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Sample records for acid catalyzed reaction

  1. Kinetic study of free fatty acid esterification reaction catalyzed by recoverable and reusable hydrochloric acid.

    PubMed

    Su, Chia-Hung

    2013-02-01

    The catalytic performance and recoverability of several homogeneous acid catalysts (hydrochloric, sulfuric, and nitric acids) for the esterification of enzyme-hydrolyzed free fatty acid (FFA) and methanol were studied. Although all tested catalysts drove the reaction to a high yield, hydrochloric acid was the only catalyst that could be considerably recovered and reused. The kinetics of the esterification reaction catalyzed by hydrochloric acid was investigated under varying catalyst loading (0.1-1M), reaction temperature (303-343K), and methanol/FFA molar ratio (1:1-20:1). In addition, a pseudo-homogeneous kinetic model incorporating the above factors was developed. A good agreement (r(2)=0.98) between the experimental and calculated data was obtained, thus proving the reliability of the model. Furthermore, the reusability of hydrochloric acid in FFA esterification can be predicted by the developed model. The recoverable hydrochloric acid achieved high yields of FFA esterification within five times of reuse.

  2. Cascade dearomatization of N-substituted tryptophols via Lewis acid-catalyzed Michael reactions.

    PubMed

    Liu, Chuan; Zhang, Wei; Dai, Li-Xin; You, Shu-Li

    2012-09-21

    Lewis acid-catalyzed cascade dearomatization of N-substituted tryptophols via Michael addition reaction was developed. The generality of the method has been demonstrated by the synthesis of versatile furoindoline derivatives with a quaternary carbon center in good yields.

  3. Enantioselective aldol reaction between isatins and cyclohexanone catalyzed by amino acid sulphonamides.

    PubMed

    Wang, Jun; Liu, Qi; Hao, Qing; Sun, Yanhua; Luo, Yiming; Yang, Hua

    2015-04-01

    Sulphonamides derived from primary α-amino acid were successfully applied to catalyze the aldol reaction between isatin and cyclohexanone under neat conditions. More interestingly, molecular sieves, as privileged additives, were found to play a vital role in achieving high enantioselectivity. Consequently, high yields (up to 99%) along with good enantioselectivities (up to 92% ee) and diastereoselectivities (up to 95:5 dr) were obtained. In addition, this reaction was also conveniently scaled up, demonstrating the applicability of this protocol.

  4. Chiral phosphoric acid catalyzed enantioselective 1,3-dipolar cycloaddition reaction of azlactones.

    PubMed

    Zhang, Zhenhua; Sun, Wangsheng; Zhu, Gongming; Yang, Junxian; Zhang, Ming; Hong, Liang; Wang, Rui

    2016-01-25

    The first chiral phosphoric acid catalyzed highly diastereo- and enantioselective 1,3-dipolar cycloaddition reaction of azlactones and methyleneindolinones was disclosed. By using a BINOL-derived chiral phosphoric acid as the catalyst, azlactones were activated as chiral anti N-protonated 1,3-dipoles to react with methyleneindolinones to yield biologically important 3,3'-pyrrolidonyl spirooxindole scaffolds in high yields, with good-to-excellent diastereo- and enantioselectivity.

  5. Water-catalyzed gas-phase reaction of formic acid with hydroxyl radical: A computational investigation

    NASA Astrophysics Data System (ADS)

    Luo, Yi; Maeda, Satoshi; Ohno, Koichi

    2009-02-01

    The reaction of formic acid with hydroxyl radical, which is considered to be relevant to atmospheric chemistry, has been extensively studied. A water-catalyzed process of this reaction is computationally studied here for the first time. The scaled hypersphere search method was used for global exploration of pre-reaction complexes. Calculations were performed at high level of theory, such as CCSD(T)/cc-pVTZ//B3LYP/6-311+G(2df, 2p) and CCSD(T)/cc-pVTZ//MP2/aug-cc-pVDZ. It is found that the water-catalyzed process of this reaction is more kinetically favorable than its non-catalytic process. Such catalytic process may also be of interest for atmospheric chemistry, like the non-catalytic one.

  6. Lewis acid catalyzed cascade reaction to carbazoles and naphthalenes via dehydrative [3 + 3]-annulation.

    PubMed

    Wang, Shaoyin; Chai, Zhuo; Wei, Yun; Zhu, Xiancui; Zhou, Shuangliu; Wang, Shaowu

    2014-07-03

    A novel Lewis acid catalyzed dehydrative [3 + 3]-annulation of readily available benzylic alcohols and propargylic alcohols was developed to give polysubstituted carbazoles and naphthalenes in moderate to good yields with water as the only byproduct. The reaction was presumed to proceed via a cascade process involving Friedel-Crafts-type allenylation, 1,5-hydride shift, 6π-eletrocyclization, and Wagner-Meerwein rearrangement.

  7. Isotope Effects and Mechanism of the Asymmetric BOROX Brønsted Acid Catalyzed Aziridination Reaction

    PubMed Central

    Vetticatt, Mathew J.; Desai, Aman A.; Wulff, William D.

    2013-01-01

    The mechanism of the chiral VANOL-BOROX Brønsted acid catalyzed aziridination reaction of imines and ethyldiazoacetate has been studied using a combination of experimental kinetic isotope effects and theoretical calculations. A stepwise mechanism where reversible formation of a diazonium ion intermediate precedes rate-limiting ring-closure to form the cis-aziridine is implicated. A revised model for the origin of enantio- and diastereoselectivity is proposed based on relative energies of the ring closing transition structures. PMID:23687986

  8. Synthesis of 2-monoacylglycerols and structured triacylglycerols rich in polyunsaturated fatty acids by enzyme catalyzed reactions.

    PubMed

    Rodríguez, Alicia; Esteban, Luis; Martín, Lorena; Jiménez, María José; Hita, Estrella; Castillo, Beatriz; González, Pedro A; Robles, Alfonso

    2012-08-10

    This paper studies the synthesis of structured triacylglycerols (STAGs) by a four-step process: (i) obtaining 2-monoacylglycerols (2-MAGs) by alcoholysis of cod liver oil with several alcohols, catalyzed by lipases Novozym 435, from Candida antartica and DF, from Rhizopus oryzae, (ii) purification of 2-MAGs, (iii) formation of STAGs by esterification of 2-MAGs with caprylic acid catalyzed by lipase DF, from R. oryzae, and (iv) purification of these STAGs. For the alcoholysis of cod liver oil, absolute ethanol, ethanol 96% (v/v) and 1-butanol were compared; the conditions with ethanol 96% were then optimized and 2-MAG yields of around 54-57% were attained using Novozym 435. In these 2-MAGs, DHA accounted for 24-31% of total fatty acids. In the operational conditions this lipase maintained a stable level of activity over at least 11 uses. These results were compared with those obtained with lipase DF, which deactivated after only three uses. The alcoholysis of cod liver oil and ethanol 96% catalyzed by Novozym 435 was scaled up by multiplying the reactant amounts 100-fold and maintaining the intensity of treatment constant (IOT=3g lipase h/g oil). In these conditions, the 2-MAG yield attained was about 67%; these 2-MAGs contained 36.6% DHA. The synthesized 2-MAGs were separated and purified from the alcoholysis reaction products by solvent extraction using solvents of low toxicity (ethanol and hexane); 2-MAG recovery yield and purity of the target product were approximately 96.4% and 83.9%, respectively. These 2-MAGs were transformed to STAGs using the optimal conditions obtained in a previous work. After synthesis and purification, 93% pure STAGs were obtained, containing 38% DHA at sn-2 position and 60% caprylic acid (CA) at sn-1,3 positions (of total fatty acids at these positions), i.e. the major TAG is the STAG with the structure CA-DHA-CA.

  9. Palladium-atom catalyzed formic acid decomposition and the switch of reaction mechanism with temperature.

    PubMed

    He, Nan; Li, Zhen Hua

    2016-04-21

    Formic acid decomposition (FAD) reaction has been an innovative way for hydrogen energy. Noble metal catalysts, especially palladium-containing nanoparticles, supported or unsupported, perform well in this reaction. Herein, we considered the simplest model, wherein one Pd atom is used as the FAD catalyst. With high-level theoretical calculations of CCSD(T)/CBS quality, we investigated all possible FAD pathways. The results show that FAD catalyzed by one Pd atom follows a different mechanism compared with that catalyzed by surfaces or larger clusters. At the initial stage of the reaction, FAD follows a dehydration route and is quickly poisoned by CO due to the formation of very stable PdCO. PdCO then becomes the actual catalyst for FAD at temperatures approximately below 1050 K. Beyond 1050 K, there is a switch of catalyst from PdCO to Pd atom. The results also show that dehydration is always favoured over dehydrogenation on either the Pd-atom or PdCO catalyst. On the Pd-atom catalyst, neither dehydrogenation nor dehydration follows the formate mechanism. In contrast, on the PdCO catalyst, dehydrogenation follows the formate mechanism, whereas dehydration does not. We also systematically investigated the performance of 24 density functional theory methods. We found that the performance of the double hybrid mPW2PLYP functional is the best, followed by the B3LYP, B3PW91, N12SX, M11, and B2PLYP functionals.

  10. Mechanism of arylboronic acid-catalyzed amidation reaction between carboxylic acids and amines.

    PubMed

    Wang, Chen; Yu, Hai-Zhu; Fu, Yao; Guo, Qing-Xiang

    2013-04-07

    Arylboronic acids were found to be efficient catalysts for the amidation reactions between carboxylic acids and amines. Theoretical calculations have been carried out to investigate the mechanism of this catalytic process. It is found that the formation of the acyloxyboronic acid intermediates from the carboxylic acid and the arylboronic acid is kinetically facile but thermodynamically unfavorable. Removal of water (as experimentally accomplished by using molecular sieves) is therefore essential for overall transformation. Subsequently C-N bond formation between the acyloxyboronic acid intermediates and the amine occurs readily to generate the desired amide product. The cleavage of the C-O bond of the tetracoordinate acyl boronate intermediates is the rate-determining step in this process. Our analysis indicates that the mono(acyloxy)boronic acid is the key intermediate. The high catalytic activity of ortho-iodophenylboronic acid is attributed to the steric effect as well as the orbital interaction between the iodine atom and the boron atom.

  11. A preliminary investigation of acid-catalyzed polymerization reactions of shale oil distillates

    SciTech Connect

    Netzel, D.A.

    1991-04-01

    Sinor (1989) reported that a major specialty market may exist for shale oil as an asphalt blending material. Shale oil can be converted to an asphalt blending material by acid catalyzed condensation and polymerization reactions of the many molecular species comprising the composition of shale oil. To simplify the investigation, crude shale oil was separated by distillation into three distillates of different hydrocarbon and heteroaromatic compositions. These distillates were then treated with two different types of acids to determine the effect of acid type on the end products. Three western shale oil distillates, a naphtha, a middle distillate, and an atmospheric gas oil, were reacted with anhydrous AlCl{sub 3} and 85% H{sub 2}SO{sub 4} under low-severity conditions. At relatively low temperatures, little change in the hydrocarbon composition was noted for the AlCl{sub 3} reactions. AlCl{sub 3}{center_dot} (a polymerized product and/or complex) was formed. However, it is assumed that the sludge was mainly the result of heteroaromatic-AlCl{sub 3} reactions.

  12. A preliminary investigation of acid-catalyzed polymerization reactions of shale oil distillates

    SciTech Connect

    Netzel, D.A.

    1991-04-01

    Sinor (1989) reported that a major specialty market may exist for shale oil as an asphalt blending material. Shale oil can be converted to an asphalt blending material by acid catalyzed condensation and polymerization reactions of the many molecular species comprising the composition of shale oil. To simplify the investigation, crude shale oil was separated by distillation into three distillates of different hydrocarbon and heteroaromatic compositions. These distillates were then treated with two different types of acids to determine the effect of acid type on the end products. Three western shale oil distillates, a naphtha, a middle distillate, and an atmospheric gas oil, were reacted with anhydrous AlCl{sub 3} and 85% H{sub 2}SO{sub 4} under low-severity conditions. At relatively low temperatures, little change in the hydrocarbon composition was noted for the AlCl{sub 3} reactions. AlCl{sub 3}{center dot} (a polymerized product and/or complex) was formed. However, it is assumed that the sludge was mainly the result of heteroaromatic-AlCl{sub 3} reactions.

  13. REACTION MECHANISMS OF 15-HYDROPEROXYEICOSATETRAENOIC ACID CATALYZED BY HUMAN PROSTACYCLIN AND THROMBOXANE SYNTHASES

    PubMed Central

    Yeh, Hui-Chun; Tsai, Ah-Lim; Wang, Lee-Ho

    2007-01-01

    Prostacyclin synthase (PGIS) and thromboxane synthase (TXAS) are atypical cytochrome P450s. They do not require NADPH or dioxygen for isomerization of prostaglandin H2 (PGH2) to produce prostacyclin (PGI2) and thromboxane A2 (TXA2). PGI2 and TXA2 have opposing actions on platelet aggregation and blood vessel tone. In this report, we use a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), to explore the active site characteristics of PGIS and TXAS. The two enzymes transformed 15-HPETE not only into 13-hydroxy-14,15-epoxy-5,8,11-eicosatrienoic acid (13-OH-14,15-EET), like many microsomal P450s, but also to 15-ketoeicosatetraenoic acid (15-KETE) and 15-hydroxyeicosatetraenoic acid (15-HETE). 13-OH-14,15-EET and 15-KETE result from homolytic cleavage of the O–O bond, whereas 15-HETE results from heterolytic cleavage, a common peroxidase pathway. About 80% of 15-HPETE was homolytically cleaved by PGIS and 60% was homolytically cleaved by TXAS. The Vmax of homolytic cleavage is 3.5-fold faster than heterolytic cleavage for PGIS-catalyzed reactions (1100 min−1 vs. 320 min−1) and 1.4-fold faster for TXAS (170 min−1 vs. 120 min−1). Similar KM values for homolytic and heterolytic cleavages were found for PGIS (∼60 μM 15-HPETE) and TXAS (∼80 μM 15-HPETE), making PGIS a more efficient catalyst for the 15-HPETE reaction. PMID:17459323

  14. Role of Lewis acid additives in a palladium catalyzed directed C-H functionalization reaction of benzohydroxamic acid to isoxazolone.

    PubMed

    Athira, C; Sunoj, Raghavan B

    2016-12-20

    Metallic salts as well as protic additives are widely employed in transition metal catalyzed C-H bond functionalization reactions to improve the efficiency of catalytic protocols. In one such example, ZnCl2 and pivalic acid are used as additives in a palladium catalyzed synthesis of isoxazolone from a readily available benzohydroxamic acid under one pot conditions. In this article, we present some important mechanistic insights into the role of ZnCl2 and pivalic acid, gained by using density functional theory (M06) computations. Two interesting modes of action of ZnCl2 are identified in various catalytic steps involved in the formation of isoxazolone. The conventional Lewis acid coordination wherein zinc chloride (ZnCl2·(DMA)) binds to the carbonyl group is found to be more favored in the C-H activation step. However, the participation of a hetero-bimetallic Pd-Zn species is preferred in reductive elimination leading to Caryl-N bond formation. Pivalic acid helps in relay proton transfer in C-H bond activation through a cyclometallation deprotonation (CMD) process. The explicit inclusion of ZnCl2 and solvent N,N-dimethyl acetamide (DMA) stabilizes the transition state and also helps reduce the activation barrier for the C-H bond activation step. The electronic communication between the two metal species is playing a crucial role in stabilizing the Caryl-N bond formation transition state through a Pd-Zn hetero-bimetallic interaction.

  15. Lewis acid catalyzed cascade reaction of 3-(2-benzenesulfonamide)propargylic alcohols to spiro[indene-benzosultam]s.

    PubMed

    Sun, Lang; Zhu, Yuanxun; Wang, Jing; Lu, Ping; Wang, Yanguang

    2015-01-16

    A highly efficient and convenient construction of the spiro[indene-benzosultam] skeleton from propargylic alcohols has been developed. The reaction proceeded in a Lewis acid catalyzed cascade process, including the trapping of allene carbocation with sulfonamide, electrophilic cyclization, and intramolecular Friedel-Crafts alkylation. In the presence of NIS or NBS, iodo/bromo-substituted spiro[indene-benzosultam]s could be prepared in excellent yields.

  16. Synthesis of phosphatidylcholine with defined fatty acid in the sn-1 position by lipase-catalyzed esterification and transesterification reaction.

    PubMed

    Adlercreutz, Dietlind; Budde, Heike; Wehtje, Ernst

    2002-05-20

    The incorporation of caproic acid in the sn-1 position of phosphatidylcholine (PC) catalyzed by lipase from Rhizopus oryzae was investigated in a water activity-controlled organic medium. The reaction was carried out either as esterification or transesterification. A comparison between these two reaction modes was made with regard to product yield, product purity, reaction time, and byproduct formation as a consequence of acyl migration. The yield in the esterification and transesterification reaction was the same under identical conditions. The highest yield (78%) was obtained at a water activity (a(w)) of 0.11 and a caproic acid concentration of 0.8 M. The reaction time was shorter in the esterification reaction than in the transesterification reaction. The difference in reaction time was especially pronounced at low water activities and high fatty acid concentrations. The loss in yield due to acyl migration and consequent enzymatic side reactions was around 16% under a wide range of conditions. The incorporation of a fatty acid in the sn-1 position of PC proved to be thermodynamically much more favorable than the incorporation of a fatty acid in the sn-2 position.

  17. Silylium ion-catalyzed challenging Diels-Alder reactions: the danger of hidden proton catalysis with strong Lewis acids.

    PubMed

    Schmidt, Ruth K; Müther, Kristine; Mück-Lichtenfeld, Christian; Grimme, Stefan; Oestreich, Martin

    2012-03-07

    The pronounced Lewis acidity of tricoordinate silicon cations brings about unusual reactivity in Lewis acid catalysis. The downside of catalysis with strong Lewis acids is, though, that these do have the potential to mediate the formation of protons by various mechanisms, and the thus released Brønsted acid might even outcompete the Lewis acid as the true catalyst. That is an often ignored point. One way of eliminating a hidden proton-catalyzed pathway is to add a proton scavenger. The low-temperature Diels-Alder reactions catalyzed by our ferrocene-stabilized silicon cation are such a case where the possibility of proton catalysis must be meticulously examined. Addition of the common hindered base 2,6-di-tert-butylpyridine resulted, however, in slow decomposition along with formation of the corresponding pyridinium ion. Quantitative deprotonation of the silicon cation was observed with more basic (Mes)(3)P to yield the phosphonium ion. A deuterium-labeling experiment verified that the proton is abstracted from the ferrocene backbone. A reasonable mechanism of the proton formation is proposed on the basis of quantum-chemical calculations. This is, admittedly, a particular case but suggests that the use of proton scavengers must be carefully scrutinized, as proton formation might be provoked rather than prevented. Proton-catalyzed Diels-Alder reactions are not well-documented in the literature, and a representative survey employing TfOH is included here. The outcome of these catalyses is compared with our silylium ion-catalyzed Diels-Alder reactions, thereby clearly corroborating that hidden Brønsted acid catalysis is not operating with our Lewis acid. Several simple-looking but challenging Diels-Alder reactions with exceptionally rare dienophile/enophile combinations are reported. Another indication is obtained from the chemoselectivity of the catalyses. The silylium ion-catalyzed Diels-Alder reaction is general with regard to the oxidation level of the

  18. Organic acids tunably catalyze carbonic acid decomposition.

    PubMed

    Kumar, Manoj; Busch, Daryle H; Subramaniam, Bala; Thompson, Ward H

    2014-07-10

    Density functional theory calculations predict that the gas-phase decomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transfer reaction, can be catalyzed by a monocarboxylic acid or a dicarboxylic acid, including carbonic acid itself. Carboxylic acids are found to be more effective catalysts than water. Among the carboxylic acids, the monocarboxylic acids outperform the dicarboxylic ones wherein the presence of an intramolecular hydrogen bond hampers the hydrogen transfer. Further, the calculations reveal a direct correlation between the catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzed hydrogen-transfer reactions. The catalytic efficacy of a dicarboxylic acid, on the other hand, is significantly affected by the strength of an intramolecular hydrogen bond. Transition-state theory estimates indicate that effective rate constants for the acid-catalyzed decomposition are four orders-of-magnitude larger than those for the water-catalyzed reaction. These results offer new insights into the determinants of general acid catalysis with potentially broad implications.

  19. Reactivity of Cations and Zwitterions Formed in Photochemical and Acid-Catalyzed Reactions from m-Hydroxycycloalkyl-Substituted Phenol Derivatives.

    PubMed

    Cindro, Nikola; Antol, Ivana; Mlinarić-Majerski, Kata; Halasz, Ivan; Wan, Peter; Basarić, Nikola

    2015-12-18

    Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis, which could ultimately drive the excited-state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations, which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, upon photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol, coupled with elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit reactivity different from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less nonclassical character than the corresponding cation, so it does not undergo 1,2-shift of the carbon atom, as observed in the acid-catalyzed reaction.

  20. Bidentate Lewis Acid Catalyzed Domino Diels-Alder Reaction of Phthalazine for the Synthesis of Bridged Oligocyclic Tetrahydronaphthalenes.

    PubMed

    Schweighauser, Luca; Bodoky, Ina; Kessler, Simon N; Häussinger, Daniel; Donsbach, Carsten; Wegner, Hermann A

    2016-03-18

    A domino process consisting of an inverse and a normal electron-demand Diels-Alder reaction is presented for the formation of bridged tri- and tetracyclic 1,2,3,4-tetrahydronaphthalenes catalyzed by a bidentate Lewis acid. The products were synthesized in a one-pot reaction from commercially available starting materials and contain up to six stereogenic centers. The tetrahydronaphthalenes were isolated as single diastereomers and are derivatives of phenylethylamine, which is well-known as a scaffold of amphetamine or dopamine.

  1. Catalyzed asymmetric aryl transfer reactions to aldehydes with boronic acids as aryl source.

    PubMed

    Bolm, Carsten; Rudolph, Jens

    2002-12-18

    Chiral diaryl methanols are important intermediates for the synthesis of biologically active compounds. Here, we describe a flexible method for their catalyzed asymmetric synthesis from readily available starting materials. Noteworthy is the fact that with a single catalyst both enantiomers of the product are accessible simply by choosing the appropriate combination of aryl boronic acid or aldehyde as aryl donor and acceptor, respectively. The catalysis with a planar-chiral ferrocene is easy to perform and yields a broad range of products with excellent enantioselectivities (up to 98% ee).

  2. Acid-, base-, and lewis-acid-catalyzed heterolysis of methoxide from an alpha-hydroxy-beta-methoxy radical: models for reactions catalyzed by coenzyme B12-dependent diol dehydratase.

    PubMed

    Xu, Libin; Newcomb, Martin

    2005-11-11

    [Reaction: see text].A model for glycol radicals was employed in laser flash photolysis kinetic studies of catalysis of the fragmentation of a methoxy group adjacent to an alpha-hydroxy radical center. Photolysis of a phenylselenylmethylcyclopropane precursor gave a cyclopropylcarbinyl radical that rapidly ring opened to the target alpha-hydroxy-beta-methoxy radical (3). Heterolysis of the methoxy group in 3 gave an enolyl radical (4a) or an enol ether radical cation (4b), depending upon pH. Radicals 4 contain a 2,2-diphenylcyclopropane reporter group, and they rapidly opened to give UV-observable diphenylalkyl radicals as the final products. No heterolysis was observed for radical 3 under neutral conditions. In basic aqueous acetonitrile solutions, specific base catalysis of the heterolysis was observed; the pK(a) of radical 3 was determined to be 12.5 from kinetic titration plots, and the ketyl radical formed by deprotonation of 3 eliminated methoxide with a rate constant of 5 x 10(7) s(-1). In the presence of carboxylic acids in acetonitrile solutions, radical 3 eliminated methanol in a general acid-catalyzed reaction, and rate constants for protonation of the methoxy group in 3 by several acids were measured. Radical 3 also reacted by fragmentation of methoxide in Lewis-acid-catalyzed heterolysis reactions; ZnBr2, Sc(OTf)3, and BF3 were found to be efficient catalysts. Catalytic rate constants for the heterolysis reactions were in the range of 3 x 10(4) to 2 x 10(6) s(-1). The Lewis-acid-catalyzed heterolysis reactions are fast enough for kinetic competence in coenzyme B12 dependent enzyme-catalyzed reactions of glycols, and Lewis-acid-catalyzed cleavages of beta-ethers in radicals might be applied in synthetic reactions.

  3. Envisioning an enzymatic Diels-Alder reaction by in situ acid-base catalyzed diene generation.

    PubMed

    Linder, Mats; Johansson, Adam Johannes; Manta, Bianca; Olsson, Philip; Brinck, Tore

    2012-06-07

    We present and evaluate a new and potentially efficient route for enzyme-mediated Diels-Alder reactions, utilizing general acid-base catalysis. The viability of employing the active site of ketosteroid isomerase is demonstrated.

  4. Brønsted acid catalyzed asymmetric aldol reaction: a complementary approach to enamine catalysis.

    PubMed

    Pousse, Guillaume; Le Cavelier, Fabien; Humphreys, Luke; Rouden, Jacques; Blanchet, Jérôme

    2010-08-20

    A syn-enantioselective aldol reaction has been developed using Brønsted acid catalysis based on H(8)-BINOL-derived phosphoric acids. This method affords an efficient synthesis of various beta-hydroxy ketones, some of which could not be synthesized using enamine organocatalysis.

  5. Mechanism of an Organoboron-Catalyzed Domino Reaction: Kinetic and Computational Studies of Borinic Acid-Catalyzed Regioselective Chloroacylation of 2,3-Epoxy Alcohols.

    PubMed

    Garrett, Graham E; Tanveer, Kashif; Taylor, Mark S

    2017-01-20

    A mechanistic study of the borinic acid-catalyzed chloroacylation of 2,3-epoxy alcohols is presented. In this unusual mode of catalysis, the borinic acid activates the substrate toward sequential reactions with a nucleophile (epoxide ring-opening by chloride) and an electrophile (O-acylation of the resulting alkoxide). Reaction progress kinetic analysis of data obtained through in situ FTIR spectroscopy is consistent with a mechanism involving turnover-limiting acylation of a chlorohydrin-derived borinic ester. This proposal is further supported by investigations of the effects of aroyl chloride substitution on reaction rate. The kinetics experiments also shed light on the effects of chloride concentration on reaction rate and indicate that the catalyst is subject to inhibition by the product of the chloroacylation reaction. Computational modeling is employed to gain insight into the effects of the organoboron catalyst on the regioselectivities of the epoxide ring-opening and acylation steps. The density functional theory calculations provide a plausible pathway for selective chlorinolysis at C-3 and benzoylation at O-1, as is observed experimentally.

  6. Acid-catalyzed Reactions in Model Secondary Organic Aerosol (SOA): Insights using Desorption-electrospray Ionization (DESI) Tandem Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Fiddler, M. N.; Cooks, R. G.; Shepson, P.

    2008-12-01

    Atmospheric aerosols are presently little understood in terms of their sources, formation, and effect on climate forcing, despite their significant impacts on climate change and respiratory health. Secondary organic aerosols (SOA), which were thought to arise entirely from simple gas-particle partitioning, have recently been found to contain oligomeric species which result from the condensed-phase reactions of volatile organic compounds (VOCs). The non-methane VOC with the greatest emission flux, isoprene, is known to produce aerosols through chemistry involving its oxidation products. We selected one of its major oxidation product, methacrolein, to assess its role in oligomeric SOA formation in response to the acidic conditions found in cloud water. Since it has been found that acidified aerosol produces oligomeric species with greater molecular weight and yield, acid-catalyzed oligomerization is likely a significant process in the formation of SOA. Aqueous solutions of methacrolein were acidified with sulfuric acid, and studied using linear ion trap mass spectrometry (LIT-MS) with a home-built desorption-electrospray ionization (DESI) source. An extremely heterogeneous mixture of products was produced in this system, resulting from hydrolysis, acid- catalyzed oxidation, reduction, and organosulfate formation. Evidence for disproportionation and heterocycle formation are proposed as reaction mechanisms hitherto unrecognized in the production of SOA. The proposed structure and formation mechanism for several species, based upon their MS/MS spectra, will also be presented.

  7. Studies of the Mechanism and Origins of Enantioselectivity for the Chiral Phosphoric Acid-Catalyzed Stereoselective Spiroketalization Reactions.

    PubMed

    Khomutnyk, Yaroslav Ya; Argüelles, Alonso J; Winschel, Grace A; Sun, Zhankui; Zimmerman, Paul M; Nagorny, Pavel

    2016-01-13

    Mechanistic and computational studies were conducted to elucidate the mechanism and the origins of enantiocontrol for asymmetric chiral phosphoric acid-catalyzed spiroketalization reactions. These studies were designed to differentiate between the S(N)1-like, S(N)2-like, and covalent phosphate intermediate-based mechanisms. The chiral phosphoric acid-catalyzed spiroketalization of deuterium-labeled cyclic enol ethers revealed a highly diastereoselective syn-selective protonation/nucleophile addition, thus ruling out long-lived oxocarbenium intermediates. Hammett analysis of the reaction kinetics revealed positive charge accumulation in the transition state (ρ = -2.9). A new computational reaction exploration method along with dynamics simulations supported an asynchronous concerted mechanism with a relatively short-lived polar transition state (average lifetime = 519 ± 240 fs), which is consistent with the observed inverse secondary kinetic isotope effect of 0.85. On the basis of these studies, a transition state model explaining the observed stereochemical outcome has been proposed. This model predicts the enantioselective formation of the observed enantiomer of the product with 92% ee, which matches the experimentally observed value.

  8. Bifunctional acid base catalyzed reactions in zeolites from the HSAB viewpoint

    NASA Astrophysics Data System (ADS)

    Hemelsoet, K.; Lesthaeghe, D.; Speybroeck, V. Van; Waroquier, M.

    2006-02-01

    The applicability of the hard and soft acids and bases principle is investigated for the interaction of 5T zeolite clusters with probe molecules such as chloromethane, methanol and olefins. The reactions are intermediately hard-hard and, therefore, mainly charge-controlled. This is confirmed by the success of the atomic charges and the electrostatic interaction energy at the acid site as correct descriptors of regio-selectivity and reactivity sequences. Both acid and basic reactive sites can be clearly indicated using frontier orbitals. Moreover, an excellent correlation is found between the activation hardnesses and the energy barriers at the absolute zero.

  9. Chemoselective Boron-Catalyzed Nucleophilic Activation of Carboxylic Acids for Mannich-Type Reactions.

    PubMed

    Morita, Yuya; Yamamoto, Tomohiro; Nagai, Hideoki; Shimizu, Yohei; Kanai, Motomu

    2015-06-10

    The carboxyl group (COOH) is an omnipresent functional group in organic molecules, and its direct catalytic activation represents an attractive synthetic method. Herein, we describe the first example of a direct catalytic nucleophilic activation of carboxylic acids with BH3·SMe2, after which the acids are able to act as carbon nucleophiles, i.e. enolates, in Mannich-type reactions. This reaction proceeds with a mild organic base (DBU) and exhibits high levels of functional group tolerance. The boron catalyst is highly chemoselective toward the COOH group, even in the presence of other carbonyl moieties, such as amides, esters, or ketones. Furthermore, this catalytic method can be extended to highly enantioselective Mannich-type reactions by using a (R)-3,3'-I2-BINOL-substituted boron catalyst.

  10. Brønsted-acid-catalyzed asymmetric multicomponent reactions for the facile synthesis of highly enantioenriched structurally diverse nitrogenous heterocycles.

    PubMed

    Yu, Jie; Shi, Feng; Gong, Liu-Zhu

    2011-11-15

    Optically pure nitrogenous compounds, and especially nitrogen-containing heterocycles, have drawn intense research attention because of their frequent isolation as natural products. These compounds have wide-ranging biological and pharmaceutical activities, offering potential as new drug candidates. Among the various synthetic approaches to nitrogenous heterocycles, the use of asymmetric multicomponent reactions (MCRs) catalyzed by chiral phosphoric acids has recently emerged as a particularly robust tool. This method combines the prominent merits of MCRs with organocatalysis, thus affording enantio-enriched nitrogenous heterocyclic compounds with excellent enantioselectivity, atom economy, bond-forming efficiency, structural diversity, and complexity. In this Account, we discuss a variety of asymmetric MCRs catalyzed by chiral phosphoric acids that lead to the production of structurally diverse nitrogenous heterocycles. In MCRs, three or more reagents are combined simultaneously to produce a single product containing structural contributions from all the components. These one-pot processes are especially useful in the construction of heterocyclic cores: they can provide a high degree of both complexity and diversity for a targeted set of scaffolds while minimizing the number of synthetic operations. Unfortunately, enantioselective MCRs have thus far been relatively underdeveloped. Particularly lacking are reactions that proceed through imine intermediates, which are formed from the condensation of carbonyls and amines. The concomitant generation of water in the condensation reaction can deactivate some Lewis acid catalysts, resulting in premature termination of the reaction. Thus, chiral catalysts typically must be compatible with water for MCRs to generate nitrogenous compounds. Recently, organocatalytic MCRs have proven valuable in this respect. Brønsted acids, an important class of organocatalysts, are highly compatible with water and thereby offer great

  11. Origin of asymmetric induction in bicyclic guanidine-catalyzed thio-Michael reaction: a bifunctional mode of Lewis acid-Brønsted acid activation.

    PubMed

    Cho, Bokun; Tan, Choon-Hong; Wong, Ming Wah

    2012-08-03

    In addition to a bifunctional Brønsted acid activation mode, an unconventional bifunctional mode of Lewis and Brønsted acid activations was revealed in a DFT study of bicyclic guanidine-catalyzed thio-Michael reaction. This activation mode provides an alternate reaction pathway for the C-S bond forming step and influences the final stereochemical outcome. The calculated turnover frequencies of the R- and S-products, based on the energetic span model, are in good accord with the observed high stereoselectivity toward the S-product.

  12. Acetylation of bacterial cellulose catalyzed by citric acid: Use of reaction conditions for tailoring the esterification extent.

    PubMed

    Ávila Ramírez, Jhon Alejandro; Gómez Hoyos, Catalina; Arroyo, Silvana; Cerrutti, Patricia; Foresti, María Laura

    2016-11-20

    Bacterial cellulose (BC) nanoribbons were partially acetylated by a simple direct solvent-free route catalyzed by citric acid. The assay of reaction conditions within chosen intervals (i.e. esterification time (0.5-7h), catalyst content (0.08-1.01mmol/mmol AGU), and temperature (90-140°C)), illustrated the flexibility of the methodology proposed, with reaction variables which can be conveniently manipulated to acetylate BC to the required degree of substitution (DS) within the 0.20-0.73 interval. Within this DS interval, characterization results indicated a surface-only process in which acetylated bacterial cellulose with tunable DS, preserved fibrous structure and increased hydrophobicity could be easily obtained. The feasibility of reusing the catalyst/excess acylant in view of potential scale-up was also illustrated.

  13. Graphene oxide for acid catalyzed-reactions: Effect of drying process

    NASA Astrophysics Data System (ADS)

    Gong, H. P.; Hua, W. M.; Yue, Y. H.; Gao, Z.

    2017-03-01

    Graphene oxides (GOs) were prepared by Hummers method through various drying processes, and characterized by XRD, SEM, FTIR, XPS and N2 adsorption. Their acidities were measured using potentiometric titration and acid-base titration. The catalytic properties were investigated in the alkylation of anisole with benzyl alcohol and transesterification of triacetin with methanol. GOs are active catalysts for both reaction, whose activity is greatly affected by their drying processes. Vacuum drying GO exhibits the best performance in transesterification while freezing drying GO is most active for alkylation. The excellent catalytic behavior comes from abundant surface acid sites as well as proper surface functional groups, which can be obtained by selecting appropriate drying process.

  14. Topological analysis of the electronic charge density in the ethene protonation reaction catalyzed by acidic zeolite.

    PubMed

    Zalazar, M Fernanda; Peruchena, Nélida M

    2007-08-16

    In the present work, the distribution of the electronic charge density in the ethene protonation reaction by a zeolite acid site is studied within the framework of the density functional theory and the atoms in molecules (AIM) theory. The key electronic effects such as topological distribution of the charge density involved in the reaction are presented and discussed. The results are obtained at B3LYP/6-31G(**) level theory. Attention is focused on topological parameters such as electron density, its Laplacian, kinetic energy density, potential energy density, and electronic energy density at the bond critical points (BCP) in all bonds involved in the interaction zone, in the reactants, pi-complex, transition state, and alkoxy product. In addition, the topological atomic properties are determined on the selected atoms in the course of the reaction (average electron population, N(Omega), atomic net charge, q(Omega), atomic energy, E(Omega), atomic volume, v(Omega), and first moment of the atomic charge distribution, M(Omega)) and their changes are analyzed exhaustively. The topological study clearly shows that the ethene interaction with the acid site of the zeolite cluster, T5-OH, in the ethene adsorbed, is dominated by a strong O-H...pi interaction with some degree of covalence. AIM analysis based on DFT calculation for the transition state (TS) shows that the hydrogen atom from the acid site in the zeolitic fragment is connected to the carbon atom by a covalent bond with some contribution of electrostatic interaction and to the oxygen atom by closed shell interaction with some contribution of covalent character. The C-O bond formed in the alkoxy product can be defined as a weaker shared interaction. Our results show that in the transition state, the dominant interactions are partially electrostatic and partially covalent in nature, in which the covalent contribution increases as the concentration and accumulation of the charge density along the bond path between

  15. Expanding the scope of Lewis acid catalysis in water: remarkable ligand acceleration of aqueous ytterbium triflate catalyzed Michael addition reactions.

    PubMed

    Ding, Rui; Katebzadeh, Kambiz; Roman, Lisa; Bergquist, Karl-Erik; Lindström, Ulf M

    2006-01-06

    [reaction: see text] Significant rate acceleration of metal-catalyzed Michael addition reactions in water was observed upon addition of small, dibasic ligands. Ytterbium triflate and TMEDA was the most effective combination leading to a nearly 20-fold faster reaction than in the absence of ligand.

  16. Enantioconvergent Nucleophilic Substitution Reaction of Racemic Alkyne-Dicobalt Complex (Nicholas Reaction) Catalyzed by Chiral Brønsted Acid.

    PubMed

    Terada, Masahiro; Ota, Yusuke; Li, Feng; Toda, Yasunori; Kondoh, Azusa

    2016-08-31

    Catalytic enantioselective syntheses enable a practical approach to enantioenriched molecules. While most of these syntheses have been accomplished by reaction at the prochiral sp(2)-hybridized carbon atom, little attention has been paid to enantioselective nucleophilic substitution at the sp(3)-hybridized carbon atom. In particular, substitution at the chiral sp(3)-hybridized carbon atom of racemic electrophiles has been rarely exploited. To establish an unprecedented enantioselective substitution reaction of racemic electrophiles, enantioconvergent Nicholas reaction of an alkyne-dicobalt complex derived from racemic propargylic alcohol was developed using a chiral phosphoric acid catalyst. In the present enantioconvergent process, both enantiomers of the racemic alcohol were transformed efficiently to a variety of thioethers with high enantioselectivity. The key to achieving success is dynamic kinetic asymmetric transformation (DYKAT) of enantiomeric cationic intermediates generated via dehydroxylation of the starting racemic alcohol under the influence of the chiral phosphoric acid catalyst. The present fascinating DYKAT involves the efficient racemization of these enantiomeric intermediates and effective resolution of these enantiomers through utilization of the chiral conjugate base of the phosphoric acid.

  17. Chiral Brønsted Acid-Catalyzed Enantioselective α-Amidoalkylation Reactions: A Joint Experimental and Predictive Study.

    PubMed

    Aranzamendi, Eider; Arrasate, Sonia; Sotomayor, Nuria; González-Díaz, Humberto; Lete, Esther

    2016-12-01

    Enamides with a free NH group have been evaluated as nucleophiles in chiral Brønsted acid-catalyzed enantioselective α-amidoalkylation reactions of bicyclic hydroxylactams for the generation of quaternary stereocenters. A quantitative structure-reactivity relationship (QSRR) method has been developed to find a useful tool to rationalize the enantioselectivity in this and related processes and to orient the catalyst choice. This correlative perturbation theory (PT)-QSRR approach has been used to predict the effect of the structure of the substrate, nucleophile, and catalyst, as well as the experimental conditions, on the enantioselectivity. In this way, trends to improve the experimental results could be found without engaging in a long-term empirical investigation.

  18. Scope and limitations of aliphatic Friedel-Crafts alkylations. Lewis acid catalyzed addition reactions of alkyl chlorides to carbon-carbon double bonds

    SciTech Connect

    Mayr, H.; Striepe, W.

    1983-04-22

    Lewis acid catalyzed addition reactions of alkyl halides with unsaturated hydrocarbons have been studied. 1:1 addition products are formed if the addends dissociate faster than the corresponding products; otherwise, polymerization takes place. For reaction conditions under which these compounds exist mainly undissociated, solvolysis constants of model compounds can be used to predict the outcome of any such addition reactions if systems with considerable steric hindrance are excluded.

  19. Sulfonic acid resin-catalyzed addition of phenols, carboxylic acids, and water to olefins: Model reactions for catalytic upgrading of bio-oil.

    PubMed

    Zhang, Zhi-Jun; Wang, Qing-Wen; Yang, Xu-Lai; Chatterjee, Sabornie; Pittman, Charles U

    2010-05-01

    Acid-catalyzed 1-octene reactions with phenol and mixtures of phenol with water, acetic acid and 1-butanol were studied as partial bio-oil upgrading models. Bio-oil from fast biomass pyrolysis has poor fuel properties due to the presence of substantial amounts of water, carboxylic acid, phenolic derivatives and other hydroxyl-containing compounds. Additions across olefins offer a route to simultaneously lower water content and acidity while increasing hydrophobicity, stability and heating value. Amberlyst15, Dowex50WX2 and Dowex50WX4 effectively catalyzed phenol O- and C-alkylation from 65 to 120 degrees C, giving high O-alkylation selectivities in the presence of water, acetic acid and 1-butanol. Octanols and dioctyl ethers were formed from water and octyl acetates and phenol acetates from acetic acid. Phenol alkylation slowed in the presence of water. Dowex50WX2 and Dowex50WX4 were more stable in the presence of water than Amberlyst15 and were successfully recycled. Adding 1-butanol to phenol/water/1-octene, gave emulsion-like mixtures which improved phenol conversion and olefin hydration.

  20. Thermodynamics of Enzyme-Catalyzed Reactions Database

    National Institute of Standards and Technology Data Gateway

    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.

  1. Chiral phosphoric acid catalyzed highly enantioselective Friedel-Crafts alkylation reaction of C3-substituted indoles to β,γ-unsaturated α-ketimino esters.

    PubMed

    Bi, Bo; Lou, Qin-Xin; Ding, Yu-Yang; Chen, Sheng-Wei; Zhang, Sha-Sha; Hu, Wen-Hui; Zhao, Jun-Ling

    2015-02-06

    A highly enantioselective C2 Friedel-Crafts alkylation reaction of 3-substituted indoles to β,γ-unsaturated α-ketimino esters has been developed. This reaction was efficiently catalyzed by a chiral phosphoric acid catalyst. The corresponding C2-substituted indole derivatives, bearing an α-ketimino ester motif, were obtained in moderate to high yields (up to 93%) and with high enantioselectivities (up to >99% ee).

  2. Regio-, Diastereo-, and Enantioselective Nitroso-Diels-Alder Reaction of 1,3-Diene-1-carbamates Catalyzed by Chiral Phosphoric Acids.

    PubMed

    Pous, Jonathan; Courant, Thibaut; Bernadat, Guillaume; Iorga, Bogdan I; Blanchard, Florent; Masson, Géraldine

    2015-09-23

    Chiral phosphoric acid-catalyzed asymmetric nitroso-Diels-Alder reaction of nitrosoarenes with carbamate-dienes afforded cis-3,6-disubstituted dihydro-1,2-oxazines in high yields with excellent regio-, diastereo-, and enantioselectivities. Interestingly, we observed that the catalyst is able not only to control the enantioselectivity but also to reverse the regioselectivity of the noncatalyzed nitroso-Diels-Alder reaction. The regiochemistry reversal and asynchronous concerted mechanism were confirmed by DFT calculations.

  3. A Computational Study of Acid Catalyzed Aerosol Reactions of Atmospherically Relevant Epoxides

    EPA Science Inventory

    Epoxides are important intermediates of atmospheric isoprene oxidation. Their subsequent reactions in the particle phase lead to the production of organic compounds detected in ambient aerosols. We apply density functional theory to determine the important kinetic factors that ...

  4. Recent Developments in the Chiral Brønsted Acid-catalyzed Allylboration Reaction with Polyfunctionalized Substrates.

    PubMed

    Barrio, Pablo; Rodríguez, Elsa; Fustero, Santos

    2016-08-01

    Asymmetric allylboration has played a central role in organic synthesis ever since the pioneering work by Hoffman and Brown, having found applications in the total synthesis of many natural products. A new dawn for this 40 year-old reaction occurred with the beginning of the new century when the first catalytic asymmetric methods came into play. In less than one decade, several methodologies, able to achieve the desired homoallylic alcohols with ee ranges in the high 90s, were developed. Among them, in the present account, we will disclose our contribution to the development of the chiral binolphosphoric-derived Brønsted acid-catalyzed allylboration of aldehydes originally reported by Antilla in 2010. Our contribution to this field lies in its application to polyfunctionalized systems, both on the aldehyde and the allylboronate in question, which enables the rapid construction of molecular diversity and complexity. Parts of the work described herein have been carried out in collaboration with the groups of Profs. Akiyama and Houk.

  5. Enantioselective Lewis acid-catalyzed Mukaiyama-Michael reactions of acyclic enones. Catalysis by allo-threonine-derived oxazaborolidinones.

    PubMed

    Wang, Xiaowei; Adachi, Shinya; Iwai, Hiroyoshi; Takatsuki, Hiroshi; Fujita, Katsuhiro; Kubo, Mikako; Oku, Akira; Harada, Toshiro

    2003-12-26

    allo-Threonine-derived O-aroyl-B-phenyl-N-tosyl-1,3,2-oxazaborolidin-5-ones 1g,n catalyze the asymmetric Mukaiyama-Michael reaction of acyclic enones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions. The effects of the additives are discussed in terms of the retardation of an Si(+)-catalyzed racemic pathway, which seriously deteriorates the enantioselectivity of asymmetric Mukaiyama-Michael reactions. A working model for asymmetric induction is proposed based on correlation between catalyst structures and enantioselectivities.

  6. Ascorbic acid and 4-hexylresorcinol effects on pear PPO and PPO catalyzed browning reaction.

    PubMed

    Arias, E; González, J; Oria, R; Lopez-Buesa, P

    2007-10-01

    The effects of ascorbic acid (AA) and 4-hexylresorcinol (4-HR) on pear polyphenoloxidase (PPO) activity and stability have been investigated in vitro. AA does not interact directly with PPO but prevents browning by reducing oxidized substrates. The 4-HR exerts a dual role on PPO. If no substrates are present, it interacts preferably with the deoxy form of PPO inactivating it. If substrates and 4-HR are both present they compete for the catalytic site. The 4-HR behaves then as a canonical enzyme inhibitor, binding to the met form of PPO. Simultaneous addition of 4-HR and AA has synergistic inhibition or inactivatory effects depending on the presence or the absence of PPO substrates.

  7. The acid-catalyzed hydrolysis of an α-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact

    NASA Astrophysics Data System (ADS)

    Rindelaub, Joel D.; Borca, Carlos H.; Hostetler, Matthew A.; Slade, Jonathan H.; Lipton, Mark A.; Slipchenko, Lyudmila V.; Shepson, Paul B.

    2016-12-01

    The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO + NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long-range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, the hydrolysis mechanism and rate constants were elucidated for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the tertiary APN lifetime ranging from 8.3 min at acidic pH (0.25) to 8.8 h at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant

  8. Unmasking the Action of Phosphinous Acid Ligands in Nitrile Hydration Reactions Catalyzed by Arene-Ruthenium(II) Complexes.

    PubMed

    Tomás-Mendivil, Eder; Cadierno, Victorio; Menéndez, María I; López, Ramón

    2015-11-16

    The catalytic hydration of benzonitrile and acetonitrile has been studied by employing different arene-ruthenium(II) complexes with phosphinous (PR2OH) and phosphorous acid (P(OR)2OH) ligands as catalysts. Marked differences in activity were found, depending on the nature of both the P-donor and η(6)-coordinated arene ligand. Faster transformations were always observed with the phosphinous acids. DFT computations unveiled the intriguing mechanism of acetonitrile hydration catalyzed by these arene-ruthenium(II) complexes. The process starts with attack on the nitrile carbon atom of the hydroxyl group of the P-donor ligand instead of on a solvent water molecule, as previously suggested. The experimental results presented herein for acetonitrile and benzonitrile hydration catalyzed by different arene-ruthenium(II) complexes could be rationalized in terms of such a mechanism.

  9. Pyrrole-2-Carboxylic Acid as a Ligand for the Cu-Catalyzed Reactions of Primary Anilines with Aryl Halides

    PubMed Central

    Altman, Ryan A.; Anderson, Kevin W.; Buchwald, Stephen L.

    2008-01-01

    Pyrrole 2-carboxylic acid (L5) was found to be an effective ligand for the Cu-catalyzed mono-arylation of anilines with aryl iodides and bromides. Under the reported conditions (10% CuI/20% L5/DMSO/K3PO4/80–100 °C/20–24 h), a variety of useful functional groups were tolerated, and moderate to good yields of the diaryl amine products were obtained. PMID:18543973

  10. Escherichia coli unsaturated fatty acid synthesis: complex transcription of the fabA gene and in vivo identification of the essential reaction catalyzed by FabB.

    PubMed

    Feng, Youjun; Cronan, John E

    2009-10-23

    Although the unsaturated fatty acid (UFA) synthetic pathway of Escherichia coli is the prototype of such pathways, several unresolved issues have accumulated over the years. The key players are the fabA and fabB genes. Earlier studies of fabA transcription showed that the gene was transcribed from two promoters, with one being positively regulated by the FadR protein. The other weaker promoter (which could not be mapped with the technology then available) was considered constitutive because its function was independent of FadR. However, the FabR negative regulator was recently shown to represses fabA transcription. We report that the weak promoter overlaps the FadR-dependent promoter and is regulated by FabR. This promoter is strictly conserved in all E. coli and Salmonella enterica genomes sequenced to date and is thought to provide insurance against inappropriate regulation of fabA transcription by exogenous saturated fatty acids. Also, the fabAup promoter, a mutant promoter previously isolated by selection for increased FabA activity, was shown to be a promoter created de novo by a four-base deletion within the gene located immediately upstream of fabA. Demonstration of the key UFA synthetic reaction catalyzed by FabB has been elusive, although it was known to catalyze an elongation reaction. Strains lacking FabB are UFA auxotrophs indicating that the enzyme catalyzes an essential step in UFA synthesis. Using thioesterases specific for hydrolysis of short chain acyl-ACPs, the intermediates of the UFA synthetic pathway have been followed in vivo for the first time. These experiments showed that a fabB mutant strain accumulated less cis-5-dodecenoic acid than the parental wild-type strain. These data indicate that the key reaction in UFA synthesis catalyzed by FabB is elongation of the cis-3-decenoyl-ACP produced by FabA.

  11. Influence of organic acids on oscillations and waves in the ferroin-catalyzed Belousov-Zhabotinsky reaction

    NASA Astrophysics Data System (ADS)

    Krüger, Frank; Nagy-Ungvárai, Zsuzsanna; Müller, Stefan C.

    Experiments of the influence of mesoxalic and tartronic acid on the oscillatory behavior and on the spiral tip motion in a ferroin-catalyzed Belousov-Zhabotinsky (BZ) solution are reported. The oscillations were observed in batch and CSTR systems, and for the investigations of the spiral tip motion an open gel reactor was used. A characteristic shoulder in the oscillations is associated with an additional Br - production phase. The chemical parameters for a transition from a hypocycloidal to a circular tip trajectory are found. The findings are compared with the temporal and spatial dynamic behavior, occurring during the ageing process of the solution.

  12. H₈-BINOL chiral imidodiphosphoric acid catalyzed highly enantioselective aza-Friedel-Crafts reactions of pyrroles and enamides/imines.

    PubMed

    Wu, Kun; Zhuo, Ming-Hua; Sha, Di; Fan, Yan-Sen; An, Dong; Jiang, Yi-Jun; Zhang, Suoqin

    2015-05-11

    The first enantioselective aza-Friedel-Crafts reaction between pyrroles and enamides has been achieved by using a novel H8-BINOL-type imidodiphosphoric acid catalyst. This methodology was also applied to the highly enantioselective aza-Friedel-Crafts reaction between pyrroles and imines. The catalyst loadings in these two reactions are low (0.3-2 mol%). Both processes are amenable to gram scales.

  13. Characterization of a Cross-Linked Protein-Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

    SciTech Connect

    Silakov, Alexey; Grove, Tyler L.; Radle, Matthew I.; Bauerle, Matthew R.; Green, Michael T.; Rosenzweig, Amy C.; Boal, Amie K.; Booker, Squire J.

    2014-08-14

    RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate to detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl-13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process

  14. Characterization of a Cross-Linked Protein–Nucleic Acid Substrate Radical in the Reaction Catalyzed by RlmN

    PubMed Central

    2015-01-01

    RlmN and Cfr are methyltransferases/methylsynthases that belong to the radical S-adenosylmethionine superfamily of enzymes. RlmN catalyzes C2 methylation of adenosine 2503 (A2503) of 23S rRNA, while Cfr catalyzes C8 methylation of the exact same nucleotide, and will subsequently catalyze C2 methylation if the site is unmethylated. A key feature of the unusual mechanisms of catalysis proposed for these enzymes is the attack of a methylene radical, derived from a methylcysteine residue, onto the carbon center undergoing methylation to generate a paramagnetic protein–nucleic acid cross-linked species. This species has been thoroughly characterized during Cfr-dependent C8 methylation, but does not accumulate to detectible levels in RlmN-dependent C2 methylation. Herein, we show that inactive C118S/A variants of RlmN accumulate a substrate-derived paramagnetic species. Characterization of this species by electron paramagnetic resonance spectroscopy in concert with strategic isotopic labeling shows that the radical is delocalized throughout the adenine ring of A2503, although predominant spin density is on N1 and N3. Moreover, 13C hyperfine interactions between the radical and the methylene carbon of the formerly [methyl-13C]Cys355 residue show that the radical species exists in a covalent cross-link between the protein and the nucleic acid substrate. X-ray structures of RlmN C118A show that, in the presence of SAM, the substitution does not alter the active site structure compared to that of the wild-type enzyme. Together, these findings have new mechanistic implications for the role(s) of C118 and its counterpart in Cfr (C105) in catalysis, and suggest involvement of the residue in resolution of the cross-linked species via a radical mediated process. PMID:24806349

  15. Acid-catalyzed condensed-phase reactions of limonene and terpineol and their impacts on gas-to-particle partitioning in the formation of organic aerosols.

    PubMed

    Li, Yong Jie; Cheong, Gema Y L; Lau, Arthur P S; Chan, Chak K

    2010-07-15

    We investigated the condensed-phase reactions of biogenic VOCs with C double bond C bonds (limonene, C(10)H(16), and terpineol, C(10)H(18)O) catalyzed by sulfuric acid by both bulk solution (BS) experiments and gas-particle (GP) experiments using a flow cell reactor. Product analysis by gas chromatography-mass spectrometry (GC-MS) showed that cationic polymerization led to dimeric and trimeric product formation under conditions of relative humidity (RH) <20% (in the GP experiments) and a sulfuric acid concentration of 57.8 wt % (in the BS experiments), while hydration occurred under conditions of RH > 20% (in the GP experiments) and sulfuric acid concentrations of 46.3 wt % or lower (in the BS experiments). Apparent partitioning coefficients (K(p,rxn)) were estimated from the GP experiments by including the reaction products. Only under extremely low RH conditions (RH < 5%) did the values of K(p,rxn) ( approximately 5 x 10(-6) m(3)/microg for limonene and approximately 2 x 10(-5) m(3)/microg for terpineol) substantially exceed the physical partitioning coefficients (K(p) = 6.5 x 10(-8) m(3)/microg for limonene and =2.3 x 10(-6) m(3)/microg for terpineol) derived from the absorptive partitioning theory. At RH higher than 5%, the apparent partitioning coefficients (K(p,rxn)) of both limonene and terpineol were in the same order of magnitude as the K(p) values derived from the absorptive partitioning theory. Compared with other conditions including VOC concentration and degree of neutralization (by ammonium) of acidic particles, RH is a critical parameter that influences both the reaction mechanisms and the uptake ability (K(p,rxn) values) of these processes. The finding suggests that RH needs to be considered when taking the effects of acid-catalyzed reactions into account in estimating organic aerosol formation from C double bond C containing VOCs.

  16. Iodide effects in transition metal catalyzed reactions.

    PubMed

    Maitlis, Peter M; Haynes, Anthony; James, Brian R; Catellani, Marta; Chiusoli, Gian Paolo

    2004-11-07

    The unique properties of I(-) allow it to be involved in several different ways in reactions catalyzed by the late transition metals: in the oxidative addition, the migration, and the coupling/reductive elimination steps, as well as in substrate activation. Most steps are accelerated by I(-)(for example through an increased nucleophilicity of the metal center), but some are retarded, because a coordination site is blocked. The "soft" iodide ligand binds more strongly to soft metals (low oxidation state, electron rich, and polarizable) such as the later and heavier transition metals, than do the other halides, or N- and O-centered ligands. Hence in a catalytic cycle that includes the metal in a formally low oxidation state there will be less tendency for the metal to precipitate (and be removed from the cycle) in the presence of I(-) than most other ligands. Iodide is a good nucleophile and is also easily and reversibly oxidized to I(2). In addition, I(-) can play key roles in purely organic reactions that occur as part of a catalytic cycle. Thus to understand the function of iodide requires careful analysis, since two or sometimes more effects occur in different steps of one single cycle. Each of these topics is illustrated with examples of the influence of iodide from homogeneous catalytic reactions in the literature: methanol carbonylation to acetic acid and related reactions; CO hydrogenation; imine hydrogenation; and C-C and C-N coupling reactions. General features are summarised in the Conclusions.

  17. Enantioselective Cycloaddition Reactions Catalyzed by BINOL-Derived Phosphoric Acids and N-Triflyl Phosphoramides: Recent Advances.

    PubMed

    Held, Felix E; Grau, Dominik; Tsogoeva, Svetlana B

    2015-09-03

    Over the last several years there has been a huge increase in the development and applications of new efficient organocatalysts for enantioselective pericyclic reactions, which represent one of the most powerful types of organic transformations. Among these processes are cycloaddition reactions (e.g., [3+2]; formal [3+3]; [4+2]; vinylogous [4+2] and 1,3-dipolar cycloadditions), which belong to the most utilized reactions in organic synthesis of complex nitrogen- and oxygen-containing heterocyclic molecules. This review presents the breakthrough realized in this field using chiral BINOL-derived phosphoric acids and N-triflyl phosphoramide organocatalysts.

  18. Advances in lipase-catalyzed esterification reactions.

    PubMed

    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.

  19. Development of a Lewis Base Catalyzed Selenocyclization Reaction

    ERIC Educational Resources Information Center

    Collins, William

    2009-01-01

    The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

  20. Highly enantioselective aza-Diels-Alder reaction of 1-azadienes with enecarbamates catalyzed by chiral phosphoric acids.

    PubMed

    He, Long; Laurent, Gregory; Retailleau, Pascal; Folléas, Benoît; Brayer, Jean-Louis; Masson, Géraldine

    2013-10-11

    On demand: A highly enantio- and diastereoselective synthesis of 6-amino- trisubstituted tetrahydropyridine compounds has been developed through the inverse-electron-demand aza-Diels-Alder reaction of N-aryl α,β-unsaturated ketimines with enecarbamates (E)-1. Chiral phosphoric acid catalysts achieve simultaneous activation of both the 1-azadiene and dienophile partners.

  1. Mechanistic investigation of chiral phosphoric acid catalyzed asymmetric Baeyer-Villiger reaction of 3-substituted cyclobutanones with H2O2 as the oxidant.

    PubMed

    Xu, Senmiao; Wang, Zheng; Li, Yuxue; Zhang, Xumu; Wang, Haiming; Ding, Kuiling

    2010-03-08

    The mechanism of the chiral phosphoric acid catalyzed Baeyer-Villiger (B-V) reaction of cyclobutanones with hydrogen peroxide was investigated by using a combination of experimental and theoretical methods. Of the two pathways that have been proposed for the present reaction, the pathway involving a peroxyphosphate intermediate is not viable. The reaction progress kinetic analysis indicates that the reaction is partially inhibited by the gamma-lactone product. Initial rate measurements suggest that the reaction follows Michaelis-Menten-type kinetics consistent with a bifunctional mechanism in which the catalyst is actively involved in both carbonyl addition and the subsequent rearrangement steps through hydrogen-bonding interactions with the reactants or the intermediate. High-level quantum chemical calculations strongly support a two-step concerted mechanism in which the phosphoric acid activates the reactants or the intermediate in a synergistic manner through partial proton transfer. The catalyst simultaneously acts as a general acid, by increasing the electrophilicity of the carbonyl carbon, increases the nucleophilicity of hydrogen peroxide as a Lewis base in the addition step, and facilitates the dissociation of the OH group from the Criegee intermediate in the rearrangement step. The overall reaction is highly exothermic, and the rearrangement of the Criegee intermediate is the rate-determining step. The observed reactivity of this catalytic B-V reaction also results, in part, from the ring strain in cyclobutanones. The sense of chiral induction is rationalized by the analysis of the relative energies of the competing diastereomeric transition states, in which the steric repulsion between the 3-substituent of the cyclobutanone and the 3- and 3'-substituents of the catalyst, as well as the entropy and solvent effects, are found to be critically important.

  2. Domino rhodium/palladium-catalyzed dehydrogenation reactions of alcohols to acids by hydrogen transfer to inactivated alkenes.

    PubMed

    Trincado, Mónica; Grützmacher, Hansjörg; Vizza, Francesco; Bianchini, Claudio

    2010-03-01

    The combination of the d(8) Rh(I) diolefin amide [Rh(trop(2)N)(PPh(3))] (trop(2)N=bis(5-H-dibenzo[a,d]cyclohepten-5-yl)amide) and a palladium heterogeneous catalyst results in the formation of a superior catalyst system for the dehydrogenative coupling of alcohols. The overall process represents a mild and direct method for the synthesis of aromatic and heteroaromatic carboxylic acids for which inactivated olefins can be used as hydrogen acceptors. Allyl alcohols are also applicable to this coupling reaction and provide the corresponding saturated aliphatic carboxylic acids. This transformation has been found to be very efficient in the presence of silica-supported palladium nanoparticles. The dehydrogenation of benzyl alcohol by the rhodium amide, [Rh]N, follows the well established mechanism of metal-ligand bifunctional catalysis. The resulting amino hydride complex, [RhH]NH, transfers a H(2) molecule to the Pd nanoparticles, which, in turn, deliver hydrogen to the inactivated alkene. Thus a domino catalytic reaction is developed which promotes the reaction R-CH(2)-OH+NaOH+2 alkene-->R-COONa+2 alkane.

  3. The decolorization of Acid Orange II in non-homogeneous Fenton reaction catalyzed by natural vanadium-titanium magnetite.

    PubMed

    Liang, Xiaoliang; Zhong, Yuanhong; Zhu, Sanyuan; Zhu, Jianxi; Yuan, Peng; He, Hongping; Zhang, Jing

    2010-09-15

    The catalytic activity of natural vanadium-titanium magnetite was investigated in the decolorization of Acid Orange II by non-homogeneous Fenton process. The natural catalysts purified by magnetic separation were characterized using X-ray diffraction (XRD), polarizing microscope, X-ray absorption fine structure (XAFS) analysis and Mössbauer spectroscopy. The obtained results show that the natural samples after magnetic separation mainly contain titanomagnetite, with a small amount of ilmenite and chlorite. Titanomagnetite is doped with vanadium, whose the valency is mainly +3 and occupies the octahedral site. Batch decolorization studies were performed to evaluate the influences of various experimental parameters like initial pH, the amount of catalyst and initial concentration of hydrogen peroxide on the decolorization efficiency of Acid Orange II. The decolorization of the dye mainly relied on degradation. The degradation efficiency was strongly dependent on pH of the medium where it increased as the pH decreased in acid range. The increase of catalyst and hydrogen peroxide could accelerate the degradation. The catalytic property of natural vanadium-titanium magnetite in the degradation of Acid Orange II was stronger than that of synthetic magnetite (Fe(3)O(4)). The catalytic activity of the natural samples was greatly related to the titanomagnetite content. The degradation process was dominated by heterogeneous Fenton reaction, complying with pseudo-first-order rate law. The natural catalyst has a good catalytic stability.

  4. An alternative reaction for heme degradation catalyzed by the Escherichia coli O157:H7 ChuS protein: Release of hematinic acid, tripyrrole and Fe(III).

    PubMed

    Ouellet, Yannick H; Ndiaye, Cheikh Tidiane; Gagné, Stéphane M; Sebilo, Anne; Suits, Michael D L; Jubinville, Éric; Jia, Zongchao; Ivancich, Anabella; Couture, Manon

    2016-01-01

    As part of the machinery to acquire, internalize and utilize heme as a source of iron from the host, some bacteria possess a canonical heme oxygenase, where heme plays the dual role of substrate and cofactor, the later catalyzing the cleavage of the heme moiety using O2 and electrons, and resulting in biliverdin, carbon monoxide and ferrous non-heme iron. We have previously reported that the Escherichia coli O157:H7 ChuS protein, which is not homologous to heme oxygenases, can bind and degrade heme in a reaction that releases carbon monoxide. Here, we have pursued a detailed characterization of such heme degradation reaction using stopped-flow UV-visible absorption spectrometry, the characterization of the intermediate species formed in such reaction by EPR spectroscopy and the identification of reaction products by NMR spectroscopy and Mass spectrometry. We show that hydrogen peroxide (in molar equivalent) is the key player in the degradation reaction, at variance to canonical heme oxygenases. While the initial intermediates of the reaction of ChuS with hydrogen peroxide (a ferrous keto π neutral radical and ferric verdoheme, both identified by EPR spectroscopy) are in common with heme oxygenases, a further and unprecedented reaction step, involving the cleavage of the porphyrin ring at adjacent meso-carbons, results in the release of hematinic acid (a monopyrrole moiety identified by NMR spectroscopy), a tripyrrole product (identified by Mass spectrometry) and non-heme iron in the ferric oxidation state (identified by EPR spectroscopy). Overall, the unprecedented reaction of E. coli O157:H7 ChuS provides evidence for a novel heme degradation activity in a Gram-negative bacterium.

  5. Visual detection of trace copper ions based on copper-catalyzed reaction of ascorbic acid with oxygen

    NASA Astrophysics Data System (ADS)

    Hou, Xin Yan; Chen, Shu; Shun, Lian Ju; Zhao, Yi Ni; Zhang, Zhi Wu; Long, Yun Fei; Zhu, Li

    2015-10-01

    A visual detection method for trace Cu2+ in aqueous solutions using triangular silver nanoplates (abbreviated as TAgNPs) as the probe was developed. The method is based on that TAgNPs could be corroded in sodium thiosulfate (Na2S2O3) solutions. The absorption spectrum of TAgNPs solution changed when it is corroded by Na2S2O3. The reaction of oxygen with ascorbic acid (Vc) in the presence of a low concentration of Cu2+ generates hydrogen peroxide that reacts with Na2S2O3, which leads the concentration of Na2S2O3 in the solution to be decreased. Therefore, the reaction between TAgNPs and the reacted mixture of Na2S2O3/Vc/Cu2+ was prevented efficiently. When the Na2S2O3 concentration and reaction time are constant, the decrease in the concentration of Na2S2O3 is directly proportional to the Cu2+ concentration. Thus, morphology, color, and maximum absorption wavelength of TAgNPs changed with the change of Cu2+ concentration. The changed maximum absorption wavelength of TAgNPs (Δλ) is proportional to Cu2+ concentration in the range from 7.5 × 10-9 to 5.0 × 10-7 M with a correlation coefficient of r = 0.9956. Moreover, color change of TAgNP solution was observed clearly over a Cu2+ concentration range from 7.5 × 10-8 to 5.0 × 10-7 M. This method has been used to detect the Cu2+ content of a human hair sample, and the result is in agreement with that obtained by the atomic absorption spectroscopy (AAS) method.

  6. Surface catalyzed mercury transformation reactions

    NASA Astrophysics Data System (ADS)

    Varanasi, Patanjali

    Mercury is a known pollutant that has detrimental effect on human health and environment. The anthropogenic emissions of mercury account for 10 to 30% of worldwide mercury emissions. There is a need to control/reduce anthropogenic mercury emissions. Many mercury control technologies are available but their effectiveness is dependent on the chemical form of mercury, because different chemical forms of mercury have different physical and chemical properties. Mercury leaves the boiler in its elemental form but goes through various transformations in the post-combustion zone. There is a need to understand how fly ash and flue gas composition affect speciation, partitioning, and reactions of mercury under the full range of post-combustion zone conditions. This knowledge can then be used to predict the chemical transformation of mercury (elemental, oxidized or particulate) in the post combustion zone and thus help with the control of mercury emissions from coal-burning power plants. To accomplish this goal present study was conducted using five coal fly ashes. These ashes were characterized and their catalytic activity was compared under selected reaction conditions in a fixed bed reactor. Based on the results from these fly ash experiments, three key components (carbon, iron oxide and calcium oxide) were chosen. These three components were then used to prepare model fly ashes. Silica/alumina was used as a base for these model fly ashes. One, two or three component model fly ashes were then prepared to investigate mercury transformation reactions. The third set of experiments was performed with five different oxidation catalysts to further understand the mercury oxidation process. Based on the results of these three studies the key components were predicted for different fly ash compositions under variety of flue gas conditions. A fixed bed reactor system was used to conduct this study. In all the experiments, the inlet concentration of Hg0(g) was maintained at 35 mug

  7. Following Solid-Acid-Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase -Zeolite-Catalyzed Conversion of Cyclohexanol in Water

    SciTech Connect

    Vjunov, Aleksei; Hu, Mary Y.; Feng, Ju; Camaioni, Donald M.; Mei, Donghai; Hu, Jian Z.; Zhao, Chen; Lercher, Johannes A.

    2014-01-07

    The catalytic conversion of cyclohexanol on zeolite HBEA in hot liquid water leads to dehydration as well as alkylation products. A novel micro autoclave suitable for application in MAS NMR at high temperatures and pressures is developed and successfully applied to obtain new insight into the mechanistic pathway leading to an understanding of the reactions under selected experimental conditions.

  8. Unsymmetrical Diarylmethanes by Ferroceniumboronic Acid Catalyzed Direct Friedel-Crafts Reactions with Deactivated Benzylic Alcohols: Enhanced Reactivity due to Ion-Pairing Effects.

    PubMed

    Mo, Xiaobin; Yakiwchuk, Joshua; Dansereau, Julien; McCubbin, J Adam; Hall, Dennis G

    2015-08-05

    The development of general and more atom-economical catalytic processes for Friedel-Crafts alkylations of unactivated arenes is an important objective of interest for the production of pharmaceuticals and commodity chemicals. Ferroceniumboronic acid hexafluoroantimonate salt (1) was identified as a superior air- and moisture-tolerant catalyst for direct Friedel-Crafts alkylations of a variety of slightly activated and neutral arenes with stable and readily available primary and secondary benzylic alcohols. Compared to the use of classical metal-catalyzed alkylations with toxic benzylic halides, this methodology employs exceptionally mild conditions to provide a wide variety of unsymmetrical diarylmethanes and other 1,1-diarylalkane products in high yield with good to high regioselectivity. The optimal method, using the bench-stable ferroceniumboronic acid salt 1 in hexafluoroisopropanol as cosolvent, displays a broader scope compared to previously reported catalysts for similar Friedel-Crafts reactions of benzylic alcohols, including other boronic acids such as 2,3,4,5-tetrafluorophenylboronic acid. The efficacy of the new boronic acid catalyst was confirmed by its ability to activate primary benzylic alcohols functionalized with destabilizing electron-withdrawing groups like halides, carboxyesters, and nitro substituents. Arene benzylation was demonstrated on a gram scale at up to 1 M concentration with catalyst recovery. Mechanistic studies point toward the importance of the ionic nature of the catalyst and suggest that factors other than the Lewis acidity (pKa) of the boronic acid are at play. A SN1 mechanism is proposed where ion exchange within the initial boronate anion affords a more reactive carbocation paired with the non-nucleophilic hexafluoroantimonate counteranion.

  9. Mechanism of cooperative catalysis in a Lewis acid promoted nickel-catalyzed dual C-H activation reaction.

    PubMed

    Anand, Megha; Sunoj, Raghavan B

    2012-09-07

    The mechanism of cooperativity offered by AlMe(3) in a Ni-catalyzed dehydrogenative cycloaddition between substituted formamides and an alkyne is investigated by using DFT(SMD(toluene)/M06/6-31G**) methods. The preferred pathway is identified to involve dual C-H activation, with first a higher barrier formyl C(sp(2))-H oxidative insertion followed by benzylic methyl C(sp(3))-H activation. The cooperativity is traced to be of kinetic origin as evidenced by stabilized transition states when AlMe(3) is bound to the formyl group, particularly in the oxidative insertion step.

  10. Horseradish-Peroxidase-Catalyzed Tyrosine Click Reaction.

    PubMed

    Sato, Shinichi; Nakamura, Kosuke; Nakamura, Hiroyuki

    2017-03-02

    The efficiency of protein chemical modification on tyrosine residues with N-methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H2 O2 , oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N-methylluminol derivatives with a minimum amount of H2 O2 prevented the occurrence of oxidative side reactions under HRP-catalyzed conditions. As probes for HRP-catalyzed protein modification, N-methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β-nicotinamide adenine dinucleotide (NADH, H2 O2 -free conditions).

  11. Metal Catalyzed Oligomerization Reactions of Organosiloxanes.

    DTIC Science & Technology

    1982-10-28

    metallacycle from a mixture of stereo- isomers of the starting disiloxane is observed. The catalytic activity of these complexes for the oligomeriza... catalysts were adsorbed on oxide supports. Although the goal of synthesizing stereoregular silicones has not yet been achieved, the results warrant further...implicated as intermediates in several transi- tion metal-catalyzed reactions, e.g. olefin metathesis . 1 3 Metallacycles are also probable

  12. Asymmetric Stetter reactions catalyzed by thiamine diphosphate-dependent enzymes.

    PubMed

    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.

  13. Palladium(III)-Catalyzed Fluorination of Arylboronic Acid Derivatives

    PubMed Central

    Tang, Pingping; Murphy, Jennifer M.; Ritter, Tobias

    2013-01-01

    A practical, palladium-catalyzed synthesis of aryl fluorides from arylboronic acid derivatives is presented. The reaction is operationally simple and amenable to multi-gram-scale synthesis. Evaluation of the reaction mechanism suggests a single-electron-transfer pathway, involving a Pd(III) intermediate that has been isolated and characterized. PMID:24040932

  14. Palladium(III)-catalyzed fluorination of arylboronic acid derivatives.

    PubMed

    Mazzotti, Anthony R; Campbell, Michael G; Tang, Pingping; Murphy, Jennifer M; Ritter, Tobias

    2013-09-25

    A practical, palladium-catalyzed synthesis of aryl fluorides from arylboronic acid derivatives is presented. The reaction is operationally simple and amenable to multigram-scale synthesis. Evaluation of the reaction mechanism suggests a single-electron-transfer pathway, involving a Pd(III) intermediate that has been isolated and characterized.

  15. Bisoxazoline-Lewis acid-catalyzed direct-electron demand oxo-hetero-Diels-Alder reactions of N-oxy-pyridine aldehyde and ketone derivatives.

    PubMed

    Landa, Aitor; Richter, Bo; Johansen, Rasmus Lyng; Minkkilä, Anna; Jørgensen, Karl Anker

    2007-01-05

    A general catalytic oxo-hetero-Diels-Alder reaction for pro-chiral aldehyde and ketone N-oxy-pyridines is presented. The catalytic and asymmetric oxo-hetero-Diels-Alder reaction of electron-rich dienes with N-oxy-pyridine-2-carbaldehyde and ketone derivatives, catalyzed by chiral copper(II)-bisoxazoline complexes, gives optically active six-membered oxygen heterocycles in moderate to good yields and with excellent enantioselectivities.

  16. Studies of manufacturing controlled-release graphene acid and catalyzing synthesis of chalcone with Claisen-Schmidt condensation reaction

    NASA Astrophysics Data System (ADS)

    Li, Jihui; Feng, Jia; Li, Mei; Wang, Qiaolian; Su, Yumin; Jia, Zhixin

    2013-07-01

    In the paper, graphene acid (GA) was manufactured, using flake graphite as raw material, and the acidity and the structure of GA were characterized as well as. Then, chalcone was synthesized in the presence of GA, using acetophenone and benzaldehyde as the reactant. The results showed that the acidity of GA was for pH = 1.12 in aqueous solution, and it was structured by the graphene sheets with the spaces between the graphene sheet and the graphene sheet and sulfuric acid (H2SO4) and acetic acid (CH3CO2H) inside the spaces. At the same time, the results also exhibited that the chalcone yield was able to reach 60.36% when GA dosage was 5 g, and the chalcone yields could attain apart 60.36, 52.05 and 31.16% when 5 g of GA was used thrice. This shows that GA is not only a high-performance catalyst, but also a controlled-release catalyst.

  17. Kinetics of an acid-base catalyzed reaction (aspartame degradation) as affected by polyol-induced changes in buffer pH and pK values.

    PubMed

    Chuy, S; Bell, L N

    2009-01-01

    The kinetics of an acid-base catalyzed reaction, aspartame degradation, were examined as affected by the changes in pH and pK(a) values caused by adding polyols (sucrose, glycerol) to phosphate buffer. Sucrose-containing phosphate buffer solutions had a lower pH than that of phosphate buffer alone, which contributed, in part, to reduced aspartame reactivity. A kinetic model was introduced for aspartame degradation that encompassed pH and buffer salt concentrations, both of which change with a shift in the apparent pK(a) value. Aspartame degradation rate constants in sucrose-containing solutions were successfully predicted using this model when corrections (that is, lower pH, lower apparent pK(a) value, buffer dilution from the polyol) were applied. The change in buffer properties (pH, pK(a)) from adding sucrose to phosphate buffer does impact food chemical stability. These effects can be successfully incorporated into predictive kinetic models. Therefore, pH and pK(a) changes from adding polyols to buffer should be considered during food product development.

  18. Molecular Design of a Chiral Brønsted Acid with Two Different Acidic Sites: Regio-, Diastereo-, and Enantioselective Hetero-Diels-Alder Reaction of Azopyridinecarboxylate with Amidodienes Catalyzed by Chiral Carboxylic Acid-Monophosphoric Acid.

    PubMed

    Momiyama, Norie; Tabuse, Hideaki; Noda, Hirofumi; Yamanaka, Masahiro; Fujinami, Takeshi; Yamanishi, Katsunori; Izumiseki, Atsuto; Funayama, Kosuke; Egawa, Fuyuki; Okada, Shino; Adachi, Hiroaki; Terada, Masahiro

    2016-09-07

    A chiral Brønsted acid containing two different acidic sites, chiral carboxylic acid-monophosphoric acid 1a, was designed to be a new and effective concept in catalytic asymmetric hetero-Diels-Alder reactions of azopyridinecarboxylate with amidodienes. The multipoint hydrogen-bonding interactions among the carboxylic acid, monophosphoric acid, azopyridinecarboxylate, and amidodiene achieved high catalytic and chiral efficiency, producing substituted 1,2,3,6-tetrahydropyridazines with excellent stereocontrol in a single step. This constitutes the first example of regio-, diastereo-, and enantioselective azo-hetero-Diels-Alder reactions by chiral Brønsted acid catalysis.

  19. Synthesis of novel dendritic 2,2'-bipyridine ligands and their application to Lewis acid-catalyzed diels-alder and three-component condensation reactions.

    PubMed

    Muraki, Takahito; Fujita, Ken-ichi; Kujime, Masato

    2007-10-12

    A series of dendritic ligands with a 2,2'-bipyridine core was synthesized through the coupling of 4,4'-dihydroxy-2,2'-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf)2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.

  20. Ultrasonic irradiation accelerated cyclopalladated ferrocenylimines catalyzed Suzuki reaction in neat water.

    PubMed

    Zhang, Jinli; Yang, Fan; Ren, Gerui; Mak, Thomas C W; Song, Maoping; Wu, Yangjie

    2008-02-01

    Both conventional heating and ultrasound effect on the cyclopalladated ferrocenylimines catalyzed Suzuki reaction of phenylboronic acid with a range of arylhalides in neat water was investigated. Heterogenous reaction of electron-withdrawing arylchlorides with phenylboronic acid could also result in good yields by using Cat. 2. It was found that the ultrasonic irradiation could dramatically accelerate the Suzuki reaction to achieve comparable results.

  1. Transformation of D-(-)-ribose into a natural product-like scaffold via a Lewis acid catalyzed intramolecular hetero-Diels-Alder reaction.

    PubMed

    Messer, Roland; Fuhrer, Cyril A; Häner, Robert

    2007-01-01

    Starting from D-(-)-ribose, a tricyclic natural product-like scaffold suitable for combinatorial derivatization was synthesized via an intramolecular hetero-Diels-Alder reaction. Lithium perchlorate was found to enhance the reaction rate and, at the same time, had a pronounced influence on the chemoselectivity of the reaction. The stereochemical course of the reaction, however, was not influenced by the Lewis acid.

  2. Thermodynamic limitations on microbially catalyzed reaction rates

    NASA Astrophysics Data System (ADS)

    LaRowe, Douglas E.; Dale, Andrew W.; Amend, Jan P.; Van Cappellen, Philippe

    2012-08-01

    Quantification of global biogeochemical cycles requires knowledge of the rates at which microorganisms catalyze chemical reactions. In order for models that describe these processes to capture global patterns of change, the underlying formulations in them must account for biogeochemical transformations over seasonal and millennial time scales in environments characterized by different energy levels. Building on existing models, a new thermodynamic limiting function is introduced. With only one adjustable parameter, this function that can be used to model microbial metabolism throughout the range of conditions in which organisms are known to be active. The formulation is based on a comparison of the amount of energy available from any redox reaction to the energy required to maintain a membrane potential, a proxy for the minimum amount of energy required by an active microorganism. This function does not require species- or metabolism-specific parameters, and can be used to model metabolisms that capture any amount of energy. The utility of this new thermodynamic rate limiting term is illustrated by applying it to three low-energy processes: fermentation, methanogenesis and sulfate reduction. The model predicts that the rate of fermentation will be reduced by half once the Gibbs energy of the catalyzed reaction reaches -12 kJ (mol e-)-1, and then slowing exponentially until the energy yield approaches zero. Similarly, the new model predicts that the low energy yield of methanogenesis, -4 to -0.5 kJ (mol e-)-1, for a partial pressure of H2 between 11 and 0.6 Pa decreases the reaction rate by 95-99%. Finally, the new function's utility is illustrated through its ability to accurately model sulfate concentration data in an anoxic marine sediment.

  3. Representing Rate Equations for Enzyme-Catalyzed Reactions

    ERIC Educational Resources Information Center

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  4. Acid-catalyzed dehydrogenation of amine-boranes

    DOEpatents

    Stephens, Frances Helen; Baker, Ralph Thomas

    2010-01-12

    A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R.sup.1R.sup.2B--NR.sup.3R.sup.4].sub.n product. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources.

  5. Enzyme-catalyzed, gas-phase reactions.

    PubMed

    Barzana, E; Klibanov, A M; Karel, M

    1987-06-01

    Dehydrated preparations of alcohol oxidase adsorbed on DEAE-cellulose vigorously catalyze a gas-phase oxidation of ethanol vapors with molecular oxygen. The gas-phase reaction is strongly dependent on the water activity of the system. The enzymatic activity is severely inhibited by the product hydrogen peroxide. This inhibition can be alleviated, however, by an addition of catalase or peroxidase to the dry preparation. Such dehydrated, bienzymic catalysts afford a complete and selective conversion of the substrate to acetaldehyde. Dry alcohol oxidase is much more thermostable than in aqueous solution. The results of this work suggest that dehydrated enzymes have potential applications in the analysis of gaseous compounds and in the development of novel gas-solid bioreactors.

  6. Production of L-malic acid with fixation of HCO3(-) by malic enzyme-catalyzed reaction based on regeneration of coenzyme on electrode modified by layer-by-layer self-assembly method.

    PubMed

    Zheng, Haitao; Ohno, Yoko; Nakamori, Toshihiko; Suye, Shin-Ichiro

    2009-01-01

    Malic enzyme prepared and purified from Brevundimonas diminuta IFO13182 catalyzed the decarboxylation reaction of malate to pyruvate and CO2 using NAD+ as the coenzyme, and the reverse reaction was used in the present study for L-malic acid production with fixation of HCO3(-) as a model compound for carbon source. The L-malic acid production was based on electrochemical regeneration of NADH on a carbon plate electrode modified by layer-by-layer adsorption of polymer-bound mediator (Alginic acid bound viologen derivative, Alg-V), polymer-bound coenzyme (Alginic acid bound NAD+, Alg-NAD+), and lipoamide dehydrogenase (LipDH). Electrochemical reduction of immobilized NAD+ catalyzed by LipDH in a multilayer film was achieved, and the L-malic acid production with HCO3(-) fixation system with layer-by-layer immobilization of Alg-V/LipDH/Alg-NAD+/malic enzyme multilayer film on the electrode gave an L-malic acid production of nearly 11.9 mmol and an HCO3(-) fixation rate of nearly 47.4% in a buffer containing only KHCO3 and pyruvic acid potassium salt, using a cation exchange membrane. The total turnover number of NADH within 48 h was about 19,000, which suggests that efficient NADH regeneration and fast electron transfer were achieved within the multilayer film, and that the modified electrode is a potential method for the fixation of HCO3(-) without addition of free coenzyme.

  7. O2 and H2O2 transformation steps for the oxygen reduction reaction catalyzed by graphitic nitrogen-doped carbon nanotubes in acidic electrolyte from first principles calculations.

    PubMed

    Li, Yuhang; Zhong, Guoyu; Yu, Hao; Wang, Hongjuan; Peng, Feng

    2015-09-14

    It is highly challenging but extremely desirable to develop carbon catalysts with high oxygen reduction reaction (ORR) activity and stability in acidic medium for commercial application. In this paper, based on density functional theory (DFT) calculations with long range interaction correction and solvation effects, the elementary transformations of all the probable intermediates in the ORR and the hydrogen peroxide reduction reaction (HPRR) over graphitic nitrogen-doped carbon nanotubes (NCNTs) in acidic medium were evaluated, and it was found that all the rate determining steps are related to the bonding hydroxyl group because of the strong interaction between the hydroxyl group and carbon. Thus, it is hard for the direct four-electron ORR and the two-electron HPRR to proceed. Together with hydrogen peroxide disproportionation (HPD), a mixed mechanism for the ORR in acidic electrolyte was proposed, where the two-electron and three-electron ORRs and HPD dominate the electrode reaction. The experimental result for the ORR catalyzed by NCNTs in acidic electrolyte also well illustrated the rationality of the theoretical calculations. This study not only gives new insights into the effect of graphitic nitrogen doping on the ORR catalyzed by carbon, but also provides a guide to design carbon catalysts with high ORR activity in acidic electrolyte.

  8. Peptide-catalyzed 1,4-addition reactions of aldehydes to nitroolefins.

    PubMed

    Kastl, Robert; Arakawa, Yukihiro; Duschmalé, Jörg; Wiesner, Markus; Wennemers, Helma

    2013-01-01

    Conjugate addition reactions of aldehydes to nitroolefins provide synthetically useful gamma-nitroaldehydes. Here we summarize our research on peptide-catalyzed conjugate addition reactions of aldehydes to differently substituted nitroolefins. We show that peptides of the general type Pro-Pro-Xaa (Xaa = acidic amino acid) are not only highly active, robust and stereoselective catalysts but have also remarkable chemoselectivities.

  9. Kinetics of acid-catalyzed cleavage of cumene hydroperoxide.

    PubMed

    Levin, M E; Gonzales, N O; Zimmerman, L W; Yang, J

    2006-03-17

    The cleavage of cumene hydroperoxide, in the presence of sulfuric acid, to form phenol and acetone has been examined by adiabatic calorimetry. As expected, acid can catalyze cumene hydroperoxide reaction at temperatures below that of thermally-induced decomposition. At elevated acid concentrations, reactivity is also observed at or below room temperature. The exhibited reactivity behavior is complex and is significantly affected by the presence of other species (including the products). Several reaction models have been explored to explain the behavior and these are discussed.

  10. Cascade reactions catalyzed by metal organic frameworks.

    PubMed

    Dhakshinamoorthy, Amarajothi; Garcia, Hermenegildo

    2014-09-01

    Cascade or tandem reactions where two or more individual reactions are carried out in one pot constitute a clear example of process intensification, targeting the maximization of spatial and temporal productivity with mobilization of minimum resources. In the case of catalytic reactions, cascade processes require bi-/multifunctional catalysts that contain different classes of active sites. Herein, we show that the features and properties of metal-organic frameworks (MOFs) make these solids very appropriate materials for the development of catalysts for cascade reactions. Due to composition and structure, MOFs can incorporate different types of sites at the metal nodes, organic linkers, or at the empty internal pores, allowing the flexible design and synthesis of multifunctional catalysts. After some introductory sections on the relevance of cascade reactions from the point of view of competitiveness, sustainability, and environmental friendliness, the main part of the text provides a comprehensive review of the literature reporting the use of MOFs as heterogeneous catalysts for cascade reactions including those that combine in different ways acid/base, oxidation/reduction, and metal-organic centers. The final section summarizes the current state of the art, indicating that the development of a first commercial synthesis of a high-added-value fine chemical will be a crucial milestone in this area.

  11. Silver and gold-catalyzed multicomponent reactions

    PubMed Central

    Abbiati, Giorgio

    2014-01-01

    Summary Silver and gold salts and complexes mainly act as soft and carbophilic Lewis acids even if their use as σ-activators has been rarely reported. Recently, transformations involving Au(I)/Au(III)-redox catalytic systems have been reported in the literature. In this review we highlight all these aspects of silver and gold-mediated processes and their application in multicomponent reactions. PMID:24605168

  12. Acid and base catalyzed Davis-Beirut reaction: experimental and theoretical mechanistic studies and synthesis of novel 3-amino-2H-indazoles.

    PubMed

    Avila, Belem; El-Dakdouki, Mohammad H; Nazer, Musa Z; Harrison, Jason G; Tantillo, Dean J; Haddadin, Makhluf J; Kurth, Mark J

    2012-11-28

    The Davis-Beirut reaction, which provides an efficient synthesis of 2H-indazoles and, subsequently, indazolones, is shown to proceed rapidly from o-nitrosobenzaldehyde and primary amines under both acid or base catalysis. Experimental and theoretical evidence in support of a reaction mechanism is provided in which o-nitrosobenzylidine imine is a pivotal intermediate in this N,N-bond forming heterocyclization reaction. The Davis-Beirut reaction is also shown to effectively synthesize a number of novel 3-amino-2H-indazole derivatives.

  13. Palladium(0)-catalyzed coupling-cyclization reaction of polymer-supported aryl iodides with 1,2-allenyl carboxylic acids. Solid-phase parallel synthesis of butenolides.

    PubMed

    Ma, Shengming; Duan, Dehui; Wang, Yizhong

    2002-01-01

    In this contribution, we constructed a library of butenolides with 77 members by parallel synthesis strategy on Merrifield resin. Sixteen 2,3-allenoic acids and 12 polymer-bound aryl iodides were combined to react with each other, and then the polymer-supported products were cleaved to release butenolide derivatives. The reactions with alkyl-substituted 2,3-allenoic acids in acetonitrile afforded the corresponding products in high yields and high purities, whereas those with aryl-substituted acids in acetonitrile failed. After some reaction conditions were screened, the solid-phase reactions with aryl-substituted 2,3-allenoic acids were realized in toluene, and the products are of good purities albeit in slightly low yields. In the benzyl ether linkage, a new cleavage model was found. By adding 6 equiv of acetyl bromide, we can get single (5-oxo-2,5-dihydrofuran-3-yl)benzyl bromide other than the corresponding benzyl acetate. To further increase the diversities, a dihydropyran (DHP) linker was introduced into our combinatorial synthesis of butenolides. By reversing the addition sequence of 2,3-allenoic acids and organic base, we realized the solid-phase cyclization reaction of polymer-bound aryl iodides with the THP linkage in moderate yields and good purities. Now the library of butenolides includes (5-oxo-2,5-dihydrofuran-3-yl)benzoic acids, -aryl acetates, -benzyl bromides, -benzyl alcohols, and -phenols, which are difficult to synthesize with conventional solution methods.

  14. Microwave-Assisted Condensation Reactions of Acetophenone Derivatives and Activated Methylene Compounds with Aldehydes Catalyzed by Boric Acid under Solvent-Free Conditions.

    PubMed

    Brun, Elodie; Safer, Abdelmounaim; Carreaux, François; Bourahla, Khadidja; L'helgoua'ch, Jean-Martial; Bazureau, Jean-Pierre; Villalgordo, Jose Manuel

    2015-06-23

    We here disclosed a new protocol for the condensation of acetophenone derivatives and active methylene compounds with aldehydes in the presence of boric acid under microwave conditions. Implementation of the reaction is simple, healthy and environmentally friendly owing to the use of a non-toxic catalyst coupled to a solvent-free procedure. A large variety of known or novel compounds have thus been prepared, including with substrates bearing acid or base-sensitive functional groups.

  15. Enantioselective direct Mannich reactions of cyclic β-ketoesters catalyzed by chiral phosphine via a novel dual-reagent catalysis.

    PubMed

    Lou, Yan-Peng; Zheng, Chang-Wu; Pan, Ren-Ming; Jin, Qiao-Wen; Zhao, Gang; Li, Zhong

    2015-02-06

    A combination of an amino acid derived chiral phosphine catalyst and methyl acrylate efficiently catalyzed the direct Mannich reaction of cyclic β-ketoesters and N-Boc-aldimines. The dual-reagent catalysis was presumed to function through the formation of a zwitterion, which catalyzed the reaction with excellent stereocontrol via a hydrogen-bonding assisted chiral ion-pair pathway.

  16. The rhodium catalyzed three-component reaction of diazoacetates, titanium(IV) alkoxides and aldehydes.

    PubMed

    Lu, Chong-Dao; Liu, Hui; Chen, Zhi-Yong; Hu, Wen-Hao; Mi, Ai-Qiao

    2005-05-28

    The rhodium(II)-catalyzed three-component reaction of diazoacetates, titanium alkoxides and aldehydes is shown to give alpha-alkoxyl-beta-hydroxyl acid derivatives; the novel C-C bond formation reaction is proposed to occur through oxonium ylides derived from diazo compounds and titanium alkoxides, and followed by intermolecular trapping by aldehydes.

  17. Aldehyde-alcohol reactions catalyzed under mild conditions by chromium(III) terephthalate metal organic framework (MIL-101) and phosphotungstic acid composites.

    PubMed

    Bromberg, Lev; Hatton, T Alan

    2011-12-01

    Porous materials based on chromium(III) terephthalate metal organic frameworks (MIL-101) and their composites with phosphotungstic acid (PTA) were studied as heterogeneous acid catalysts in aldehyde-alcohol reactions exemplified by acetaldehyde-phenol (A-P) condensation and dimethylacetal formation from benzaldehyde and methanol (B-M reaction). The MIL-101 was synthesized solvothermically in water, and the MIL101/PTA composite materials were obtained by either impregnation of the already prepared MIL-101 porous matrix with phosphotungstic acid solution or by solvothermic treatment of aqueous mixtures of Cr(NO(3))(3), and terephthalic and phosphotungstic acids. The MIL101/PTA materials appeared to be effective catalysts for both A-P and B-M reactions occurring at room temperature, with half-lives ranging from 0.5 h (A-P) to 1.5-2 h (B-M) and turnover numbers over 600 for A-P and over 2900 for the B-M reaction, respectively. A synergistic effect of the strong acidic moieties (PTA) addition to mildly acidic Brønsted and Lewis acid cites of the MIL-101 was observed with the MIL101/PTA composites. The ability of the PTA and MIL101/PTA materials to strongly absorb and condense acetaldehyde vapors was discovered, with the MIL101/PTA absorbing over 10-fold its dry weight of acetaldehyde condensate at room temperature. The acetaldehyde was converted rapidly to crotonaldehyde and higher-molecular-weight compounds while in contact with MIL-101 and MIL101/PTA materials. The stability of the MIL-101 and MIL101/PTA catalysts was assessed within four cycles of the 1-day alcohol-aldehyde reactions in terms of the overall catalyst recovery, PTA or Cr content, and reaction rate constants in each cycle. The loss of the catalyst over 4 cycles was approximately 10 wt % for all tested catalysts due to the incomplete recovery and minute dissolution of the components. The reaction rates in all cycles remained unchanged and the catalyst losses stopped after the third cycle. The developed

  18. Factors that Affect Oxygen Activation and Coupling of the Two Redox Cycles in the Aromatization Reaction Catalyzed by NikD, an Unusual Amino Acid Oxidase†‡

    PubMed Central

    Kommoju, Phaneeswara-Rao; Bruckner, Robert C.; Ferreira, Patricia; Carrell, Christopher J.; Mathews, F. Scott; Jorns, Marilyn Schuman

    2009-01-01

    NikD is a flavoprotein oxidase that catalyzes the oxidation of piperideine-2-carboxylate (P2C) to picolinate in a remarkable aromatization reaction comprising two redox cycles and at least one isomerization step. Tyr258 forms part of an "aromatic cage" that surrounds the ring in picolinate and its precursors. Mutation of Tyr258 to Phe does not perturb the structure of nikD but does affect the coupling of the two redox cycles and causes a 10-fold decrease in turnover rate. Tyr258Phe catalyzes a quantitative 2-electron oxidation of P2C but only 60% of the resulting dihydropicolinate intermediate undergoes a second redox cycle to produce picolinate. The mutation does not affect product yield with an alternate substrate (3,4-dehydro-L-proline) that is aromatized in a single 2-electron oxidation step. Wild-type and mutant enzyme exhibit identical rate constants for P2C oxidation to dihydropicolinate and isomerization of a reduced enzyme•dihydropicolinate complex. The observed rates are 200- and 10-fold faster, respectively, than the mutant turnover rate. Picolinate release from Tyr258Phe is 100-fold faster than turnover. The presence of bound substrate or product is a key factor in oxygen activation by wild-type nikD, as judged by the 10- to 75-fold faster rates observed for complexes of the reduced enzyme with picolinate, benzoate or 1-cyclohexenoate, a 1-deaza P2C analog. The reduced Tyr258Phe•1-cyclohexenoate complex is 25-fold less reactive with oxygen than the wild-type complex. We postulate that mutation of Tyr258 causes subtle changes in active site dynamics that promote release of the reactive dihydropicolinate intermediate and disrupt the efficient synchronization of oxygen activation observed with wild-type nikD. PMID:19702312

  19. Microorganisms detected by enzyme-catalyzed reaction

    NASA Technical Reports Server (NTRS)

    Vango, S. P.; Weetall, H. H.; Weliky, N.

    1966-01-01

    Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

  20. Stereoselective synthesis of 2,5-disubstituted morpholines using a palladium-catalyzed hydroamination reaction.

    PubMed

    McGhee, Alicia; Cochran, Brian M; Stenmark, Torrey A; Michael, Forrest E

    2013-08-04

    A palladium-catalyzed hydroamination reaction is the key step in a stereoselective synthesis of 2,5-disubstituted and 2,3,5-trisubsituted morpholines from carbamate-protected aziridines. Aziridines are selectively attacked at the more substituted position by unsaturated alcohol nucleophiles using Lewis acid catalysts. Palladium-catalyzed hydroamination of the resulting aminoalkenes gives morpholines as a single diastereomer in excellent yield.

  1. Stau-catalyzed big-bang nucleosynthesis reactions

    NASA Astrophysics Data System (ADS)

    Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

    2010-06-01

    We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X-) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X- particle has a lifetime of τX>~103 s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X- acts as a catalyst. Some of these X- catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  2. Decomposition of peracetic acid catalyzed by vanadium complexes

    SciTech Connect

    Makarov, A.P.; Gekhman, A.E.; Moiseev, I.I.; Polotryuk, O.Y.

    1986-02-01

    This paper studies the decomposition of peracetic acid (AcOOH) in acetic acid (AcOH) catalyzed by vanadium complexes. It is shown that peractic acid in acetic acid solutions of ammonium anadate decomposes with the predominant formation of 0/sub 2/ and small amounts of CO/sub 2/, the yield of which increases with increasing temperature and peracetic acid concentration. Both reactions proceed without the formation of free radicals in amounts detectable by ESR spectroscopy. The rate of oxygen release under conditions in which the formation of CO/sub 2/ is insignificant obeys a kinetic equation indicating the intermediate formation of a complex between V/sup 5 +/ ions and peracetic acid and the slow conversion of this complex into the observed products.

  3. Ruthenium(II)/chiral Brønsted acid co-catalyzed enantioselective four-component reaction/cascade aza-Michael addition for efficient construction of 1,3,4-tetrasubstituted tetrahydroisoquinolines.

    PubMed

    Jiang, Jun; Ma, Xiaochu; Ji, Changge; Guo, Zhenqiu; Shi, Taoda; Liu, Shunying; Hu, Wenhao

    2014-02-03

    An elegant synergistic catalytic system comprising a ruthenium complex with a chiral Brønsted acid was developed for a four-component Mannich/cascade aza-Michael reaction. The ruthenium-associated ammonium ylides successfully trapped with in situ generated imines indicates a stepwise process of proton transfer in the ruthenium-catalyzed carbenoid N-H insertion reaction. The different decomposition abilities of various ruthenium complexes towards diazo compounds were well explained by the calculated thermodynamic data. The transformation features a mild, rapid, and efficient method for the synthesis of enantiomerically pure 1,3,4-tetrasubstituted tetrahydroquinolines bearing a quaternary stereogenic carbon center from simple starting precursors in moderate yields with high diastereo- and enantioselectivity.

  4. Iridium-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

    PubMed

    Zhu, Shou-Fei; Zhou, Qi-Lin

    2017-04-04

    Chiral carboxylic acid moieties are widely found in pharmaceuticals, agrochemicals, flavors, fragrances, and health supplements. Although they can be synthesized straightforwardly by transition-metal-catalyzed enantioselective hydrogenation of unsaturated carboxylic acids, because the existing chiral catalysts have various disadvantages, the development of new chiral catalysts with high activity and enantioselectivity is an important, long-standing challenge. Ruthenium complexes with chiral diphosphine ligands and rhodium complexes with chiral monodentate or bidentate phosphorus ligands have been the predominant catalysts for asymmetric hydrogenation of unsaturated acids. However, the efficiency of these catalysts is highly substrate-dependent, and most of the reported catalysts require a high loading, high hydrogen pressure, or long reaction time for satisfactory results. Our recent studies have revealed that chiral iridium complexes with chiral spiro-phosphine-oxazoline ligands and chiral spiro-phosphine-benzylamine ligands exhibit excellent activity and enantioselectivity in the hydrogenation of α,β-unsaturated carboxylic acids, including α,β-disubstituted acrylic acids, trisubstituted acrylic acids, α-substituted acrylic acids, and heterocyclic α,β-unsaturated acids. On the basis of an understanding of the role of the carboxy group in iridium-catalyzed asymmetric hydrogenation reactions, we developed a carboxy-group-directed strategy for asymmetric hydrogenation of olefins. Using this strategy, we hydrogenated several challenging olefin substrates, such as β,γ-unsaturated carboxylic acids, 1,1-diarylethenes, 1,1-dialkylethenes, and 1-alkyl styrenes in high yield and with excellent enantioselectivity. All these iridium-catalyzed asymmetric hydrogenation reactions feature high turnover numbers (up to 10000) and turnover frequencies (up to 6000 h(-1)), excellent enantioselectivities (greater than 95% ee with few exceptions), low hydrogen pressure (<12 atm

  5. Ligand Intermediates in Metal-Catalyzed Reactions

    SciTech Connect

    Gladysz, John A.

    1999-07-31

    The longest-running goal of this project has been the synthesis, isolation, and physical chemical characterization of homogeneous transition metal complexes containing ligand types believed to be intermediates in the metal-catalyzed conversion of CO/H{sub 2}, CO{sub 2}, CH{sub 4}, and similar raw materials to organic fuels, feedstocks, etc. In the current project period, complexes that contain unusual new types of C{sub x}(carbide) and C{sub x}O{sub y} (carbon oxide) ligands have been emphasized. A new program in homogeneous fluorous phase catalysis has been launched as described in the final report.

  6. Diamine Ligands in Copper-Catalyzed Reactions

    PubMed Central

    Surry, David S.

    2012-01-01

    The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands has been important in these advances and in this review we discuss these systems, including the choice of reaction conditions and applications in the synthesis of pharmaceuticals, natural products and designed materials. PMID:22384310

  7. Organic reactions catalyzed by methylrhenium trioxide: Reactions of ethyl diazoacetate and organic azides

    SciTech Connect

    Zhu, Z.; Espenson, J.H. |

    1996-10-16

    Methylrhenium trioxide (CH{sub 3}ReO{sub 3} or MTO) catalyzes several classes of reactions of ethyl diazoacetate, EDA. It is the first high valent oxo complex for carbene transfer. Under mild conditions and in the absence of other substrates, EDA was converted to a 9:1 mixture of diethyl maleate and diethyl fumarate. In the presence of alcohols, {alpha}-alkoxy ethyl acetates were obtained in good yield. The yields dropped for the larger and more branched alcohols, the balance of material being diethyl maleate and fumarate. An electron-donating group in the para position of phenols favors the formation of {alpha}-phenoxy ethyl acetates. The use of EDA to form {alpha}-thio ethyl acetates and N-substituted glycine ethyl esters, on the other hand, is hardly affected by the size or structure of the parent thiol or amine, with all of these reactions proceeding in high yield. MTO-catalyzed cycloaddition reactions occur between EDA and aromatic imines, olefins, and carbonyl compounds. Three-membered ring products are formed: aziridines, cyclopropanes, and epoxides, respectively. The reactions favor the formation of trans products, and provide a convenient route for the preparation of aziridines. Intermediate carbenoid and nitrenoid species have been proposed. In the presence of an oxygen source such as an epoxide, ethyl diazoacetate and azibenzil are converted to an oxalic acid monoethyl ester and to benzil; at the same time the epoxide was converted to an olefin. 75 refs., 1 fig., 7 tabs.

  8. An acid-catalyzed macrolactonization protocol.

    PubMed

    Trost, Barry M; Chisholm, John D

    2002-10-17

    [reaction: see text] An efficient macrolactonization protocol devoid of any base was developed derived from the use of vinyl esters in transesterification. Subjecting a hydroxy acid and ethoxyacetylene to 2 mol % [RuCl(2)(p-cymene)](2) in toluene followed by addition of camphorsulfonic acid or inverse addition provided macrolactones in good yields.

  9. Acid-Catalyzed Isomerization of Carvone to Carvacrol

    ERIC Educational Resources Information Center

    Kjonaas, Richard A.; Mattingly, Shawn P.

    2005-01-01

    The acid-catalyzed isomerization of carvone to carvacrol, first reported by Ritter and Ginsburg, is especially well suited with a permanent-magnet FT instrument. The acid-catalyzed isomerization of carvone to carvacrol produced a 61% yield after a three hour reflux with 30% aqueous sulfuric acid.

  10. Method for predicting enzyme-catalyzed reactions

    DOEpatents

    Hlavacek, William S.; Unkefer, Clifford J.; Mu, Fangping; Unkefer, Pat J.

    2013-03-19

    The reactivity of given metabolites is assessed using selected empirical atomic properties in the potential reaction center. Metabolic reactions are represented as biotransformation rules. These rules are generalized from the patterns in reactions. These patterns are not unique to reactants but are widely distributed among metabolites. Using a metabolite database, potential substructures are identified in the metabolites for a given biotransformation. These substructures are divided into reactants or non-reactants, depending on whether they participate in the biotransformation or not. Each potential substructure is then modeled using descriptors of the topological and electronic properties of atoms in the potential reaction center; molecular properties can also be used. A Support Vector Machine (SVM) or classifier is trained to classify a potential reactant as a true or false reactant using these properties.

  11. Thermodynamics of Enzyme-Catalyzed Reactions: Part 4. Lyases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1995-09-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the lyase class of enzymes have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement (temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used); the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 106 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  12. Thermodynamics of Enzyme-Catalyzed Reactions: Part 2. Transferases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1994-07-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the transferase class of enzymes have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used]; the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 285 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  13. Thermodynamics of Enzyme-Catalyzed Reactions. Part 3. Hydrolases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1994-11-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the hydrolase class of enzymes have been compiled. For each reaction the following information is given: The reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used]; the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 145 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  14. Reaction Pathway for Cocaine Hydrolase-Catalyzed Hydrolysis of (+)-Cocaine

    PubMed Central

    Yao, Yuan; Liu, Junjun; Zheng, Fang; Zhan, Chang-Guo

    2017-01-01

    A recently designed and discovered cocaine hydrolase (CocH), engineered from human butyrylcholinesterase (BChE), has been proven promising as a novel enzyme therapy for treatment of cocaine overdose and addiction because it is highly efficient in catalyzing hydrolysis of naturally occurring (−)-cocaine. It has been known that the CocH also has a high catalytic efficiency against (+)-cocaine, a synthetic enantiomer of cocaine. Reaction pathway and the corresponding free energy profile for the CocH-catalyzed hydrolysis of (+)-cocaine have been determined, in the present study, by performing first-principles pseudobond quantum mechanical/molecular mechanical (QM/MM)-free energy (FE) calculations. Acordingt to the QM/MM-FE results, the catalytic hydrolysis process is initiated by the nucleophilic attack on carbonyl carbon of (−)-cocaine benzoyl ester via hydroxyl oxygen of S198 side chain, and the second reaction step (i.e. dissociation of benzoyl ester) is rate-determining. This finding for CocH-catalyzed hydrolysis of (+)-cocaine is remarkably different from that for the (+)-cocaine hydrolysis catalyzed by bacterial cocaine esterase in which the first reaction step of the deacylation is associated with the highest free energy barrier (~17.9 kcal/mol). The overall free energy barrier (~16.0 kcal/mol) calculated for the acylation stage of CocH-catalyzed hydrolysis of (+)-cocaine is in good agreement with the experimental free energy barrier of ~14.5 kcal/mol derivated from the experimental kinetic data.

  15. Theoretical Study of Nickel-Catalyzed Selective Alkenylation of Pyridine: Reaction Mechanism and Crucial Roles of Lewis Acid and Ligands in Determining the Selectivity.

    PubMed

    Singh, Vijay; Nakao, Yoshiaki; Sakaki, Shigeyoshi; Deshmukh, Milind M

    2017-01-06

    Selective alkenylation of pyridine is challenging in synthetic organic chemistry due to the poor reactivity and regioselectivity of the aromatic ring. We theoretically investigated Ni-catalyzed selective alkenylation of pyridine with DFT. The first step is coordination of the pyridine-AlMe3 adduct with the active species Ni((0))(NHC)(C2H2) 1 in an η(2)-fashion to form an intermediate Int1. After the isomerization of Int1, the oxidative addition of the C-H bond of pyridine across the nickel-acetylene moiety occurs via a transition state TS2 to form a Ni((II))(NHC) pyridyl vinyl intermediate Int3. This oxidative addition is rate-determining. The next step is C-C bond formation between pyridyl and vinyl groups leading to the formation of vinyl-pyridine (P1). One of the points at issue in this type of functionalization is how to control the regioselectivity. With the use of Ni(NHC)/AlMe3 catalyst, the C(4)- and C(3)-alkenylated products (ΔG°(⧧) = 17.4 and 21.5 kcal mol(-1), respectively) are formed preferably to the C(2) one (ΔG°(⧧) = 22.0 kcal mol(-1)). The higher selectivity of the C(4)-alkenylation over the C(3) and the C(2) ones is attributed to the small steric repulsion between NHC and AlMe3 in the C(4)-alkenylation. Interestingly, with Ni(P(i-Pr)3)/AlMe3 catalyst, the C(2)-alkenylation occurs more easily than the C(3) and C(4) ones. This regioselectivity arises from the smaller steric repulsion induced by P(i-Pr)3 than by bulky NHC. It is notable that AlMe3 accelerates the alkenylation by inducing the strong CT from Ni to pyridine-AlMe3. In the absence of AlMe3, pyridine strongly coordinates with the Ni atom through the N atom, which increases Gibbs activation energy (ΔG°(⧧) = ∼27 kcal mol(-1)) of the C-H bond activation. In other words, AlMe3 plays two important roles, acceleration of the reaction and enhancement of the regioselectivity for the C(4)-alkenylation.

  16. Palladium-Catalyzed, Enantioselective Heine Reaction

    PubMed Central

    2016-01-01

    Aziridines are important synthetic intermediates for the generation of nitrogen-containing molecules. N-Acylaziridines undergo rearrangement by ring expansion to produce oxazolines, a process known as the Heine reaction. The first catalytic, enantioselective Heine reaction is reported for meso-N-acylaziridines where a palladium(II)–diphosphine complex is employed. The highly enantioenriched oxazoline products are valuable organic synthons and potential ligands for transition-metal catalysis. PMID:27398262

  17. Palladium-Catalyzed, Enantioselective Heine Reaction.

    PubMed

    Punk, Molly; Merkley, Charlotte; Kennedy, Katlyn; Morgan, Jeremy B

    2016-07-01

    Aziridines are important synthetic intermediates for the generation of nitrogen-containing molecules. N-Acylaziridines undergo rearrangement by ring expansion to produce oxazolines, a process known as the Heine reaction. The first catalytic, enantioselective Heine reaction is reported for meso-N-acylaziridines where a palladium(II)-diphosphine complex is employed. The highly enantioenriched oxazoline products are valuable organic synthons and potential ligands for transition-metal catalysis.

  18. Rh(III)-catalyzed synthesis of sultones through C-H activation directed by a sulfonic acid group.

    PubMed

    Qi, Zisong; Wang, Mei; Li, Xingwei

    2014-09-04

    A new rhodium-catalyzed synthesis of sultones via the oxidative coupling of sulfonic acids with internal alkynes is described. The reaction proceeds via aryl C-H activation assisted by a sulfonic acid group.

  19. Direct ortho-arylation of ortho-substituted benzoic acids: overriding Pd-catalyzed protodecarboxylation.

    PubMed

    Arroniz, Carlos; Ironmonger, Alan; Rassias, Gerry; Larrosa, Igor

    2013-02-15

    ortho-Arylation of ortho-substituted benzoic acids is a challenging process due to the tendency of the reaction products toward Pd-catalyzed protodecarboxylation. A simple method for preventing decarboxylation in sterically hindered benzoic acids is reported. The method described represents a reliable and broadly applicable entry to 2-aryl-6-substituted benzoic acids.

  20. Lipase-catalyzed domino kinetic resolution/intramolecular Diels-Alder reaction: one-pot synthesis of optically active 7-oxabicyclo[2.2.1]heptenes from furfuryl alcohols and beta-substituted acrylic acids.

    PubMed

    Akai, Shuji; Naka, Tadaatsu; Omura, Sohei; Tanimoto, Kouichi; Imanishi, Masashi; Takebe, Yasushi; Matsugi, Masato; Kita, Yasuyuki

    2002-09-16

    The first lipase-catalyzed domino reaction is described in which the acyl moiety formed during the enzymatic kinetic resolution of furfuryl alcohols (+/-)-3 with a 1-ethoxyvinyl ester 2 was utilized as a part of the constituent structure for the subsequent Diels-Alder reaction. The preparation of ester 2 from carboxylic acid 1 and the subsequent domino reaction were carried out in a one-pot reaction. Therefore, this procedure provides a convenient preparation of the optically active 7-oxabicyclo[2.2.1]heptene derivatives 5, which has five chiral, non-racemic carbon centers, from achiral 1 and racemic 3. The overall efficiency of this process was dependent on the substituent at the C-3 position of 3, and the use of the 3-methylfurfuryl derivatives, (+/-)-3 b and (+/-)-3 f, exclusively produced diastereoselectivity with excellent enantioselectivity to give (2R)-syn-5 (91->/=99 % ee) and (S)-3 (96->/=99 % ee). Similar procedures starting from the 3-bromofurfuryl alcohols (+/-)-3 h-j provided the cycloadducts (2R)-syn-5 j-q (93->/=99 % ee), in which the bromo group was utilized for the installation of bulky substituents to the 7-oxabicycloheptene core.

  1. Computational Studies on Cinchona Alkaloid-Catalyzed Asymmetric Organic Reactions.

    PubMed

    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

  2. Interconversion of ketoprofen recognition in firefly luciferase-catalyzed enantioselective thioesterification reaction using from Pylocoeria miyako (PmL) and Hotaria parvura (HpL) just by mutating two amino acid residues.

    PubMed

    Kato, Dai-ichiro; Hiraishi, Yoshihiro; Maenaka, Mika; Yokoyama, Keisuke; Niwa, Kazuki; Ohmiya, Yoshihiro; Takeo, Masahiro; Negoro, Seiji

    2013-11-01

    We identified the critical amino acid residues for substrate recognition using two firefly luciferases from Pylocoeria miyako (PmL) and Hotaria parvura (HpL), as these two luciferase enzymes exhibit different activities toward ketoprofen. Specifically, PmL can catalyze the apparent enantioselective thioesterification reaction, while HpL cannot. By comparing the amino acid sequences around the active site, we identified two residues (I350 and M397 in PmL and F351 and S398 in HpL) that were different between the two enzymes, and the replacement of these amino acids resulted in changing the ketoprofen recognition pattern. The inactive HpL was converted to the active enzyme toward ketoprofen and vice versa for PmL. These residues also affected the enantioselectivity toward ketoprofen; however, the bioluminescent color was not affected. In addition, using molecular dynamics calculations, the replacement of these two amino acids induced changes in the state of hydrogen bonding between ketoprofen and the S349 side chain through the active site water. As S349 is not considered to influence color tuning, these changes specifically caused the differences in ketoprofen recognition in the enzyme.

  3. Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.

    PubMed Central

    Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

    1993-01-01

    The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images PMID:8441626

  4. Copper-Catalyzed Divergent Addition Reactions of Enoldiazoacetamides with Nitrones.

    PubMed

    Cheng, Qing-Qing; Yedoyan, Julietta; Arman, Hadi; Doyle, Michael P

    2016-01-13

    Catalyst-controlled divergent addition reactions of enoldiazoacetamides with nitrones have been developed. By using copper(I) tetrafluoroborate/bisoxazoline complex as the catalyst, a [3+3]-cycloaddition reaction was achieved with excellent yield and enantioselectivity under exceptionally mild conditions, which represents the first highly enantioselective base-metal-catalyzed vinylcarbene transformation. When the catalyst was changed to copper(I) triflate, Mannich addition products were formed in high yields with near exclusivity under otherwise identical conditions.

  5. Catalyzed reactions at illuminated semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Wrighton, M. S.

    1984-06-01

    It is pointed out that thermodynamically unfavorable chemical redox reactions can be effected by using optical energy as the driving force. To date, the best man-contrived systems for the direct conversion of optical energy to high energy redox products are semiconductor-based photoelectrochemical devices. The present investigation is concerned with the possibility that the minority carrier redox process at a semiconductor electrode may be too slow to compete with the recombination of photogenerated carriers. Attention is given to the photoelectrochemical generation of hydrogen, the photoelectrochemical reduction of carbon dioxide, the photo-oxidation of halides to halogens, and photo-oxidation of water. It is concluded that redox reactions of possible significance in solar fuel generation require rate acceleration to achieve high solar energy conversion efficiency.

  6. Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?

    NASA Technical Reports Server (NTRS)

    Richardson, S. L.; Francisco, J. S.; Mebel, A. M.; Morokuma, K.

    1997-01-01

    The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

  7. Synthesis of annulated bis-indoles through Au(i)/Brønsted acid-catalyzed reactions of (1H-indol-3-yl)(aryl)methanols with 2-(arylethynyl)-1H-indoles.

    PubMed

    Inamdar, Suleman M; Gonnade, Rajesh G; Patil, Nitin T

    2017-01-25

    A general method to access annulated bis-indoles from (1H-indol-3-yl)(aryl)methanols and 2-(arylethynyl)-1H-indoles under the catalysis of the Ph3PAuOTf/Brønsted acid binary catalyst system has been developed. The reaction was found to proceed in a highly efficient manner and benefit from easy-to-make starting materials, broad substrate scope and operational simplicity. The potential of this method has also been exemplified for the synthesis of pyrrole-annulated indoles using 2-(phenylethynyl)-1H-indoles and phenyl(1H-pyrrol-2-yl)methanols. Furthermore, the use of a ternary catalyst system, involving PdCl2/Brønsted acid/Ph3PAuOTf catalysts, has been realized for the synthesis of annulated bis-indoles starting directly from 2-(phenylbuta-1,3-diyn-1-yl)aniline and (1H-indol-3-yl)(aryl)methanol. Mechanistically, this reaction is very interesting since the overall process involves three different catalytic cycles catalyzed by three different catalysts in a relay fashion.

  8. Secondary kinase reactions catalyzed by yeast pyruvate kinase.

    PubMed

    Leblond, D J; Robinson, J L

    1976-06-07

    1. Yeast pyruvate kinase (EC 2.7.1.40) catalyzes, in addition to the primary, physiologically important reaction, three secondary kinase reactions, the ATP-dependent phosphorylations of fluoride (fluorokinase), hydroxylamine (hydroxylamine kinase) and glycolate (glycolate kinase). 2. These reactions are accelerated by fructose-1,6-bisphosphate, the allosteric activator of the primary reaction. Wth Mg2+ as the required divalent cation, none of these reactions are observed in the absence of fructose-biphosphate. With Mn2+, fructose-bisphosphate is required for the glycolate kinase reaction, but merely stimulates the other reactions. 3. The effect of other divalent cations and pH on three secondary kinase reactions was also examined. 4. Results are compared with those obtained from muscle pyruvate kinase and the implications of the results for the mechanism of the yeast enzyme are discussed.

  9. (Ligand intermediates in metal-catalyzed reactions)

    SciTech Connect

    Not Available

    1992-01-01

    This report consists of sections on sigma bond complexes of alkenes, a new carbon-hydrogen bond activation reaction of alkene complexes, carbon-hydrogen bond migrations in alkylidene complexes, carbon- hydrogen bond migrations in alkyne complexes, synthesis, structure and reactivity of C{sub x} complexes, synthesis and reactivity of alcohol and ether complexes, new catalysts for the epimerization of secondary alcohols; carbon-hydrogen bond activation in alkoxide complexes, pi/sigma equilibria in metal/O=CXX' complexes, and other hydrocarbon ligands; miscellaneous.(WET)

  10. Stau-catalyzed big-bang nucleosynthesis reactions

    SciTech Connect

    Kamimura, Masayasu; Kino, Yasushi; Hiyama, Emiko

    2010-06-01

    We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X{sup -}) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X{sup -} particle has a lifetime of tau{sub X} > or approx. 10{sup 3} s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X{sup -} acts as a catalyst. Some of these X{sup -} catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

  11. Levulinic acid production by two-step acid-catalyzed treatment of Quercus mongolica using dilute sulfuric acid.

    PubMed

    Jeong, Hanseob; Jang, Soo-Kyeong; Hong, Chang-Young; Kim, Seon-Hong; Lee, Su-Yeon; Lee, Soo Min; Choi, Joon Weon; Choi, In-Gyu

    2017-02-01

    The objectives of this research were to produce a levulinic acid by two-step acid-catalyzed treatment of Quercus mongolica and to investigate the effect of treatment parameter (reaction temperature range: 100-230°C; sulfuric acid (SA) concentration range: 0-2%) on the levulinic acid yield. After 1(st) step acid-catalyzed treatment, most of the hemicellulosic C5 sugars (15.6gg/100gbiomass) were released into the liquid hydrolysate at the reaction temperature of 150°C in 1% SA; the solid fraction, which contained 53.5% of the C6 sugars, was resistant to further loss of C6 sugars. Subsequently, 2(nd) step acid-catalyzed treatment of the solid fractions was performed under more severe conditions. Finally, 16.5g/100g biomass of levulinic acid was produced at the reaction temperature of 200°C in 2% SA, corresponding to a higher conversion rate than during single-step treatment.

  12. Ammonia Catalyzed Formation of Sulfuric Acid in Troposphere: The Curious Case of A Base Promoting Acid Rain.

    PubMed

    Bandyopadhyay, Biman; Kumar, Pradeep; Biswas, Partha

    2017-04-03

    Electronic structure calculations have been performed to investigate the role of ammonia in catalyzing the formation of sulfuric acid through hydrolysis of SO3 in Earth's atmosphere. The uncatalyzed process involves a high activation barrier and, till date, is mainly known to occur in Earth's atmosphere only when catalyzed by water and acids. Here we show that hydrolysis of SO3 can be very efficiently catalyzed by ammonia, the most abundant basic component in Earth's atmosphere. It was found, based on magnitude of relative potential energies as well as rate coefficients, that ammonia is the best among all the catalysts studied until now (water and acids) and could be a considerable factor in formation of sulfuric acid in troposphere. The calculated rate coefficient (at 298 K) of ammonia catalyzed reaction has been found to be ~10^5 - 10^7 times greater than that for water catalyzed ones. It was found, based on relative rates of ammonia and water catalyzed processes that in troposphere ammonia, together with water, could be the key factor in determining the rate of formation of sulfuric acid. In fact ammonia could surpass water in catalyzing formation of sulfuric acid via hydrolysis of SO3 at various altitudes in troposphere depending upon their relative concentrations.

  13. Thermodynamics of Enzyme-Catalyzed Reactions: Part 1. Oxidoreductases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.; Bell, Donna; Fazio, Kari; Anderson, Ellen

    1993-03-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by oxidoreductases have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement (temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used); the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it. The thermodynamic conventions pertinent to the tabulation of equilibrium data are discussed. A distinction is made between those thermodynamic quantities which pertain to the overall biochemical reaction and those which pertain to a reference reaction that involves specific species. The data from 205 references have been examined and evaluated. Chemical Abstract Service Registry Numbers have been assigned to the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participated.

  14. Silver-catalyzed arylation of (hetero)arenes by oxidative decarboxylation of aromatic carboxylic acids.

    PubMed

    Kan, Jian; Huang, Shijun; Lin, Jin; Zhang, Min; Su, Weiping

    2015-02-09

    A long-standing challenge in Minisci reactions is achieving the arylation of heteroarenes by oxidative decarboxylation of aromatic carboxylic acids. To address this challenge, the silver-catalyzed intermolecular Minisci reaction of aromatic carboxylic acids was developed. With an inexpensive silver salt as a catalyst, this new reaction enables a variety of aromatic carboxylic acids to undergo decarboxylative coupling with electron-deficient arenes or heteroarenes regardless of the position of the substituents on the aromatic carboxylic acid, thus eliminating the need for ortho-substituted aromatic carboxylic acids, which were a limitation of previously reported methods.

  15. Chemical and genomic evolution of enzyme-catalyzed reaction networks.

    PubMed

    Kanehisa, Minoru

    2013-09-02

    There is a tendency that a unit of enzyme genes in an operon-like structure in the prokaryotic genome encodes enzymes that catalyze a series of consecutive reactions in a metabolic pathway. Our recent analysis shows that this and other genomic units correspond to chemical units reflecting chemical logic of organic reactions. From all known metabolic pathways in the KEGG database we identified chemical units, called reaction modules, as the conserved sequences of chemical structure transformation patterns of small molecules. The extracted patterns suggest co-evolution of genomic units and chemical units. While the core of the metabolic network may have evolved with mechanisms involving individual enzymes and reactions, its extension may have been driven by modular units of enzymes and reactions.

  16. Lipase-catalyzed aza-Michael reaction on acrylate derivatives.

    PubMed

    Steunenberg, Peter; Sijm, Maarten; Zuilhof, Han; Sanders, Johan P M; Scott, Elinor L; Franssen, Maurice C R

    2013-04-19

    A methodology has been developed for an efficient and selective lipase-catalyzed aza-Michael reaction of various amines (primary and secondary) with a series of acrylates and alkylacrylates. Reaction parameters were tuned, and under the optimal conditions it was found that Pseudomonas stutzeri lipase and Chromobacterium viscosum lipase showed the highest selectivity for the aza-Michael addition to substituted alkyl acrylates. For the first time also, some CLEAs were examined that showed a comparable or higher selectivity and yield than the free enzymes and other formulations.

  17. The Iron-Catalyzed Oxidation of Hydrazine by Nitric Acid

    SciTech Connect

    Karraker, D.G.

    2001-07-17

    To assess the importance of iron to hydrazine stability, the study of hydrazine oxidation by nitric acid has been extended to investigate the iron-catalyzed oxidation. This report describes those results.

  18. Iron-catalyzed hydrogen production from formic acid.

    PubMed

    Boddien, Albert; Loges, Björn; Gärtner, Felix; Torborg, Christian; Fumino, Koichi; Junge, Henrik; Ludwig, Ralf; Beller, Matthias

    2010-07-07

    Hydrogen represents a clean energy source, which can be efficiently used in fuel cells generating electricity with water as the only byproduct. However, hydrogen generation from renewables under mild conditions and efficient hydrogen storage in a safe and reversible manner constitute important challenges. In this respect formic acid (HCO(2)H) represents a convenient hydrogen storage material, because it is one of the major products from biomass and can undergo selective decomposition to hydrogen and carbon dioxide in the presence of suitable catalysts. Here, the first light-driven iron-based catalytic system for hydrogen generation from formic acid is reported. By application of a catalyst formed in situ from inexpensive Fe(3)(CO)(12), 2,2':6'2''-terpyridine or 1,10-phenanthroline, and triphenylphosphine, hydrogen generation is possible under visible light irradiation and ambient temperature. Depending on the kind of N-ligands significant catalyst turnover numbers (>100) and turnover frequencies (up to 200 h(-1)) are observed, which are the highest known to date for nonprecious metal catalyzed hydrogen generation from formic acid. NMR, IR studies, and DFT calculations of iron complexes, which are formed under reaction conditions, confirm that PPh(3) plays an active role in the catalytic cycle and that N-ligands enhance the stability of the system. It is shown that the reaction mechanism includes iron hydride species which are generated exclusively under irradiation with visible light.

  19. Firefly bioluminescence: a mechanistic approach of luciferase catalyzed reactions.

    PubMed

    Marques, Simone M; Esteves da Silva, Joaquim C G

    2009-01-01

    Luciferase is a general term for enzymes catalyzing visible light emission by living organisms (bioluminescence). The studies carried out with Photinus pyralis (firefly) luciferase allowed the discovery of the reaction leading to light production. It can be regarded as a two-step process: the first corresponds to the reaction of luciferase's substrate, luciferin (LH(2)), with ATP-Mg(2+) generating inorganic pyrophosphate and an intermediate luciferyl-adenylate (LH(2)-AMP); the second is the oxidation and decarboxylation of LH(2)-AMP to oxyluciferin, the light emitter, producing CO(2), AMP, and photons of yellow-green light (550- 570 nm). In a dark reaction LH(2)-AMP is oxidized to dehydroluciferyl-adenylate (L-AMP). Luciferase also shows acyl-coenzyme A synthetase activity, which leads to the formation of dehydroluciferyl-coenzyme A (L-CoA), luciferyl-coenzyme A (LH(2)-CoA), and fatty acyl-CoAs. Moreover luciferase catalyzes the synthesis of dinucleoside polyphosphates from nucleosides with at least a 3'-phosphate chain plus an intact terminal pyrophosphate moiety. The LH(2) stereospecificity is a particular feature of the bioluminescent reaction where each isomer, D-LH(2) or L-LH(2), has a specific function. Practical applications of the luciferase system, either in its native form or with engineered proteins, encloses the analytical assay of metabolites like ATP and molecular biology studies with luc as a reporter gene, including the most recent and increasing field of bioimaging.

  20. Rh(II)-catalyzed Reactions of Diazoesters with Organozinc Reagents

    PubMed Central

    Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M.

    2015-01-01

    Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethylacetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed. PMID:26241081

  1. Rh(II)-Catalyzed Reactions of Diazoesters with Organozinc Reagents.

    PubMed

    Panish, Robert; Selvaraj, Ramajeyam; Fox, Joseph M

    2015-08-21

    Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethyl acetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed.

  2. Substrate-Assisted Catalysis in the Reaction Catalyzed by Salicylic Acid Binding Protein 2 (SABP2), a Potential Mechanism of Substrate Discrimination for Some Promiscuous Enzymes

    SciTech Connect

    Yao, Jianzhuang; Guo, Haobo; Chaiprasongsuk, Minta; Zhao, Nan; Chen, Feng; Yang, Xiaohan; Guo, Hong

    2015-08-05

    Although one of an enzyme’s hallmarks is the high specificity for their natural substrates, substrate promiscuity has been reported more frequently. We know that promiscuous enzymes generally show different catalytic efficiencies to different substrates, but our understanding of the origin of such differences is still lacking. We report the results of quantum mechanical/molecular mechanical simulations and an experimental study of salicylic acid binding protein 2 (SABP2). SABP2 has promiscuous esterase activity toward a series of substrates but shows a high activity toward its natural substrate, methyl salicylate (MeSA). Finally, our results demonstrate that this enzyme may use substrate-assisted catalysis involving the hydroxyl group from MeSA to enhance the activity and achieve substrate discrimination.

  3. Substrate-Assisted Catalysis in the Reaction Catalyzed by Salicylic Acid Binding Protein 2 (SABP2), a Potential Mechanism of Substrate Discrimination for Some Promiscuous Enzymes

    DOE PAGES

    Yao, Jianzhuang; Guo, Haobo; Chaiprasongsuk, Minta; ...

    2015-08-05

    Although one of an enzyme’s hallmarks is the high specificity for their natural substrates, substrate promiscuity has been reported more frequently. We know that promiscuous enzymes generally show different catalytic efficiencies to different substrates, but our understanding of the origin of such differences is still lacking. We report the results of quantum mechanical/molecular mechanical simulations and an experimental study of salicylic acid binding protein 2 (SABP2). SABP2 has promiscuous esterase activity toward a series of substrates but shows a high activity toward its natural substrate, methyl salicylate (MeSA). Finally, our results demonstrate that this enzyme may use substrate-assisted catalysis involvingmore » the hydroxyl group from MeSA to enhance the activity and achieve substrate discrimination.« less

  4. Substrate-Assisted Catalysis in the Reaction Catalyzed by Salicylic Acid Binding Protein 2 (SABP2), a Potential Mechanism of Substrate Discrimination for Some Promiscuous Enzymes.

    PubMed

    Yao, Jianzhuang; Guo, Haobo; Chaiprasongsuk, Minta; Zhao, Nan; Chen, Feng; Yang, Xiaohan; Guo, Hong

    2015-09-01

    Although one of an enzyme's hallmarks is the high specificity for their natural substrates, substrate promiscuity has been reported more frequently. It is known that promiscuous enzymes generally show different catalytic efficiencies to different substrates, but our understanding of the origin of such differences is still lacking. Here we report the results of quantum mechanical/molecular mechanical simulations and an experimental study of salicylic acid binding protein 2 (SABP2). SABP2 has promiscuous esterase activity toward a series of substrates but shows a high activity toward its natural substrate, methyl salicylate (MeSA). Our results demonstrate that this enzyme may use substrate-assisted catalysis involving the hydroxyl group from MeSA to enhance the activity and achieve substrate discrimination.

  5. Kinetics of acid base catalyzed transesterification of Jatropha curcas oil.

    PubMed

    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.

  6. Activity of formylphosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Jahansouz, H.; Kofron, J.L.; Smithers, G.W.; Himes, R.H.; Reed, G.H.

    1986-05-01

    Formylphosphate (FP), a putative enzyme-bound intermediate in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase, was synthesized from formylfluoride and Pi. Measurement of hydrolysis rates by /sup 31/P NMR showed that FP is very unstable with a half-life of 48 min at 20/sup 0/C and pH 7. At pH 7 hydrolysis occurs with O-P bond cleavage as shown by /sup 18/O incorporation from /sup 18/O-H/sub 2/O into Pi. The substrate activity of FP was tested in the reaction catalyzed by N/sup 10/-formylH/sub 4/folate synthetase isolated from Clostridium cylindrosporum. MgATP + H/sub 4/folate + HCOO/sup -/ in equilibrium MgADP + Pi +N/sup 10/-formylH/sub 4/folate FP supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formylH/sub 4/folate is produced from H/sub 4/-folate and FP but only if ADP is present, and ATP is produced from FP and ADP but only if H/sub 4/folate is present. The requirements for H/sub 4/folate in the synthesis of ATP from ADP and FP and for ADP in the synthesis of N/sup 10/-formylH/sub 4/folate from FP and H/sub 4/folate, are consistent with past kinetic and isotope exchange studies which showed that the reaction proceeds by a sequential mechanism and that all three substrates must be present for any reaction to occur.

  7. Mechanism Studies of Ir-Catalyzed Asymmetric Hydrogenation of Unsaturated Carboxylic Acids.

    PubMed

    Li, Mao-Lin; Yang, Shuang; Su, Xun-Cheng; Wu, Hui-Ling; Yang, Liang-Liang; Zhu, Shou-Fei; Zhou, Qi-Lin

    2017-01-11

    The Ir-catalyzed asymmetric hydrogenation of olefins is widely used for production of value-added bulk and fine chemicals. The iridium catalysts with chiral spiro phosphine-oxazoline ligands developed in our group show high activity and high enantioselectivity in the hydrogenation of olefins bearing a coordinative carboxyl group, such as α,β-unsaturated carboxylic acids, β,γ-unsaturated carboxylic acids, and γ,δ-unsaturated carboxylic acids. Here we conducted detailed mechanistic studies on these Ir-catalyzed asymmetric hydrogenation reactions by using (E)-2-methyl-3-phenylacrylic acid as a model substrate. We isolated and characterized several key intermediates having Ir-H bonds under the real hydrogenation conditions. Particularly, an Ir(III) migratory insertion intermediate was first isolated in an asymmetric hydrogenation reaction promoted by chiral Ir catalysts. That this intermediate cannot undergo reductive elimination in the absence of hydrogen strongly supports the involvement of an Ir(III)/Ir(V) cycle in the hydrogenation. On the basis of the structure of the Ir(III) intermediate, variable-temperature NMR spectroscopy, and density functional theory calculations, we elucidated the mechanistic details of the Ir-catalyzed hydrogenation of unsaturated carboxylic acids and explained the enantioselectivity of the reactions. These findings experimentally and computationally elucidate the mechanism of Ir-catalyzed asymmetric hydrogenation of olefins with a strong coordinative carboxyl group and will likely inspire further catalyst design.

  8. Kinetic analysis of the transglycosidation reaction catalyzed by rabbit spleen pyridine nucleotide glycohydrolase.

    PubMed

    Imai, T

    1989-11-01

    Properties of the transglycosidation reaction catalyzed by rabbit spleen pyridine nucleotide glycohydrolase were characterized using a modified cyanide addition method by which initial velocities of the transglycosidation (vT) and hydrolysis (vH) of pyridine nucleotides could be monitored simultaneously. (1) The vT was routinely determined with NMN and nicotinic acid used as substrates and was observed to be maximal at pH 6. Arrhenius plots of vT and vH indicated that the activation energies for transglycosidation and hydrolysis were 8.7 and 10.7 kcal/mol, respectively. (2) The enzyme showed a broad spectrum of substrate specificity with respect to both pyridine nucleotides and bases. Of the compounds tested, NMN and nicotinic acid were shown to be the best substrates when compared on the basis of Vmax/Km values. Kinetic constants for the enzyme-catalyzed transglycosidation reaction were as follows; Km(NMN) = 0.53 mM, Km(nicotinic acid), as acid form = 15 mM, apparent Vmax = 7.8 mumol/min/mg protein, in the presence of 0.2 M nicotinic acid. (3) The ratio of vT/vH was shown to be dependent on both pH and nicotinic acid concentration. However, transglycosidation versus hydrolysis partition at a fixed pH was constant regardless of the nicotinic acid concentration employed and approximated to be 1.2 x 10(4) at the maximal pH. (4) Nicotinamide, one of the most potent inhibitors for the enzyme-catalyzed hydrolysis, was shown to function as an antagonist for the transglycosidation reaction with NMN and nicotinic acid used as substrates. The inhibition mechanism with nicotinamide was purely noncompetitive with respect to nicotinic acid; on the other hand, the double reciprocal plot of the transglycosidation velocity against NMN concentration at a fixed concentration of nicotinamide was concave downwards. (5) The equilibrium constant of the reaction, NMN + 3-acetylpyridine----3-acetylpyridine mononucleotide + nicotinamide, was 0.61, whereas the conversion of NMN with

  9. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    ERIC Educational Resources Information Center

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  10. Cu-Catalyzed Click Reaction in Carbohydrate Chemistry.

    PubMed

    Tiwari, Vinod K; Mishra, Bhuwan B; Mishra, Kunj B; Mishra, Nidhi; Singh, Anoop S; Chen, Xi

    2016-03-09

    Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

  11. Copper-Catalyzed Click Reaction on/in Live Cells.

    PubMed

    Li, Siheng; Wang, Lin; Yu, Fei; Zhu, Zhiling; Shobaki, Dema; Chen, Haoqing; Wang, Mu; Wang, Jun; Qin, Guoting; Erasquin, Uriel J; Ren, Li; Wang, Yingjun; Cai, Chengzhi

    2017-03-01

    We demonstrated that copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction could be performed inside live mammalian cells without using a chelating azide. Under optimized conditions, the reaction was performed in human ovary cancer cell line OVCAR5 in which newly synthesized proteins were metabolically modified with homopropargylglycine (HPG). This model system allowed us to estimate the efficiency of the reaction on the cell membranes and in the cytosol using mass spectrometry. We found that the reaction was greatly promoted by a tris(triazolylmethyl)amine Cu(I) ligand tethering a cell-penetrating peptide. Uptake of the ligand, copper, and a biotin-tagged azide in the cells was determined to be 69 ± 2, 163 ± 3 and 1.3 ± 0.1 µM, respectively. After 10 minutes of reaction, the product yields on the membrane and cytosolic proteins were higher than 18% and 0.8%, respectively, while 75% cells remained viable. By reducing the biothiols in the system by scraping or treatment with N-ethylmalemide, the reaction yield on the cytosolic proteins was greatly improved to ~9% and ~14%, respectively, while the yield on the membrane proteins remained unchanged. The results indicate that out of many possibilities, deactivation of the current copper catalysts by biothiols is the major reason for the low yield of CuAAC reaction in the cytosol. Overall, we have improved the efficiency for CuAAC reaction on live cells by 3-fold. Despite the low yielding inside live cells, the products that strongly bind to the intracellular targets can be detected by mass spectrometry. Hence, the in situ CuAAC reaction can be potentially used for screening of cell-specific enzyme inhibitors or biomarkers containing 1,4-substituted 1,2,3-triazoles.

  12. Reactions of ethyl diazoacetate catalyzed by methylrhenium trioxide

    SciTech Connect

    Zhu, Z.; Espenson, H.

    1995-11-03

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

  13. Clay-catalyzed reactions of coagulant polymers during water chlorination

    USGS Publications Warehouse

    Lee, J.-F.; Liao, P.-M.; Lee, C.-K.; Chao, H.-P.; Peng, C.-L.; Chiou, C.T.

    2004-01-01

    The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence. ?? 2003 Elsevier Inc. All rights reserved.

  14. Palladium(II)-Catalyzed Enantioselective Reactions Using COP Catalysts.

    PubMed

    Cannon, Jeffrey S; Overman, Larry E

    2016-10-18

    Allylic amides, amines, and esters are key synthetic building blocks. Their enantioselective syntheses under mild conditions is a continuing pursuit of organic synthesis methods development. One opportunity for the synthesis of these building blocks is by functionalization of prochiral double bonds using palladium(II) catalysis. In these reactions, nucleopalladation mediated by a chiral palladium(II) catalyst generates a new heteroatom-substituted chiral center. However, reactions where nucleopalladation occurs with antarafacial stereoselectivity are difficult to render enantioselective because of the challenge of transferring chiral ligand information across the square-planar palladium complex to the incoming nucleophile. In this Account, we describe the development and use of enantiopure palladium(II) catalysts of the COP (chiral cobalt oxazoline palladacyclic) family for the synthesis of enantioenriched products from starting materials derived from prochiral allylic alcohols. We begin with initial studies aimed at rendering catalyzed [3,3]-sigmatropic rearrangements of allylic imidates enantioselective, which ultimately led to the identification of the significant utility of the COP family of Pd(II) catalysts. The first use of an enantioselective COP catalyst was reported by Richards' and our laboratories in 2003 for the enantioselective rearrangement of allylic N-arylimidates. Shortly thereafter, we discovered that the chloride-bridged COP dimer, [COP-Cl]2, was an excellent enantioselective catalyst for the rearrangement of (E)-allylic trichloroacetimidates to enantioenriched allylic trichloroacetamides, this conversion being the most widely used of the allylic imidate rearrangements. We then turn to discuss SN2' reactions catalyzed by the acetate-bridged COP dimer, [COP-OAc]2, which proceed by a unique mechanism to provide branched allylic esters and allylic phenyl ethers in high enantioselectivity. Furthermore, because of the unique nucleopalladation

  15. Silver-catalyzed protodecarboxylation of heteroaromatic carboxylic acids.

    PubMed

    Lu, Pengfei; Sanchez, Carolina; Cornella, Josep; Larrosa, Igor

    2009-12-17

    A simple and highly efficient protodecarboxylation procedure for a variety of heteroaromatic carboxylic acids catalyzed by Ag(2)CO(3) and AcOH in DMSO is described. This methodology can also perform the selective monoprotodecarboxylation of several aromatic dicarboxylic acids.

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

    PubMed

    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

  17. A thermodynamic investigation of reactions catalyzed by tryptophan synthase.

    PubMed

    Kishore, N; Tewari, Y B; Akers, D L; Goldberg, R N; Miles, E W

    1998-07-27

    Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of the following reactions catalyzed by the tryptophan synthase alpha 2 beta 2 complex (EC 4.2.1.20) and its subunits: indole(aq) + L-serine(aq) = L-tryptophan(aq) + H2O(1); L-serine(aq) = pyruvate(aq) + ammonia(aq); indole(aq) + D-glyceraldehyde 3-phosphate(aq) = 1-(indol-3-yl)glycerol 3-phosphate(aq); L-serine(aq) + 1-(indol-3-yl)glycerol 3-phosphate(aq) = L-tryptophan(aq) + D-glyceraldehyde 3-phosphate(aq) + H2O(1). The calorimetric measurements led to standard molar enthalpy changes for all four of these reactions. Direct measurements yielded an apparent equilibrium constant for the third reaction; equilibrium constants for the remaining three reactions were obtained by using thermochemical cycle calculations. The results of the calorimetric and equilibrium measurements were analyzed in terms of a chemical equilibrium model that accounted for the multiplicity of the ionic states of the reactants and products. Thermodynamic quantities for chemical reference reactions involving specific ionic forms have been obtained. These quantities permit the calculation of the position of equilibrium of the above four reactions as a function of temperature, pH, and ionic strength. Values of the apparent equilibrium constants and standard transformed Gibbs free energy changes delta r G'(m) degree under approximately physiological conditions are given. Le Châtelier's principle provides an explanation as to why, in the metabolic pathway leading to the synthesis of L-tryptophan, the third reaction proceeds in the direction of formation of indole and D-glyceraldehyde 3-phosphate even though the apparent equilibrium constant greatly favors the formation of 1-(indol-3-yl)glycerol 3-phosphate.

  18. Deuterium isotope effect on the induction period of the cerium catalyzed Belousov-Zhabotinsky reaction

    NASA Astrophysics Data System (ADS)

    Rossi, Federico; Simoncini, Eugenio; Marchettini, Nadia; Tiezzi, Enzo

    2009-02-01

    In this work we present results about the deuterium isotopic effect on the global kinetics of a cerium catalyzed Belousov-Zhabotinsky reaction. A nonlinear dependence of the induction period upon the percentage of deuterated reactants was found in batch conditions. In order to understand this result, we investigated two reaction pathways responsible for the length of the induction period, namely: (a) the reaction between the enolic form of the malonic acid with molecular bromine and (b) the oxidation of malonic acid by the Ce(IV) ion. In both cases we obtained a linear dependence of the kinetic constants on the percentage of deuterated reactants. Nevertheless, by inserting the experimental values in the MBM (Marburg-Budapest-Missoula) model, we were able to qualitatively simulate the observed trend of the induction period.

  19. Copper-catalyzed formic acid synthesis from CO2 with hydrosilanes and H2O.

    PubMed

    Motokura, Ken; Kashiwame, Daiki; Miyaji, Akimitsu; Baba, Toshihide

    2012-05-18

    A copper-catalyzed formic acid synthesis from CO2 with hydrosilanes has been accomplished. The Cu(OAc)2·H2O-1,2-bis(diphenylphosphino)benzene system is highly effective for the formic acid synthesis under 1 atm of CO2. The TON value approached 8100 in 6 h. The reaction pathway was revealed by in situ NMR analysis and isotopic experiments.

  20. Stability of prostacyclin analogues: an unusual lack of reactivity in acid-catalyzed alkene hydration.

    PubMed

    Magill, A; O'Yang, C; Powell, M F

    1988-04-01

    Prostacyclin analogue 5 undergoes specific acid-catalyzed hydration (kH+ = 1.9 x 10(-7)M-1 sec-1 at 25 degrees C) and a pH-independent oxidation reaction (k0 = 1.2 x 10(-10) sec-1 at 25 degrees C) above pH approximately 5. The hydration reaction for 5 is much slower than for other structurally similar exocyclic alkenes, even though the rate-determining step is proton transfer. This slowness of reaction and an analysis of the pH-rate profile show that 5 does not exhibit significant intramolecular general acid catalysis, as does prostacyclin.

  1. Effectiveness of immobilized lipase Thermomyces lanuginosa in catalyzing interesterification of palm olein in batch reaction.

    PubMed

    Saw, Mei Huey; Siew, Wai Lin

    2014-01-01

    Lipase Thermomyces lanuginosa has shown potential in modifying oils and fats through interesterification. Analyzing the physicochemical properties of the modified oils is important to determine the effectiveness of lipase in catalyzing interesterification. In this study, the effectiveness of the immobilized lipase (Lipozyme(®) TL IM) in catalyzing interesterification of palm olein in pilot-scale batch reactor was determined. The evaluation was done by analyzing the changes of triacylglycerol (TAGs) composition, sn-2 position fatty acids composition and the physical properties of the palm olein after the interesterifications. The pilot-scale batch reaction was conducted for 8 hours with 5 %w/w enzyme dosage based on the results of TAGs composition of the laboratory-scale interesterified products. The pilot-scale results showed that Lipozyme(®) TL IM act as an effective enzyme in converting TAGs, in which 4.5% of trisaturated TAGs (PPP and PPS) were produced in the batch reaction. The formation of these new TAGs had also altered the thermal and physical properties of the palm olein. These interesterified products showed a broad peak and shoulder at high temperature, ranging from 10°C to 40°C, indicating the formation of some new TAGs with high melting points. However, the enzyme did not perform perfectly as a 1,3-specific enzyme in the reaction as a significant reduction of oleic acid and an increment of palmitic acid at the sn-2 position was observed.

  2. TBAF-catalyzed deacylation of cellulose esters: reaction scope and influence of reaction parameters.

    PubMed

    Zheng, Xueyan; Gandour, Richard D; Edgar, Kevin J

    2013-10-15

    In order to expand its utility and understand how to carry it out most efficiently, the scope of the highly regioselective, tetrabutylammonium fluoride (TBAF) catalyzed deacylation of cellulose acetates has been investigated, including the influence of key process parameters: solvent, temperature, and water content. Reactions in DMSO, THF, MEK and acetone afforded similar extents of deacylation and regioselectivity. Reaction with TBAF in DMSO at 50 °C for 18 h was the most efficient process providing regioselective deacylation at O-2/3. All results were consistent with our previous mechanistic proposals. Furthermore, we demonstrate that TBAF-catalyzed deacylation is also effective and regioselective with cellulose acetate, butyrate, and hexanoate triesters, and even with a cellulose ester devoid of alpha protons, cellulose tribenzoate. These reactions displayed regioselectivity for deacylation at O-2/3 similar to that observed earlier with cellulose acetate (DS 2.4).

  3. Silver-Catalyzed Decarboxylative Bromination of Aliphatic Carboxylic Acids.

    PubMed

    Tan, Xinqiang; Song, Tao; Wang, Zhentao; Chen, He; Cui, Lei; Li, Chaozhong

    2017-03-13

    The silver-catalyzed Hunsdiecker bromination of aliphatic carboxylic acids is described. With Ag(Phen)2OTf as the catalyst and dibromoisocyanuric acid as the brominating agent, various aliphatic carboxylic acids underwent decarboxylative bromination to provide the corresponding alkyl bromides under mild conditions. This method not only is efficient and general but also enjoys wide functional group compatibility. An oxidative radical mechanism involving Ag(II) intermediates is proposed.

  4. Bis(oxazoline) Lewis acid catalyzed aldol reactions of pyridine N-oxide aldehydes--synthesis of optically active 2-(1-hydroxyalkyl)pyridine derivatives: development, scope, and total synthesis of an indolizine alkaloid.

    PubMed

    Landa, Aitor; Minkkilä, Anna; Blay, Gonzalo; Jørgensen, Karl Anker

    2006-04-24

    A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.

  5. Mechanism of maltal hydration catalyzed by. beta. -amylase: Role of protein structure in controlling the steric outcome of reactions catalyzed by a glycosylase

    SciTech Connect

    Kitahata, Sumio ); Chiba, S. ); Brewer, C.F.; Hehre, E.J. )

    1991-07-09

    Crystalline (monomeric) soybean and (tetrameric) sweet potato {beta}-amylase were shown to catalyze the cis hydration of maltal ({alpha}-D-glucopyranosyl-2-deoxy-D-arabino-hex-1-enitol) to form {beta}-2-deoxymaltose. As reported earlier with the sweet potato enzyme, maltal hydration in D{sub 2}O by soybean {beta}-amylase was found to exhibit an unusually large solvent deuterium kinetic isotope effect (V{sub H}/V{sub D}=6.5), a reaction rate linearly dependent on the mole fraction of deuterium, and 2-deoxy-(2(a)-{sup 2}H)maltose as product. These results indicate (for each {beta}-amylase) that protonation is the rate-limiting step in a reaction involving a nearly symmetric one-proton transition state and that maltal is specifically protonated from above the double bond. That maltal undergoes cis hydration provides evidence in support of a general-acid-catalyzed, carbonium ion mediated reaction. Of fundamental significance is that {beta}-amylase protonates maltal from a direction opposite that assumed for protonating strach, yet creates products of the same anomeric configuration from both. Such stereochemical dichotomy argues for the overriding role of protein structures is dictating the steric outcome of reactions catalyzed by a glycosylase, by limiting the approach and orientation of water or other acceptors to the reaction center.

  6. Copper-catalyzed cascade reactions of α,β-unsaturated esters with keto esters

    PubMed Central

    Wang, Chongnian; Li, Zengchang

    2015-01-01

    Summary A copper-catalyzed cascade reaction of α,β-unsaturated esters with keto esters is reported. It features a copper-catalyzed reductive aldolization followed by a lactonization. This method provides a facile approach to prepare γ-carboxymethyl-γ-lactones and δ-carboxymethyl-δ-lactones under mild reaction conditions. PMID:25815072

  7. Acid-catalyzed esterification of Zanthoxylum bungeanum seed oil with high free fatty acids for biodiesel production.

    PubMed

    Zhang, Junhua; Jiang, Lifeng

    2008-12-01

    A technique to produce biodiesel from crude Zanthoxylum bungeanum seed oil (ZSO) with high free fatty acids (FFA) was developed. The acid value of ZSO was reduced to 1.16mg KOH/g from 45.51mg KOH/g by only one-step acid-catalyzed esterification with methanol-to-oil molar ratio 24:1, H(2)SO(4) 2%, temperature 60 degrees C and reaction time 80min, which was selected as optimum for the acid-catalyzed esterification. During the acid-catalyzed esterification, FFA was converted into fatty acid methyl esters, which was confirmed by (1)H NMR spectrum. Compared with the other two-step pretreatment procedure, this one-step pretreatment can reduce the production cost of ZSO biodiesel. Alkaline-catalyzed transesterification converted the pretreated ZSO into ZSO biodiesel. The yield of ZSO biodiesel was above 98% determined by (1)H NMR spectrum. This study supports the use of crude ZSO as a viable and valuable raw feedstock for biodiesel production.

  8. Cobalt(II)-catalyzed 1,4-addition of organoboronic acids to activated alkenes: an application to highly cis-stereoselective synthesis of aminoindane carboxylic acid derivatives.

    PubMed

    Chen, Min-Hsien; Mannathan, Subramaniyan; Lin, Pao-Shun; Cheng, Chien-Hong

    2012-11-19

    It all adds up: The 1,4-addition of organoboronic acids to activated alkenes catalyzed by [Co(dppe)Cl(2)] is described. A [3+2]-annulation reaction of ortho-iminoarylboronic acids with acrylates to give various aminoindane carboxylic acid derivatives with cis-stereoselectivity is also demonstrated (see scheme; dppe = 1,2-bis(diphenylphosphino)ethane).

  9. An approach to the synthesis of dimeric resveratrol natural products via a palladium-catalyzed domino reaction

    PubMed Central

    Jeffrey, Jenna L.; Sarpong, Richmond

    2009-01-01

    A route for the rapid assembly of the carbon framework of several resveratrol natural products is presented. A palladium-catalyzed domino reaction of bromostilbene derivative 6 and tolane 7, involving two sequential Heck coupling reactions, provides access to the benzofulvene-based core of various resveratrol-derived natural products. The carbon skeleton of pallidol and its congeners is achieved by a Lewis acid-induced Nazarov-type oxidative cyclization of 9. PMID:20161322

  10. New Stetter reactions catalyzed by thiamine diphosphate dependent MenD from E. coli.

    PubMed

    Beigi, Maryam; Waltzer, Simon; Zarei, Mostafa; Müller, Michael

    2014-12-10

    The intermolecular asymmetric Stetter reaction is a rarely found biocatalysts transformation. MenD, the second enzyme of the menaquinone biosynthetic pathway, catalyzes as a physiological reaction a Stetter-like addition of α-ketoglutarate to isochorismate. The substrate range of MenD for similar 1,4-additions is highly restricted. All other thiamine diphosphate dependent enzymes known to act as stetterases are members of the PigD enzyme subfamily, which accept aliphatic and aromatic α,β-unsaturated ketones and thioesters as Michael acceptor substrates. Here, we describe the unexpected activity of MenD with short-chain α,β-unsaturated acids and derivatives as substrates in Stetter reactions. MenD possesses a characteristic substrate range with respect to Michael acceptor substrates which is distinctly different from the classical stetterases. This provides biocatalytic access to new types of products which are not related to the products currently accessible by thiamine diphosphate dependent enzyme catalysis.

  11. Asymmetric synthesis of allylic sulfonic acids: enantio- and regioselective iridium-catalyzed allylations of Na2SO3.

    PubMed

    Liu, Wei; Zhao, Xiao-ming; Zhang, Hong-bo; Zhang, Liang; Zhao, Ming-zhu

    2014-12-15

    An enantioselective allylation reaction of allylic carbonates with sodium sulfite (Na2 SO3 ) catalyzed by Ir complex was accomplished, providing allylic sulfonic acids in good to excellent yields with a high level of enantio- and regioselectivities. (R)-2-Phenyl-2-sulfoacetic acid, a key intermediate for the synthesis of Cefsulodin and Sulbenicillin, was synthesized as well.

  12. Kinetics of Ethyl Acetate Synthesis Catalyzed by Acidic Resins

    ERIC Educational Resources Information Center

    Antunes, Bruno M.; Cardoso, Simao P.; Silva, Carlos M.; Portugal, Ines

    2011-01-01

    A low-cost experiment to carry out the second-order reversible reaction of acetic acid esterification with ethanol to produce ethyl acetate is presented to illustrate concepts of kinetics and reactor modeling. The reaction is performed in a batch reactor, and the acetic acid concentration is measured by acid-base titration versus time. The…

  13. Asymmetric induction in the zirconium catalyzed ethylmagnesiation reaction

    SciTech Connect

    Bell, J.L.; Whitby, R.J.; Jones, R.V.H.

    1995-12-31

    In 1985 Dzhemilev reported the zirconium catalysed ethylmagnesiation of terminal alkenes. A chiral centre is formed during the reaction which occurs under mild conditions. The authors have applied this reaction to a number of substrates and a mechanism has been elucidated. In order to induce asymmetry into the reaction, several chiral literature catalysts were synthesised including Ethylenebis(tetrahydroindenyl)zirconium dichloride and two more hindered complexes reported by Erker. All of these catalysts displayed low activity and poor asymmetric induction with terminal alkenes. The synthesis and properties of two novel catalysts will be described. Results show high activity furnishing carbomagnesiated products in excellent yields with as little as 2 mol% catalyst. The enantiomeric excesses induced by the complexes are as high as 79% with terminal alkenes but are >95% with cyclic ethers. The catalyst has proved recoverable. Ethylmagnesiation of an amine followed by an acidic workup furnishes the chiral complex in a quantitative return.

  14. Regioselective Versatility of Monooxygenase Reactions Catalyzed by CYP2B6 and CYP3A4: Examples with Single Substrates.

    PubMed

    Erratico, Claudio A; Deo, Anand K; Bandiera, Stelvio M

    2015-01-01

    Hepatic microsomal cytochrome P450 (CYP) enzymes have broad and overlapping substrate specificity and catalyze a variety of monooxygenase reactions, including aliphatic and aromatic hydroxylations, N-hydroxylations, oxygenations of heteroatoms (N, S, P and I), alkene and arene epoxidations, dehalogenations, dehydrogenations and N-, O- and S-dealkylations. Individual CYP enzymes typically catalyze the oxidative metabolism of a common substrate in a regioselective and stereoselective manner. In addition, different CYP enzymes often utilize different monooxygenase reactions when oxidizing a common substrate. This review examines various oxidative reactions catalyzed by a CYP enzyme acting on a single substrate. In the first example, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a halogenated aromatic environmental contaminant, was oxidatively biotransformed by human CYP2B6. Nine different metabolites of BDE-47 were produced by CYP2B6 via monooxygenase reactions that included aromatic hydroxylation, with and without an NIH-shift, dealkylation and debromination. In the second example, lithocholic acid (3α-hydroxy-5β-cholan-24-oic acid), an endogenous bile acid, served as a substrate for human CYP3A4 and yielded five different metabolites via aliphatic hydroxylation and dehydrogenation reactions.

  15. An analytical method for determining relative specificities for sequential reactions catalyzed by the same enzyme: general formulation.

    PubMed

    Mitchell, David Alexander; Carrière, Frédéric; Krieger, Nadia

    2008-04-01

    We present a general formulation of a model that can be used to analyze reaction profiles in systems in which a single enzyme catalyzes several sequential reactions with the same molecular backbone. The analysis of these so-called "repeated-attack systems" allows estimation of the specificities that the enzyme has for the various intermediate substrates that appear in the reaction mixture, relative to the specificity that it has for the initial substrate. Our analytical method has the important advantage that it is not affected by competitive or uncompetitive inhibition, nor by denaturation of the enzyme during the reaction. We carry out case studies in three different systems, the lipase-catalyzed alcoholysis of triacylglycerols, the phytase-catalyzed removal of phosphate groups from phytic acid and the beta-amylase-catalyzed removal of maltose units from maltoheptaose. Our model fits well to all reaction profiles in which the phenomenon of processivity does not occur. It can therefore be used as a general tool for characterizing the relative specificities of "repeated-attack enzymes".

  16. GSTP1-1 stereospecifically catalyzes glutathione conjugation of ethacrynic acid.

    PubMed

    van Iersel, M L; van Lipzig, M M; Rietjens, I M; Vervoort, J; van Bladeren, P J

    1998-12-11

    Using 1H NMR two diastereoisomers of the ethacrynic acid glutathione conjugate (EASG) as well as ethacrynic acid (EA) could be distinguished and quantified individually. Chemically prepared EASG consists of equal amounts of both diastereoisomers. GSTP1-1 stereospecifically catalyzes formation of one of the diastereoisomers (A). The GSTP1-1 mutant C47S and GSTA1-1 preferentially form the same diastereoisomer of EASG as GSTP1-1. Glutathione conjugation of EA by GSTA1-2 and GSTA2-2 is not stereoselective. When human melanoma cells, expressing GSTP1-1, were exposed to ethacrynic acid, diastereoisomer A was the principal conjugate formed, indicating that even at physiological pH the enzyme catalyzed reaction dominates over the chemical conjugation.

  17. Asymmetric synthesis of dihydropyranones from ynones by sequential copper(I)-catalyzed direct aldol and silver(I)-catalyzed oxy-Michael reactions.

    PubMed

    Shi, Shi-Liang; Kanai, Motomu; Shibasaki, Masakatsu

    2012-04-16

    Ynones as diene surrogates: the asymmetric synthesis of enantiomerically enriched substituted dihydropyranones is described. The products are obtained in two steps by a copper(I)-catalyzed direct aldol reaction of ynones followed by a silver-catalyzed oxy-Michael reaction. This easy method is compatible with both aromatic and aliphatic substrates, and provides excellent chemoselectivity under mild reaction conditions.

  18. Cinchona Alkaloid Catalyzed Sulfa-Michael Addition Reactions Leading to Enantiopure β-Functionalized Cysteines.

    PubMed

    Breman, Arjen C; Telderman, Suze E M; van Santen, Roy P M; Scott, Jamie I; van Maarseveen, Jan H; Ingemann, Steen; Hiemstra, Henk

    2015-11-06

    Sulfa-Michael additions to α,β-unsaturated N-acylated oxazolidin-2-ones and related α,β-unsaturated α-amino acid derivatives have been enantioselectively catalyzed by Cinchona alkaloids functionalized with a hydrogen bond donating group at the C6' position. The series of Cinchona alkaloids includes known C6' (thio)urea and sulfonamide derivatives and several novel species with a benzimidazole, squaramide or a benzamide group at the C6' position. The sulfonamides were especially suited as bifunctional organocatalysts as they gave the products in very good diastereoselectivity and high enantioselectivity. In particular, the C6' sulfonamides catalyzed the reaction with the α,β-unsaturated α-amino acid derivatives to afford the products in a diastereomeric ratio as good as 93:7, with the major isomer being formed in an ee of up to 99%. The products of the organocatalytic sulfa-Michael addition to α,β-unsaturated α-amino acid derivatives were subsequently converted in high yields to enantiopure β-functionalized cysteines suitable for native chemical ligation.

  19. The Acid Catalyzed Nitration of Methanol: Formation of Methyl Nitrate via Aerosol Chemistry

    NASA Technical Reports Server (NTRS)

    Riffel, Brent G.; Michelsen, Rebecca R.; Iraci, Laura T.

    2004-01-01

    The liquid phase acid catalyzed reaction of methanol with nitric acid to yield methyl nitrate under atmospheric conditions has been investigated using gas phase infrared spectroscopy. This nitration reaction is expected to occur in acidic aerosol particles found in the upper troposphere/lower stratosphere as highly soluble methanol and nitric acid diffuse into these aerosols. Gaseous methyl nitrate is released upon formation, suggesting that some fraction of NO(x) may he liberated from nitric acid (methyl nitrate is later photolyzed to NO(x)) before it is removed from the atmosphere by wet deposition. Thus, this reaction may have important implications for the NO(x) budget. Reactions have been initiated in 45-62 wt% H2SO4 solutions at 10.0 C. Methyl nitrate production rates increased exponentially with acidity within the acidity regime studied. Preliminary calculations suggest that the nitronium ion (NO2(+) is the active nitrating agent under these conditions. The reaction order in methanol appears to depend on the water/methanol ratio and varies from first to zeroth order under conditions investigated. The nitration is first order in nitronium at all acidities investigated. A second order rate constant, kappa(sub 2), has been calculated to be 1 x 10(exp 8)/ M s when the reaction is first order in methanol. Calculations suggest the nitration is first order in methanol under tropospheric conditions. The infinitesimal percentage of nitric acid in the nitronium ion form in this acidity regime probably makes this reaction insignificant for the upper troposphere; however, this nitration may become significant in the mid stratosphere where colder temperatures increase nitric acid solubility and higher sulfuric acid content shifts nitric acid speciation toward the nitronium ion.

  20. Microwave-assisted 18O-labeling of proteins catalyzed by formic acid.

    PubMed

    Liu, Ning; Wu, Hanzhi; Liu, Hongxia; Chen, Guonan; Cai, Zongwei

    2010-11-01

    Oxygen exchange may occur at carboxyl groups catalyzed by acid. The reaction, however, takes at least several days at room temperature. The long-time exchanging reaction often prevents its application from protein analysis. In this study, an (18)O-labeling method utilizing microwave-assisted acid hydrolysis was developed. After being dissolved in (16)O/(18)O (1:1) water containing 2.5% formic acid, protein samples were exposed to microwave irradiation. LC-MS/MS analysis of the resulted peptide mixtures indicated that oxygen in the carboxyl groups from glutamic acid, aspartic acid, and the C-terminal residues could be efficiently exchanged with (18)O within less than 15 min. The rate of back exchange was so slow that no detectable back exchange could be found during the HPLC run.

  1. Laboratory Studies of Hydrogen Gas Generation Using the Cobalt Chloride Catalyzed Sodium Borohydride-Water Reaction

    DTIC Science & Technology

    2015-07-01

    TECHNICAL REPORT 2082 July 2015 Laboratory Studies of Hydrogen Gas Generation Using the Cobalt Chloride Catalyzed Sodium ...describes experiments to generate hydrogen gas using the cobalt chloride catalyzed sodium borohydride-water reaction. Space and Naval Warfare Systems...to inflate LTAs. Of the metal hydrides, we chose to explore the sodium borohydride chemistry. We chose this chemistry because of its energy density

  2. The enzymatic reaction catalyzed by lactate dehydrogenase exhibits one dominant reaction path

    NASA Astrophysics Data System (ADS)

    Masterson, Jean E.; Schwartz, Steven D.

    2014-10-01

    Enzymes are the most efficient chemical catalysts known, but the exact nature of chemical barrier crossing in enzymes is not fully understood. Application of transition state theory to enzymatic reactions indicates that the rates of all possible reaction paths, weighted by their relative probabilities, must be considered in order to achieve an accurate calculation of the overall rate. Previous studies in our group have shown a single mechanism for enzymatic barrier passage in human heart lactate dehydrogenase (LDH). To ensure that this result was not due to our methodology insufficiently sampling reactive phase space, we implement high-perturbation transition path sampling in both microcanonical and canonical regimes for the reaction catalyzed by human heart LDH. We find that, although multiple, distinct paths through reactive phase space are possible for this enzymatic reaction, one specific reaction path is dominant. Since the frequency of these paths in a canonical ensemble is inversely proportional to the free energy barriers separating them from other regions of phase space, we conclude that the rarer reaction paths are likely to have a negligible contribution. Furthermore, the non-dominate reaction paths correspond to altered reactive conformations and only occur after multiple steps of high perturbation, suggesting that these paths may be the result of non-biologically significant changes to the structure of the enzymatic active site.

  3. An atom-economic approach to carboxylic acids via Pd-catalyzed direct addition of formic acid to olefins with acetic anhydride as a co-catalyst.

    PubMed

    Wang, Yang; Ren, Wenlong; Shi, Yian

    2015-08-21

    An effective Pd-catalyzed hydrocarboxylation of olefins using formic acid with acetic anhydride as a co-catalyst is described. A variety of carboxylic acids are obtained in good yields with high regioselectivities under mild reaction conditions without the use of toxic CO gas.

  4. Acid-catalyzed furfurly alcohol polymerization : characterizations of molecular structure and thermodynamic properties.

    SciTech Connect

    Kim, T.; Assary, R. S.; Marshall, C. L.; Gosztola, D. J.; Curtiss, L. A.; Stair, P. C.

    2011-01-01

    The liquid-phase polymerization of furfuryl alcohol catalyzed by sulfuric acid catalysts and the identities of molecular intermediates were investigated by using Raman spectroscopy and density functional theory calculation. At room temperature, with an acid catalyst, a vigorous furfuryl alcohol polymerization reaction was observed, whereas even at a high water concentration, furfuryl alcohol was very stable in the absence of an acid catalyst. Theoretical studies were carried out to investigate the thermodynamics of protonation of furfuryl alcohol, initiation of polymerization, and formation of conjugated dienes and diketonic species by using the B3LYP level of theory. A strong aliphatic C=C band observed in the calculated and measured Raman spectra provided crucial evidence to understand the polymerization reaction mechanism. It is confirmed that the formation of a conjugated diene structure rather than a diketone structure is involved in the furfuryl alcohol polymerization reaction.

  5. Acid-catalyzed Furfuryl Alcohol Polymerization: Characterizations of Molecular Structure and Thermodynamic Properties

    SciTech Connect

    Kim, Taejin; Assary, Rajeev A.; Marshall, Christopher L.; Gosztola, David J.; Curtiss, Larry A.; Stair, Peter C.

    2011-07-22

    The liquid-phase polymerization of furfuryl alcohol catalyzed by sulfuric acid catalysts and the identities of molecular intermediates were investigated by using Raman spectroscopy and density functional theory calculation. At room temperature, with an acid catalyst, a vigorous furfuryl alcohol polymerization reaction was observed, whereas even at a high water concentration, furfuryl alcohol was very stable in the absence of an acid catalyst. Theoretical studies were carried out to investigate the thermodynamics of protonation of furfuryl alcohol, initiation of polymerization, and formation of conjugated dienes and diketonic species by using the B3LYP level of theory. A strong aliphatic C=C band observed in the calculated and measured Raman spectra provided crucial evidence to understand the polymerization reaction mechanism. It is confirmed that the formation of a conjugated diene structure rather than a diketone structure is involved in the furfuryl alcohol polymerization reaction.

  6. Fujiwara-Moritani Reaction of Weinreb Amides using a Ruthenium-Catalyzed C-H Functionalization Reaction.

    PubMed

    Das, Riki; Kapur, Manmohan

    2015-07-01

    The ruthenium-catalyzed Fujiwara-Moritani reaction (oxidative-Heck reaction) of Weinreb amides is reported herein. The reaction affords exclusively ortho-C-H olefination products, has excellent substrate scope and tolerates halogen functionalities, which increase the synthetic utility of the method. A variety of activated olefins as well as styrenes can be employed as coupling partners.

  7. 4-Dimenthylaminopyridine or Acid-Catalyzed Synthesis of Esters: A Comparison

    ERIC Educational Resources Information Center

    van den Berg, Annemieke W. C.; Hanefeld, Ulf

    2006-01-01

    A set of highly atom-economic experiments was developed to highlight the differences between acid- and base-catalyzed ester syntheses and to introduce the principles of atom economy. The hydrochloric acid-catalyzed formation of an ester was compared with the 4-dimethylaminopyradine-catalyzed ester synthesis.

  8. First Novozym 435 lipase-catalyzed Morita-Baylis-Hillman reaction in the presence of amides.

    PubMed

    Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

    2016-03-01

    The first Novozym 435 lipase-catalyzed Morita-Baylis-Hillman (MBH) reaction with amides as co-catalyst was realized. Results showed that neither Novozym 435 nor amide can independently catalyze the reaction. This co-catalytic system that used a catalytic amount of Novozym 435 with a corresponding amount of amide was established and optimized. The MBH reaction strongly depended on the structure of aldehyde substrate, amide co-catalyst, and reaction additives. The optimized reaction yield (43.4%) was achieved in the Novozym 435-catalyzed MBH reaction of 2, 4-dinitrobenzaldehyde and cyclohexenone with isonicotinamide as co-catalyst and β-cyclodextrin as additive only in 2 days. Although enantioselectivity of Novozym 435 was not found, the results were still significant because an MBH reaction using lipase as biocatalyst was realized for the first time.

  9. Asymmetric Synthesis of Hydrocarbazoles Catalyzed by an Octahedral Chiral-at-Rhodium Lewis Acid.

    PubMed

    Huang, Yong; Song, Liangliang; Gong, Lei; Meggers, Eric

    2015-12-01

    A bis-cyclometalated chiral-at-metal rhodium complex catalyzes the Diels-Alder reaction between N-Boc-protected 3-vinylindoles (Boc = tert-butyloxycarbonyl) and β-carboxylic ester-substituted α,β-unsaturated 2-acyl imidazoles with good-to-excellent regioselectivity (up to 99:1) and excellent diastereoselectivity (>50:1 d.r.) as well as enantioselectivity (92-99% ee) under optimized conditions. The rhodium catalyst serves as a chiral Lewis acid to activate the 2-acyl imidazole dienophile by two-point binding and overrules the preferred regioselectivity of the uncatalyzed reaction.

  10. Copper(II)-catalyzed hydroxylation of aryl halides using glycolic acid as a ligand.

    PubMed

    Xiao, Yan; Xu, Yongnan; Cheon, Hwan-Sung; Chae, Junghyun

    2013-06-07

    Copper(II)-catalyzed hydroxylation of aryl halides has been developed to afford functionalized phenols. The protocol utilizes the reagent combination of Cu(OH)2, glycolic acid, and NaOH in aqueous DMSO, all of which are cheap, readily available, and easily removable after the reaction. A broad range of aryl iodides and activated aryl bromides were transformed into the corresponding phenols in excellent yields. Moreover, it has been shown that C-O(alkyl)-coupled product, instead of phenol, can be predominantly formed under similar reaction conditions.

  11. PALLADIUM-CATALYZED OXIDATION OF STYRENE AND ALKENES IN PRESENCE OF IONIC LIQUIDS (WACKER REACTION)

    EPA Science Inventory

    The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...

  12. Enantioselective synthesis of SSR 241586 by using an organo-catalyzed Henry reaction.

    PubMed

    Cochi, Anne; Métro, Thomas-Xavier; Pardo, Domingo Gomez; Cossy, Janine

    2010-08-20

    An organo-catalyzed Henry reaction, applied to an alpha-keto ester, has allowed the enantioselective synthesis of SSR 241586, a 2,2-disubstituted morpholine active in the treatment of schizophrenia and irritable bowel syndrome (IBS).

  13. 1H NMR studies of substrate hydrogen exchange reactions catalyzed by L-methionine gamma-lyase.

    PubMed

    Esaki, N; Nakayama, T; Sawada, S; Tanaka, H; Soda, K

    1985-07-16

    Hydrogen exchange reactions of various L-amino acids catalyzed by L-methionine gamma-lyase (EC 4.4.1.11) have been studied. The enzyme catalyzes the rapid exchange of the alpha- and beta-hydrogens of L-methionine and S-methyl-L-cysteine with deuterium from the solvent. The rate of alpha-hydrogen exchange was about 40 times faster than that of the enzymatic elimination reaction of the sulfur-containing amino acids. The enzyme also catalyzes the exchange reaction of alpha- and beta-hydrogens of the following straight-chain L-amino acids which are not susceptible to elimination: norleucine, norvaline, alpha-aminobutyrate, and alanine. The exchange rates of the alpha-hydrogen and the total beta-hydrogens of L-alanine and L-alpha-aminobutyrate with deuterium followed first-order kinetics. For L-norvaline, L-norleucine, S-methyl-L-cysteine, and L-methionine, the rate of alpha-hydrogen exchange followed first-order kinetics, but the rate of total beta-hydrogen exchange decreased due to a primary isotope effect at the alpha-position. One beta-hydrogen of S-methyl-L-cysteine was exchanged faster than the other, although both the beta-hydrogens were exchanged completely with deuterium ultimately. L-Phenylalanine and L-tryptophan slowly underwent alpha-hydrogen exchange. The pro-R hydrogen of glycine was deuterated stereospecifically. None of the following amino acids were susceptible to the enzymatic hydrogen exchange: D isomers of the above amino acids, branched chain L-amino acids, acidic L-amino acids, and basic L-amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

  14. Ni(II) Tol-BINAP-catalyzed enantioselective Michael reactions of beta-ketoesters and unsaturated N-acylthiazolidinethiones.

    PubMed

    Evans, David A; Thomson, Regan J; Franco, Francisco

    2005-08-10

    The enantioselective addition of beta-ketoesters to unsaturated N-acylthiazolidinethiones catalyzed by Ni(II) Tol-BINAP Lewis acid complexes is reported. Notable features of this reaction are its operation simplicity, the obviated need for the addition of an external base, and the ease with which the adducts are converted into a range of potentially useful derivatives. In particular, the dihydropyrone adducts are versatile scaffolds for further stereoselective elaboration.

  15. Iron-catalyzed cross-coupling reactions of alkyl Grignards with aryl sulfamates and tosylates.

    PubMed

    Agrawal, Toolika; Cook, Silas P

    2013-01-04

    The iron-catalyzed cross-coupling of aryl sulfamates and tosylates has been achieved with primary and secondary alkyl Grignards. This study of iron-catalyzed cross-coupling reactions also examines the isomerization and β-hydride elimination problems that are associated with the use of isopropyl nucleophiles. While a variety of iron sources were competent in the reaction, the use of FeF(3)•3H(2)O was critical to minimize nucleophile isomerization.

  16. Iron-Catalyzed Decarboxylative Alkyl Etherification of Vinylarenes with Aliphatic Acids as the Alkyl Source.

    PubMed

    Jian, Wujun; Ge, Liang; Jiao, Yihang; Qian, Bo; Bao, Hongli

    2017-03-20

    Because of the lack of effective alkylating reagents, alkyl etherification of olefins with general alkyl groups has not been previously reported. In this work, a variety of alkyl diacyl peroxides and peresters generated from aliphatic acids have been found to enable the first iron-catalyzed alkyl etherification of olefins with general alkyl groups. Primary, secondary and tertiary aliphatic acids are suitable for this reaction, delivering products with yields up to 97 %. Primary and secondary alcohols react well, affording products in up to 91 % yield.

  17. First principles (DFT) characterization of Rh(I) /dppp-catalyzed C-H activation by tandem 1,2-addition/1,4-Rh shift reactions of norbornene to phenylboronic acid.

    PubMed

    Kantchev, Eric Assen B; Pangestu, Surya R; Zhou, Feng; Sullivan, Michael B; Su, Hai-Bin

    2014-11-17

    The C-H activation in the tandem, "merry-go-round", [(dppp)Rh]-catalyzed (dppp=1,3-bis(diphenylphosphino)propane), four-fold addition of norborene to PhB(OH)2 has been postulated to occur by a C(alkyl)H oxidative addition to square-pyramidal Rh(III) -H species, which in turn undergoes a C(aryl)-H reductive elimination. Our DFT calculations confirm the Rh(I) /Rh(III) mechanism. At the IEFPCM(toluene, 373.15 K)/PBE0/DGDZVP level of theory, the oxidative addition barrier was calculated to be 12.9 kcal mol(-1) , and that of reductive elimination was 5.0 kcal mol(-1) . The observed selectivity of the reaction correlates well with the relative energy barriers of the cycle steps. The higher barrier (20.9 kcal mol(-1) ) for norbornyl-Rh protonation ensures that the reaction is steered towards the 1,4-shift (total barrier of 16.3 kcal mol(-1) ), acting as an equilibration shuttle. The carborhodation (13.2 kcal mol(-1) ) proceeds through a lower barrier than the protonation (16.7 kcal mol(-1) ) of the rearranged aryl-Rh species in the absence of o- or m-substituents, ensuring multiple carborhodations take place. However, for 2,5-dimethylphenyl, which was used as a model substrate, the barrier for carborhodation is increased to 19.4 kcal mol(-1) , explaining the observed termination of the reaction at 1,2,3,4-tetra(exo-norborn-2-yl)benzene. Finally, calculations with (Z)-2-butene gave a carborhodation barrier of 20.2 kcal mol(-1) , suggesting that carborhodation of non-strained, open-chain substrates would be disfavored relative to protonation.

  18. Investigating the mechanism of the selective hydrogenation reaction of cinnamaldehyde catalyzed by Ptn clusters.

    PubMed

    Li, Laicai; Wang, Wei; Wang, Xiaolan; Zhang, Lin

    2016-08-01

    Cinnamaldehyde (CAL) belongs to the group of aromatic α,β-unsaturated aldehydes; the selective hydrogenation of CAL plays an important role in the fine chemical and pharmaceutical industries. Using Ptn clusters as catalytic models, we studied the selective hydrogenation reaction mechanism for CAL catalyzed by Ptn (n = 6, 10, 14, 18) clusters by means of B3LYP in density functional theory at the 6-31+ G(d) level (the LanL2DZ extra basis set was used for the Pt atom). The rationality of the transition state was proved by vibration frequency analysis and intrinsic reaction coordinate computation. Moreover, atoms in molecules theory and nature bond orbital theory were applied to discuss the interaction among orbitals and the bonding characteristics. The results indicate that three kinds of products, namely 3-phenylpropyl aldehyde, 3-phenyl allyl alcohol and cinnamyl alcohol, are produced in the selective hydrogenation reaction catalyzed by Ptn clusters; each pathway possesses two reaction channels. Ptn clusters are more likely to catalyze the activation and hydrogenation of the C = O bond in CAL molecules, eventually producing cinnamic alcohol, which proves that Ptn clusters have a strong reaction selectivity to catalyze CAL. The reaction selectivity of the catalyzer cluster is closely related to the size of the Ptn cluster, with Pt14 clusters having the greatest reaction selectivity. Graphical Abstract The reaction mechanism for the selective hydrogenation reaction ofcinnamaldehyde catalyzed by Ptn clusters was studied by densityfunctional theory. The reactionselectivity of cluster catalyzer was concluded to be closely related to the size of Ptn clusters, with Pt14 clusters having the greatest reaction selectivity.

  19. Gold(III)-catalyzed three-component coupling reaction (TCC) selective toward furans.

    PubMed

    Li, Jian; Liu, Li; Ding, Dong; Sun, Jiangtao; Ji, Yangxuan; Dong, Jialing

    2013-06-07

    An efficient three-component coupling reaction toward a variety of furan derivatives has been developed. This cascade transformation proceeds via the gold-catalyzed coupling reaction of phenylglyoxal derivatives, secondary amines, and terminal alkynes, under the reaction conditions, that undergoes cyclization into the furan core.

  20. Copper-Catalyzed SN2'-Selective Allylic Substitution Reaction of gem-Diborylalkanes.

    PubMed

    Zhang, Zhen-Qi; Zhang, Ben; Lu, Xi; Liu, Jing-Hui; Lu, Xiao-Yu; Xiao, Bin; Fu, Yao

    2016-03-04

    A Cu/(NHC)-catalyzed SN2'-selective substitution reaction of allylic electrophiles with gem-diborylalkanes is reported. Different substituted gem-diborylalkanes and allylic electrophiles can be employed in this reaction, and various synthetic valuable functional groups can be tolerated. The asymmetric version of this reaction was initially researched with chiral N-heterocyclic carbene (NHC) ligands.

  1. Highly diastereoselective and regioselective copper-catalyzed nitrosoformate dearomatization reaction under aerobic-oxidation conditions.

    PubMed

    Yang, Weibo; Huang, Long; Yu, Yang; Pflästerer, Daniel; Rominger, Frank; Hashmi, A Stephen K

    2014-04-01

    An unprecedented copper-catalyzed acylnitroso dearomatization reaction, which expands the traditional acylnitroso ene reaction and acylnitroso Diels-Alder reaction to a new type of transformation, has been developed under aerobic oxidation. Intermolecular and intra-/intermolecular reaction modes demonstrate an entirely different N- or O-acylnitroso selectivity. Hence, we can utilize this reaction as a highly diastereoselective access to a series of new pyrroloindoline derivatives, which are important structural motifs for natural-product synthesis.

  2. First principle kinetic studies of zeolite-catalyzed methylation reactions.

    PubMed

    Van Speybroeck, Veronique; Van der Mynsbrugge, Jeroen; Vandichel, Matthias; Hemelsoet, Karen; Lesthaeghe, David; Ghysels, An; Marin, Guy B; Waroquier, Michel

    2011-02-02

    Methylations of ethene, propene, and butene by methanol over the acidic microporous H-ZSM-5 catalyst are studied by means of state of the art computational techniques, to derive Arrhenius plots and rate constants from first principles that can directly be compared with the experimental data. For these key elementary reactions in the methanol to hydrocarbons (MTH) process, direct kinetic data became available only recently [J. Catal.2005, 224, 115-123; J. Catal.2005, 234, 385-400]. At 350 °C, apparent activation energies of 103, 69, and 45 kJ/mol and rate constants of 2.6 × 10(-4), 4.5 × 10(-3), and 1.3 × 10(-2) mol/(g h mbar) for ethene, propene, and butene were derived, giving following relative ratios for methylation k(ethene)/k(propene)/k(butene) = 1:17:50. In this work, rate constants including pre-exponential factors are calculated which give very good agreement with the experimental data: apparent activation energies of 94, 62, and 37 kJ/mol for ethene, propene, and butene are found, and relative ratios of methylation k(ethene)/k(propene)/k(butene) = 1:23:763. The entropies of gas phase alkenes are underestimated in the harmonic oscillator approximation due to the occurrence of internal rotations. These low vibrational modes were substituted by manually constructed partition functions. Overall, the absolute reaction rates can be calculated with near chemical accuracy, and qualitative trends are very well reproduced. In addition, the proposed scheme is computationally very efficient and constitutes significant progress in kinetic modeling of reactions in heterogeneous catalysis.

  3. Two-step one-pot synthesis of benzoannulated spiroacetals by Suzuki-Miyaura coupling/acid-catalyzed spiroacetalization.

    PubMed

    Butkevich, Alexey N; Corbu, Andrei; Meerpoel, Lieven; Stansfield, Ian; Angibaud, Patrick; Bonnet, Pascal; Cossy, Janine

    2012-10-05

    Substituted benzoannulated spiroacetals were prepared from (2-haloaryl)alkyl alcohols and dihydropyranyl or dihydrofuranyl pinacol boronates using a Suzuki-Miyaura coupling followed by an acid-catalyzed spirocyclization. Application of the reaction to a glycal boronate provides an approach to annulated spiroacetals in enantiopure form.

  4. Palladium-Catalyzed Enantioselective C-H Activation of Aliphatic Amines Using Chiral Anionic BINOL-Phosphoric Acid Ligands.

    PubMed

    Smalley, Adam P; Cuthbertson, James D; Gaunt, Matthew J

    2017-02-01

    The design of an enantioselective Pd(II)-catalyzed C-H amination reaction is described. The use of a chiral BINOL phosphoric acid ligand enables the conversion of readily available amines into synthetically valuable aziridines in high enantiomeric ratios. The aziridines can be derivatized to afford a range of chiral amine building blocks incorporating motifs readily encountered in pharmaceutically relevant molecules.

  5. Iron-catalyzed cycloaddition reaction of diynes and cyanamides at room temperature.

    PubMed

    Wang, Chunxiang; Wang, Dongping; Xu, Fen; Pan, Bin; Wan, Boshun

    2013-04-05

    An iron-catalyzed [2 + 2 + 2] cycloaddition reaction of diynes and cyanamides at room temperature is reported. Highly substituted 2-aminopyridines were obtained in good to excellent yields with high regioselectivity. Insights toward the reaction process were investigated through in situ IR spectra and control experiments. In this iron-catalyzed cycloaddition reaction, the active iron species was generated only in the presence of both alkynes and nitriles. The lower reaction temperature, broad substrates scope, and inversed regioselectivity make it a complementary method to the previously developed iron catalytic system.

  6. Heterometallic Metal-Organic Frameworks That Catalyze Two Different Reactions Sequentially.

    PubMed

    Saha, Debraj; Hazra, Dipak K; Maity, Tanmoy; Koner, Subratanath

    2016-06-20

    A series of copper- and alkaline-earth-metal-based multidimensional metal-organic frameworks, {[CuMg(pdc)2(H2O)4]·2H2O}n (1), [CuCa(pdc)2]n (2), [CuSr(pdc)2(H2O)3]n (3), and {[CuBa(pdc)2(H2O)5]·H2O}n (4), where H2Pdc = pyridine-2,5-dicarboxylic acid, were hydrothermally synthesized and characterized. Two different metals act as the active center to catalyze two kinds of reactions, viz., olefin to its epoxide followed by epoxide ring opening to afford the corresponding vicinal diol in a sequential manner.

  7. Solid acid-catalyzed depolymerization of barley straw driven by ball milling.

    PubMed

    Schneider, Laura; Haverinen, Jasmiina; Jaakkola, Mari; Lassi, Ulla

    2016-04-01

    This study describes a time and energy saving, solvent-free procedure for the conversion of lignocellulosic barley straw into reducing sugars by mechanocatalytical pretreatment. The catalytic conversion efficiency of several solid acids was tested which revealed oxalic acid dihydrate as a potential catalyst with high conversion rate. Samples were mechanically treated by ball milling and subsequently hydrolyzed at different temperatures. The parameters of the mechanical treatment were optimized in order to obtain sufficient amount of total reducing sugar (TRS) which was determined following the DNS assay. Additionally, capillary electrophoresis (CE) and Fourier transform infrared spectrometry (FT-IR) were carried out. Under optimal conditions TRS 42% was released using oxalic acid dihydrate as a catalyst. This study revealed that the acid strength plays an important role in the depolymerization of barley straw and in addition, showed, that the oxalic acid-catalyzed reaction generates low level of the degradation product 5-hydroxymethylfurfural (HMF).

  8. Transformation of triclosan by laccase catalyzed oxidation: The influence of humic acid-metal binding process.

    PubMed

    Lu, Junhe; Shi, Yuanyuan; Ji, Yuefei; Kong, Deyang; Huang, Qingguo

    2017-01-01

    Laccase is a widely present extracellular phenoloxidase excreted by fungi, bacteria, and high plants. It is able to catalyze one-electron oxidation of phenolic compounds into radical intermediates that can subsequently couple to each other via covalent bonds. These reactions are believed to play an important role in humification process and the transformation of contaminants containing phenolic functionalities in the environment. In this study, we investigated the kinetics of triclosan transformation catalyzed by laccase. It was found that the rate of triclosan oxidation was first order to the concentrations of both substrate and enzyme. Humic acid (HA) could inhibit the reaction by quenching the radical intermediate of triclosan generated by laccase oxidation. Such inhibition was more significant in the presence of divalent metal cations. This is because that binding to metal ions neutralized the negative charge of HA molecules, thus making them more accessible to laccase molecule that is also negatively charged. Therefore, it has greater chance to quench the radical intermediate that is very unstable and can only diffuse a limited distance after being released from the enzyme catalytic center. Based on these understandings, a reaction model was developed by integration of metal-HA binding equilibriums and kinetic equations. This model precisely predicted the transformation rate of triclosan in the presence of HA and divalent metal ions including Ca(2+), Mg(2+), Cd(2+), Co(2+), Mn(2+), Ba(2+), and Zn(2+). Overall, this work reveals important insights into laccase catalyzed oxidative coupling process.

  9. Application of Grote-Hynes theory to the reaction catalyzed by thymidylate synthase.

    PubMed

    Kanaan, Natalia; Roca, Maite; Tuñón, Iñaki; Martí, Sergio; Moliner, Vicent

    2010-10-28

    A theoretical study of dynamic effects on the rate-limiting step of the thymidylate synthase catalyzed reaction has been carried out by means of Grote-Hynes theory, successfully predicting the values of the recrossing effects for a chemical reaction that involves the transfer of a classical light particle. The transmission coefficients, obtained at 278, 293, 303, and 313 K, are almost invariant and in all cases far from unity, revealing a significant coupling of the environment motions and the reaction coordinate. Nevertheless, their energetic contribution to the activation free energy represents less than 0.50 kcal/mol for each of the four tested temperatures. Calculation of the transmission coefficient for the isotopically labeled hydride transfer has rendered almost the same values, in agreement with the experimentally observed temperature-independent KIEs. Fourier transform of the time-dependent friction kernel at these four temperatures has allowed obtaining the transition-state friction spectra, which present very small dependence with temperature. Their analysis has led to the identification of some key vibrational modes governing the coupling between the reaction coordinate and the protein environment, thus identifying the relevant motions in the active site and obtaining a full picture of the role of each amino acid.

  10. Fenton-Like Reaction Catalyzed by the Rare Earth Inner Transition Metal Cerium

    PubMed Central

    HECKERT, ERIC G.; SEAL, SUDIPTA; SELF, WILLIAM T.

    2011-01-01

    Cerium (Ce) is a rare earth metal that is not known to have any biological role. Cerium oxide materials of several sizes and shapes have been developed in recent years as a scaffold for catalysts. Indeed even cerium oxide nanoparticles themselves have displayed catalytic activities and antioxidant properties in tissue culture and animal models. Because of ceria's ability to cycle between the +3 and +4 states at oxygen vacancy sites, we investigated whether cerium metal would catalyze a Fenton-like reaction with hydrogen peroxide. Indeed, cerium chloride did exhibit radical production in the presence of hydrogen peroxide, as assessed by relaxation of supercoiled plasmid DNA. Radical production in this reaction was also followed by production of radical cation of 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). Radical scavengers and spin traps were capable of competing with ABTS for radicals produced in this cerium dependent Fenton-like reaction. Electron paramagnetic resonance experiments reveal both hydroxyl radical and superoxide anion in a reaction containing cerium and hydrogen peroxide. Based on these results we propose that cerium is capable of redox-cycling with peroxide to generate damaging oxygen radicals. PMID:18678042

  11. Fenton-like reaction catalyzed by the rare earth inner transition metal cerium.

    PubMed

    Heckert, Eric G; Seal, Sudipta; Self, William T

    2008-07-01

    Cerium (Ce) is a rare earth metal that is not known to have any biological role. Cerium oxide materials of several sizes and shapes have been developed in recent years as a scaffold for catalysts. Indeed even cerium oxide nanoparticles themselves have displayed catalytic activities and antioxidant properties in tissue culture and animal models. Because of ceria's ability to cycle between the +3 and +4 states at oxygen vacancy sites, we investigated whether cerium metal would catalyze a Fenton-like reaction with hydrogen peroxide. Indeed, cerium chloride did exhibit radical production in the presence of hydrogen peroxide, as assessed by relaxation of supercoiled plasmid DNA. Radical production in this reaction was also followed by production of radical cation of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). Radical scavengers and spin traps were capable of competing with ABTS for radicals produced in this cerium dependent Fenton-like reaction. Electron paramagnetic resonance experiments reveal both hydroxyl radical and superoxide anion in a reaction containing cerium and hydrogen peroxide. Based on these results we propose that cerium is capable of redox-cycling with peroxide to generate damaging oxygen radicals.

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

    PubMed

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

    2015-08-17

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

  13. Lanthanum(III)-Catalyzed Three-Component Reaction of Coumarin-3-carboxylates for the Synthesis of Indolylmalonamides and Analysis of Their Photophysical Properties.

    PubMed

    Jennings, Julia J; Bhatt, Chinmay P; Franz, Annaliese K

    2016-08-05

    New methodology has been developed for the Lewis acid catalyzed synthesis of malonamides. First, the scandium(III)-catalyzed addition of diverse nucleophiles (e.g., indoles, N,N-dimethyl-m-anisidine, 2-ethylpyrrole, and 2-methylallylsilane) to coumarin-3-carboxylates has been developed to afford chromanone-3-carboxylates in high yields as a single diastereomer. Upon investigating a subsequent lanthanum(III)-catalyzed amidation reaction, a new multicomponent reaction was designed by bringing together coumarin-3-carboxylates with indoles and amines to afford indolylmalonamides, which were identified to exhibit fluorescent properties. The photophysical properties for selected compounds have been analyzed, including quantum yield, molar absorptivity, and Stokes shift. Synthetic studies of several reaction byproducts involved in the network of reaction equilibria for the three-component reaction provide mechanistic insight for the development of this methodology.

  14. Deoxycholic acid transformations catalyzed by selected filamentous fungi.

    PubMed

    Kollerov, V V; Lobastova, T G; Monti, D; Deshcherevskaya, N O; Ferrandi, E E; Fronza, G; Riva, S; Donova, M V

    2016-03-01

    More than 100 filamentous fungi strains, mostly ascomycetes and zygomycetes from different phyla, were screened for the ability to convert deoxycholic acid (DCA) to valuable bile acid derivatives. Along with 11 molds which fully degraded DCA, several strains were revealed capable of producing cholic acid, ursocholic acid, 12-keto-lithocholic acid (12-keto-LCA), 3-keto-DCA, 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA as major products from DCA. The last metabolite was found to be a new compound. The ability to catalyze the introduction of a hydroxyl group at the 7(α/β)-positions of the DCA molecule was shown for 32 strains with the highest 7β-hydroxylase activity level for Fusarium merismoides VKM F-2310. Curvularia lunata VKM F-644 exhibited 12α-hydroxysteroid dehydrogenase activity and formed 12-keto-LCA from DCA. Acremonium rutilum VKM F-2853 and Neurospora crassa VKM F-875 produced 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA, respectively, as major products from DCA, as confirmed by MS and NMR analyses. For most of the positive strains, the described DCA-transforming activity was unreported to date. The presented results expand the knowledge on bile acid metabolism by filamentous fungi, and might be suitable for preparative-scale exploitation aimed at the production of marketed bile acids.

  15. Reaction mechanism for cocaine esterase-catalyzed hydrolyses of (+)- and (-)-cocaine: unexpected common rate-determining step.

    PubMed

    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.

  16. Transition-metal-catalyzed group transfer reactions for selective C-H bond functionalization of artemisinin.

    PubMed

    Liu, Yungen; Xiao, Wenbo; Wong, Man-Kin; Che, Chi-Ming

    2007-10-11

    Three types of novel artemisinin derivatives have been synthesized through transition-metal-catalyzed intramolecular carbenoid and nitrenoid C-H bond insertion reactions. With rhodium complexes as catalysts, lactone 11 was synthesized via carbene insertion reaction at the C16 position in 90% yield; oxazolidinone 13 was synthesized via nitrene insertion reaction at the C10 position in 87% yield based on 77% conversion; and sulfamidate 14 was synthesized via nitrene insertion reaction at the C8 position in 87% yield.

  17. Fluorometric assay protocol for protease-catalyzed transesterification reactions in organic solvents.

    PubMed

    Han, Min Su; Jung, Sang Oh; Kim, Mahn-Joo; Kim, Dong H

    2004-04-16

    A flourometric assay protocol for a subtilisin-catalyzed transesterification reaction in n-hexane has been developed. The method makes use of a Michael acceptor that forms a fluorescent adduct with thiophenol, one of the products generated in the transesterification reaction. The method may be employed for screening a biocatalyst useful for transesterification reactions in organic solvents and for optimizing the transesterification reaction conditions.

  18. Brønsted-Evans-Polanyi relationships for C–C bond forming and C–C bond breaking reactions in thiamine-catalyzed decarboxylation of 2-keto acids using density functional theory

    SciTech Connect

    Assary, Rajeev Surendran; Broadbelt, Linda J.; Curtiss, Larry A.

    2011-04-27

    The concept of generalized enzyme reactions suggests that a wide variety of substrates can undergo enzymatic transformations, including those whose biotransformation has not yet been realized. The use of quantum chemistry to evaluate kinetic feasibility is an attractive approach to identify enzymes for the proposed transformation. However, the sheer number of novel transformations that can be generated makes this impractical as a screening approach. Therefore, it is essential to develop structure/activity relationships based on quantities that are more efficient to calculate. In this work, we propose a structure/activity relationship based on the free energy of binding or reaction of non-native substrates to evaluate the catalysis relative to that of native substrates. While Brønsted-Evans-Polanyi (BEP) relationships such as that proposed here have found broad application in heterogeneous catalysis, their extension to enzymatic catalysis is limited. We report here on density functional theory (DFT) studies for C–C bond formation and C–C bond cleavage associated with the decarboxylation of six 2-keto acids by a thiamine-containing enzyme (EC 1.2.7.1) and demonstrate a linear relationship between the free energy of reaction and the activation barrier. We then applied this relationship to predict the activation barriers of 17 chemically similar novel reactions. These calculations reveal that there is a clear correlation between the free energy of formation of the transition state and the free energy of the reaction, suggesting that this method can be further extended to predict the kinetics of novel reactions through our computational framework for discovery of novel biochemical transformations.

  19. Bronsted-Evans-Polany relationships for C-C bond forming and C-C bond breaking reactions in thiamine-catalyzed decarboxylation of 2-keto acids using density functional theory.

    SciTech Connect

    Assary, R. S.; Broadbelt, L. J.; Curtiss, L. A.

    2012-01-01

    The concept of generalized enzyme reactions suggests that a wide variety of substrates can undergo enzymatic transformations, including those whose biotransformation has not yet been realized. The use of quantum chemistry to evaluate kinetic feasibility is an attractive approach to identify enzymes for the proposed transformation. However, the sheer number of novel transformations that can be generated makes this impractical as a screening approach. Therefore, it is essential to develop structure/activity relationships based on quantities that are more efficient to calculate. In this work, we propose a structure/activity relationship based on the free energy of binding or reaction of non-native substrates to evaluate the catalysis relative to that of native substrates. While Broensted-Evans-Polanyi (BEP) relationships such as that proposed here have found broad application in heterogeneous catalysis, their extension to enzymatic catalysis is limited. We report here on density functional theory (DFT) studies for C-C bond formation and C-C bond cleavage associated with the decarboxylation of six 2-keto acids by a thiamine-containing enzyme (EC 1.2.7.1) and demonstrate a linear relationship between the free energy of reaction and the activation barrier. We then applied this relationship to predict the activation barriers of 17 chemically similar novel reactions. These calculations reveal that there is a clear correlation between the free energy of formation of the transition state and the free energy of the reaction, suggesting that this method can be further extended to predict the kinetics of novel reactions through our computational framework for discovery of novel biochemical transformations.

  20. Brønsted-Evans-Polanyi relationships for C-C bond forming and C-C bond breaking reactions in thiamine-catalyzed decarboxylation of 2-keto acids using density functional theory.

    PubMed

    Assary, Rajeev Surendran; Broadbelt, Linda J; Curtiss, Larry A

    2012-01-01

    The concept of generalized enzyme reactions suggests that a wide variety of substrates can undergo enzymatic transformations, including those whose biotransformation has not yet been realized. The use of quantum chemistry to evaluate kinetic feasibility is an attractive approach to identify enzymes for the proposed transformation. However, the sheer number of novel transformations that can be generated makes this impractical as a screening approach. Therefore, it is essential to develop structure/activity relationships based on quantities that are more efficient to calculate. In this work, we propose a structure/activity relationship based on the free energy of binding or reaction of non-native substrates to evaluate the catalysis relative to that of native substrates. While Brønsted-Evans-Polanyi (BEP) relationships such as that proposed here have found broad application in heterogeneous catalysis, their extension to enzymatic catalysis is limited. We report here on density functional theory (DFT) studies for C-C bond formation and C-C bond cleavage associated with the decarboxylation of six 2-keto acids by a thiamine-containing enzyme (EC 1.2.7.1) and demonstrate a linear relationship between the free energy of reaction and the activation barrier. We then applied this relationship to predict the activation barriers of 17 chemically similar novel reactions. These calculations reveal that there is a clear correlation between the free energy of formation of the transition state and the free energy of the reaction, suggesting that this method can be further extended to predict the kinetics of novel reactions through our computational framework for discovery of novel biochemical transformations.

  1. Bulk Gold-Catalyzed Reactions of Isocyanides, Amines, and Amine N-Oxides

    SciTech Connect

    Klobukowski, Erik; Angelici, Robert; Woo, Keith L.

    2012-01-26

    Bulk gold powder (5–50 μm particles) catalyzes the reactions of isocyanides with amines and amine N-oxides to produce ureas. The reaction of n-butyl isocyanide (nBu–N≡C) with di-n-propylamine and N-methylmorpholine N-oxide in acetonitrile, which was studied in the greatest detail, produced 3-butyl-1,1-dipropylurea (O═C(NHnBu)(NnPr2)) in 99% yield at 60 °C within 2 h. Sterically and electronically different isocyanides, amines, and amine N-oxides react successfully under these conditions. Detailed studies support a two-step mechanism that involves a gold-catalyzed reaction of adsorbed isocyanide with the amine N-oxide to form an isocyanate (RN═C═O), which rapidly reacts with the amine to give the urea product. These investigations show that bulk gold, despite its reputation for poor catalytic activity, is capable of catalyzing these reactions.

  2. Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications.

    PubMed

    Johansson, Johan R; Beke-Somfai, Tamás; Said Stålsmeden, Anna; Kann, Nina

    2016-12-14

    The ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) affords 1,5-disubstituted 1,2,3-triazoles in one step and complements the more established copper-catalyzed reaction providing the 1,4-isomer. The RuAAC reaction has quickly found its way into the organic chemistry toolbox and found applications in many different areas, such as medicinal chemistry, polymer synthesis, organocatalysis, supramolecular chemistry, and the construction of electronic devices. This Review discusses the mechanism, scope, and applications of the RuAAC reaction, covering the literature from the last 10 years.

  3. Origins of Stereoselectivity of Chiral Vicinal Diamine-Catalyzed Aldol Reactions.

    PubMed

    Simon, Adam; Yeh, Alexander J; Lam, Yu-Hong; Houk, K N

    2016-12-16

    The sources of asymmetric induction in aldol reactions catalyzed by cinchona alkaloid-derived amines, and chiral vicinal diamines in general, have been determined by density functional theory calculations. Four vicinal diamine-catalyzed aldol reactions were examined. The cyclic transition states of these reactions involve nine-membered hydrogen-bonded rings in distinct conformations. Using nomenclature from eight-membered cycloalkanes, the heavy atoms of the low-energy transition states are in crown (chair-chair) and chair-boat conformations. The factors that control which of these are favored have been identified.

  4. Recent advances in transition metal-catalyzed N -atom transfer reactions of azides

    PubMed Central

    Driver, Tom G.

    2011-01-01

    Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids. PMID:20617243

  5. Highly efficient chemical process to convert mucic acid into adipic acid and DFT studies of the mechanism of the rhenium-catalyzed deoxydehydration.

    PubMed

    Li, Xiukai; Wu, Di; Lu, Ting; Yi, Guangshun; Su, Haibin; Zhang, Yugen

    2014-04-14

    The production of bulk chemicals and fuels from renewable bio-based feedstocks is of significant importance for the sustainability of human society. Adipic acid, as one of the most-demanded drop-in chemicals from a bioresource, is used primarily for the large-volume production of nylon-6,6 polyamide. It is highly desirable to develop sustainable and environmentally friendly processes for the production of adipic acid from renewable feedstocks. However, currently there is no suitable bio-adipic acid synthesis process. Demonstrated herein is the highly efficient synthetic protocol for the conversion of mucic acid into adipic acid through the oxorhenium-complex-catalyzed deoxydehydration (DODH) reaction and subsequent Pt/C-catalyzed transfer hydrogenation. Quantitative yields (99 %) were achieved for the conversion of mucic acid into muconic acid and adipic acid either in separate sequences or in a one-step process.

  6. Kinetic resolution of racemic 1-phenyl 1-propanol by lipase catalyzed enantioselective esterification reaction.

    PubMed

    Karadeniz, Fatma; Bayraktar, Emine; Mehmetoglu, Ulkü

    2010-10-01

    In this study, resolution of (R,S)-1-phenyl 1-propanol by lipase-catalyzed enantioselective esterification was achieved. To investigate the effect of lipase type on enantiomeric excess, three different lipases were used. Novozym 435 exhibited the highest enantioselectivity for resolution of (R,S)-1-phenyl 1-propanol. The effects of carbon length of fatty acids from C12 to C16, which were used as acyl donor, organic solvents with Log P values from 0.5 to 4.5, acyl donor/alcohol molar ratio (1:1, 3:2, 2:1, 3:1), amount of added molecular sieves (0-133.2 kg/m(3)), and temperature (10-60° C) on the enantioselectivity were investigated. The best reaction conditions were comprised of using toluene (Log P= 2.5) as solvent, lauric acid (12C) as acyl donor, 133.2 kg/m(3) molecular sieves at 50° C and acyl donor/alcohol molar ratio as 1:1. Under these conditions, the enantiomeric excess of S enantiomer ee (S) was obtained as 95% for a reaction time of 2.5 hours.

  7. Selective Formation of Secondary Amides via the Copper-Catalyzed Cross-Coupling of Alkylboronic Acids with Primary Amides

    PubMed Central

    Rossi, Steven A.; Shimkin, Kirk W.; Xu, Qun; Mori-Quiroz, Luis M.; Watson, Donald A.

    2014-01-01

    For the first time, a general catalytic procedure for the cross coupling of primary amides and alkylboronic acids is demonstrated. The key to the success of this reaction was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the mono-alkylation of amides. PMID:23611591

  8. Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

    PubMed Central

    Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

    2016-01-01

    Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway. PMID:26922910

  9. Unexpected Reaction Pathway for butyrylcholinesterase-catalyzed inactivation of “hunger hormone” ghrelin

    NASA Astrophysics Data System (ADS)

    Yao, Jianzhuang; Yuan, Yaxia; Zheng, Fang; Zhan, Chang-Guo

    2016-02-01

    Extensive computational modeling and simulations have been carried out, in the present study, to uncover the fundamental reaction pathway for butyrylcholinesterase (BChE)-catalyzed hydrolysis of ghrelin, demonstrating that the acylation process of BChE-catalyzed hydrolysis of ghrelin follows an unprecedented single-step reaction pathway and the single-step acylation process is rate-determining. The free energy barrier (18.8 kcal/mol) calculated for the rate-determining step is reasonably close to the experimentally-derived free energy barrier (~19.4 kcal/mol), suggesting that the obtained mechanistic insights are reasonable. The single-step reaction pathway for the acylation is remarkably different from the well-known two-step acylation reaction pathway for numerous ester hydrolysis reactions catalyzed by a serine esterase. This is the first time demonstrating that a single-step reaction pathway is possible for an ester hydrolysis reaction catalyzed by a serine esterase and, therefore, one no longer can simply assume that the acylation process must follow the well-known two-step reaction pathway.

  10. Enzyme-Catalyzed Henry Reaction in Choline Chloride-Based Deep Eutectic Solvents.

    PubMed

    Tian, Xuemei; Zhang, Suoqin; Zheng, Liangyu

    2016-01-01

    The enzyme-catalyzed Henry reaction was realized using deep eutectic solvents (DESs) as a reaction medium. The lipase from Aspergillus niger (lipase AS) showed excellent catalytic activity toward the substrates aromatic aldehydes and nitromethane in choline chloride:glycerol at a molar ratio of 1:2. Addition of 30 vol% water to DES further improved the lipase activity and inhibited DES-catalyzed transformation. A final yield of 92.2% for the lipase AS-catalyzed Henry reaction was achieved under optimized reaction conditions in only 4 h. In addition, the lipase AS activity was improved by approximately 3-fold in a DES-water mixture compared with that in pure water, which produced a final yield of only 33.4%. Structural studies with fluorescence spectroscopy showed that the established strong hydrogen bonds between DES and water may be the main driving force that affects the spatial conformation of the enzyme, leading to a change in lipase activity. The methodology was also extended to the aza-Henry reaction, which easily occurred in contrast to that in pure water. The enantioselectivity of both Henry and aza-Henry reactions was not found. However, the results are still remarkable, as we report the first use of DES as a reaction medium in a lipase-catalyzed Henry reaction.

  11. Nickel-Catalyzed Heck-Type Reactions of Benzyl Chlorides and Simple Olefins

    PubMed Central

    Matsubara, Ryosuke; Gutierrez, Alicia C.; Jamison, Timothy F.

    2011-01-01

    Nickel-catalyzed intermolecular benzylation and heterobenzylation of unactivated alkenes to provide functionalized allylbenzene derivatives is described. A wide range of both the benzyl chloride and alkene coupling partners are tolerated. In contrast to analogous palladium-catalyzed variants of this process, all reactions described herein employ electronically unbiased aliphatic olefins (including ethylene), proceed at room temperature and provide 1,1-disubstituted olefins over the more commonly observed 1,2-disubstituted olefins with very high selectivity. PMID:22066899

  12. Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase

    PubMed Central

    Míguez, David G.; Vanag, Vladimir K.; Epstein, Irving R.

    2007-01-01

    Waves and patterns in living systems are often driven by biochemical reactions with enzymes as catalysts and regulators. We present a reaction–diffusion system catalyzed by the enzyme glucose oxidase that exhibits traveling wave patterns in a spatially extended medium. Fronts and pulses propagate as a result of the coupling between the enzyme-catalyzed autocatalytic production and diffusion of hydrogen ions. A mathematical model qualitatively explains the experimental observations. PMID:17420460

  13. Mechanism of Brønsted acid-catalyzed glucose dehydration.

    PubMed

    Yang, Liu; Tsilomelekis, George; Caratzoulas, Stavros; Vlachos, Dionisios G

    2015-04-24

    We present the first DFT-based microkinetic model for the Brønsted acid-catalyzed conversion of glucose to 5-hydroxylmethylfurfural (HMF), levulinic acid (LA), and formic acid (FA) and perform kinetic and isotopic tracing NMR spectroscopy mainly at low conversions. We reveal that glucose dehydrates through a cyclic path. Our modeling results are in excellent agreement with kinetic data and indicate that the rate-limiting step is the first dehydration of protonated glucose and that the majority of glucose is consumed through the HMF intermediate. We introduce a combination of 1) automatic mechanism generation with isotopic tracing experiments and 2) elementary reaction flux analysis of important paths with NMR spectroscopy and kinetic experiments to assess mechanisms. We find that the excess formic acid, which appears at high temperatures and glucose conversions, originates from retro-aldol chemistry that involves the C6 carbon atom of glucose.

  14. Relative reactivity of alkenyl alcohols in the palladium-catalyzed redox-relay Heck reaction.

    PubMed

    Hilton, Margaret J; Cheng, Bin; Buckley, Benjamin R; Xu, Liping; Wiest, Olaf; Sigman, Matthew S

    2015-09-16

    The relative rates of alkenyl alcohols in the Pd-catalyzed redox-relay Heck reaction were measured in order to examine the effect of their steric and electronic properties on the rate-determining step. Competition experiments between an allylic alkenyl alcohol and two substrates with differing chain lengths revealed that the allylic alcohol reacts 3-4 times faster in either case. Competition between di- and trisubstituted alkenyl alcohols provided an interesting scenario, in which the disubstituted alkene was consumed first followed by reaction of the trisubstituted alkene. Consistent with this observation, the transition structures for the migratory insertion of the aryl group into the di- and trisubstituted alkenes were calculated with a lower barrier for the former. An internal competition between a substrate containing two alcohols with differing chain lengths demonstrated the catalyst's preference for migrating towards the closest alcohol. Additionally, it was observed that increasing the electron density in the arene boronic acid promotes a faster reaction, which correlates with Hammett σp values to give a ρ of -0.87.

  15. Novel syn intramolecular pathway in base-catalyzed 1,2-elimination reactions of beta-acetoxy esters.

    PubMed

    Mohrig, Jerry R; Carlson, Hans K; Coughlin, Jane M; Hofmeister, Gretchen E; McMartin, Lea A; Rowley, Elizabeth G; Trimmer, Elizabeth E; Wild, Andrew J; Schultz, Steve C

    2007-02-02

    As part of a comprehensive investigation of electronic effects on the stereochemistry of base-catalyzed 1,2-elimination reactions, we observed a new syn intramolecular pathway in the elimination of acetic acid from beta-acetoxy esters and thioesters. 1H and 2H NMR investigation of reactions using stereospecifically labeled tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanoate (1) and its (2R*,3S*) diastereomer (2) shows that 23 +/- 2% syn elimination occurs. The elimination reactions were catalyzed with KOH or (CH3)4NOH in ethanol/water under rigorously non-ion-pairing conditions. By contrast, the more sterically hindered beta-trimethylacetoxy ester produces only 6 +/- 1% syn elimination. These data strongly support an intramolecular (Ei) syn path for elimination of acetic acid, most likely through the oxyanion produced by nucleophilic attack at the carbonyl carbon of the beta-acetoxy group. The analogous thioesters, S-tert-butyl (2R*,3R*)-3-acetoxy-2,3-2H2-butanethioate (3) and its (2R*,3S*) diastereomer (4), showed 18 +/- 2% syn elimination, whereas the beta-trimethylacetoxy substrate gave 5 +/- 1% syn elimination. The more acidic thioester substrates do not produce an increased amount of syn stereoselectivity even though their elimination reactions are at the E1cb interface.

  16. Synthesis of cyclopropyl-substituted furans by brønsted Acid promoted cascade reactions.

    PubMed

    Clark, J Stephen; Romiti, Filippo; Hogg, Kirsten F; Hamid, Malai Haniti S A; Richter, Sven C; Boyer, Alistair; Redman, Joanna C; Farrugia, Louis J

    2015-05-04

    Chloroacetic acid promotes an efficient and diastereoselective intramolecular cascade reaction of electron-deficient ynenones to deliver products featuring a 2,3,5-trisubstituted furan bearing a fused cyclopropyl substituent at the 5-position. Synthetically relevant polycyclic building blocks featuring rings of various sizes and heteroatoms have been synthesized in high yield using this mild acid-catalyzed reaction.

  17. Enantioselective Synthesis of β-Arylamines via Chiral Phosphoric Acid-Catalyzed Asymmetric Reductive Amination.

    PubMed

    Kim, Kyung-Hee; Lee, Chun-Young; Cheon, Cheol-Hong

    2015-06-19

    A new method for the synthesis of chiral β-aryl amines via chiral phosphoric acid-catalyzed enantioselective reductive amination of benzyl methyl ketone derivatives with Hantzsch ester was developed. Various chiral β-aryl amines were obtained in high yields and with good to high enantioselectivities. This transformation is applicable to gram-scale reactions, and the catalyst loading can be reduced to 1 mol % without sacrificing any catalytic efficacy. Furthermore, the resulting β-aryl amine was successfully converted into a tetrahydroisoquinoline compound without any loss of enantioselectivity.

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

    SciTech Connect

    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.

  19. Palladium-catalyzed fluorocarbonylation using N-formylsaccharin as CO source: general access to carboxylic acid derivatives.

    PubMed

    Ueda, Tsuyoshi; Konishi, Hideyuki; Manabe, Kei

    2013-10-18

    N-formylsaccharin, an easily accessible crystalline compound, has been employed as an efficient CO source in Pd-catalyzed fluorocarbonylation of aryl halides to afford the corresponding acyl fluorides in high yields. The reactions use a near-stoichiometric amount of the CO source (1.2 equiv) and tolerate diverse functional groups. The acyl fluorides obtained could be readily transformed into various carboxylic acid derivatives such as carboxylic acid, esters, thioesters, and amides in a one-pot procedure.

  20. Microwave-accelerated Pd-catalyzed desulfitative direct C2-arylation of free (NH)-indoles with arylsulfinic acids.

    PubMed

    Miao, Tao; Li, Pinhua; Wang, Guan-Wu; Wang, Lei

    2013-12-01

    The rapid and efficient direct C2-arylation of free (NH)-indoles with arylsulfinic acids proceeded through a microwave-accelerated palladium-catalyzed desulfitation reaction. By using PdCl2 as a catalyst, silver acetate as an oxidant, and H2SO4 as an additive, arylsulfinic acids with both electron-donating and electron-withdrawing groups underwent desulfitative coupling with an array of free (NH)-indoles, thereby selectively providing C2-arylindoles in good yields.

  1. Advances in nickel-catalyzed cycloaddition reactions to construct carbocycles and heterocycles.

    PubMed

    Thakur, Ashish; Louie, Janis

    2015-08-18

    Transition-metal catalysis has revolutionized the field of organic synthesis by facilitating the construction of complex organic molecules in a highly efficient manner. Although these catalysts are typically based on precious metals, researchers have made great strides in discovering new base metal catalysts over the past decade. This Account describes our efforts in this area and details the development of versatile Ni complexes that catalyze a variety of cycloaddition reactions to afford interesting carbocycles and heterocycles. First, we describe our early work in investigating the efficacy of N-heterocyclic carbene (NHC) ligands in Ni-catalyzed cycloaddition reactions with carbon dioxide and isocyanate. The use of sterically hindered, electron donating NHC ligands in these reactions significantly improved the substrate scope as well as reaction conditions in the syntheses of a variety of pyrones and pyridones. The high reactivity and versatility of these unique Ni(NHC) catalytic systems allowed us to develop unprecedented Ni-catalyzed cycloadditions that were unexplored due to the inefficacy of early Ni catalysts to promote hetero-oxidative coupling steps. We describe the development and mechanistic analysis of Ni/NHC catalysts that couple diynes and nitriles to form pyridines. Kinetic studies and stoichiometric reactions confirmed a hetero-oxidative coupling pathway associated with this Ni-catalyzed cycloaddition. We then describe a series of new substrates for Ni-catalyzed cycloaddition reactions such as vinylcyclopropanes, aldehydes, ketones, tropones, 3-azetidinones, and 3-oxetanones. In reactions with vinycyclopropanes and tropones, DFT calculations reveal noteworthy mechanistic steps such as a C-C σ-bond activation and an 8π-insertion of vinylcyclopropane and tropone, respectively. Similarly, the cycloaddition of 3-azetidinones and 3-oxetanones also requires Ni-catalyzed C-C σ-bond activation to form N- and O-containing heterocycles.

  2. Acid catalyzed alcoholysis of sulfinamides: unusual stereochemistry, kinetics and a question of mechanism involving sulfurane intermediates and their pseudorotation.

    PubMed

    Bujnicki, Bogdan; Drabowicz, Józef; Mikołajczyk, Marian

    2015-02-11

    The synthesis of optically active sulfinic acid esters has been accomplished by the acid catalyzed alcoholysis of optically active sulfinamides. Sulfinates are formed in this reaction with a full or predominant inversion of configuration at chiral sulfur or with predominant retention of configuration. The steric course of the reaction depends mainly on the size of the dialkylamido group in the sulfinamides and of the alcohols used as nucleophilic reagents. It has been found that bulky reaction components preferentially form sulfinates with retention of configuration. It has been demonstrated that the stereochemical outcome of the reaction can be changed from inversion to retention and vice versa by adding inorganic salts to the acidic reaction medium. The unusual stereochemistry of this typical bimolecular nucleophilic substitution reaction, as confirmed by kinetic measurements, has been rationalized in terms of the addition-elimination mechanism, A-E, involving sulfuranes as intermediates which undergo pseudorotations.

  3. Transition-metal-catalyzed carbonylation reactions of olefins and alkynes: a personal account.

    PubMed

    Wu, Xiao-Feng; Fang, Xianjie; Wu, Lipeng; Jackstell, Ralf; Neumann, Helfried; Beller, Matthias

    2014-04-15

    Carbon monoxide was discovered and identified in the 18th century. Since the first applications in industry 80 years ago, academic and industrial laboratories have broadly explored CO's use in chemical reactions. Today organic chemists routinely employ CO in organic chemistry to synthesize all kinds of carbonyl compounds. Despite all these achievements and a century of carbonylation catalysis, many important research questions and challenges remain. Notably, apart from academic developments, industry applies carbonylation reactions with CO on bulk scale. In fact, today the largest applications of homogeneous catalysis (regarding scale) are carbonylation reactions, especially hydroformylations. In addition, the vast majority of acetic acid is produced via carbonylation of methanol (Monsanto or Cativa process). The carbonylation of olefins/alkynes with nucleophiles, such as alcohols and amines, represent another important type of such reactions. In this Account, we discuss our work on various carbonylations of unsaturated compounds and related reactions. Rhodium-catalyzed isomerization and hydroformylation reactions of internal olefins provide straightforward access to higher value aldehydes. Catalytic hydroaminomethylations offer an ideal way to synthesize substituted amines and even heterocycles directly. More recently, our group has also developed so-called alternative metal catalysts based on iridium, ruthenium, and iron. What about the future of carbonylation reactions? CO is already one of the most versatile C1 building blocks for organic synthesis and is widely used in industry. However, because of CO's high toxicity and gaseous nature, organic chemists are often reluctant to apply carbonylations more frequently. In addition, new regulations have recently made the transportation of carbon monoxide more difficult. Hence, researchers will need to develop and more frequently use practical and benign CO-generating reagents. Apart from formates, alcohols, and metal

  4. Noble metal catalyzed hydrogen generation from formic acid in nitrite-containing simulated nuclear waste media

    SciTech Connect

    King, R.B.; Bhattacharyya, N.K.; Wiemers, K.D.

    1994-08-01

    Simulants for the Hanford Waste Vitrification Plant (HWVP) feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO{sub 3}{sup 2{minus}}, NO{sub 3}-, and NO{sub 2}- were used as media to evaluate the stability of formic acid towards hydrogen evolution by the reaction HCO{sub 2}H {yields} H{sub 2} + CO{sub 2} catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Small scale experiments using 40-50 mL of feed simulant in closed glass reactors (250-550 mL total volume) at 80-100{degree}C were used to study the effect of nitrite and nitrate ion on the catalytic activities of the noble metals for formic acid decomposition. Reactions were monitored using gas chromatography to analyze the CO{sub 2}, H{sub 2}, NO, and N{sub 2}O in the gas phase as a function of time. Rhodium, which was introduced as soluble RhCl{sub 3}{center_dot}3H{sub 2}O, was found to be the most active catalyst for hydrogen generation from formic acid above {approx}80{degree}C in the presence of nitrite ion in accord with earlier observations. The inherent homogeneous nature of the nitrite-promoted Rh-catalyzed formic acid decomposition is suggested by the approximate pseudo first-order dependence of the hydrogen production rate on Rh concentration. Titration of the typical feed simulants containing carbonate and nitrite with formic acid in the presence of rhodium at the reaction temperature ({approx}90{degree}C) indicates that the nitrite-promoted Rh-catalyzed decomposition of formic acid occurs only after formic acid has reacted with all of the carbonate and nitrite present to form CO{sub 2} and NO/N{sub 2}O, respectively. The catalytic activities of Ru and Pd towards hydrogen generation from formic acid are quite different than those of Rh in that they are inhibited rather than promoted by the presence of nitrite ion.

  5. Changes in the standard transformed thermodynamic properties of enzyme-catalyzed reactions with ionic strength.

    PubMed

    Alberty, Robert A

    2007-04-12

    The ionic strength has significant effects on the thermodynamic properties of ionic species and on the transformed thermodynamic properties of biochemical reactants at specified pH values. These effects are discussed for species, reactants, and enzyme-catalyzed reactions. This has led to three new thermodynamic properties: (z(j)(2) - NH(j)), (z(2) - N(H))(i), and Delta(r)(z((2)-N(H)), which are referred to as ionic strength coefficients. The first of these is a property of a species, the second is a property of a reactant, and the third is the property of an enzyme-catalyzed reaction. The effects of ionic strength on standard thermodynamic properties of species, standard transformed thermodynamic properties of reactants, and standard transformed thermodynamic properties of enzyme-catalyzed reactions are proportional to these new thermodynamic properties.

  6. Continuous In Vitro Evolution of a Ribozyme that Catalyzes Three Successive Nucleotidyl Addition Reactions

    NASA Technical Reports Server (NTRS)

    McGinness, Kathleen E.; Wright, Martin C.; Joyce, Gerald F.

    2002-01-01

    Variants of the class I ligase ribozyme, which catalyzes joining of the 3' end of a template bound oligonucleotide to its own 5' end, have been made to evolve in a continuous manner by a simple serial transfer procedure that can be carried out indefinitely. This process was expanded to allow the evolution of ribozymes that catalyze three successive nucleotidyl addition reactions, two template-directed mononucleotide additions followed by RNA ligation. During the development of this behavior, a population of ribozymes was maintained against an overall dilution of more than 10(exp 406). The resulting ribozymes were capable of catalyzing the three-step reaction pathway, with nucleotide addition occurring in either a 5' yieldig 3' or a 3' yielding 5' direction. This purely chemical system provides a functional model of a multi-step reaction pathway that is undergoing Darwinian evolution.

  7. Lipase-catalyzed regioselective preparation of fatty acid esters of hydrocortisone.

    PubMed

    Quintana, Paula G; Baldessari, Alicia

    2009-01-01

    A series of fatty acid derivatives of hydrocortisone has been prepared by an enzymatic methodology. Nine 21-monoacyl products and one 3,11,17-triacetyl derivative, nine of them novel compounds, were obtained in a highly regioselective way through lipase-catalyzed esterification, transesterification and alcoholysis reactions. The influence of various reaction parameters such as acylating agent: substrate ratio, enzyme: substrate ratio, solvent, temperature and nature of acylating agent and alcohol was evaluated. Among the tested lipases, Candida antarctica lipase appeared to be the most appropriate and showed a high efficient behavior especially in a one-pot transesterification. The advantages presented by this methodology, such as mild reaction conditions and low environmental impact, make the biocatalysis a convenient way to prepare acyl derivatives of hydrocortisone. These lipophilic compounds are potential products in the pharmaceutical industry.

  8. Temperature effects on enzyme-catalyzed reactions within a cell: Monte Carlo simulations for coupled reaction and diffusion

    NASA Astrophysics Data System (ADS)

    Nangia, Shivangi; Anderson, James B.

    2013-01-01

    We report Monte Carlo simulations of temperature effects on single-step enzymatic reactions with varied rate constants and diffusion coefficients. For typical systems, where the intrinsic reaction rate is more sensitive to temperature than diffusion, the overall reaction is rate-limited at low temperatures and diffusion-limited at high temperatures. The effective activation energy shifts to a much lower value as temperature is increased. Our results show that the temperature dependence of enzyme-catalyzed reactions within a cell may be only loosely related to a potential energy barrier height. The effective activation energy may be strongly affected by coupling of reaction and diffusion.

  9. Combined cross-linked enzyme aggregates of horseradish peroxidase and glucose oxidase for catalyzing cascade chemical reactions.

    PubMed

    Nguyen, Le Truc; Yang, Kun-Lin

    2017-05-01

    Cascade reactions involved unstable intermediates are often encountered in biological systems. In this study, we developed combined cross-linked enzyme aggregates (combi-CLEA) to catalyze a cascade reaction which involves unstable hydrogen peroxide as an intermediate. The combi-CLEA contains two enzymes̶ glucose oxidase (GOx) and horseradish peroxidase (HRP) which are cross-linked together as solid aggregates. The first enzyme GOx catalyzes the oxidation of glucose and produces hydrogen peroxide, which is used by the second enzyme HRP to oxidize 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The apparent reaction rate of the cascade reaction reaches 10.5±0.5μM/min when the enzyme ratio is 150:1 (GOx:HRP). Interestingly, even in the presence of catalase, an enzyme that quickly decomposes hydrogen peroxide, the reaction rate only decreases by 18.7% to 8.3±0.3μM/min. This result suggests that the intermediate hydrogen peroxide is not decomposed by catalase due to a short diffusion distance between GOx and HRP in the combi-CLEA. Scanning electron microscopy images suggest that combi-CLEA particles are hollow spheres and have an average diameter around 250nm. Because of their size, combi-CLEA particles can be entrapped inside a nylon membrane for detecting glucose by using the cascade reaction.

  10. Intensification of heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction using ultrasound: Understanding effect of operating parameters.

    PubMed

    Sancheti, Sonam V; Gogate, Parag R

    2017-01-27

    Palladium-catalyzed Suzuki-Miyaura cross-coupling reaction is a significant reaction for obtaining industrially important products. The current research work deals with intensification of reaction of 4-bromoanisole and phenylboronic acid catalyzed with 5wt% Pd/C (5% by weight Pd supported on C available as commercial catalyst) using ultrasound and more importantly, without use of any additional phase transfer catalyst. Heterogeneous catalyst has been selected in the present work so as to harness the benefits of easy separation and the possible limitations of heterogeneous operation are minimized by introducing ultrasonic irradiations. The effect of operating parameters such as ultrasound power, temperature, catalyst loading and molar ratio on the progress of reaction has been investigated. It has been observed that an optimum power, temperature and catalyst loading exist for maximum benefits whereas higher molar ratio was found to be favourable for the progress of the reaction. Also, the use of ultrasound reduced the reaction time from 70min required in conventional approach to only 35min under conditions of frequency of 22kHz, power dissipation of 40W and catalyst loading as 1.5mol% (refers to total quantum of catalyst used in the work) in ethanol-water system under ambient conditions. The work also demonstrated successful results at ten times higher volume as compared to the normally used volumes in the case of simple ultrasonic horn. Overall, the work has successfully demonstrated process intensification benefits obtained due to the use of ultrasound for heterogeneously catalyzed Suzuki-Miyaura cross-coupling reaction.

  11. Copper(I)-Catalyzed Interrupted Click Reaction: Synthesis of Diverse 5-Hetero-Functionalized Triazoles.

    PubMed

    Wang, Weiguo; Peng, Xianglong; Wei, Fang; Tung, Chen-Ho; Xu, Zhenghu

    2016-01-11

    The 5-heterofunctionalized triazoles are important scaffolds in bioactive compounds, but current click reactions (CuAAC) cannot produce these core structures. A copper(I)-catalyzed interrupted click reaction to access diverse 5-functionalized triazoles is reported. Various 5-amino-, thio-, and selenotriazoles were readily assembled in one step in high yields. The reaction proceeds under mild conditions with complete regioselectivity. It also features a broad substrate scope and good functional group compatibility.

  12. Functional Group Tolerant Nickel-Catalyzed Cross-Coupling Reaction for Enantioselective Construction of 30 Methyl-Bearing Stereocenters

    PubMed Central

    Wisniewska, Hanna M.; Swift, Elizabeth C.; Jarvo, Elizabeth R.

    2013-01-01

    The first Negishi nickel-catalyzed stereospecific cross-coupling reaction of secondary benzylic esters is reported. A series of traceless directing groups are evaluated for ability to promote cross-coupling with dimethylzinc. Esters with a chelating thioether derived from commercially-available 2-(methylthio)acetic acid are most effective. The products are formed in high yield and with excellent stereospecificity. A variety of functional groups are tolerated in the reaction including alkenes, alkynes, esters, amines, imides, and O-, S-, and N-heterocycles. The utility of this transformation is highlighted in the enantioselective synthesis of a retinoic acid receptor (RAR) agonist and a fatty acid amide hydrolase (FAAH) inhibitor. PMID:23751004

  13. Chromium-Catalyzed Asymmetric Dearomatization Addition Reactions of Halomethyl Heteroarenes.

    PubMed

    Tian, Qingshan; Bai, Jing; Chen, Bin; Zhang, Guozhu

    2016-04-15

    The first asymmetric dearomatization addition reaction of halomethyl arenes including benzofuran and benzothiophene was enabled by chromium catalysis. A variety of aldehydes served as suitable electrophiles under mild reaction conditions. Molecular complexities are quickly increased in a highly diastereo- and enantioselective manner.

  14. Regioselective, borinic acid-catalyzed monoacylation, sulfonylation and alkylation of diols and carbohydrates: expansion of substrate scope and mechanistic studies.

    PubMed

    Lee, Doris; Williamson, Caitlin L; Chan, Lina; Taylor, Mark S

    2012-05-16

    Synthetic and mechanistic aspects of the diarylborinic acid-catalyzed regioselective monofunctionalization of 1,2- and 1,3-diols are presented. Diarylborinic acid catalysis is shown to be an efficient and general method for monotosylation of pyranoside derivatives bearing three secondary hydroxyl groups (7 examples, 88% average yield). In addition, the scope of the selective acylation, sulfonylation, and alkylation is extended to 1,2- and 1,3-diols not derived from carbohydrates (28 examples); the efficiency, generality, and operational simplicity of this method are competitive with those of state-of-the-art protocols including the broadly applied organotin-catalyzed or -mediated reactions. Mechanistic details of the organoboron-catalyzed processes are explored using competition experiments, kinetics, and catalyst structure-activity relationships. These experiments are consistent with a mechanism in which a tetracoordinate borinate complex reacts with the electrophilic species in the turnover-limiting step of the catalytic cycle.

  15. Acid-Catalyzed Preparation of Biodiesel from Waste Vegetable Oil: An Experiment for the Undergraduate Organic Chemistry Laboratory

    ERIC Educational Resources Information Center

    Bladt, Don; Murray, Steve; Gitch, Brittany; Trout, Haylee; Liberko, Charles

    2011-01-01

    This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when…

  16. Production of dicarboxylic acids from novel unsaturated fatty acids by laccase-catalyzed oxidative cleavage.

    PubMed

    Takeuchi, Michiki; Kishino, Shigenobu; Park, Si-Bum; Kitamura, Nahoko; Watanabe, Hiroko; Saika, Azusa; Hibi, Makoto; Yokozeki, Kenzo; Ogawa, Jun

    2016-06-27

    The establishment of renewable biofuel and chemical production is desirable because of global warming and the exhaustion of petroleum reserves. Sebacic acid (decanedioic acid), the material of 6,10-nylon, is produced from ricinoleic acid, a carbon-neutral material, but the process is not eco-friendly because of its energy requirements. Laccase-catalyzing oxidative cleavage of fatty acid was applied to the production of dicarboxylic acids using hydroxy and oxo fatty acids involved in the saturation metabolism of unsaturated fatty acids in Lactobacillus plantarum as substrates. Hydroxy or oxo fatty acids with a functional group near the carbon-carbon double bond were cleaved at the carbon-carbon double bond, hydroxy group, or carbonyl group by laccase and transformed into dicarboxylic acids. After 8 h, 0.58 mM of sebacic acid was produced from 1.6 mM of 10-oxo-cis-12,cis-15-octadecadienoic acid (αKetoA) with a conversion rate of 35% (mol/mol). This laccase-catalyzed enzymatic process is a promising method to produce dicarboxylic acids from biomass-derived fatty acids.

  17. Structural characterization of tartrate dehydrogenase: a versatile enzyme catalyzing multiple reactions

    SciTech Connect

    Malik, Radhika; Viola, Ronald E.

    2010-10-28

    The first structure of an NAD-dependent tartrate dehydrogenase (TDH) has been solved to 2 {angstrom} resolution by single anomalous diffraction (SAD) phasing as a complex with the intermediate analog oxalate, Mg{sup 2+} and NADH. This TDH structure from Pseudomonas putida has a similar overall fold and domain organization to other structurally characterized members of the hydroxy-acid dehydrogenase family. However, there are considerable differences between TDH and these functionally related enzymes in the regions connecting the core secondary structure and in the relative positioning of important loops and helices. The active site in these complexes is highly ordered, allowing the identification of the substrate-binding and cofactor-binding groups and the ligands to the metal ions. Residues from the adjacent subunit are involved in both the substrate and divalent metal ion binding sites, establishing a dimer as the functional unit and providing structural support for an alternating-site reaction mechanism. The divalent metal ion plays a prominent role in substrate binding and orientation, together with several active-site arginines. Functional groups from both subunits form the cofactor-binding site and the ammonium ion aids in the orientation of the nicotinamide ring of the cofactor. A lysyl amino group (Lys192) is the base responsible for the water-mediated proton abstraction from the C2 hydroxyl group of the substrate that begins the catalytic reaction, followed by hydride transfer to NAD. A tyrosyl hydroxyl group (Tyr141) functions as a general acid to protonate the enolate intermediate. Each substrate undergoes the initial hydride transfer, but differences in substrate orientation are proposed to account for the different reactions catalyzed by TDH.

  18. Ionic liquid supported acid/base-catalyzed production of biodiesel.

    PubMed

    Lapis, Alexandre A M; de Oliveira, Luciane F; Neto, Brenno A D; Dupont, Jairton

    2008-01-01

    The transesterification (alcoholysis) reaction was successfully applied to synthesize biodiesel from vegetable oils using imidazolium-based ionic liquids under multiphase acidic and basic conditions. Under basic conditions, the combination of the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMINTf2), alcohols, and K2CO3 (40 mol %) results in the production of biodiesel from soybean oil in high yields (>98%) and purity. H2SO4 immobilized in BMINTf2 efficiently promotes the transesterification reaction of soybean oil and various primary and secondary alcohols. In this multiphase process the acid is almost completely retained in the ionic liquid phase, while the biodiesel forms a separate phase. The recovered ionic liquid containing the acid could be reused at least six times without any significant loss in the biodiesel yield or selectivity. In both catalytic processes (acid and base), the reactions proceed as typical multiphasic systems in which the formed biodiesel accumulates as the upper phase and the glycerol by-product is selectively captured by the alcohol-ionic liquid-acid/base phase. Classical ionic liquids such as 1-n-butyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate are not stable under these acidic or basic conditions and decompose.

  19. Tritium secondary kinetic isotope effect on phenylalanine ammonia-lyase-catalyzed reaction.

    PubMed

    Lewandowicz, A; Jemielity, J; Kańska, M; Zoń, J; Paneth, P

    1999-10-15

    The mechanism by which phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) catalyzes the reversible elimination of ammonia from phenylalanine yielding (E)-cinnamic acid has gained much attention in the recent years. Dehydroalanine is essential for the catalysis. It was assumed that this prostetic group acts as the electrophile, leading to a covalently bonded enzyme-intermediate complex with quarternary nitrogen of phenylalanine. Recently, an alternative mechanism has been suggested in which the enzyme-intermediate complex is formed in a Friedel-Crafts reaction between dehydroalanine and orthocarbon of the aromatic ring. Using semiempirical calculations we have shown that these two alternative mechanisms can be distinguished on the basis of the hydrogen secondary kinetic isotope effect when tritium label is placed in the orthopositions. Our calculations indicated also that the kinetic isotope effect measured using ring-labeled d(5)-phenylalanine could not be used to differentiate these alternative mechanisms. Measured secondary tritium kinetic isotope effect shows strong dependence on the reaction progress, starting at the inverse value of k(H)/k(T) = 0.85 for 5% conversion and reaching the normal value of about 1.15 as the conversion increases to 20%. This dependence has been interpreted in terms of a complex mechanism with initial formation of the Friedel-Crafts type intermediate.

  20. Does metabolite channeling accelerate enzyme-catalyzed cascade reactions?

    PubMed Central

    Poshyvailo, Liubov; von Lieres, Eric

    2017-01-01

    Metabolite or substrate channeling is a direct transfer of metabolites from one enzyme to the next enzyme in a cascade. Among many potential advantages of substrate channeling, acceleration of the total reaction rate is considered as one of the most important and self-evident. However, using a simple model, supported by stochastic simulations, we show that it is not always the case; particularly at long times (i.e. in steady state) and high substrate concentrations, a channeled reaction cannot be faster, and can even be slower, than the original non-channeled cascade reaction. In addition we show that increasing the degree of channeling may lead to an increase of the metabolite pool size. We substantiate that the main advantage of channeling likely lies in protecting metabolites from degradation or competing side reactions. PMID:28234973

  1. Thermodynamics of Enzyme-Catalyzed Reactions: Part 6--1999 Update

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.

    1999-07-01

    This review serves to update previously published evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used]; the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 96 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is also a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  2. Thermodynamics of Enzyme-Catalyzed Reactions: Part 5. Isomerases and Ligases

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.

    1995-11-01

    Equilibrium constants and enthalpy changes for reactions catalyzed by the isomerase and ligase classes of enzymes have been compiled. For each reaction the following information is given: the reference for the data; the reaction studied; the name of the enzyme used and its Enzyme Commission number; the method of measurement; the conditions of measurement (temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used); the data and an evaluation of it; and, sometimes, commentary on the data and on any corrections which have been applied to it or any calculations for which the data have been used. The data from 176 references have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  3. Thermodynamics of Enzyme-Catalyzed Reactions: Part 7-2007 Update

    NASA Astrophysics Data System (ADS)

    Goldberg, Robert N.; Tewari, Yadu B.; Bhat, Talapady N.

    2007-12-01

    This review serves to update previously published evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction, the following information is given: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the conditions of measurement [temperature, pH, ionic strength, and the buffer(s) and cofactor(s) used], the data and their evaluation, and, sometimes, commentary on the data and on any corrections which have been applied to the data or any calculations for which the data have been used. The review contains data from 119 references which have been examined and evaluated. Chemical Abstract Service registry numbers are given for the substances involved in these various reactions. There is also a cross reference between the substances and the Enzyme Commission numbers of the enzymes used to catalyze the reactions in which the substances participate.

  4. Global conformational change associated with the two-step reaction catalyzed by Escherichia coli lipoate-protein ligase A.

    PubMed

    Fujiwara, Kazuko; Maita, Nobuo; Hosaka, Harumi; Okamura-Ikeda, Kazuko; Nakagawa, Atsushi; Taniguchi, Hisaaki

    2010-03-26

    Lipoate-protein ligase A (LplA) catalyzes the attachment of lipoic acid to lipoate-dependent enzymes by a two-step reaction: first the lipoate adenylation reaction and, second, the lipoate transfer reaction. We previously determined the crystal structure of Escherichia coli LplA in its unliganded form and a binary complex with lipoic acid (Fujiwara, K., Toma, S., Okamura-Ikeda, K., Motokawa, Y., Nakagawa, A., and Taniguchi, H. (2005) J Biol. Chem. 280, 33645-33651). Here, we report two new LplA structures, LplA.lipoyl-5'-AMP and LplA.octyl-5'-AMP.apoH-protein complexes, which represent the post-lipoate adenylation intermediate state and the pre-lipoate transfer intermediate state, respectively. These structures demonstrate three large scale conformational changes upon completion of the lipoate adenylation reaction: movements of the adenylate-binding and lipoate-binding loops to maintain the lipoyl-5'-AMP reaction intermediate and rotation of the C-terminal domain by about 180 degrees . These changes are prerequisites for LplA to accommodate apoprotein for the second reaction. The Lys(133) residue plays essential roles in both lipoate adenylation and lipoate transfer reactions. Based on structural and kinetic data, we propose a reaction mechanism driven by conformational changes.

  5. Iron- and indium-catalyzed reactions toward nitrogen- and oxygen-containing saturated heterocycles.

    PubMed

    Cornil, Johan; Gonnard, Laurine; Bensoussan, Charlélie; Serra-Muns, Anna; Gnamm, Christian; Commandeur, Claude; Commandeur, Malgorzata; Reymond, Sébastien; Guérinot, Amandine; Cossy, Janine

    2015-03-17

    A myriad of natural and/or biologically active products include nitrogen- and oxygen-containing saturated heterocycles, which are thus considered as attractive scaffolds in the drug discovery process. As a consequence, a wide range of reactions has been developed for the construction of these frameworks, much effort being specially devoted to the formation of substituted tetrahydropyrans and piperidines. Among the existing methods to form these heterocycles, the metal-catalyzed heterocyclization of amino- or hydroxy-allylic alcohol derivatives has emerged as a powerful and stereoselective strategy that is particularly interesting in terms of both atom-economy and ecocompatibility. For a long time, palladium catalysts have widely dominated this area either in Tsuji-Trost reactions [Pd(0)] or in an electrophilic activation process [Pd(II)]. More recently, gold-catalyzed formation of saturated N- and O-heterocycles has received growing attention because it generally exhibits high efficiency and diastereoselectivity. Despite their demonstrated utility, Pd- and Au-complexes suffer from high costs, toxicity, and limited natural abundance, which can be barriers to their widespread use in industrial processes. Thus, the replacement of precious metals with less expensive and more environmentally benign catalysts has become a challenging issue for organic chemists. In 2010, our group took advantage of the ability of the low-toxicity and inexpensive FeCl3 in activating allylic or benzylic alcohols to develop iron-catalyzed N- and O-heterocylizations. We first focused on N-heterocycles, and a variety of 2,6-disubstituted piperidines as well as pyrrolidines were synthesized in a highly diastereoselective fashion in favor of the cis-compounds. The reaction was further extended to the construction of substituted tetrahydropyrans. Besides triggering the formation of heterocycles, the iron salts were shown to induce a thermodynamic epimerization, which is the key to reach the high

  6. Solid acid-catalyzed cellulose hydrolysis monitored by in situ ATR-IR spectroscopy.

    PubMed

    Zakzeski, Joseph; Grisel, Ruud J H; Smit, Arjan T; Weckhuysen, Bert M

    2012-02-13

    The solid acid-catalyzed hydrolysis of cellulose was studied under elevated temperatures and autogenous pressures using in situ ATR-IR spectroscopy. Standards of cellulose and pure reaction products, which include glucose, fructose, hydroxymethylfurfural (HMF), levulinic acid (LA), formic acid, and other compounds, were measured in water under ambient and elevated temperatures. A combination of spectroscopic and HPLC analysis revealed that the cellulose hydrolysis proceeds first through the disruption of the glycosidic linkages of cellulose to form smaller cellulose molecules, which are readily observed by their distinctive C-O vibrational stretches. The continued disruption of the linkages in these oligomers eventually results in the formation and accumulation of monomeric glucose. The solid-acid catalyst accelerated the isomerization of glucose to fructose, which then rapidly reacted under hydrothermal conditions to form degradation products, which included HMF, LA, formic acid, and acetic acid. The formation of these species could be suppressed by decreasing the residence time of glucose in the reactor, reaction temperature, and contact with the metal reactor. The hydrolysis of regenerated cellulose proceeded faster and under milder conditions than microcrystalline cellulose, which resulted in increased glucose yield and selectivity.

  7. Pilot-scale study on the acid-catalyzed steam explosion of rice straw using a continuous pretreatment system.

    PubMed

    Chen, Wen-Hua; Tsai, Chia-Chin; Lin, Chih-Feng; Tsai, Pei-Yuan; Hwang, Wen-Song

    2013-01-01

    A continuous acid-catalyzed steam explosion pretreatment process and system to produce cellulosic ethanol was developed at the pilot-scale. The effects of the following parameters on the pretreatment efficiency of rice straw feedstocks were investigated: the acid concentration, the reaction temperature, the residence time, the feedstock size, the explosion pressure and the screw speed. The optimal presteaming horizontal reactor conditions for the pretreatment process are as follows: 1.7 rpm and 100-110 °C with an acid concentration of 1.3% (w/w). An acid-catalyzed steam explosion is then performed in the vertical reactor at 185 °C for 2 min. Approximately 73% of the total saccharification yield was obtained after the rice straw was pretreated under optimal conditions and subsequent enzymatic hydrolysis at a combined severity factor of 0.4-0.7. Moreover, good long-term stability and durability of the pretreatment system under continuous operation was observed.

  8. Potential of phosphoric acid-catalyzed pretreatment and subsequent enzymatic hydrolysis for biosugar production from Gracilaria verrucosa.

    PubMed

    Kwon, Oh-Min; Kim, Sung-Koo; Jeong, Gwi-Taek

    2016-07-01

    This study combined phosphoric acid-catalyzed pretreatment and enzymatic hydrolysis to produce biosugars from Gracilaria verrucosa as a potential renewable resource for bioenergy applications. We optimized phosphoric acid-catalyzed pretreatment conditions to 1:10 solid-to-liquid ratio, 1.5 % phosphoric acid, 140 °C, and 60 min reaction time, producing a 32.52 ± 0.06 % total reducing sugar (TRS) yield. By subsequent enzymatic hydrolysis, a 68.61 ± 0.90 % TRS yield was achieved. These results demonstrate the potential of phosphoric acid to produce biosugars for biofuel and biochemical production applications.

  9. Chiral diphosphine and monodentate phosphorus ligands on a spiro scaffold for transition-metal-catalyzed asymmetric reactions.

    PubMed

    Xie, Jian-Hua; Zhou, Qi-Lin

    2008-05-01

    hydrogenations of ketones, alpha-arylaldehydes and alpha,beta-unsaturated acids. The rhodium complexes of chiral spiro monophosphorus ligands are highly enantioselective for the asymmetric hydrogenations of alpha- and beta-dehydroamino acid derivatives, alpha-arylethenyl acetamides and non- N-acyl enamines. The spiro monophosphorus ligands were demonstrated to be highly efficient for the Rh-catalyzed asymmetric addition of arylboronic acids to aldehydes and N-tosylarylimines, Pd-catalyzed asymmetric allylation of aldehydes with allylic alcohols, Cu-catalyzed asymmetric ring opening reactions with Grignard reagents, and Ni-catalyzed asymmetric hydrovinylation of styrene derivatives with ethylene. The chiral spiro phosphorus ligands show high enantioselectivities for a wide range of transition-metal-catalyzed asymmetric reactions. In most of these transformations, the enantioselectivities of spiro phosphorus ligands are superior to those obtained by using the corresponding phosphorus ligands with other backbones. These results arise from the intriguing chiral inducement of spiro structures of the ligands.

  10. An Investigation of Model Catalyzed Hydrocarbon Formation Reactions

    SciTech Connect

    Tysoe, W. T.

    2001-05-02

    Work was focused on two areas aimed at understanding the chemistry of realistic catalytic systems: (1) The synthesis and characterization of model supported olefin metathesis catalysts. (2) Understanding the role of the carbonaceous layer present on Pd(111) single crystal model catalysts during reaction.

  11. Energy Diagrams for Enzyme-Catalyzed Reactions: Concepts and Misconcepts

    ERIC Educational Resources Information Center

    Aledo, J. Carlos; Lobo, Carolina; del Valle, Alicia Esteban

    2003-01-01

    Despite the utility that energy diagrams have as a teaching and learning tool, a survey of their use, in seven popular Biochemistry textbooks, reveals that there is certain confusion around this topic. In our opinion, this confusion arises from the reluctance of authors to consider and indicate the conditions under which the reaction being…

  12. Dirhodium carboxylates catalyzed enantioselective coupling reactions of α-diazophosphonates, anilines, and electron-deficient aldehydes.

    PubMed

    Zhou, Cong-Ying; Wang, Jing-Cui; Wei, Jinhu; Xu, Zhen-Jiang; Guo, Zhen; Low, Kam-Hung; Che, Chi-Ming

    2012-11-05

    Chiral dirhodium carboxylate complexes ([Rh(2)(S-PTAD)(4)] or [Rh(2)(S-PTTL)(4)]) efficiently catalyze asymmetric three-component coupling reactions of α-diazophosphonates, anilines, and electron-deficient aldehydes to give α-amino-β-hydroxyphosphonates. The high level of enantiocontrol provides evidence for the intermediacy of metal-bound ammonium ylide in the product-forming step.

  13. Asymmetric Michael addition reactions of nitroalkanes to 2-furanones catalyzed by bifunctional thiourea catalysts.

    PubMed

    Bai, Zhushuang; Ji, Ling; Ge, Zemei; Wang, Xin; Li, Runtao

    2015-05-21

    The first bifunctional thiourea catalyzed asymmetric Michael addition reactions of nitroalkanes to 2-furanones are described. The highly functionalized γ-lactones with two or three consecutive stereogenic carbons were obtained in high yields (up to 99%), high diastereoselectivities (up to >20 : 1 dr) and enantioselectivities (up to >99% ee).

  14. Efficient palladium-catalyzed coupling reactions of aryl bromides and chlorides with phenols.

    PubMed

    Hu, Tongjie; Schulz, Thomas; Torborg, Christian; Chen, Xiaorong; Wang, Jun; Beller, Matthias; Huang, Jun

    2009-12-21

    A convenient and general palladium-catalyzed coupling reaction of aryl bromides and chlorides with phenols was developed. Various functional groups such as nitriles, aldehydes, ketones and esters are well tolerated and the corresponding products are obtained in good to excellent yield.

  15. The effect of Mg/2+/ and Ca/2+/ on urea-catalyzed phosphorylation reactions

    NASA Technical Reports Server (NTRS)

    Handschuk, G. J.; Lohrmann, R.; Orgel, L. E.

    1973-01-01

    The effect of Mg(2+) and Ca(2+) on phosphorylation reactions catalyzed by urea is investigated, showing that Mg(2+) improves markedly the yield of products containing pyrophosphate bonds. Yields of up to 25% of uridine diphosphate can be obtained with struvite at temperatures as low as 65 C.

  16. Textured catalysts, methods of making textured catalysts, and methods of catalyzing reactions conducted in hydrothermal conditions

    DOEpatents

    Werpy, Todd [West Richland, WA; Wang, Yong [Richland, WA

    2003-12-30

    A textured catalyst having a hydrothermally-stable support, a metal oxide and a catalyst component is described. Methods of conducting aqueous phase reactions that are catalyzed by a textured catalyst are also described. The invention also provides methods of making textured catalysts and methods of making chemical products using a textured catalyst.

  17. Chiral holmium complex-catalyzed Diels-Alder reaction of silyloxyvinylindoles: stereoselective synthesis of hydrocarbazoles.

    PubMed

    Harada, Shinji; Morikawa, Takahiro; Nishida, Atsushi

    2013-10-18

    The catalytic and asymmetric cycloaddition between 3-[1-(silyloxy)vinyl]indoles and electron-deficient olefins gave substituted hydrocarbazoles in up to 99% yield and 94% ee. This reaction was catalyzed by a novel chiral holmium(III) complex. Alkylation of the cycloadduct gave a tricyclic compound with four continuous chiral centers, one of which was a quaternary carbon.

  18. Synthesis of anthranilic acid derivatives through iron-catalyzed ortho amination of aromatic carboxamides with N-chloroamines.

    PubMed

    Matsubara, Tatsuaki; Asako, Sobi; Ilies, Laurean; Nakamura, Eiichi

    2014-01-15

    Arenes possessing an 8-quinolinylamide group as a directing group are ortho aminated with N-chloroamines and N-benzoyloxyamines in the presence of an iron/diphosphine catalyst and an organometallic base to produce anthranilic acid derivatives in high yield. The reaction proceeds via iron-catalyzed C-H activation, followed by the reaction of the resulting iron intermediate with N-chloroamine. The choice of the directing group and diphosphine ligand is crucial for obtaining the anthranilic acid derivative with high yield and product selectivity.

  19. Unexpected ring-opening reactions of aziridines with aldehydes catalyzed by nucleophilic carbenes under aerobic conditions.

    PubMed

    Liu, Yan-Kai; Li, Rui; Yue, Lei; Li, Bang-Jing; Chen, Ying-Chun; Wu, Yong; Ding, Li-Sheng

    2006-04-13

    [reaction: see text] The chemoselective ring opening of N-tosyl aziridines with aldehydes catalyzed by an N-heterocyclic carbene was investigated under aerobic conditions. Unexpected carboxylates of 1,2-amino alcohols from the corresponding aldehydes, rather than the acyl anion ring-opened beta-amino ketones, were exclusively obtained. A plausible mechanism for this unprecedented carbene-mediated reaction was also proposed.

  20. N-Substituted Imines by the Copper-Catalyzed N-Imination of Boronic Acids and Organostannanes with O-Acyl Ketoximes

    PubMed Central

    Liu, Songbai; Yu, Ying; Liebeskind, Lanny S.

    2009-01-01

    Catalytic quantities of copper (I) or copper (II) sources catalyze the N-imination of boronic acids and organostannanes through reaction with oxime O-carboxylates under non-basic conditions. This method tolerates various functional groups and takes place efficiently using aryl, heteroaryl, and alkenyl boronic acids and stannanes. PMID:17444649

  1. Enantioselective Nitroaldol Reaction of α-Ketoesters Catalyzed by Cinchona Alkaloids

    PubMed Central

    Li, Hongming; Wang, Baomin; Deng, Li

    2011-01-01

    The development of highly enantioselective and general catalytic nitroaldol (Henry) reactions with ketones is a challenging yet desirable task in organic synthesis. In this communication, we report an asymmetric nitroaldol reaction with α-ketoesters catalyzed by a new C6′-OH cinchona alkaloid catalyst. This is the first highly efficient organocatalytic asymmetric Henry reaction with ketones. This reaction is operationally simple and affords high enantioselectivity as well as good to excellent yield for a broad range of α-ketoesters. PMID:16417358

  2. Purification and characterization of cannabidiolic-acid synthase from Cannabis sativa L.. Biochemical analysis of a novel enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid.

    PubMed

    Taura, F; Morimoto, S; Shoyama, Y

    1996-07-19

    We identified a unique enzyme that catalyzes the oxidocyclization of cannabigerolic acid to cannabidiolic acid (CBDA) in Cannabis sativa L. (CBDA strain). The enzyme, named CBDA synthase, was purified to apparent homogeneity by a four-step procedure: ammonium sulfate precipitation followed by chromatography on DEAE-cellulose, phenyl-Sepharose CL-4B, and hydroxylapatite. The active enzyme consists of a single polypeptide with a molecular mass of 74 kDa and a pI of 6.1. The NH2-terminal amino acid sequence of CBDA synthase is similar to that of Delta1-tetrahydrocannabinolic-acid synthase. CBDA synthase does not require coenzymes, molecular oxygen, hydrogen peroxide, and metal ion cofactors for the oxidocyclization reaction. These results indicate that CBDA synthase is neither an oxygenase nor a peroxidase and that the enzymatic cyclization does not proceed via oxygenated intermediates. CBDA synthase catalyzes the formation of CBDA from cannabinerolic acid as well as cannabigerolic acid, although the kcat for the former (0.03 s-1) is lower than that for the latter (0.19 s-1). Therefore, we conclude that CBDA is predominantly biosynthesized from cannabigerolic acid rather than cannabinerolic acid.

  3. Bioengineering of bacterial polymer inclusions catalyzing the synthesis of N-acetylneuraminic acid.

    PubMed

    Hooks, David O; Blatchford, Paul A; Rehm, Bernd H A

    2013-05-01

    N-Acetylneuraminic acid is produced by alkaline epimerization of N-acetylglucosamine to N-acetylmannosamine and then subsequent condensation with pyruvate catalyzed by free N-acetylneuraminic acid aldolase. The high-alkaline conditions of this process result in the degradation of reactants and products, while the purification of free enzymes to be used for the synthesis reaction is a costly process. The use of N-acetylglucosamine 2-epimerase has been seen as an alternative to the alkaline epimerization process. In this study, these two enzymes involved in N-acetylneuraminic acid production were immobilized to biopolyester beads in vivo in a one-step, cost-efficient process of production and isolation. Beads with epimerase-only, aldolase-only, and combined epimerase/aldolase activity were recombinantly produced in Escherichia coli. The enzymatic activities were 32 U, 590 U, and 2.2 U/420 U per gram dry bead weight, respectively. Individual beads could convert 18% and 77% of initial GlcNAc and ManNAc, respectively, at high substrate concentrations and near-neutral pH, demonstrating the application of this biobead technology to fine-chemical synthesis. Beads establishing the entire N-acetylneuraminic acid synthesis pathway were able to convert up to 22% of the initial N-acetylglucosamine after a 50-h reaction time into N-acetylneuraminic acid.

  4. Layered materials with coexisting acidic and basic sites for catalytic one-pot reaction sequences.

    PubMed

    Motokura, Ken; Tada, Mizuki; Iwasawa, Yasuhiro

    2009-06-17

    Acidic montmorillonite-immobilized primary amines (H-mont-NH(2)) were found to be excellent acid-base bifunctional catalysts for one-pot reaction sequences, which are the first materials with coexisting acid and base sites active for acid-base tamdem reactions. For example, tandem deacetalization-Knoevenagel condensation proceeded successfully with the H-mont-NH(2), affording the corresponding condensation product in a quantitative yield. The acidity of the H-mont-NH(2) was strongly influenced by the preparation solvent, and the base-catalyzed reactions were enhanced by interlayer acid sites.

  5. Enantioselective TADMAP-Catalyzed Carboxyl Migration Reactions for the Synthesis of Stereogenic Quaternary Carbon

    PubMed Central

    Shaw, Scott A.; Aleman, Pedro; Christy, Justin; Kampf, Jeff W.; Va, Porino

    2008-01-01

    The chiral, nucleophilic catalyst TADMAP (1) has been prepared from 3-lithio-4-dimethylamino-pyridine (5) and triphenylacetaldehyde (3), followed by acylation and resolution. TADMAP catalyzes the carboxyl migration of oxazolyl, furanyl, and benzofuranyl enol carbonates with good to excellent levels of enantioselection. The oxazole reactions are especially efficient, and are used to prepare chiral lactams (23) and lactones (30) containing a quaternary asymmetric carbon. TADMAP-catalyzed carboxyl migrations in the indole series are relatively slow and proceed with inconsistent enantioselectivity. Modeling studies (B3LYP/6-31G*) have been used in qualitative correlations of catalyst conformation, reactivity, and enantioselectivity. PMID:16417383

  6. Enhanced Diffusion of Enzymes that Catalyze Exothermic Reactions

    NASA Astrophysics Data System (ADS)

    Golestanian, Ramin

    2015-09-01

    Enzymes have been recently found to exhibit enhanced diffusion due to their catalytic activities. A recent experiment [C. Riedel et al., Nature (London) 517, 227 (2015)] has found evidence that suggests this phenomenon might be controlled by the degree of exothermicity of the catalytic reaction involved. Four mechanisms that can lead to this effect, namely, self-thermophoresis, boost in kinetic energy, stochastic swimming, and collective heating are critically discussed, and it is shown that only the last two can be strong enough to account for the observations. The resulting quantitative description is used to examine the biological significance of the effect.

  7. Module degradation catalyzed by metal-encapsulation reactions

    NASA Technical Reports Server (NTRS)

    Gallagher, B. D.

    1983-01-01

    Four major properties are considered to be relevant in determining service life of a photovoltaic module: (1) Mechanical: creep resistance, modulus, tensile strength; (2) Optical: integrated transmission at 0.4 to 1.1 m wavelength; (3) Chemical: inertness with respect to metals and other components, retention of stabilizers, etc. and (4) Electrical; maintaining effective isolation of conductive components. These properties were measured after exposing polymer specimens to three types of accelerated stress: thermal, ultraviolet radiation and metal catalysts. These conditions give rise to a large number of complex interrelated free-radical reactions that result in the deterioration of polymeric materials.

  8. A facile phenol-driven intramolecular diastereoselective thermal/base-catalyzed dipolar [2+2] annulation reactions: an easy access to complex bioactive natural and unnatural benzopyran congeners.

    PubMed

    Mondal, Mukulesh; Puranik, Vedavati G; Argade, Narshinha P

    2007-03-16

    The complex bioactive natural and unnatural benzopyran congeners have been synthesized using one-/two-step approaches in very good yields from the reactions of two different dihydroxyphthalides, natural resorcyclic acid derivative, and trihydroxybenzophenone with citral and/or farnesal, via the phenol-driven intramolecular diastereoselective thermal/base-catalyzed dipolar [2+2] cycloaddition reactions and three different thermal intramolecular cyclization reactions. The effects of the nature and the position of phenolic groups in the starting materials on the course of these cycloaddition reactions have also been described. Depending upon the absence or presence of intramolecular hydrogen bonding of the phenolic group with the carbonyl moiety in the starting materials, these phenol-driven intramolecular thermal/base-catalyzed dipolar [2+2] cycloaddition reactions either furnished the kinetically controlled products or directly formed the thermodynamically controlled rearranged products, respectively.

  9. An Evaluation of Formic Acid as an Electron Donor for Palladium (PD) Catalyzed Destruction of Nitroaromatic Compounds

    DTIC Science & Technology

    2006-05-31

    AN EVALUATION OF FORMIC ACID AS AN ELECTRON DONOR FOR PALLADIUM (PD) CATALYZED DESTRUCTION OF NITROAROMATIC COMPOUNDS Mark R. Stevens, Capt...AN EVALUATION OF FORMIC ACID AS AN ELECTRON DONOR FOR PALLADIUM (PD) CATALYZED DESTRUCTION OF NITROAROMATIC COMPOUNDS THESIS...UNLIMITED. AFIT/GEM/ENV/04M-19 AN EVALUATION OF FORMIC ACID AS AN ELECTRON DONOR FOR PALLADIUM (PD) CATALYZED DESTRUCTION OF

  10. Probing the "additive effect" in the proline and proline hydroxamic acid catalyzed asymmetric addition of nitroalkanes to cyclic enones.

    PubMed

    Hanessian, Stephen; Govindan, Subramaniyan; Warrier, Jayakumar S

    2005-11-01

    The effect of chirality and steric bulk of 2,5-disubstituted piperazines as additives in the conjugate addition of 2-nitropropane to cyclohexenone, catalyzed by l-proline, was investigated. Neither chirality nor steric bulk affects the enantioselectivity of addition, which gives 86-93% ee in the presence of achiral and chiral nonracemic 2,5-disubstituted piperazines. Proline hydroxamic acid is shown for the first time to be an effective organocatalyst in the same Michael reaction.

  11. Chiral Phosphoric Acid-Catalyzed Enantioselective Reductive Amination of 2-Pyridyl Ketones: Construction of Structurally Chiral Pyridine-Based Ligands.

    PubMed

    Abudu Rexit, Abulikemu; Luo, Shiwei; Mailikezati, Maihemuti

    2016-11-18

    A chiral phosphoric acid-catalyzed one-pot enantioselective reductive amination of 2-pyridyl ketones was realized to provide chiral pyridine-based ligands in excellent yields with high enantioselectivities (up to 98% yield, 94% ee). Computational studies on the key intermediate imine and transition state of the hydride transfer process revealed that the nitrogen atom of the pyridyl ring might be an important factor to significantly promote both the reaction activity and enantioselectivity.

  12. Mutagenicity screening of reaction products from the enzyme-catalyzed oxidation of phenolic pollutants

    SciTech Connect

    Massey, I.J.; Aitken, M.D.; Ball, L.M.; Heck, P.E. . Dept. of Environmental Sciences and Engineering)

    1994-11-01

    Phenol-oxidizing enzymes such as peroxidases, laccases, and mushroom polyphenol oxidase are capable of catalyzing the oxidation of a wide range of phenolic pollutants. Although the use of these enzymes in waste-treatment applications has been proposed by a number of investigators, little information exists on the toxicological characteristics of the oxidation products. The enzymes chloroperoxidase, horseradish peroxidase, lignin peroxidase, and mushroom polyphenol oxidase were used in this study to catalyze the oxidation of phenol, several mono-substituted phenols, and pentachlorophenol. Seventeen reaction mixtures representing selected combinations of enzyme and parent phenol were subjected to mutagenicity screening using the Ames Salmonella typhimurium plate incorporation assay; five selected mixtures were also incubated with the S9 microsomal preparation to detect the possible presence of promutagens. The majority of reaction mixtures tested were not directly mutagenic, and none of those tested with S9 gave a positive response. Such lack of mutagenicity of enzymatic oxidation products provides encouragement for establishing the feasibility of enzyme-catalyzed oxidation as a waste-treatment process. The only positive responses were obtained with reaction products from the lignin peroxidase-catalyzed oxidation of 2-nitrophenol and 4-nitrophenol. Clear positive responses were observed when strain TA100 was incubated with 2-nitrophenol reaction-product mixtures, and when strain TA98 was incubated with the 4-nitrophenol reaction mixture. Additionally, 2,4-dinitrophenol was identified as a reaction product from 4-nitrophenol, and preliminary evidence indicates that both 2,4- and 2,6-dinitrophenol are produced from the oxidation of 2-nitrophenol. Possible mechanism by which these nitration reactions occur are discussed.

  13. Pericyclic reactions catalyzed by chorismate-utilizing enzymes.

    PubMed

    Lamb, Audrey L

    2011-09-06

    One of the fundamental questions of enzymology is how catalytic power is derived. This review focuses on recent developments in the structure--function relationships of chorismate-utilizing enzymes involved in siderophore biosynthesis to provide insight into the biocatalysis of pericyclic reactions. Specifically, salicylate synthesis by the two-enzyme pathway in Pseudomonas aeruginosa is examined. The isochorismate-pyruvate lyase is discussed in the context of its homologues, the chorismate mutases, and the isochorismate synthase is compared to its homologues in the MST family (menaquinone, siderophore, or tryptophan biosynthesis) of enzymes. The tentative conclusion is that the activities observed cannot be reconciled by inspection of the active site participants alone. Instead, individual activities must arise from unique dynamic properties of each enzyme that are tuned to promote specific chemistries.

  14. Catalyzed hydrolytic cleavage reaction of carbon-carbon bond

    SciTech Connect

    Ioffe, I.I.; Rubinskaya, E.V.

    1986-12-01

    The authors split the carbon-carbon bond for a series of simple and complex organic compounds in neutral aqueous solutions on a heterogeneous metal-containing catalyst, palladium on carbon. The experimental results are given. In each case, the catalytic effect was controlled by a blank experiment, without a catalyst, where there was no decomposition of the substrate. The occurrence of the heterogeneous-catalytic cleavage reaction of the carbon-carbon bonds in the molecules is indicated not only by their extensive conversion, but also by the almost complete depletion of the content of organic carbon, confirmed by a similar decrease in the chemical consumption of oxygen coefficient in the system, which is possible only in the complete decomposition of the organic compounds to gaseous products or with the formation of inappreciable amounts of low-molecular-weight water-soluble compounds.

  15. Copper-catalyzed selective hydroamination reactions of alkynes

    PubMed Central

    Shi, Shi-Liang; Buchwald, Stephen L.

    2014-01-01

    The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a longstanding goal of chemical research. Despite the centrality of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective, and step-efficient synthesis of amines is still needed. In this work we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines, and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio-, and stereoselectivity. This methodology was applied to the asymmetric synthesis of rivastigmine and the formal synthesis of several other pharmaceutical agents, including duloxetine, atomoxetine, fluoxetine, and tolterodine. PMID:25515888

  16. Pericyclic reactions catalyzed by chorismate-utilizing enzymes

    PubMed Central

    Lamb, Audrey L.

    2011-01-01

    One of the fundamental questions of enzymology is how catalytic power is derived. This review focuses on recent developments in the structure-function relationships of chorismate-utilizing enzymes involved in siderophore biosynthesis to provide insight into the biocatalysis of pericyclic reactions. Specifically, salicylate synthesis by the two-enzyme pathway in Pseudomonas aeruginosa is examined. The isochorismate-pyruvate lyase is discussed in the context of its homologues, the chorismate mutases, and the isochorismate synthase is compared to its homologues in the MST-family (menaquinone, siderophore or tryptophan biosynthesis) of enzymes. The tentative conclusion is that the activities observed cannot be reconciled by inspection of the active site participants alone. Instead, individual activities must arise from unique dynamic properties of each enzyme that are tuned to promote specific chemistries. PMID:21823653

  17. Comparative Studies of Cathodically-Promoted and Base-Catalyzed Michael Addition Reactions of Levoglucosenone.

    PubMed

    Samet, Alexander V.; Niyazymbetov, Murat E.; Semenov, Victor V.; Laikhter, Andrei L.; Evans, Dennis H.

    1996-12-13

    Regioselective Michael addition of nitro and heterocyclic compounds to levoglucosenone, 1, is effectively catalyzed by amines and also by cathodic electrolysis. In comparison to the base-catalyzed reaction, it was found that under electrochemical conditions the reaction proceeds under milder conditions and with higher yields. Cathodically-initiated Michael addition of thiols to levoglucosenone using small currents produces the previously unknown threo addition product in several instances. The normal erythro isomer, identified as the kinetic product, tends to be formed when large currents are used. In contrast, slow, low current electrolyses promote equilibration of the two forms so that erythro can be converted to threo by the retro reaction and readdition. Addition of 2-naphthalenethiol to (R)-(+)-apoverbenone is also reported.

  18. Laccase-catalyzed bisphenol A oxidation in the presence of 10-propyl sulfonic acid phenoxazine.

    PubMed

    Ivanec-Goranina, Rūta; Kulys, Juozas; Bachmatova, Irina; Marcinkevičienė, Liucija; Meškys, Rolandas

    2015-04-01

    The kinetics of the Coriolopsis byrsina laccase-catalyzed bisphenol A (BisA) oxidation was investigated in the absence and presence of electron-transfer mediator 3-phenoxazin-10-yl-propane-1-sulfonic acid (PPSA) at pH5.5 and 25°C. It was shown that oxidation rate of the hardly degrading compound BisA increased in the presence of the highly reactive substrate PPSA. The increase of reaction rate depends on PPSA and BisA concentrations as well on their ratio, e.g., at 0.2 mmol/L of BisA and 2 μmol/L of PPSA the rate increased 2 times. The kinetic data were analyzed using a scheme of synergistic laccase-catalyzed BisA oxidation. The calculated constant, characterizing reactivity of PPSA with laccase, is almost 1000 times higher than the constant, characterizing reactivity of BisA with laccase. This means that mediator-assisted BisA oxidation rate can be 1000 times higher in comparison to non-mediator reaction if compounds concentration is equal but very low.

  19. Oxidation of benzene with hydrogen peroxide catalyzed with ferrocene in the presence of pyrazine carboxylic acid

    NASA Astrophysics Data System (ADS)

    Shul'pina, L. S.; Durova, E. L.; Kozlov, Yu. N.; Kudinov, A. R.; Strelkova, T. V.; Shul'pin, G. B.

    2013-12-01

    It is found that ferrocene in the presence of small amounts of pyrazine carboxylic acid (PCA) effectively catalyzes the oxidation of benzene to phenol with hydrogen peroxide. Two main differences upon the oxidation of two different substrates, i.e., cyclohexane and benzene, with the same H2O2-ferrocene-PCA catalytic system are revealed: the rates of benzene oxidation and hydrogen peroxide decomposition are several times lower than the rate of cyclohexane oxidation at close concentrations of both substrates, and the rate constant ratios for the reactions of oxidizing particles with benzene and acetonitrile are significantly lower than would be expected for reactions involving free hydroxyl radicals. The overall rate of hydrogen peroxide decomposition, including both the catalase and oxidase routes, is lower in the presence of benzene than in the presence of cyclohexane. It is suggested on the grounds of these data that a catalytically active particle different from the one generated in the absence of benzene is formed in the presence of benzene. This particle catalyzes hydrogen peroxide decomposition less efficiently than the initial complex and generates a dissimilar oxidizing particle that exhibits higher selectivity. It is shown that reactivity of the system at higher concentrations of benzene differs from that of an initial system not containing an aromatic component with the capability of π-coordination with metal ions.

  20. Synthesis of 1,5-benzothiazepine dipeptide mimetics via two CuI-catalyzed cross coupling reactions.

    PubMed

    Gan, Jiangang; Ma, Dawei

    2009-07-02

    CuI-catalyzed coupling of 4-methylphenyl bromide with amino acids gives N-aryl amino acids, which are converted into linear dipeptides via iodination and condensation with L-cysteine derived acyl chloride. Cyclization is achieved via a CuI/N,N-dimethylglycine catalyzed intramolecular coupling of aryl iodides with the liberated thiol to afford 1,5-benzothiazepine dipeptide mimetics.

  1. Steroid hydroxylations: A paradigm for cytochrome P450 catalyzed mammalian monooxygenation reactions

    SciTech Connect

    Estabrook, Ronald W. . E-mail: Ronald.estabrook@utsouthwestern.edu

    2005-12-09

    The present article reviews the history of research on the hydroxylation of steroid hormones as catalyzed by enzymes present in mammalian tissues. The report describes how studies of steroid hormone synthesis have played a central role in the discovery of the monooxygenase functions of the cytochrome P450s. Studies of steroid hydroxylation reactions can be credited with showing that: (a) the adrenal mitochondrial enzyme catalyzing the 11{beta}-hydroxylation of deoxycorticosterone was the first mammalian enzyme shown by O{sup 18} studies to be an oxygenase; (b) the adrenal microsomal enzyme catalyzing the 21-hydroxylation of steroids was the first mammalian enzyme to show experimentally the proposed 1:1:1 stoichiometry (substrate:oxygen:reduced pyridine nucleotide) of a monooxygenase reaction; (c) application of the photochemical action spectrum technique for reversal of carbon monoxide inhibition of the 21-hydroxylation of 17{alpha}-OH progesterone was the first demonstration that cytochrome P450 was an oxygenase; (d) spectrophotometric studies of the binding of 17{alpha}-OH progesterone to bovine adrenal microsomal P450 revealed the first step in the cyclic reaction scheme of P450, as it catalyzes the 'activation' of oxygen in a monooxygenase reaction; (e) purified adrenodoxin was shown to function as an electron transport component of the adrenal mitochondrial monooxygenase system required for the activity of the 11{beta}-hydroxylase reaction. Adrenodoxin was the first iron-sulfur protein isolated and purified from mammalian tissues and the first soluble protein identified as a reductase of a P450; (f) fractionation of adrenal mitochondrial P450 and incubation with adrenodoxin and a cytosolic (flavoprotein) fraction were the first demonstration of the reconstitution of a mammalian P450 monooxygenase reaction.

  2. Nickel-Catalyzed Reactions Directed toward the Formation of Heterocycles.

    PubMed

    Kurahashi, Takuya; Matsubara, Seijiro

    2015-06-16

    Heterocycles have garnered significant attention because they are important functional building blocks in various useful molecules, such as pharmaceuticals, agricultural chemicals, pesticides, and materials. Several studies have been conducted regarding the preparation of heterocyclic skeletons with an emphasis on selectivity and efficiency. Three strategies are typically employed to construct cyclic molecules, namely, cyclization, cycloaddition, and ring-size alterations. Although each method has certain advantages, cycloaddition may be superior from the viewpoint of divergence. Specifically, cycloadditions enable the construction of rings from several pieces. However, the construction of heterocycles via cycloadditions is more challenging than the construction of carbocycles. For heterocycle construction, simple pericyclic reactions rarely work smoothly because of the large HOMO-LUMO gap unless well-designed combinations, such as electron-rich dienes and aldehydes, are utilized. Thus, a different approach should be employed to prepare heterocycles via cycloadditions. To this end, the use of metallacycles containing heteroatoms is expected to serve as a promising solution. In this study, we focused on the preparation of heteroatom-containing nickelacycles. Because nickel possesses a relatively high redox potential and an affinity for heteroatoms, several methods were developed to synthesize heteronickelacycles from various starting materials. The prepared nickelacycles were demonstrated to be reasonable intermediates in cycloaddition reactions, which were used to prepare various heterocycles. In this Account, we introduce the following four methods to prepare heterocycles via heteronickelacycles. (1) Direct oxidative insertion of Ni(0) to α,β-unsaturated enone derivatives: treatment of 3-ethoxycarbonyl-4-phenyl-3-buten-2-one with Ni(0) afforded an oxa-nickelacycle, which reacted with alkynes to give pyrans. (2) Substitution of a part of a cyclic compound with

  3. Hypersensitive radical probe studies of chloroperoxidase-catalyzed hydroxylation reactions.

    PubMed

    Toy, P H; Newcomb, M; Hager, L P

    1998-07-01

    The oxidation of hypersensitive radical probes by chloroperoxidase from Caldariomyces fumago (CPO) was studied in an attempt to "time" a putative radical intermediate. Oxidation of (trans-2-phenylcyclopropyl)methane, previously studied by Zaks and Dodds [Zaks, A., and Dodds, D. R. (1995) J. Am. Chem. Soc. 115, 10419-10424] was reinvestigated. Unrearranged oxidation products were found as previously reported, and control experiments demonstrated that the cyclic alcohol from oxidation at the cyclopropylcarbinyl position, while subject to further oxidation, survives CPO oxidation as detectable species. However, in contrast to the report by Zaks and Dodds, the rearranged alcohol product expected from ring opening of a cyclopropylcarbinyl radical intermediate was shown to be unstable toward the enzyme oxidation reaction. Because of this instability, two new hypersensitive radical probes, (trans-2-phenylcyclopropyl)ethane and 2-(trans-2-phenylcyclopropyl)propane, and their potential cyclic and acyclic products from oxidation at the cyclopropylcarbinyl position were synthesized and tested. Oxidation of both of these probes at the cyclopropylcarbinyl position by CPO gave unrearranged alcohol products only, but control experiments again demonstrated that the rearranged alcohol products were unstable toward CPO oxidation conditions. From the combination of the probe and control studies, the lifetime of a putative radical intermediate must be less than 3 ps. Whereas the results are consistent with an insertion mechanism for production of alcohol product, they do not exclude a very short-lived intermediate.

  4. Palladium-catalyzed cross-coupling reactions of silanolates: a paradigm shift in silicon-based cross-coupling reactions.

    PubMed

    Denmark, Scott E; Baird, John D

    2006-06-23

    This paper chronicles the conceptual development, proof of principle experiments, and recent advances in the palladium-catalyzed cross-coupling reactions of the conjugate bases of organosilanols. The discovery that led to the design and refinement of this process represents a classical illustration of how mechanistic studies can provide a fertile ground for the invention of new reactions. On the basis of a working hypothesis (which ultimately proved to be incorrect) and the desire to effect silicon-based cross-coupling without the agency of fluoride activation, a mild and practical palladium-catalyzed cross-coupling of alkenyl-, aryl-, and heteroaryl silanolates has been developed. The mechanistic underpinnings, methodological extensions, and the successful applications of this technology to the synthesis of complex molecules are described.

  5. A transition path sampling study of the reaction catalyzed by the enzyme chorismate mutase.

    PubMed

    Crehuet, Ramon; Field, Martin J

    2007-05-24

    The study of the chemical steps in enzyme-catalyzed reactions represents a challenge for molecular simulation techniques. One concern is how to calculate paths for the reaction. Common techniques include the definition of a reaction coordinate in terms of a small set of (normally) geometrical variables or the determination of minimum energy paths on the potential energy surface of the reacting system. Both have disadvantages, the former because it presupposes knowledge of which variables are likely to be important for reaction and the latter because it provides a static picture and dynamical effects are ignored. In this paper, we employ the transition path sampling method developed by Chandler and co-workers, which overcomes some of these limitations. The reaction that we have chosen is the chorismate-mutase-catalyzed conversion of chorismate into prephenate, which has become something of a test case for simulation studies of enzyme mechanisms. We generated an ensemble of approximately 1000 independent transition paths for the reaction in the enzyme and another approximately 500 for the corresponding reaction in solution. A large variety of analyses of these paths was performed, but we have concentrated on characterizing the transition state ensemble, particularly the flexibility of its structures with respect to other ligands of the enzyme and the time evolution of various geometrical and energetic properties as the reaction proceeds. We have also devised an approximate technique for locating transition state structures along the paths.

  6. Enantioselective Multicomponent Condensation Reactions of Phenols, Aldehydes, and Boronates Catalyzed by Chiral Biphenols.

    PubMed

    Barbato, Keith S; Luan, Yi; Ramella, Daniele; Panek, James S; Schaus, Scott E

    2015-12-04

    Chiral diols and biphenols catalyze the multicomponent condensation reaction of phenols, aldehydes, and alkenyl or aryl boronates. The condensation products are formed in good yields and enantioselectivities. The reaction proceeds via an initial Friedel-Crafts alkylation of the aldehyde and phenol to yield an ortho-quinone methide that undergoes an enantioselective boronate addition. A cyclization pathway was discovered while exploring the scope of the reaction that provides access to chiral 2,4-diaryl chroman products, the core of which is a structural motif found in natural products.

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

    PubMed Central

    Tait, Katrina; Alrifai, Oday; Boutin, Rebecca; Haner, Jamie

    2016-01-01

    Summary Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN)2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases. PMID:27829926

  8. Combination of Microwave Reactions with Fluorous Separations in the Palladium-Catalyzed Synthesis of Aryl Sulfides

    PubMed Central

    Zhang, Wei; Lu, Yimin; Chen, Christine Hiu-Tung

    2007-01-01

    Coupling of microwave reactions with fluorous separations can dramatically increase the efficiency of high-speed synthesis. Described in this paper is a fluorous synthesis of aryl sulfides by palladium-catalyzed cross-coupling of aryl perfluoroalkylsulfonates (C8F17O2SOAr) with thiols (RSH) under microwave irradiation. Fluorous solid-phase extractions (F-SPE) are employed for the purification of reaction mixtures. No fluorous solvents are involved in reaction and separation processes. The fluorous synthesis is further extended to the multi-step synthesis of substituted hydantoin and amide scaffolds. PMID:14870851

  9. Enantioselective Multicomponent Condensation Reactions of Phenols, Aldehydes, and Boronates Catalyzed by Chiral Biphenols

    PubMed Central

    Barbato, Keith S.; Luan, Yi; Ramella, Daniele; Panek, James S.; Schaus, Scott E.

    2015-01-01

    Chiral diols and biphenols catalyze the multicomponent condensation reaction of phenols, aldehydes, and alkenyl or aryl boronates. The condensation products are formed in good yields and enantioselectivities. The reaction proceeds via an initial Friedel Crafts alkylation of the aldehyde and phenol to yield an ortho-quinone methide that undergoes an enantioselective boronate addition. A cyclization pathway was discovered while exploring the scope of the reaction that provides access to chiral 2,4-diaryl chroman products, the core of which is a structural motif found in natural products. PMID:26576776

  10. Study of the mechanism of muon-catalyzed t + t fusion reaction

    SciTech Connect

    Bogdanova, L. N.; Demin, D. L.; Filchenkov, V. V.

    2015-01-15

    The mechanism for the muon catalyzed fusion reaction t + t → {sup 4}He + 2n + 11.33 MeV is investigated. The model of the cascade reaction with {sup 5}He as an intermediate state is considered, both the ground and the first exited states being taken into account. The neutron energy spectrum measured in the recent experiment is compared with the Monte-Carlo-simulated one. Varying reaction parameters, we obtain optimum values for the relative weights of the {sup 5}He ground and excited states and for the excitation energy and width of the excited state.

  11. Integrated Production of Xylonic Acid and Bioethanol from Acid-Catalyzed Steam-Exploded Corn Stover.

    PubMed

    Zhu, Junjun; Rong, Yayun; Yang, Jinlong; Zhou, Xin; Xu, Yong; Zhang, Lingling; Chen, Jiahui; Yong, Qiang; Yu, Shiyuan

    2015-07-01

    High-efficiency xylose utilization is one of the restrictive factors of bioethanol industrialization. However, xylonic acid (XA) as a new bio-based platform chemical can be produced by oxidation of xylose with microbial. So, an applicable technology of XA bioconversion was integrated into the process of bioethanol production. After corn stover was pretreated with acid-catalyzed steam-explosion, solid and liquid fractions were obtained. The liquid fraction, also named as acid-catalyzed steam-exploded corn stover (ASC) prehydrolyzate (mainly containing xylose), was catalyzed with Gluconobacter oxydans NL71 to prepare XA. After 72 h of bioconversion of concentrated ASC prehydrolyzate (containing 55.0 g/L of xylose), the XA concentration reached a peak value of 54.97 g/L, the sugar utilization ratio and XA yield were 94.08 and 95.45 %, respectively. The solid fraction was hydrolyzed to produce glucose with cellulase and then fermented with Saccharomyces cerevisiae NL22 to produce ethanol. After 18 h of fermentation of concentrated enzymatic hydrolyzate (containing 86.22 g/L of glucose), the ethanol concentration reached its highest value of 41.48 g/L, the sugar utilization ratio and ethanol yield were 98.72 and 95.25 %, respectively. The mass balance showed that 1 t ethanol and 1.3 t XA were produced from 7.8 t oven dry corn stover.

  12. Optimizing the Acid Catalyzed Synthesis of Hyperbranched Poly(Glycerol-diacids) Oligomers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Oligomeric pre-polymers were synthesized by the acid-catalyzed condensation of glycerol with succinic acid, glutaric acid and azelaic acid in dimethylsulfoxide (DMSO) or dimethylformamide (DMF). The prepolymers were obtained, on average in 84% yield, and were characterized by proton NMR, MALDI-TOF ...

  13. Iodide-catalyzed reductions: development of a synthesis of phenylacetic acids.

    PubMed

    Milne, Jacqueline E; Storz, Thomas; Colyer, John T; Thiel, Oliver R; Dilmeghani Seran, Mina; Larsen, Robert D; Murry, Jerry A

    2011-11-18

    A new convenient and scalable synthesis of phenylacetic acids has been developed via the iodide catalyzed reduction of mandelic acids. The procedure relies on in situ generation of hydroiodic acid from catalytic sodium iodide, employing phosphorus acid as the stoichiometric reductant.

  14. Glutathiolactaldehyde as a probe of the overall stereochemical course of glyoxalase-I catalyzed reactions

    SciTech Connect

    Brush, E.J.; Kozarich, J.W.

    1986-05-01

    The overall stereochemical course of the reactions catalyzed by glyoxalase-I (GX-I) has remained elusive as the substrates are equilibrium mixtures of rapidly interconverting diastereomeric thiohemiacetals. However, with the discovery of inverse substrate processing by Kozarich and coworkers, it is possible to design GX-I substrate analogs that are intrinsically more stable than the thiohemiacetals. Hence, Chari and Kozarich reported that glutathiohydroxyacetone (GHA, GSCH/sub 2/COCH/sub 2/OH) undergoes GX-I catalyzed exchange of the pro-S hydroxymethyl proton with solvent deuterium. Their data suggest that GX-I processes a single diastereomeric thiohemiacetal, and are consistent with a cis-enediol intermediate. To test this hypothesis and to follow the overall stereochemistry on a single substrate, they have prepared glutathiolactaldehyde (GLA, GSCH/sub 2/CHOHCHO) as a potential inverse substrate. Human erythrocyte GX-I catalyzes the isomerization of GLA to GHA as evidenced by UV and NMR spectra of the product. Solvent deuterium is incorporated into the hydroxymethyl position, and NMR data suggest that incorporation is stereospecific. Furthermore, 50% of the expected amount of GHA is produced indicating that only one diastereomer of GLA is processed by GX-I. Identification of the absolute stereochemistry of the substrate diastereomer will lead to a clarification of the overall stereochemical and mechanistic course of GX-I catalyzed reactions.

  15. Existence of efficient divalent metal ion-catalyzed and inefficient divalent metal ion-independent channels in reactions catalyzed by a hammerhead ribozyme

    PubMed Central

    Zhou, Jing-Min; Zhou, De-Min; Takagi, Yasuomi; Kasai, Yasuhiro; Inoue, Atsushi; Baba, Tadashi; Taira, Kazunari

    2002-01-01

    The hammerhead ribozyme is generally accepted as a well characterized metalloenzyme. However, the precise nature of the interactions of the RNA with metal ions remains to be fully defined. Examination of metal ion-catalyzed hammerhead reactions at limited concentrations of metal ions is useful for evaluation of the role of metal ions, as demonstrated in this study. At concentrations of Mn2+ ions from 0.3 to 3 mM, addition of the ribozyme to the reaction mixture under single-turnover conditions enhances the reaction with the product reaching a fixed maximum level. Further addition of the ribozyme inhibits the reaction, demonstrating that a certain number of divalent metal ions is required for proper folding and also for catalysis. At extremely high concentrations, monovalent ions, such as Na+ ions, can also serve as cofactors in hammerhead ribozyme-catalyzed reactions. However, the catalytic efficiency of monovalent ions is extremely low and, thus, high concentrations are required. Furthermore, addition of monovalent ions to divalent metal ion-catalyzed hammerhead reactions inhibits the divalent metal ion-catalyzed reactions, suggesting that the more desirable divalent metal ion–ribozyme complexes are converted to less desirable monovalent metal ion–ribozyme complexes via removal of divalent metal ions, which serve as a structural support in the ribozyme complex. Even though two channels appear to exist, namely an efficient divalent metal ion-catalyzed channel and an inefficient monovalent metal ion-catalyzed channel, it is clear that, under physiological conditions, hammerhead ribozymes are metalloenzymes that act via the significantly more efficient divalent metal ion-dependent channel. Moreover, the observed kinetic data are consistent with Lilley’s and DeRose’s two-phase folding model that was based on ground state structure analyses. PMID:12034824

  16. Cationic Pd(II)-catalyzed C-H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies.

    PubMed

    Nishikata, Takashi; Abela, Alexander R; Huang, Shenlin; Lipshutz, Bruce H

    2016-01-01

    Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C-H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C-H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C-H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C-H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied.

  17. Cationic Pd(II)-catalyzed C–H activation/cross-coupling reactions at room temperature: synthetic and mechanistic studies

    PubMed Central

    Nishikata, Takashi; Abela, Alexander R; Huang, Shenlin

    2016-01-01

    Summary Cationic palladium(II) complexes have been found to be highly reactive towards aromatic C–H activation of arylureas at room temperature. A commercially available catalyst [Pd(MeCN)4](BF4)2 or a nitrile-free cationic palladium(II) complex generated in situ from the reaction of Pd(OAc)2 and HBF4, effectively catalyzes C–H activation/cross-coupling reactions between aryl iodides, arylboronic acids and acrylates under milder conditions than those previously reported. The nature of the directing group was found to be critical for achieving room temperature conditions, with the urea moiety the most effective in promoting facile coupling reactions at an ortho C–H position. This methodology has been utilized in a streamlined and efficient synthesis of boscalid, an agent produced on the kiloton scale annually and used to control a range of plant pathogens in broadacre and horticultural crops. Mechanistic investigations led to a proposed catalytic cycle involving three steps: (1) C–H activation to generate a cationic palladacycle; (2) reaction of the cationic palladacycle with an aryl iodide, arylboronic acid or acrylate, and (3) regeneration of the active cationic palladium catalyst. The reaction between a cationic palladium(II) complex and arylurea allowed the formation and isolation of the corresponding palladacycle intermediate, characterized by X-ray analysis. Roles of various additives in the stepwise process have also been studied. PMID:27340491

  18. Membrane protein complexes catalyze both 4- and 3-hydroxylation of cinnamic acid derivatives in monolignol biosynthesis

    PubMed Central

    Chen, Hsi-Chuan; Li, Quanzi; Shuford, Christopher M.; Liu, Jie; Muddiman, David C.; Sederoff, Ronald R.; Chiang, Vincent L.

    2011-01-01

    The hydroxylation of 4- and 3-ring carbons of cinnamic acid derivatives during monolignol biosynthesis are key steps that determine the structure and properties of lignin. Individual enzymes have been thought to catalyze these reactions. In stem differentiating xylem (SDX) of Populus trichocarpa, two cinnamic acid 4-hydroxylases (PtrC4H1 and PtrC4H2) and a p-coumaroyl ester 3-hydroxylase (PtrC3H3) are the enzymes involved in these reactions. Here we present evidence that these hydroxylases interact, forming heterodimeric (PtrC4H1/C4H2, PtrC4H1/C3H3, and PtrC4H2/C3H3) and heterotrimeric (PtrC4H1/C4H2/C3H3) membrane protein complexes. Enzyme kinetics using yeast recombinant proteins demonstrated that the enzymatic efficiency (Vmax/km) for any of the complexes is 70–6,500 times greater than that of the individual proteins. The highest increase in efficiency was found for the PtrC4H1/C4H2/C3H3-mediated p-coumaroyl ester 3-hydroxylation. Affinity purification-quantitative mass spectrometry, bimolecular fluorescence complementation, chemical cross-linking, and reciprocal coimmunoprecipitation provide further evidence for these multiprotein complexes. The activities of the recombinant and SDX plant proteins demonstrate two protein-complex–mediated 3-hydroxylation paths in monolignol biosynthesis in P. trichocarpa SDX; one converts p-coumaric acid to caffeic acid and the other converts p-coumaroyl shikimic acid to caffeoyl shikimic acid. Cinnamic acid 4-hydroxylation is also mediated by the same protein complexes. These results provide direct evidence for functional involvement of membrane protein complexes in monolignol biosynthesis. PMID:22160716

  19. Degradation of trichloroethene by siderite-catalyzed hydrogen peroxide and persulfate: Investigation of reaction mechanisms and degradation products

    PubMed Central

    Yan, Ni; Liu, Fei; Xue, Qiang; Brusseau, Mark L.; Liu, Yali; Wang, Junjie

    2015-01-01

    A binary catalytic system, siderite-catalyzed hydrogen peroxide (H2O2) coupled with persulfate (S2O82−), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO·), sulfate (SO4−·), hydroperoxyl (HO2·), and superoxide (O2−·)) in the siderite-catalyzed H2O2-S2O82− system. In the absence of S2O82− (i.e., siderite-catalyzed H2O2), a majority of H2O2 was decomposed in the first hour of the experiment, resulting in the waste of HO·. The addition of S2O82− moderated the H2O2 decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by H2O2 decomposition accelerated the activation of S2O82−, and the resultant SO4−· was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was firstly detected by ion chromatography (IC). The results of this study indicate a new insight to the reaction mechanism for the catalytic binary H2O2-S2O82− oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater. PMID:26236152

  20. Degradation of trichloroethene by siderite-catalyzed hydrogen peroxide and persulfate: Investigation of reaction mechanisms and degradation products.

    PubMed

    Yan, Ni; Liu, Fei; Xue, Qiang; Brusseau, Mark L; Liu, Yali; Wang, Junjie

    2015-08-15

    A binary catalytic system, siderite-catalyzed hydrogen peroxide (H2O2) coupled with persulfate (S2O8(2-)), was investigated for the remediation of trichloroethene (TCE) contamination. Batch experiments were conducted to investigate reaction mechanisms, oxidant decomposition rates, and degradation products. By using high performance liquid chromatography (HPLC) coupled with electron paramagnetic resonance (EPR), we identified four radicals (hydroxyl (HO·), sulfate (SO4(-)·), hydroperoxyl (HO2·), and superoxide (O2(-)·)) in the siderite-catalyzed H2O2-S2O8(2-) system. In the absence of S2O8(2-) (i.e., siderite-catalyzed H2O2), a majority of H2O2 was decomposed in the first hour of the experiment, resulting in the waste of HO·. The addition of S2O8(2-) moderated the H2O2 decomposition rate, producing a more sustainable release of hydroxyl radicals that improved the treatment efficiency. Furthermore, the heat released by H2O2 decomposition accelerated the activation of S2O8(2-), and the resultant SO4(-)· was the primary oxidative agent during the first two hours of the reaction. Dichloroacetic acid was firstly detected by ion chromatography (IC). The results of this study indicate a new insight to the reaction mechanism for the catalytic binary H2O2-S2O8(2-) oxidant system, and the delineation of radicals and the discovery of the chlorinated byproduct provide useful information for efficient treatment of chlorinated-solvent contamination in groundwater.

  1. Computational Mechanistic Studies of Acid-Catalyzed Lignin Model Dimers for Lignin Depolymerization

    SciTech Connect

    Kim, S.; Sturgeon, M. R.; Chmely, S. C.; Paton, R. S.; Beckham, G. T.

    2013-01-01

    Lignin is a heterogeneous alkyl-aromatic polymer that constitutes up to 30% of plant cell walls, and is used for water transport, structure, and defense. The highly irregular and heterogeneous structure of lignin presents a major obstacle in the development of strategies for its deconstruction and upgrading. Here we present mechanistic studies of the acid-catalyzed cleavage of lignin aryl-ether linkages, combining both experimental studies and quantum chemical calculations. Quantum mechanical calculations provide a detailed interpretation of reaction mechanisms including possible intermediates and transition states. Solvent effects on the hydrolysis reactions were incorporated through the use of a conductor-like polarizable continuum model (CPCM) and with cluster models including explicit water molecules in the first solvation shell. Reaction pathways were computed for four lignin model dimers including 2-phenoxy-phenylethanol (PPE), 1-(para-hydroxyphenyl)-2-phenoxy-ethanol (HPPE), 2-phenoxy-phenyl-1,3-propanediol (PPPD), and 1-(para-hydroxyphenyl)-2-phenoxy-1,3-propanediol (HPPPD). Lignin model dimers with a para-hydroxyphenyl ether (HPPE and HPPPD) show substantial differences in reactivity relative to the phenyl ether compound (PPE and PPPD) which have been clarified theoretically and experimentally. The significance of these results for acid deconstruction of lignin in plant cell walls will be discussed.

  2. Brønsted acid-catalyzed Nazarov cyclization of pyrrole derivatives accelerated by microwave irradiation.

    PubMed

    Bachu, Prabhakar; Akiyama, Takahiko

    2009-07-15

    The Brønsted acid-catalyzed Nazarov cyclization of pyrrole derivatives was developed. Microwave irradiation accelerated the Nazarov cyclization significantly at 40 degrees C to give cyclopenta[b]pyrrole derivatives in excellent yields with high trans selectivity.

  3. Oxidation of tolualdehydes to toluic acids catalyzed by cytochrome P450-dependent aldehyde oxygenase in the mouse liver.

    PubMed

    Watanabe, K; Matsunaga, T; Yamamoto, I; Yashimura, H

    1995-02-01

    Mouse hepatic microsomal enzymes catalyzed the oxidation of o-, m-, and p-tolualdehydes, intermediate metabolites of xylene, to the corresponding toluic acids. Cofactor requirement for the catalytic activity indicates that the microsomes contain NAD- and NADPH-dependent enzymes for this reaction. GC/MS analyses of the carboxylic acids formed by incubation under oxygen-18 gas indicate that the mechanism for this oxidation is an oxygenation and a dehydrogenation for the NADPH- and NAD-dependent reaction. Vmax/Km (nmol/min/mg protein) ratios indicate that the NADPH-dependent activity is more pronounced than the NAD-dependent activity. These results suggest that the NADPH-dependent reaction is mainly responsible for the microsomal oxidation of tolualdehydes. The NADPH-dependent activity was significantly inhibited by SKF 525-A, disulfiram and menadione, inhibitors of cytochrome P450 (P450), suggesting the involvement of P450 in the reaction. In a reconstituted system, P450 MUT-2 (CYP2C29) purified from mouse hepatic microsomes catalyzed the oxidation of o-, m-, and p-tolualdehydes to the carboxylic acids, and the specific activities (nmol/min/nmol P450) were 1.44, 2.81, and 2.32, respectively. Rabbit antibody raised against P450 MUT-2 significantly inhibited the NADPH-dependent oxidation of tolualdehydes to toluic acids by 88% (o-), 63% (m-), and 62% (p-) using mouse hepatic microsomes. The present study demonstrated that a mouse hepatic microsomal aldehyde oxygenase, P450 MUT-2, catalyzed the most of oxidative activity of tolualdehydes to toluic acids in the microsomes.

  4. Gold-Catalyzed Cycloisomerization of 1,5-Allenynes via Dual Activation of an Ene Reaction

    PubMed Central

    Cheong, Paul Ha-Yeon; Morganelli, Philip; Luzung, Michael R.; Houk, K. N.; Toste, F. Dean

    2010-01-01

    A tris-triphenylphosphinegold oxonium tetrafluoroborate, [(Ph3PAu)3O]BF4, catalyzes the rearrangement of 1,5-allenynes to produce cross-conjugated trienes. Experimental and computational evidence shows that the ene reaction proceeds through a unique nucleophilic addition of an allene double bond to a cationic phosphinegold(I) complexed phosphinegold(I) acetylide, followed by a 1,5-hydrogen shift. PMID:18327944

  5. Chiral Calcium Phosphate Catalyzed Asymmetric Alkenylation Reaction of Arylglyoxals with 3-Vinylindoles.

    PubMed

    Li, Xiao-Yun; Yuan, Wen-Qiang; Tang, Sheng; Huang, Yi-Wei; Xue, Jia-Hui; Fu, Li Na; Guo, Qi-Xiang

    2017-03-03

    A highly efficient alkenylation reaction of arylglyoxals with 3-vinylindoles catalyzed by chiral calcium phosphate is described. Structurally diverse allylic alcohols bearing indole and carbonyl units are prepared in excellent yields, good diastereoselectivities, and high to excellent enantioselectivities. These products are good building blocks for the synthesis of polysubstituted chiral tetrahydrocarbozol-2-ones. The mechanism study indicates that the most likely role of the catalyst is to activate the hydrate of arylglyoxal and control the stereoselectivity via desymmetric coordination.

  6. Metal-Catalyzed β-Functionalization of Michael Acceptors through Reductive Radical Addition Reactions.

    PubMed

    Streuff, Jan; Gansäuer, Andreas

    2015-11-23

    Transition-metal-catalyzed radical reactions are becoming increasingly important in modern organic chemistry. They offer fascinating and unconventional ways for connecting molecular fragments that are often complementary to traditional methods. In particular, reductive radical additions to α,β-unsaturated compounds have recently gained substantial attention as a result of their broad applicability in organic synthesis. This Minireview critically discusses the recent landmark achievements in this field in context with earlier reports that laid the foundation for today's developments.

  7. Asymmetric PTC C-alkylation catalyzed by chiral derivatives of tartaric acid and aminophenols. Synthesis Of (R)- and (S)-alpha-methyl amino acids

    PubMed

    Belokon; Kochetkov; Churkina; Ikonnikov; Chesnokov; Larionov; Singh; Parmar; Vyskocil; Kagan

    2000-10-20

    A new type of efficient chiral catalyst has been elaborated for asymmetric C-alkylation of CH acids under PTC conditions. Sodium alkoxides formed from chiral derivatives of tartaric acid and aminophenols (TADDOL's 2a-e and NOBIN's 3a-h) can be used as chiral catalysts in the enantioselective alkylation, as exemplified by the reaction of Schiff's bases 1a-e derived from alanine esters and benzaldehydes with active alkyl halides. Acid-catalyzed hydrolysis of the products formed in the reaction afforded (R)-alpha-methylphenylalanine, (R)-alpha-naphthylmethylalanine, and (R)-alpha-allylalanine in 61-93% yields and with ee 69-93%. The procedure could be successfully scaled up to 6 g of substrate 1b. When (S,S)-TADDOL or (R)-NOBIN are used, the (S)-amino acids are formed. A mechanism rationalizing the observed features of the reaction has been suggested.

  8. Iridium-Catalyzed Intramolecular Asymmetric Allylic Dearomatization Reaction of Pyridines, Pyrazines, Quinolines, and Isoquinolines.

    PubMed

    Yang, Ze-Peng; Wu, Qing-Feng; Shao, Wen; You, Shu-Li

    2015-12-23

    The first Ir-catalyzed intramolecular asymmetric allylic dearomatization reaction of pyridines, pyrazines, quinolines, and isoquinolines has been developed. Enabled by in situ formed chiral Ir-catalyst, the dearomatized products were isolated in high levels of yield (up to 99% yield) and enantioselectivity (up to 99% ee). It is worth noting that the Me-THQphos ligand is much more efficient than other tested ligands for the dearomatization of pyrazines and certain quinolines. Mechanistic studies of the dearomatization reaction were carried out, and the results suggest the feasibility of an alternative process which features the formation of a quinolinium as the key intermediate. The mechanistic findings render this reaction a yet unknown type in the chemistry of Reissert-type reactions. In addition, the utility of this method was showcased by a large-scale reaction and formal synthesis of (+)-gephyrotoxin.

  9. Asymmetric Petasis Borono-Mannich Allylation Reactions Catalyzed by Chiral Biphenols.

    PubMed

    Jiang, Yao; Schaus, Scott E

    2017-02-01

    Chiral biphenols catalyze the asymmetric Petasis borono-Mannich allylation of aldehydes and amines through the use of a bench-stable allyldioxaborolane. The reaction proceeds via a two-step, one-pot process and requires 2-8 mole % of 3,3'-Ph2 -BINOL as the optimal catalyst. Under microwave heating the reaction affords chiral homoallylic amines in excellent yields (up to 99 %) and high enantioselectivies (er up to 99:1). The catalytic reaction is a true multicomponent condensation reaction whereas both the aldehyde and the amine can possess a wide range of structural and electronic properties. Use of crotyldioxaborolane in the reaction results in stereodivergent products with anti- and syn-diastereomers both in good diastereoselectivities and enantioselectivities from the corresponding E- and Z-borolane stereoisomers.

  10. A 11-Steps Total Synthesis of Magellanine through a Gold(I)-Catalyzed Dehydro Diels-Alder Reaction.

    PubMed

    McGee, Philippe; Bétournay, Geneviève; Barabé, Francis; Barriault, Louis

    2017-01-12

    We have developed an innovative strategy for the formation of angular carbocycles via a gold(I)-catalyzed dehydro Diels-Alder reaction. This transformation provides rapid access to a variety of complex angular cores in excellent diastereoselectivities and high yields. The usefulness of this Au(I) -catalyzed cycloaddition was further demonstrated by accomplishing a 11-steps total synthesis of (±)-magellanine.

  11. A Mini-Review on Solid Acid Catalysts for Esterification Reactions

    NASA Astrophysics Data System (ADS)

    Sirsam, Rajkumar; Hansora, Dharmesh; Usmani, Ghayas A.

    2016-10-01

    This paper presents an overview of research pertaining to solid acid catalysts for esterification reactions. Prominence has been given to the literatures that have been appeared during the last two decades. A variety of reactions catalyzed by solid acid catalysts have been tabulated according to their broad classification; industrially important reactions have been outlined. Examples, where the use of various solid acid catalysts have led to an improvement in the selectivity of the desired products, have also been discussed. Various catalyzed esterification reactions using different approaches and previous kinetic studies have been reviewed. Types, preparation and synthesis of various solid acid catalysts have been reviewed and discussed. Suggestions have been summarized for their implementation in future work.

  12. Palladium(II)-catalyzed enantioselective C(sp³)-H activation using a chiral hydroxamic acid ligand.

    PubMed

    Xiao, Kai-Jiong; Lin, David W; Miura, Motofumi; Zhu, Ru-Yi; Gong, Wei; Wasa, Masayuki; Yu, Jin-Quan

    2014-06-04

    An enantioselective method for Pd(II)-catalyzed cross-coupling of methylene β-C(sp(3))-H bonds in cyclobutanecarboxylic acid derivatives with arylboron reagents is described. High yields and enantioselectivities were achieved through the development of chiral mono-N-protected α-amino-O-methylhydroxamic acid (MPAHA) ligands, which form a chiral complex with the Pd(II) center. This reaction provides an alternative approach to the enantioselective synthesis of cyclobutanecarboxylates containing α-chiral quaternary stereocenters. This new class of chiral catalysts also show promises for enantioselective β-C(sp(3))-H activation of acyclic amides.

  13. Computational analysis of the stereochemical outcome in the imidazolidinone-catalyzed enantioselective (4 + 3)-cycloaddition reaction.

    PubMed

    Krenske, Elizabeth H; Houk, K N; Harmata, Michael

    2015-01-16

    Computations show why the catalytic, asymmetric (4 + 3)-cycloaddition reaction developed in the Harmata laboratories proceeds with facial selectivity opposite to that for models proposed for related catalyzed Diels-Alder reactions. Computations with M06-2X/6-311+G(d,p)//B3LYP/6-31G(d) show that iminium ions derived from MacMillan's chiral 2-tert-butyl-5-benzylimidazolidinone and siloxypentadienals undergo (4 + 3)-cycloadditions with furans preferentially on the more crowded face. Conformational reorganization of the benzyl group, to avoid intramolecular interaction with the silyl group, is responsible for differentiating the activation barriers of top- and bottom-face attack.

  14. Peptide-Catalyzed Stereoselective Conjugate Addition Reactions of Aldehydes to Maleimide.

    PubMed

    Grünenfelder, Claudio E; Kisunzu, Jessica K; Wennemers, Helma

    2016-07-18

    The tripeptide H-dPro-Pro-Asn-NH2 is presented as a catalyst for asymmetric conjugate addition reactions of aldehydes to maleimide. The peptidic catalyst promotes the reaction between various aldehydes and unprotected maleimide with high stereoselectivities and yields. The obtained products were readily derivatized to the corresponding pyrrolidines, lactams, lactones, and peptide-like compounds. (1) H NMR spectroscopic, crystallographic, and computational investigations provided insight into the conformational properties of H-dPro-Pro-Asn-NH2 and revealed the importance of hydrogen bonding between the peptide and maleimide for catalyzing the stereoselective C-C bond formation.

  15. Transition-Metal-Catalyzed Laboratory-Scale Carbon–Carbon Bond-Forming Reactions of Ethylene

    PubMed Central

    Saini, Vaneet; Stokes, Benjamin J.; Sigman, Matthew S.

    2014-01-01

    Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transitionmetal–catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon–carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product. PMID:24105881

  16. Nickel-Catalyzed Allylic Alkylation with Diarylmethane Pronucleophiles: Reaction Development and Mechanistic Insights.

    PubMed

    Sha, Sheng-Chun; Jiang, Hui; Mao, Jianyou; Bellomo, Ana; Jeong, Soo A; Walsh, Patrick J

    2016-01-18

    Palladium-catalyzed allylic substitution reactions are among the most efficient methods to construct C-C bonds between sp(3)-hybridized carbon atoms. In contrast, much less work has been done with nickel catalysts, perhaps because of the different mechanisms of the allylic substitution reactions. Palladium catalysts generally undergo substitution by a "soft"-nucleophile pathway, wherein the nucleophile attacks the allyl group externally. Nickel catalysts are usually paired with "hard" nucleophiles, which attack the metal before C-C bond formation. Introduced herein is a rare nickel-based catalyst which promotes substitution with diarylmethane pronucleophiles by the soft-nucleophile pathway. Preliminary studies on the asymmetric allylic alkylation are promising.

  17. Stereoselective Synthesis of Saturated Heterocycles via Pd-Catalyzed Alkene Carboetherification and Carboamination Reactions

    PubMed Central

    Wolfe, John P.

    2009-01-01

    The development of Pd-catalyzed carboetherification and carboamination reactions between aryl/alkenyl halides and alkenes bearing pendant heteroatoms is described. These transformations effect the stereoselective construction of useful heterocycles such as tetrahydrofurans, pyrrolidines, imidazolidin-2-ones, isoxazolidines, and piperazines. The scope, limitations, and applications of these reactions are presented, and current stereochemical models are described. The mechanism of product formation, which involves an unusual intramolecular syn-insertion of an alkene into a Pd-Heteroatom bond is also discussed in detail. PMID:19183704

  18. Refined transition-state models for proline-catalyzed asymmetric Michael reactions under basic and base-free conditions.

    PubMed

    Sharma, Akhilesh K; Sunoj, Raghavan B

    2012-12-07

    The stereocontrolling transition state (TS) models for C-C bond formation relying on hydrogen bonding have generally been successful in proline-catalyzed aldol, Mannich, α-amination, and α-aminoxylation reactions. However, the suitability of the hydrogen-bonding model in protic and aprotic conditions as well as under basic and base-free conditions has not been well established for Michael reactions. Through a comprehensive density functional theory investigation, we herein analyze different TS models for the stereocontrolling C-C bond formation, both in the presence and absence of a base in an aprotic solvent (THF). A refined stereocontrolling TS for the Michael reaction between cyclohexanone and nitrostyrene is proposed. The new TS devoid of hydrogen bonding between the nitro group of nitrostyrene and carboxylic acid of proline, under base-free conditions, is found to be more preferred over the conventional hydrogen-bonding model besides being able to reproduce the experimentally observed stereochemical outcome. A DBU-bound TS is identified as more suitable for rationalizing the origin of asymmetric induction under basic reaction conditions. In both cases, the most preferred approach of nitrostyrene is identified as occurring from the face anti to the carboxylic acid of proline-enamine. The predicted enantio- and diastereoselectivities are in very good agreement with the experimental observations.

  19. Transition-metal-catalyzed enantioselective heteroatom-hydrogen bond insertion reactions.

    PubMed

    Zhu, Shou-Fei; Zhou, Qi-Lin

    2012-08-21

    Carbon-heteroatom bonds (C-X) are ubiquitous and are among the most reactive components of organic compounds. Therefore investigations of the construction of C-X bonds are fundamental and vibrant fields in organic chemistry. Transition-metal-catalyzed heteroatom-hydrogen bond (X-H) insertions via a metal carbene or carbenoid intermediate represent one of the most efficient approaches to form C-X bonds. Because of the availability of substrates, neutral and mild reaction conditions, and high reactivity of these transformations, researchers have widely applied transition-metal-catalyzed X-H insertions in organic synthesis. Researchers have developed a variety of rhodium-catalyzed asymmetric C-H insertion reactions with high to excellent enantioselectivities for a wide range of substrates. However, at the time that we launched our research, very few highly enantioselective X-H insertions had been documented primarily because of a lack of efficient chiral catalysts and indistinct insertion mechanisms. In this Account, we describe our recent studies of copper- and iron-catalyzed asymmetric X-H insertion reactions by using chiral spiro-bisoxazoline and diimine ligands. The copper complexes of chiral spiro-bisoxazoline ligands proved to be highly enantioselective catalysts for N-H insertions of α-diazoesters into anilines, O-H insertions of α-diazoesters into phenols and water, O-H insertions of α-diazophosphonates into alcohols, and S-H insertions of α-diazoesters into mercaptans. The iron complexes of chiral spiro-bisoxazoline ligands afforded the O-H insertion of α-diazoesters into alcohols and water with unprecedented enantioselectivities. The copper complexes of chiral spiro-diimine ligands exhibited excellent reactivity and enantioselectivity in the Si-H insertion of α-diazoacetates into a wide range of silanes. These transition-metal-catalyzed X-H insertions have many potential applications in organic synthesis because the insertion products, including chiral

  20. Cumene hydroperoxide-supported demethylation reactions catalyzed by cytochrome P450 2B4 lacking the NH2-terminal sequence.

    PubMed

    Zhang, Y; Pernecky, S J

    1999-04-29

    Catalytic activities of cytochrome P450 2B4 lacking NH2-terminal amino acids 2-27 (wt Delta2B4) and that of truncated 2B4 containing a Pro to Ser mutation at position 221 were examined in a system supported by cumene hydroperoxide. Demethylation activities of either truncated 2B4 with N-methylaniline, N,N-dimethylaniline, and d-benzphetamine were lower than those of liver microsomal 2B4, whereas the rate of 1-phenylethanol oxidation to acetophenone catalyzed by liver microsomal and truncated 2B4 enzymes was nearly the same. The Km and Vmax values for cumene hydroperoxide in the demethylation of N-methylaniline by wt Delta2B4 were 20% and 28%, respectively, of those obtained for 2B4. The reaction with wt Delta2B4 displayed a lesser dependence on phospholipid than did that with 2B4, and a complex relationship between activity and substrate concentration. The results suggest that the NH2-terminal region contributes to interaction of oxidant, substrate, and phospholipid in cumene hydroperoxide-supported reactions catalyzed by cytochrome P450 2B4.

  1. Antioxidant activity of minimally processed red chicory (Cichorium intybus L.) evaluated in xanthine oxidase-, myeloperoxidase-, and diaphorase-catalyzed reactions.

    PubMed

    Lavelli, Vera

    2008-08-27

    Minimally processed red chicory products (Cichorium intybus L. var. silvestre) were studied for their polyphenol content and antioxidant activity evaluated by using the synthetic 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical and three model reactions catalyzed by relevant enzymatic sources of reactive oxygen species, namely, xanthine oxidase, myeloperoxidase, and diaphorase. Products were analyzed at the time of production and after storage at 4 degrees C within either a gas permeable film or a gas barrier film. The antioxidant activity and contents of hydroxycinnamic acids and flavonoids decreased by less than 20% during storage of the minimally processed red chicory products. Total phenolics were significantly correlated with the antioxidant activity evaluated with both the synthetic radical and the enzyme-catalyzed reactions. On a molar basis, red chicory phenolics were as efficient as the reference compound Trolox in scavenging the synthetic radical. However, red chicory phenolics had a much higher inhibitory activity than Trolox in the model enzymatic systems.

  2. Click with a boronic acid handle: a neighboring group-assisted click reaction that allows ready secondary functionalization.

    PubMed

    Draganov, Alexander B; Wang, Ke; Holmes, Jalisa; Damera, Krishna; Wang, Danzhu; Dai, Chaofeng; Wang, Binghe

    2015-10-21

    The feasibility of a neighboring boronic acid-facilitated facile condensation of an aldehyde is described. This reaction is bio-orthogonal, complete at room temperature within minutes, and suitable for bioconjugation chemistry. The boronic acid group serves the dual purpose of catalyzing the condensation reaction and being a handle for secondary functionalization.

  3. Production of high-oleic acid tallow fractions using lipase-catalyzed directed interesterification, using both batch and continuous processing.

    PubMed

    MacKenzie; Stevenson

    2000-08-01

    Immobilized lipases were used to catalyze batch-directed interesterification of tallow, resulting in oleins containing significantly higher levels of unsaturated fatty acids than obtained by fractionation without lipase. After 14 days, a reaction catalyzed by 2% Novozym 435 yielded 57% olein unsaturation, compared with 45% in a no-enzyme control. Free fatty acid levels increased to 2-3% during reactions. Incubation of the enzyme in multiple batches of melted fat caused a gradual loss of interesterification activity, apparently due to progressive dehydration. The activity could be restored by addition of water to the reaction medium. Immobilized lipase was also used to catalyze directed interesterification in a continuous flow reactor. Melted tallow was circulated through a packed bed enzyme reactor and a separate crystallization vessel. The temperatures of the two parts of the apparatus were controlled separately to allow crystallization to occur separately from interesterification. Operation of the reactor with conventionally dry, prefractionated tallow allowed the formation of an olein consisting of up to 60% unsaturated fatty acids. The greatest changes in olein fatty acid composition were achieved when the fractionation temperature was kept constant at a value that promoted selective crystallization of trisaturated triglycerides that were continuously produced by enzymic interesterification. The enzyme could be reused without apparent loss of activity, and its activity was apparently enhanced by preincubation in melted tallow for up to several days. Control of both the water activity of the enzyme and tallow feedstock and of the absorption of atmospheric water vapor were required to maintain enzyme activity, during multiple reuse and minimize free fatty acid formation. This method may form the basis for a process to produce highly mono-unsaturated tallow fractions for use in food applications (e.g. frying) where a "healthy" low saturated fat product is required.

  4. Fundamental reaction mechanism and free energy profile for (-)-cocaine hydrolysis catalyzed by cocaine esterase.

    PubMed

    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.

  5. Ruthenium-catalyzed decarbonylative addition reaction of anhydrides with alkynes: a facile synthesis of isocoumarins and α-pyrones.

    PubMed

    Prakash, Rashmi; Shekarrao, Kommuri; Gogoi, Sanjib; Boruah, Romesh C

    2015-06-21

    A novel ruthenium catalyzed straightforward and efficient synthesis of isocoumarin and α-pyrone derivatives has been accomplished by the decarbonylative addition reaction of anhydrides with alkynes under thermal conditions.

  6. An enigmatic peptide ligation reaction: protease-catalyzed oligomerization of a native protein segment in neat aqueous solution.

    PubMed

    Kumaran, S; Datta, D; Roy, R P

    2000-04-01

    We report an enigmatic peptide ligation reaction catalyzed by Glu-specific Staphylococcus aureus V8 protease that occurs in neat aqueous solution around neutral pH utilizing a totally unprotected peptide substrate containing free alpha-carboxyl and alpha-amino groups. V8 protease catalyzed a chain of ligation steps between pH 6 and 8 at 4 degrees C, producing a gamut of covalent oligomers (dimer through octamer or higher) of a native protein segment TAAAKFE (S39) derived from ribonuclease A (RNAse A). Size-exclusion chromatography suggested the absence of strong interaction between the reacting peptides. The circular dichroism spectra of monomer through pentamer showed length-dependent enhancement of secondary structure in the oligomers, suggesting that protease-catalyzed ligation of a monomer to an oligomer resulted in a product that was more structured than its precursor. The relative conformational stability of the oligomers was reflected in their ability to resist proteolysis, indicating that the oligomerization reaction was facilitated as a consequence of the "conformational trapping" of the product. The ligation reaction proceeded in two phases-slow formation and accumulation of the dimer followed by a fast phase of oligomerization, implying that the conformational trap encountered in the oligomerization reaction was a two-step process. The Gly substitution at any position of the TAAAKFE sequence was deleterious, suggesting that the first step of the conformational trap, namely the dimerization reaction, that proceeded very slowly even with the parent peptide, was quite sensitive to amino acid sequence. In contrast, the oligomerization reaction of an Ala analog, AAAAKFE, occurred in much the same way as S39, albeit with faster rate, suggesting that Ala substitution stabilized the overall conformational trapping process. The results suggest the viability of the product-directed "conformational trap" as a mechanism to achieve peptide ligation of totally

  7. One-pot lipase-catalyzed aldol reaction combination of in situ formed acetaldehyde.

    PubMed

    Wang, Na; Zhang, Wei; Zhou, Long-Hua; Deng, Qing-Feng; Xie, Zong-Bo; Yu, Xiao-Qi

    2013-12-01

    A facile tandem route to α,β-unsaturated aldehydes was developed by combining the two catalytic activities of the same enzyme in a one-pot strategy for the aldol reaction and in situ generation of acetaldehyde. Lipase from Mucor miehei was found to have conventional and promiscuous catalytic activities for the hydrolysis of vinyl acetate and aldol condensation with in situ formed acetaldehyde. The first reaction continuously provided material for the second reaction, which effectively reduced the volatilization loss, oxidation, and polymerization of acetaldehyde, as well as avoided a negative effect on the enzyme of excessive amounts of acetaldehyde. After optimizing the process, several substrates participated in the reaction and provided the target products in moderate to high yields using this single lipase-catalyzed one-pot biotransformation.

  8. Lewis acid-catalyzed Friedel-Crafts alkylations of 3-hydroxy-2-oxindole: an efficient approach to the core structure of azonazine.

    PubMed

    Ghosh, Santanu; Kinthada, Lakshmana K; Bhunia, Subhajit; Bisai, Alakesh

    2012-10-18

    A Lewis acid catalyzed Friedel-Crafts reaction of electron rich aromatics with 3-alkyl-3-hydroxy-2-oxindole (5) has been developed. The methodology provides a straightforward access to the core of azonazine (2) sharing an all-carbon quaternary stereocenter at the tetracyclic ring junction.

  9. Organosolv liquefaction of sugarcane bagasse catalyzed by acidic ionic liquids.

    PubMed

    Chen, Zhengjian; Long, Jinxing

    2016-08-01

    An efficient and eco-friendly process is proposed for sugarcane bagasse liquefaction under mild condition using IL catalyst and environmental friendly solvent of ethanol/H2O. The relationship between IL acidic strength and its catalytic performance is investigated. The effects of reaction condition parameters such as catalyst dosage, temperature, time and solvent are also intensively studied. The results show that ethanol/H2O has a significant promotion effect on the simultaneous liquefaction of sugarcane bagasse carbohydrate and lignin. 97.5% of the bagasse can be liquefied with 66.46% of volatile product yield at 200°C for 30min. Furthermore, the IL catalyst shows good recyclability where no significant loss of the catalytic activity is exhibited even after five runs.

  10. Copper-catalyzed extended Pummerer reactions of ketene dithioacetal monoxides with alkynyl sulfides and ynamides with an accompanying oxygen rearrangement.

    PubMed

    Murakami, Kei; Imoto, Junichi; Matsubara, Hiroshi; Yoshida, Suguru; Yorimitsu, Hideki; Oshima, Koichiro

    2013-04-26

    The first examples of metal-catalyzed extended Pummerer reactions through the activation of sulfoxides are described. The copper-catalyzed reactions of ketene dithioacetal monoxides with alkynyl sulfides and ynamides provided a wide variety of γ,γ-disulfanyl-β,γ-unsaturated carbonyl compounds with an accompanying oxygen rearrangement. The products can be easily converted into 1,4-dicarbonyl compounds and substituted heteroaromatics. DFT calculations and mechanistic experiments revealed a new interesting stepwise addition/oxygen rearrangement mechanism.

  11. Substrate activity of synthetic formyl phosphate in the reaction catalyzed by formyltetrahydrofolate synthetase

    SciTech Connect

    Smithers, G.W.; Jahansouz, H.; Kofron, J.L.; Himes, R.H.; Reed, G.H.

    1987-06-30

    Formyl phosphate, a putative enzyme-bound intermediate in the reaction catalyzed by formyltetrahydrofolate synthetase (EC 6.3.4.3), was synthesized from formyl fluoride and inorganic phosphate, and the product was characterized by /sup 31/P, /sup 1/H, and /sup 13/C nuclear magnetic resonance (NMR). Measurement of hydrolysis rates by /sup 31/P NMR indicates that formyl phosphate is particularly labile, with a half-life of 48 min in a buffered neutral solution at 20 /sup 0/C. At pH 7, hydrolysis occurs with P-O bond cleavage, as demonstrated by /sup 18/O incorporation from H/sub 2//sup 18/O into P/sub i/, while at pH 1 and pH 13 hydrolysis occurs with C-O bond cleavage. The substrate activity of formyl phosphate was tested in the reaction catalyzed by formyltetrahydrofolate synthetase isolated from Clostridium cylindrosporum. Formyl phosphate supports the reaction in both the forward and reverse directions. Thus, N/sup 10/-formyltetrahydrofolate is produced from tetrahydrofolate and formyl phosphate in a reaction mixture that contains enzyme, Mg(II), and ADP, and ATP is produced from formyl phosphate and ADP with enzyme, Mg(II), and tetrahydrofolate present. The requirements for ADP and for tetrahydrofolate as cofactors in these reactions are consistent with previous steady-state kinetic and isotope exchange studies, which demonstrated that all substrate subsites must be occupied prior to catalysis. The k/sub cat/ values for both the forward and reverse directions, with formyl phosphate as the substrate, are much lower than those for the normal forward and reverse reactions. Kinetic analysis of the formyl phosphate supported reactions indicates that the low steady-state rates observed for the synthetic intermediate are most likely due to the sequential nature of the normal reaction.

  12. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    PubMed

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  13. The mechanism of the NHC catalyzed aza-Morita-Baylis-Hillman reaction: insights into a new substrate-catalyzed bimolecular pathway.

    PubMed

    Verma, Pritha; Verma, Pragya; Sunoj, Raghavan B

    2014-04-14

    The first mechanistic study on the NHC-catalyzed aza-MBH reaction between cyclopentenone and N-mesylbenzaldimine using density functional theory reveals that a bimolecular mechanism, involving two molecules of benzaldimine in the proton transfer, is energetically more preferred over the conventional direct proton transfer.

  14. Thermodynamic parameters monitoring the equilibrium shift of enzyme-catalyzed hydrolysis/synthesis reactions in favor of synthesis in mixtures of water and organic solvent.

    PubMed

    Deschrevel, Brigitte; Vincent, Jean-Claude; Ripoll, Camille; Thellier, Michel

    2003-01-20

    The main strategy developed to shift the equilibrium state of a hydrolase-catalyzed hydrolysis/synthesis reaction consists in reducing water activity by addition of organic solvents in the reaction medium. We have used several mixtures of water and 1,4-butanediol, ranging from pure water to pure 1,4-butanediol, to study the hydrolysis/synthesis reaction of the N-Cbz-L-tryptophanyl-glycineamide dipeptide, catalyzed by alpha-chymotrypsin. In the presence of 1,4-butanediol, alpha-chymotrypsin also catalyzed the esterification reaction between this diol and N-Cbz-L-tryptophan; this ester hydrolysis/synthesis reaction has thus also been examined. The dipeptide and ester equilibrium concentrations increase when the water content of the reaction medium is decreased. Using our experimental data, we have determined the equilibrium constants of the hydrolysis/synthesis equilibria involving the nonionized forms of the protected amino acids, the estimated values of which are Ksp = 8 10(5) for the dipeptide and Kse = 78 for the ester respectively. They are true thermodynamic equilibrium constants, each related to a single, well-defined reaction equilibrium and with water activity being taken into account. If an organic solvent is added to the reaction medium these equilibria can be shifted towards synthesis by decreasing the water activity but also by modifying the ionization/neutralization equilibrium constant of the ionizable groups. These two effects depend both on the water content and on the nature of the organic solvent used, and, in particular, on its dielectric constant. Because of the importance of this parameter in our study, we discuss using it as an indicator to select an appropriate organic solvent to perform an enzyme-catalyzed synthesis.

  15. Pd- and Ni-catalyzed cross-coupling reactions in the synthesis of organic electronic materials.

    PubMed

    Xu, Shiqing; Kim, Eun Hoo; Wei, Alexander; Negishi, Ei-Ichi

    2014-08-01

    Organic molecules and polymers with extended π-conjugation are appealing as advanced electronic materials, and have already found practical applications in thin-film transistors, light emitting diodes, and chemical sensors. Transition metal (TM)-catalyzed cross-coupling methodologies have evolved over the past four decades into one of the most powerful and versatile methods for C-C bond formation, enabling the construction of a diverse and sophisticated range of π-conjugated oligomers and polymers. In this review, we focus our discussion on recent synthetic developments of several important classes of π-conjugated systems using TM-catalyzed cross-coupling reactions, with a perspective on their utility for organic electronic materials.

  16. Pd- and Ni-catalyzed cross-coupling reactions in the synthesis of organic electronic materials

    NASA Astrophysics Data System (ADS)

    Xu, Shiqing; Hoo Kim, Eun; Wei, Alexander; Negishi, Ei-ichi

    2014-08-01

    Organic molecules and polymers with extended π-conjugation are appealing as advanced electronic materials, and have already found practical applications in thin-film transistors, light emitting diodes, and chemical sensors. Transition metal (TM)-catalyzed cross-coupling methodologies have evolved over the past four decades into one of the most powerful and versatile methods for C-C bond formation, enabling the construction of a diverse and sophisticated range of π-conjugated oligomers and polymers. In this review, we focus our discussion on recent synthetic developments of several important classes of π-conjugated systems using TM-catalyzed cross-coupling reactions, with a perspective on their utility for organic electronic materials.

  17. Helical-Peptide-Catalyzed Enantioselective Michael Addition Reactions and Their Mechanistic Insights.

    PubMed

    Ueda, Atsushi; Umeno, Tomohiro; Doi, Mitsunobu; Akagawa, Kengo; Kudo, Kazuaki; Tanaka, Masakazu

    2016-08-05

    Helical peptide foldamer catalyzed Michael addition reactions of nitroalkane or dialkyl malonate to α,β-unsaturated ketones are reported along with the mechanistic considerations of the enantio-induction. A wide variety of α,β-unsaturated ketones, including β-aryl, β-alkyl enones, and cyclic enones, were found to be catalyzed by the helical peptide to give Michael adducts with high enantioselectivities (up to 99%). On the basis of X-ray crystallographic analysis and depsipeptide study, the amide protons, N(2)-H and N(3)-H, at the N terminus in the α-helical peptide catalyst were crucial for activating Michael donors, while the N-terminal primary amine activated Michael acceptors through the formation of iminium ion intermediates.

  18. Pd- and Ni-catalyzed cross-coupling reactions in the synthesis of organic electronic materials

    PubMed Central

    Xu, Shiqing; Kim, Eun Hoo; Wei, Alexander; Negishi, Ei-ichi

    2014-01-01

    Organic molecules and polymers with extended π-conjugation are appealing as advanced electronic materials, and have already found practical applications in thin-film transistors, light emitting diodes, and chemical sensors. Transition metal (TM)-catalyzed cross-coupling methodologies have evolved over the past four decades into one of the most powerful and versatile methods for C–C bond formation, enabling the construction of a diverse and sophisticated range of π-conjugated oligomers and polymers. In this review, we focus our discussion on recent synthetic developments of several important classes of π-conjugated systems using TM-catalyzed cross-coupling reactions, with a perspective on their utility for organic electronic materials. PMID:27877696

  19. Conversion of waste cellulose to ethanol. Phase II. Reaction kinetics with phosphoric acid

    SciTech Connect

    Moeller, M.B.; Isbell, R.E.

    1982-05-01

    Waste cellulosic material can be hydrolyzed in dilute acid solution to produce fermentable sugars which can then be converted into ethanol. A laboratory investigation was made of the feasibility of using phosphoric acid as the hydrolysis catalyst. The hydrolysis reaction with phosphoric acid solutions was compared with the reaction employing the more conventional dilute sulfuric acid catalyst. The purpose of this research was to examine the hydrolysis step in a proposed process for the conversion of cellulose (from wood, newspapers, municipal solid waste, or other sources) into ethanol - by which a potentially valuable co-product, DICAL (dicalcium phosphate), might be made and sold with or without the lignin content as a fertilizer. The pertinent reaction kinetics for the acid catalyzed production of glucose from cellulose consists of consecutive, pseudo-first order reactions. The first reaction forms glucose by hydrolyzing the cellulose polymer and a subsequent reaction decomposes the glucose. The maximum theoretical yield depends on the ratio of the rate constants for these two reactions. The rate constants of both reactions were measured in a series of experiments studying temperature and concentration effects. The results suggest that the glucose decomposition reaction is similar with the two acids but that the cellulose hydrolysis reaction mechanism with phosphoric acid may be different than with sulfuric acid. The studies show phosphoric acid is unpromising and much inferior to sulfuric acid as the catalytic agent. Under the conditions studied, 0.8 wt % sulfuric acid gives a greater yield of glucose than 8.0 wt % phosphoric acid.

  20. Silver-Catalyzed Formal Inverse Electron-Demand Diels-Alder Reaction of 1,2-Diazines and Siloxy Alkynes

    PubMed Central

    Türkmen, Yunus E.; Montavon, Timothy J.; Kozmin, Sergey A.; Rawal, Viresh H.

    2012-01-01

    A highly effective silver-catalyzed formal inverse electron-demand Diels-Alder reaction of 1,2-diazines and siloxy alkynes has been developed. The reactions provide ready access to a wide range of siloxy naphthalenes and anthracenes, which are formed in good to high yields, under mild reaction conditions, using low catalyst loadings. PMID:22607029

  1. Kinetic studies on enzyme-catalyzed reactions: oxidation of glucose, decomposition of hydrogen peroxide and their combination.

    PubMed

    Tao, Zhimin; Raffel, Ryan A; Souid, Abdul-Kader; Goodisman, Jerry

    2009-04-08

    The kinetics of the glucose oxidase-catalyzed reaction of glucose with O2, which produces gluconic acid and hydrogen peroxide, and the catalase-assisted breakdown of hydrogen peroxide to generate oxygen, have been measured via the rate of O2 depletion or production. The O2 concentrations in air-saturated phosphate-buffered salt solutions were monitored by measuring the decay of phosphorescence from a Pd phosphor in solution; the decay rate was obtained by fitting the tail of the phosphorescence intensity profile to an exponential. For glucose oxidation in the presence of glucose oxidase, the rate constant determined for the rate-limiting step was k = (3.0 +/- 0.7) x 10(4) M(-1) s(-1) at 37 degrees C. For catalase-catalyzed H2O2 breakdown, the reaction order in [H2O2] was somewhat greater than unity at 37 degrees C and well above unity at 25 degrees C, suggesting different temperature dependences of the rate constants for various steps in the reaction. The two reactions were combined in a single experiment: addition of glucose oxidase to glucose-rich cell-free media caused a rapid drop in [O2], and subsequent addition of catalase caused [O2] to rise and then decrease to zero. The best fit of [O2] to a kinetic model is obtained with the rate constants for glucose oxidation and peroxide decomposition equal to 0.116 s(-1) and 0.090 s(-1) respectively. Cellular respiration in the presence of glucose was found to be three times as rapid as that in glucose-deprived cells. Added NaCN inhibited O2 consumption completely, confirming that oxidation occurred in the cellular mitochondrial respiratory chain.

  2. Quantitative characterization of hydroxyl radical generation in a goethite-catalyzed Fenton-like reaction.

    PubMed

    Lin, Zhi-Rong; Zhao, Ling; Dong, Yuan-Hua

    2015-12-01

    In order to find out the truth of influence of solution chemistry on the oxidation efficiency of a goethite-catalyzed Fenton-like reaction, the amount of hydroxyl radicals (OH) was quantified by using coumarin as its trapping agent to produce the only fluorescent derivative 7-hydroxycoumarin (7-HC), because OH was the reactive species responsible for the oxidation activity of Fenton reactions. The concentration of OH achieved maximum at solution pH of 3 and decreased with an increase of solution pH value. However, considerable amount of OH can also generate at near neutral pH (i.e. pH 6 and 7). The concentration of OH was increased both with increasing of goethite and H2O2 dosages, but H2O2 could compete with coumarin to scavenge OH to reduce the formation of 7-HC when the concentration of H2O2 was too high. Anions inhibited OH generation followed an order of H2PO4(-)>SO4(2-)>Cl(-)>NO3(-)>ClO4(-). Higher concentrations of Cl(-) and SO4(2-) resulted in greater inhibition of OH generation. Results of this study demonstrated that the influence of solution chemistry on the oxidation efficiency of the goethite-catalyzed Fenton-like reaction was greatly attributed to the effect of solution chemistry on the amount of OH formed in the process of reaction.

  3. Asymmetric 1,3-Dipolar Cycloaddition Reactions Catalyzed by Heterocycle-Based Metal Complexes

    NASA Astrophysics Data System (ADS)

    Suga, Hiroyuki

    Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, α-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.

  4. Contribution of flavin covalent linkage with histidine 99 to the reaction catalyzed by choline oxidase.

    PubMed

    Quaye, Osbourne; Cowins, Sharonda; Gadda, Giovanni

    2009-06-19

    The FAD-dependent choline oxidase has a flavin cofactor covalently attached to the protein via histidine 99 through an 8alpha-N(3)-histidyl linkage. The enzyme catalyzes the four-electron oxidation of choline to glycine betaine, forming betaine aldehyde as an enzyme-bound intermediate. The variant form of choline oxidase in which the histidine residue has been replaced with asparagine was used to investigate the contribution of the 8alpha-N(3)-histidyl linkage of FAD to the protein toward the reaction catalyzed by the enzyme. Decreases of 10-fold and 30-fold in the k(cat)/K(m) and k(cat) values were observed as compared with wild-type choline oxidase at pH 10 and 25 degrees C, with no significant effect on k(cat)/K(O) using choline as substrate. Both the k(cat)/K(m) and k(cat) values increased with increasing pH to limiting values at high pH consistent with the participation of an unprotonated group in the reductive half-reaction and the overall turnover of the enzyme. The pH independence of both (D)(k(cat)/K(m)) and (D)k(cat), with average values of 9.2 +/- 3.3 and 7.4 +/- 0.5, respectively, is consistent with absence of external forward and reverse commitments to catalysis, and the chemical step of CH bond cleavage being rate-limiting for both the reductive half-reaction and the overall enzyme turnover. The temperature dependence of the (D)k(red) values suggests disruption of the preorganization in the asparagine variant enzyme. Altogether, the data presented in this study are consistent with the FAD-histidyl covalent linkage being important for the optimal positioning of the hydride ion donor and acceptor in the tunneling reaction catalyzed by choline oxidase.

  5. Spontaneous, Metal-Catalyzed, and Enzyme-Catalyzed Decarboxylation of Oxalosuccinic Acid.

    DTIC Science & Technology

    1980-01-01

    The Ohio State University, 1980 309 Pages Professor Daniel Leussing, Advisor Decarboxylation rates of oxalosuccinic acid , a tricarboxylic acid , thas...been studied in detail. It was shown that the keto forms of the acid spontaneously decarboxylate. The catalytic effect of three metals were examined. The...overall effectiveness of the metals were , This catalysis resulted from the formation of a 1:1 complex between the acid and the metal ions. The

  6. Contribution to the chemistry of the Belousov-Zhabotinsky reaction. Products of the Ferriin-Bromomalonic acid and the Ferriin-Malonic acid reactions.

    PubMed

    Hegedüs, Laszló; Försterling, Horst-Dieter; Onel, Lavinia; Wittmann, Maria; Noszticzius, Zoltan

    2006-11-30

    In the present mechanistic schemes of the ferroin-catalyzed oscillatory Belousov-Zhabotinsky (BZ) reaction the oxidation of the organic substrates (bromomalonic or malonic acid) by ferriin (the oxidized form of the catalyst) plays an important role. As the organic products of these reactions were not yet identified experimentally, they were studied here by an HPLC technique. It was found that the main organic oxidation product of bromomalonic acid is bromo-ethene-tricarboxylic acid (BrEETRA), the same compound that is formed when bromomalonic acid is oxidized by Ce4+ (another catalyst of the BZ reaction). Formation of BrEETRA is explained here by a new mechanism that is more realistic than the one suggested earlier. To find any oxidation product of malonic acid in the ferriin-malonic acid reaction was not successful, however. Neither ethane-tetracarboxylic acid (ETA) nor malonyl malonate (MAMA), the usual products of the Ce4+- malonic acid reaction, nor any other organic acid, not even CO2, was found as a product of the reaction. We propose that malonic acid is not oxidized in the ferriin-malonic acid reaction, and it plays only the role of a complex forming catalyst in a process where Fe3+ oxidizes mostly its phenantroline ligand.

  7. 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

    SciTech Connect

    Klobukowski, Erik

    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

  8. Chemiluminescent Reactions Catalyzed by Nanoparticles of Gold, Silver, and Gold/Silver Alloys

    NASA Astrophysics Data System (ADS)

    Abideen, Saqib Ul

    Chemiluminescence (CL) reactions are catalyzed by metals nanoparticles, which display unique catalytic properties due to an increased surface area. The present study describes the catalytic effects of nanoparticles (NP) of silver, gold, and alloys of Au/Ag nanoparticles on the chemiluminescent reaction taking place between luminol and potassium ferricyanide. It was found that silver nanoparticles and alloy nanoparticles enhance the CL process when their sizes remained in the range of 30 nm to 50 nm. The data show that the intensity and rate of chemiluminescence were influenced by the mole fraction of gold and silver in the alloy. Data to this chemiluminescence reaction are modeled by a double exponential curve, which indicates that two competing processes are occurring.

  9. Organic carbonates as alternative solvents for palladium-catalyzed substitution reactions.

    PubMed

    Schäffner, Benjamin; Holz, Jens; Verevkin, Sergey P; Börner, Armin

    2008-01-01

    Organic carbonates, such as propylene carbonate, butylene carbonate, and diethyl carbonate, were tested in the Pd-catalyzed asymmetric allylic substitution reactions of rac-1,3-diphenyl-3-acetoxy-prop-1-ene with dimethyl malonate or benzylamine as nucleophiles. Bidentate diphosphanes were used as chiral ligands. The application of monodentate phosphanes capable of self-assembling with the metal was likewise tested. In the substitution reaction with dimethyl malonate, enantioselectivities up to 98% were achieved. In the amination reaction, the chiral product was obtained with up to 83% ee. The results confirm that these "green solvents" can be advantageously used for this catalytic transformation as an alternative to those solvents usually employed which run some risk of being harmful to the environment.

  10. Acid-Catalyzed Conversion of Furfuryl Alcohol to Ethyl Levulinate in Liquid Ethanol.

    PubMed

    González Maldonado, Gretchen M; Assary, Rajeev S; Dumesic, James; Curtiss, Larry A

    2012-09-20

    Reaction pathways for the acid-catalyzed conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) in ethanol were investigated using liquid chromatography-mass spectrometry (LC-MS), 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, and ab initio high-level quantum chemical (G4MP2) calculations. Our combined studies show that the production of EL at high yields from FAL is not accompanied by stoichiometric production of diethyl either (DEE), indicating that ethoxymethyl furan (EMF) is not an intermediate in the major reaction pathway. Several intermediates were observed using an LC-MS system, and three of these intermediates were isolated and subjected to reaction conditions. The structures of two intermediates were elucidated using 1D and 2D NMR techniques. One of these intermediates is EMF, which forms EL and DEE in a secondary reaction pathway. The second intermediate identified is 4,5,5-triethoxypentan-2-one, which is analogous to one of the intermediates observed in the conversion of FAL to LA in water (i.e. 4,5,5-trihydroxypentan-2-one). Furthermore, conversion of this intermediate to EL again involves the formation of DEE, indicating that it is also part of a secondary pathway. The primary pathway for production of EL involves solvent-assisted transfer of a water molecule from the partially detached protonated hydroxyl group of FAL to a ring carbon, followed by intra-molecular hydrogen shift, where the apparent reaction barrier for the hydrogen shift is relatively smaller in ethanol (21.1 kcal/mol) than that in water (26.6 kcal/mol).

  11. Benzoic acid 2-hydroxylase, a soluble oxygenase from tobacco, catalyzes salicylic acid biosynthesis

    SciTech Connect

    Leon, J.; Shulaev, V.; Yalpani, N.

    1995-10-24

    Benzoic acid 2-hydroxylase (BA2H) catalyzes the biosynthesis of salicylic acid from benzoic acid. The enzyme has been partially purified and characterized as a soluble protein of 160 kDa. High-efficiency in vivo labeling of salicyclic acid with {sup 18}O{sub 2} suggested that BA2H is an oxygenase that specifically hydroxylates the ortho position of benzoic acid. The enzyme was strongly induced by either tobacco mosaic virus inoculation of benzoic acid infiltration of tobacco leaves and it was inhibited by CO and other inhibitors of cytochrome P450 hydroxylases. The BA2H activity was immunodepleted by antibodies raised against SU2, a soluble cytochrome P450 from Streptomyces griseolus. The anti-SU2 antibodies immunoprecipitated a radiolabeled polypeptide of around 160 kDa from the soluble protein extracts of L-[{sup 35}S]-methionine-fed tobacco leaves. Purified BA2H showed CO-difference spectra with a maximum at 457 nm. These data suggest that BA2H belongs to a novel class of soluble, high molecular weight cytochrome P450 enzymes. 21 refs., 6 figs., 1 tab.

  12. Formation of Linear Polyenes in Thermal Dehydration of Polyvinyl Alcohol, Catalyzed by Phosphotungstic Acid

    NASA Astrophysics Data System (ADS)

    Tretinnikov, O. N.; Sushko, N. I.

    2015-01-01

    In order to obtain linear polyenes in polyvinyl alcohol films via acid-catalyzed thermal dehydration of the polyvinyl alcohol, we used phosphotungstic acid as the catalyst: a safe and heat-stable solid chemical compound. We established that phosphotungstic acid, introduced as solid nanoparticles into polyvinyl alcohol films, is a more effective dehydration catalyst than hydrochloric acid, since in contrast to HCl it does not evaporate from the film during heat treatment.

  13. In situ Regeneration of NADH via Lipoamide Dehydrogenase-catalyzed Electron Transfer Reaction Evidenced by Spectroelectrochemistry

    SciTech Connect

    Tam, Tsz Kin; Chen, Baowei; Lei, Chenghong; Liu, Jun

    2012-08-01

    NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80 {+-} 0.15 mM and 1.91 {+-} 0.09 {micro}M s-1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

  14. Mild copper-catalyzed vinylation reactions of azoles and phenols with vinyl bromides.

    PubMed

    Taillefer, Marc; Ouali, Armelle; Renard, Brice; Spindler, Jean-Francis

    2006-07-05

    An efficient and straightforward copper-catalyzed method allowing vinylation of N- or O-nucleophiles with di- or trisubstituted vinyl bromides is reported. The procedure is applicable to a broad range of substrates since N-vinylation of mono-, di-, and triazoles as well as O-vinylation of phenol derivatives can be performed with catalytic amounts of copper iodide and inexpensive nitrogen ligands 3 or 8. In the case of more hindered vinyl bromides, the use of the original bidentate chelator 8 was shown to be more efficient to promote the coupling reactions than our key tetradentate ligand 3. The corresponding N-(1-alkenyl)azoles and alkenyl aryl ethers are obtained in high yields and selectivities under very mild temperature conditions (35-110 degrees C for N-vinylation reactions and 50-80 degrees C for O-vinylation reactions). Moreover, to our knowledge, this method is the first example of a copper-catalyzed vinylation of various azoles. Finally, this protocol, practical on a laboratory scale and easily adaptable to an industrial scale, is very competitive compared to the existing methods that allow the synthesis of such compounds.

  15. The Lewis-acid-catalyzed synthesis of hyperbranched poly(glycerol-diacid)s in toluene

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The first examples of monomeric glycerol-derived hyperbranched polyesters produced in a non-polar solvent system are reported here. The polymers were made by the Lewis acid (dibutyltin(IV)oxide)-catalyzed polycondensation of glycerol with either succinic acid (n (aliphatic chain length)=2), glutari...

  16. Catalyzed ring-opening polymerization of epoxidized soybean oil by hydrated and anhydrous fluoroantimonic acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by the super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), and the anhydrous form (HSbF6) in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO and SAA-...

  17. Low-temperature superacid catalysis: Reactions of n - butane and propane catalyzed by iron- and manganese-promoted sulfated zirconia

    SciTech Connect

    Tsz-Keung, Cheung; d`Itri, J.L.; Lange, F.C.; Gates, B.C.

    1995-12-31

    The primary goal of this project is to evaluate the potential value of solid superacid catalysts of the sulfated zirconia type for light hydrocarbon conversion. The key experiments catalytic testing of the performance of such catalysts in a flow reactor fed with streams containing, for example, n-butane or propane. Fe- and Mn-promoted sulfated zirconia was used to catalyze the conversion of n-butane at atmospheric pressure, 225-450{degrees}C, and n-butane partial pressures in the range of 0.0025-0.01 atm. At temperatures <225{degrees}C, these reactions were accompanied by cracking; at temperatures >350{degrees}C, cracking and isomerization occurred. Catalyst deactivation, resulting at least in part from coke formation, was rapid. The primary cracking products were methane, ethane, ethylene, and propylene. The observation of these products along with an ethane/ethylene molar ratio of nearly 1 at 450{degrees}C is consistent with cracking occurring, at least in part, by the Haag-Dessau mechanism, whereby the strongly acidic catalyst protonates n-butane to give carbonium ions. The rate of methane formation from n-butane cracking catalyzed by Fe- and Mn-promoted sulfated zirconia at 450{degrees}C was about 3 x 10{sup -8} mol/(g of catalyst {center_dot}s). The observation of butanes, pentanes, and methane as products is consistent with Olah superacid chemistry, whereby propane is first protonated by a very strong acid to form a carbonium ion. The carbonium ion then decomposes into methane and an ethyl cation which undergoes oligocondensation reactions with propane to form higher molecular weight alkanes. The results are consistent with the identification of iron- and manganese-promoted sulfated zirconia as a superacid.

  18. N-heterocyclic carbene catalyzed asymmetric intermolecular Stetter reaction: origin of enantioselectivity and role of counterions.

    PubMed

    Kuniyil, Rositha; Sunoj, Raghavan B

    2013-10-04

    The mechanism and the role of KOtBu in an enantioselective NHC-catalyzed Stetter reaction between p-chlorobenzaldehyde and N-acylamido acrylate is established using DFT(M06-2X) methods. The Gibbs free energies are found to be significantly lower for transition states with explicit bound KOtBu as compared to the conventional pathways without the counterions. An intermolecular proton transfer from HOtBu to the prochiral carbon is identified as the stereocontrolling step. The computed enantioselectivities are in excellent agreement with the experimental results.

  19. Highly selective room-temperature copper-catalyzed C-N coupling reactions.

    PubMed

    Shafir, Alexandr; Buchwald, Stephen L

    2006-07-12

    Through the use of cyclic beta-diketones as supporting ligands, the copper-catalyzed coupling of aryl iodides with aliphatic amines occurs at room temperature in as little as 1 h. These high reaction rates allow for the coupling of a wide range of aryl and heteroaryl iodides at room temperature. This method is highly tolerant of a number of reactive functional groups, including -Br and aromatic -NH2 as well as phenolic and aliphatic -OH. The high selectivity of the CuI-beta-diketone catalyst for aliphatic amines represents a useful complement to the palladium-based methods.

  20. Pathways of electrophilic aromatic substitution reactions catalyzed by group 13 trihalides: An ab initio study

    NASA Astrophysics Data System (ADS)

    Volkov, Alexey N.; Timoshkin, Alexey Y.; Suvorov, Andrew V.

    An ab initio study of the two possible pathways of ectrophilic aromatic substitution reaction catalyzed by monomeric and dimeric forms of group 13 metal halides has been performed. Optimized geometries of π, σ-complexes and corresponding transition states have been obtained at second-order Møller-Plesset/ LANL2DZ(d)+ level of theory. It is found that operation of the dimeric pathway is more favorable both thermodynamically and kinetically. Thus, it is expected that catalytical activity of the metal halide will be greatly increased if the stoichiometric ratio 2:1 is employed. Obtained results are in qualitative agreement with available experimental data.

  1. Efficient Lewis acid ionic liquid-catalyzed synthesis of the key intermediate of coenzyme Q10 under microwave irradiation.

    PubMed

    Chen, Yue; Zu, Yuangang; Fu, Yujie; Zhang, Xuan; Yu, Ping; Sun, Guoyong; Efferth, Thomas

    2010-12-22

    An efficient synthesis of a valuable intermediate of coenzyme Q(10) by microwave-assisted Lewis acidic ionic liquid (IL)-catalyzed Friedel-Crafts alkylation is reported. The acidity of six [Etpy]BF(4)-based ionic liquids was characterized by means of the FT-IR technique using acetonitrile as a molecular probe. The catalytic activities of these ionic liquids were correlated with their Lewis acidity. With increasing Lewis acid strength of the ionic liquids, their catalytic activity in the Friedel-Crafts reaction increased, except for [Etpy]BF(4)-AlCl(3). The effects of the reaction system, the molar fraction of Lewis acid in the Lewis acid ILs and heating techniques were also investigated. Among the six Lewis acid ionic liquids tested [Etpy]BF(4)-ZnCl(2) showed the best catalytic activity, with a yield of 89% after a very short reaction time (150 seconds). This procedure has the advantages of higher efficiency, better reusability of ILs, energy conservation and eco-friendliness. The method has practical value for preparation of CoQ(10) on an industrial scale.

  2. New Mechanistic Insights on the Selectivity of Transition-Metal-Catalyzed Organic Reactions: The Role of Computational Chemistry.

    PubMed

    Zhang, Xinhao; Chung, Lung Wa; Wu, Yun-Dong

    2016-06-21

    With new advances in theoretical methods and increased computational power, applications of computational chemistry are becoming practical and routine in many fields of chemistry. In organic chemistry, computational chemistry plays an indispensable role in elucidating reaction mechanisms and the origins of various selectivities, such as chemo-, regio-, and stereoselectivities. Consequently, mechanistic understanding improves synthesis and assists in the rational design of new catalysts. In this Account, we present some of our recent works to illustrate how computational chemistry provides new mechanistic insights for improvement of the selectivities of several organic reactions. These examples include not only explanations for the existing experimental observations, but also predictions which were subsequently verified experimentally. This Account consists of three sections discuss three different kinds of selectivities. The first section discusses the regio- and stereoselectivities of hydrosilylations of alkynes, mainly catalyzed by [Cp*Ru(MeCN)3](+) or [CpRu(MeCN)3](+). Calculations suggest a new mechanism that involves a key ruthenacyclopropene intermediate. This mechanism not only explains the unusual Markovnikov regio-selectivity and anti-addition stereoselectivity observed by Trost and co-workers, but also motivated further experimental investigations. New intriguing experimental observations and further theoretical studies led to an extension of the reaction mechanism. The second section includes three cases of meta-selective C-H activation of aryl compounds. In the case of Cu-catalyzed selective meta-C-H activation of aniline, a new mechanism that involves a Cu(III)-Ar-mediated Heck-like transition state, in which the Ar group acts as an electrophile, was proposed. This mechanism predicted a higher reactivity for more electron-deficient Ar groups, which was supported by experiments. For two template-mediated, meta-selective C-H bond activations catalyzed by

  3. From formamide to purine: a self-catalyzed reaction pathway provides a feasible mechanism for the entire process.

    PubMed

    Wang, Jing; Gu, Jiande; Nguyen, Minh Tho; Springsteen, Greg; Leszczynski, Jerzy

    2013-08-15

    A formamide self-catalyzed mechanistic pathway that transforms formamide to purine through a five-membered ring intermediate has been explored by density functional theory calculations. The highlight of the mechanistic route detailed here is that the proposed pathway represents the simplest and lowest energy reaction pathway. All necessary reactants, including catalysts, are generated from a single initial compound, formamide. The most catalytically effective form of formamide is found to be the imidic acid isomer. The catalytic effect of formamide has been found to be much more significant than that of water. The self-catalytic mechanism revealed here provides a pathway with the lowest energy barriers among all reaction routes previously published. Several important reaction steps are involved in this mechanistic route: formylation-dehydration, Leuckart reduction, five- and six-member ring-closing, and deamination. Overall, a five-membered ring-closing is the rate-determining step in the present catalytic route, which is consistent with our previous mechanistic investigations. The activation energy of this rate-controlling step (ca. 27 kcal/mol) is significantly lower than the rate-determining step (ca. 34 kcal/mol) in the pathway from 4-aminoimidazole-5-carboxamidine described by Schleyer's group (Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 17272-17277) and in the pyrimidine pathway (ca. 44 kcal/mol) reported by Sponer et al. (J. Phys. Chem. A 2012, 116, 720-726). The self-catalyzed mechanistic pathway reported herein is less energetically demanding than previously proposed routes.

  4. Mechanistic insights on platinum- and palladium-pincer catalyzed coupling and cyclopropanation reactions between olefins.

    PubMed

    Rajeev, Ramanan; Sunoj, Raghavan B

    2012-07-21

    The mechanism of M(II)-PNP-pincer catalyzed reaction between (i) ethene, (ii) trans-butene with 2-methylbut-2-ene, 2,3-dimethylbut-2-ene and tert-butylbutene is examined by using density functional theory methods (where M = Pt or Pd). All key intermediates and transition states involved in the reaction are precisely located on the respective potential energy surfaces using the popular DFT functionals such as mPW1K, M06-2X, and B3LYP in conjunction with the 6-31+G** basis set. The reaction between these olefins can lead to a linear coupling product or a substituted cyclopropane. The energetic comparison between coupling as well as cyclopropanation pathways involving four pairs of olefins for both platinum (1-4) and palladium (5-8) catalyzed reactions is performed. The key events in the lower energy pathway in the mechanistic course involves (i) a C-C bond formation between the metal bound olefin (ethene or trans-butene) and a free olefin, and (ii) two successive [1,2] hydrogen migrations in the ensuing carbocationic intermediates (1c-4c, and 1d-4d), toward the formation of the coupling product. The computed barriers for these steps in the reaction of metal bound ethene to free tert-butylbutene (or other butenes) are found to be much lower than the corresponding steps when trans-butene is bound to the metal pincer. The Gibbs free energy differences between the transition states leading to the coupling product (TS(d-e)) and that responsible for cyclopropanated product (TS(d-g)) are found to be diminishingly closer in the case of the platinum pincer as compared to that in the palladium system. The computed energetics indicate that the coupled product prefers to remain as a metal olefin complex, consistent with the earlier experimental reports.

  5. Application of chiral mixed phosphorus/sulfur ligands to enantioselective rhodium-catalyzed dehydroamino acid hydrogenation and ketone hydrosilylation processes.

    PubMed

    Evans, David A; Michael, Forrest E; Tedrow, Jason S; Campos, Kevin R

    2003-03-26

    Chiral mixed phosphorus/sulfur ligands 1-3 have been shown to be effective in enantioselective Rh-catalyzed dehydroamino acid hydrogenation and ketone hydrosilylation reactions (eqs 1, 2). After assaying the influence of the substituents at sulfur, the substituents on the ligand backbone, the relative stereochemistry within the ligand backbone, and the substituents at phosphorus, ligands 2c (R = 3,5-dimethylphenyl) and 3 were found to be optimal in the Rh-catalyzed hydrogenation of a variety of alpha-acylaminoacrylates in high enantioselectivity (89-97% ee). A similar optimization of the catalyst for the Rh-catalyzed hydrosilylation of ketones showed that ligand 3 afforded the highest enantioselectivities for a wide variety of aryl alkyl and dialkyl ketones (up to 99% ee). A model for asymmetric induction in the hydrogenation reaction is discussed in the context of existing models, based on the absolute stereochemistry of the products and the X-ray crystal structures of catalyst precursors and intermediates.

  6. Role of keto-enol tautomerization in a chiral phosphoric acid catalyzed asymmetric thiocarboxylysis of meso-epoxide: a DFT study.

    PubMed

    Ajitha, Manjaly J; Huang, Kuo-Wei

    2015-12-07

    The mechanism of a chiral phosphoric acid catalyzed thiocarboxylysis of meso-epoxide was investigated by density functional theory (DFT) calculations (M06-2X). The nucleophilic ring opening of epoxide by thiobenzoic acid was found to proceed via a concerted termolecular transition state with a simultaneous dual proton transfer to yield the β-hydroxy thioester product. Electrostatic interactions together with the steric environment inside the chiral catalyst play an important role in determining the enantioselectivity of the reaction.

  7. Cure reaction of epoxy resins catalyzed by graphite-based nanofiller

    NASA Astrophysics Data System (ADS)

    Corcione, C. Esposito; Acocella, Maria Rosaria; Giuri, Antonella; Maffezzoli, Alfonso; Guerra, Gaetano

    2015-12-01

    A significant effort was directed to the synthesis of graphene stacks/epoxy nanocomposites and to the analysis of the effect of a graphene precursor on cure reaction of a model epoxy matrix. A comparative thermal analysis of epoxy resins filled with an exfoliated graphite oxide eGO were conducted. The main aim was to understand the molecular origin of the influence of eGO on the Tg of epoxy resins. The higher Tg values previously observed for low curing temperatures, for epoxy resins with graphite-based nanofillers, were easily rationalized by a catalytic activity of graphitic layers on the reaction between the epoxy and amine groups of the resin, which leads to higher crosslinking density in milder conditions. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based filler was performed by isothermal DSC measurements. The DSC results showed that the addition of graphite based filler greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an auto-catalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller.

  8. A convenient synthesis of anthranilic acids by Pd-catalyzed direct intermolecular ortho-C-H amidation of benzoic acids.

    PubMed

    Ng, Ka-Ho; Ng, Fo-Ning; Yu, Wing-Yiu

    2012-12-11

    An efficient method for synthesis of anthranilic acids by Pd-catalyzed ortho-C-H amidation of benzoic acids is disclosed. The amidation is proposed to proceed by carboxylate-assisted ortho-C-H palladation to form an arylpalladium(II) complex, followed by nitrene insertion to the Pd-C bond.

  9. Stereospecific Nickel-Catalyzed Cross-Coupling Reactions of Benzylic Ethers with Isotopically-Labeled Grignard Reagents

    PubMed Central

    2015-01-01

    In this manuscript we highlight the potential of stereospecific nickel-catalyzed cross-coupling reactions for applications in the pharmaceutical industry. Using an inexpensive and sustainable nickel catalyst, we report a gram-scale Kumada cross-coupling reaction. Reactions are highly stereospecific and proceed with inversion at the benzylic position. We also expand the scope of our reaction to incorporate isotopically labeled substituents. PMID:27458328

  10. Dual Lewis Acid/Lewis Base Catalyzed Acylcyanation of Aldehydes: A Mechanistic Study.

    PubMed

    Laurell Nash, Anna; Hertzberg, Robin; Wen, Ye-Qian; Dahlgren, Björn; Brinck, Tore; Moberg, Christina

    2016-03-07

    A mechanistic investigation, which included a Hammett correlation analysis, evaluation of the effect of variation of catalyst composition, and low-temperature NMR spectroscopy studies, of the Lewis acid-Lewis base catalyzed addition of acetyl cyanide to prochiral aldehydes provides support for a reaction route that involves Lewis base activation of the acyl cyanide with formation of a potent acylating agent and cyanide ion. The cyanide ion adds to the carbonyl group of the Lewis acid activated aldehyde. O-Acylation by the acylated Lewis base to form the final cyanohydrin ester occurs prior to decomplexation from titanium. For less reactive aldehydes, the addition of cyanide is the rate-determining step, whereas, for more reactive, electron-deficient aldehydes, cyanide addition is rapid and reversible and is followed by rate-limiting acylation. The resting state of the catalyst lies outside the catalytic cycle and is believed to be a monomeric titanium complex with two alcoholate ligands, which only slowly converts into the product.

  11. Glycolic acid-catalyzed deamidation of asparagine residues in degrading PLGA matrices: a computational study.

    PubMed

    Manabe, Noriyoshi; Kirikoshi, Ryota; Takahashi, Ohgi

    2015-03-31

    Poly(lactic-co-glycolic acid) (PLGA) is a strong candidate for being a drug carrier in drug delivery systems because of its biocompatibility and biodegradability. However, in degrading PLGA matrices, the encapsulated peptide and protein drugs can undergo various degradation reactions, including deamidation at asparagine (Asn) residues to give a succinimide species, which may affect their potency and/or safety. Here, we show computationally that glycolic acid (GA) in its undissociated form, which can exist in high concentration in degrading PLGA matrices, can catalyze the succinimide formation from Asn residues by acting as a proton-transfer mediator. A two-step mechanism was studied by quantum-chemical calculations using Ace-Asn-Nme (Ace = acetyl, Nme = NHCH3) as a model compound. The first step is cyclization (intramolecular addition) to form a tetrahedral intermediate, and the second step is elimination of ammonia from the intermediate. Both steps involve an extensive bond reorganization mediated by a GA molecule, and the first step was predicted to be rate-determining. The present findings are expected to be useful in the design of more effective and safe PLGA devices.

  12. Regioselective Copper-Catalyzed Amination of Chlorobenzoic Acids: Synthesis and Solid-State Structures of N-Aryl Anthranilic Acid Derivatives

    PubMed Central

    Mei, Xuefeng; August, Adam T.; Wolf, Christian

    2008-01-01

    A chemo- and regioselective copper-catalyzed cross-coupling reaction for effective amination of 2-chlorobenzoic acids with aniline derivatives has been developed. The method eliminates the need for acid protection and produces a wide range of N-aryl anthranilic acid derivatives in up to 99%. The amination was found to proceed with both electron-rich and electron-deficient aryl chlorides and anilines and also utilizes sterically hindered anilines such as 2,6-dimethylaniline and 2-tert-butylaniline. The conformational isomerism of appropriately substituted N-aryl anthranilic acids has been investigated in the solid state. Crystallographic analysis of seven anthranilic acid derivatives showed formation of two distinct supramolecular architectures exhibiting trans-anti- and unprecedented trans-syn-dimeric structures. PMID:16388629

  13. Enantiodivergent Atroposelective Synthesis of Chiral Biaryls by Asymmetric Transfer Hydrogenation: Chiral Phosphoric Acid Catalyzed Dynamic Kinetic Resolution.

    PubMed

    Mori, Keiji; Itakura, Tsubasa; Akiyama, Takahiko

    2016-09-12

    Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosphoric acid, dynamic kinetic resolution (DKR) involving a reductive amination reaction proceeded smoothly to furnish both R and S isomers of chiral biaryls with excellent enantioselectivities by proper choice of hydroxyaniline derivative. This trend was observed in wide variety of substrates, and various chiral biphenyl and phenyl naphthyl adducts were synthesized with satisfactory enantioselectivities in enantiodivergent fashion. The enantiodivergent synthesis of synthetically challenging, chiral o-tetrasubstituted biaryls were also accomplished, and suggests high synthetic potential of the present method.

  14. Transition-metal-catalyzed Suzuki-Miyaura cross-coupling reactions: a remarkable advance from palladium to nickel catalysts.

    PubMed

    Han, Fu-She

    2013-06-21

    In the transition-metal-catalyzed cross-coupling reactions, the use of the first row transition metals as catalysts is much more appealing than the precious metals owing to the apparent advantages such as cheapness and earth abundance. Within the last two decades, particularly the last five years, explosive interests have been focused on the nickel-catalyzed Suzuki-Miyaura reactions. This has greatly advanced the chemistry of transition-metal-catalyzed cross-coupling reactions. Most notably, a broad range of aryl electrophiles such as phenols, aryl ethers, esters, carbonates, carbamates, sulfamates, phosphates, phosphoramides, phosphonium salts, and fluorides, as well as various alkyl electrophiles, which are conventionally challenging, by applying palladium catalysts can now be coupled efficiently with boron reagents in the presence of nickel catalysts. In this review, we would like to summarize the progress in this reaction.

  15. Non-Precious Metals Catalyze Formal [4 + 2] Cycloaddition Reactions of 1,2-Diazines and Siloxyalkynes under Ambient Conditions

    PubMed Central

    2015-01-01

    Copper(I) and nickel(0) complexes catalyze the formal [4 + 2] cycloaddition reactions of 1,2-diazines and siloxyalkynes, a reaction hitherto best catalyzed by silver salts. These catalysts based on earth abundant metals are not only competent, but the copper catalyst, in particular, promotes cycloadditions of pyrido[2,3-d]pyridazine and pyrido[3,4-d]pyridazine, enabling a new synthesis of quinoline and isoquinoline derivatives, as well as the formal [2 + 2] cycloaddition reaction of cyclohexenone with a siloxyalkyne. PMID:24911346

  16. Theoretical insights into the sites and mechanisms for base catalyzed esterification and aldol condensation reactions over Cu.

    PubMed

    Neurock, Matthew; Tao, Zhiyuan; Chemburkar, Ashwin; Hibbitts, David D; Iglesia, Enrique

    2017-03-23

    Condensation and esterification are important catalytic routes in the conversion of polyols and oxygenates derived from biomass to fuels and chemical intermediates. Previous experimental studies show that alkanal, alkanol and hydrogen mixtures equilibrate over Cu/SiO2 and form surface alkoxides and alkanals that subsequently promote condensation and esterification reactions. First-principle density functional theory (DFT) calculations were carried out herein to elucidate the elementary paths and the corresponding energetics for the interconversion of propanal + H2 to propanol and the subsequent C-C and C-O bond formation paths involved in aldol condensation and esterification of these mixtures over model Cu surfaces. Propanal and hydrogen readily equilibrate with propanol via C-H and O-H addition steps to form surface propoxide intermediates and equilibrated propanal/propanol mixtures. Surface propoxides readily form via low energy paths involving a hydrogen addition to the electrophilic carbon center of the carbonyl of propanal or via a proton transfer from an adsorbed propanol to a vicinal propanal. The resulting propoxide withdraws electron density from the surface and behaves as a base catalyzing the activation of propanal and subsequent esterification and condensation reactions. These basic propoxides can readily abstract the acidic Cα-H of propanal to produce the CH3CH((-))CH2O* enolate, thus initiating aldol condensation. The enolate can subsequently react with a second adsorbed propanal to form a C-C bond and a β-alkoxide alkanal intermediate. The β-alkoxide alkanal can subsequently undergo facile hydride transfer to form the 2-formyl-3-pentanone intermediate that decarbonylates to give the 3-pentanone product. Cu is unique in that it rapidly catalyzes the decarbonylation of the C2n intermediates to form C2n-1 3-pentanone as the major product with very small yields of C2n products. This is likely due to the absence of Brønsted acid sites, present on

  17. Stable carbon isotope fractionation during trichloroethene degradation in magnetite-catalyzed Fenton-like reaction

    NASA Astrophysics Data System (ADS)

    Liu, Yunde; Zhou, Aiguo; Gan, Yiqun; Liu, Cunfu; Yu, Tingting; Li, Xiaoqian

    2013-02-01

    Mineral-catalyzed Fenton-like oxidation of chlorinated ethylenes is an attractive technique for in situ soil and groundwater remediation. Stable carbon isotope enrichment factors associated with magnetite-catalyzed Fenton-like oxidation of trichloroethylene (TCE) have been determined, to study the possibility of applying stable carbon isotope analysis as a technique to assess the efficacy of remediation implemented by Fenton-like oxidation. The carbon enrichment factors (ɛ values) ranged from - 2.7‰ to - 3.6‰ with a mean value of - 3.3 ± 0.3‰, and only small differences were observed for different initial reactive conditions. The ɛ values were robust and reproducible, and were relatively insensitive to a number of environmental factors such as ratios of reactants and PCE co-contamination, which can reduce the uncertainty associated with application of isotope enrichment factors for quantification of in situ remediation by Fenton-like reaction. ɛ values for Fenton-like oxidation of TCE were intermediate in those previously reported for aerobic biological processes (ɛ = - 1.1 to - 20.7‰). Thus, field-derived ɛ values that are more negative than those for Fenton-like oxidation, may indicate the occurrence of aerobic biodegradation at contaminated sites undergoing in situ remediation with Fenton-like reaction. However, stable carbon isotope analysis is unable to determine whether there is the occurrence of biodegradation processes if field-derived ɛ values are less negative than those for Fenton-like oxidation.

  18. Nitrous Oxide-dependent Iron-catalyzed Coupling Reactions of Grignard Reagents.

    PubMed

    Döhlert, Peter; Weidauer, Maik; Enthaler, Stephan

    2015-01-01

    The formation of carbon-carbon bonds is one of the fundamental transformations in chemistry. In this regard the application of palladium-based catalysts has been extensively investigated during recent years, but nowadays research focuses on iron catalysis, due to sustainability, costs and toxicity issues; hence numerous examples for iron-catalyzed cross-coupling reactions have been established, based on the coupling of electrophiles (R(1)-X, X = halide) with nucleophiles (R(2)-MgX). Only a small number of protocols deals with the iron-catalyzed oxidative coupling of nucleophiles (R(1)-MgX + R(2)-MgX) with the aid of oxidants (1,2-dihaloethanes). However, some issues arise with these oxidants; hence more recently the potential of the industrial waste product nitrous oxide (N(2)O) was investigated, because the unproblematic side product N(2) is formed. Based on that, we demonstrate the catalytic potential of easily accessible iron complexes in the oxidative coupling of Grignard reagents. Importantly, nitrous oxide was essential to obtain yields up to >99% at mild conditions (e.g. 1 atm, ambient temperature) and low catalyst loadings (0.1 mol%) Excellent catalyst performance is realized with turnover numbers of up to 1000 and turnover frequencies of up to 12000 h(-1). Moreover, a good functional group tolerance is observed (e.g. amide, ester, nitrile, alkene, alkyne). Afterwards the reaction of different Grignard reagents revealed interesting results with respect to the selectivity of cross-coupling product formation.

  19. Bimetallic oxidative addition involving radical intermediates in nickel-catalyzed alkyl-alkyl Kumada coupling reactions.

    PubMed

    Breitenfeld, Jan; Ruiz, Jesus; Wodrich, Matthew D; Hu, Xile

    2013-08-14

    Many nickel-based catalysts have been reported for cross-coupling reactions of nonactivated alkyl halides. The mechanistic understanding of these reactions is still primitive. Here we report a mechanistic study of alkyl-alkyl Kumada coupling catalyzed by a preformed nickel(II) pincer complex ([(N2N)Ni-Cl]). The coupling proceeds through a radical process, involving two nickel centers for the oxidative addition of alkyl halide. The catalysis is second-order in Grignard reagent, first-order in catalyst, and zero-order in alkyl halide. A transient species, [(N2N)Ni-alkyl(2)](alkyl(2)-MgCl), is identified as the key intermediate responsible for the activation of alkyl halide, the formation of which is the turnover-determining step of the catalysis.

  20. A two-dimensional energy surface of the phosphoryl transfer reaction catalyzed by phosphoserine phosphatase

    NASA Astrophysics Data System (ADS)

    Re, Suyong; Jung, Jaewoon; Ten-no, Seiichiro; Sugita, Yuji

    2009-10-01

    The phosphoryl transfer reaction from phospho- L-serine (pSer), catalyzed by phosphoserine phosphatase, is investigated using the hybrid quantum mechanics/molecular mechanics calculations. The two-dimensional energy surface along the phosphoryl and proton transfer distances reveals early protonation of the leaving group oxygen of pSer, prior to the transition state (TS), which triggers subsequent phosphoryl transfer reaction. Calculated electronic properties of the phosphoryl group at the active site suggest significant metaphosphate-like character of TS, which is consistent with kinetic experiments on related phosphatases. The features are not obtained with a one-dimensional search along the phosphoryl transfer coordinate, due to inadequate description of proton movement.

  1. Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies

    NASA Technical Reports Server (NTRS)

    Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

    1988-01-01

    The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.

  2. Car--Parrinello Molecular Dynamics Study of Base-Catalyzed Hydrolysis Reactions

    NASA Astrophysics Data System (ADS)

    Alnemrat, Sufian; Vasiliev, Igor; Wang, Haobin

    2011-03-01

    We apply the first principles metadynamics simulation technique implemented in the Car-Parrinello molecular dynamics package to study the base-catalyzed hydrolysis of N-methylacetamide in aqueous solution. Our calculations are carried out in the framework of density functional theory combined with the hybrid BLYP exchange-correlation functional The free energy surfaces and hydrolysis reaction pathways for N-methylacetamide are examined in the presence of a hydroxide ion, and 4, 32, and 64 water molecules. We find that at least 32 water molecules must be explicitly included in metadynamics simulations to accurately describe the mechanism of the hydrolysis reaction of N-Methylacetamide. Our theoretical estimate for the dissociation energy of N-Methylacetamide is in good agreement with the results of previous experimental and theoretical studies. Supported by LANL-NMSU MOU.

  3. Gold-Catalyzed Reactions via Cyclopropyl Gold Carbene-like Intermediates.

    PubMed

    Dorel, Ruth; Echavarren, Antonio M

    2015-08-07

    Cycloisomerizations of 1,n-enynes catalyzed by gold(I) proceed via electrophilic species with a highly distorted cyclopropyl gold(I) carbene-like structure, which can react with different nucleophiles to form a wide variety of products by attack at the cyclopropane or the carbene carbons. Particularly important are reactions in which the gold(I) carbene reacts with alkenes to form cyclopropanes either intra- or intermolecularly. In the absence of nucleophiles, 1,n-enynes lead to a variety of cycloisomerized products including those resulting from skeletal rearrangements. Reactions proceeding through cyclopropyl gold(I) carbene-like intermediates are ideally suited for the bioinspired synthesis of terpenoid natural products by the selective activation of the alkyne in highly functionalized enynes or polyenynes.

  4. Progress of Chiral Schiff Bases with C1 Symmetry in Metal-Catalyzed Asymmetric Reactions.

    PubMed

    Hayashi, Masahiko

    2016-12-01

    In this Personal Account, various chiral Schiff base-metal-catalyzed enantioselective organic reactions are reported; the Schiff bases used were O,N,O- as well as N,N,P-tridentate ligands and N,N-bidentate ligands having C1 symmetry. In particular, the enantioselective addition of trimethylsilyl cyanide, dialkylzinc, and organozinc halides to aldehydes, enantioselective 1,4-addition of dialkylzinc to cyclic and acyclic enones, and asymmetric allylic oxidation are reported. Typically, ketimine-type Schiff base-metal complexes exhibited higher reactivity and enantioselectivity compared with the corresponding aldimine-type Schiff base-metal complexes. Notably, remarkable ligand acceleration was observed for all reactions. The obtained products can be used as key intermediates for optically active natural products and pharmaceuticals.

  5. The Onset Of Fluctuations In The Ferroin-Catalyzed Belousov-Zhabotinski Reaction

    NASA Astrophysics Data System (ADS)

    Hastings, Harold M.; Sobel, Sabrina G.; Fenton, Flavio H.; Chaterpaul, Stephen; Frank, Claudia; Pekor, Jordan; Russell, Elizabeth

    2003-08-01

    We report on an experimental study of the onset of target waves in the ferroin-catalyzed Belousov-Zhabotinski (BZ) reaction. In the cardiac electrical system, another excitable medium, spontaneous activity can initiate ventricular tachycardia by interacting with normal or other spontaneous electrical activity to generate spiral waves. In normal hearts, these spiral waves generally break down to cause ventricular fibrillation (VF), leading to sudden cardiac death. Our results for the BZ reaction: (1) centers of target waves are spatially correlated, with the correlation likely due to mixing effects and long range modes arising in the "clocking phase", (2) activitations begin after concentrations track an equilibrium through a Hopf bifurcation into an unstable "supercritical" state, (3) allowing very small fluctuations can generate targets.

  6. Dynamics of the onset of target waves in the ferroin-catalyzed Belousov-Zhabotinski reaction

    NASA Astrophysics Data System (ADS)

    Hastings, Harold M.; Sobel, Sabrina G.; Chaterpaul, Stephen; Frank, Claudia; Pekor, Jordan; Russell, Elizabeth; Fenton, Flavio

    2002-03-01

    We report on an experimental study of the onset of target waves in the excitable ferroin-catalyzed Belousov-Zhabotinski (BZ) reaction. In the cardiac electrical system, another excitable medium, the onset of spontaneous activity can initiate ventricular tachycardia by interacting with normal or other spontaneous electrical activity to generate spiral waves. In normal hearts, these spiral waves then generally break down to cause ventricular fibrillation (VF), and thus sudden cardiac death. Our results for the BZ reaction: (1) the onset of activity is a complex, multi-scale process, (2) centers of target waves are spatially correlated, (3) there are several spatial scales in the mm range, larger than the critical radius and the diffusion scale, and (4) simulations suggest how a chemical amplifier, suggested previously as a mechanism for microscopic fluctuations to generate chemical chaos [N Ganapathisubramanian and RM Noyes, J. Phys. Chem 76, 1770 (1982)], might play a similar role in the onset of activity.

  7. Gold-Catalyzed Reactions via Cyclopropyl Gold Carbene-like Intermediates

    PubMed Central

    2015-01-01

    Cycloisomerizations of 1,n-enynes catalyzed by gold(I) proceed via electrophilic species with a highly distorted cyclopropyl gold(I) carbene-like structure, which can react with different nucleophiles to form a wide variety of products by attack at the cyclopropane or the carbene carbons. Particularly important are reactions in which the gold(I) carbene reacts with alkenes to form cyclopropanes either intra- or intermolecularly. In the absence of nucleophiles, 1,n-enynes lead to a variety of cycloisomerized products including those resulting from skeletal rearrangements. Reactions proceeding through cyclopropyl gold(I) carbene-like intermediates are ideally suited for the bioinspired synthesis of terpenoid natural products by the selective activation of the alkyne in highly functionalized enynes or polyenynes. PMID:26061916

  8. Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions

    SciTech Connect

    Zhai, Y.; Pierre, D; Si, R; Deng, W; Ferrin, P; Nilekar, A; Peng, G; Herron, J; Bell, D; et. al.

    2010-01-01

    We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H{sub 2}O + CO {yields} H{sub 2} + CO{sub 2}) used for producing H{sub 2}. The alkali ion-associated surface OH groups are activated by CO at low temperatures ({approx}100 C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O{sub x}(OH){sub y} species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

  9. PtI2-catalyzed tandem 3,3-rearrangement/Nazarov reaction of arylpropargylic esters: synthesis of indanone derivatives.

    PubMed

    Zheng, Huaiji; Xie, Xingang; Yang, Juan; Zhao, Changgui; Jing, Peng; Fang, Bowen; She, Xuegong

    2011-10-26

    An efficient PtI(2)-catalyzed tandem reaction of arylpropargylic esters, involving 3,3-rearrangement and Nazarov reaction, has been developed to produce 3-substituted and 3,3-disubstituted indanone derivatives. This approach provided a pathway to the synthesis of indanone skeletons in natural products.

  10. Influence of Ionic Liquids on an Iron(III) Catalyzed Three-Component Coupling/Hydroarylation/Dehydrogenation Tandem Reaction.

    PubMed

    Muntzeck, Maren; Wilhelm, René

    2016-06-01

    A three-component oxidative dehydrogenation tandem reaction via the coupling and hydroarylation of benzaldehyde, aniline and phenylacetylene to a quinoline derivate was catalyzed by an iron-containing ionic liquid. The reaction was air mediated and could be performed under neat conditions. The iron(III) of the ionic liquid was the oxidizing species.

  11. Influence of Ionic Liquids on an Iron(III) Catalyzed Three-Component Coupling/Hydroarylation/Dehydrogenation Tandem Reaction

    PubMed Central

    Muntzeck, Maren; Wilhelm, René

    2016-01-01

    A three-component oxidative dehydrogenation tandem reaction via the coupling and hydroarylation of benzaldehyde, aniline and phenylacetylene to a quinoline derivate was catalyzed by an iron-containing ionic liquid. The reaction was air mediated and could be performed under neat conditions. The iron(III) of the ionic liquid was the oxidizing species. PMID:27258264

  12. In(III)-catalyzed tandem reaction of chromone-derived Morita-Baylis-Hillman alcohols with amines.

    PubMed

    Wu, Chen; Liu, Yuliang; Zeng, Hao; Liu, Li; Wang, Dong; Chen, Yongjun

    2011-01-07

    The reaction of chromone-derived cyclic Morita-Baylis-Hillman alcohols with amines catalyzed by In(OTf)(3) in a one pot process was developed for the convenient and efficient synthesis of 2-substituted-3-aminomethylenechromans. The tandem allylic amination/chromen ring-opening/Michael cyclization reactions were involved in this protocol.

  13. The First Example of Nickel-Catalyzed Silyl-Heck Reactions: Direct Activation of Silyl Triflates Without Iodide Additives

    PubMed Central

    McAtee, Jesse R.; Martin, Sara E. S.; Cinderella, Andrew P.; Reid, William B.; Johnson, Keywan A.

    2014-01-01

    For the first time, nickel-catalyzed silyl-Heck reactions are reported. Using simple phosphine-supported nickel catalysts, direct activation of silyl triflates has been achieved. These results contrast earlier palladium-catalyzed systems, which require iodide additives to activate silyl-triflates. These nickel-based catalysts exhibit good functional group tolerance in the preparation of vinyl silanes, and unlike earlier systems, allows for the incorporation of trialkylsilanes larger than Me3Si. PMID:24914247

  14. Palladium-Catalyzed Cross-Coupling Reactions of Organosilanols and their Salts

    PubMed Central

    Denmark, Scott E.; Regens, Christopher S.

    2009-01-01

    Conspectus In the panoply of modern synthetic methods for forming carbon-carbon and carbon-heteroatom bonds, the transition metal-catalyzed cross coupling of organometallic nucleophiles with organic electrophiles enjoys a preeminent status. The preparative utility of these reactions is, in large measure, a consequence of the wide variety of organometallic donors that have been conscripted into service. The most common of these reagents are organic derivatives of tin, boron, and zinc, which each possess unique advantages and shortcomings. Because of their low cost, low toxicity, and high chemical stability, organosilanes have emerged as viable alternatives to the conventional reagents in recent years. However, unlike the tin- and zinc-based reactions that require no activation or the boron-based reactions that require only heating with mild bases, silicon-based cross-coupling reactions often require heating in the presence of a fluoride source; this has significantly hampered the widespread acceptance of organosilanes. To address the “fluoride problem”, we have introduced a new paradigm for palladium-catalyzed, silicon-based cross-coupling reactions that employs organosilanols, a previously underutilized class of silicon reagents. The use of organosilanols either in the presence of Brønsted bases or as their silanolate salts represents a simple and mild alternative to the classic fluoride-based activation method. Organosilanols are easily available by many well-established methods for introducing carbon-silicon bonds onto alkenes, alkynes and arenes, and heteroarenes. Moreover, we have developed four different protocols for the generation of alkali metal salts of, vinyl-, alkenyl-, alkynyl-, aryl-, and heteroarylsilanolates: (1) reversible deprotonation with weak Brønsted bases, (2) irreversible deprotonation with strong Brønsted bases, (3) isolation of the salts from irreversible deprotonation, and (4) silanolate exchange with disiloxanes. We have

  15. Differential quantum tunneling contributions in nitroalkane oxidase catalyzed and the uncatalyzed proton transfer reaction

    PubMed Central

    Major, Dan T.; Heroux, Annie; Orville, Allen M.; Valley, Michael P.; Fitzpatrick, Paul F.; Gao, Jiali

    2009-01-01

    The proton transfer reaction between the substrate nitroethane and Asp-402 catalyzed by nitroalkane oxidase and the uncatalyzed process in water have been investigated using a path-integral free-energy perturbation method. Although the dominating effect in rate acceleration by the enzyme is the lowering of the quasiclassical free energy barrier, nuclear quantum effects also contribute to catalysis in nitroalkane oxidase. In particular, the overall nuclear quantum effects have greater contributions to lowering the classical barrier in the enzyme, and there is a larger difference in quantum effects between proton and deuteron transfer for the enzymatic reaction than that in water. Both experiment and computation show that primary KIEs are enhanced in the enzyme, and the computed Swain-Schaad exponent for the enzymatic reaction is exacerbated relative to that in the absence of the enzyme. In addition, the computed tunneling transmission coefficient is approximately three times greater for the enzyme reaction than the uncatalyzed reaction, and the origin of the difference may be attributed to a narrowing effect in the effective potentials for tunneling in the enzyme than that in aqueous solution. PMID:19926855

  16. Organocatalytic Enantioselective Aza-Friedel-Crafts Reaction of Cyclic Ketimines with Pyrroles using Imidazolinephosphoric Acid Catalysts.

    PubMed

    Nakamura, Shuichi; Matsuda, Nazumi; Ohara, Mutsuyo

    2016-07-04

    Organocatalytic enantioselective aza-Friedel-Crafts reactions of cyclic ketimines with pyrroles or indoles were catalyzed by imidazoline/phosphoric acid catalysts. The reaction was applied to various 3H-indol-3-ones to afford products in excellent yields and enantioselectivities. The chiral catalysts can be recovered by a single separation step using column chromatography and are reusable without further purification. Based on the experimental investigations, a possible transition state has been proposed to explain the origin of the asymmetric induction.

  17. Acid-catalyzed autohydrolysis of wheat straw to improve sugar recovery.

    PubMed

    Ertas, Murat; Han, Qiang; Jameel, Hasan

    2014-10-01

    A comparison study of autohydrolysis and acid-catalyzed autohydrolysis of wheat straw was performed to understand the impact of acid addition on overall sugar recovery. Autohydrolysis combined with refining is capable of achieving sugar recoveries in the mid 70s. If the addition of a small amount of acid is capable of increasing the sugar recovery even higher it may be economically attractive. Acetic, sulfuric, hydrochloric and sulfurous acids were selected for acid-catalyzed autohydrolysis pretreatments. Autohydrolysis with no acid at 190 °C showed the highest total sugar in the prehydrolyzate. Enzymatic hydrolysis was performed for all the post-treated solids with and without refining at enzyme loadings of 4 and 10 FPU/g for 96 h. Acid-catalyzed autohydrolysis at 190 °C with sulfurous acid showed the highest total sugar recovery of 81.2% at 4 FPU/g enzyme charge compared with 64.3% at 190 °C autohydrolysis without acid.

  18. Stratospheric Reactions of Peroxynitric Acid.

    DTIC Science & Technology

    1981-04-23

    was always at least 10 times greater than the HOONO2 concentration at the time of the 03 addition. Because of the small absorption coefficient [ Herzberg ...and J. N. Pitts, Jr., Pressure and temperature dependence of the unimolecular decomposition of HO2N02, J. Chem. Phys., 68, 4505, 1978. Herzberg ... Gerhard , Infrared and Raman Spectra, Vol. II, van Nostrand Reinhold Company, 1945, p. 286. Howard, C. J., Kinetics of the reaction of HO2 with NO2, J. Chem

  19. Heme oxygenase reveals its strategy for catalyzing three successive oxygenation reactions.

    PubMed

    Matsui, Toshitaka; Unno, Masaki; Ikeda-Saito, Masao

    2010-02-16

    Heme oxygenase (HO) is an enzyme that catalyzes the regiospecific conversion of heme to biliverdin IXalpha, CO, and free iron. In mammals, HO has a variety of physiological functions, including heme catabolism, iron homeostasis, antioxidant defense, cellular signaling, and O(2) sensing. The enzyme is also found in plants (producing light-harvesting pigments) and in some pathogenic bacteria, where it acquires iron from the host heme. The HO-catalyzed heme conversion proceeds through three successive oxygenations, a process that has attracted considerable attention because of its reaction mechanism and physiological importance. The HO reaction is unique in that all three O(2) activations are affected by the substrate itself. The first step is the regiospecific self-hydroxylation of the porphyrin alpha-meso carbon atom. The resulting alpha-meso-hydroxyheme reacts in the second step with another O(2) to yield verdoheme and CO. The third O(2) activation, by verdoheme, cleaves its porphyrin macrocycle to release biliverdin and free ferrous iron. In this Account, we provide an overview of our current understanding of the structural and biochemical properties of the complex self-oxidation reactions in HO catalysis. The first meso-hydroxylation is of particular interest because of its distinct contrast with O(2) activation by cytochrome P450. Although most heme enzymes oxidize exogenous substrates by high-valent oxo intermediates, HO was proposed to utilize the Fe-OOH intermediate for the self-hydroxylation. We have succeeded in preparing and characterizing the Fe-OOH species of HO at low temperature, and an analysis of its reaction, together with mutational and crystallographic studies, reveals that protonation of Fe-OOH by a distal water molecule is critical in promoting the unique self-hydroxylation. The second oxygenation is a rapid, spontaneous auto-oxidation of the reactive alpha-meso-hydroxyheme; its mechanism remains elusive, but the HO enzyme has been shown not to

  20. Carboxylic acids as traceless directing groups for the rhodium(III)-catalyzed decarboxylative C-H arylation of thiophenes.

    PubMed

    Zhang, Yuanfei; Zhao, Huaiqing; Zhang, Min; Su, Weiping

    2015-03-16

    A rhodium(III)-catalyzed carboxylic acid directed decarboxylative C-H/C-H cross-coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one-step gram-scale synthesis of a biologically active 3,5-substituted 2-arylthiophene by way of the current method.

  1. Lewis Acid Catalyzed Friedel-Crafts Alkylation of Alkenes with Trifluoropyruvates.

    PubMed

    Xiang, Bin; Xu, Teng-Fei; Wu, Liang; Liu, Ren-Rong; Gao, Jian-Rong; Jia, Yi-Xia

    2016-05-06

    A Friedel-Crafts alkylation reaction of styrenes with trifluoropyruvates has been developed, which delivered allylic alcohols in excellent yields (up to 98%) using the Ni(ClO4)2·6H2O/bipyridine complex as a catalyst. The asymmetric reaction was catalyzed by the chiral Cu(OTf)2/bisoxazoline complex to afford the corresponding chiral allylic alcohols bearing trifluoromethylated quaternary stereogenic centers in moderate enantioselectivities (up to 75% ee).

  2. Effect of osmolytes on protein dynamics in the lactate dehydrogenase-catalyzed reaction.

    PubMed

    Zhadin, Nickolay; Callender, Robert

    2011-03-15

    Laser-induced temperature jump relaxation spectroscopy was used to probe the effect of osmolytes on the microscopic rate constants of the lactate dehydrogenase-catalyzed reaction. NADH fluorescence and absorption relaxation kinetics were measured for the lactate dehydrogenase (LDH) reaction system in the presence of varying amounts of trimethylamine N-oxide (TMAO), a protein-stabilizing osmolyte, or urea, a protein-destabilizing osmolyte. Trimethylamine N-oxide (TMAO) at a concentration of 1 M strongly increases the rate of hydride transfer, nearly nullifies its activation energy, and also slightly increases the enthalpy of hydride transfer. In 1 M urea, the hydride transfer enthalpy is almost nullified, but the activation energy of the step is not affected significantly. TMAO increases the preference of the closed conformation of the active site loop in the LDH·NAD(+)·lactate complex; urea decreases it. The loop opening rate in the LDH·NADH·pyruvate complex changes its temperature dependence to inverse Arrhenius with TMAO. In this complex, urea accelerates the loop motion, without changing the loop opening enthalpy. A strong, non-Arrhenius decrease in the pyruvate binding rate in the presence of TMAO offers a decrease in the fraction of the open loop, pyruvate binding competent form at higher temperatures. The pyruvate off rate is not affected by urea but decreases with TMAO. Thus, the osmolytes strongly affect the rates and thermodynamics of specific events along the LDH-catalyzed reaction: binding of substrates, loop closure, and the chemical event. Qualitatively, these results can be understood as an osmolyte-induced change in the energy landscape of the protein complexes, shifting the conformational nature of functional substates within the protein ensemble.

  3. Biocatalytic carbon capture via reversible reaction cycle catalyzed by isocitrate dehydrogenase.

    PubMed

    Xia, Shunxiang; Frigo-Vaz, Benjamin; Zhao, Xueyan; Kim, Jungbae; Wang, Ping

    2014-09-12

    The practice of carbon capture and storage (CCS) requires efficient capture and separation of carbon dioxide from its gaseous mixtures such as flue gas, followed by releasing it as a pure gas which can be subsequently compressed and injected into underground storage sites. This has been mostly achieved via reversible thermochemical reactions which are generally energy-intensive. The current work examines a biocatalytic approach for carbon capture using an NADP(H)-dependent isocitrate dehydrogenase (ICDH) which catalyzes reversibly carboxylation and decarboxylation reactions. Different from chemical carbon capture processes that rely on thermal energy to realize purification of carbon dioxide, the biocatalytic strategy utilizes pH to leverage the reaction equilibrium, thereby realizing energy-efficient carbon capture under ambient conditions. Results showed that over 25 mol of carbon dioxide could be captured and purified from its gas mixture for each gram of ICDH applied for each carboxylation/decarboxylation reaction cycle by varying pH between 6 and 9. This work demonstrates the promising potentials of pH-sensitive biocatalysis as a green-chemistry route for carbon capture.

  4. Reaction rate modeling in cryoconcentrated solutions: alkaline phosphatase catalyzed DNPP hydrolysis.

    PubMed

    Champion, D; Blond, G; Le Meste, M; Simatos, D

    2000-10-01

    The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 degrees C, and the enzymatic characteristics K(M) and V(max) were calculated. The experimental data were compared to the kinetics predicted by assuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reaction demonstrated that both the diffusion of the substrate and the flexibility of the enzyme segments were controlled by the high viscosity of the media. When the temperature was too low for the viscosity to be measured simply, the Williams-Landel-Ferry equation was used to predict the viscosity, taking, as reference temperature, the glass transition temperature (T(g)) corresponding to the concentration of the freeze-concentrated phase at the test temperature. Predicted values of the reaction rate were very close to the experimental ones in the studied temperature range.

  5. Biocatalytic Synthesis of Allylic and Allenyl Sulfides through a Myoglobin-Catalyzed Doyle-Kirmse Reaction.

    PubMed

    Tyagi, Vikas; Sreenilayam, Gopeekrishnan; Bajaj, Priyanka; Tinoco, Antonio; Fasan, Rudi

    2016-10-17

    The first example of a biocatalytic [2,3]-sigmatropic rearrangement reaction involving allylic sulfides and diazo reagents (Doyle-Kirmse reaction) is reported. Engineered variants of sperm whale myoglobin catalyze this synthetically valuable C-C bond-forming transformation with high efficiency and product conversions across a variety of sulfide substrates (e.g., aryl-, benzyl-, and alkyl-substituted allylic sulfides) and α-diazo esters. Moreover, the scope of this myoglobin-mediated transformation could be extended to the conversion of propargylic sulfides to give substituted allenes. Active-site mutations proved effective in enhancing the catalytic efficiency of the hemoprotein in these reactions as well as modulating the enantioselectivity, resulting in the identification of the myoglobin variant Mb(L29S,H64V,V68F), which is capable of mediating asymmetric Doyle-Kirmse reactions with an enantiomeric excess up to 71 %. This work extends the toolbox of currently available biocatalytic strategies for the asymmetric formation of carbon-carbon bonds.

  6. The hydrothermal reaction kinetics of aspartic acid

    NASA Astrophysics Data System (ADS)

    Cox, Jenny S.; Seward, Terry M.

    2007-02-01

    Experimental data on the hydrothermal reaction kinetics of aspartic acid were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. The results of this study indicate that the reaction kinetics of dilute aspartic acid solutions are significantly different depending on the presence or absence of catalytic surfaces such as standard metal alloys. The spectroscopic data presented here represent the first direct observations, in situ and in real time, of an amino acid reacting in a hydrothermal solution. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a chemometric approach based on factor analysis/principle component analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Identification of the products was confirmed where possible by high pressure anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The reaction kinetics of aspartic acid under hydrothermal conditions was observed to be highly complex, in contrast to previous studies which indicated almost exclusively deamination. At lower temperatures (120-170 °C), several different reaction pathways were observed, including decarboxylation and polymerization, and the catalytic effects of reactor surfaces on the aspartic acid system were clearly demonstrated. At higher temperatures (above 170 °C), aspartic acid exhibited highly complex behaviour, with evidence indicating that it can simultaneously dimerize and cyclize, deaminate (by up to two pathways), and decarboxylate (by up to two pathways). These higher temperature kinetics were not fully resolvable in a quantitative manner due to the complexity of the system and the constraints of UV spectroscopy. The results of this study provide strong evidence that the reaction

  7. Conversion of waste cellulose to ethanol. Phase 2: Reaction kinetics with phosphoric acid

    NASA Astrophysics Data System (ADS)

    Moeller, M. B.; Isbell, R. E.

    1982-05-01

    Waste cellulosic material can be hydrolyzed in dilute acid solution to produce fermentable sugars which can then be converted into ethanol. A laboratory investigation was made of the feasibility of using phosphoric acid as the hydrolysis catalyst. The hydrolysis reaction with phosphoric acid solutions was compared with the reaction employing the more conventional dilute sulfuric acid catalyst. The purpose of this research was to examine the hydrolysis step in a proposed process for the conversion of cellulose (from wood, newspapers, municipal solid waste, or other sources) into ethanol - by which a potentially valuable co-product, DICAL (dicalcium phosphate), might be made and sold with or without the lignin content as a fertilizer. The pertinent reaction kinetics for the acid catalyzed production of glucose from cellulose consists of consecutive, pseudo-first order reactions.

  8. Chiral phosphoric acid-catalyzed asymmetric transfer hydrogenation of 3-trifluoromethylthioquinolines.

    PubMed

    Zhou, Ji; Zhang, Qian-Fan; Zhao, Wei-Hao; Jiang, Guo-Fang

    2016-08-07

    A chiral phosphoric acid-catalyzed asymmetric transfer hydrogenation of 3-trifluoromethylthioquinolines has been successfully developed, providing direct and facile access to chiral 2,3-disubstituted 1,2,3,4-tetrahydroquinoline derivatives containing a stereogenic trifluoromethylthio group with up to 99% enantioselectivity.

  9. Enantioselective synthesis of planar chiral ferrocenes via palladium-catalyzed direct coupling with arylboronic acids.

    PubMed

    Gao, De-Wei; Shi, Yan-Chao; Gu, Qing; Zhao, Zheng-Le; You, Shu-Li

    2013-01-09

    Enantioselective Pd(II)-catalyzed direct coupling of aminomethylferrocene derivatives with boronic acids was realized. With commercially available Boc-L-Val-OH as a ligand, planar-chiral ferrocenes could be synthesized in yields of 14-81% with up to 99% ee under mild conditions.

  10. Evidence for coupled motion and hydrogen tunneling of the reaction catalyzed by glutamate mutase.

    PubMed

    Cheng, Mou-Chi; Marsh, E Neil G

    2007-01-23

    Glutamate mutase is one of a group of adenosylcobalamin-dependent enzymes that catalyze unusual isomerizations that proceed through organic radical intermediates generated by homolytic fission of the coenzyme's unique cobalt-carbon bond. These enzymes are part of a larger family of enzymes that catalyze radical chemistry in which a key step is the abstraction of a hydrogen atom from an otherwise inert substrate. To gain insight into the mechanism of hydrogen transfer, we previously used pre-steady-state, rapid-quench techniques to measure the alpha-secondary tritium kinetic and equilibrium isotope effects associated with the formation of 5'-deoxyadenosine when glutamate mutase was reacted with [5'-(3)H]adenosylcobalamin and L-glutamate. We showed that both the kinetic and equilibrium isotope effects are large and inverse, 0.76 and 0.72, respectively. We have now repeated these measurements using glutamate deuterated in the position of hydrogen abstraction. The effect of introducing a primary deuterium kinetic isotope effect on the hydrogen transfer step is to reduce the magnitude of the secondary kinetic isotope effect to a value close to unity, 1.05 +/- 0.08, whereas the equilibrium isotope effect is unchanged. The significant reduction in the secondary kinetic isotope effect is consistent with motions of the 5'-hydrogen atoms being coupled in the transition state to the motion of the hydrogen undergoing transfer, in a reaction that involves a large degree of quantum tunneling.

  11. Ternary copper complexes and manganese (III) tetrakis(4-benzoic acid) porphyrin catalyze peroxynitrite-dependent nitration of aromatics.

    PubMed

    Ferrer-Sueta, G; Ruiz-Ramírez, L; Radi, R

    1997-12-01

    Peroxynitrite is a powerful oxidant formed in biological systems from the reaction of nitrogen monoxide and superoxide and is capable of nitrating phenols at neutral pH and ambient temperature. This peroxynitrite-mediated nitration is catalyzed by a number of Lewis acids, including CO2 and transition-metal ion complexes. Here we studied the effect of ternary copper-(II) complexes constituted by a 1,10-phenanthroline and an amino acid as ligands. All the complexes studied accelerate both the decomposition of peroxynitrite and its nitration of 4-hydroxyphenylacetic acid at pH > 7. The rate of these reactions depends on the copper complex concentration in a hyperbolic plus linear manner. The yield of nitrated products increases up to 2.6-fold with respect to proton-catalyzed nitration and has a dependency on the concentration of copper complexes which follows the same function as observed for the rate constants. The manganese porphyrin complex, Mn(III)tetrakis(4-benzoic acid)porphyrin [Mn(tbap)], also promoted peroxynitrite-mediated nitration with an even higher yield (4-fold increase) than the ternary copper complexes. At pH = 7.5 +/- 0.2 the catalytic behavior of the copper complexes can be linearly correlated with the pKa of the phenanthroline present as a ligand, implying that a peroxynitrite anion is coordinated to the copper ion prior to the nitration reaction. These observations may prove valuable to understand the biological effects of these transition-metal complexes (i.e., copper and manganese) that can mimic superoxide dismutase activity and, in the case of the ternary copper complexes, show antineoplastic activity.

  12. Activation Energies for an Enzyme-Catalyzed and Acid-Catalyzed Hydrolysis: An Introductory Interdisciplinary Experiment for Chemists and Biochemists.

    ERIC Educational Resources Information Center

    Adams, K. R.; Meyers, M. B.

    1985-01-01

    Background information, procedures used, and typical results obtained are provided for an experiment in which students determine and compare the Arrhenius activation energies (Ea) for the hydrolysis of salicin. This reaction is subject to catalysis both by acid and by the enzyme emulsin (beta-d-glucoside glycohydrolase). (JN)

  13. Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

    PubMed Central

    Fructos, Manuel R; Urbano, Juan

    2015-01-01

    Summary Kinetic experiments based on the measurement of nitrogen evolution in the reaction of ethyl diazoacetate (N2CHCO2Et, EDA) and styrene or methanol catalyzed by the [IPrAu]+ core (IPr = 1,3-bis(diisopropylphenyl)imidazole-2-ylidene) have provided evidence that the transfer of the carbene group CHCO2Et to the substrate (styrene or methanol) takes place in the coordination sphere of Au(I) by means of an inner-sphere mechanism, in contrast to the generally accepted proposal of outer-sphere mechanisms for Au(I)-catalyzed reactions. PMID:26664649

  14. Stereoselective Alkane Oxidation with meta-Chloroperoxybenzoic Acid (MCPBA) Catalyzed by Organometallic Cobalt Complexes.

    PubMed

    Shul'pin, Georgiy B; Loginov, Dmitriy A; Shul'pina, Lidia S; Ikonnikov, Nikolay S; Idrisov, Vladislav O; Vinogradov, Mikhail M; Osipov, Sergey N; Nelyubina, Yulia V; Tyubaeva, Polina M

    2016-11-22

    Cobalt pi-complexes, previously described in the literature and specially synthesized and characterized in this work, were used as catalysts in homogeneous oxidation of organic compounds with peroxides. These complexes contain pi-butadienyl and pi-cyclopentadienyl ligands: [(tetramethylcyclobutadiene)(benzene)cobalt] hexafluorophosphate, [(C₄Me₄)Co(C₆H₆)]PF₆ (1); diiodo(carbonyl)(pentamethylcyclopentadienyl)cobalt, Cp*Co(CO)I₂ (2); diiodo(carbonyl)(cyclopentadienyl)cobalt, CpCo(CO)I₂ (3); (tetramethylcyclobutadiene)(dicarbonyl)(iodo)cobalt, (C₄Me₄)Co(CO)₂I (4); [(tetramethylcyclobutadiene)(acetonitrile)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [(C₄Me₄)Co(bipy)(MeCN)]PF₆ (5); bis[dicarbonyl(B-cyclohexylborole)]cobalt, [(C₄H₄BCy)Co(CO)₂]₂ (6); [(pentamethylcyclopentadienyl)(iodo)(1,10-phenanthroline)cobalt] hexafluorophosphate, [Cp*Co(phen)I]PF₆ (7); diiodo(cyclopentadienyl)cobalt, [CpCoI₂]₂ (8); [(cyclopentadienyl)(iodo)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [CpCo(bipy)I]PF₆ (9); and [(pentamethylcyclopentadienyl)(iodo)(2,2'-bipyridyl)cobalt] hexafluorophosphate, [Cp*Co(bipy)I]PF₆ (10). Complexes 1 and 2 catalyze very efficient and stereoselective oxygenation of tertiary C-H bonds in isomeric dimethylcyclohexanes with MCBA: cyclohexanols are produced in 39 and 53% yields and with the trans/cis ratio (of isomers with mutual trans- or cis-configuration of two methyl groups) 0.05 and 0.06, respectively. Addition of nitric acid as co-catalyst dramatically enhances both the yield of oxygenates and stereoselectivity parameter. In contrast to compounds 1 and 2, complexes 9 and 10 turned out to be very poor catalysts (the yields of oxygenates in the reaction with cis-1,2-dimethylcyclohexane were only 5%-7% and trans/cis ratio 0.8 indicated that the oxidation is not stereoselective). The chromatograms of the reaction mixture obtained before and after reduction with PPh₃ are very similar, which testifies that alkyl

  15. Isolation of bis(copper) key intermediates in Cu-catalyzed azide-alkyne "click reaction".

    PubMed

    Jin, Liqun; Tolentino, Daniel R; Melaimi, Mohand; Bertrand, Guy

    2015-06-01

    The copper-catalyzed 1,3-dipolar cycloaddition of an azide to a terminal alkyne (CuAAC) is one of the most popular chemical transformations, with applications ranging from material to life sciences. However, despite many mechanistic studies, direct observation of key components of the catalytic cycle is still missing. Initially, mononuclear species were thought to be the active catalysts, but later on, dinuclear complexes came to the front. We report the isolation of both a previously postulated π,σ-bis(copper) acetylide and a hitherto never-mentioned bis(metallated) triazole complex. We also demonstrate that although mono- and bis-copper complexes promote the CuAAC reaction, the dinuclear species are involved in the kinetically favored pathway.

  16. Transition Metal Catalyzed Reactions of Carbohydrates: a Nonoxidative Approach to Oxygenated Organics

    SciTech Connect

    Andrews, Mark

    1997-01-08

    There is a critical need for new environmentally friendly processes in the United States chemical industry as legislative and economic pressures push the industry to zero-waste and cradle-to-grave responsibility for the products they produce. Carbohydrates represent a plentiful, renewable resource, which for some processes might economically replace fossil feedstocks. While the conversion of biomass to fuels, is still not generally economical, the selective synthesis of a commodity or fine chemical, however, could compete effectively if appropriate catalytic conversion systems can be found. Oxygenated organics, found in a variety of products such as nylon and polyester, are particularly attractive targets. We believe that with concerted research efforts, homogeneous transition metal catalyzed reactions could play a significant role in bringing about this future green chemistry technology.

  17. Multiple mechanisms in Pd(II)-catalyzed S(N)2' reactions of allylic alcohols.

    PubMed

    Ghebreghiorgis, Thomas; Kirk, Brian H; Aponick, Aaron; Ess, Daniel H

    2013-08-02

    Density functional calculations and experiments were used to examine mechanisms of Pd(II) catalyzed intramolecular cyclization and dehydration in acyclic and bicyclic monoallylic diols, a formal S(N)2' reaction. In contrast to the previously proposed syn-oxypalladation mechanism for acyclic monoallylic diols, calculations and experiments strongly suggest that hydrogen bonding templates a hydroxyl group and Pd addition across the alkene and provides a low energy pathway via anti-addition (anti-oxypalladation) followed by intramolecular proton transfer and anti-elimination of water. This anti-addition, anti-elimination pathway also provides a simple rationale for the observed stereospecificity. For bicyclic monoallylic diol compounds, Pd(II) is capable of promoting either anti- or syn-addition. In addition, palladium chloride ligands can mediate proton transfer to promote dehydration when direct intramolecular proton transfer between diol groups is impossible.

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

    PubMed

    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.

  19. Holliday junctions generate super-bright antibodies and antibody fragments in sortase-catalyzed reactions

    PubMed Central

    Li, Zeyang; Theile, Christopher S.; Chen, Guan-Yu; Bilate, Angelina M.; Duarte, Joao N.; Avalos, Ana M.; Fang, Tao; Barberena, Roberto; Sato, Shuji; Ploegh, Hidde L.

    2015-01-01

    Site-specific modification of proteins with fluorophores can render a protein fluorescent without compromising its function. To avoid self-quenching of multiple fluorophores installed in close proximity, we used Holliday junctions to label proteins site-specifically. Holliday junctions enable modification with multiple fluorophores at reasonably precise spacing. We designed a Holliday junction with three of its four arms modified with a fluorophore of choice and the remaining arm equipped with a dibenzocyclooctyne substituent to render it reactive with an azide-modified, fluorescent single domain antibody fragment or an intact immunoglobulin, produced in a sortase-catalyzed reaction. We conclude that fluorescent Holliday junctions improve fluorescence yields for both single domain and full-sized antibodies, without deleterious effects on antigen binding. PMID:26252716

  20. Photoinduced Vesicle Formation via the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction.

    PubMed

    Konetski, Danielle; Gong, Tao; Bowman, Christopher N

    2016-08-16

    Synthetic vesicles have a wide range of applications from drug and cosmetic delivery to artificial cell and membrane studies, making simple and controlled formation of vesicles a large focus of the field today. Here, we report the use of the photoinitiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using visible light to introduce spatiotemporal control into the formation of vesicles. Upon the establishment of the spatiotemporal control over vesicle formation, it became possible to adjust initiation conditions to modulate vesicle sizes resulting in the formation of controllably small or large vesicles based on light intensity or giant vesicles when the formation was initiated in flow-free conditions. Additionally, this photoinitiated method enables vesicle formation at a density 400-fold higher than initiation using sodium ascorbate as the catalyst. Together, these advances enable the formation of high-density, controlled size vesicles using low-energy wavelengths while producing enhanced control over the formation characteristics of the vesicle.

  1. Recent developments in the metal-catalyzed reactions of metallocarbenoids from propargylic esters.

    PubMed

    Marco-Contelles, José; Soriano, Elena

    2007-01-01

    The transition-metal-catalyzed intramolecular cycloisomerization of propargylic carboxylates provides functionalized bicyclo[n.1.0]enol esters in a very diastereoselective manner and, depending on the structure, with partial or complete transfer of chirality from enantiomerically pure precursors. The subsequent methanolysis gives bicyclo[n.1.0] ketones, hence resulting in a very efficient two-step protocol for the syntheses of alpha,beta-unsaturated cyclopropyl ketones, key intermediates for the preparation of natural products. The results from mechanistic computational studies suggest that they probably proceed through cyclopropyl metallocarbenoids, formed by endo-cyclopropanation, that undergo a 1,2-acyl migration. Finally, the potential of the intermolecular reaction and the related pentannulation of propargylic esters bearing pendant aromatic rings are also discussed.

  2. Isotope Effects as Probes for Enzyme Catalyzed Hydrogen-Transfer Reactions

    PubMed Central

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2015-01-01

    Kinetic Isotope effects (KIEs) have long served as a probe for the mechanisms of both enzymatic and solution reactions. Here, we discuss various models for the physical sources of KIEs, how experimentalists can use those models to interpret their data, and how the focus of traditional models has grown to a model that includes motion of the enzyme and quantum mechanical nuclear tunneling. We then present two case studies of enzymes, thymidylate synthase and alcohol dehydrogenase, and discuss how KIEs have shed light on the C-H bond cleavages those enzymes catalyze. We will show how the combination of both experimental and computational studieshas changed our notion of how these enzymes exert their catalytic powers. PMID:23673528

  3. Adrenodoxin supports reactions catalyzed by microsomal steroidogenic cytochrome P450s

    SciTech Connect

    Pechurskaya, Tatiana A. . E-mail: usanov@iboch.bas-net.by

    2007-02-16

    The interaction of adrenodoxin (Adx) and NADPH cytochrome P450 reductase (CPR) with human microsomal steroidogenic cytochrome P450s was studied. It is found that Adx, mitochondrial electron transfer protein, is able to support reactions catalyzed by human microsomal P450s: full length CYP17, truncated CYP17, and truncated CYP21. CPR, but not Adx, supports activity of truncated CYP19. Truncated and the full length CYP17s show distinct preference for electron donor proteins. Truncated CYP17 has higher activity with Adx compared to CPR. The alteration in preference to electron donor does not change product profile for truncated enzymes. The electrostatic contacts play a major role in the interaction of truncated CYP17 with either CPR or Adx. Similarly electrostatic contacts are predominant in the interaction of full length CYP17 with Adx. We speculate that Adx might serve as an alternative electron donor for CYP17 at the conditions of CPR deficiency in human.

  4. On the Need for Spin Polarization in Heterogeneously Catalyzed Reactions on Nonmagnetic Metallic Surfaces.

    PubMed

    Fajín, José L C; D S Cordeiro, M Natália; Gomes, José R B; Illas, Francesc

    2012-05-08

    A series of reactions including water, oxygen, hydrogen and nitric oxide dissociation and carbon monoxide or nitric oxide oxidations catalyzed by metallic surfaces have been investigated by means of periodic density functional calculations with the main aim of establishing the importance of spin polarization when the substrate is nonmagnetic. Numerical differences in the calculated total energies and bond lengths of the breaking/forming bonds corresponding to spin restricted or spin unrestricted formalisms are usually smaller than the inherent error of density functional theory based methods. Nevertheless, it is important to insist on the fact that the spin polarized solution exists and is lower in energy than the one corresponding to the spin restricted formalism, as one would expect, and from a practical point of view, results obtained without taking spin polarization into account lead to the same description of the potential energy surface.

  5. Dynamics of surface catalyzed reactions; the roles of surface defects, surface diffusion, and hot electrons.

    PubMed

    Somorjai, Gabor A; Bratlie, Kaitlin M; Montano, Max O; Park, Jeong Y

    2006-10-12

    The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path

  6. Brønsted Acid Catalyzed Oxygenative Bimolecular Friedel-Crafts-type Coupling of Ynamides.

    PubMed

    Patil, Dilip V; Kim, Seung Woo; Nguyen, Quynh H; Kim, Hanbyul; Wang, Shan; Hoang, Tuan; Shin, Seunghoon

    2017-03-20

    A non-metal approach for accessing α-oxo carbene surrogates for a C-C bond-forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid-catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of SN 2' mechanism has been provided by employing chiral N,N'-dioxides which also enlightens the nature of the intermediates in related metal-catalyzed processes.

  7. Optimizing Metalloporphyrin-Catalyzed Reduction Reactions for In Situ Remediation of DOE Contaminants

    SciTech Connect

    Schlautman, Mark A.

    2013-07-14

    Past activities have resulted in a legacy of contaminated soil and groundwater at Department of Energy facilities nationwide. Uranium and chromium are among the most frequently encountered and highest-priority metal and radionuclide contaminants at DOE installations. Abiotic chemical reduction of uranium and chromium at contaminated DOE sites can be beneficial because the reduced metal species are less soluble in water, less mobile in the environment, and less toxic to humans and ecosystems. Although direct biological reduction has been reported for U(VI) and Cr(VI) in laboratory studies and at some field sites, the reactions can sometimes be slow or even inhibited due to unfavorable environmental conditions. One promising approach for the in-situ remediation of DOE contaminants is to develop electron shuttle catalysts that can be delivered precisely to the specific subsurface locations where contaminants reside. Previous research has shown that reduction of oxidized organic and inorganic contaminants often can be catalyzed by electron shuttle systems. Metalloporphyrins and their derivatives are well known electron shuttles for many biogeochemical systems, and thus were selected to study their catalytic capabilities for the reduction of chromium and uranium in the presence of reducing agents. Zero valent iron (ZVI) was chosen as the primary electron donor in most experimental systems. Research proceeded in three phases and the key findings of each phase are reported here. Phase I examined Cr(VI) reduction and utilized micro- and nano-sized ZVI as the electron donors. Electron shuttle catalysts tested were cobalt- and iron-containing metalloporphyrins and Vitamin B12. To aid in the recycle and reuse of the nano-sized ZVI and soluble catalysts, sol-gels and calcium-alginate gel beads were tested as immobilization/support matrices. Although the nano-sized ZVI could be incorporated within the alginate gel beads, preliminary attempts to trap it in sol-gels were not

  8. Palladium-Based Nanomaterials: A Platform to Produce Reactive Oxygen Species for Catalyzing Oxidation Reactions.

    PubMed

    Long, Ran; Huang, Hao; Li, Yaping; Song, Li; Xiong, Yujie

    2015-11-25

    Oxidation reactions by molecular oxygen (O2 ) over palladium (Pd)-based nanomaterials are a series of processes crucial to the synthesis of fine chemicals. In the past decades, investigations of related catalytic materials have mainly been focused on the synthesis of Pd-based nanomaterials from the angle of tailoring their surface structures, compositions and supporting materials, in efforts to improve their activities in organic reactions. From the perspective of rational materials design, it is imperative to address the fundamental issues associated with catalyst performance, one of which should be oxygen activation by Pd-based nanomaterials. Here, the fundamentals that account for the transformation from O2 to reactive oxygen species over Pd, with a focus on singlet O2 and its analogue, are introduced. Methods for detecting and differentiating species are also presented to facilitate future fundamental research. Key factors for tuning the oxygen activation efficiencies of catalytic materials are then outlined, and recent developments in Pd-catalyzed oxygen-related organic reactions are summarized in alignment with each key factor. To close, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

  9. Novel palladium complex-catalyzed reaction of magnesium amides with allylic electrophiles

    SciTech Connect

    Dzhemilev, U.M.; Ibragimov, A.G.; Minsker, D.L.; Muslukhov, R.R.

    1987-08-20

    In order to develop an efficient method for the synthesis of higher order unsaturated tertiary amines, and also to explore a new method for the formation of C-N bonds, they have investigated the transition metal complex-catalyzed reaction of magnesium amides with electrophiles; the electrophiles selected for study included allyl ethers and esters, as well as sulfones, sulfides and quaternized allylamines. The effects of the nature and structure of the catalyst components, as well as of the reaction conditions, on product yield were examined in the case of the reaction of diethyl (bromomagnesium)amine with diallyl ether, and revealed that the highest yield of diethylallyl-amine (I) was achieved using Pd(acac)/sub 2/ (3-5 mole %) and Ph/sub 3/P (1:2) as catalyst in THF solution at 50/sup 0/C for 5 h. Other transition metal (Ni, Fe, Zr, Ti, Cu) compounds were also examined as catalysts, but the yield of (I) did not exceed 15% with these compounds. Bimetallic catalysts based on Zr (Cp/sub 2/ZrCl, Py/sub 2/ZrCl/sub 6/, (RO)/sub 4/Zr) and Ni (Ni(acac)/sub 2/ and NiCl/sub 2/) were successful in forming (I) from diethyl (bromomagnesium)amine and diallyl ether in 60% yield.

  10. Analysis of the HindIII-catalyzed reaction by time-resolved crystallography

    SciTech Connect

    Kawamura, Takashi; Kobayashi, Tomoki; Watanabe, Nobuhisa

    2015-02-01

    A time-resolved study using the freeze-trap method elucidates the mechanism of the DNA-cleaving reaction of HindIII. In order to investigate the mechanism of the reaction catalyzed by HindIII, structures of HindIII–DNA complexes with varying durations of soaking time in cryoprotectant buffer containing manganese ions were determined by the freeze-trap method. In the crystal structures of the complexes obtained after soaking for a longer duration, two manganese ions, indicated by relatively higher electron density, are clearly observed at the two metal ion-binding sites in the active site of HindIII. The increase in the electron density of the two metal-ion peaks followed distinct pathways with increasing soaking times, suggesting variation in the binding rate constant for the two metal sites. DNA cleavage is observed when the second manganese ion appears, suggesting that HindIII uses the two-metal-ion mechanism, or alternatively that its reactivity is enhanced by the binding of the second metal ion. In addition, conformational change in a loop near the active site accompanies the catalytic reaction.

  11. Lipase-catalyzed synthesis of ascorbyl oleate in acetone: optimization of reaction conditions and lipase reusability.

    PubMed

    Stojanović, Marija; Velićković, Dušan; Dimitrijević, Aleksandra; Milosavić, Nenad; Knežević-Jugović, Zorica; Bezbradica, Dejan

    2013-01-01

    Lipase-catalyzed ascorbyl oleate synthesis is eco-friendly and selective way of production of liposoluble biocompatible antioxidants, but still not present on an industrial level due to the high biocatalyst costs. In this study, response surface methodology was applied in order to estimate influence of individual experimental factors, identify interactions among them, and to determine optimum conditions for enzymatic synthesis of ascorbyl oleate in acetone, in terms of limiting substrate conversion, product yield, and yield per mass of consumed enzyme. As a biocatalyst, commercial immobilized preparation of lipase B from Candida antarctica, Novozym 435, was used. In order to develop cost-effective process, at reaction conditions at which maximum amount of product per mass of biocatalyst was produced (60°C, 0.018 % (v/v) of water, 0.135 M of vitamin C, substrates molar ratio 1:8, and 0.2 % (w/v) of lipase), possibilities for further increase of ester yield were investigated. Addition of molecular sieves at 4(th) hour of reaction enabled increase of yield from 16.7 mmol g⁻¹ to 19.3 mmol g⁻¹. Operational stability study revealed that after ten reaction cycles enzyme retained 48 % of its initial activity. Optimized synthesis with well-timed molecular sieves addition and repeated use of lipase provided production of 153 mmol per gram of enzyme. Further improvement of productivity was achieved using procedure for the enzyme reactivation.

  12. A novel glucosylation reaction on anthocyanins catalyzed by acyl-glucose-dependent glucosyltransferase in the petals of carnation and delphinium.

    PubMed

    Matsuba, Yuki; Sasaki, Nobuhiro; Tera, Masayuki; Okamura, Masachika; Abe, Yutaka; Okamoto, Emi; Nakamura, Haruka; Funabashi, Hisakage; Takatsu, Makoto; Saito, Mikako; Matsuoka, Hideaki; Nagasawa, Kazuo; Ozeki, Yoshihiro

    2010-10-01

    Glucosylation of anthocyanin in carnations (Dianthus caryophyllus) and delphiniums (Delphinium grandiflorum) involves novel sugar donors, aromatic acyl-glucoses, in a reaction catalyzed by the enzymes acyl-glucose-dependent anthocyanin 5(7)-O-glucosyltransferase (AA5GT and AA7GT). The AA5GT enzyme was purified from carnation petals, and cDNAs encoding carnation Dc AA5GT and the delphinium homolog Dg AA7GT were isolated. Recombinant Dc AA5GT and Dg AA7GT proteins showed AA5GT and AA7GT activities in vitro. Although expression of Dc AA5GT in developing carnation petals was highest at early stages, AA5GT activity and anthocyanin accumulation continued to increase during later stages. Neither Dc AA5GT expression nor AA5GT activity was observed in the petals of mutant carnations; these petals accumulated anthocyanin lacking the glucosyl moiety at the 5 position. Transient expression of Dc AA5GT in petal cells of mutant carnations is expected to result in the transfer of a glucose moiety to the 5 position of anthocyanin. The amino acid sequences of Dc AA5GT and Dg AA7GT showed high similarity to glycoside hydrolase family 1 proteins, which typically act as β-glycosidases. A phylogenetic analysis of the amino acid sequences suggested that other plant species are likely to have similar acyl-glucose-dependent glucosyltransferases.

  13. Detoxification of acidic catalyzed hydrolysate of Kappaphycus alvarezii (cottonii).

    PubMed

    Meinita, Maria Dyah Nur; Hong, Yong-Ki; Jeong, Gwi-Taek

    2012-01-01

    Red seaweed, Kappaphycus alvarezii, holds great promise for use in biofuel production due to its high carbohydrate content. In this study, we investigated the effect of fermentation inhibitors to the K. alvarezii hydrolysate on cell growth and ethanol fermentation. In addition, detoxification of fermentation inhibitors was performed to decrease the fermentation inhibitory effect. 5-Hydroxymethylfurfural and levulinic acid, which are liberated from acidic hydrolysis, was also observed in the hydrolysate of K. alvarezii. These compounds inhibited ethanol fermentation. In order to remove these inhibitors, activated charcoal and calcium hydroxide were introduced. The efficiency of activated charcoals was examined and over-liming was used to remove the inhibitors. Activated charcoal was found to be more effective than calcium hydroxide to remove the inhibitors. Detoxification by activated charcoal strongly improved the fermentability of dilute acid hydrolysate in the production of bioethanol from K. alvarezii with Saccharomyces cerevisiae. The optimal detoxifying conditions were found to be below an activated charcoal concentration of 5%.

  14. 40 CFR 721.10679 - Carboxylic acid, substituted alkylstannylene ester, reaction products with inorganic acid tetra...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... alkylstannylene ester, reaction products with inorganic acid tetra alkyl ester (generic). 721.10679 Section 721... Carboxylic acid, substituted alkylstannylene ester, reaction products with inorganic acid tetra alkyl ester... identified generically as carboxylic acid, substituted alkylstannylene ester, reaction products...

  15. Formose reaction controlled by boronic acid compounds

    PubMed Central

    Imai, Toru; Michitaka, Tomohiro

    2016-01-01

    Formose reactions were carried out in the presence of low molecular weight and macromolecular boronic acid compounds, i.e., sodium phenylboronate (SPB) and a copolymer of sodium 4-vinylphenylboronate with sodium 4-styrenesulfonate (pVPB/NaSS), respectively. The boronic acid compounds provided different selectivities; sugars of a small carbon number were formed favorably in the presence of SPB, whereas sugar alcohols of a larger carbon number were formed preferably in the presence of pVPB/NaSS. PMID:28144337

  16. Choline Chloride Catalyzed Amidation of Fatty Acid Ester to Monoethanolamide: A Green Approach.

    PubMed

    Patil, Pramod; Pratap, Amit

    2016-01-01

    Choline chloride catalyzed efficient method for amidation of fatty acid methyl ester to monoethanolamide respectively. This is a solvent free, ecofriendly, 100% chemo selective and economically viable path for alkanolamide synthesis. The Kinetics of amidation of methyl ester were studied and found to be first order with respect to the concentration of ethanolamine. The activation energy (Ea) for the amidation of lauric acid methyl ester catalyzed by choline chloride was found to be 50.20 KJ mol(-1). The 98% conversion of lauric acid monoethanolamide was obtained at 110°C in 1 h with 6% weight of catalyst and 1:1.5 molar ratio of methyl ester to ethanolamine under nitrogen atmosphere.

  17. Examination of Organic Reactions in UT/LS Aerosols: Temperature Dependence in Sulfuric Acid Solution

    NASA Astrophysics Data System (ADS)

    Iraci, L. T.; Michelsen, R. R.

    2004-12-01

    Sulfuric acid has been used for decades as an industrial catalyst for organic reactions, but its parallel role in atmospheric aerosols is relatively unexplored, despite identification of a wide array of organic compounds in particles. Several recent studies have demonstrated possible reactions in acidic particles, generally involving carbonyl groups (C=O) and leading to the formation of larger molecules. Reactions of oxygenated organic compounds in acidic solution are most often studied near room temperature, while the sulfate particles of the upper troposphere and lower stratosphere are significantly colder. Our studies of ethanal (acetaldehyde) suggest that reactivity in ~50 wt% H2SO4 solutions may be enhanced at lower temperatures, contrary to expectations. We will present temperature-dependent results of acid catalyzed condensation reactions, leading to formation of higher molecular weight products. Implications for aerosol composition and reactivity will be discussed.

  18. Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with αα Domain Architecture That Catalyzes a Unique Cyclization-Fragmentation Reaction Sequence.

    PubMed

    Harris, Golda G; Lombardi, Patrick M; Pemberton, Travis A; Matsui, Tsutomu; Weiss, Thomas M; Cole, Kathryn E; Köksal, Mustafa; Murphy, Frank V; Vedula, L Sangeetha; Chou, Wayne K W; Cane, David E; Christianson, David W

    2015-12-08

    Geosmin synthase from Streptomyces coelicolor (ScGS) catalyzes an unusual, metal-dependent terpenoid cyclization and fragmentation reaction sequence. Two distinct active sites are required for catalysis: the N-terminal domain catalyzes the ionization and cyclization of farnesyl diphosphate to form germacradienol and inorganic pyrophosphate (PPi), and the C-terminal domain catalyzes the protonation, cyclization, and fragmentation of germacradienol to form geosmin and acetone through a retro-Prins reaction. A unique αα domain architecture is predicted for ScGS based on amino acid sequence: each domain contains the metal-binding motifs typical of a class I terpenoid cyclase, and each domain requires Mg(2+) for catalysis. Here, we report the X-ray crystal structure of the unliganded N-terminal domain of ScGS and the structure of its complex with three Mg(2+) ions and alendronate. These structures highlight conformational changes required for active site closure and catalysis. Although neither full-length ScGS nor constructs of the C-terminal domain could be crystallized, homology models of the C-terminal domain were constructed on the basis of ∼36% sequence identity with the N-terminal domain. Small-angle X-ray scattering experiments yield low-resolution molecular envelopes into which the N-terminal domain crystal structure and the C-terminal domain homology model were fit, suggesting possible αα domain architectures as frameworks for bifunctional catalysis.

  19. Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with Alpha-Alpha Domain Architecture that Catalyzes a Unique Cyclization-Fragmentation Reaction Sequence

    PubMed Central

    Harris, Golda G.; Lombardi, Patrick M.; Pemberton, Travis A.; Matsui, Tsutomu; Weiss, Thomas M.; Cole, Kathryn E.; Köksal, Mustafa; Murphy, Frank V.; Vedula, L. Sangeetha; Chou, Wayne K.W.; Cane, David E.; Christianson, David W.

    2015-01-01

    Geosmin synthase from Streptomyces coelicolor (ScGS) catalyzes an unusual, metal-dependent terpenoid cyclization and fragmentation reaction sequence. Two distinct active sites are required for catalysis: the N-terminal domain catalyzes the ionization and cyclization of farnesyl diphosphate to form germacradienol and inorganic pyrophosphate (PPi), and the C-terminal domain catalyzes the protonation, cyclization, and fragmentation of germacradienol to form geosmin and acetone through a retro-Prins reaction. A unique αα domain architecture is predicted for ScGS based on amino acid sequence: each domain contains the metal-binding motifs typical of a class I terpenoid cyclase, and each domain requires Mg2+ for catalysis. Here, we report the X-ray crystal structure of the unliganded N-terminal domain of ScGS and the structure of its complex with 3 Mg2+ ions and alendronate. These structures highlight conformational changes required for active site closure and catalysis. Although neither full-length ScGS nor constructs of the C-terminal domain could be crystallized, homology models of the C-terminal domain were constructed based on ~36% sequence identity with the N-terminal domain. Small-angle X-ray scattering experiments yield low resolution molecular envelopes into which the N-terminal domain crystal structure and the C-terminal domain homology model were fit, suggesting possible αα domain architectures as frameworks for bifunctional catalysis. PMID:26598179

  20. Brønsted Acid Catalyzed Addition of Enamides to ortho-Quinone Methide Imines-An Efficient and Highly Enantioselective Synthesis of Chiral Tetrahydroacridines.

    PubMed

    Kretzschmar, Martin; Hodík, Tomáš; Schneider, Christoph

    2016-08-08

    The direct and highly enantioselective synthesis of tetrahydroacridines was achieved through the phosphoric acid catalyzed addition of enamides to in situ generated ortho-quinone methide imines and subsequent elimination. This novel one-step process constitutes a very efficient, elegant, and selective synthetic approach to valuable N-heterocycles with a 1,4-dihydroquinoline motif. By subsequent highly diastereoselective hydrogenation and N-deprotection the reaction products were easily converted into free hexahydroacridines with a total of three new stereogenic centers.

  1. Ligand intermediates in metal catalyzed reactions. Technical report: third budget year

    SciTech Connect

    Gladysz, J.A.

    1988-04-01

    A progress report is presented in which a new method for the activation of metal-bound methyl groups and the oxidative disproportionation of coordinated ethylene and methane are discussed. Also considered in the report is the divergent kinetic and thermodynamic acidity in organotransition metal hydride complexes and the synthesis, structure, and reactions of chiral rhenium vinylidene complexes.

  2. Palladium-catalyzed cross-coupling reactions of arylsiloxanes with aryl halides: application to solid-supported organic synthesis.

    PubMed

    Traficante, Carla I; Delpiccolo, Carina M L; Mata, Ernesto G

    2014-05-12

    The solid-phase version of the Pd-catalyzed Hiyama reaction between a variety of aryltriethoxysilanes and immobilized aryl halides was developed. Smooth cross-coupling was achieved to afford the corresponding biaryl products in moderate to excellent yields. The described protocol would be particularly useful for the construction of 4'-substituted 1,1'-biphenyl derivatives.

  3. Nafion®-catalyzed microwave-assisted Ritter reaction: An atom-economic solvent-free synthesis of amides

    EPA Science Inventory

    An atom-economic solvent-free synthesis of amides by the Ritter reaction of alcohols and nitriles under microwave irradiation is reported. This green protocol is catalyzed by solid supported Nafion®NR50 with improved efficiency and reduced waste production.

  4. A General and Highly Selective Cobalt-Catalyzed Hydrogenation of N-Heteroarenes under Mild Reaction Conditions.

    PubMed

    Adam, Rosa; Cabrero-Antonino, Jose R; Spannenberg, Anke; Junge, Kathrin; Jackstell, Ralf; Beller, Matthias

    2017-02-14

    Herein, a general and efficient method for the homogeneous cobalt-catalyzed hydrogenation of N-heterocycles, under mild reaction conditions, is reported. Key to success is the use of the tetradentate ligand tris(2-(diphenylphosphino)phenyl)phosphine). This non-noble metal catalyst system allows the selective hydrogenation of heteroarenes in the presence of a broad range of other sensitive reducible groups.

  5. Simple citric acid-catalyzed surface esterification of cellulose nanocrystals.

    PubMed

    Ávila Ramírez, Jhon Alejandro; Fortunati, Elena; Kenny, José María; Torre, Luigi; Foresti, María Laura

    2017-02-10

    A simple straightforward route for the surface esterification of cellulose nanocrystals (CNC) is herein proposed. CNC obtained from microcrystalline cellulose were acetylated using as catalyst citric acid, a α-hydroxy acid present in citrus fruits and industrially produced by certain molds in sucrose or glucose-containing medium. No additional solvent was added to the system; instead, the acylant (acetic anhydride) was used in sufficient excess to allow CNC dispersion and proper suspension agitation. By tuning the catalyst load, CNC with two different degree of substitution (i.e. DS=0.18 and 0.34) were obtained. Acetylated cellulose nanocrystals were characterized in terms of chemical structure, crystallinity, morphology, thermal decomposition and dispersion in a non-polar solvent. Results illustrated for the first time the suitability of the protocol proposed for the simple surface acetylation of cellulose nanocrystals.

  6. Mechanistic Studies Lead to Dramatically Improved Reaction Conditions for the Cu-Catalyzed Asymmetric Hydroamination of Olefins

    PubMed Central

    2015-01-01

    Enantioselective copper(I) hydride (CuH)-catalyzed hydroamination has undergone significant development over the past several years. To gain a general understanding of the factors governing these reactions, kinetic and spectroscopic studies were performed on the CuH-catalyzed hydroamination of styrene. Reaction profile analysis, rate order assessment, and Hammett studies indicate that the turnover-limiting step is regeneration of the CuH catalyst by reaction with a silane, with a phosphine-ligated copper(I) benzoate as the catalyst resting state. Spectroscopic, electrospray ionization mass spectrometry, and nonlinear effect studies are consistent with a monomeric active catalyst. With this insight, targeted reagent optimization led to the development of an optimized protocol with an operationally simple setup (ligated copper(II) precatalyst, open to air) and short reaction times (<30 min). This improved protocol is amenable to a diverse range of alkene and alkyne substrate classes. PMID:26522837

  7. Proton transfer reactions between nitric acid and acetone, hydroxyacetone, acetaldehyde and benzaldehyde in the solid phase.

    PubMed

    Lasne, Jérôme; Laffon, Carine; Parent, Philippe

    2012-12-05

    The heterogeneous and homogeneous reactions of acetone, hydroxyacetone, acetaldehyde and benzaldehyde with solid nitric acid (HNO(3)) films have been studied with Reflection-Absorption Infrared Spectroscopy (RAIRS) under Ultra-High Vacuum (UHV) conditions in the 90-170 K temperature range. In the bulk or at the surface of the films, nitric acid transfers its proton to the carbonyl function of the organic molecules, producing protonated acetone-H(+), hydroxyacetone-H(+), acetaldehyde-H(+) and benzaldehyde-H(+), and nitrate anions NO(3)(-), a reaction not observed when nitric acid is previously hydrated [J. Lasne, C. Laffon and Ph. Parent, Phys. Chem. Chem. Phys., 2012, 14, 697]. This provides a molecular-scale description of the carbonyl protonation reaction in an acid medium, the first step of the acid-catalyzed condensation of carbonyl compounds, fuelling the growth of secondary organic aerosols (SOA) in the atmosphere.

  8. Of the ortho effect in palladium/norbornene-catalyzed reactions: a theoretical investigation.

    PubMed

    Maestri, Giovanni; Motti, Elena; Della Ca', Nicola; Malacria, Max; Derat, Etienne; Catellani, Marta

    2011-06-08

    Mechanistic questions concerning palladium and norbornene catalyzed aryl-aryl coupling reactions are treated in this paper: how aryl halides react with the intermediate palladacycles, formed by interaction of the two catalysts with an aryl halide, and what is the rational explanation of the "ortho effect" (caused by an ortho substituent in the starting aryl halide), which leads to aryl-aryl coupling with a second molecule of aryl halide rather than to aryl-norbornyl coupling. Two possible pathways have been proposed, one involving aryl halide oxidative addition to the palladacycle, the other passing through a palladium(II) transmetalation, also involving the palladacycle, as previously proposed by Cardenas and Echavarren. Our DFT calculations using M06 show that, in palladium-catalyzed reaction of aryl halides, not containing ortho substituents, and norbornene, the intermediate palladacycle formed has a good probability to undergo transmetalation, energetically favored over the oxidative addition leading to Pd(IV). The unselective sp(2)-sp(2) and sp(2)-sp(3) coupling, experimentally observed in this case, can be explained in the framework of the transmetalation pathway since the energetic difference between aryl attack onto the aryl or norbornyl carbon of the palladacycle intermediate is quite small. On the other hand, according to the experimentally observed "ortho effect", selective aryl-aryl coupling only occurs in the reactions of ortho-substituted metallacycles. The present work offers the first possible rationalization of this finding. These in situ formed palladacycles containing an ortho substituent could more easily undergo oxidative addition of an aryl halide rather than reductive elimination from the transmetalation intermediate as a result of a steric clash in the transition state of the latter. The now energetically accessible Pd(IV) intermediate, featuring a Y-distorted trigonal bipyramidal structure, can account for the reported selective aryl

  9. Efficient production of free fatty acids from ionic liquid-based acid- or enzyme-catalyzed bamboo hydrolysate.

    PubMed

    Mi, Le; Qin, Dandan; Cheng, Jie; Wang, Dan; Li, Sha; Wei, Xuetuan

    2017-03-01

    Two engineered Escherichia coli strains, DQ101 (MG1655 fadD (-))/pDQTES and DQ101 (MG1655 fadD (-))/pDQTESZ were constructed to investigate the free fatty acid production using ionic liquid-based acid- or enzyme-catalyzed bamboo hydrolysate as carbon source in this study. The plasmid, pDQTES, carrying an acyl-ACP thioesterase 'TesA of E. coli in pTrc99A was constructed firstly, and then (3R)-hydroxyacyl-ACP dehydratase was ligated after the TesA to give the plasmid pDQTESZ. These two strains exhibited efficient fatty acid production when glucose was used as the sole carbon source, with a final concentration of 2.45 and 3.32 g/L, respectively. The free fatty acid production of the two strains on xylose is not as efficient as that on glucose, which was 2.32 and 2.96 g/L, respectively. For mixed sugars, DQ101 (MG1655 fadD (-))-based strains utilized glucose and pentose sequentially under the carbon catabolite repression (CCR) regulation. The highest total FFAs concentration from the mixed sugar culture reached 2.81 g/L by DQ101 (MG1655 fadD (-))/pDQTESZ. Furthermore, when ionic liquid-based enzyme-catalyzed bamboo hydrolysate was used as the carbon source, the strain DQ101 (MG1655 fadD (-))/pDQTESZ could produce 1.23 g/L FFAs with a yield of 0.13 g/g, and while it just produced 0.65 g/L free fatty acid with the ionic liquid-based acid-catalyzed bamboo hydrolysate as the feedstock. The results suggested that enzymatic catalyzed bamboo hydrolysate with ionic liquid pretreatment could serve as an efficient feedstock for free fatty acid production.

  10. Mechanism of the Orotidine 5′-Monophosphate Decarboxylase-Catalyzed Reaction: Evidence for Substrate Destabilization

    SciTech Connect

    Chan, K.; Wood, M; Fedorov, A; Fedorov, E; Imker, H; Amyes, T; Richard, J; Almo, S; Gerlt, J

    2009-01-01

    The reaction catalyzed by orotidine 5'-monophosphate decarboxylase (OMPDC) involves a stabilized anionic intermediate, although the structural basis for the rate acceleration (kcat/knon, 7.1 x 1016) and proficiency (kcat/KM)/knon, 4.8 x 1022 M-1 is uncertain. That the OMPDCs from Methanothermobacter thermautotrophicus (MtOMPDC) and Saccharomyces cerevisiae (ScOMPDC) catalyze the exchange of H6 of the UMP product with solvent deuterium allows an estimate of a lower limit on the rate acceleration associated with stabilization of the intermediate and its flanking transition states (=1010). The origin of the 'missing' contribution, =107 (1017 total - =1010), is of interest. Based on structures of liganded complexes, unfavorable electrostatic interactions between the substrate carboxylate group and a proximal Asp (Asp 70 in MtOMPDC and Asp 91 in ScOMPDC) have been proposed to contribute to the catalytic efficiency. We investigated that hypothesis by structural and functional characterization of the D70N and D70G mutants of MtOMPDC and the D91N mutant of ScOMPDC. The substitutions for Asp 70 in MtOMPDC significantly decrease the value of kcat for decarboxylation of FOMP (a more reactive substrate analogue) but have little effect on the value of kex for exchange of H6 of FUMP with solvent deuterium; the structures of wild-type MtOMPDC and its mutants are superimposable when complexed with 6-azaUMP. In contrast, the D91N mutant of ScOMPDC does not catalyze exchange of H6 of FUMP; the structures of wild-type ScOMPDC and its D91N mutant are not superimposable when complexed with 6-azaUMP, with differences in both the conformation of the active site loop and the orientation of the ligand vis vis the active site residues. We propose that the differential effects of substitutions for Asp 70 of MtOMPDC on decarboxylation and exchange provide additional evidence for a carbanionic intermediate as well as the involvement of Asp 70 in substrate destabilization.

  11. Iodine-catalyzed disproportionation of aryl-substituted ethers under solvent-free reaction conditions.

    PubMed

    Jereb, Marjan; Vražič, Dejan

    2013-03-28

    Iodine was demonstrated to be an efficient catalyst for disproportionation of aryl-substituted ethers under solvent-free reaction conditions. Variously substituted 1,1,1',1'-tetraaryldimethyl ethers were transformed into the corresponding diarylketone and diarylmethane derivatives. I2-catalyzed transformation of 4-methoxyphenyl substituted ethers yielded mono- and dialkylated Friedel-Crafts products as well. Treatment of trityl alkyl and trityl benzyl ethers with a catalytic amount of iodine produced triphenylmethane and the corresponding aldehydes and ketones. The electron-donating substituents facilitated the reaction, while the electron-withdrawing groups retarded it; the difference in reactivity is not very high. Such an observation may be in favour of hydride transfer, predominantly from the less electron rich side of the ether with more stable carbocation formation. With the isotopic studies it was established that a substantial portion of the C-H bond scission took place in the rate-determining step, while the carbonyl oxygen atom originated from the starting ether, and not from the air. The transformation took place under air and under argon, and HI was not a functioning catalyst.

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

    PubMed Central

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

    2013-01-01

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

  13. Polyoxymetalate liquid-catalyzed polyol fuel cell and the related photoelectrochemical reaction mechanism study

    NASA Astrophysics Data System (ADS)

    Wu, Weibing; Liu, Wei; Mu, Wei; Deng, Yulin

    2016-06-01

    A novel design of liquid catalyzed fuel cell (LCFC), which uses polyoxometalates (POMs) as the photocatalyst and charge carrier has been reported previously. In this paper, the adaptability of biomass fuels (e.g., glycerol and glucose) to the LCFC and corresponding cell performance were studied in detail here. An interesting finding that greatly differs from conventional fuel cell is that high molecular weight fuels rather than small molecule fuels (e.g., methanol and ethylene glycol) are favored by the novel LCFC with respect to the power densities. The power output of LCFC strongly depends on the number and structure of hydroxyl groups in the biomass fuels. The evidence of UV-Vis and 1H NMR spectra shows that the preassociation between POM and alcohol fuels, which determines the photoelectrochemical reaction pathway of POM, is enhanced as the number of hydroxyl increases. Experimental results also demonstrate that more hydroxyl groups in the molecules lead to faster photoelectrochemical reaction between POM and fuels, higher reduction degree of POM, and further higher power output of LCFC. Our study reveals that biomass-based polyhydroxyl compounds such as starch, hemicellulose and cellulose are potential high-performance fuels for LCFC.

  14. Probing Nonadiabaticity in the Proton-Coupled Electron Transfer Reaction Catalyzed by Soybean Lipoxygenase

    PubMed Central

    2014-01-01

    Proton-coupled electron transfer (PCET) plays a vital role in many biological and chemical processes. PCET rate constant expressions are available for various well-defined regimes, and determining which expression is appropriate for a given system is essential for reliable modeling. Quantitative diagnostics have been devised to characterize the vibronic nonadiabaticity between the electron–proton quantum subsystem and the classical nuclei, as well as the electron–proton nonadiabaticity between the electrons and proton(s) within the quantum subsystem. Herein these diagnostics are applied to a model of the active site of the enzyme soybean lipoxygenase, which catalyzes a PCET reaction that exhibits unusually high deuterium kinetic isotope effects at room temperature. Both semiclassical and electronic charge density diagnostics illustrate vibronic and electron–proton nonadiabaticity for this PCET reaction, supporting the use of the Golden rule nonadiabatic rate constant expression with a specific form of the vibronic coupling. This type of characterization will be useful for theoretical modeling of a broad range of PCET processes. PMID:25258676

  15. Activation of Two Sequential H-transfers in the Thymidylate Synthase Catalyzed Reaction

    PubMed Central

    Islam, Zahidul; Strutzenberg, Timothy S.; Ghosh, Ananda K.; Kohen, Amnon

    2015-01-01

    Thymidylate synthase (TSase) catalyzes the de novo biosynthesis of thymidylate, a precursor for DNA, and is thus an important target for chemotherapeutics and antibiotics. Two sequential C-H bond cleavages catalyzed by TSase are of particular interest: a reversible proton abstraction from the 2′-deoxy-uridylate substrate, followed by an irreversible hydride transfer forming the thymidylate product. QM/MM calculations of the former predicted a mechanism where the abstraction of the proton leads to formation of a novel nucleotide-folate intermediate that is not covalently bound to the enzyme (Wang, Z.; Ferrer, S.; Moliner, V.; Kohen, A. Biochemistry 2013, 52, 2348–2358). Existence of such intermediate would hold promise as a target for a new class of drugs. Calculations of the subsequent hydride transfer predicted a concerted H-transfer and elimination of the enzymatic cysteine (Kanaan, N.; Ferrer, S.; Marti, S.; Garcia-Viloca, M.; Kohen, A.; Moliner, V. J. Am. Chem. Soc. 2011, 133, 6692–6702). A key to both C-H activations is a highly conserved arginine (R166) that stabilizes the transition state of both H-transfers. Here we test these predictions by studying the R166 to lysine mutant of E. coli TSase (R166K) using intrinsic kinetic isotope effects (KIEs) and their temperature dependence to assess effects of the mutation on both chemical steps. The findings confirmed the predictions made by the QM/MM calculations, implicate R166 as an integral component of both reaction coordinates, and thus provide critical support to the nucleotide-folate intermediate as a new target for rational drug design. PMID:26576323

  16. Palladium-Catalyzed α-Arylation of Aryl Acetic Acid Derivatives via Dienolate Intermediates with Aryl Chlorides and Bromides

    PubMed Central

    2016-01-01

    To date, examples of α-arylation of carboxylic acids remain scarce. Using a deprotonative cross-coupling process (DCCP), a method for palladium-catalyzed γ-arylation of aryl acetic acids with aryl halides has been developed. This protocol is applicable to a wide range of aryl bromides and chlorides. A procedure for the palladium-catalyzed α-arylation of styryl acetic acids is also described. PMID:25582024

  17. The Aerobic Oxidation of Bromide to Dibromine Catalyzed by Homogeneous Oxidation Catalysts and Initiated by Nitrate in Acetic Acid

    SciTech Connect

    Partenheimer, Walt; Fulton, John L.; Sorensen, Christina M.; Pham, Van Thai; Chen, Yongsheng

    2014-06-01

    A small amount of nitrate, ~0.002 molal, initiates the Co/Mn catalyzed aerobic oxidation of bromide compounds (HBr,NaBr,LiBr) to dibromine in acetic acid at room temperature. At temperatures 40oC or less , the reaction is autocatalytic. Co(II) and Mn(II) themselves and mixed with ionic bromide are known homogeneous oxidation catalysts. The reaction was discovered serendipitously when a Co/Br and Co/Mn/Br catalyst solution was prepared for the aerobic oxidation of methyaromatic compounds and the Co acetate contained a small amount of impurity i.e. nitrate. The reaction was characterized by IR, UV-VIS, MALDI and EXAFS spectroscopies and the coordination chemistry is described. The reaction is inhibited by water and its rate changed by pH. The change in these variables, as well as others, are identical to those observed during homogeneous, aerobic oxidation of akylaromatics. A mechanism is proposed. Accidental addition of a small amount of nitrate compound into a Co/Mn/Br/acetic acid mixture in a large, commercial feedtank is potentially dangerous.

  18. Scope and Mechanisms of Frustrated Lewis Pair Catalyzed Hydrogenation Reactions of Electron-Deficient C=C Double Bonds.

    PubMed

    Morozova, Varvara; Mayer, Peter; Berionni, Guillaume

    2015-11-23

    Several phosphonium and ammonium triarylborohydrides, which are intermediates in hydrogenation reactions catalyzed by frustrated Lewis pairs, were synthesized in high yield under mild conditions from triaryl boranes, ammonium or phosphonium halides, and triethylsilane. The kinetics and mechanisms of the reactions of these hydridoborate salts with benzhydrylium ions, iminium ions, quinone methides, and Michael acceptors were investigated, and their nucleophilicity was determined and compared with that of other hydride donors.

  19. Pd(Quinox)-Catalyzed Allylic Relay Suzuki Reactions of Secondary Homostyrenyl Tosylates via Alkene-Assisted Oxidative Addition.

    PubMed

    Stokes, Benjamin J; Bischoff, Amanda J; Sigman, Matthew S

    2014-06-01

    Pd-catalyzed allylic relay Suzuki cross-coupling reactions of secondary alkyl tosylates, featuring a sterically-hindered oxidative addition and precise control of β-hydride elimination, are reported. The identification of a linear free energy relationship between the relative rates of substrate consumption and the electronic nature of the substrate alkene suggests that the oxidative addition requires direct alkene involvement. A study of the effect of chain length on the reaction outcome supports a chelation-controlled oxidative addition.

  20. A novel synthesis of 2-aryl-2H-indazoles via a palladium-catalyzed intramolecular amination reaction.

    PubMed

    Song, J J; Yee, N K

    2000-02-24

    [reaction: see text] A variety of 2-aryl-2H-indazoles were synthesized by the palladium-catalyzed intramolecular amination of the corresponding N-aryl-N(o-bromobenzyl)hydrazines. Of several sets of reaction conditions surveyed, the combination of Pd(OAc)2/dppf/tBuONa gave the best results. This method applies to a wide scope of substrates containing electron-donating and electron-withdrawing substituents.

  1. Pd(0)-Catalyzed PMHS reductions of aromatic acid chlorides to aldehydes.

    PubMed

    Lee, Kyoungsoo; Maleczka, Robert E

    2006-04-27

    [reaction: see text] Contrary to previous reports, polymethylhydrosiloxane (PMHS) under Pd(0) catalysis can efficiently reduce aryl acid chlorides to their corresponding aldehydes without requiring an additional reductant, provided the reactions are run in the presence of fluoride.

  2. Grape skins (Vitis vinifera L.) catalyze the in vitro enzymatic hydroxylation of p-coumaric acid to caffeic acid.

    PubMed

    Arnous, Anis; Meyer, Anne S

    2009-12-01

    The ability of grape skins to catalyze in vitro conversion of p-coumaric acid to the more potent antioxidant caffeic acid was studied. Addition of different concentrations of p-coumaric to red grape skins (Cabernet Sauvignon) resulted in formation of caffeic acid. This caffeic acid formation (Y) correlated positively and linearly to p-coumaric acid consumption (X): Y = 0.5 X + 9.5; R (2) = 0.96, P < 0.0001. The kinetics of caffeic acid formation with time in response to initial p-coumaric acid levels and at different grape skin concentrations, indicated that the grape skins harboured an o-hydroxylation activity, proposedly a monophenol- or a flavonoid 3'-monooxygenase activity (EC 1.14.18.1 or EC 1.14.13.21). The K (m) of this crude o-hydroxylation activity in the red grape skin was 0.5 mM with p-coumaric acid.

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

    PubMed

    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.

  4. Knoevenagel reaction in water catalyzed by amine supported on silica gel.

    PubMed

    Isobe, Kohei; Hoshi, Takashi; Suzuki, Toshio; Hagiwara, Hisahiro

    2005-01-01

    An environmentally benign and sustainable Knoevenagel reaction of aldehyde with ethyl cyanoacetate has been achieved at ambient temperature in water employing 3-aminopropylated silica gel (NAP) as a catalyst. Wide applicability of the reaction is illustrated by the results that not only arylaldehydes of both electronic characters but also aliphatic aldehydes afforded the products. The reaction condition was so mild that aldehydes having acid- or base-sensitive substituents provided substituted alpha-cyano-alpha, beta-unsaturated esters. The catalyst has been efficiently recycled more than five times without any pre-treatment. Catalyst loading was successfully reduced to 0.0029 mmol% (TON = up to 9,226). This protocol was also applicable to the Knoevenagel reaction of malononitrile in good yields in water.

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

    PubMed

    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.

  6. Iodine-Catalyzed Polysaccharide Esterification

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A review is provided of the recent reports to use iodine-catalyzed esterification reaction to produce esters from polysaccharides. The process entails reaction of the polysaccharide with an acid anhydride in the presence of a catalytic level of iodine, and in the absence of additional solvents. T...

  7. Trypsin-catalyzed multicomponent reaction: A novel and efficient one-pot synthesis of thiazole-2-imine derivatives.

    PubMed

    Zhou, Junbin; Huang, Xingtian; Zhang, Zhuan; Song, Ping; Li, Yiqun

    2017-01-10

    The first Trypsin from porcine pancreas catalyzed a novel one-pot three-component reaction of α-bromoketone, primary alkylamines, and phenylisothiocyanate for the synthesis of thiazole-imine derivatives with high yields (up to 98%) in a short time under mild conditions. The results revealed that Trypsin exhibited excellent catalytic activity and great tolerance for broad substrates. This Trypsin-catalyzed three component convergent method provides a novel strategy for the synthesis of thiazole-2-imine derivatives and expands the promiscuous functions of enzymes in organic synthesis.

  8. DNA and Protein Requirements for Substrate Conformational Changes Necessary for Human Flap Endonuclease-1-catalyzed Reaction.

    PubMed

    Algasaier, Sana I; Exell, Jack C; Bennet, Ian A; Thompson, Mark J; Gotham, Victoria J B; Shaw, Steven J; Craggs, Timothy D; Finger, L David; Grasby, Jane A

    2016-04-08

    Human flap endonuclease-1 (hFEN1) catalyzes the essential removal of single-stranded flaps arising at DNA junctions during replication and repair processes. hFEN1 biological function must be precisely controlled, and consequently, the protein relies on a combination of protein and substrate conformational changes as a prerequisite for reaction. These include substrate bending at the duplex-duplex junction and transfer of unpaired reacting duplex end into the active site. When present, 5'-flaps are thought to thread under the helical cap, limiting reaction to flaps with free 5'-terminiin vivo Here we monitored DNA bending by FRET and DNA unpairing using 2-aminopurine exciton pair CD to determine the DNA and protein requirements for these substrate conformational changes. Binding of DNA to hFEN1 in a bent conformation occurred independently of 5'-flap accommodation and did not require active site metal ions or the presence of conserved active site residues. More stringent requirements exist for transfer of the substrate to the active site. Placement of the scissile phosphate diester in the active site required the presence of divalent metal ions, a free 5'-flap (if present), a Watson-Crick base pair at the terminus of the reacting duplex, and the intact secondary structure of the enzyme helical cap. Optimal positioning of the scissile phosphate additionally required active site conserved residues Tyr(40), Asp(181), and Arg(100)and a reacting duplex 5'-phosphate. These studies suggest a FEN1 reaction mechanism where junctions are bound and 5'-flaps are threaded (when present), and finally the substrate is transferred onto active site metals initiating cleavage.

  9. Dynamic and Electrostatic Effects on the Reaction Catalyzed by HIV-1 Protease.

    PubMed

    Krzemińska, Agnieszka; Moliner, Vicent; Świderek, Katarzyna

    2016-12-21

    HIV-1 Protease (HIV-1 PR) is one of the three enzymes essential for the replication process of HIV-1 virus, which explains why it has been the main target for design of drugs against acquired immunodeficiency syndrome (AIDS). This work is focused on exploring the proteolysis reaction catalyzed by HIV-1 PR, with special attention to the dynamic and electrostatic effects governing its catalytic power. Free energy surfaces for all possible mechanisms have been computed in terms of potentials of mean force (PMFs) within hybrid QM/MM potentials, with the QM subset of atoms described at semiempirical (AM1) and DFT (M06-2X) level. The results suggest that the most favorable reaction mechanism involves formation of a gem-diol intermediate, whose decomposition into the product complex would correspond to the rate-limiting step. The agreement between the activation free energy of this step with experimental data, as well as kinetic isotope effects (KIEs), supports this prediction. The role of the protein dynamic was studied by protein isotope labeling in the framework of the Variational Transition State Theory. The predicted enzyme KIEs, also very close to the values measured experimentally, reveal a measurable but small dynamic effect. Our calculations show how the contribution of dynamic effects to the effective activation free energy appears to be below 1 kcal·mol(-1). On the contrary, the electric field created by the protein in the active site of the enzyme emerges as being critical for the electronic reorganization required during the reaction. These electrostatic properties of the active site could be used as a mold for future drug design.

  10. Gallic Acid, Ellagic Acid and Pyrogallol Reaction with Metallic Iron

    NASA Astrophysics Data System (ADS)

    Jaén, J. A.; González, L.; Vargas, A.; Olave, G.

    2003-06-01

    The reaction between gallic acid, ellagic acid and pyrogallol with metallic iron was studied using infrared and Mössbauer spectroscopy. Most hydrolysable tannins with interesting anticorrosive or inhibition properties are structurally related to these compounds, thus they may be used as models for the study of hydrolysable tannins and related polyphenols. The interaction was followed up to 3 months. Results indicated two different behaviors. At polyphenol concentrations higher than 1% iron converts to sparingly soluble and amorphous ferric (and ferrous) polyphenolate complexes. At lower concentrations (0.1%), the hydrolysis reactions are dominant, resulting in the formation of oxyhydroxides, which can be further reduced to compounds like magnetite by the polyphenols.

  11. Noble metal-catalyzed homogeneous and heterogeneous processes in treating simulated nuclear waste media with formic acid

    SciTech Connect

    King, R.B.; Bhattacharyya, N.K.; Smith, H.D.

    1995-09-01

    Simulants for the Hanford Waste Vitrification Plant feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO{sub 3}{sup 2}-, NO{sub 3}-, and NO{sub 2}- were used to study reactions of formic acid at 90{degrees}C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the CO{sub 2}, H{sub 2}, NO, and N{sub 2}O in the gas phase and a microammonia electrode to analyze the NH{sub 4}+/NH{sub 3} in the liquid phase as a function of time. The following reactions have been studied in these systems since they are undesirable side reactions in nuclear waste processing: (1) Decomposition of formic acid to CO{sub 2} + H{sub 2} is undesirable because of the potential fire and explosion hazard of H{sub 2}. Rhodium, which was introduced as soluble RhCl{sub 3}-3H{sub 2}O, was found to be the most active catalyst for H{sub 2} generation from formic acid above {approximately} 80{degrees}C in the presence of nitrite ion. The H{sub 2} production rate has an approximate pseudo first-order dependence on the Rh concentration, (2) Generation of NH{sub 3} from the formic acid reduction of nitrate and/or nitrite is undesirable because of a possible explosion hazard from NH{sub 4}NO{sub 3} accumulation in a waste processing plant off-gas system. The Rh-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was found to exhibit the following features: (a) Nitrate rather than nitrite is the principal source of NH{sub 3}. (b) Ammonia production occurs at the expense of hydrogen production. (c) Supported rhodium metal catalysts are more active than rhodium in any other form, suggesting that ammonia production involves heterogeneous rather than homogeneous catalysis.

  12. Boron-Catalyzed N-Alkylation of Amines using Carboxylic Acids.

    PubMed

    Fu, Ming-Chen; Shang, Rui; Cheng, Wan-Min; Fu, Yao

    2015-07-27

    A boron-based catalyst was found to catalyze the straightforward alkylation of amines with readily available carboxylic acids in the presence of silane as the reducing agent. Various types of primary and secondary amines can be smoothly alkylated with good selectivity and good functional-group compatibility. This metal-free amine alkylation was successfully applied to the synthesis of three commercial medicinal compounds, Butenafine, Cinacalcet. and Piribedil, in a one-pot manner without using any metal catalysts.

  13. CHLORINATION OF AMINO ACIDS: REACTION PATHWAYS AND REACTION RATES.

    PubMed

    How, Zuo Tong; Linge, Kathryn; Busetti, Francesco; Joll, Cynthia A

    2017-03-15

    Chlorination of amino acids can result in the formation of organic monochloramines or organic dichloramines, depending on the chlorine to amino acid ratio (Cl:AA). After formation, organic chloramines degrade into aldehydes, nitriles and N-chloraldimines. In this paper, the formation of organic chloramines from chlorination of lysine, tyrosine and valine were investigated. Chlorination of tyrosine and lysine demonstrated that the presence of a reactive secondary group can increase the Cl:AA ratio required for the formation of N,N-dichloramines, and potentially alter the reaction pathways between chlorine and amino acids, resulting in the formation of unexpected by-products. In a detailed investigation, we report rate constants for all reactions in the chlorination of valine, for the first time, using experimental results and modelling. At Cl:AA = 2.8, the chlorine was found to first react quickly with valine (5.4x104 M-1 s-1) to form N-monochlorovaline, with a slower subsequent reaction with N-monochlorovaline to form N,N-dichlorovaline (4.9x102 M-1 s-1), although some N-monochlorovaline degraded into isobutyraldehyde (1.0x10-4 s-1). The N,N-dichlorovaline then competitively degraded into isobutyronitrile (1.3x10-4 s-1) and N-chloroisobutyraldimine (1.2x10-4 s-1). In conventional drinking water disinfection, N-chloroisobutyraldimine can potentially be formed in concentrations higher than its odour threshold concentration, resulting in aesthetic challenges and an unknown health risk.

  14. Impact of copper-catalyzed cross-coupling reactions in natural product synthesis: the emergence of new retrosynthetic paradigms.

    PubMed

    Evano, Gwilherm; Theunissen, Cédric; Pradal, Alexandre

    2013-12-01

    Copper-catalyzed Ullmann-Goldberg-type cross-coupling reactions have undergone nothing short of a renaissance over the last decade and an impressive number of procedures are now available for the formation of C-N, C-O and C-S bonds with remarkable efficiencies and surgical precision. These reactions have been recently integrated into natural product synthesis, which clearly resulted in the emergence of new retrosynthetic paradigms and bond disconnections. The impact of copper-catalyzed cross-coupling reactions in natural product synthesis will be overviewed in this article with an emphasis on the evolution of strategies due to copper catalysis, mostly by comparison with alternative tactics and their relative efficiencies.

  15. Pd(II)-Catalyzed C–H Activation/C–C Cross-Coupling Reactions: Versatility and Practicality

    PubMed Central

    Chen, Xiao; Engle, Keary M.; Wang, Dong-Hui; Yu, Jin-Quan

    2009-01-01

    In the past decade, palladium-catalyzed C–H activation/C–C bond forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming C–C bonds from C–H bonds: Pd(II)/Pd(0), Pd(II)/Pd(IV), Pd(0)/Pd(II)/Pd(IV) and Pd(0)/Pd(II) catalysis. More detailed discussion is then directed towards the recent development of Pd(II)-catalyzed coupling of C–H bonds with organometallic reagents through a Pd(II)/Pd(0) catalytic cycle. Despite much progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge. PMID:19557755

  16. Acetic acid-catalyzed formation of N-phenylphthalimide from phthalanilic acid: a computational study of the mechanism.

    PubMed

    Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

    2015-05-28

    In glacial acetic acid, phthalanilic acid and its monosubstituents are known to be converted to the corresponding phthalimides in relatively good yields. In this study, we computationally investigated the experimentally proposed two-step (addition-elimination or cyclization-dehydration) mechanism at the second-order Møller-Plesset perturbation (MP2) level of theory for the unsubstituted phthalanilic acid, with an explicit acetic acid molecule included in the calculations. In the first step, a gem-diol tetrahedral intermediate is formed by the nucleophilic attack of the amide nitrogen. The second step is dehydration of the intermediate to give N-phenylphthalimide. In agreement with experimental findings, the second step has been shown to be rate-determining. Most importantly, both of the steps are catalyzed by an acetic acid molecule, which acts both as proton donor and acceptor. The present findings, along with those from our previous studies, suggest that acetic acid and other carboxylic acids (in their undissociated forms) can catalyze intramolecular nucleophilic attacks by amide nitrogens and breakdown of the resulting tetrahedral intermediates, acting simultaneously as proton donor and acceptor. In other words, double proton transfers involving a carboxylic acid molecule can be part of an extensive bond reorganization process from cyclic hydrogen-bonded complexes.

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

    PubMed Central

    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

  18. Investigating Students' Reasoning about Acid-Base Reactions

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Kouyoumdjian, Hovig; Underwood, Sonia M.

    2016-01-01

    Acid-base chemistry is central to a wide range of reactions. If students are able to understand how and why acid-base reactions occur, it should provide a basis for reasoning about a host of other reactions. Here, we report the development of a method to characterize student reasoning about acid-base reactions based on their description of…

  19. The Acid Hydrolysis Mechanism of Acetals Catalyzed by a Supramolecular Assembly in Basic Solution

    SciTech Connect

    Pluth, Michael D.; Bergman, Robert G.; Raymond, Kenneth N.

    2008-09-24

    A self-assembled supramolecular host catalyzes the hydrolysis of acetals in basic aqueous solution. The mechanism of hydrolysis is consistent with the Michaelis-Menten kinetic model. Further investigation of the rate limiting step of the reaction revealed a negative entropy of activation ({Delta}S{double_dagger} = -9 cal mol{sup -1}K{sup -1}) and an inverse solvent isotope effect (k(H{sub 2}O)/k(D{sub 2}O) = 0.62). These data suggest that the mechanism of hydrolysis that takes place inside the assembly proceeds through an A-2 mechanism, in contrast to the A-1 mechanism operating in the uncatalyzed reaction. Comparison of the rates of acetal hydrolysis in the assembly with the rate of the reaction of unencapsulated substrates reveals rate accelerations of up to 980 over the background reaction for the substrate diethoxymethane.

  20. Semicontinuous measurements of organic carbon and acidity during the Pittsburgh air quality study: implications for acid-catalyzed organic aerosol formation

    SciTech Connect

    S. Takahama; C.I. Davidson; S.N. Pandis

    2006-04-01

    Laboratory evidence suggests that inorganic acid seed particles may increase secondary organic aerosol yields secondary organic aerosol (SOA) through heterogeneous chemistry. Additional laboratory studies, however, report that organic acidity generated in the same photochemical process by which SOA is formed may be sufficient to catalyze these heterogeneous reactions. Understanding the interaction between inorganic acidity and SOA mass is important when evaluating emission controls to meet PM2.5 regulations. Semicontinuous measurements of organic carbon (OC), elemental carbon (EC), and inorganic species from the Pittsburgh Air Quality Study were examined to determine if coupling in the variations of inorganic acidity and OC could be detected. Significant enhancements of SOA production could not be detected due to inorganic acidity in Western Pennsylvania most of the time, but its signal might have been lost in the noise. If a causal relationship between inorganic acidity and OC is assumed, reductions in OC for Western Pennsylvania that might result from drastic reductions in inorganic acidity were estimated to be 2 {+-} 4% by a regression technique, and an upper bound for this geographic area was estimated to be 5 {+-} 8% based on calculations from laboratory measurements. 48 refs., 7 figs., 3 tabs.