawadjoon, Supaporn

    2013-01-01

    This thesis deals with the palladium-catalyzed nucleophilic substitution of π-activated alcohols in which the C–O bond of a non-manipulated hydroxyl group is cleaved. The thesis is divided in two chapters describing two different catalytic systems. Chapter 2 describes a heterogeneous palladium-catalyzed transfer hydrogenolysis of primary, secondary, and tertiary benzylic alcohols to generate the corresponding aromatic hydrocarbons using formic acid as the hydrogen donor. A detailed mechanisti...

  20. Physiological characterization of lipid accumulation and in vivo ester formation in Gordonia sp. KTR9.

    Science.gov (United States)

    Eberly, Jed O; Ringelberg, David B; Indest, Karl J

    2013-02-01

    Previous work has demonstrated the feasibility of in vivo biodiesel synthesis in Escherichia coli, however, ethyl ester formation was dependent on an external fatty acid feedstock. In contrast to E. coli, actinomycetes may be ideal organisms for direct biodiesel synthesis because of their capacity to synthesize high levels of triacylglcerides (TAGs). In this study, we investigated the physiology and associated TAG accumulation along with the in vivo ability to catalyze ester formation from exogenous short chain alcohol sources in Gordonia sp. KTR9, a strain that possesses a large number of genes dedicated to fatty acid and lipid biosynthesis. Total lipid fatty acids content increased by 75 % and TAG content increased by 50 % under nitrogen starvation conditions in strain KTR9. Strain KTR9 tolerated the exogenous addition of up to 4 % methanol, 4 % ethanol and 2 % propanol in the media. Increasing alcohol concentrations resulted in a decrease in the degree of saturation of recovered fatty acid alcohol esters and a slight increase in the fatty acid chain length. A linear dose dependency in fatty alcohol ester synthesis was observed in the presence of 0.5-2 % methanol and ethanol compared to control KTR9 strains grown in the absence of alcohols. An inspection of the KTR9 genome revealed the presence of several putative wax ester synthase/acyl-coenzyme A : diacylglycerol acyltransferase (WS/DGAT) enzymes, encoded by atf gene homologs, that may catalyze the in vivo synthesis of fatty acid esters from short chain alcohols. Collectively, these results indicate that Gordonia sp. KTR9 may be a suitable actinomycete host strain for in vivo biodiesel synthesis.

  1. Papain-Catalyzed Synthesis of Polyglutamate Containing a Nylon Monomer Unit

    OpenAIRE

    Kenjiro Yazawa; Keiji Numata

    2016-01-01

    Peptides have the potential to serve as an alternative for petroleum-based polymers to support a sustainable society. However, they lack thermoplasticity, owing to their strong intermolecular interactions. In contrast, nylon is famous for its thermoplasticity and chemical resistance. Here, we synthesized peptides containing a nylon unit to modify their thermal properties by using papain-catalyzed chemoenzymatic polymerization. We used l-glutamic acid alkyl ester as the amino acid monomer and ...

  2. 微波辐射对甲苯磺酸催化合成对羟基苯甲酸乙二醇单酯%Synthesis of mono-4-hydroxybenzoic acid ethylene glycol ester catalyzed by p-toluene sulfonic acid under microwave radiation

    Institute of Scientific and Technical Information of China (English)

    杨晓军; 冯小丽; 张谋真

    2012-01-01

    Mono 4-hydroxybenzoic acid ethylene glycol ester was synthesized by using 4-hydroxybenzoic acid and ethylene glycol as the raw materials and p -methyl benzene sulfonic acid as the catalyst under microwave radiation. The product was characterized by IR and NMR. The influence of microwave radiation power and time, catalyst dosage, and molar ratio of the reactants on the yield was investigated. The results showed that the esterification yield of 92. 1 % was attained under the optimal synthesis condition as follows ; microwave radiation power 500 W, catalyst dosage 0.28 g, molar ratio of the reactants 1:3.5 and microwave radiation time 20 min.%在微波辐射下,研究了以对甲苯磺酸为催化剂,对羟基苯甲酸和乙二醇为原料合成对羟基苯甲酸乙二醇单酯的工艺条件.用红外光谱分析和核磁共振光谱等方法对产物的结构进行表征,考察微波辐射功率、催化剂用量、酸醇物质的量比以及微波辐射时间对酯化率的影响.结果表明,合成对羟基苯甲酸乙二醇单酯的优化条件为:微波辐射功率500W,酸醇物质的量比为1∶3.5,催化剂用量0.28 g,微波辐射时间20 min,此条件下,酯化率达92.1%.

  3. DFT characterization of key intermediates in thiols oxidation catalyzed by amavadin.

    Science.gov (United States)

    Bertini, Luca; Barbieri, Valentina; Fantucci, Piercarlo; De Gioia, Luca; Zampella, Giuseppe

    2011-08-14

    Amavadin is an unusual octa-coordinated V(IV) complex isolated from Amanita muscaria mushrooms. The outer-sphere catalytic properties of such a complex toward several oxidation reactions are well known. Nevertheless, a remarkable example exists, in which the V(V) (d(0)) oxidized form of amavadin is able to electro-catalyze the oxidation of some thiols to the corresponding disulfides through an inner-sphere mechanism (Guedes da Silva et al. J. Am. Chem. Soc.1996, 118, 7568-7573.) The reaction mechanism implies the formation of an amavadin-substrate intermediate, whose half-life is about 0.3 s. By means of Density Functional Theory (DFT) computations and Quantum Theory of Atoms in Molecules (QTAIM) analysis of the electron density, we have first characterized the stereoelectronic features of the V(IV) (inactive) and V(V) (active) states of amavadin. Then, the formation of the V(V) complex with methyl mercaptoacetate (MMA), which has been chosen as a prototypical substrate, has been characterized both thermodynamically and kinetically. DFT results reveal that protonation of V(V) amavadin at a carboxylate oxygen not directly involved in the V coordination, favors MMA binding into the first coordination sphere of vanadium, by substitution of the amavadin carboxylate oxygen with that of the substrate and formation of an S-HO hydrogen bond interaction. The latter interaction can promote SH deprotonation and binding of the thiolate group to vanadium. The kinetic and thermodynamic feasibility of the V(V)-MMA intermediates formation is in agreement, along with electrochemical experimental data, also with the biological role exerted by amavadin. Finally, the presence of an ester functional group as an essential requisite for MMA oxidation has been rationalized.

  4. Lubricating and Waxy Esters. VI. Effect of Symmetry about Ester on Crystallization of Linear Monoester Isomers

    Directory of Open Access Journals (Sweden)

    Laziz Bouzidi

    2014-08-01

    Full Text Available The crystal structure development of jojoba-like esters incorporating either 1-decenoic acid and/or 1-decenol, namely octadec-9-enyl dec-9-enoate (JLE-281, and its isomer dec-9-enyl oleate (JLE-282 was investigated to reveal the effect of symmetry about the ester group on crystallization of aliphatic fatty monoesters. The phase transformation path was investigated with temperature-time resolved X-ray diffraction during stepped isothermal crystallization, and while cooling from the melt at a fixed rate. Startling differences in phase behavior were uncovered between the isomers. When stepped isothermals were used, selective extinctions occurred at a transition temperature for JLE-281 but not for JLE-282. The extinctions, which are due to dramatic changes in the electronic density of certain families of planes, indicate a phase transition attributed to a brusque rearrangement of the oxygen atoms in the crystal subcell. The phase transition did not occur when the JLEs were cooled continuously. The crucial role played by the position of the alkyl chain and its orientation relative to the easy rotation site of the C–O bond in the phase trajectories of the JLEs was particularly highlighted.

  5. Synthesis, spectroscopic and chromatographic studies of sunflower oil biodiesel using optimized base catalyzed methanolysis.

    Science.gov (United States)

    Naureen, Rizwana; Tariq, Muhammad; Yusoff, Ismail; Chowdhury, Ahmed Jalal Khan; Ashraf, Muhammad Aqeel

    2015-05-01

    Methyl esters from vegetable oils have attracted a great deal of interest as substitute for petrodiesel to reduce dependence on imported petroleum and provide an alternate and sustainable source for fuel with more benign environmental properties. In the present study biodiesel was prepared from sunflower seed oil by transesterification by alkali-catalyzed methanolysis. The fuel properties of sunflower oil biodiesel were determined and discussed in the light of ASTM D6751 standards for biodiesel. The sunflower oil biodiesel was chemically characterized with analytical techniques like FT-IR, and NMR ((1)H and (13)C). The chemical composition of sunflower oil biodiesel was determined by GC-MS. Various fatty acid methyl esters (FAMEs) were identified by retention time data and verified by mass fragmentation patterns. The percentage conversion of triglycerides to the corresponding methyl esters determined by (1)H NMR was 87.33% which was quite in good agreement with the practically observed yield of 85.1%.

  6. Synthesis of substituted 2-cyanoarylboronic esters

    DEFF Research Database (Denmark)

    Lysén, Morten; Hansen, Henriette M; Begtrup, Mikael

    2006-01-01

    The synthesis of substituted 2-cyanoarylboronic esters is described via lithiation/in situ trapping of the corresponding methoxy-, trifluoromethyl-, fluoro-, chloro-, and bromobenzonitriles. The crude arylboronic esters were obtained in high yields and purities and with good regioselectivities....

  7. Ester Tuiksoo otsib endiselt pesa / Paavo Kangur

    Index Scriptorium Estoniae

    Kangur, Paavo, 1966-

    2012-01-01

    Maadevahetuse protsessi raames süüdistati Ester Tuiksood, et põllumajandusministrina sai ta altkäemaksu Rävala 19 asunud korteri kasutamise eest. Ester Tuiksoo ja kinnisvaraeksperdi Tõnis Rüütli kommentaarid

  8. Liquid Crystalline Thermosets from Ester, Ester-imide, and Ester-amide Oligomers

    Science.gov (United States)

    Dingemans, Theodorus J. (Inventor); Weiser, Erik S. (Inventor); St. Clair, Terry L. (Inventor)

    2009-01-01

    Main chain thermotropic liquid crystal esters, ester-imides, and ester-amides were prepared from AA, BB, and AB type monomeric materials and end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive end-groups. The end-capped liquid crystal oligomers are thermotropic and have, preferably, molecular weights in the range of approximately 1000-15,000 grams per mole. The end-capped liquid crystaloligomers have broad liquid crystalline melting ranges and exhibit high melt stability and very low melt viscosities at accessible temperatures. The end-capped liquid crystal oli-gomers are stable forup to an hour in the melt phase. They are highly processable by a variety of melt process shape forming and blending techniques. Once processed and shaped, the end-capped liquid crystal oigomers were heated to further polymerize and form liquid crystalline thermosets (LCT). The fully cured products are rubbers above their glass transition temperatures.

  9. Hydrolyzable polyureas bearing hindered urea bonds.

    Science.gov (United States)

    Ying, Hanze; Cheng, Jianjun

    2014-12-10

    Hydrolyzable polymers are widely used materials that have found numerous applications in biomedical, agricultural, plastic, and packaging industrials. They usually contain ester and other hydrolyzable bonds, such as anhydride, acetal, ketal, or imine, in their backbone structures. Here, we report the first design of hydrolyzable polyureas bearing dynamic hindered urea bonds (HUBs) that can reversibly dissociate to bulky amines and isocyanates, the latter of which can be further hydrolyzed by water, driving the equilibrium to facilitate the degradation of polyureas. Polyureas bearing 1-tert-butyl-1-ethylurea bonds that show high dynamicity (high bond dissociation rate), in the form of either linear polymers or cross-linked gels, can be completely degraded by water under mild conditions. Given the simplicity and low cost for the production of polyureas by simply mixing multifunctional bulky amines and isocyanates, the versatility of the structures, and the tunability of the degradation profiles of HUB-bearing polyureas, these materials are potentially of very broad applications.

  10. Increased production of wax esters in transgenic tobacco plants by expression of a fatty acid reductase:wax synthase gene fusion.

    Science.gov (United States)

    Aslan, Selcuk; Hofvander, Per; Dutta, Paresh; Sun, Chuanxin; Sitbon, Folke

    2015-12-01

    Wax esters are hydrophobic lipids consisting of a fatty acid moiety linked to a fatty alcohol with an ester bond. Plant-derived wax esters are today of particular concern for their potential as cost-effective and sustainable sources of lubricants. However, this aspect is hampered by the fact that the level of wax esters in plants generally is too low to allow commercial exploitation. To investigate whether wax ester biosynthesis can be increased in plants using transgenic approaches, we have here exploited a fusion between two bacterial genes together encoding a single wax ester-forming enzyme, and targeted the resulting protein to chloroplasts in stably transformed tobacco (Nicotiana benthamiana) plants. Compared to wild-type controls, transgenic plants showed both in leaves and stems a significant increase in the total level of wax esters, being eight-fold at the whole plant level. The profiles of fatty acid methyl ester and fatty alcohol in wax esters were related, and C16 and C18 molecules constituted predominant forms. Strong transformants displayed certain developmental aberrations, such as stunted growth and chlorotic leaves and stems. These negative effects were associated with an accumulation of fatty alcohols, suggesting that an adequate balance between formation and esterification of fatty alcohols is crucial for a high wax ester production. The results show that wax ester engineering in transgenic plants is feasible, and suggest that higher yields may become achieved in the near future.

  11. Mechanical properties and chemical stability of pivalolactone-based poly(ether ester)s

    NARCIS (Netherlands)

    Tijsma, E.J.; Does, van der L.; Bantjes, A.; Vulic, I.

    1994-01-01

    The processing, mechanical and chemical properties of poly(ether ester)s, prepared from pivalolactone (PVL), 1,4-butanediol (4G) and dimethyl terephthalate (DMT), were studied. The poly(ether ester)s could easily be processed by injection moulding, owing to their favourable rheological and thermal p

  12. 40 CFR 721.3034 - Methylamine esters.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Methylamine esters. 721.3034 Section... Substances § 721.3034 Methylamine esters. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as methylamine esters (PMN P-94-982) is...

  13. 40 CFR 721.2805 - Acrylate ester.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Acrylate ester. 721.2805 Section 721... Acrylate ester. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an acrylate ester (PMN P-96-824) is subject to reporting under...

  14. 40 CFR 721.537 - Organosilane ester.

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Organosilane ester. 721.537 Section... § 721.537 Organosilane ester. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an organosilane ester (PMN P-96-1661/P-95-1654)...

  15. Esters van tetrathioorthokiezelzuur en tetrathioorthogermaniumzuur

    NARCIS (Netherlands)

    Stienstra, Folkert Jans

    1934-01-01

    The germaniun tetrachloride required was prepared from the mineral germanite. For this a simpler method was elaborated. For the preparation of the esters of tetrathioorthosilicic acid and tetrathioorthogermanic acid, silicon tetrachloride and germanium tetrachloride were made to react with a suspens

  16. 氮杂冠醚化单 Schiff 碱锰(III)配合物催化 PNPP 水解研究%Study on aza crown ether substituted mono-Schiff base managnese(III) complexes catalyze carboxyli c acid esters hydor lysis

    Institute of Scientific and Technical Information of China (English)

    黄生田; 李建章; 肖正华; 胡伟

    2013-01-01

    Four mono-Schiff base manganese (III) complexes with either benzo-10-aza-crown ether pendants (MnL12Cl,MnL22Cl, MnL32 Cl) or morpholino pendants( MnL 42 Cl) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate ( PNPP) .The effects of the different ligands and the position of the aza-crown in the Schiff base complexes on the kinetics of PNPP hydrolysis were investigated .In addition ,a kinetic mathematical model of PNPP cleavage catalyzed by these complexes was established.The results showed that the rate of the catalytic PNPP hydrolysis increased as the pH of the buffer solution increased .All four complexes exhibited high activity in the catalytic PNPP hydrolysis ,which was in-fluenced by the structures of the different Schiff base ligand .%将4种氮杂冠醚或吗啉取代的单Schiff碱锰( III)配合物作为仿水解酶模型催化α-吡啶甲酸对硝基苯酯( PNPP)水解。考察了单Schiff 碱配体中取代基类型、氮杂冠醚取代的位置对其仿水解酶性能的影响;探讨了Schiff 配合物催化PNPP水解的动力学和机理;提出了配合物催化PNPP水解的动力学模型。结果表明,在25℃条件下随着缓冲溶液 pH值的增大,配合物催化PNPP水解速率提高,氮杂冠醚化单Schiff碱锰( III)配合物在催化PNPP水解反应中表现出良好的催化活性,Schiff碱配体结构显著影响配合物催化活性。

  17. Distinction between esterases and lipases: a kinetic study with vinyl esters and TAG.

    Science.gov (United States)

    Chahinian, Henri; Nini, Lylia; Boitard, Elisabeth; Dubès, Jean-Paul; Comeau, Louis-Claude; Sarda, Louis

    2002-07-01

    The better to characterize enzymes hydrolyzing carboxyl ester bonds (carboxyl ester hydrolases), we have compared the kinetic behavior of various lipases and esterases against solutions and emulsions of vinyl esters and TAG. Short-chain vinyl esters are hydrolyzed at comparable rates by esterases and lipases and have higher limits of solubility in water than corresponding TAG. Therefore, they are suited to study the influence of the physical state of the substrate on carboxyl ester hydrolase activity within a large concentration range. Enzymes used in this study are TAG lipases from microorganisms, lipases from human and guinea pig pancreas, pig liver esterase, and acetylcholinesterase. This study also includes cutinase, a fungal enzyme that displays functional properties between esterases and lipases. Esterases display maximal activity against solutions of short-chain vinyl esters (vinyl acetate, vinyl propionate, and vinyl butyrate) and TAG (triacetin, tripropionin, and tributyrin). Half-maximal activity is reached at ester concentrations far below the solubility limit. The transition from solution to emulsion at substrate concentrations exceeding the solubility limit has no effect on esterase activity. Lipases are active on solutions of short-chain vinyl esters and TAG but, in contrast to esterases, they all display maximal activity against emulsified substrates and half-maximal activity is reached at substrate concentrations near the solubility limit of the esters. The kinetics of hydrolysis of soluble substrates by lipases are either hyperbolic or deviate from the Michaelis-Menten model and show no or weak interfacial activation. The presence of molecular aggregates in solutions of short-chain substrates, as evidenced by a spectral dye method, likely accounts for the activity of lipases against soluble esters. Unlike esterases, lipases hydrolyze emulsions of water-insoluble medium- and long-chain vinyl esters and TAG such as vinyl laurate, trioctanoin, and

  18. Clicked Cinnamic/Caffeic Esters and Amides as Radical Scavengers and 5-Lipoxygenase Inhibitors

    Directory of Open Access Journals (Sweden)

    Jérémie A. Doiron

    2014-01-01

    Full Text Available 5-Lipoxygenase (5-LO is the key enzyme responsible for the conversion of arachidonic acid to leukotrienes, a class of lipid mediators implicated in inflammatory disorders. In this paper, we describe the design, synthesis, and preliminary activity studies of novel clicked caffeic esters and amides as radical scavengers and 5-LO inhibitors. From known 5-LO inhibitor 3 as a lead, cinnamic esters 8a–h and amides 9a–h as well as caffeic esters 15a–h and amides 16a–h were synthesized by Cu(I-catalyzed [1,3]-dipolar cycloaddition with the appropriate azide precursors and terminal alkynes. All caffeic analogs are proved to be good radical scavengers (IC50: 10–20 μM. Esters 15g and 15f possessed excellent 5-LO inhibition activity in HEK293 cells and were equipotent with the known 5-LO inhibitor CAPE and more potent than Zileuton. Several synthesized esters possess activities rivaling Zileuton in stimulated human polymorphonuclear leukocytes.

  19. Toxicological assessment of 3-chloropropane-1,2-diol and glycidol fatty acid esters in food.

    Science.gov (United States)

    Bakhiya, Nadiya; Abraham, Klaus; Gürtler, Rainer; Appel, Klaus Erich; Lampen, Alfonso

    2011-04-01

    Fatty acid esters of 3-chloropropane-1,2-diol (3-MCPD) and glycidol are a newly identified class of food process contaminants. They are widespread in refined vegetable oils and fats and have been detected in vegetable fat-containing products, including infant formulas. There are no toxicological data available yet on the 3-MCPD and glycidol esters, and the primary toxicological concern is based on the potential release of 3-MCPD or glycidol from the parent esters by lipase-catalyzed hydrolysis in the gastrointestinal tract. Although 3-MCPD is assessed as a nongenotoxic carcinogen with a tolerable daily intake (TDI) of 2 μg/kg body weight (bw), glycidol is a known genotoxic carcinogen, which induces tumors in numerous organs of rodents. The initial exposure estimates, conducted by Federal Institute for Risk Assessment (BfR) under the assumption that 100% of the 3-MPCD and glycidol are released from their esters, revealed especially that infants being fed commercial infant formula could ingest harmful amounts of 3-MCPD and glycidol. However, the real oral bioavailability may be lower. As this gives rise for toxicological concern, the currently available toxicological data of 3-MCPD and glycidol and their esters are summarized in this review and discussed with regard to data gaps and further research needs.

  20. Acceleration effect of ionic liquids on polycyclotrimerization of dicyanate esters

    Directory of Open Access Journals (Sweden)

    A. Fainleib

    2016-09-01

    Full Text Available The polycyclotrimerization reaction of dicyanate ester of bisphenol E (DCBE in the presence of varying amounts (from 0.5 to 5 wt% of 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF4] ionic liquid has been investigated using differential scanning calorimetry (DSC and Fourier transform infrared spectroscopy (FTIR techniques, after a curing stage at 150 °C for 6 h. It is noteworthy that an amount of [OMIm][BF4] as low as 0.5 wt% accelerates dramatically the thermal curing process leading to the formation of a polycyanurate network. The conversion of DCBE increased with increasing [OMIm][BF4] content in the temperature range studied. A reaction mechanism associated with the ionic liquid-catalyzed DCBE polycyclotrimerization is newly proposed via the involvement of a [CN]δ+–[OMIm]δ– complex as a key intermediate.

  1. Cooperative Reinforcement of Ionic Liquid and Reactive Solvent on Enzymatic Synthesis of Caffeic Acid Phenethyl Ester as an In Vitro Inhibitor of Plant Pathogenic Bacteria

    Directory of Open Access Journals (Sweden)

    Yan Xu

    2017-01-01

    Full Text Available It is widely believed that lipases in ionic liquids (ILs possess higher enzyme activity, stability and selectivity; however, reaction equilibrium is always limited by product inhibition, and the product is difficult to separate from non-volatile ILs using distillation. To solve this problem, using trialkylphosphine oxide (TOPO as a complexing agent, a novel biphase of reactive solvent and IL was firstly reported for caffeic acid phenethyl ester (CAPE production from methyl caffeate (MC and 2-phenylethanol (PE catalyzed by lipase via transesterification. The effects of the reaction parameters and their action mechanism were investigated, and the inhibition of CAPE against bacterial wilt pathogen Ralstonia solanacearum was firstly measured. The MC conversion of 98.83% ± 0.76% and CAPE yield of 96.29% ± 0.07% were obtained by response surface methodology in the 25 g/L TOPO-cyclohexane/[Bmim][Tf2N] (1:1, v/v; the complex stoichiometry calculation and FTIR spectrum confirmed that the reversible hydrogen-bond complexation between TOPO and caffeates significantly enhances the cooperative effect of two phases on the lipase-catalyzed reaction. The temperature was reduced by 14 °C; the MC concentration increased by 3.33-fold; the ratio of catalyst to donor decreased by 4.5-fold; and Km decreased 1.08-fold. The EC50 of CAPE against R. solanacearum was 0.17–0.75 mg/mL, suggesting that CAPE is a potential in vitro inhibitor of plant pathogenic bacteria.

  2. Study on the Stereoselective Synthesis of Carbapenem Sidechain (2S,4S)-4-Acetylsulphanyl-2-[(S)-1-phenylethylcarbamoyl]-pyrrolidine-1-carboxylic Acid 4-Nitrobenzyl Ester

    Institute of Scientific and Technical Information of China (English)

    Qian LIU; Gang FANG; Li Ping WU; Jian Mei CUI; Xiao Tian LIANG; Song WU

    2004-01-01

    A stereoselective and economic synthesis of the carbapenem sidechain (2S, 4S)-4-ace-tylsulphanyl-2-[ (S)1-phenylethyl-carbamoyl] pyrrolidine-l-carboxylic acid 4-nitrobenzyl ester was developed. Due to the effect of spatial hindrance, only the (2S,4S) diastereomer 3 was obtained by coupling 1 and the inexpensive racemic 2 catalyzed by EEDQ.

  3. Sinapate esters in brassicaceous plants: biochemistry, molecular biology, evolution and metabolic engineering.

    Science.gov (United States)

    Milkowski, Carsten; Strack, Dieter

    2010-06-01

    Brassicaceous plants are characterized by a pronounced metabolic flux toward sinapate, produced by the shikimate/phenylpropanoid pathway, which is converted into a broad spectrum of O-ester conjugates. The abundant sinapate esters in Brassica napus and Arabidopsis thaliana reflect a well-known metabolic network, including UDP-glucose:sinapate glucosyltransferase (SGT), sinapoylglucose:choline sinapoyltransferase (SCT), sinapoylglucose:L-malate sinapoyltransferase (SMT) and sinapoylcholine (sinapine) esterase (SCE). 1-O-Sinapoylglucose, produced by SGT during seed development, is converted to sinapine by SCT and hydrolyzed by SCE in germinating seeds. The released sinapate feeds via sinapoylglucose into the biosynthesis of sinapoylmalate in the seedlings catalyzed by SMT. Sinapoylmalate is involved in protecting the leaves against the deleterious effects of UV-B radiation. Sinapine might function as storage vehicle for ready supply of choline for phosphatidylcholine biosynthesis in young seedlings. The antinutritive character of sinapine and related sinapate esters hamper the use of the valuable seed protein of the oilseed crop B. napus for animal feed and human nutrition. Due to limited variation in seed sinapine content within the assortment of B. napus cultivars, low sinapine lines cannot be generated by conventional breeding giving rise to genetic engineering of sinapate ester metabolism as a promising means. In this article we review the progress made throughout the last decade in identification of genes involved in sinapate ester metabolism and characterization of the encoded enzymes. Based on gene structures and enzyme recruitment, evolution of sinapate ester metabolism is discussed. Strategies of targeted metabolic engineering, designed to generate low-sinapate ester lines of B. napus, are evaluated.

  4. Chiral benzimidazoles as hydrogen bonding organocatalysts

    OpenAIRE

    Nájera Domingo, Carmen; Yus Astiz, Miguel

    2015-01-01

    Several bifunctional organocatalysts bearing the benzimidazole unit have been designed in order to act as bifunctional systems by hydrogen bonding. Chiral 2-aminobenzimidazoles are conformational rigid guanidines able to catalyze enantioselectively Michael reaction, direct SN1 of alcohols, and aldol reactions. Some of these organocatalysts can be easily recovered by simple isolation methods and reused without loss of catalytic activity. Related (2-aminoalkyl)benzimidazoles have been used as c...

  5. Synthesis of sulfur-containing lubricant additives on the basis of fatty acid ethyl esters

    Directory of Open Access Journals (Sweden)

    Iurii S. Bodachivskyi

    2016-12-01

    Full Text Available The study reveals an energy-, resource- and eco-friendly method for preparation of sulfur-containing lubricant additives via interaction of fatty acid ethyl esters of rapeseed oil with elemental sulfur. The structure of synthesized compounds under various reactants ratio (5–50 wt.% of sulfur, duration (30–240 min and temperature of the process (160–215°С was investigated using various analytical techniques. According to the established data, aside from addition to double bonds, the side reaction of hydrogen substitution at α-methylene groups near these bonds occurs and induces the formation of conjugated systems and chromophoric sulfur-rich derivatives. Also, we found that increase of process duration evokes growth of polysulfane chains, in contrast to the raise of temperature, which leads to the formation of sulfur-containing heterocycles and hydrogen sulfide, as a result of elimination. Influence of accelerators on sulfurization of fatty acid ethyl esters was also examined. The most effective among them are mixtures of zinc dibutyldithiocarbamate with zinc oxide or stearic acid, which soften synthesis conditions and doubly decrease duration of the high-temperature stage. In addition, sulfur-containing compositions of ethyl esters and α-olefins, vulcanized esters by benzoyl peroxide, nonylphenols and zinc dinonylphenyldithiophosphate were designed. The study identified that lithium lubricant with sulfurized vulcanized esters provides improved tribological properties, in comparison with base lubricant or lubricant with the non-modified product.

  6. Inhibition of insect juvenile hormone epoxide hydrolase: asymmetric synthesis and assay of glycidol-ester and epoxy-ester inhibitors of trichoplusia ni epoxide hydrolase.

    Science.gov (United States)

    Linderman, R J; Roe, R M; Harris, S V; Thompson, D M

    2000-01-01

    Juvenile hormone (JH) undergoes metabolic degradation by two major pathways involving JH esterase and JH epoxide hydrolase (EH). While considerable effort has been focussed on the study of JH esterase and the development of inhibitors for this enzyme, much less has been reported on the study of JH-EH. In this work, the asymmetric synthesis of two classes of inhibitors of recombinant JH-EH from Trichoplusia ni, a glycidol-ester series and an epoxy-ester series is reported. The most effective glycidol-ester inhibitor, compound 1, exhibited an I(50) of 1.2x10(-8) M, and the most effective epoxy-ester inhibitor, compound 11, exhibited an I(50) of 9.4x10(-8) M. The potency of the inhibitors was found to be dependent on the absolute configuration of the epoxide. In both series of inhibitors, the C-10 R-configuration was found to be significantly more potent that the corresponding C-10 S-configuration. A mechanism for epoxide hydration catalyzed by insect EH is also presented.

  7. A novel bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase mediates wax ester and triacylglycerol biosynthesis in Acinetobacter calcoaceticus ADP1.

    Science.gov (United States)

    Kalscheuer, Rainer; Steinbüchel, Alexander

    2003-03-07

    Triacylglycerols (TAGs) and wax esters are neutral lipids with considerable importance for dietetic, technical, cosmetic, and pharmaceutical applications. Acinetobacter calcoaceticus ADP1 accumulates wax esters and TAGs as intracellular storage lipids. We describe here the identification of a bifunctional enzyme from this bacterium exhibiting acyl-CoA:fatty alcohol acyltransferase (wax ester synthase, WS) as well as acyl-CoA:diacylglycerol acyltransferase (DGAT) activity. Experiments with a knock-out mutant demonstrated the key role of the bifunctional WS/DGAT for biosynthesis of both storage lipids in A. calcoaceticus. This novel type of long-chain acyl-CoA acyltransferase is not related to known acyltransferases including the WS from jojoba (Simmondsia chinensis), the DGAT1 or DGAT2 families present in yeast, plants, and animals, and the phospholipid:diacylglycerol acyltransferase catalyzing TAG formation in yeast and plants. A large number of WS/DGAT-related proteins were identified in Mycobacterium and Arabidopsis thaliana indicating an important function of these proteins. WS and DGAT activity was demonstrated for the translational product of one WS/DGAT homologous gene from M. smegmatis mc(2)155. The potential of WS/DGAT to establish novel processes for biotechnological production of jojoba-like wax esters was demonstrated by heterologous expression in recombinant Pseudomonas citronellolis. The potential of WS/DGAT as a selective therapeutic target of mycobacterial infections is discussed.

  8. Diastereoselective B(C6F5)3-Catalyzed Reductive Carbocyclization of Unsaturated Carbohydrates.

    Science.gov (United States)

    Bender, Trandon A; Dabrowski, Jennifer A; Zhong, Hongyu; Gagné, Michel R

    2016-08-19

    A B(C6F5)3-catalyzed method for the selective conversion of unsaturated carbohydrates to cyclopentanes and cyclopropanes is disclosed. Catalyst activation of tertiary silanes generates the ion pair [(C6F5)3B-H][ROSi2] whose components synergistically activate C-O bonds for diastereoselective C-C bond formation. Sila-THF cations are invoked as key intermediates facilitating carbocyclizations. Complex chiral synthons are thereby obtained in a single pot.

  9. Advances in Metal-Catalyzed Cross-Coupling Reactions of Halogenated Quinazolinones and Their Quinazoline Derivatives

    Directory of Open Access Journals (Sweden)

    Malose Jack Mphahlele

    2014-10-01

    Full Text Available Halogenated quinazolinones and quinazolines are versatile synthetic intermediates for the metal-catalyzed carbon–carbon bond formation reactions such as the Kumada, Stille, Negishi, Sonogashira, Suzuki-Miyaura and Heck cross-coupling reactions or carbon-heteroatom bond formation via the Buchwald-Hartwig cross-coupling to yield novel polysubstituted derivatives. This review presents an overview of the application of these methods on halogenated quinazolin-4-ones and their quinazolines to generate novel polysubstituted derivatives.

  10. Palladium(II)-catalyzed direct alkoxylation of arenes: evidence for solvent-assisted concerted metalation deprotonation.

    Science.gov (United States)

    Anand, Megha; Sunoj, Raghavan B

    2011-09-16

    Density functional theory investigations on the mechanism of palladium acetate catalyzed direct alkoxylation of N-methoxybenzamide in methanol reveal that the key steps involve solvent-assisted N-H as well as C-H bond activations. The transition state for the critical palladium-carbon bond formation through a concerted metalation deprotonation (CMD) process leading to a palladacycle intermediate has been found to be more stable in the methanol-assisted pathway as compared to an unassisted route.

  11. Thermal studies of poly(esters) containing silicon or germanium in the main chain

    Energy Technology Data Exchange (ETDEWEB)

    Tagle, L.H. [Facultad de Quimica, Pontificia Universidad Catolica de Chile, P.O. Box 306, Santiago (Chile)]. E-mail: ltagle@puc.cl; Terraza, C. [Facultad de Quimica, Pontificia Universidad Catolica de Chile, P.O. Box 306, Santiago (Chile); Valenzuela, P. [Facultad de Quimica, Pontificia Universidad Catolica de Chile, P.O. Box 306, Santiago (Chile); Leiva, A. [Facultad de Quimica, Pontificia Universidad Catolica de Chile, P.O. Box 306, Santiago (Chile); Urzua, M. [Departamento de Quimica, Facultad de Ciencias, Universidad de Chile, Santiago de Chile (Chile)

    2005-01-20

    The thermal properties of poly(esters) containing Si and/or Ge in the main chain derived from the acid dichlorides bis(4-chloroformyl-phenyl)-dimethyl-silane, bis(4-chloroformyl-phenyl)-dimethyl-germane, bis(4-chloroformyl-phenyl)-diphenyl-silane and bis(4-chloroformyl-phenyl)-diphenyl-silane, and the diphenols bis(4-hydroxyphenyl)-dimethyl-silane, bis(4-hydroxyphenyl)-dimethyl-germane, bis(4-hydroxyphenyl)-diphenyl-silane and bis(4-hydroxyphenyl)-diphenyl-germane were studied by differential scanning calorimetry and dynamic thermogravimetry. Poly(esters) with two Si atoms in the main chain showed higher values of T{sub g} than those with two Ge atoms, and the same was observed for poly(esters) with phenyl groups bonded to the heteroatoms, instead of those with methyl groups. Thermal decomposition temperatures were also higher for those poly(esters) with two Si atoms in the main chain and those in which the heteroatom is bonded to phenyl groups, due to the higher polarity of the Si-C bond in front of the Ge-C.

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

    Directory of Open Access Journals (Sweden)

    Jubi John

    2014-06-01

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

  13. Gallium(III)- and calcium(II)-catalyzed Meyer-Schuster rearrangements followed by intramolecular aldol condensation or endo-Michael addition.

    Science.gov (United States)

    Presset, M; Michelet, B; Guillot, R; Bour, C; Bezzenine-Lafollée, S; Gandon, V

    2015-03-28

    The first gallium- and calcium-catalyzed Meyer-Schuster rearrangements are described. Under substrate control, the incipient conjugated ketones can be trapped intramolecularly by β-keto esters or amides to yield cyclic products after aldol condensation or endo-Michael addition. An interesting additive effect that promotes the latter tandem process with calcium has been found.

  14. Methods of making alkyl esters

    Science.gov (United States)

    Elliott, Brian

    2010-08-03

    A method comprising contacting an alcohol, a feed comprising one or more glycerides and equal to or greater than 2 wt % of one or more free fatty acids, and a solid acid catalyst, a nanostructured polymer catalyst, or a sulfated zirconia catalyst in one or more reactors, and recovering from the one or more reactors an effluent comprising equal to or greater than about 75 wt % alkyl ester and equal to or less than about 5 wt % glyceride.

  15. Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-11-13

    Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

  16. Retinyl ester hydrolysis and retinol efflux from BFC-1beta adipocytes.

    Science.gov (United States)

    Wei, S; Lai, K; Patel, S; Piantedosi, R; Shen, H; Colantuoni, V; Kraemer, F B; Blaner, W S

    1997-05-30

    Adipose tissue is an important storage depot for retinol, but there are no data regarding retinol mobilization from adipose stores. To address this, dibutyryl cAMP was provided to murine BFC-1beta adipocytes and its effects on retinol efflux assessed. High performance liquid chromatography analysis of retinol and retinyl esters in adipocytes and media indicated that cAMP stimulated, in a time- and dose-dependent manner, retinol accumulation in the culture media and decreased cellular retinyl ester concentrations. Study of adipocyte retinol-binding protein synthesis and secretion indicated that cAMP-stimulated retinol efflux into the media did not result from increased retinol-retinol-binding protein secretion but was dependent on the presence of fetal bovine serum in the culture media. Since our data suggested that retinyl esters can be hydrolyzed by a cAMP-dependent enzyme like hormone-sensitive lipase (HSL), in separate studies, we purified a HSL-containing fraction from BFC-1beta adipocytes and demonstrated that it catalyzed retinyl palmitate hydrolysis. Homogenates of Chinese hamster ovary cells overexpressing HSL catalyzed retinyl palmitate hydrolysis in a time-, protein-, and substrate-dependent manner, with an apparent Km for retinyl palmitate of 161 microM, whereas homogenates from control Chinese hamster ovary cells did not.

  17. Organocatalytic Asymmetric Michael Addition of 4-Hydroxycoumarin to β,γ-Unsaturated α-Keto Esters

    Energy Technology Data Exchange (ETDEWEB)

    Suh, Chang Won; Han, Tae Hyun; Kim, Dae Young [Soonchunhyang Univ., Asan (Korea, Republic of)

    2013-06-15

    In conclusion, we have developed organocatalytic enantioselective conjugate addition reaction of 4-hydroxycoumarin (1) to β,γ-unsaturated α-keto esters 2 to afford biologically valuable warfarin derivatives 3. The process is efficiently catalyzed by a binaphthyl-modified thiourea organocatalyst. The coumarin core is present as a characteristic structural motif in a large number of natural products and biologically active molecules.1 Particularly, many of these naturally occurring 4-hydroxycoumarin and their synthetic analogues are important precursors for the synthesis of natural products and pharmaceuticals. Enantioselective organocatalytic conjugate addition of 4-hydroxycoumarin to α,β-unsaturated ketones is a straightforward method to access warfarin which is an effective anticoagulants. Although a number of reactions of α,β-unsaturated ketones as Michael acceptors have been reported, the corresponding β,γ-unsaturated α-keto esters have received relatively little attention as Michael acceptors. Recently, several groups have reported the asymmetric Michael addition of 4-hydroxycoumarin to β,γ-unsaturated α-keto esters catalyzed by Cu(II)-bisoxazoline, N,N'-dioxide-Ni(II) complexes, thiourea catalysts. Although several efficient methods have been achieved by these systems, an effective method for the synthesis of warfarin analogues is still a challenge.

  18. Computational probes into the conceptual basis of silver ion chromatography: I. Silver(I) ion complexes of unsaturated fatty acids and esters

    NARCIS (Netherlands)

    Damyanova, B.; Momtchilova, S.; Bakalova, S.; Zuilhof, H.; Christie, W.W.; Kaneti, J.

    2002-01-01

    Silver ion chromatography of unsaturated fatty acid derivatives can be described satisfactorily by the suggestion of Ag(I) complexation with more than a single bonding site of esters of the 18:1, 18:2, etc. series (that is, one, two, etc. methylene-interrupted double bonds in the C18 hydrocarbon cha

  19. Fe-Catalyzed Olefin Hydroamination with Diazo Compounds for Hydrazone Synthesis.

    Science.gov (United States)

    Zheng, Jing; Qi, Jifeng; Cui, Sunliang

    2016-01-01

    A novel Fe-catalyzed olefin hydroamination with diazo compounds for accessing hydrazones has been developed. Diazo compounds are used as radical acceptors and can be trapped by the in situ generated alkyl radical toward C-N bond formation. The reaction conditions are mild, and the substrate scope is broad. Additionally, this hydroamination protocol is applicable for intramolecular reactions to construct diverse heterocycles.

  20. Synthesis of quinolones by nickel-catalyzed cycloaddition via elimination of nitrile.

    Science.gov (United States)

    Nakai, Kenichiro; Kurahashi, Takuya; Matsubara, Seijiro

    2013-02-15

    Substituted quinolones were efficiently synthesized via the nickel-catalyzed cycloaddition of o-cyanophenylbenzamide derivatives with alkynes. The reaction involves elimination of a nitrile group by cleavage of the two independent aryl-cyano and aryl-carbonyl C-C bonds of the amides.

  1. Regio- and Diasteroselectivity of Rhodium-catalyzed Ring Opening Reaction of Oxabenzonorbornadienes with Heteroatom Nucleophiles

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A new rhodium catalyzed ring opening reaction of oxabenzonorbornadienes and its derivatives was described. This reaction forms a new carbon-nitrogen bond via an intermolecular allylic displacement of the bridgehead oxygen with a piperazine's derivatives, which proceeds with very high regioselectivity.

  2. Direct synthesis of diaryl sulfides by copper-catalyzed coupling of aryl halides with aminothiourea

    Institute of Scientific and Technical Information of China (English)

    Xiang Mei Wu; Wei Ya Hu

    2012-01-01

    An efficient and simple protocol of copper-catalyzed C-S bond formation between aryl halides and inexpensive and commercially available aminothiourea is reported.A variety of symmetrical diaryl sulfides can be synthesized in good to excellent yields up to 94% with the advantage of avoiding foul-smelling thiols.

  3. Copper(II)-catalyzed electrophilic amination of quinoline N-oxides with O-benzoyl hydroxylamines.

    Science.gov (United States)

    Li, Gang; Jia, Chunqi; Sun, Kai; Lv, Yunhe; Zhao, Feng; Zhou, Kexiao; Wu, Hankui

    2015-03-21

    Copper acetate-catalyzed C-H bond functionalization amination of quinoline N-oxides was achieved using O-benzoyl hydroxylamine as an electrophilic amination reagent, thereby affording the desired products in moderate to excellent yields. Electrophilic amination can also be performed in good yield on a gram scale.

  4. Copper-catalyzed asymmetric allylic substitution reactions with organozinc and Grignard reagents

    NARCIS (Netherlands)

    Geurts, Koen; Fletcher, Stephen P.; van Zijl, Anthoni W.; Minnaard, Adriaan J.; Feringa, Ben L.; Bignall, H. E.; Jauncey, D. L.; Lovell, J. E. J.; Tzioumis, A. K.; Kedziora-Chudczer, L. L.; MacQuart, J. P.; Tingay, S. J.; Rayner, D. P.; Clay, R. W.

    2008-01-01

    Asymmetric allylic alkylations (AAAs) are among the most powerful C-C bond-forming reactions. We present a brief overview of copper-catalyzed AAAs with organometallic reagents and discuss our own contributions to this field. Work with zinc reagents and phosphoramidite ligands provided a framework fo

  5. Gemini ester quat surfactants and their biological activity.

    Science.gov (United States)

    Łuczyński, Jacek; Frąckowiak, Renata; Włoch, Aleksandra; Kleszczyńska, Halina; Witek, Stanisław

    2013-03-01

    Cationic gemini surfactants are an important class of surface-active compounds that exhibit much higher surface activity than their monomeric counterparts. This type of compound architecture lends itself to the compound being easily adsorbed at interfaces and interacting with the cellular membranes of microorganisms. Conventional cationic surfactants have high chemical stability but poor chemical and biological degradability. One of the main approaches to the design of readily biodegradable and environmentally friendly surfactants involves inserting a bond with limited stability into the surfactant molecule to give a cleavable surfactant. The best-known example of such a compound is the family of ester quats, which are cationic surfactants with a labile ester bond inserted into the molecule. As part of this study, a series of gemini ester quat surfactants were synthesized and assayed for their biological activity. Their hemolytic activity and changes in the fluidity and packing order of the lipid polar heads were used as the measures of their biological activity. A clear correlation between the hemolytic activity of the tested compounds and their alkyl chain length was established. It was found that the compounds with a long hydrocarbon chain showed higher activity. Moreover, the compounds with greater spacing between their alkyl chains were more active. This proves that they incorporate more easily into the lipid bilayer of the erythrocyte membrane and affect its properties to a greater extent. A better understanding of the process of cell lysis by surfactants and of their biological activity may assist in developing surfactants with enhanced selectivity and in widening their range of application.

  6. Mechanistic investigation into cross-linking reactions in low rank coal: formation and pyrolysis of aryl esters

    Energy Technology Data Exchange (ETDEWEB)

    Britt, P.F.; Buchanan, A.C. III; Kiddern, M.K.; Skeen, J.D. [Oak Ridge National Lab. Oak Ridge, TN (USA). Chemical Sciences Division

    2003-07-01

    In this study, the sealed tube pyrolysis of mixtures of m-phenylphenol and benzoic acid have been investigated at 400{sup o}C to determine if cross-linking reactions can occur, and to determine the low temperature pyrolysis pathways of aryl esters, which are not known. Initial studies show that condensation reactions occur between carboxylic acids and phenols to form aryl esters at temperatures as low as 200{sup o}C. With a 3:1 ratio of m-phenylphenol to benzoic acid, yields of m-phenylphenyl benzoate were as high as 50% at 400{sup o}C. At short reaction times, the dominant products were the aryl ester and benzene, formed by the acid catalyzed decarboxylation of benzoic acid, but at longer times, other arylated products grew in indicating that radical reactions were occurring. These products appear to arise from the induced decomposition of benzoic anhydride to form phenyl radicals. The thermal stability of aryl esters was investigated through the pyrolysis of phenyl benzoate at 400{sup o}C. As predicted, the aryl ester appeared to be thermally stable but hydrolytically unstable. In general, formation of aryl esters could act as a low temperature cross-link in low rank coals. 19 refs., 3 figs., 1 tab.

  7. Regiospecific synthesis of new fatty N-acyl trihalomethylated pyrazoline derivatives from fatty acid methyl esters (FAMEs)

    Energy Technology Data Exchange (ETDEWEB)

    Beck, Paulo; Santos, Juliane M. dos; D' Oca, Marcelo G. M.; Piovesan, Luciana A., E-mail: lpiovesan@gmail.com [Universidade Federal do Rio Grande (UFRS), RS (Brazil). Escola de Quimica e Alimentos; Kuhn, Bruna L.; Moreira, Dayse N.; Flores, Alex F.C.; Martins, Marcos A.P. [Universidade Federal de Santa Maria (UFSM), RS (Brazil). Dept. de Quimica

    2012-11-15

    A series of new fatty N-acyl trihalomethylated pyrazoline derivatives from fatty acid methyl esters was synthesized by the cyclo condensation of respective fatty hydrazides with 4-alkoxy- 1,1,1-trial omethyl-3-alquen-2-ones. Efficient and regiospecific cyclizations catalyzed by BF{sub 3}-MeOH gave the desired products in good to excellent yields and at high purity. (author)

  8. Ester Tuiksoo. Proua Suhkru kibedad päevad / Ester Tuiksoo ; interv. Piret Tali

    Index Scriptorium Estoniae

    Tuiksoo, Ester, 1965-

    2005-01-01

    Põllumajandusminister Ester Tuiksoo, kellel peagi täitub ministri ametis aasta Euroopa Liidu suhkrutrahvist, maaettevõtlusest, põllumajandusest, Euroopa Liidu toetustest, ministri elu- ja teenistuskäigust. Lisa: Ester Tuiksoo

  9. Thermal Decomposition of Methyl Esters in Biodiesel Fuel: Kinetics, Mechanisms and Products

    Science.gov (United States)

    Chai, Ming

    Biodiesel continues to enjoy increasing popularity. However, recent studies on carbonyl compounds emissions from biodiesel fuel are inconclusive. Emissions of carbonyl compounds from petroleum diesel fuels were compared to emissions from pure biodiesel fuels and petroleum-biodiesel blends used in a non-road diesel generator. The concentration of total carbonyl compounds was the highest when the engine was idling. The carbonyl emissions, as well as ozone formation potential, from biodiesel fuel blends were higher than those emitted from petroleum diesel fuel. The sulfur content of diesel fuel and the source of biodiesel fuel were not found to have a significant impact on emissions of carbonyl compounds. Mechanism parameters of the thermal decomposition of biodiesel-range methyl esters were obtained from the results of thermal gravimetric analysis (TGA). The overall reaction orders are between 0.49 and 0.71 and the energies of activation are between 59.9 and 101.3 kJ/mole. Methyl esters in air have lower activation energies than those in nitrogen. Methyl linoleate has the lowest activation energy, followed by methyl oleate, and methyl stearate. The pyrolysis and oxidation of the three methyl esters were investigated using a semi-isothermal tubular flow reactor. The profiles of major products versus reaction temperature are presented. In the pyrolysis of methyl stearate, the primary reaction pathway is the decarboxylic reaction at the methyl ester functional group. Methyl oleate's products indicate more reactions on its carbon-carbon double bond. Methyl linoleate shows highest reactivity among the three methyl esters, and 87 products were detected. The oxidation of three methyl esters resulted in more products in all compound classes, and 55, 114, and 127 products were detected, respectively. The oxidation of methyl esters includes decarboxylation on ester group. The methyl ester's carbon chain could be oxidized as a hydrocarbon compound and form oxidized esters and

  10. Acid-catalyzed production of biodiesel from waste frying oil

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, S.; Dube, M.A.; McLean, D.D. [Department of Chemical Engineering, University of Ottawa, Ottawa, ON (Canada); Kates, M. [Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON (Canada)

    2006-03-15

    The reaction kinetics of acid-catalyzed transesterification of waste frying oil in excess methanol to form fatty acid methyl esters (FAME), for possible use as biodiesel, was studied. Rate of mixing, feed composition (molar ratio oil:methanol:acid) and temperature were independent variables. There was no significant difference in the yield of FAME when the rate of mixing was in the turbulent range 100 to 600rpm. The oil:methanol:acid molar ratios and the temperature were the most significant factors affecting the yield of FAME. At 70{sup o}C with oil:methanol:acid molar ratios of 1:245:3.8, and at 80{sup o}C with oil:methanol:acid molar ratios in the range 1:74:1.9-1:245:3.8, the transesterification was essentially a pseudo-first-order reaction as a result of the large excess of methanol which drove the reaction to completion (99+/-1% at 4h). In the presence of the large excess of methanol, free fatty acids present in the waste oil were very rapidly converted to methyl esters in the first few minutes under the above conditions. Little or no monoglycerides were detected during the course of the reaction, and diglycerides present in the initial waste oil were rapidly converted to FAME. (author)

  11. 21 CFR 172.859 - Sucrose fatty acid esters.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Sucrose fatty acid esters. 172.859 Section 172.859... CONSUMPTION Multipurpose Additives § 172.859 Sucrose fatty acid esters. Sucrose fatty acid esters identified...) Sucrose fatty acid esters are the mono-, di-, and tri-esters of sucrose with fatty acids and are...

  12. Synthesis and emulsifying properties of carbohydrate fatty acid esters produced from Agave tequilana fructans by enzymatic acylation.

    Science.gov (United States)

    Casas-Godoy, Leticia; Arrizon, Javier; Arrieta-Baez, Daniel; Plou, Francisco J; Sandoval, Georgina

    2016-08-01

    Carbohydrate fatty acid esters are non-ionic surfactants with a broad spectrum of applications. These molecules are generally synthesized using short carbohydrates or linear fructans; however in this research carbohydrate fatty acid esters were produced for the first time with branched fructans from Agave tequilana. Using immobilized lipases we successfully acylated A. tequilana fructans with vinyl laurate, obtaining products with different degrees of polymerization (DP). Lipozyme 435 was the most efficient lipase to catalyze the transesterification reaction. HPLC and ESI-MS analysis proved the presence of a mixture of acylated products as a result of the chemical complexity of fructans in the A. tequilana. The ESI-MS spectra showed a molecular mass shift between 183 and 366g/mol for fructooligosaccharides with a DP lower than 6, which indicated the presence of Agave fructans that had been mono- and diacylated with lauric acid. The carbohydrate fatty acid esters (CFAE) obtained showed good emulsifying properties in W/O emulsions.

  13. Method of making a cyanate ester foam

    Science.gov (United States)

    Celina, Mathias C.; Giron, Nicholas Henry

    2014-08-05

    A cyanate ester resin mixture with at least one cyanate ester resin, an isocyanate foaming resin, other co-curatives such as polyol or epoxy compounds, a surfactant, and a catalyst/water can react to form a foaming resin that can be cured at a temperature greater than 50.degree. C. to form a cyanate ester foam. The cyanate ester foam can be heated to a temperature greater than 400.degree. C. in a non-oxidative atmosphere to provide a carbonaceous char foam.

  14. Synthesis and Structural Characterization of 1- and 2-Substituted Indazoles: Ester and Carboxylic Acid Derivatives

    Directory of Open Access Journals (Sweden)

    Isabel Bento

    2006-11-01

    Full Text Available A series of indazoles substituted at the N-1 and N-2 positions with ester-containing side chains -(CH2nCO2R of different lengths (n = 0-6, 9, 10 are described.Nucleophilic substitution reactions on halo esters (X(CH2nCO2R by 1H-indazole inalkaline solution lead to mixtures of N-1 and N-2 isomers, in which the N-1 isomerpredominates. Basic hydrolysis of the ester derivatives allowed the synthesis of thecorresponding indazole carboxylic acids. All compounds were fully characterised bymultinuclear NMR and IR spectroscopies, MS spectrometry and elemental analysis; theNMR spectroscopic data were used for structural assignment of the N-1 and N-2 isomers.The molecular structure of indazol-2-yl-acetic acid (5b was determined by X-raydiffraction, which shows a supramolecular architecture involving O2-H...N1intermolecular hydrogen bonds.

  15. Carotenoids in a Corynebacterineae, Gordonia terrae AIST-1: carotenoid glucosyl mycoloyl esters.

    Science.gov (United States)

    Takaichi, Shinichi; Maoka, Takashi; Akimoto, Naoshige; Carmona, Marvelisa L; Yamaoka, Yukiho

    2008-10-01

    We isolated a strain of Corynebacterineae from surface seawater from the Inland Sea of Japan. This strain, AIST-1, was determined to be a strain of Gordonia terrae based on its 16S rRNA gene sequence. The colony was red-colored, and the pigments were identified to be carotenoid derivatives. The structures of two major carotenoids were (2'S)-deoxymyxol 1'-glucoside, a dihydroxyl derivative of gamma-carotene with 12 conjugated double bonds, and (2'S)-4-ketodeoxymyxol 1'-glucoside. Their glucosyl acyl esters and mycoloyl esters were also identified. While these carotenoid moieties have been found in only a few other bacteria, the carotenoid mycoloyl esters are novel carotenoid derivatives. The type strain of G. terrae NBRC 10016T also contained the same carotenoids, but the composition of the two carotenoid glucosides was low and the total carotenoid content was less than one tenth of that of strain AIST-1.

  16. Synthesis and characterization of ester and amide derivatives of titanium(IV) carboxymethylphosphonate

    Science.gov (United States)

    Melánová, Klára; Beneš, Ludvík; Trchová, Miroslava; Svoboda, Jan; Zima, Vítězslav

    2013-06-01

    A set of layered ester and amide derivatives of titanium(IV) carboxymethylphosphonate was prepared by solvothermal treatment of amorphous titanium(IV) carboxymethylphosphonate with corresponding 1-alkanols, 1,ω-alkanediols, 1-aminoalkanes, 1,ω-diaminoalkanes and 1,ω-amino alcohols and characterized by powder X-ray diffraction, IR spectroscopy and thermogravimetric analysis. Whereas alkyl chains with one functional group form bilayers tilted to the layers, 1,ω-diaminoalkanes and most of 1,ω-alkanediols form bridges connecting the adjacent layers. In the case of amino alcohols, the alkyl chains form bilayer and either hydroxyl or amino group is used for bonding. This simple method for the synthesis of ester and amide derivatives does not require preparation of acid chloride derivative as a precursor or pre-intercalation with alkylamines and can be used also for the preparation of ester and amide derivatives of titanium carboxyethylphosphonate and zirconium carboxymethylphosphonate.

  17. Reactivity and Chemoselectivity of Allenes in Rh(I)-Catalyzed Intermolecular (5 + 2) Cycloadditions with Vinylcyclopropanes: Allene-Mediated Rhodacycle Formation Can Poison Rh(I)-Catalyzed Cycloadditions

    Science.gov (United States)

    2015-01-01

    Allenes are important 2π building blocks in organic synthesis and engage as 2-carbon components in many metal-catalyzed reactions. Wender and co-workers discovered that methyl substituents on the terminal allene double bond counterintuitively change the reactivities of allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with vinylcyclopropanes (VCPs). More sterically encumbered allenes afford higher cycloadduct yields, and such effects are also observed in other Rh(I)-catalyzed intermolecular cycloadditions. Through density functional theory calculations (B3LYP and M06) and experiment, we explored this enigmatic reactivity and selectivity of allenes in [Rh(CO)2Cl]2-catalyzed intermolecular (5 + 2) cycloadditions with VCPs. The apparent low reactivity of terminally unsubstituted allenes is associated with a competing allene dimerization that irreversibly sequesters rhodium. With terminally substituted allenes, steric repulsion between the terminal substituents significantly increases the barrier of allene dimerization while the barrier of the (5 + 2) cycloaddition is not affected, and thus the cycloaddition prevails. Computation has also revealed the origin of chemoselectivity in (5 + 2) cycloadditions with allene-ynes. Although simple allene and acetylene have similar reaction barriers, intermolecular (5 + 2) cycloadditions of allene-ynes occur exclusively at the terminal allene double bond. The terminal double bond is more reactive due to the enhanced d−π* backdonation. At the same time, insertion of the internal double bond of an allene-yne has a higher barrier as it would break π conjugation. Substituted alkynes are more difficult to insert compared with acetylene, because of the steric repulsion from the additional substituents. This leads to the greater reactivity of the allene double bond relative to the alkynyl group in allene-ynes. PMID:25379606

  18. Computational Studies on Cinchona Alkaloid-Catalyzed Asymmetric Organic Reactions.

    Science.gov (United States)

    Tanriver, Gamze; Dedeoglu, Burcu; Catak, Saron; Aviyente, Viktorya

    2016-06-21

    Remarkable progress in the area of asymmetric organocatalysis has been achieved in the last decades. Cinchona alkaloids and their derivatives have emerged as powerful organocatalysts owing to their reactivities leading to high enantioselectivities. The widespread usage of cinchona alkaloids has been attributed to their nontoxicity, ease of use, stability, cost effectiveness, recyclability, and practical utilization in industry. The presence of tunable functional groups enables cinchona alkaloids to catalyze a broad range of reactions. Excellent experimental studies have extensively contributed to this field, and highly selective reactions were catalyzed by cinchona alkaloids and their derivatives. Computational modeling has helped elucidate the mechanistic aspects of cinchona alkaloid catalyzed reactions as well as the origins of the selectivity they induce. These studies have complemented experimental work for the design of more efficient catalysts. This Account presents recent computational studies on cinchona alkaloid catalyzed organic reactions and the theoretical rationalizations behind their effectiveness and ability to induce selectivity. Valuable efforts to investigate the mechanisms of reactions catalyzed by cinchona alkaloids and the key aspects of the catalytic activity of cinchona alkaloids in reactions ranging from pharmaceutical to industrial applications are summarized. Quantum mechanics, particularly density functional theory (DFT), and molecular mechanics, including ONIOM, were used to rationalize experimental findings by providing mechanistic insights into reaction mechanisms. B3LYP with modest basis sets has been used in most of the studies; nonetheless, the energetics have been corrected with higher basis sets as well as functionals parametrized to include dispersion M05-2X, M06-2X, and M06-L and functionals with dispersion corrections. Since cinchona alkaloids catalyze reactions by forming complexes with substrates via hydrogen bonds and long

  19. Fumaric acid esters in dermatology

    Directory of Open Access Journals (Sweden)

    Uwe Wollina

    2011-01-01

    Full Text Available Fumaric acid esters (FAE are substances of interest in dermatology. FAE exert various activities on cutaneous cells and cytokine networks. So far only a mixture of dimethylfumarate (DMF and three salts of monoethylfumarate (MEF have gained approval for the oral treatment of moderate-to-severe plaque-type psoriasis in Germany. DMF seems to be the major active component. There is evidence that FAE are not only effective and safe in psoriasis but granulomatous non-infectious diseases like granuloma annulare, necrobiosis lipoidica and sarcoidosis. In vitro and animal studies suggest some activity in malignant melanoma as well.

  20. Steroidal esters from Ferula sinkiangensis.

    Science.gov (United States)

    Li, Guangzhi; Li, Xiaojin; Cao, Li; Shen, Liangang; Zhu, Jun; Zhang, Jing; Wang, Junchi; Zhang, Lijing; Si, Jianyong

    2014-09-01

    Two new steroidal esters with an unusual framework, Sinkiangenorin A and B, a new organic acid glycoside, Sinkiangenorin C, and four known lignin compounds were isolated from the seeds of Ferula sinkiangensis. The structures of these compounds were established by spectroscopic analysis and single-crystal X-ray diffraction. All of the isolated compounds were tested against Hela, K562 and AGS human cancer cell lines. Sinkiangenorin C showed cytotoxic activity against AGS cells with an IC50 of 36.9 μM.

  1. Synthesis and characterization of 5-(4-hydroxy-3-methoxy-phenyl-3,7-dimethyl-5H-thiazolo[3,2-a]pyrimidine-2,6-dicarboxylic acid 2-ethyl ester 6-methyl ester and its 6-ethyl ester 5-naphthalene derivative

    Directory of Open Access Journals (Sweden)

    H. Nagarajaiah

    2015-11-01

    Full Text Available The compounds 5-(4-hydroxy-3-methoxy-phenyl-3,7-dimethyl-5H-thiazolo[3,2-a]pyrimidine-2,6-dicarboxylic acid 2-ethyl ester 6-methyl ester (2a and 3,7-dimethyl-5-naphthalen-1-yl-5H-thiazolo[3,2-a]pyrimidine-2,6-dicarboxylic acid diethyl ester (2b were synthesized by the base catalyzed cyclocondensation of 3,4-dihydropyrimidine-2-thione with ethylacetoacetate. IR, 1H NMR, 13C NMR spectra and elemental analysis were used to characterize these compounds. The structures were determined by single crystal X-ray diffraction. The crystal structure is stabilized by intermolecular O–H…N, C–H…O, C–H…π and π…π weak interactions.

  2. Two-Step biocatalytic conversion of an ester to an aldehyde in reverse micelles.

    Science.gov (United States)

    Yang, F; Russell, A J

    1994-02-01

    Lipases from Candida cyclindracea (L-1754) and wheat germ (L-3001) have been used to hydrolyze esters to their corresponding alcohols and acids in reverse micelles. Alcohol dehydrogenase from baker's yeast (YADH) was subsequently used to reduce the alcohol products to aldehydes. Cofactor recycling in the redox reaction was achieved using a sacrificial cosubstrate, as described previously. Four surfactants (sodium dioctylsulfosuccinate, Nonidet P-40 with Triton X-35, polyoxyethylene, 10-cetyl-ether, polyoxyethylene sorbitan trioleate) were employed to determine the effect of amphiphile on ester hydrolysis and redox reaction rates separately. The effect of type of organic solvent, W(0) [(water]/[surfactant)], and substrate concentration on separte enzyme activity were also investigated. A brief investigation of a single phase, two-step reaction catalyzed by the combination of lipase and YADH in reverse micelles is also reported. The activities of the enzymes are significantly different when used together instead of independently. (c) 1994 John Wiley & Sons, Inc.

  3. Establishing very long-chain fatty alcohol and wax ester biosynthesis in Saccharomyces cerevisiae

    DEFF Research Database (Denmark)

    Wenning, Leonie; Yu, Tao; David, Florian

    2017-01-01

    for producing very long-chain fatty alcohols (VLCFOHs) up to a chain length of C22 by heterologous expression of a FAR derived from Apis mellifera (AmFAR1) or Marinobacter aquaeolei VT8 (Maqu_2220) in S. cerevisiae and achieved maximum yields of 3.22±0.36mg/g cell dry weight (CDW) and 7.84±3.09mg/g CDW......Wax esters (WEs) are neutral lipids and can be used for a broad range of commercial applications, including personal care products, lubricants, or coatings. They are synthesized by enzymatic reactions catalyzed by a fatty acyl reductase (FAR) and a wax ester synthase (WS). At present, commercially...

  4. ENZYMATIC PRODUCTION OF ETHYL OLEATE ESTER USING A LIPASE FROM CANDIDA ANTARCTICA B

    Directory of Open Access Journals (Sweden)

    N. Sampaio Neta

    2012-05-01

    Full Text Available Lipases are biocatalysts of great importance in different areas, being able to catalyze reactions in aqueous or organic media. Furthermore, these enzymes are capable of using several substrates being stable in a wide range of pH and temperatures. Lipases promote the esterification between fatty acids and ethanol producing oleate esters. The aim of this work is to produce ethyl oleate ester by enzymatic esterification of oleic acid with ethanol. A lipase from Candida antarctica type B was used at a temperature of 55 °C. The reaction was conducted using oleic acid, sodium sulfate anhydrous, lipase and ethanol, with a ratio of oleic acid (0.03 mol or 10 ml, lipase (0.1 mol or 0.01 g, sodium sulfate anhydrous (5 g and ethanol 99 % (100 ml. Several reaction times were studied, namely 48, 72, 96 and 120 hours. Nuclear Magnetic Resonance (1H and 13C and Infrared spectra confirmed the production of ethyl oleate ester for the studied conditions. The highest ethyl oleate production yield was obtained for 96 hours reaction time. Ethyl oleate esters have been reported to possess interesting applications in several industrial fields, such as food, aromatics, cosmetics, detergents, flavors and pharmaceuticals.

  5. Ionic liquids as novel solvents for the synthesis of sugar fatty acid ester.

    Science.gov (United States)

    Mai, Ngoc Lan; Ahn, Kihun; Bae, Sang Woo; Shin, Dong Woo; Morya, Vivek Kumar; Koo, Yoon-Mo

    2014-12-01

    Sugar fatty acid esters are bio-surfactants known for their non-toxic, non-ionic, and high biodegradability . With great emulsifying and conditioning effects, sugar fatty acids are widely used in the food, pharmaceutical, and cosmetic industries. Biosynthesis of sugar fatty acid esters has attracted growing attention in recent decades. In this study, the enzymatic synthesis of sugar fatty acid esters in ionic liquids was developed, optimized, and scaled up. Reaction parameters affecting the conversion yield of lipase-catalyzed synthesis of glucose laurate from glucose and vinyl laurate (i.e. temperature, vinyl laurate/glucose molar ratio, and enzyme loads) were optimized by response surface methodology (RSM). In addition, production was scaled up to 2.5 L, and recycling of enzyme and ionic liquids was investigated. The results showed that under optimal reaction conditions (66.86 °C, vinyl laurate/glucose molar ratio of 7.63, enzyme load of 73.33 g/L), an experimental conversion yield of 96.4% was obtained which is close to the optimal value predicted by RSM (97.16%). A similar conversion yield was maintained when the reaction was carried out at 2.5 L. Moreover, the enzymes and ionic liquids could be recycled and reused effectively for up to 10 cycles. The results indicate the feasibility of ionic liquids as novel solvents for the biosynthesis of sugar fatty acid esters.

  6. Regulation of ferulate-5-hydroxylase expression in Arabidopsis in the context of sinapate ester biosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Ruegger, M.; Meyer, K.; Cusumano, J.C.; Chapple, C. [Purdue Univ., West Lafayette, IN (United States). Dept. of Biochemistry

    1999-01-01

    Sinapic acid is an intermediate in syringyl lignin biosynthesis in angiosperms, and in some taxa serves as a precursor for soluble secondary metabolites. The biosynthesis and accumulation of the sinapate esters sinapoylglucose, sinapolymalate, and sinapolycholine are developmentally regulated in Arabidopsis and other members of the Brassicaceae. The FAH1 locus of Arabidopsis encodes the enzyme ferulate-5-hydroxylase (F5H), which catalyzes the rate-limiting step in syringyl lignin biosynthesis and is required for the production of sinapate esters. Here the authors show that F5H expression parallels sinapate ester accumulation in developing siliques and seedlings, but is not rate limiting for their biosynthesis. RNA gel-blot analysis indicated that the tissue-specific and developmentally regulated expression of F5H mRNA is distinct from that of other phenylpropanoid genes. Efforts to identify constructs capable of complementing the sinapate ester-deficient phenotype of fah1 mutants demonstrated that F5H expression in leaves is dependent on sequences 3{prime} of the F5H coding region. In contrast, the positive regulatory function of the downstream region is not required for F5H transcript or sinapolycholine accumulation in embryos.

  7. Development of Enantiospecific Coupling of Secondary and Tertiary Boronic Esters with Aromatic Compounds

    Science.gov (United States)

    2016-01-01

    The stereospecific cross-coupling of secondary boronic esters with sp2 electrophiles (Suzuki–Miyaura reaction) is a long-standing problem in synthesis, but progress has been achieved in specific cases using palladium catalysis. However, related couplings with tertiary boronic esters are not currently achievable. To address this general problem, we have focused on an alternative method exploiting the reactivity of a boronate complex formed between an aryl lithium and a boronic ester. We reasoned that subsequent addition of an oxidant or an electrophile would remove an electron from the aromatic ring or react in a Friedel–Crafts-type manner, respectively, generating a cationic species, which would trigger 1,2-migration of the boron substituent, creating the new C–C bond. Elimination (preceded by further oxidation in the former case) would result in rearomatization giving the coupled product stereospecifically. Initial work was examined with 2-furyllithium. Although the oxidants tested were unsuccessful, electrophiles, particularly NBS, enabled the coupling reaction to occur in good yield with a broad range of secondary and tertiary boronic esters, bearing different steric demands and functional groups (esters, azides, nitriles, alcohols, and ethers). The reaction also worked well with other electron-rich heteroaromatics and 6-membered ring aromatics provided they had donor groups in the meta position. Conditions were also found under which the B(pin)- moiety could be retained in the product, ortho to the boron substituent. This protocol, which created a new C(sp2)–C(sp3) and an adjacent C–B bond, was again applicable to a range of secondary and tertiary boronic esters. In all cases, the coupling reaction occurred with complete stereospecificity. Computational studies verified the competing processes involved and were in close agreement with the experimental observations. PMID:27384259

  8. Development of Enantiospecific Coupling of Secondary and Tertiary Boronic Esters with Aromatic Compounds.

    Science.gov (United States)

    Odachowski, Marcin; Bonet, Amadeu; Essafi, Stephanie; Conti-Ramsden, Philip; Harvey, Jeremy N; Leonori, Daniele; Aggarwal, Varinder K

    2016-08-03

    The stereospecific cross-coupling of secondary boronic esters with sp(2) electrophiles (Suzuki-Miyaura reaction) is a long-standing problem in synthesis, but progress has been achieved in specific cases using palladium catalysis. However, related couplings with tertiary boronic esters are not currently achievable. To address this general problem, we have focused on an alternative method exploiting the reactivity of a boronate complex formed between an aryl lithium and a boronic ester. We reasoned that subsequent addition of an oxidant or an electrophile would remove an electron from the aromatic ring or react in a Friedel-Crafts-type manner, respectively, generating a cationic species, which would trigger 1,2-migration of the boron substituent, creating the new C-C bond. Elimination (preceded by further oxidation in the former case) would result in rearomatization giving the coupled product stereospecifically. Initial work was examined with 2-furyllithium. Although the oxidants tested were unsuccessful, electrophiles, particularly NBS, enabled the coupling reaction to occur in good yield with a broad range of secondary and tertiary boronic esters, bearing different steric demands and functional groups (esters, azides, nitriles, alcohols, and ethers). The reaction also worked well with other electron-rich heteroaromatics and 6-membered ring aromatics provided they had donor groups in the meta position. Conditions were also found under which the B(pin)- moiety could be retained in the product, ortho to the boron substituent. This protocol, which created a new C(sp(2))-C(sp(3)) and an adjacent C-B bond, was again applicable to a range of secondary and tertiary boronic esters. In all cases, the coupling reaction occurred with complete stereospecificity. Computational studies verified the competing processes involved and were in close agreement with the experimental observations.

  9. Physio-pathological roles of transglutaminase-catalyzed reactions

    Institute of Scientific and Technical Information of China (English)

    Mariangela; Ricotta; Maura; Iannuzzi; Giulia; De; Vivo; Vittorio; Gentile

    2010-01-01

    Transglutaminases(TGs) are a large family of related and ubiquitous enzymes that catalyze post-translational modifications of proteins.The main activity of these enzymes is the cross-linking of a glutaminyl residue of a protein/peptide substrate to a lysyl residue of a protein/peptide co-substrate.In addition to lysyl residues,other second nucleophilic co-substrates may include monoamines or polyamines(to form mono-or bi-substituted/crosslinked adducts) or-OH groups(to form ester linkages) .In the absence of co-substrates,the nucleophile may be water,resulting in the net deamidation of the glutaminyl residue.The TG enzymes are also capable of catalyzing other reactions important for cell viability.The distribution and the physiological roles of TG enzymes have been widely studied in numerous cell types and tissues and their roles in several diseases have begun to be identified."Tissue" TG(TG2) ,a member of the TG family of enzymes,has definitely been shown to be involved in the molecular mechanisms responsible for a very widespread human pathology:i.e.celiac disease(CD) .TG activity has alsobeen hypothesized to be directly involved in the pathogenetic mechanisms responsible for several other human diseases,including neurodegenerative diseases,which are often associated with CD.Neurodegenerative diseases,such as Alzheimer’s disease,Parkinson’s disease,supranuclear palsy,Huntington’s disease and other recently identified polyglutamine diseases,are characterized,in part,by aberrant cerebral TG activity and by increased cross-linked proteins in affected brains.In this review,we discuss the physio-pathological role of TG-catalyzed reactions,with particular interest in the molecular mechanisms that could involve these enzymes in the physio-pathological processes responsible for human neurodegenerative diseases.

  10. The Benzyl Ester Group of Amino Acid Monomers Enhances Substrate Affinity and Broadens the Substrate Specificity of the Enzyme Catalyst in Chemoenzymatic Copolymerization.

    Science.gov (United States)

    Ageitos, Jose Manuel; Yazawa, Kenjiro; Tateishi, Ayaka; Tsuchiya, Kousuke; Numata, Keiji

    2016-01-11

    The chemoenzymatic polymerization of amino acid monomers by proteases involves a two-step reaction: the formation of a covalent acyl-intermediate complex between the protease and the carboxyl ester group of the monomer and the subsequent deacylation of the complex by aminolysis to form a peptide bond. Although the initiation with the ester group of the monomer is an important step, the influence of the ester group on the polymerization has not been studied in detail. Herein, we studied the effect of the ester groups (methyl, ethyl, benzyl, and tert-butyl esters) of alanine and glycine on the synthesis of peptides using papain as the catalyst. Alanine and glycine were selected as monomers because of their substantially different affinities toward papain. The efficiency of the polymerization of alanine and glycine benzyl esters was much greater than that of the other esters. The benzyl ester group therefore allowed papain to equally polymerize alanine and glycine, even though the affinity of alanine toward papain is substantially higher. The characterization of the copolymers of alanine and glycine in terms of the secondary structure and thermal properties revealed that the thermal stability of the peptides depends on the amino acid composition and resultant secondary structure. The current results indicate that the nature of the ester group drastically affects the polymerization efficiency and broadens the substrate specificity of the protease.

  11. Synthesis of insecticidal sucrose esters

    Institute of Scientific and Technical Information of China (English)

    Song Zi-juan; Li Shu-jun; Chen Xi; Liu Li-mei; Song Zhan-qian

    2006-01-01

    Some synthetic sucrose esters (SE) are a relatively new class of insecticidal compounds produced by reacting sugars with fatty acids, which are safe for the environment. Especially, sucrose esters composed of C6-C12 fatty acids have desirable insecticidal properties against many soft-bodied arthropod pests. In our study, sucrose octanoate which has the highest activity against a range of arthropod species was synthesized by a trans-esterification method and proved its insecticidal property. Under the condition of a homogeneous liquid, sucrose octanoate was prepared by reacting ethyl octanoate with sucrose at reduced pressure; the yield was 79.11%. Sucrose octanoate synthesized was identified and its property analyzed by IR, TLC and spectrophotometric analysis. It was shown that the ratio of monoester to polyester in sucrose octanoate was 1.48:1. The insecticidal activity of the synthetic sucrose octanoate was evaluated at a concentration of 4 and 8 mg·mL-1. The mortality of first-instar larvae ofLymantria dispar from its contact toxicity was 72.5% after 36 hours, the revision insect reduced rate of Aphis glycines reached above 80% at 4 and 8 mg·mL-1 after being treated for 5 days. Since the SE products are nontoxic to humans and higher animals, fully biodegradable and hydrolyzed to readily metabolizable sucrose and fatty acid, they are not harmful to crops and appear to be good insecticide candidates.

  12. Lactam hydrolysis catalyzed by mononuclear metallo-ß-bactamases

    DEFF Research Database (Denmark)

    Olsen, Lars; Antony, J; Ryde, U

    2003-01-01

    . For most studied systems, the tetrahedral structure is a stable intermediate. Moreover, the C-N bond in the lactam ring is intact in this intermediate, as well as in the following transition state-its cleavage is induced by proton transfer to the nitrogen atom in the lactam ring. However, for the model...... with Asp as a proton shuttle, attack of the zinc-bond hydroxide ion seems to be concerted with the proton transfer. We have also studied the effect of replacing one of the histidine ligands by an asparagine or glutamine residue, giving a zinc site representative of other subclasses of metallo......Two central steps in the hydrolysis of lactam antibiotics catalyzed by mononuclear metallo-beta-lactamases, formation of the tetrahedral intermediate and its breakdown by proton transfer, are studied for model systems using the density functional B3LYP method. Metallo-beta-lactamases have two metal...

  13. Cleavable ester linked magnetic nanoparticles for labeling of solvent exposed primary amine groups of peptides/proteins

    Science.gov (United States)

    In order to study the solvent exposed lysine residues of peptides/proteins, we previously reported disulfide linked N-hydrosuccinimide ester modified silica coated iron oxide magnetic nanoparticles (NHS-SS-SiO2@Fe3O4 MNPs). The presence of a disulfide bond in the linker limits the use of disulfide r...

  14. Sorption of organophosphate esters by carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Wei; Yan, Li [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China); Duan, Jinming [School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055 (China); Jing, Chuanyong, E-mail: cyjing@rcees.ac.cn [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085 (China)

    2014-05-01

    Graphical abstract: The interfacial interactions between the OPE molecules and CNTs. - Highlights: • Oxygen-containing groups on CNTs change the sorption property for OPEs. • Molecular configuration of OPEs has insignificant impact on their sorption. • Hydrophobic, π–π EDA and Brønsted acid–base interaction occurred between the CNTs and OPEs. - Abstract: Insights from the molecular-level mechanism of sorption of organophosphate esters (OPEs) on carbon nanotubes (CNTs) can further our understanding of the fate and transport of OPEs in the environment. The motivation for our study was to explore the sorption process of OPEs on multi-walled CNTs (MWCNTs), single-walled CNTs (SWCNTs) and their oxidized counterparts (O-MWCNTs and O-SWCNTs), and its molecular mechanism over a wide concentration range. The sorption isotherm results revealed that the hydrophobicity of OPEs dominated their affinities on a given CNT and the π–π electron donor–acceptor (EDA) interaction also played an important role in the sorption of aromatic OPEs. This π–π EDA interaction, verified with Raman and FT-IR spectroscopy, could restrict the radial vibration of SWCNTs and affect the deformation vibration γ(CH) bands of OPE molecules. The OPE surface coverage on CNTs, estimated using the nonlinear Dubinin–Ashtakhov model, indicated that the oxygen-containing functional groups on CNTs could interact with water molecules by H-bonding, resulting in a decrease in effective sorption sites. In addition, FTIR analysis also confirmed the occurrence of Brønsted acid–base interactions between OPEs and surface OH groups of SWCNTs. Our results should provide mechanistic insights into the sorption mechanism of OPE contaminants on CNTs.

  15. Esteróles en esponjas marinas

    Directory of Open Access Journals (Sweden)

    Carmenza Duque

    2009-07-01

    Full Text Available Esta revisión bibliográfica comprende la mayona del trabajo publicado hasta el momento sobre esteróles aislados de esponjas marinas. Estos esteróles comprenden compuestos desde Cig hasta C31 con estructuras convencionales y con estructuras novedosas (núcleo y/o cadena lateral no convencional.

  16. Expanding ester biosynthesis in Escherichia coli.

    Science.gov (United States)

    Rodriguez, Gabriel M; Tashiro, Yohei; Atsumi, Shota

    2014-04-01

    To expand the capabilities of whole-cell biocatalysis, we have engineered Escherichia coli to produce various esters. The alcohol O-acyltransferase (ATF) class of enzyme uses acyl-CoA units for ester formation. The release of free CoA upon esterification with an alcohol provides the free energy to facilitate ester formation. The diversity of CoA molecules found in nature in combination with various alcohol biosynthetic pathways allows for the biosynthesis of a multitude of esters. Small to medium volatile esters have extensive applications in the flavor, fragrance, cosmetic, solvent, paint and coating industries. The present work enables the production of these compounds by designing several ester pathways in E. coli. The engineered pathways generated acetate esters of ethyl, propyl, isobutyl, 2-methyl-1-butyl, 3-methyl-1-butyl and 2-phenylethyl alcohols. In particular, we achieved high-level production of isobutyl acetate from glucose (17.2 g l(-1)). This strategy was expanded to realize pathways for tetradecyl acetate and several isobutyrate esters.

  17. Competitive homolytic and heterolytic decomposition pathways of gas-phase negative ions generated from aminobenzoate esters.

    Science.gov (United States)

    Xia, Hanxue; Zhang, Yong; Pavlov, Julius; Jariwala, Freneil B; Attygalle, Athula B

    2016-03-01

    An alkyl-radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl-radical loss by a homolytic cleavage of the alkyl-oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge-mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope-labeled compounds confirmed that the alkene loss proceeds by a specific γ-hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2-phenylethyl 4-aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments.

  18. Synthesis and intrinsic blue fluorescence study of hyperbranched poly(ester-amide-ether)

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A series of hyperbranched poly(ester-amide-ether)s (H-PEAEs) were synthesized via the A2+CB3 approach by the self-transesterification of ethyl ester-amide-ethers end-capped with three hydroxyl groups and ethyl ester group at two terminals.The molecular structures were characterized with 1H NMR and FT-IR spectroscopy.The number average molecular weights were estimated by GPC analysis to possess bimodal wide distribution from 1.57 to 2.09.The strong inherent blue fluorescence was observed at 330 nm for excitation and 390 nm for emission.Moreover,the emission intensity and fluorescence quantum yield increased along with the incorporated ether chain length,as well as almost linearly with the H-PEAE concentration in an aqueous solution.For comparing the fluorescence performance,the linear poly(ester-amide-ether) (L-PEAE) and hyperbranched poly(ester-amide) (H-PEA) were synthesized.The results showed that the coexistence of ether bond and carboxyl group in the molecular chain was essential for generating the strong fluorescence.However,the compact backbone of H-PEAE would be propitious to the enhancement of fluorescence properties.

  19. Ethanolysis of rapeseed oil - distribution of ethyl esters, glycerides and glycerol between ester and glycerol phases.

    Science.gov (United States)

    Cernoch, Michal; Hájek, Martin; Skopal, Frantisek

    2010-04-01

    The distribution of ethyl esters, triglycerides, diglycerides, monoglycerides, and glycerol between the ester and glycerol phase was investigated after the ethanolysis of rapeseed oil at various reaction conditions. The determination of these substances in the ester and glycerol phases was carried out by the GC method. The amount of ethyl esters in the glycerol phase was unexpectedly high and therefore the possibility of the reduction of this amount was investigated. The distribution coefficients and the weight distributions of each investigated substance were calculated and compared mutually. The distribution coefficients between the ester and glycerol phase increase in this sequence: glycerol, monoglycerides, diglycerides, ethyl esters, and triglycerides. Soaps and monoglycerides in the reaction mixture cause a worse separation of ethyl esters from the reaction mixture. The existence of a non-separable reaction mixture was observed also, and its composition was determined.

  20. Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

    Science.gov (United States)

    Kasparyan, Elena; Richter, Michael; Dresen, Carola; Walter, Lydia S; Fuchs, Georg; Leeper, Finian J; Wacker, Tobias; Andrade, Susana L A; Kolter, Geraldine; Pohl, Martina; Müller, Michael

    2014-12-01

    The intermolecular asymmetric Stetter reaction is an almost unexplored transformation for biocatalysts. Previously reported thiamine diphosphate (ThDP)-dependent PigD from Serratia marcescens is the first enzyme identified to catalyze the Stetter reaction of α,β-unsaturated ketones (Michael acceptor substrates) and α-keto acids. PigD is involved in the biosynthesis of the potent cytotoxic agent prodigiosin. Here, we describe the investigation of two new ThDP-dependent enzymes, SeAAS from Saccharopolyspora erythraea and HapD from Hahella chejuensis. Both show a high degree of homology to the amino acid sequence of PigD (39 and 51 %, respectively). The new enzymes were heterologously overproduced in Escherichia coli, and the yield of soluble protein was enhanced by co-expression of the chaperone genes groEL/ES. SeAAS and HapD catalyze intermolecular Stetter reactions in vitro with high enantioselectivity. The enzymes possess a characteristic substrate range with respect to Michael acceptor substrates. This provides support for a new type of ThDP-dependent enzymatic activity, which is abundant in various species and not restricted to prodigiosin biosynthesis in different strains. Moreover, PigD, SeAAS, and HapD are also able to catalyze asymmetric carbon-carbon bond formation reactions of aldehydes and α-keto acids, resulting in 2-hydroxy ketones.

  1. Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

    Directory of Open Access Journals (Sweden)

    Masato Ohashi

    2014-09-01

    Full Text Available In this review, we summarize our recent development of palladium(0-catalyzed cross-coupling reactions of perfluoro organic compounds with organometallic reagents. The oxidative addition of a C–F bond of tetrafluoroethylene (TFE to palladium(0 was promoted by the addition of lithium iodide, affording a trifluorovinyl palladium(II iodide. Based on this finding, the first palladium-catalyzed cross-coupling reaction of TFE with diarylzinc was developed in the presence of lithium iodide, affording α,β,β-trifluorostyrene derivatives in excellent yield. This coupling reaction was expanded to the novel Pd(0/PR3-catalyzed cross-coupling reaction of TFE with arylboronates. In this reaction, the trifluorovinyl palladium(II fluoride was a key reaction intermediate that required neither an extraneous base to enhance the reactivity of organoboronates nor a Lewis acid additive to promote the oxidative addition of a C–F bond. In addition, our strategy utilizing the synergetic effect of Pd(0 and lithium iodide could be applied to the C–F bond cleavage of unreactive hexafluorobenzene (C6F6, leading to the first Pd(0-catalyzed cross-coupling reaction of C6F6 with diarylzinc compounds.

  2. Anticholinesterase activity of fluorochloronitroacetic acid esters

    Energy Technology Data Exchange (ETDEWEB)

    Ivanov, Yu.Ya.; Brel, V.K. Martynov, I.V.

    1984-11-01

    Results are presented from pharmacologic and biochemical experiments leading to the conclusion that fluorochloronitroacetic acid esters have anticholinesterase activity. Since the esters caused muscular weakness in mice, experiments were performed on isolated tissue preparation. The biochemical experiments consisted of finding the biomolecular constants of irreversible inhibition of acetylcholinesterase by the esters, using acetylcholinesterase from human erythrocytes, as well as horse serum cholinesterase. The ethyl and n-propyl esters of halogen nitroacetic acid were used in all experiments. It was found that the propyl ester caused an increase in the force of individual contractions in the isolated muscle specimens, plus an inability of the muscle to retain tetanus. The substances were determined to have an anticholinesterase effect. The mechanism of cholinesterase inhibition is not yet known. It is probable that the substances acylate the serine hydroxyl of the esterase center of the cholinestersase. 7 references, 1 figure.

  3. Process Technology for Immobilized LipaseProcess Technology for Immobilized Lipase-catalyzed

    DEFF Research Database (Denmark)

    Xu, Yuan

    Biocatalysis has attracted significant attention recently, mainly due to its high selectivity and potential benefits for sustainability. Applications can be found in biorefineries, turning biomass into energy and chemicals, and also for products in the food and pharmaceutical industries. However......, most applications remain in the production of high-value fine chemicals, primarily because of the expense of introducing new technology. In particular lipasecatalyzed synthesis has already achieved efficient operations for high-value products and more interesting now is to establish opportunities...... for the production of biodiesel. The two processes are focused on the conversion of the two main components of vegetable oil materials, glyceride esters and free fatty acids respectively, into fatty acid alkyl esters. Although biodiesel is conventionally prepared via chemical-catalyzed transesterification...

  4. Synthesis and enzymatic hydrolysis of esters, constituting simple models of soft drugs

    OpenAIRE

    Graffner-Nordberg, Malin; Sjödin, K; Tunek, A; Hallberg, A

    1998-01-01

    One way to minimise systemic side effects of drugs is to design molecules, soft drugs, in such a way that they are metabolically inactivated rapidly after having acted on their pharmacological target. Hydrolases (esterases, peptidases, lipases, glycosidases, etc.) are enzymes well suited to use for drug inactivation since they are ubiquitously distributed. Insertion of ester bonds susceptible to enzymatic cleavage may represent one approach to make the action of a drug more restricted to the ...

  5. Fundamental reaction mechanism and free energy profile for (-)-cocaine hydrolysis catalyzed by cocaine esterase.

    Science.gov (United States)

    Liu, Junjun; Hamza, Adel; Zhan, Chang-Guo

    2009-08-26

    The fundamental reaction mechanism of cocaine esterase (CocE)-catalyzed hydrolysis of (-)-cocaine and the corresponding free energy profile have been studied by performing pseudobond first-principles quantum mechanical/molecular mechanical free energy (QM/MM-FE) calculations. On the basis of the QM/MM-FE results, the entire hydrolysis reaction consists of four reaction steps, including the nucleophilic attack on the carbonyl carbon of (-)-cocaine benzoyl ester by the hydroxyl group of Ser117, dissociation of (-)-cocaine benzoyl ester, nucleophilic attack on the carbonyl carbon of (-)-cocaine benzoyl ester by water, and finally dissociation between the (-)-cocaine benzoyl group and Ser117 of CocE. The third reaction step involving the nucleophilic attack of a water molecule was found to be rate-determining, which is remarkably different from (-)-cocaine hydrolysis catalyzed by wild-type butyrylcholinesterase (BChE; where the formation of the prereactive BChE-(-)-cocaine complex is rate-determining) or its mutants containing Tyr332Gly or Tyr332Ala mutation (where the first chemical reaction step is rate-determining). Besides, the role of Asp259 in the catalytic triad of CocE does not follow the general concept of the "charge-relay system" for all serine esterases. The free energy barrier calculated for the rate-determining step of CocE-catalyzed hydrolysis of (-)-cocaine is 17.9 kcal/mol, which is in good agreement with the experimentally derived activation free energy of 16.2 kcal/mol. In the present study, where many sodium ions are present, the effects of counterions are found to be significant in determining the free energy barrier. The finding of the significant effects of counterions on the free energy barrier may also be valuable in guiding future mechanistic studies on other charged enzymes.

  6. Cross Shear Roll Bonding

    DEFF Research Database (Denmark)

    Bay, Niels; Bjerregaard, Henrik; Petersen, Søren. B;

    1994-01-01

    The present paper describes an investigation of roll bonding an AlZn alloy to mild steel. Application of cross shear roll bonding, where the two equal sized rolls run with different peripheral speed, is shown to give better bond strength than conventional roll bonding. Improvements of up to 20......-23% in bond strength are found and full bond strength is obtained at a reduction of 50% whereas 65% is required in case of conventional roll bonding. Pseudo cross shear roll bonding, where the cross shear effect is obtained by running two equal sized rolls with different speed, gives the same results....

  7. Lipase-catalyzed ester exchange reactions in organic media with controlled humidity.

    Science.gov (United States)

    Goderis, H L; Ampe, G; Feyten, M P; Fouwé, B L; Guffens, W M; Van Cauwenbergh, S M; Tobback, P P

    1987-08-05

    Immobilized lipase activity is studied in organic solvent systems of controlled water content under the influence of a variety of reaction parameters, such as temperature, relative humidity, substrate concentrations, and type of fatty acid used. Control of the amount of water in the reaction system was found to be a valuable tool for the orientation of the reaction process and for the determination of the final reaction products. The properties of the immobilized lipase were studied using the interesterification of triolein and palmitic acid as the model system.

  8. Molecular bonding characteristics of Self-plasticized bamboo composites.

    Science.gov (United States)

    Xue, Qiu; Peng, Wanxi; Ohkoshi, Makoto

    2014-07-01

    Bamboo biomass fibers were gradually separated, prepared, and then self-plasticized for immune composites. The molecular bonding characteristics of the self-plasticized bamboo composites were investigated by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), and thermo gravimetric analysis (TG). The important results were as follows. (1) During self-plasticizing of bamboo biomass, the cross-linking between celluloses mainly depended on carboxylic acid anhydrides and carboxylic acid esters, that between cellulose and lignin depended on carboxylic acid esters and C=O groups of aliphatic hydrocarbons, and that of hemi cellulose had a ether bond and ester bond bridging effect between lignin and cellulose. The cross-linking effects of hemi cellulose, lignin, and cellulose could be stacked and coupled. (2) After self-plasticization, the crystallinity of the lingo cellulosic biomass, lignin cellulose, and cellulose were increased by 5.8%, 2.28%, and 11.67%, respectively. While the TG curves of all samples were basically similar in shape, the weight loss rate turning points of the self-plasticized samples were delayed compared with those of the bamboo biomass fibers. This result demonstrated that the molecular integration of the bamboo biomass was increased after self-plasticization, and confirmed that bond cross-linking between the hemi cellulose, lignin and cellulose of the bamboo biomass had occurred.

  9. Characterization, quantitation and evolution of monoepoxy compounds formed in model systems of fatty acid methyl esters and monoacid triglycerides heated at high temperature

    Directory of Open Access Journals (Sweden)

    Berdeaux, O.

    1999-02-01

    Full Text Available Monoepoxy compounds formed after heating methyl oleate and linoleate, triolein and trilinolein at 180°C for 5, 10 and 15 hours, were characterized and quantitated after derivatization to fatty acid methyl esters by using two base-catalyzed procedures. Structures were identified by GC-MS before and after hydrogénation. A complete recovery of the epoxy compounds was obtained by comparing results from methyl oleate and linoleate before and after transesterification, and good repeatability was also attained. Similar amounts of epoxides were found for methyl esters and triglycerides of the same degree of unsaturation, although formation was considerably greater for the less unsaturated substrates, methyl oleate and triolein, possibly due to the absence of remaining double bonds in the molecule which would involve a lower tendency to participate in further reactions. On other hand, independently of the degree of unsaturation of the model systems and of the period of heating, significantly higher amounts of trans isomers were formed. Finally from comparison between the amounts of epoxides and the level of polar fatty acids in samples, it was deduced that monoepoxy compounds were one of the major groups formed under the conditions used.

    En este estudio se identifican y cuantifican los compuestos epoxidados formados a partir de sistemas modelo de oleato y linoleato de metilo, trioleína y trilinoleína, calentados a 180°C durante 5,10 y 15 horas. La identificación se lleva a cabo mediante CG-EM en las muestras de esteres metílicos antes y después de someter a hidrogenación y para su cuantificación se utilizan dos procedimientos de transesterificación en medio alcalino. La comparación de las cantidades obtenidas, antes y después de la derivatización de los sistemas modelo de esteres metílicos, permitió deducir que la recuperación fue completa, obteniéndose también una excelente repetibilidad. Las cantidades de ep

  10. Antifungal properties of halofumarate esters.

    Science.gov (United States)

    Gershon, H; Shanks, L

    1978-04-01

    Alkyl esters (C1--C4) of the four halofumaric acids were tested for antifungal activity against Candida albicans, Aspergillus niger, Mucor mucedo, and Trichophyton mentagrophytes at pH 5.6 and 7.0 in the absence and presence of 10% beef serum in Sabouraud dextrose agar. The most toxic compound to each organism was: C. albicans, ethyl iodofumarate (0.054 mmole/liter); A. niger, methyl bromofumarate (0.090 mmole/liter); M. mucedo, methyl fluorofumarate (0.037 mmole/liter); and T. mentagrophytes, ethyl iodofumarate (0.020 mmole/liter). The order of overall activity of the six most toxic compounds was: ethyl iodofumarate greater than ethyl chlorofumarate greater than methyl iodofumarate = methyl bromofumarate greater than methyl chlorofumarate greater than bromofumarate.

  11. Enzyme-Catalyzed Modifications of Polysaccharides and Poly(ethylene glycol

    Directory of Open Access Journals (Sweden)

    H. N. Cheng

    2012-06-01

    Full Text Available Polysaccharides are used extensively in various industrial applications, such as food, adhesives, coatings, construction, paper, pharmaceuticals, and personal care. Many polysaccharide structures need to be modified in order to improve their end-use properties; this is mostly done through chemical reactions. In the past 20 years many enzyme-catalyzed modifications have been developed to supplement chemical derivatization methods. Typical reactions include enzymatic oxidation, ester formation, amidation, glycosylation, and molecular weight reduction. These reactions are reviewed in this paper, with emphasis placed on the work done by the authors. The polymers covered in this review include cellulosic derivatives, starch, guar, pectin, and poly(ethylene glycol.

  12. Lipase-catalyzed ethanolysis of fish oils: multi-response kinetics.

    Science.gov (United States)

    Torres, Carlos F; Moeljadi, Marlina; Hill, Charles G

    2003-08-05

    The kinetics of the lipase-catalyzed (Pseudomonas cepacia) ethanolysis of fish oil has been studied in a batch reactor using menhaden oil, tuna oil, and acylglycerol mixtures derived from menhaden oil. Multi-response models derived from a generalized Michaelis-Menten mechanism were developed to describe the rates of formation of ethyl esters of the primary fatty acids present in the precursor oil. A first-order model for deactivation of the lipase was fit simultaneously to one of the data sets.

  13. [Development of novel methods for synthesis of heterocyclic compounds catalyzed by transition metals in fluorinated alcohols].

    Science.gov (United States)

    Saito, Akio

    2008-08-01

    New possibilities for catalytic syntheses of lactone derivatives and nitrogen-containing heterocyclic compounds in fluorinated alcohols are described. The cationic Rh(I) catalyst in fluorinated alcohol solvents (hexafluoroisopropanol: HFIP, trifluoroethanol: TFE) brought about not only mild cycloaddition reactions of ester-tethered compounds but also a facile formation of indole derivatives by the aromatic amino-Claisen rearrangement of N-propargyl aniline derivatives. The use of HFIP as an additive exerted a remarkable effect on the Pictet-Spengler reaction catalyzed by the fluorinated surfactant-combined Brønsted acid catalyst in water.

  14. Wire bonding in microelectronics

    CERN Document Server

    Harman, George G

    2010-01-01

    Wire Bonding in Microelectronics, Third Edition, has been thoroughly revised to help you meet the challenges of today's small-scale and fine-pitch microelectronics. This authoritative guide covers every aspect of designing, manufacturing, and evaluating wire bonds engineered with cutting-edge techniques. In addition to gaining a full grasp of bonding technology, you'll learn how to create reliable bonds at exceedingly high yields, test wire bonds, solve common bonding problems, implement molecular cleaning methods, and much more. Coverage includes: Ultrasonic bonding systems and technologies, including high-frequency systems Bonding wire metallurgy and characteristics, including copper wire Wire bond testing Gold-aluminum intermetallic compounds and other interface reactions Gold and nickel-based bond pad plating materials and problems Cleaning to improve bondability and reliability Mechanical problems in wire bonding High-yield, fine-pitch, specialized-looping, soft-substrate, and extreme-temperature wire bo...

  15. Transient silencing of the KASII genes is feasible in Nicotiana benthamiana for metabolic engineering of wax ester composition.

    Science.gov (United States)

    Aslan, Selcuk; Hofvander, Per; Dutta, Paresh; Sitbon, Folke; Sun, Chuanxin

    2015-06-11

    The beta-ketoacyl-ACP synthase II (KASII) is an enzyme in fatty acid biosynthesis, catalyzing the elongation of 16:0-acyl carrier protein (ACP) to 18:0-ACP in plastids. Mutations in KASII genes in higher plants can lead to lethality, which makes it difficult to utilize the gene for lipid metabolic engineering. We demonstrated previously that transient expression of plastid-directed fatty acyl reductases and wax ester synthases could result in different compositions of wax esters. We hypothesized that changing the ratio between C16 (palmitoyl-compounds) and C18 (stearoyl-compounds) in the plastidic acyl-ACP pool by inhibition of KASII expression would change the yield and composition of wax esters via substrate preference of the introduced enzymes. Here, we report that transient inhibition of KASII expression by three different RNAi constructs in leaves of N. benthamiana results in almost complete inhibition of KASII expression. The transient RNAi approach led to a shift of carbon flux from a pool of C18 fatty acids to C16, which significantly increased wax ester production in AtFAR6-containing combinations. The results demonstrate that transient inhibition of KASII in vegetative tissues of higher plants enables metabolic studies towards industrial production of lipids such as wax esters with specific quality and composition.

  16. Reaction mechanism for cocaine esterase-catalyzed hydrolyses of (+)- and (-)-cocaine: unexpected common rate-determining step.

    Science.gov (United States)

    Liu, Junjun; Zhao, Xinyun; Yang, Wenchao; Zhan, Chang-Guo

    2011-05-05

    First-principles quantum mechanical/molecular mechanical free energy calculations have been performed to examine the catalytic mechanism for cocaine esterase (CocE)-catalyzed hydrolysis of (+)-cocaine in comparison with CocE-catalyzed hydrolysis of (-)-cocaine. It has been shown that the acylation of (+)-cocaine consists of nucleophilic attack of the hydroxyl group of Ser117 on the carbonyl carbon of (+)-cocaine benzoyl ester and the dissociation of (+)-cocaine benzoyl ester. The first reaction step of deacylation of (+)-cocaine, which is identical to that of (-)-cocaine, is rate-determining, indicating that CocE-catalyzed hydrolyses of (+)- and (-)-cocaine have a common rate-determining step. The computational results predict that the catalytic rate constant of CocE against (+)-cocaine should be the same as that of CocE against (-)-cocaine, in contrast with the remarkable difference between human butyrylcholinesterase-catalyzed hydrolyses of (+)- and (-)-cocaine. The prediction has been confirmed by experimental kinetic analysis on CocE-catalyzed hydrolysis of (+)-cocaine in comparison with CocE-catalyzed hydrolysis of (-)-cocaine. The determined common rate-determining step indicates that rational design of a high-activity mutant of CocE should be focused on the first reaction step of the deacylation. Furthermore, the obtained mechanistic insights into the detailed differences in the acylation between the (+)- and (-)-cocaine hydrolyses provide indirect clues for rational design of amino acid mutations that could more favorably stabilize the rate-determining transition state in the deacylation and, thus, improve the catalytic activity of CocE. This study provides a valuable mechanistic base for rational design of an improved esterase for therapeutic treatment of cocaine abuse.

  17. Incorporation of a single His residue by rational design enables thiol-ester hydrolysis by human glutathione transferase A1-1

    OpenAIRE

    Hederos, Sofia; Broo, Kerstin S.; Jakobsson, Emma; Kleywegt, Gerard J.; Mannervik, Bengt; Baltzer, Lars

    2004-01-01

    A strategy for rational enzyme design is reported and illustrated by the engineering of a protein catalyst for thiol-ester hydrolysis. Five mutants of human glutathione (GSH; γ-Glu-Cys-Gly) transferase A1-1 were designed in the search for a catalyst and to provide a set of proteins from which the reaction mechanism could be elucidated. The single mutant A216H catalyzed the hydrolysis of the S-benzoyl ester of GSH under turnover conditions with a kcat/KM of 156 M–1·min–1, and a catalytic profi...

  18. Mechanistic Study of the sPLA2 Mediated Hydrolysis of a Thio-ester Pro Anticancer Ether Lipid

    DEFF Research Database (Denmark)

    Linderoth, Lars; Fristrup, Peter; Hansen, Martin;

    2009-01-01

    ether lipids, which become cytotoxic upon sPLA2-catalyzed hydrolysis has previously been established. To optimize the hydrolysis rate of the lipids and thereby optimizing the release profile of the drugs from the liposomes, we have synthesized a thio-ester pro anticancer ether lipid. Liposomes...... constituted of this lipid showed an altered rate of hydrolysis by sPLA2. We have tested the cytotoxicity of the thio-ester pro anticancer ether lipids toward cancer cells, and the results showed that the cytotoxicity is indeed maintained upon sPLA2 exposure. To further understand the origin for the observed...

  19. Biofuel-Promoted Polychlorinated Dibenzodioxin/furan Formation in an Iron-Catalyzed Diesel Particle Filter.

    Science.gov (United States)

    Heeb, Norbert V; Rey, Maria Dolores; Zennegg, Markus; Haag, Regula; Wichser, Adrian; Schmid, Peter; Seiler, Cornelia; Honegger, Peter; Zeyer, Kerstin; Mohn, Joachim; Bürki, Samuel; Zimmerli, Yan; Czerwinski, Jan; Mayer, Andreas

    2015-08-04

    Iron-catalyzed diesel particle filters (DPFs) are widely used for particle abatement. Active catalyst particles, so-called fuel-borne catalysts (FBCs), are formed in situ, in the engine, when combusting precursors, which were premixed with the fuel. The obtained iron oxide particles catalyze soot oxidation in filters. Iron-catalyzed DPFs are considered as safe with respect to their potential to form polychlorinated dibenzodioxins/furans (PCDD/Fs). We reported that a bimetallic potassium/iron FBC supported an intense PCDD/F formation in a DPF. Here, we discuss the impact of fatty acid methyl ester (FAME) biofuel on PCDD/F emissions. The iron-catalyzed DPF indeed supported a PCDD/F formation with biofuel but remained inactive with petroleum-derived diesel fuel. PCDD/F emissions (I-TEQ) increased 23-fold when comparing biofuel and diesel data. Emissions of 2,3,7,8-TCDD, the most toxic congener [toxicity equivalence factor (TEF) = 1.0], increased 90-fold, and those of 2,3,7,8-TCDF (TEF = 0.1) increased 170-fold. Congener patterns also changed, indicating a preferential formation of tetra- and penta-chlorodibenzofurans. Thus, an inactive iron-catalyzed DPF becomes active, supporting a PCDD/F formation, when operated with biofuel containing impurities of potassium. Alkali metals are inherent constituents of biofuels. According to the current European Union (EU) legislation, levels of 5 μg/g are accepted. We conclude that risks for a secondary PCDD/F formation in iron-catalyzed DPFs increase when combusting potassium-containing biofuels.

  20. Epoxidation reactions of unsaturated fatty esters with potassium peroxomonosulfate.

    Science.gov (United States)

    Lie Ken Jie, M S; Pasha, M K

    1998-06-01

    Epoxidation of the double bond in methyl oleate, octadec-11E-en-9-ynoate, ricinoleate (12-hydroxy-octadec-9Z-enoate), iso-ricinoleate (9-hydroxy-octadec-12Z-enoate), and 12-oxo-octadec-9Z-enoate with potassium peroxomonosulfate (oxone, 2 KHSO5.KHSO4.K2SO4) in the presence of trifluoroacetone or methyl pyruvate gave the corresponding monoepoxy derivatives. Reaction of Oxone with methyl linoleate and octadeca-9Z,11E-dienoate furnished the corresponding diepoxystearate derivative. Methyl 9,12-dioxo-octadec-10Z-enoate was obtained when a C18 furanoid fatty ester (methyl 9,12-epoxy-9,11-octadecadienoate) was treated with Oxone. The yield of these reactions was very high (85-99%), and the epoxy derivatives were readily isolated by solvent extraction. The products were identified by spectroscopic methods.

  1. New ester alkaloids from lupins (genus lupinus).

    Science.gov (United States)

    Mühlbauer, P; Witte, L; Wink, M

    1988-06-01

    Esters of 13-hydroxylupanine and 4-hydroxylupanine with acetic, propionic, butyric, isobutyric, valeric, isovaleric, tiglic, benzoic, and TRANS-cinnamic acid have been synthesized and characterized by capillary gas-liquid chromatography and mass spectrometry (EI-MS, CI-MS). In LUPINUS POLYPHYLLUS, L. ALBUS, L. ANGUSTIFOLIUS, and L. MUTABILIS we could identify new ester alkaloids (e.g. 13-propyloxylupanine, 13-butyryloxylupanine, 13-isobutyryloxylupanine, and 4-tigloyloxylupanine) besides the known esters, i.e. 13-acetoxylupanine, 13-isovaleroyloxylupanine, 13-angeloyloxylupanine, 13-tigloyloxylupanine, 13-benzoyloxylupanine, 13- CIS-cinnamoyloxylupanine nine, and 13- TRANS-cinnamoyloxylupanine.

  2. Cold Flow Properties of Fatty Esters

    Directory of Open Access Journals (Sweden)

    Andrea Kleinová

    2007-09-01

    Full Text Available The article is devoted to the study of cold fl ow properties of neat esters of branched chain alcohols with fatty acids and blends of these esters with fossil diesel fuel. According to the determined CFPP values, the influence of alcohol branching on the fuel filterability is negligible and was detected only in the case of 2-ethyl hexanol. Fossil fuel blending with fatty esters up to 10 % vol. does not substantially change the cold flow properties of fossil fuel. DSC cooling scan parameters should be employed to predict CFPP of blended diesel fuel.

  3. Thermodynamics of Enzyme-Catalyzed Reactions Database

    Science.gov (United States)

    SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

  4. Synthesis of Trimethylolpropane Esters of Calophyllum Methyl Esters : Effect of Temperature and Molar Ratio

    Directory of Open Access Journals (Sweden)

    Yeti Widyawati

    2014-12-01

    Full Text Available Trimethylolpropane esters were synthesized by transesterification of calophyllum methyl esters and trimethylolpropane using a calcium oxide as the catalyst. The results showed that the optimal reaction conditions (temperature: 130 0C, reaction time: 5 h, reactant molar ratio: 3.9:1, catalyst amount 3%w/w, and formed  trimethylolpropane ester of 79.0% were obtained. The basic physicochemical properties of the trimethylolpropane esters were the following : kinematic viscosities of 56.40 cSt and 8.8 cSt at 40 0C and 100 0C,  viscosity index 193, flash point 218 0C and pour point -3 0C. So Methyl esters of fatty acids of would callophylum  methyl ester is good raw material for the synthesis of lubricating oils.

  5. 21 CFR 172.854 - Polyglycerol esters of fatty acids.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Polyglycerol esters of fatty acids. 172.854 Section... HUMAN CONSUMPTION Multipurpose Additives § 172.854 Polyglycerol esters of fatty acids. Polyglycerol esters of fatty acids, up to and including the decaglycerol esters, may be safely used in food...

  6. Astaxanthin preparation by fermentation of esters from Haematococcus pluvialis algal extracts with Stenotrophomonas species.

    Science.gov (United States)

    Dong, Hao; Li, Xuemin; Xue, Changhu; Mao, Xiangzhao

    2016-05-01

    Natural astaxanthin (Ax) is an additive that is widely used because of its beneficial biochemical functions. However, the methods used to produce free Ax have drawbacks. Chemical saponification methods produce several by-products, and lipase-catalyzed hydrolysis methods are not cost effective. In this study, a bacterial strain of Stenotrophomonas sp. was selected to enzymatically catalyze the saponification of Ax esters to produce free all-trans-Ax. Through single-factor experiments and a Box-Behnken design, the optimal fermentation conditions were determined as follows: a seed culture age of 37.79 h, an inoculum concentration of 5.92%, and an initial broth pH of 6.80. Under these conditions, a fermentation curve was drawn, and the optimal fermentation time was shown to be 60 h. At 60 h, the degradation rate of the Ax esters was 98.08%, and the yield of free all-trans-Ax was 50.130 μg/mL. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:649-656, 2016.

  7. The general base in the thymidylate synthase catalyzed proton abstraction.

    Science.gov (United States)

    Ghosh, Ananda K; Islam, Zahidul; Krueger, Jonathan; Abeysinghe, Thelma; Kohen, Amnon

    2015-12-14

    The enzyme thymidylate synthase (TSase), an important chemotherapeutic drug target, catalyzes the formation of 2'-deoxythymidine-5'-monophosphate (dTMP), a precursor of one of the DNA building blocks. TSase catalyzes a multi-step mechanism that includes the abstraction of a proton from the C5 of the substrate 2'-deoxyuridine-5'-monophosphate (dUMP). Previous studies on ecTSase proposed that an active-site residue, Y94 serves the role of the general base abstracting this proton. However, since Y94 is neither very basic, nor connected to basic residues, nor located close enough to the pyrimidine proton to be abstracted, the actual identity of this base remains enigmatic. Based on crystal structures, an alternative hypothesis is that the nearest potential proton-acceptor of C5 of dUMP is a water molecule that is part of a hydrogen bond (H-bond) network comprised of several water molecules and several protein residues including H147, E58, N177, and Y94. Here, we examine the role of the residue Y94 in the proton abstraction step by removing its hydroxyl group (Y94F mutant). We investigated the effect of the mutation on the temperature dependence of intrinsic kinetic isotope effects (KIEs) and found that these KIEs are more temperature dependent than those of the wild-type enzyme (WT). These results suggest that the phenolic -OH of Y94 is a component of the transition state for the proton abstraction step. The findings further support the hypothesis that no single functional group is the general base, but a network of bases and hydroxyls (from water molecules and tyrosine) sharing H-bonds across the active site can serve the role of the general base to remove the pyrimidine proton.

  8. The effect of disulfide bond introduction and related Cys/Ser mutations on the stability of a cyclohexanone monooxygenase.

    Science.gov (United States)

    Schmidt, Sandy; Genz, Maika; Balke, Kathleen; Bornscheuer, Uwe T

    2015-11-20

    Baeyer-Villiger monooxygenases (BVMO) belong to the class B of flavin-dependent monooxygenases (type I BVMOs) and catalyze the oxidation of (cyclic) ketones into esters and lactones. The prototype BVMO is the cyclohexanone monooxygenase (CHMO) from Acinetobacter sp. NCIMB 9871. This enzyme shows an impressive substrate scope with a high chemo-, regio- and/or enantioselectivity. BVMO reactions are often difficult, if not impossible to achieve by chemical approaches and this makes these enzymes thus highly desired candidates for industrial applications. Unfortunately, the industrial use is hampered by several factors related to the lack of stability of these biocatalysts. Thus, the aim of this study was to improve the CHMO's long-term stability, one of the most relevant parameter for biocatalytic processes, and additionally its stability against oxidation. We used an easy computational method for the prediction of stabilizing disulfide bonds in the CHMO-scaffold. The three most promising predicted disulfide pairs were created and biochemically characterized. The most oxidatively stable variant (Y411C-A463C) retained nearly 60% activity after incubation with 25 mM H2O2 whereas the wild type retained only 16%. In addition, one extra disulfide pair (T415C-A463C) was created and tested for increased stability. The melting temperature (Tm) of this variant was increased by 5°C with simultaneous improved long-term stability. After verification by ABD-F labeling that this mutant does not form a disulfide bond, single and double Cys/Ser mutants were prepared and investigated. Subsequent analysis revealed that the T415C single point variant is the most stable variant with a 30-fold increased long-term stability (33% residual activity after 24h incubation at 25°C) showcasing a great achievement for practical applications.

  9. Theoretical Studies on the Iodine-catalyzed Nucleophilic Addition of Acetone with Five-membered Heterocycles

    Institute of Scientific and Technical Information of China (English)

    WANG Yan-hua; LI Li; CHEN Xue-song

    2008-01-01

    The iodine-catalyzed nucleophilic addition reactions of pyrrole,furan,or thiophene with acetone were studied in gas and solvent by the density functional theory at the level of Lan12DZ*,It was seen that the halogen bond between iodine and carbonyl oxygen appeared to have an important catalytic effect on such reactions,and the first iodine molecule maximally diminished the barrier height by 41 kJ/mol,while the second iodine molecule could not improve such reactions largely,It was concluded that the C2-addition was generally more favorable than the C3-addition for the three heterocycles;however,iodine considerably more effectively catalyzed the C3-addition than the C2-addition for pyrrole,It was also revealed by PCM calculation that the iodine-catalyzed nucleophilic additions occurred more easily in solvent than in gas,which explained the experiment performed by Bandgar et al..

  10. Iron-Catalyzed C-C Cross-Couplings Using Organometallics.

    Science.gov (United States)

    Guérinot, Amandine; Cossy, Janine

    2016-08-01

    Over the last decades, iron-catalyzed cross-couplings have emerged as an important tool for the formation of C-C bonds. A wide variety of alkenyl, aryl, and alkyl (pseudo)halides have been coupled to organometallic reagents, the most currently used being Grignard reagents. Particular attention has been devoted to the development of iron catalysts for the functionalization of alkyl halides that are generally challenging substrates in classical cross-couplings. The high functional group tolerance of iron-catalyzed cross-couplings has encouraged organic chemists to use them in the synthesis of bioactive compounds. Even if some points remain obscure, numerous studies have been carried out to investigate the mechanism of iron-catalyzed cross-coupling and several hypotheses have been proposed.

  11. Space-Qualifiable Cyanate Ester Elastomer Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Cornerstone Research Group, Inc. (CRG) proposes to design and develop a space-qualifiable cyanate ester elastomer for application in self-deployable space structures...

  12. Ester Tuiksoo - riigi peakokk / Peeter Kuimet

    Index Scriptorium Estoniae

    Kuimet, Peeter

    2007-01-01

    Põllumajandusminister Ester Tuiksoo eelseisvast vastuvõtust Estonias, jopede kinkimisest maaelu arengukava väljatöötamisega seotud inimestele. Minister Tuiksoo kohta tehtud kriitikast. SDE esimehe Ivari Padari arvamus. Lisa: Tuiksoo jopedest ja tassidest

  13. Space-Qualifiable Cyanate Ester Elastomer Project

    Data.gov (United States)

    National Aeronautics and Space Administration — In Phase 1, CRG demonstrated the feasibility of a novel approach to prepare cyanate ester based elastomers. This approach polymerizes in-situ siloxane within a...

  14. Classification of ester oils according to their Equivalent Alkane Carbon Number (EACN) and asymmetry of fish diagrams of C10E4/ester oil/water systems.

    Science.gov (United States)

    Ontiveros, Jesús F; Pierlot, Christel; Catté, Marianne; Molinier, Valérie; Pizzino, Aldo; Salager, Jean-Louis; Aubry, Jean-Marie

    2013-08-01

    The phase behavior of well-defined C10E4/ester oil/water systems versus temperature was investigated. Fifteen ester oils were studied and their Equivalent Alkane Carbon Numbers (EACNs) were determined from the so-called fish-tail temperature T* of the fish diagrams obtained with an equal weight amount of oil and water (f(w)=0.5). The influence of the chemical structure of linear monoester on EACN was quantitatively rationalized in terms of ester bonds position and total carbon number, and explained by the influence of these polar oils on the "effective" packing parameter of the interfacial surfactant, which takes into account its entire physicochemical environment. In order to compare the behaviors of typical mono-, di-, and triester oils, three fish diagrams were entirely plotted with isopropyl myristate, bis (2-ethylhexyl) adipate, and glycerol trioctanoate. When the number of ester bonds increases, a more pronounced asymmetry of the three-phase body of the fish diagram with respect to T* is observed. In this case, T* is much closer to the upper limit temperature Tu than to the lower limit temperature Tl of the three-phase zone. This asymmetry is suggested to be linked to an increased solubility of the surfactant in the oil phase, which decreases the surfactant availability for the interfacial pseudo-phase. As a consequence, the asymmetry depends on the water-oil ratio, and a method is proposed to determine the fw value at which T* is located at the mean value of Tu and Tl.

  15. Effects of bis homoallylic and homoallylic hydroxyl substitution on the olefinic 13C resonance shifts in fatty acid methyl esters.

    Science.gov (United States)

    Pfeffer, P E; Sonnet, P E; Schwartz, D P; Osman, S F; Weisleder, D

    1992-04-01

    Substitution of a hydroxyl group at the bis homoallylic position (OH group located three carbons away from the olefinic carbon) in C18 unsaturated fatty acid esters (FAE) induces a 0.73 +/- 0.05 ppm upfield and a 0.73 +/- 0.06 ppm downfield shift on the delta and epsilon olefinic 13C resonances relative to the unsubstituted FAE, respectively. If the hydroxyl group is located on the carboxyl side of the double bond of the bis homoallylic hydroxy fatty acid esters (BHAHFA), the olefinic resonances are uniformly shifted apart by [formula: see text] where delta delta dbu represents the absolute value of the double bond resonance separation in the unsubstituted FAE and 1.46 ppm is the sum of the absolute values of the delta and epsilon shift parameters. With hydroxyl substitution on the terminal methyl side of the double bond, the olefinic shift separation is equal to [formula: see text] In homoallylic (OH group located two carbons away from the olefinic carbon) substituted FAE the gamma and delta induced hydroxyl shifts for the cis double bond resonances are +3.08 and -4.63 ppm, respectively while the trans double bond parameters are +4.06 and -4.18 ppm, respectively. The double bond resonance separation in homoallylic hydroxy fatty acid esters (HAHFA) can be calculated from the formula [formula: see text] for cis and [formula: see text] for the trans case when the OH substitution is on the carboxyl side of the double bond. Conversely, when the OH resides on the terminal methyl side, the double bond shift separations for cis and trans isomers are [formula: see text] and [formula: see text] respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

  16. Phenylalanine and tyrosine methyl ester intramolecular interactions and conformational analysis by (1)H NMR and infrared spectroscopies and theoretical calculations.

    Science.gov (United States)

    Cormanich, Rodrigo A; Ducati, Lucas C; Tormena, Cláudio F; Rittner, Roberto

    2014-04-01

    Amino acid conformational analysis in solution are scarce, since these compounds present a bipolar zwitterionic structure ((+)H3NCHRCOO(-)) in these media. Also, intramolecular hydrogen bonds have been classified as the sole interactions governing amino acid conformational behavior in the literature. In the present work we propose phenylalanine and tyrosine methyl ester conformational studies in different solvents by (1)H NMR and infrared spectroscopies and theoretical calculations. Both experimental and theoretical results are in agreement and suggest that the conformational behavior of the phenylalanine and tyrosine methyl esters are similar and are dictated by the interplay between steric and hyperconjugative interactions.

  17. Conversion of carbohydrates to levulinic acid esters

    DEFF Research Database (Denmark)

    2014-01-01

    The present invention relates to the field of converting carbohydrates into levulinic acid, a platform chemical for many chemical end products. More specifically the invention relates to a method for converting carbohydrates such as mono-, di- or polysaccharides, obtained from for example biomass...... production into a suitable levulinic acid ester in the presence of a zeolite or zeotype catalyst and a suitable alcohol, and the ester may be further converted into levulinic acid if desired....

  18. Synthesis of a new energetic nitrate ester

    Energy Technology Data Exchange (ETDEWEB)

    Chavez, David E [Los Alamos National Laboratory

    2008-01-01

    Nitrate esters have been known as useful energetic materials since the discovery of nitroglycerin by Ascanio Sobrero in 1846. The development of methods to increase the safety and utility of nitroglycerin by Alfred Nobel led to the revolutionary improvement in the utility of nitroglycerin in explosive applications in the form of dynamite. Since then, many nitrate esters have been prepared and incorporated into military applications such as double-based propellants, detonators and as energetic plasticizers. Nitrate esters have also been shown to have vasodilatory effects in humans and thus have been studied and used for treatments of ailments such as angina. The mechanism of the biological response towards nitrate esters has been elucidated recently. Interestingly, many of the nitrate esters used for military purposes are liquids (ethylene glycol dinitrate, propylene glycol dinitrate, etc). Pentaerythritol tetranitrate (PETN) is one of the only solid nitrate esters, besides nitrocellulose, that is used in any application. Unfortunately, PETN melting point is above 100 {sup o}C, and thus must be pressed as a solid for detonator applications. A more practical material would be a melt-castable explosive, for potential simplification of manufacturing processes. Herein we describe the synthesis of a new energetic nitrate ester (1) that is a solid at ambient temperatures, has a melting point of 85-86 {sup o}C and has the highest density of any known nitrate ester composed only of carbon, hydrogen, nitrogen and oxygen. We also describe the chemical, thermal and sensitivity properties of 1 as well as some preliminary explosive performance data.

  19. Rapid Output Growth of Special Acrylic Esters

    Institute of Scientific and Technical Information of China (English)

    Wang Lianzhi

    2007-01-01

    @@ Acrylic esters are usually classified into general-purpose varieties and special varieties. The production and application of general-purpose varieties is already quite matured in the world and their output growth tends to be flat. Owing to the development of coatings, electronics, automobiles,textiles, printing and construction sectors, especially the application of radiation curing technology in various sectors, special acrylic esters have developed rapidly.

  20. The Role of Backbone Hydrogen Bonds in the Transition State for Protein Folding of a PDZ Domain.

    Directory of Open Access Journals (Sweden)

    Søren W. Pedersen

    Full Text Available Backbone hydrogen bonds are important for the structure and stability of proteins. However, since conventional site-directed mutagenesis cannot be applied to perturb the backbone, the contribution of these hydrogen bonds in protein folding and stability has been assessed only for a very limited set of small proteins. We have here investigated effects of five amide-to-ester mutations in the backbone of a PDZ domain, a 90-residue globular protein domain, to probe the influence of hydrogen bonds in a β-sheet for folding and stability. The amide-to-ester mutation removes NH-mediated hydrogen bonds and destabilizes hydrogen bonds formed by the carbonyl oxygen. The overall stability of the PDZ domain generally decreased for all amide-to-ester mutants due to an increase in the unfolding rate constant. For this particular region of the PDZ domain, it is therefore clear that native hydrogen bonds are formed after crossing of the rate-limiting barrier for folding. Moreover, three of the five amide-to-ester mutants displayed an increase in the folding rate constant suggesting that the hydrogen bonds are involved in non-native interactions in the transition state for folding.

  1. Application of fundamental organometallic chemistry to the development of a gold-catalyzed synthesis of sulfinate derivatives.

    Science.gov (United States)

    Johnson, Miles W; Bagley, Scott W; Mankad, Neal P; Bergman, Robert G; Mascitti, Vincent; Toste, F Dean

    2014-04-22

    The development of a gold(I)-catalyzed sulfination of aryl boronic acids is described. This transformation proceeds through an unprecedented mechanism which exploits the reactivity of gold(I)-heteroatom bonds to form sulfinate anions. Further in situ elaboration of the sulfinate intermediates leads to the corresponding sulfones and sulfonamides, two pharmacophores routinely encountered in drug discovery.

  2. Hydroformylation of methyl oleate catalyzed by rhodium complexes; Hidroformilacao do oleato de metila catalisada por complexos de rodio

    Energy Technology Data Exchange (ETDEWEB)

    Mendes, Ana Nery Furlan [Universidade Federal do Espirito Santo (UFES), Sao Mateus, ES (Brazil). Centro Universitario Norte do Espirito Santo. Dept. de Ciencias Naturais; Rosa, Ricardo Gomes da; Gregorio, Jose Ribeiro, E-mail: jrg@iq.ufrgs.br [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Quimica

    2012-07-01

    In this work, we describe the hydroformylation of methyl oleate catalyzed by several rhodium complexes. Parameters including total pressure, phosphorous/rhodium and CO/H{sub 2} ratio, temperature and phosphorous ligands were scanned. Total conversion of the starting double bonds was achieved while maintaining excellent selectivity in aldehydes. (author)

  3. Palladium-catalyzed regioselective intramolecular coupling of o-carborane with aromatics via direct cage B-H activation.

    Science.gov (United States)

    Quan, Yangjian; Xie, Zuowei

    2015-03-18

    Palladium-catalyzed intramolecular coupling of o-carborane with aromatics via direct cage B-H bond activation has been achieved, leading to the synthesis of a series of o-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom.

  4. Synthesis of alkyl esters by cutinase in miniemulsion and organic solvent media.

    Science.gov (United States)

    de Barros, Dragana P C; Fonseca, Luís P; Cabral, Joaquim M S; Weiss, Clemens K; Landfester, Katharina

    2009-05-01

    The main objective of this work was studying and testing the nature and influence of reaction media (organic solvent vs. miniemulsion system) on the synthesis of alkyl esters catalyzed by Fusarium solani pisi cutinase. Ester synthesis and cutinase selectivity for different chain length of acids and alcohols (ethyl and hexyl) were evaluated. In iso-octane, after 1 h of reaction, cutinase exhibits rates of esterification between 0.24 micromol x mg(-)1 x min(-1) for ethyl oleate and 1.15 micromol x mg(-)1 x min(-1) for ethyl butyrate, while in a miniemulsion system the rates were from 0.05 for ethyl heptanoate to 0.76 micromol x mg(-1) x min(-1) for ethyl decanoate. The reaction rate for the synthesis of hexyl esters in a miniemulsion system was from 0.19 for hexyl heptanoate to 1.07 micromol x mg(-)1 x min(-1) for hexyl decanoate. High conversion yields of 95% at equilibrium after 8 h of reaction in iso-octane for pentanoic acid (C(5)) with ethanol at equimolar concentration (0.1 M) was achieved. Additionally, this work showed that a significant and unexpected shift in cutinase selectivity occurred towards longer chain length carboxylic acids (C(8)-C(10)) in miniemulsion system as compared to organic solvent (iso-octane) and previous studies in reverse micellar systems. The possibility of working with higher concentration of substrates, without inhibitory effect on the enzyme, was another advantage of the miniemulsion system.

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

    Science.gov (United States)

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

    1998-01-01

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

  6. Hyperbranched Poly(amide-ester) Mildly Synthesized and Its Characterization

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    AB2-type-prepolymerized monomer was rapidly (2 h) prepared atIoom temperature (25℃) using commercially available maleic anhydride (MA) and diethanolamine (DEA) as raw materials.By employing toluene-p-sulfonic acid as a catalyzer, a series of hyperbranched poly(amide-ester) (HBPAE) were successfully synthesized from prepared AB2 monomer by solution condensation polymerization through "one-step process" or "pseudo one-step process" (using pen taerythritol as a center core).The processes were carried out at high temperature of 120 C for 6 h in air atmosphere (inert protection free) with reduced pressure distillation (0.08~0.096 MPa).The results of FT-IR, UV-Vis, TGA, and intrinsic viscosity testing by Ubbelodhe viscometer showed that the prepared HBPAEspossess three-dimensional configuration with unsaturated conjugate structure,large numbers of branches and numerous terminal hydroxyl groups.These result in their lowviscosity, high solubility and thermal stability.

  7. Regio-selectivity of the Oxidative C-S Bond Formation in Ergothioneine and Ovothiol Biosyntheses

    Science.gov (United States)

    Song, Heng; Leninger, Maureen; Lee, Norman

    2014-01-01

    Ergothioneine (5) and ovothiol (8) are two novel thiol-containing natural products. Their C-S bonds are formed by oxidative coupling reactions catalyzed by EgtB and OvoA enzymes, respectively. In this work, it was discovered that besides catalyzing the oxidative coupling between histidine and cysteine (1 → 6 conversion), OvoA can also catalyze a direct oxidative coupling between hercynine (2) and cysteine (2 → 4 conversion), which can shorten the ergothioneine biosynthetic pathway by two steps. PMID:24016264

  8. Regioselectivity of the oxidative C-S bond formation in ergothioneine and ovothiol biosyntheses.

    Science.gov (United States)

    Song, Heng; Leninger, Maureen; Lee, Norman; Liu, Pinghua

    2013-09-20

    Ergothioneine (5) and ovothiol (8) are two novel thiol-containing natural products. Their C-S bonds are formed by oxidative coupling reactions catalyzed by EgtB and OvoA enzymes, respectively. In this work, it was discovered that in addition to catalyzing the oxidative coupling between histidine and cysteine (1 → 6 conversion), OvoA can also catalyze a direct oxidative coupling between hercynine (2) and cysteine (2 → 4 conversion), which can shorten the ergothioneine biosynthetic pathway by two steps.

  9. Lipase-catalyzed biodiesel production with methyl acetate as acyl acceptor

    Energy Technology Data Exchange (ETDEWEB)

    Huang Ying; Yan Yunjun [School of Life Science and Technology, Huazhong Univ. of Science and Technology, Wuhan (China)

    2008-03-15

    Biodiesel is an alternative diesel fuel made from renewable biological resources. During the process of biodiesel production, lipase-catalyzed transesterification is a crucial step. However, current techniques using methanol as acyl acceptor have lower enzymatic activity; this limits the application of such techniques in large-scale biodiesel production. Furthermore, the lipid feedstock of currently available techniques is limited. In this paper, the technique of lipase-catalyzed transesterification of five different oils for biodiesel production with methyl acetate as acyl acceptor was investigated, and the transesterification reaction conditions were optimized. The operation stability of lipase under the obtained optimal conditions was further examined. The results showed that under optimal transesterification conditions, both plant oils and animal fats led to high yields of methyl ester: cotton-seed oil, 98%; rape-seed oil, 95%; soybean oil, 91%; tea-seed oil, 92%; and lard, 95%. Crude and refined cotton-seed oil or lard made no significant difference in yields of methyl ester. No loss of enzymatic activity was detected for lipase after being repeatedly used for 40 cycles (ca. 800 h), which indicates that the operational stability of lipase was fairly good under these conditions. Our results suggest that cotton-seed oil, rape-seed oil and lard might substitute soybean oil as suitable lipid feedstock for biodiesel production. Our results also show that our technique is fit for various lipid feedstocks both from plants and animals, and presents a very promising way for the large-scale biodiesel production. (orig.)

  10. Base catalyzed transesterification of acid treated vegetable oil blend for biodiesel production

    Energy Technology Data Exchange (ETDEWEB)

    Yusup, Suzana; Khan, Modhar Ali [Chemical Engineering Department, Universiti Teknologi PETRONAS, Seri Iskandar, Tronoh, Perak 31750 (Malaysia)

    2010-10-15

    Biodiesel can be produced from low cost non-edible oils and fats. However, most of these sources are of high free fatty acid content which requires two stage transesterification to reduce the acid value and produce biodiesel. The acid treatment step is usually followed by base transesterification since the latter can yield higher conversions of methyl esters at shorter reaction time when compared with acid catalyzed reaction. In the current study, base transesterification in the second stage of biodiesel synthesis is studied for a blend of crude palm/crude rubber seed oil that had been characterized and treated with acid esterification. Optimum conditions for the reaction were established and effect of each variable was investigated. The base catalyzed transesterification favored a temperature of 55 C with methanol/oil molar ratio of 8/1 and potassium hydroxide at 2% (ww{sup -1}) (oil basis). The conversion of methyl esters exceeded 98% after 5 h and the product quality was verified to match that for biodiesel with international standards. (author)

  11. Cobalt-Catalyzed Vinylation of Organozinc Reagents with Aldehydes

    Institute of Scientific and Technical Information of China (English)

    WANG; JinXian

    2001-01-01

    Transtion metal catalyzed vinylation of organic halides are known to be a very convenient method for forming carbon-carbon bonds at unsubstituted vinylic position. The versatility of stilbenes is well known because of its various biological active components, the variety of its reactions in organic syntheses, and its ability to function as a bonding partner for metals in complexes.  Many methods have been described for the synthesis of stilbenes. The reduction, dehydrogenation, and elimination reactions leading to stilbenes without formation of new carbon-carbon bonds are known to be a very convenient methods. Synthetically more important are the dimerization reactions: oxidative or eleminative dimerization of a suitable methylarene often constitutes the method of choice for the preparation of a symmetric stilbene. Meerwein arylation and Heck reaction are prominent examples for the synthesis of stilbenes from arenes and styrenes. Moreover, condensation reactions of a nucleophilic with an electrophilic arylmethyl compound include Knoevenagel type reactions and the very general Wittig and Wittig-Horner reactions are also known methods.  ……

  12. Iridium-catalyzed intermolecular dehydrogenative silylation of polycyclic aromatic compounds without directing groups.

    Science.gov (United States)

    Murai, Masahito; Takami, Keishi; Takai, Kazuhiko

    2015-03-16

    This study describes the iridium-catalyzed intermolecular dehydrogenative silylation of C(sp(2))-H bonds of polycyclic aromatic compounds without directing groups. The reaction produced various arylsilanes through both Si-H and C-H bond activation, with hydrogen as the sole byproduct. Reactivity was affected by the electronic nature of the aromatic compounds, and silylation of electron-deficient and polycyclic aromatic compounds proceeded efficiently. Site-selectivity was controlled predominantly by steric factors. Therefore, the current functionalization proceeded with opposite chemo- and site-selectivity compared to that observed for general electrophilic functionalization of aromatic compounds.

  13. Why You Really Should Consider Using Palladium-Catalyzed Cross-Coupling of Silanols and Silanolates

    OpenAIRE

    Denmark, Scott E; Ambrosi, Andrea

    2015-01-01

    The transition metal-catalyzed cross-coupling of organometallic nucleophiles derived from tin, boron, and zinc with organic electrophiles enjoys a preeminent status among modern synthetic methods for the formation of carbon-carbon bonds. In recent years, organosilanes have emerged as viable alternatives to the conventional reagents, with the added benefits of low cost, low toxicity and high chemical stability. However, silicon-based cross-coupling reactions often require heating in the presen...

  14. Palladium-catalyzed 1,4-difunctionalization of butadiene to form skipped polyenes.

    Science.gov (United States)

    McCammant, Matthew S; Liao, Longyan; Sigman, Matthew S

    2013-03-20

    A palladium-catalyzed 1,4-addition across the commodity chemical 1,3-butadiene to afford skipped polyene products is reported. Through a palladium σ → π → σ allyl isomerization, two new carbon-carbon bonds are formed with high regioselectivity and trans stereoselectivity of the newly formed alkene. The utility of this method is highlighted by the successful synthesis of the ripostatin A skipped triene core.

  15. A novel copper-catalyzed reductive coupling of N-tosylhydrazones with H-phosphorus oxides.

    Science.gov (United States)

    Wu, Lei; Zhang, Xio; Chen, Qing-Qing; Zhou, An-Kun

    2012-10-21

    We report here a novel C(sp(3))-P bonds formation via copper-catalyzed reductive coupling of N-tosylhydrazones with H-phosphorus oxides. A variety of aliphatic and aromatic substrates bearing electron-rich and electron-deficient substituents affords phosphine oxide derivatives with moderate to good yields. This work suggests a new transformation of aldehydes/ketones via N-tosylhydrazones to organophosphorus compounds.

  16. Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism.

    Energy Technology Data Exchange (ETDEWEB)

    Lohr, Tracy L.; Li, Zhi; Assary, Rajeev S.; Curtiss, Larry A.; Marks, Tobin J.

    2016-01-01

    The scope and mechanism of thermodynamically leveraged ester RC(O)O-R' bond hydrogenolysis by tandem metal triflate + supported Pd catalysts are investigated both experimentally and theoretically by DFT and energy span analysis. This catalytic system has a broad scope, with relative cleavage rates scaling as, tertiary 4 secondary 4 primary ester at 1 bar H-2, yielding alkanes and carboxylic acids with high conversion and selectivity. Benzylic and allylic esters display the highest activity. The rate law is nu = k[M(OTf )(n)](1)[ester](0)[H-2](0) with an H/D kinetic isotope effect = 6.5 +/- 0.5, implying turnover-limiting C-H scission following C-O cleavage, in agreement with theory. Intermediate alkene products are then rapidly hydrogenated. Applying this approach with the very active Hf(OTf)(4) catalyst to bio-derived triglycerides affords near-quantitative yields of C-3 hydrocarbons rather than glycerol. From model substrates, it is found that RC(O)O-R' cleavage rates are very sensitive to steric congestion and metal triflate identity. For triglycerides, primary/external glyceryl CH2-O cleavage predominates over secondary/internal CH-O cleavage, with the latter favored by less acidic or smaller ionic radius metal triflates, raising the diester selectivity to as high as 48% with Ce(OTf)(3).

  17. Detection of testosterone esters in blood.

    Science.gov (United States)

    Forsdahl, Guro; Erceg, Damir; Geisendorfer, Thomas; Turkalj, Mirjana; Plavec, Davor; Thevis, Mario; Tretzel, Laura; Gmeiner, Günter

    2015-01-01

    Injections of synthetic esters of testosterone are among the most common forms of testosterone application. In doping control, the detection of an intact ester of testosterone in blood gives unequivocal proof of the administration of exogenous testosterone. The aim of the current project was to investigate the detection window for injected testosterone esters as a mixed substance preparation and as a single substance preparation in serum and plasma. Furthermore, the suitability of different types of blood collection devices was evaluated. Collection tubes with stabilizing additives, as well as non-stabilized serum separation tubes, were tested. A clinical study with six participants was carried out, comprising a single intramuscular injection of either 1000 mg testosterone undecanoate (Nebido(®)) or a mixture of 30 mg testosterone propionate, 60 mg testosterone phenylpropionate, 60 mg testosterone isocaproate, and 100 mg testosterone decanoate (Sustanon(®)). Blood was collected throughout a testing period of 60 days. The applied analytical method for blood analysis included liquid-liquid extraction and preparation of oxime derivatives, prior to TLX-sample clean-up and liquid chromatography-tandem mass spectrometry (LC-MS/MS) detection. All investigated testosterone esters could be detected in post-administration blood samples. The detection time depended on the type of ester administered. Furthermore, results from the study show that measured blood concentrations of especially short-chained testosterone esters are influenced by the type of blood collection device applied. The testosterone ester detection window, however, was comparable.

  18. Bonding with Your Baby

    Science.gov (United States)

    ... in infant massage in your area. Breastfeeding and bottle-feeding are both natural times for bonding. Infants respond ... activities include: participating together in labor and delivery feeding ( breast or bottle ); sometimes dad forms a special bond with baby ...

  19. Catalysis of Protein Disulfide Bond Isomerization in a Homogeneous Substrate†

    Science.gov (United States)

    Kersteen, Elizabeth A.; Barrows, Seth R.; Raines, Ronald T.

    2008-01-01

    Protein disulfide isomerase (PDI) catalyzes the rearrangement of nonnative disulfide bonds in the endoplasmic reticulum of eukaryotic cells, a process that often limits the rate at which polypeptide chains fold into a native protein conformation. The mechanism of the reaction catalyzed by PDI is unclear. In assays involving protein substrates, the reaction appears to involve the complete reduction of some or all of its nonnative disulfide bonds followed by oxidation of the resulting dithiols. The substrates in these assays are, however, heterogeneous, which complicates mechanistic analyses. Here, we report the first analysis of disulfide bond isomerization in a homogeneous substrate. Our substrate is based on tachyplesin I, a 17-mer peptide that folds into a _-hairpin stabilized by two disulfide bonds. We describe the chemical synthesis of a variant of tachyplesin I in which its two disulfide bonds are in a nonnative state and side chains near its N-and C-terminus contain a fluorescence donor (tryptophan) and acceptor (N_-dansyllysine). Fluorescence resonance energy transfer from 280 to 465 nm increases by 28-fold upon isomerization of the disulfide bonds into their native state (which has a lower E°_ = -0.313 V than does PDI). We use this continuous assay to analyze catalysis by wild-type human PDI and a variant in which the C-terminal cysteine residue within each Cys—Gly—His—Cys active site is replaced with alanine. We find that wild-type PDI catalyzes the isomerization of the substrate with kcat/KM = 1.7 _ 105 M–1M s–1, which is the largest value yet reported for catalysis of disulfide bond isomerization. The variant, which is a poor catalyst of disulfide bond reduction and dithiol oxidation, retains virtually all of the activity of wild-type PDI in catalysis of disulfide bond isomerization. Thus, the C-terminal cysteine residues play an insignificant role in the isomerization of the disulfide bonds in nonnative tachyplesin I. We conclude that

  20. Catalysis of protein disulfide bond isomerization in a homogeneous substrate.

    Science.gov (United States)

    Kersteen, Elizabeth A; Barrows, Seth R; Raines, Ronald T

    2005-09-13

    Protein disulfide isomerase (PDI) catalyzes the rearrangement of nonnative disulfide bonds in the endoplasmic reticulum of eukaryotic cells, a process that often limits the rate at which polypeptide chains fold into a native protein conformation. The mechanism of the reaction catalyzed by PDI is unclear. In assays involving protein substrates, the reaction appears to involve the complete reduction of some or all of its nonnative disulfide bonds followed by oxidation of the resulting dithiols. The substrates in these assays are, however, heterogeneous, which complicates mechanistic analyses. Here, we report the first analysis of disulfide bond isomerization in a homogeneous substrate. Our substrate is based on tachyplesin I, a 17-mer peptide that folds into a beta hairpin stabilized by two disulfide bonds. We describe the chemical synthesis of a variant of tachyplesin I in which its two disulfide bonds are in a nonnative state and side chains near its N and C terminus contain a fluorescence donor (tryptophan) and acceptor (N(epsilon)-dansyllysine). Fluorescence resonance energy transfer from 280 to 465 nm increases by 28-fold upon isomerization of the disulfide bonds into their native state (which has a lower E(o') = -0.313 V than does PDI). We use this continuous assay to analyze catalysis by wild-type human PDI and a variant in which the C-terminal cysteine residue within each Cys-Gly-His-Cys active site is replaced with alanine. We find that wild-type PDI catalyzes the isomerization of the substrate with kcat/K(M) = 1.7 x 10(5) M(-1) s(-1), which is the largest value yet reported for catalysis of disulfide bond isomerization. The variant, which is a poor catalyst of disulfide bond reduction and dithiol oxidation, retains virtually all of the activity of wild-type PDI in catalysis of disulfide bond isomerization. Thus, the C-terminal cysteine residues play an insignificant role in the isomerization of the disulfide bonds in nonnative tachyplesin I. We conclude

  1. The chemistry of dimethacrylate-styrene networks, and, Development of flame retardant, halogen-free fiber reinforced vinyl ester composites

    Science.gov (United States)

    Rosario, Astrid Christa

    One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is vinyl ester resin. Vinyl ester resin is comprised of low molecular weight poly(hydroxyether) oligomers with methacrylate endgroups diluted with styrene monomer. The methacrylate endgroups cure with styrene via free radical copolymerization to yield thermoset networks. The copolymerization behavior of these networks was monitored by Fourier Transform Infrared Spectroscopy (FTIR) at various cure conditions. Reactions of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1 ) were followed independently. Oligomers possessing number average molecular weights of 700 g/mole were studied with systematically increasing levels of styrene. The Mortimer-Tidwell reactivity ratios indicated that at low conversion more styrene was incorporated into the network at lower cure temperatures. The experimental vinyl ester-styrene network compositions deviated significantly from those predicted by the Meyer-Lowry integrated copolymer equation at higher conversion, implying that the reactivity ratios for these networks may change with conversion. The kinetic data were used to provide additional insight into the physical and mechanical properties of these materials. In addition to establishing the copolymerization kinetics of these materials, the development of halogen free fiber reinforced vinyl ester composites exhibiting good flame properties was of interest. Flame retardant vinyl ester resins are used by many industries for applications requiring good thermal resistance. The current flame-retardant technology is dependent on brominated vinyl esters, which generate high levels of smoke and carbon monoxide. A series of halogen free binder systems has been developed and dispersed in the vinyl ester to improve flame retardance. The binder approach enables the vinyl ester resin to maintain its low

  2. Acrylic mechanical bond tests

    Energy Technology Data Exchange (ETDEWEB)

    Wouters, J.M.; Doe, P.J.

    1991-02-01

    The tensile strength of bonded acrylic is tested as a function of bond joint thickness. 0.125 in. thick bond joints were found to posses the maximum strength while the acceptable range of joints varied from 0.063 in. to almost 0.25 in. Such joints are used in the Sudbury Neutrino Observatory.

  3. Bond percolation in films

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1988-04-01

    Bond percolation in films with simple cubic structure is considered. It is assumed that the probability of a bond being present between nearest-neighbor sites depends on the distances to surfaces. Based on the relation between the Potts model and the bond percolation model, and using the mean-field approximation, the phase diagram and profiles of the percolation probability have been obtained.

  4. Chemical bond fundamental aspects of chemical bonding

    CERN Document Server

    Frenking, Gernot

    2014-01-01

    This is the perfect complement to ""Chemical Bonding - Across the Periodic Table"" by the same editors, who are two of the top scientists working on this topic, each with extensive experience and important connections within the community. The resulting book is a unique overview of the different approaches used for describing a chemical bond, including molecular-orbital based, valence-bond based, ELF, AIM and density-functional based methods. It takes into account the many developments that have taken place in the field over the past few decades due to the rapid advances in quantum chemica

  5. Optimization of Alkali Catalyzed Transesterification of Safflower Oil for Production of Biodiesel

    Directory of Open Access Journals (Sweden)

    M. C. Math

    2016-01-01

    Full Text Available The Central Composite Design is used for the optimization of alkaline catalyzed transesterification parameters such as methanol quantity, catalytic concentration, and rotational speed by keeping the temperature and reaction time constant. The Central Composite Design method is employed to get the maximum safflower oil methyl ester yield. The combined effects of catalyst concentration, rotational speed, and molar ratio of alcohol to oil were investigated and optimized using response surface methodology. A statistical model has predicted the maximum yield of safflower oil methyl ester (94.69% volume of oil parameters such as catalyst concentration (0.6 grams, methanol amount (30 mL, rotational speed (600 rpm, and keeping constant reaction temperature (55°C to 65°C and reaction time (60 minutes. Experimental maximum yield of 91.66% was obtained at above parameters. XLSTAT is used to generate a linear model to predict the methyl ester yield as a function of methanol quantity, catalyst concentration, and rotational speed by keeping constant reaction temperature (55°C to 65°C and reaction time (60 minutes. MINITAB is used to draw the 3D response surface plot and 2D contour plot to predict the maximum biodiesel yield.

  6. Lipase-catalyzed kinetic resolution of (±)-1-(2-furyl) ethanol in nonaqueous media.

    Science.gov (United States)

    Devendran, Saravanan; Yadav, Ganapati D

    2014-06-01

    S-1-(2-Furyl) ethanol serves as an important chiral building block for the preparation of various natural products, fine chemicals, and is widely used in the chemical and pharmaceutical industries. In this work, lipase-catalyzed kinetic resolution of (R/S)-1-(2-furyl) ethanol using different acyl donors was investigated. Vinyl esters are good acyl donors vis-à-vis alkyl esters for kinetic resolution. Among them, vinyl acetate was found to be the best acyl donor. Different immobilized lipases such as Rhizomucor miehei lipase, Thermomyces lanuginosus lipase, and Candida antarctica lipase B were evaluated for this reaction, among which C. antarctica lipase B, immobilized on acrylic resin (Novozym 435), was found to be the best catalyst in n-heptane as solvent. The effect of various parameters was studied in a systematic manner. Maximum conversion of 47% and enantiomeric excess of the substrate (ees ) of 89% were obtained in 2 h using 5 mg of enzyme loading with an equimolar ratio of alcohol to vinyl acetate at 60 °C at a speed of 300 rpm in a batch reactor. From the analysis of progress curve and initial rate data, it was concluded that the reaction followed the ordered bi-bi mechanism with dead-end ester inhibition. Kinetic parameters were obtained by using nonlinear regression. This process is more economical, green, and easily scalable than the chemical processes.

  7. Ruthenium-catalyzed α-(hetero)arylation of saturated cyclic amines: reaction scope and mechanism.

    Science.gov (United States)

    Peschiulli, Aldo; Smout, Veerle; Storr, Thomas E; Mitchell, Emily A; Eliáš, Zdeněk; Herrebout, Wouter; Berthelot, Didier; Meerpoel, Lieven; Maes, Bert U W

    2013-07-29

    Transition-metal-catalyzed sp(3) C-H activation has emerged as a powerful approach to functionalize saturated cyclic amines. Our group recently disclosed a direct catalytic arylation reaction of piperidines at the α position to the nitrogen atom. 1-(Pyridin-2-yl)piperidine could be smoothly α-arylated if treated with an arylboronic ester in the presence of a catalytic amount of [Ru3(CO)12] and one equivalent of 3-ethyl-3-pentanol. A systematic study on the substrate and reagent scope of this transformation is disclosed in this paper. The effect of substitution on both the piperidine ring and the arylboronic ester has been investigated. Smaller (pyrrolidine) and larger (azepane) saturated ring systems, as well as benzoannulated derivatives, were found to be compatible substrates with the α-arylation protocol. The successful use of a variety of heteroarylboronic esters as coupling partners further proved the power of this direct functionalization method. Mechanistic studies have allowed for a better understanding of the catalytic cycle of this remarkable transformation featuring an unprecedented direct transmetalation on a Ru(II)-H species.

  8. Curdlan ester derivatives: synthesis, structure, and properties.

    Science.gov (United States)

    Marubayashi, Hironori; Yukinaka, Kazuyori; Enomoto-Rogers, Yukiko; Takemura, Akio; Iwata, Tadahisa

    2014-03-15

    A series of ester derivatives of curdlan, which is a β-(1 → 3)-D-glucan extracellularly produced by microorganism, with varying alkyl chain lengths (C2-C12) were synthesized by the heterogeneous reaction using trifluoroacetic anhydride. As a result, high-molecular-weight (Mw ≥ 6 × 10(5)) and fully-acylated curdlan was obtained with relatively high yield (>70%). Thermal stability of curdlan was greatly improved by esterification. Crystallization was observed for curdlan esters with C2-C6 side chains. Both Tg (170 → 50 °C) and Tm (290 → 170 °C) of curdlan esters decreased with increasing the side-chain length. By the increase in the side-chain carbon number, curdlan esters showed lower Young's modulus and tensile strength, and larger elongation at break. Thus, material properties of curdlan esters can be controlled by changing the side-chain length. It was found that the increase of the side-chain length resulted in the decrease of crystallinity and the change of crystal structures.

  9. Investigation on the mechanism of aminosilane-mediated bonding of thermoplastics and poly(dimethylsiloxane).

    Science.gov (United States)

    Sunkara, Vijaya; Cho, Yoon-Kyoung

    2012-12-01

    A possible mechanism for the aminosilane-mediated room-temperature (RT) bonding of thermoplastics and poly(dimethylsiloxane) (PDMS) is presented. The plasma-activated thermoplastic or PDMS substrates were modified with alkoxy silanes having different organo functional groups, and their bonding characteristics were studied. Manual peeling tests revealed that strong bonding was realized only when the silane had a free amino group and at least two alkoxy groups on the silicon. Silanization was carried out in both aqueous and anhydrous conditions; bonding occurred readily at RT in the former case, but a longer incubation time or a higher temperature was needed for the latter. The presence of the silane on the surface was confirmed by contact-angle measurements and UV spectrophotometric, attenuated total reflectance infrared spectroscopic (ATR-IR) and X-ray photoelectron spectroscopic (XPS) analyses. In the case where the aminosilane was deposited from aqueous solution, the amino functionality of the silane-catalyzed siloxane bond formation between the silanol on the modified thermoplastic surface and the silanol of the plasma-activated PDMS. In the case of anhydrous phase deposition, the aminosilane first catalyzed the hydrolysis of the ethoxy groups on the silicon, and then, catalyzed the condensation between the silanol groups of both materials. Shelf life tests of the modified thermoplastics showed that the aminosilane was stable over 2 weeks, and that bonding occurred at RT when the substrates were soaked in water before bonding.

  10. Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.

    Science.gov (United States)

    Jain, Siddharth; Sharma, M P

    2010-10-01

    Out of various non-edible oil resources, Jatropha curcas oil (JCO) is considered as future feedstock for biodiesel production in India. Limited work is reported on the kinetics of transesterification of high free fatty acids containing oil. The present study reports the results of kinetic study of two-step acid base catalyzed transesterification process carried out at an optimum temperature of 65 °C and 50 °C for esterification and transesterification respectively under the optimum methanol to oil ratio of 3:7 (v/v), catalyst concentration 1% (w/w) for H₂SO₄ and NaOH. The yield of methyl ester (ME) has been used to study the effect of different parameters. The results indicate that both esterification and transesterification reaction are of first order with reaction rate constant of 0.0031 min⁻¹ and 0.008 min⁻¹ respectively. The maximum yield of 21.2% of ME during esterification and 90.1% from transesterification of pretreated JCO has been obtained.

  11. Lipase catalyzed esterification of glycidol in organic solvents.

    Science.gov (United States)

    Martins, J F; Da Ponte, M N; Barreiros, S

    1993-08-05

    We studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiomeric purity (e. p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35 degrees C. The enzyme exhibited maximum activity at a water content of 13 +/- 2% (w/w). The enantiomeric purity obtained was 83 +/- 2% of (S)-glycidyl butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism.

  12. Synthesis and Crystal Structure of a Sodium Monosulfuron-ester (N-[2'-(4-Methyl)pyrimidinyl]-2-carbomethoxy Benzyl Sulfonylurea Sodium)

    Institute of Scientific and Technical Information of China (English)

    KOU Jun-Jie; LI Zheng-Ming; SONG Hai-Bin

    2006-01-01

    Monosulfuron-ester is a novel sulfonylurea herbicide with ultra-low dosage. Herein sodium monosulfuron-ester was synthesized and its crystal structure was determined by X-ray diffraction method. The title compound belongs to monoclinic, space group P21/c with a = 9.335(5), b = 20.632(12), c = 13.853(8) (A), β = 107.193(9)°, Mr = 487.46, Z = 4, Dc = 1.270 g/cm3, μ = 0.293 mm-1, F(000) = 1015, R = 0.0859 and wR = 0.2633. In the title compound, Na coordinates with N(1), O(1) and O(3) from one monosulfuron-ester molecule, N(4A) and O(5A) from the other monosulfuron-ester molecule and one oxygen atom from DMSO to give six coordination bonds.

  13. Plasticization effect of triacetin on structure and properties of starch ester film.

    Science.gov (United States)

    Zhu, Jie; Li, Xiaoxi; Huang, Chen; Chen, Ling; Li, Lin

    2013-05-15

    The aim of this work was to evaluate the plasticizing effect of triacetin on the structure and properties of starch ester film and further establish the structure-property relationships. The presence of triacetin resulted in multiple structure changes of the film. The mobility of macromolecular chain was increased to form scattered crystallite during the film formation process. The amorphous region was enlarged to contain more triacetin squeezed from crystalline region. The plasticization of triacetin and restriction of crystallite oppositely influenced the mobility of macromolecular chains in different regions. The thermal stability of triacetin changed along with its fluctuant interaction with macromolecules. Comparatively, the enhanced ether bond and the restriction from crystalline regions on the mobility of the amorphous chain consequently improved the thermal stability of the film matrix. The interaction between triacetin and starch ester was essential to film forming but unexpectedly lowered the triacetin stability.

  14. Parallel Synthesis of an Imidazole-4,5-dicarboxamide Library Bearing Amino Acid Esters and Alkanamines

    Directory of Open Access Journals (Sweden)

    Rosanna Solinas

    2008-12-01

    Full Text Available The imidazole-4,5-dicarboxylic acid scaffold is readily derivatized with amino acid esters and alkanamines to afford compounds with intramolecularly hydrogen bonded conformations that mimic substituted purines and therefore are hypothesized to be potential inhibitors of kinases through competitive binding to the ATP site. In this work, a total of 126 dissymmetrically disubstituted imidazole-4,5-dicarboxamides with amino acid ester and alkanamide substituents were prepared by parallel synthesis. The library members were purified by column chromatography on silica gel and the purified compounds characterized by LC-MS with LC detection at 214 nm. A selection of the final compounds was also analyzed by 1H-NMR spectroscopy. The analytically pure final products have been submitted to the Molecular Library Small Molecule Repository (MLSMR for screening in the Molecular Library Screening Center Network (MLSCN as part of the NIH Roadmap.

  15. Native lignin for bonding fiber boards - evaluation of bonding mechanisms in boards made from laccase-treated fibers of beech (Fagus sylvatica)

    DEFF Research Database (Denmark)

    Felby, Claus; Thygesen, Lisbeth Garbrecht; Sanadi, Anand;

    2004-01-01

    The auto-adhesion of beech wood (Fagus sylvatica) fibers can be enhanced by a pretreatment of the fibers with a phenol oxidase enzyme. The mechanism of enzymatic catalyzed bonding is linked to the generation of stable radicals in lignin by oxidation. Fiberboards made from laccase-treated fibers...

  16. In vivo and in vitro antıneoplastic actions of caffeic acid phenethyl ester (CAPE): therapeutic perspectives.

    Science.gov (United States)

    Akyol, Sumeyya; Ozturk, Gulfer; Ginis, Zeynep; Armutcu, Ferah; Yigitoglu, M Ramazan; Akyol, Omer

    2013-01-01

    Cancer prevention and treatment strategies have attracted increasing interest. Caffeic acid phenethyl ester (CAPE), an active component of propolis extract, specifically inhibits NF-κB at μM concentrations and shows ability to stop 5-lipoxygenase-catalyzed oxygenation of linoleic acid and arachidonic acid. Previous studies have demonstrated that CAPE exhibits antioxidant, antiinflammatory, antiproliferative, cytostatic, antiviral, antibacterial, antifungal, and, most improtantly, antineoplastic properties. The primary goal of the present review is to summarize and critically evaluate the current knowledge regarding the anticancer effect of CAPE in different cancer types.

  17. Application conditions for ester cured alkaline phenolic resin sand

    Institute of Scientific and Technical Information of China (English)

    Ren-he Huang; Bao-ping Zhang; Yao-ji Tang

    2016-01-01

    Five organic esters with different curing speeds: propylene carbonate (i.e. high-speed ester A); 1, 4-butyrolactone; glycerol triacetate (i.e. medium-speed ester B); glycerol diacetate; dibasic ester (DBE) (i.e. low-speed ester C), were chosen to react with alkaline phenolic resin to analyze the application conditions of ester cured alkaline phenolic resin. The relationships between the curing performances of the resin (including pH value, gel pH value, gel time of resin solution, heat release rate of the curing reaction and tensile strength of the resin sand) and the amount of added organic ester and curing temperature were investigated. The results indicated the folowing: (1) The optimal added amount of organic ester should be 25wt.%-30wt.% of alkaline phenolic resin and it must be above 20wt.%-50 wt.% of the organic ester hydrolysis amount. (2) High-speed ester A (propylene carbonate) has a higher curing speed than 1, 4-butyrolactone, and they were both used as high-speed esters. Glycerol diacetate is not a high-speed ester in alkaline phenolic resin although it was used as a high-speed ester in ester cured sodium silicate sand; glycerol diacetate and glycerol triacetate can be used as medium-speed esters in alkaline phenolic resin. (3) High-speed ester A, medium-speed ester B (glycerol triacetate) and low-speed ester C (dibasic ester, i.e., DBE) should be used below 15 ºC, 35 ºC and 50 ºC, respectively. High-speed ester A or low-speed ester C should not be used alone but mixed with medium-speed ester B to improve the strength of the resin sand. (4) There should be a suitable solid content (generaly 45wt.%-65wt.% of resin), alkali content (generaly 10wt.%-15wt.% of resin) and viscosity of alkaline phenolic resin (generaly 50-300 mPa·s) in the preparation of alkaline phenolic resin. Finaly, the technique conditions of alkaline phenolic resin preparation and the application principles of organic ester were discussed.

  18. Biodiesel synthesis combining pre-esterification with alkali catalyzed process from rapeseed oil deodorizer distillate

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yun; Wang, Ling; Yan, Yunjun [College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, 430074 (China)

    2009-07-15

    A two-step technique combining pre-esterification catalyzed by cation exchange resin with transesterification catalyzed by base alkali was developed to produce biodiesel from rapeseed oil deodorizer distillate (RDOD). The free fatty acids (FFAs) in the feedstock were converted to methyl esters in the pre-esterification step using a column reactor packed with cation exchange resin. The acid value of oil was reduced from the initial 97.60 mg-KOH g{sup -1} oil to 1.12 mg-KOH g{sup -1} oil under the conditions of cation exchange resin D002 catalyst packed dosage 18 wt.% (based on oil weight), oil to methanol molar ratio 1:9, reaction temperature 60 C, and reaction time 4 h. The biodiesel yield by transesterification was 97.4% in 1.5 h using 0.8 wt.% KOH as catalyst and a molar ratio of oil to methanol 1:4 at 60 C. The properties of RDOD biodiesel production in a packed column reactor followed by KOH catalyzed transesterification were measured up the standards of EN14214 and ASTM6751-03. (author)

  19. Effect of Ozone Produced from Antibody-catalyzed Water Oxidation on Pathogenesis of Atherosclerosis

    Institute of Scientific and Technical Information of China (English)

    Ke-Jun PENG; Yu-Shan HUANG; Li-Na AN; Xiao-Qun HAN; Jing-Ge ZHANG; Qiu-Lin WANG; Jing SUN; Shu-Ren WANG

    2006-01-01

    Recent studies have suggested that antibodies can catalyze the generation of unknown oxidants including hydrogen peroxide (H2O2) and ozone (O3) from singlet oxygen (1O2) and water. This study is aimedto detect the effect of antibody-catalyzed water oxidation on atherosclerosis. Our results showed that both H2O2 and O3 were produced in human leukemia THP- 1 monocytes incubated with human immunoglobulin G and phorbol myristate acetate. In the THP-1 monocytes incubated with human immunoglobulin G, phorbol myristate acetate and low density lipoprotein, the intracellular total cholesterol, free cholesterol, cholesteryl ester and lipid peroxides clearly increased, and a larger number of foam cells were observed by oil red O staining. The accumulation of all intracellular lipids was significantly inhibited by vinylbenzoic acid, and only slightly affected by catalase. These findings suggested that the production of O3, rather than H2O2, might be involved in the pathogenesis of atherosclerosis through the antibody-catalyzed water oxidation pathway.

  20. Identification of the catalytic residues of alpha-amino acid ester hydrolase from Acetobacter turbidans by labeling and site-directed mutagenesis

    NARCIS (Netherlands)

    Polderman - Tijmes, Jolanda j.; Jekel, Peter A.; Jeronimus-Stratingh, CM; Bruins, Andries P.; van der Laan, Jan-Metske; Sonke, Theo; Janssen, Dick B.

    2002-01-01

    The alpha-amino acid ester hydrolase from Acetobacter turbidans ATCC 9325 is capable of hydrolyzing and synthesizing the side chain peptide bond in beta-lactam antibiotics. Data base searches revealed that the enzyme contains an active site serine consensus sequence Gly-X-Ser-Tyr-X-Gly that is also