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1

Mukaiyama Aldol Reactions in Aqueous Media  

PubMed Central

Mukaiyama aldol reactions in aqueous media have been surveyed. While the original Mukaiyama aldol reactions entailed stoichiometric use of Lewis acids in organic solvents under strictly anhydrous conditions, Mukaiyama aldol reactions in aqueous media are not only suitable for green sustainable chemistry but are found to produce singular phenomena. These findings led to the discovery of a series of water-compatible Lewis acids such as lanthanide triflates in 1991. Our understanding on these beneficial effects in the presence of water will be deepened through the brilliant examples collected in this review. 1 Introduction 2 Rate Enhancement by Water in the Mukaiyama Aldol Reaction 3 Lewis Acid Catalysis in Aqueous or Organic Solvents 3.1 Water-Compatible Lewis Acids 4 Lewis-Base Catalysis in Aqueous or Organic Solvents 5 The Mukaiyama Aldol Reactions in 100% Water 6 Asymmetric Catalysts in Aqueous Media and Water 7 Conclusions and Perspective PMID:24971045

Kitanosono, Taku; Kobayashi, Shu

2013-01-01

2

Enantioselective relay catalytic cascade intramolecular hydrosiloxylation and Mukaiyama aldol reaction.  

PubMed

Cascading chemistry! The first practical relay catalytic cascade intramolecular hydrosiloxylation of arylacetylene and asymmetric Mukaiyama aldol reaction has been established to give synthetically useful products in high yields and with excellent ee (see scheme). PMID:23526692

Wang, Pu-Sheng; Li, Kang-Nan; Zhou, Xiao-Le; Wu, Xiang; Han, Zhi-Yong; Guo, Rui; Gong, Liu-Zhu

2013-05-10

3

Asymmetric vinylogous Mukaiyama aldol reaction of aldehyde-derived dienolates.  

PubMed

Unsaturated aldehydes are exquisite building blocks for further transformations in polyketide synthesis. Besides standard transformations that take advantage of the aldehyde functionality, the conjugate addition of hydrides followed by internal protonation allows access to alpha chiral aldehydes. Even though vinylogous Mukaiyama aldol reactions have been used in natural product syntheses before, the first enantioselective Mukaiyama aldol reaction of aldehyde-derived dienolates is described. PMID:21473644

Gieseler, Marc T; Kalesse, Markus

2011-05-01

4

The vinylogous Mukaiyama aldol reaction (VMAR) in natural product synthesis.  

PubMed

The vinylogous Mukaiyama aldol reaction (VMAR) allows efficient access to larger segments for complex natural product synthesis, primarily polyketides, through the construction of vicinal hydroxyl and methyl groups as well as di and tri-substituted double bonds in one single operation. In this review, we will highlight stereoselective protocols that have been used in natural product synthesis and cluster them into the four groups that can be obtained from different silyl ketene acetals or enol ethers. At the beginning, an overview on different stereoselective VMARs is presented; disregarding their applications in total syntheses. PMID:24595879

Kalesse, Markus; Cordes, Martin; Symkenberg, Gerrit; Lu, Hai-Hua

2014-04-01

5

Highly enantioselective Mukaiyama aldol reaction in aqueous conditions using a chiral iron(II) bipyridine catalyst.  

PubMed

A highly enantioselective method for the catalytic Mukaiyama aldol reaction of silyl enol ethers with aldehydes in aqueous conditions was developed. The desired aldol products were obtained in excellent yields, diastereo- and enantioselectivities. Structural evidence of the pre-catalyst revealed an unprecedented heptadentate Fe(II) complex with the chiral bipyridine ligand. PMID:22080154

Ollevier, Thierry; Plancq, Baptiste

2012-02-25

6

Lewis base catalysis of the Mukaiyama directed aldol reaction: 40 years of inspiration and advances.  

PubMed

Since the landmark publications of the first directed aldol addition reaction in 1973, the site, diastereo-, and enantioselective aldol reaction has been elevated to the rarefied status of being both a named and a strategy-level reaction (the Mukaiyama directed aldol reaction). The importance of this reaction in the stereoselective synthesis of untold numbers of organic compounds, both natural and unnatural, cannot be overstated. However, its impact on the field extends beyond the impressive applications in synthesis. The directed aldol reaction has served as a fertile proving ground for new concepts and new methods for stereocontrol and catalysis. This Minireview provides a case history of how the challenges of merging site selectivity, diastereoselectivity, enantioselectivity, and catalysis into a unified reaction manifold stimulated the development of Lewis base catalyzed aldol addition reactions. The evolution of this process is chronicled from the authors' laboratories as well as in those of Professor Teruaki Mukaiyama. PMID:23843275

Beutner, Gregory L; Denmark, Scott E

2013-08-26

7

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis  

Microsoft Academic Search

BACKGROUND: The diastereoselectivity of a vinylogous Mukaiyama aldol reaction of a series of N-substituted 4-oxy-2-trimethylsilyloxypyrroles with a tartrate-based aldehyde has been explored as a model reaction for castanospermine synthesis. RESULTS: The study has revealed that the reaction is sensitive to the nature of the combination of N- and 4-oxy substituents. With a N-PMB or N-Bn and 4-methoxy combination, the reaction

Roger Hunter; Sophie CM Rees-Jones; Hong Su

2007-01-01

8

Total Synthesis of Leucascandrolide A: A New Application of the Mukaiyama Aldol-Prins Reaction  

PubMed Central

A total synthesis of the marine natural product leucascandrolide A has been completed. The titanium tetrabromide-mediated Mukaiyama aldol-Prins (MAP) reaction with aldehydes developed in our group provided a highly convergent and stereoselective method for assembling the core of the molecule. A new class of MAP reactions with acetals is introduced and mechanistic considerations for both MAP methods are described. The total synthesis was completed by coupling of the side chain through two avenues: A known Still–Gennari olefination and a new Z-selective aldol/dehydroselenation reaction. Both procedures were highly selective and provided the natural product. PMID:17595145

Van Orden, Lori J.; Patterson, Brian D.; Rychnovsky, Scott D.

2008-01-01

9

Chemoselective silyl transfer in the Mukaiyama aldol reaction promoted by super silyl Lewis acid.  

PubMed

In the silyl Lewis acid-promoted Mukaiyama aldol reaction, the steric and electronic properties of the silyl group on the silyl Lewis acid influence the reaction mechanism and product distribution. When super silyl triflates such as (TMS)3SiOTf and (TES)3SiOTf are used as Lewis acids, the silyl group of the silyl enol ether chemoselectively transfers to the product. The mechanistic details have been investigated using density functional theory (DFT) calculations. PMID:25338752

Sai, Masahiro; Akakura, Matsujiro; Yamamoto, Hisashi

2014-11-01

10

Diastereoselectivity in Lewis-Acid Catalyzed Mukaiyama Aldol Reactions: A DFT Study  

PubMed Central

The basis for diastereoselectivity in Lewis acid-catalyzed Mukaiyama aldol reactions was studied using density functional theory. By exploring the conformations of the transition structures for the diastereodifferentiating step of seven different reactions, simple models were generated. The effects of varying the substituents on the enol carbon and the ?-carbon of the silyl enol ether from methyl to tert-butyl groups and the substituent on the aldehyde between methyl and phenyl groups were investigated by comparison of the transition structures for different reactions. Expanding on the previous qualitative models by Heathcock and Denmark, we found that while the pro-anti pathways takes place via antiperiplanar transition structures, the pro-syn pathways prefer synclinal transition structures. The relative steric effects of the Lewis acid and trimethyl silyl groups and the influence of E/Z isomerism on the aldol transition state were investigated. By calculating 36 transition structures at the M06/6-311G*//B3LYP/6-31G* level of theory and employing the IEFPCM polarizable continuum model for solvation effects, this study expands the mechanistic knowledge and provides a model for understanding the diastereoselectivity in Lewis acid-catalyzed Mukaiyama aldol reactions. PMID:22891640

Lee, Joshua M.; Helquist, Paul; Wiest, Olaf

2012-01-01

11

A New Class of Ligands for Aqueous, Lanthanide-Catalyzed, Enantioselective Mukaiyama Aldol Reactions  

PubMed Central

The development of aqueous methods to generate enantiopure ?-hydroxy carbonyl compounds is an important goal because these subunits compose many bioactive compounds, and the ability to synthesis these groups in water has environmental and cost benefits. In this communication, we report a new class of ligands for aqueous, lanthanide-catalyzed, asymmetric Mukaiyama aldol reactions to synthesize chiral ?-hydroxy ketones. Furthermore, we use luminescence-decay measurements to unveil mechanistic information regarding the catalytic reaction via changes of water-coordination number. The precatalysts presented here yielded ?-hydroxy carbonyls from aliphatic and aryl substrates with outstanding syn:anti ratios and enantiometric excesses of up to 49:1 and 97%. PMID:20806902

Mei, Yujiang; Dissanayake, Prabani; Allen, Matthew J.

2010-01-01

12

Having played a key role in such powerful reactions as the Mukaiyama aldol and the Nobel prize winning Sharpless  

E-print Network

metal salt and thus enhance the rate and selectivity of nucleophilic substitution reactions," explained as the chelating arm. The rate study of nucleophilic substitution reactions of NALGs sulfo- nate ester of alcoholHaving played a key role in such powerful reactions as the Mukaiyama aldol and the Nobel prize

Lepore, Salvatore D.

13

Combined C-H functionalization/Cope rearrangement with vinyl ethers as a surrogate for the vinylogous Mukaiyama aldol reaction.  

PubMed

Vinyl ethers selectively undergo the combined C-H functionalization/Cope rearrangement reaction via an s-cis/boat transition state. With chiral dirhodium catalysts, products are generated in a highly diastereoselective and enantioselective fashion. This reaction can be considered as a surrogate to the traditional vinylogous Mukaiyama aldol reaction. Effective kinetic resolution has been achieved, leading to the recovery of a cyclic vinyl ether with axial chirality of high enantiomeric purity. PMID:21739977

Lian, Yajing; Davies, Huw M L

2011-08-10

14

Synthesis of Poly(Ethylene Glycol)–Supported (R)-BINOL Derivatives and Their First Application in Enantioselective Mukaiyama Aldol Reactions  

Microsoft Academic Search

The Mukaiyama aldol reaction of 2-styryl-oxazole-4-carbaldehyde (1) as model substrate with S-ketene silyl acetal 2 catalyzed by poly(ethylene glycol)-supported binaphthyl-derived chiral titanium(IV) complexes afforded the corresponding aldol product in good to excellent yields and enantioselectivities up to 94% ee. The chemical yields and\\/or the enantioselectivities are enhanced by generating the active catalyst from Ti(OiPr)4, polymer-supported ligands (R)-6 or (R)-8, and

Reinhold Zimmer; Vjekoslav Dekaris; Markus Knauer; Luise Schefzig; Hans-Ulrich Reissig

2009-01-01

15

FeCl3·6H2O-Catalyzed Mukaiyama-Aldol Type Reactions of Enolizable Aldehydes and Acetals.  

PubMed

Mukaiyama-aldol type reactions of acetals derived from enolizable aldehydes with FeCl3·6H2O, an eco-friendly, low-cost, and stable catalyst, lead to ?-methoxycarbonyl compounds with nearly quantitative yields. The methodology is extended to the parent aldehydes as starting materials, leading to the corresponding aldols with lower yields, but efficiently. Different alkyl and aryl substituted acetals and aldehydes have been tested in the reaction with linear and cyclic silyl enol ethers. Reactions are carried out in an open air atmosphere, and additives are not required. Acetals can be considered activating groups of the carbonyl moiety rather than a protecting group in this type of FeCl3·6H2O-catalyzed condensation. PMID:25102027

Rodríguez-Gimeno, Alejandra; Cuenca, Ana B; Gil-Tomás, Jesús; Medio-Simón, Mercedes; Olmos, Andrea; Asensio, Gregorio

2014-09-01

16

Lewis Acid-Promoted Mukaiyama Aldol-Prins (MAP) Cyclizations of Acetals, Ketals, ?-Acetoxy Ethers, and Orthoformates  

PubMed Central

The Mukaiyama aldol–Prins (MAP) cyclization of acetals stereoselectively provided substituted tetrahydropyrans. The scope of the reaction has been expanded to include other electrophiles, including ketals and ?-acetoxy ethers. Finally, a double MAP cyclization with orthoformates is described. PMID:20936058

Gesinski, Michael R.; Van Orden, Lori J.; Rychnovsky, Scott D.

2009-01-01

17

Organolanthanide reagents and the Mukaiyama reaction  

SciTech Connect

The bis(pentamethylcyclopentadienyl) lutetium halide complex ((C/sub 5/Me/sub 5/)/sub 2/LuCl/center dot/THF) was synthesized and characterized. The crystal structure of this complex shows that the Lu is at the center of a distorted tetrahedron consisting of the centroids of two cyclopentadienyl rings, the oxygen atom of a tetrahydrofuran molecule and a chlorine atom. /sup 1/H NMR studies of toluene-d/sub 8/ solutions of (C/sub 5/Me/sub 5/LuCl(THF) + THF, (TMS/sub 2/CP)/sub 2/LuCl(THF) + THF, and (MeCp)/sub 2/LuCl(THF) + THF at various temperatures showed exchange processes between co- ordinated THF and free THF with average values of ..delta..G/sup ne/ of 13.0 /+-/ 0.3 kcal/mol, 11.1 /+-/ 0.1 kcal/mol and <11 kcal/mol at 0/degree/C, respectively. It has been found that under the influence of a catalytic amount (1--5 mol %) of (TMS/sub 2/Cp)/sub 2/YbCl dimer, silyl enol ethers (R/sub 1/R/sub 2/C = C(OR/sub 3/)OSiMe/sub 3/)) react with benzaldehyde smoothly in dichloromethane at room temperature, giving >99% of the aldol silyl ether (isolated yield: 90%) within 3 h. At /minus/78/degrees/C, the reaction gives kinetically controlled diastereoselectivity, which was not observed in the TiCl/sub 4/-mediated aldol reaction. The use of organoytterbium enolates shows promise result with respect to increased stereoselectivity, and indicates the importance of the bulky ligands on the metal center. In addition, Yb(III) species can retard retroaldol reaction owing to its mild Lewis acidity. 118 refs., 14 figs., 30 tabs.

Gong, L.

1989-01-01

18

Diastereoselective, Three-Component, Cascade Synthesis of Tetrahydrofurans and Tetrahydropyrans Employing the Tandem Mukaiyama Aldol-Lactonization (TMAL) Process  

PubMed Central

A full account of studies leading to the development of a cascade sequence that generates as many as 2 C-C bonds, 1 C-O bond, and three new stereocenters providing substituted tetrahydrofurans (THFs) from simple ?-ketoaldehydes and thiopyridyl ketene acetals is described. The process involves a tandem Mukaiyama aldol-lactonization (TMAL) and accumulated evidence suggests the intermediacy of a silylated ?-lactone that is intercepted by the pendant ketone. Formation of a cyclic oxocarbenium is followed by reduction with silicon-based nucleophiles leading to a highly diastereoselective synthesis of tetrahydrofurans. This cascade process has now been extended to the synthesis of tetrahydropyrans from simple ?-ketoaldehydes. The stereochemical outcome of the cascade processes described was determined by NOE correlations, coupling constant analysis, and x-ray crystallography of the derived oxygen heterocycles and is in accord with established and recently proposed models for nucleophilic additions to cyclic 5- and 6-membered oxocarbenium ions. The utility of this process was demonstrated by the synthesis of the tetrahydrofuran fragment of colopsinol B. PMID:19053579

Mitchell, T. Andrew; Zhao, Cunxiang; Romo, Daniel

2009-01-01

19

Organolanthanide catalysis of Mukaiyama addition reaction  

SciTech Connect

Bis(bis(1,3-trimethylsilyl)cyclopentadienyl)ytterbium(III) chloride, Cp{double prime}{sub 2}YbCl, 2, is an effective catalyst in the presence of additional trimethylsiyl chloride for the reaction of silyl ester enolates, such as the trimethylsilyl enolate of methyl isobutyrate, 1, with aliphatic and aromatic aldehydes, to yield {beta}-silyoxy esters. The reaction shows good diastereoselection that is readily rationalized with a cyclic transition-state mechanism in which a key feature is the important role played by restricted coordination space around the lanthanide cation.

Lehi Gong; Streitwieser, A. (Lawrence Berkeley Lab., CA (United States))

1990-12-21

20

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two ? position(s) of a carbonyl group) with high diastereo- and enantioselectivities. PMID:23828817

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-08-01

21

The Direct Catalytic Asymmetric Aldol Reaction  

PubMed Central

Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets PMID:20419212

Brindle, Cheyenne S.

2013-01-01

22

4,5- erythro\\/5,6- threo-Stereoselectivity in vinylogous Mukaiyama aldol addition of a silyloxypyrrole to a threose derivative: stereochemical rationalization and relevance to (+)-castanospermine synthesis  

Microsoft Academic Search

Vinylogous Mukaiyama aldol addition of N-p-methoxybenzyl-4-methoxy-2-trimethylsilyloxypyrrole 7 to bis-MOM threose 6 using SnCl4 as promoter gave the 4,5-erythro\\/5,6-threo adduct 8, with the correct absolute configurations for the castanospermine framework as determined by a single-crystal X-ray structure. A transition-state model is presented to rationalize the stereoselectivity.

Roger Hunter; Sophie C. M. Rees-Jones; Hong Su

2007-01-01

23

New approaches toward the synthesis of (D-homo) steroid skeletons using Mukaiyama reactions  

Microsoft Academic Search

New, short, and flexible procedures have been developed for syntheses of steroid and D-homo steroid skeletons. A Mukaiyama reaction between the silyl enol ether of 6-methoxytetralone and 2-methyl-2-cyclopentenone or carvone, with transfer of the silyl group to the receiving enone, gave a second silyl enol ether. Addition of a carbocation, generated under Lewis acid conditions from 3-methoxy-2-butenol, 3-ethoxy-3-phenyl-2-propenol or 3-methoxy-2-propenol

Florence C. E. Sarabèr; Alexander Baranovsky; Ben J. M. Jansen; Maarten A. Posthumus; Aede de Groot

2006-01-01

24

Asymmetric Disulfonimide-Catalyzed Synthesis of ?-Amino-?-Ketoester Derivatives by Vinylogous Mukaiyama-Mannich Reactions.  

PubMed

An organocatalytic asymmetric synthesis of ?-amino-?-ketoester derivatives has been developed. A chiral disulfonimide (DSI) serves as a highly efficient precatalyst for a vinylogous Mukaiyama-Mannich reaction of readily available dioxinone-derived silyloxydienes with N-Boc-protected imines, delivering products in excellent yields and enantioselectivities. The synthetic utility of this reaction is illustrated in various transformations, including a new C?C bond-forming reaction, which provide useful enantioenriched building blocks. The methodology is applied in a formal synthesis of (-)-lasubin. PMID:25348924

Wang, Qinggang; van Gemmeren, Manuel; List, Benjamin

2014-12-01

25

Direct enantioselective aldol-Tishchenko reaction catalyzed by chiral lithium diphenylbinaphtholate.  

PubMed

Chiral lithium diphenylbinaphtholate is an effective catalyst for the enantioselective aldol-Tishchenko reaction, affording 1,3-diol derivatives with three contiguous chiral centers and high stereoselectivities. Successive aldol-aldol-Tishchenko reactions gave a triol derivative with five consecutive chiral centers. The present reaction was applicable to highly enantioselective Evans-Tishchenko reduction. PMID:21355567

Ichibakase, Tomonori; Nakajima, Makoto

2011-04-01

26

Enantioselective organocatalytic aldol reaction of ynones and its synthetic applications.  

PubMed

[Structure: see text] For the first time, unmodified ynones were used in organocatalytic asymmetric aldol reactions delivering monoprotected anti-alpha,beta-dihydroxyynones in high yields, dr's up to 19:1, and ee's up to 95%. These products can be either reduced to afford enantioenriched unsaturated anti,anti-triol or cyclized using a novel intramolecular phosphine-catalyzed alpha-addition to the ynone. This organocatalytic sequential aldol-cyclization process provides a concise entry to unusual enantioenriched oxygenated heterocycles, which can be used for subsequent structural manipulations. PMID:17078732

Silva, Franck; Sawicki, Marcin; Gouverneur, Véronique

2006-11-01

27

Catalytic enantioselective O-nitrosocarbonyl aldol reaction of ?-dicarbonyl compounds.  

PubMed

The first example of a Cu-catalyzed asymmetric O-nitrosocarbonyl aldol reaction is described. This novel protocol allows convenient access to highly enantioenriched ?-hydroxy-?-ketoesters including the antibacterial natural product kjellmanianone (up to 99% ee). MnO(2) was introduced as a mild efficient oxidant for the in situ generation of nitrosocarbonyl species from hydroxamic acid derivatives. PMID:23106266

Baidya, Mahiuddin; Griffin, Kimberly A; Yamamoto, Hisashi

2012-11-14

28

Catalytic Enantioselective O-Nitrosocarbonyl Aldol Reaction of ?-Dicarbonyl Compounds  

PubMed Central

The first example of Cu–catalyzed asymmetric O–nitrosocarbonyl aldol reaction is described. This novel protocol allows convenient access to highly enantioenriched ?–hydroxy–?–ketoesters including the antibacterial natural product kjellmanianone (up to 99% ee). MnO2 was introduced as a mild efficient oxidant for the in situ generation of nitrosocarbonyl species from hydroxamic acid derivatives. PMID:23106266

Baidya, Mahiuddin; Griffin, Kimberly A.; Yamamoto, Hisashi

2012-01-01

29

(Diisopinocampheyl)borane-Mediated Reductive Aldol Reactions of Acrylate Esters: Enantioselective Synthesis of Anti-Aldols  

PubMed Central

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). Results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R.

2013-01-01

30

(Diisopinocampheyl)borane-mediated reductive aldol reactions of acrylate esters: enantioselective synthesis of anti-aldols.  

PubMed

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-?-methyl-?-hydroxy esters 9 or 10 with excellent diastereo- (up to ?20:1 dr) and enantioselectivity (up to 87% ee). The results of double asymmetric reactions of 5E with several chiral aldehydes are also presented. PMID:23885946

Allais, Christophe; Nuhant, Philippe; Roush, William R

2013-08-01

31

Concise enantioselective synthesis of duloxetine via direct catalytic asymmetric aldol reaction of thioamide.  

PubMed

Direct catalytic asymmetric aldol reaction of thioamide offers a new entry to the concise enantioselective synthesis of duloxetine. The direct aldol protocol was scalable (>20 g) to afford the aldol product in 92% ee after LiAlH(4) reduction, and 84% of the chiral ligand was recovered after recrystallization. The following four steps of transformation delivered duloxetine. PMID:22494391

Suzuki, Yuta; Iwata, Mitsutaka; Yazaki, Ryo; Kumagai, Naoya; Shibasaki, Masakatsu

2012-05-01

32

Investigating Ionic Effects Applied to Water Based Organocatalysed Aldol Reactions  

PubMed Central

Saturated aqueous solutions of various common salts were examined for their effect on aqueous aldol reactions catalysted by a highly active C2-symmetric diprolinamide organocatalyst developed in our laboratory. With respect to the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde, deionised water was always a superior medium to salt solutions though some correlation to increasing anion size and depression in enantiomeric excess could be observed. Additionally, the complete inhibition of catalyst activity observed when employing tap water could be alleviated by the inclusion of ethylenediaminetetraacetate (EDTA) into the aqueous media prior to reaction initiation. Extension of these reaction conditions demonstrated that these ionic effects vary on a case-to-case basis depending on the ketone/aldehyde combination. PMID:22272120

Delaney, Joshua P.; Henderson, Luke C.

2011-01-01

33

(Diisopinocampheyl)borane-Mediated Reductive Aldol Reactions: Highly Enantio and Diastereoselective Synthesis of Syn-Aldols from N-Acryloylmorpholine**  

PubMed Central

An efficient and highly enantio- and diastereoselective synthesis of syn propionamide aldols is described. Formation of the Z-enolborinate via the hydroboration of 4-acryloylmorpholine with (diisopinocampheyl)borane followed by aldol reactions with representative achiral and chiral aldehydes provided syn-?-methyl-?-hydroxy morpholine carboxamides with excellent enantio- and diastereoselectivity (96–98% ee and d.r. >20:1). PMID:23818095

Nuhant, Philippe; Allais, Christophe

2013-01-01

34

Catalytic enantioselective N-nitroso aldol reaction of ?,?-unsaturated ?-lactones.  

PubMed

A catalytic asymmetric N-nitroso aldol reaction of ?,?-didehydro-?-lactones with nitrosoarenes was achieved using chiral tin dibromide as the chiral precatalyst and sodium ethoxide as the base precatalyst in the presence of ethanol. Optically active ?-hydroxyamino ketones with up to 99% ee were regioselectively obtained in moderate to high yields from various ?-aryl-substituted ?,?-didehydro-?-valerolactones and o-substituted nitrosoarenes. PMID:22568583

Yanagisawa, Akira; Fujinami, Takeo; Oyokawa, Yu; Sugita, Takuya; Yoshida, Kazuhiro

2012-05-18

35

Organocatalytic asymmetric aldol reaction of hydroxyacetone with ?,?-unsaturated ?-keto esters: facile access to chiral tertiary alcohols.  

PubMed

An efficient direct asymmetric aldol reaction between hydroxyacetone and ?,?-unsaturated ?-keto esters has been successfully developed. In the presence of 9-amino-9-deoxy-epi-cinchonine and trifluoroacetic acid, the direct aldol reaction of O-protected hydroxyacetone proceeded in a highly enantioselective manner, affording the desired adducts containing a chiral tertiary alcohol in high yields and with excellent enantioselectivities. The aldol products obtained are valuable precursors for the synthesis of 2-substituted glycerol derivatives. PMID:21902199

Liu, Chen; Dou, Xiaowei; Lu, Yixin

2011-10-01

36

Organocatalytic asymmetric direct vinylogous aldol reactions of ?-crotonolactone with aromatic aldehydes.  

PubMed

The direct aldol reaction of ?-crotonolactone and various aromatic aldehydes is catalyzed by bifunctional aminothiourea and aminosquaramide organocatalysts to provide diastereomerically and enantiomerically enriched 5-substituted 2(5H) furanones (?-butenolides). The reaction is a simple alternative to the classical vinylogous aldol reaction of silyloxy furans. PMID:21069217

Pansare, Sunil V; Paul, Eldho K

2011-01-21

37

Molecular recognition of ketomalonates by asymmetric aldol reaction of aldehydes with secondary-amine organocatalysts.  

PubMed

A diastereo- and enantioselective aldol reaction between aldehydes and a synthetically useful ketomalonate 1c as a hydrated form was developed, and either anti- or syn-aldol adducts having a chiral tetrasubstituted carbon center were obtained in high enantioselectivities by use of a tetrazole analogue of L-proline (S)-2 or an axially chiral amino sulfonamide (S)-3 as catalyst. PMID:22684237

Kano, Taichi; Song, Sunhwa; Maruoka, Keiji

2012-07-18

38

Method of carbon chain extension using novel aldol reaction  

DOEpatents

Method of producing C.sub.8-C.sub.15 hydrocarbons. comprising providing a ketone starting material; providing an aldol starting material comprising chloromethylfurfural; mixing the ketone starting material and the aldol starting material in a reaction in the presence of a proline-containing catalyst selected from the group consisting of Zn(Pro).sub.2, Yb(Pro).sub.3, and combinations thereof, or a catalyst having one of the structures (I), (II) or (III), and in the presence of a solvent, wherein the solvent comprises water and is substantially free of organic solvents, where (I), (II) and (III) respectively are: ##STR00001## where R.sub.1 is a C.sub.1-C.sub.6 alkyl moiety, X=(OH) and n=2. ##STR00002## In (III), X may be CH.sub.2, sulfur or selenium, M may be Zn, Mg, or a lanthanide, and R.sub.1 and R.sub.2 each independently may be a methyl, ethyl, phenyl moiety.

Silks, Louis A; Gordon, John C; Wu, Ruilan; Hanson, Susan Kloek

2013-07-30

39

Structural constraints for C 2-symmetric heterocyclic organocatalysts in asymmetric aldol reactions  

Microsoft Academic Search

Asymmetric aldol reactions were studied in the presence of heterocyclic bimorpholine- and bipiperidine-type organocatalysts. Bimorpholine derivatives were found to be more reactive and more selective in intramolecular, as well as intermolecular, reactions.

Marju Laars; Kadri Kriis; Tiiu Kailas; Aleksander-Mati Müürisepp; Tõnis Pehk; Tõnis Kanger; Margus Lopp

2008-01-01

40

Phosphine oxide-catalyzed enantioselective intramolecular aldol reaction via regioselective enolization of unsymmetrical diketones with tetrachlorosilane.  

PubMed

The phosphine oxide-catalyzed asymmetric intramolecular aldol reactions of diketones were investigated. The combination of tetrachlorosilane and a chiral phosphine oxide catalyst promoted the acetyl-selective enolization of diketones, and the subsequent intramolecular aldol reaction occurred in an enantioselective manner. The introduction of two trimethylsilyl groups at the 4- and 4'-positions in BINAP dioxide catalyst improved the enantioselectivity. This reaction provides an effective synthetic method to access ?-tertiary-hydroxy cyclohexanones in high yields and with high enantioselectivity. PMID:25192225

Kotani, Shunsuke; Aoki, Shohei; Sugiura, Masaharu; Ogasawara, Masamichi; Nakajima, Makoto

2014-09-19

41

Biomimetic catalytic enantioselective decarboxylative aldol reaction of ?-ketoacids with trifluoromethyl ketones.  

PubMed

We disclose an organocatalyzed enantioselective decarboxylative ketone aldol reaction of ?-ketoacids with trifluoromethyl ketones in the presence of biscinchona alkaloid (DHQD)(2)AQN, affording chiral tertiary alcohols in up to 98% yield and 90% ee. PMID:22472878

Zheng, Yan; Xiong, Heng-Ying; Nie, Jing; Hua, Ming-Qing; Ma, Jun-An

2012-05-01

42

Synthesis of a potential intermediate for TMC-95A via an organocatalyzed aldol reaction.  

PubMed

N-Prolinylanthranilamide-based pseudopeptide organocatalyst 14 was shown to promote enantioselective direct aldol reaction of 7-iodoisatin and 2,2-dimethyl-1,3-dioxan-5-one with 90% conversion (75% isolated yield), 90% enantioselectivity, and 23:1 diastereoselectivity. To demonstrate the synthetic utility of this chemistry, the racemic aldol reaction product was converted in five steps to a potential intermediate for construction of the natural product TMC-95A. PMID:24024913

Pearson, Anthony J; Panda, Santanu; Bunge, Scott D

2013-10-01

43

Effects of Lewis acid-surfactant-combined catalysts on aldol and Diels-Alder reactions in water  

Microsoft Academic Search

Aldol and Diels-Alder reactions in water in the presence of various dodecyl sulfate and dodecanesulfonate salts as Lewis acid-surfactant-combined catalysts have been studied. In the aldol reactions, these salts differed from each other with respect to their catalytic ability at the initial stage of the reaction and to the final yields of the aldol product, while these salts did not

Kei Manabe; Yuichiro Mori; Sh? Kobayashi

1999-01-01

44

(+)-(R,Z)-5-Muscenone and (-)-(R)-muscone by enantioselective aldol reaction and Grob fragmentation.  

PubMed

(+)-(R,Z)-5-Muscenone ((R)-1) was synthesized by an enantioselective aldol reaction, catalyzed by new ephedrine-type Ti reagents (up to 70 % enantiomeric excess). Substrate-directed diastereoselective reduction of the aldol product and Grob fragmentation of the tosylate of the resultant 1,3-diol afforded (+)-1. This approach also gave access to (-)-(R,E)-5-muscenone and (-)-(R)-muscone. PMID:20077541

Fehr, Charles; Buzas, Andrea K; Knopff, Oliver; de Saint Laumer, Jean-Yves

2010-02-22

45

Synthesis and structure of an extremely air-stable binuclear hafnocene perfluorooctanesulfonate complex and its use in Lewis acid-catalyzed reactions.  

PubMed

Stable complexes: An extremely air-stable mu(2)-hydroxy-bridged binuclear hafonocene perfluorooctanesulfoante complex shows high catalytic efficiency in Lewis acid-catalyzed reactions, such as esterification, Friedel-Crafts acylation, the Mukaiyama aldol reation, and the allylation of aldehyde (see scheme).An extremely air-stable mu(2)-hydroxy-bridged binuclear hafonocene perfluorooctanesulfoante complex was successfully synthesized. This complex showed high catalytic efficiency in the esterification of alcohols, phenol, thiol, and amines, in the Friedel-Crafts acylation of alylaryl ethers, in the Mukaiyama aldol reaction, and in the allylation of aldehydes and could be reused. PMID:19462386

Qiu, Renhua; Zhang, Guoping; Zhu, Yuyang; Xu, Xinhua; Shao, Lingling; Li, Yinhui; An, Delie; Yin, Shuangfeng

2009-06-22

46

Synthesis of the PMB ether of 5,6-epoxyisoprostane E2 through aldol reaction of the ?-bromocyclopentanone.  

PubMed

5,6-Epoxyisoprostane E2 was synthesized via bromohydrination of the cyclopentene and aldol reaction of the ?-bromocyclopentanone with the epoxyaldehyde. High regioselectivity in the bromohydrination was attained with recrystallized NBS and pyridine in aqueous DMSO. The enolate for the aldol reaction was generated by adding t-BuLi to the mixture of the ?-bromocyclopentanone and ZnI2. This aldol protocol was applied successfully to several cyclopentanones and aldehydes. PMID:24761743

Kawashima, Hidehisa; Kobayashi, Yuichi

2014-05-16

47

Developing novel organocatalyzed aldol reactions for the enantioselective synthesis of biologically active molecules.  

PubMed

Aldol reaction is one of the most important methods for the formation of carbon-carbon bonds. Because of its significance and usefulness, asymmetric versions of this reaction have been realized with different approaches in the past. Over the last decade, the area of organocatalysis has made significant progresses. As one of most studied reactions in organocatalyses, organocatalyzed aldol reaction has emerged as a powerful tool for the synthesis of a large number of useful products in optically enriched forms. In this review, we summarize our efforts on the development of novel organocatalyzed aldol reactions for the enantioselective synthesis of biological active molecules. Literatures closely related to our studies are also covered. PMID:21918584

Bhanushali, Mayur; Zhao, Cong-Gui

2011-06-01

48

A Tandem Michael-Aldol Reaction Sequence: An Undergraduate Research Organic Experiment.  

ERIC Educational Resources Information Center

Presents a short reaction sequence that allows the student to determine by spectroscopic methods the constitution and stereochemistry of the reaction products. Reports the interpretations needed to illustrate the usefulness of the spectroscopic method. Notes the products of the Michael-Aldol reaction have not been reported in the literature. (MVL)

Coutlangus, Marilyn L.; And Others

1989-01-01

49

Rapid and Efficient Functionalized Ionic Liquid-Catalyzed Aldol Condensation Reactions Associated with Microwave Irradiation  

PubMed Central

Five quaternary ammonium ionic liquid (IL) and two tetrabutylphosphonium ILs were prepared and characterized. An environmentally benign and convenient functionalized ionic liquid catalytic system was thus explored in the aldol condensation reactions of aromatic aldehydes with acetone. The aldol reactions proceeded more efficiently through microwave-assisted heating than through conventional thermal heating. The yield of products obtained under microwave heating for 30 min was approximately 90%, and the ILs can be recovered and reused at least five times without apparent loss of activity. In addition, this catalytic system can be successfully extended to the Henry reactions. PMID:24445262

Wang, Chang; Liu, Jing; Leng, Wenguang; Gao, Yanan

2014-01-01

50

Trichlorosilyl triflate-mediated enantioselective directed cross-aldol reaction between ketones using a chiral phosphine oxide as an organocatalyst.  

PubMed

Trichlorosilyl triflate-promoted directed cross-aldol reaction between ketones in the presence of a chiral phosphine oxide as an organocatalyst is described. This is the first enantioselective cross-aldol reaction between simple ketones with good enantioselectivity. PMID:22543407

Aoki, Shohei; Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2012-06-01

51

Direct asymmetric aldol reactions inspired by two types of natural aldolases: water-compatible organocatalysts and Zn(II) complexes.  

PubMed

In this article the utility of water-compatible amino-acid-based catalysts was explored in the development of diastereo- and enantioselective direct aldol reactions of a broad range of substrates. Chiral C(2)-symmetrical proline- and valine-based amides and their Zn(II) complexes were designed for use as efficient and flexible chiral catalysts for enantioselective aldol reactions in water, on water, and in the presence of water. The presence of 5 mol % of the prolinamide-based catalyst affords asymmetric intermolecular aldol reactions between unmodified ketones and various aldehydes to give anti products with excellent enantioselectivities. We also demonstrate aldol reactions of more demanding substrates with high affinity to water (i.e., acetone and formaldehyde). Newly designed serine-based organocatalyst promoted aldol reaction of hydroxyacetone leading to syn-diols. For presented catalytic systems organic solvent-free conditions are also acceptable, making the elaborated methodology interesting from a green chemistry perspectives. PMID:22136201

Paradowska, Joanna; Pasternak, Monika; Gut, Bartosz; Gryz?o, Beata; Mlynarski, Jacek

2012-01-01

52

Computational investigations of the stereoselectivities of proline-related catalysts for aldol reactions  

PubMed Central

Computational investigation of the aldol reaction of benzaldehyde with acetone catalyzed by various proline derivatives and 2-azetidine carboxylic acid reveal the origins of stereoselectivities of these reactions. Structural differences between catalysts and transition states were analyzed with density functional theory geometries in order to establish the key factors that will help in the design of new catalysts. PMID:20634993

Allemann, Christophe; Um, Joann M.; Houk, K. N.

2010-01-01

53

Direct catalytic enantioselective vinylogous aldol reaction of ?-branched enals with isatins.  

PubMed

The direct vinylogous aldol reaction of ?-substituted ?,?-unsaturated aldehydes with isatins is described. The chemistry provides easy access to valuable 3-substituted 3-hydroxyoxindole derivatives with high stereocontrol and perfect ?-site selectivity. Preliminary mechanistic studies suggest that, depending on the nature of the ?-branched enal substituents, two divergent reaction mechanisms can be operating, leading to different products and stereochemical outcomes. PMID:23075306

Cassani, Carlo; Melchiorre, Paolo

2012-11-01

54

A convenient imino aldol reaction in ethyl alcohol catalyzed by a cation-exchange resin.  

PubMed

Imino aldol reaction of ketene silyl acetals with imines proceeds smoothly to give beta-amino esters in good yields under the influence of a cation-exchange resin in ethanol, and the work-up of the reaction consists only of a simple filtration followed by concentration of the crude mixture and purification. PMID:12240054

Shimizu, M; Itohara, S; Hase, E

2001-11-21

55

A solid-supported organocatalyst for continuous-flow enantioselective aldol reactions.  

PubMed

Asymmetric aldol reactions catalyzed by a novel polystyrene-immobilized proline derivative occur in short reaction times with excellent diastereo- and enantioselectivity. The catalyst can be recovered by simple filtration and shows very high reusability. The high activity depicted by the supported catalyst and its chemical and mechanical stability have allowed its application in packed-bed reactors for continuous flow processing. This system can produce enantio- and diastereomerically pure aldol adducts under continuous flow conditions with a residence time of 26 min. Furthermore, the reactor allowed processing of four different aldol products in sequence without any decrease in both catalytic activity and optical purity. The effective catalyst loading could be reduced to 1.6% (six-fold reduction of catalyst loading compared to the corresponding batch process). PMID:22442839

Ayats, Carles; Henseler, Andrea H; Pericàs, Miquel A

2012-02-13

56

Asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones via enantioselective tandem Michael-aldol reaction.  

PubMed

A simple and efficient method for the asymmetric synthesis of ?-alkylidene-?-hydroxy-?-butyrolactones and related natural products was developed on the basis of the catalytic asymmetric tandem Michael-aldol reaction and simple transformations. The synthetic utility of this method was illustrated by the facile synthesis of trisubstituted ?-butyrolactone natural products. PMID:23252990

Lee, Sung Il; Jang, Jin Hee; Hwang, Geum-Sook; Ryu, Do Hyun

2013-01-18

57

ALDOL- AND MANNICH-TYPE REACTIONS VIA IN SITU OLEFIN MIGRATION IN IONIC LIQUID  

EPA Science Inventory

An aldol-type and a Mannich-type reaction via the cross-coupling of aldehydes and imines with allylic alcohols catalyzed by RuCl2(PPh3)3 was developed with ionic liquid as the solvent. The solvent/catalyst system could be reused for at least five times with no loss of reactiv...

58

N-(heteroarenesulfonyl)prolinamides-catalyzed aldol reaction between acetone and aryl trihalomethyl ketones.  

PubMed

Enantiomerically enriched trihalomethyl-substituted alcohols having a quaternary chiral carbon center can be prepared by the catalytic enantioselective cross-aldol reaction of acetone with trihalomethyl ketones by using N-(8-quinolinesulfonyl)prolinamide as an organocatalyst. The MO calculations elucidate that the hydrogen bonding between the sulfonimide proton and the 8-quinolyl nitrogen atom plays an important role in exerting the enantioselectivity of the reaction. PMID:21366293

Hara, Noriyuki; Tamura, Ryota; Funahashi, Yasuhiro; Nakamura, Shuichi

2011-04-01

59

Highly diastereofacial anti-aldol reaction: practical synthesis of optically active anti-2-alkyl-3-hydroxycarboxylic acid ester units.  

PubMed

A variety of esters derived from commercially available norephedrine were used in diastereoselective anti-aldol reactions. The aldol reaction of designed 2-(N-2-methylbenzyl-N-2,4,6-trimethylbenzyl)amino-1-phenylpropanol esters 4a-d with aldehydes furnished anti-2-alkyl-3-hydroxycarboxylic acid esters in excellent diastereomeric ratios (>98:2) when LDA-Cp2ZrCl2 (0.3 equiv) was used for enolization, followed by transmetalation into the zirconium enolate for aldolization. The novel auxiliary 3 for the anti-aldol reaction does not exhibit the ordinary basicity of tertiary amines; 3 can be extracted from acidic media with organic solvents. Its use is, therefore, very advantageous not only for extraction of the aldol products from the acidic water solutions, but also for recovering the chiral auxiliary 3 after the reductive cleavage. Treatment of aldol or 3-protected aldol products with DIBAL-H or LiAlH4 affords the versatile synthons, 2-alkyl-propane-1,3-diols or those 3-protected diols in >98% ee's together with 3 in nearly quantitative recovery. PMID:11312949

Kurosu, M; Lorca, M

2001-02-23

60

Highly enantioselective aldol reaction of acetone with ?,?-unsaturated ?-keto esters promoted by simple chiral primary-tertiary diamine catalysts.  

PubMed

A series of primary-tertiary diamine catalysts were successfully applied to promote the enantioselective aldol reaction of acetone with ?,?-unsaturated ?-keto esters in excellent yields (up to 99%) and enantioselectivities (up to 96% ee). PMID:21614388

Peng, Lin; Wang, Liang-Liang; Bai, Jian-Fei; Jia, Li-Na; Guo, Yun-Long; Luo, Xi-Ya; Wang, Fei-Ying; Xu, Xiao-Ying; Wang, Li-Xin

2011-07-01

61

Memory of chirality (MOC) concept in imino-aldol reaction: enantioselective synthesis of ?,?-diamino esters and aziridines.  

PubMed

A simple strategy for the synthesis of chiral ?,?-diamino- and ?-amino,?-hydroxy ester derivatives in high yields with moderate to high ee has been developed via asymmetric imino-aldol and aldol reactions, respectively, starting from protected aminoesters employing memory of chirality concept for chiral induction. This strategy has been extended for the enantioselective synthesis of aziridines (ee up to 92%). The absolute configuration of the imino-aldol adducts has been determined. The stereochemical outcome of the products has been explained by a suitable mechanism and supported by computational studies. PMID:23320819

Ghorai, Manas K; Ghosh, Koena; Yadav, A K; Nanaji, Y; Halder, Sandipan; Sayyad, Masthanvali

2013-03-15

62

Organocatalytic enantioselective tandem aldol-cyclization reaction of ?-isothiocyanato imides and activated carbonyl compounds.  

PubMed

The organocatalytic enantioselective tandem aldol-cyclization reactions of ?-isothiocyanato imides and activated carbonyl compounds, such as isatins, an ?-ketolactone and a 1,2-dione, have been studied with cinchona alkaloid-derived thiourea-catalysts. This methodology provided an easy way to access enantiomerically enriched spirobicyclic thiocarbamates with high yields and good to excellent stereoselectivity, which have been demonstrated to be useful precursors for the synthesis of biologically active molecules. PMID:21921975

Guang, Jie; Zhao, Cong-Gui

2011-06-15

63

Dinuclear Zinc-Prophenol-Catalyzed Enantioselective ?-Hydroxyacetate Aldol Reaction with Activated Ester Equivalents  

PubMed Central

An enantioselective ?-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc Prophenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting ?,?-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Trost, Barry M.; Michaelis, David J.; Truica, Mihai I.

2013-01-01

64

Asymmetric vinylogous aldol reaction via H-bond-directing dienamine catalysis.  

PubMed

The enantioselective direct vinylogous aldol reaction of 3-methyl 2-cyclohexen-1-one with ?-keto esters has been developed. The key to success was the design of a bifunctional primary amine-thiourea catalyst that can combine H-bond-directing activation and dienamine catalysis. The simultaneous dual activation of the two reacting partners results in high reactivity while securing high levels of stereocontrol. PMID:23259650

Bastida, David; Liu, Yankai; Tian, Xu; Escudero-Adán, Eduardo; Melchiorre, Paolo

2013-01-01

65

Dinuclear zinc-ProPhenol-catalyzed enantioselective ?-hydroxyacetate aldol reaction with activated ester equivalents.  

PubMed

An enantioselective ?-hydroxyacetate aldol reaction that employs N-acetyl pyrroles as activated ester equivalents and generates syn 1,2-diols in good yield and diastereoselectivity is reported. This dinuclear zinc-ProPhenol-catalyzed transformation proceeds with high enantioselectivity with a wide variety of substrates including aryl, alyl, and alkenyl aldehydes. The resulting ?,?-dihydroxy activated esters are versatile intermediates for the synthesis of a variety of carboxylic acid derivatives including amides, esters, and unsymmetrical ketones. PMID:23947595

Trost, Barry M; Michaelis, David J; Truica, Mihai I

2013-09-01

66

Kinetic isotope and thermodynamic analysis of the nornicotine-catalyzed aqueous aldol reaction  

Microsoft Academic Search

A series of kinetic isotope effects and thermodynamic studies were performed to test key predictions of a computationally derived model for a nornicotine-catalyzed aqueous aldol reaction. The relative energies of the two computationally-derived transition states were challenged using the proton inventory, which demonstrated that a single water molecule from the solvent is involved in, or before, the rate-limiting step. These

Claude J. Rogers; Tobin J. Dickerson; Kim D. Janda

2006-01-01

67

Aldol reactions with kinetic resolution: scope and limitations of ketal- and dithioketal-protected ?-ketoaldehydes.  

PubMed

The multiplicativity rule suggests that aldol coupling of chiral reactants will proceed with substantial mutual kinetic enantioselection (MKE) (racemic reactants) or via a highly enantioselective kinetic resolution (KR) (one enantiopure reactant) if the relative topicity is highly selective and the ketone enolate and aldehyde each have high diastereoface selectivity. The scope and limitations of that paradigm were explored by determining the stereoselectivities of aldol reactions of ketone 1a (known to give 3,5-trans aldol adducts with high selectivity) with a series of ketal- and dithioketal-protected ?-ketoaldehydes (±)-5 (predicted to have high Felkin diastereoface selectivity). Using racemic reactants, all reactions of the (c-Hex)(2)B enolates (highly anti-selective relative topicity) were remarkably selective and gave the 3,5-trans-3,1"-anti-1",2"-syn adduct, one of eight possible diastereomers, via a diastereoselective (dr > 20) preferential reaction (MKE > 17) of like reactant enantiomers [i.e., (3R)-1a + (R)-5 and (3S)-1a + (S)-5]. Reactions of the corresponding Ti(IV) "ate" enolates (anticipated syn-selective relative topicity) were much less selective, and only those of MOM-protected 1a with dithiolane-protected (±)-5 (i.e., X = S, n = 1) gave high selectivity in favor of the 3,5-trans-3,1"-syn-1",2"-syn adduct via a diastereoselective (dr > 20) preferential reaction (MKE ? 6) of unlike reactant enantiomers [i.e., (3R)-1a + (S)-5 and (3S)-1a + (R)-5]. Analogous reactions of the (c-Hex)(2)B and Ti(IV) "ate" enolates of enantiopure (+)-1a (R = MOM) with (±)-5c (R(2) = Me, X = S, n = 1) occurred with KR to give the corresponding enantiopure adducts with the expected stereoselectivity. The adducts have applications in polyproionate synthesis. PMID:23137001

Ward, Dale E; Kazemeini, Alieh

2012-12-01

68

Enzymatic enantioselective aldol reactions of isatin derivatives with cyclic ketones under solvent-free conditions.  

PubMed

Nuclease p1 from Penicillium citrinum was observed to directly catalyze the asymmetric aldol reactions between isatin derivatives and cyclic ketones with high isolated yields (up to 95%) and moderate to good stereoselectivity (dr up to >99/1, ee up to 82%). A series of reaction conditions were investigated in detail, and the addition of deionized water had a big influence upon the enzyme activity. This case of biocatalytic promiscuity not only widens the applicability of nuclease p1 to new chemical transformation in organic synthesis, but also provides a potentially valuable method to construct pharmaceutically active compounds in medicinal chemistry. PMID:24440638

Liu, Zhi-Qiang; Xiang, Zi-Wei; Shen, Zhou; Wu, Qi; Lin, Xian-Fu

2014-06-01

69

Asymmetric synthesis of trisubstituted oxazolidinones by the thiourea-catalyzed aldol reaction of 2-isocyanatomalonate diester.  

PubMed

A new method has been developed for the synthesis of chiral 4-carboxyl oxazolidinones by the catalytic asymmetric aldol reaction of an isocyanatomalonate diester with an aldehyde in the presence of a thiourea catalyst. The resulting chiral 4-carboxyl oxazolidinones are the equivalent of ?-hydroxy-?-amino acids bearing a tri- or tetrasubstituted carbon center at their ? position. With this in mind, this procedure was successfully applied to the first total synthesis of mycestericin C, which was completed in 12 steps and represents one of the shortest reported sequences for the construction of natural products of this type. PMID:25203516

Sakamoto, Shota; Kazumi, Naoya; Kobayashi, Yusuke; Tsukano, Chihiro; Takemoto, Yoshiji

2014-09-19

70

Organocatalytic Asymmetric Synthesis of Functionalized 1,3,5-Triarylpyrrolidin-2-ones via an Aza-Michael/Aldol Domino Reaction  

PubMed Central

The organocatalytic asymmetric synthesis of functionalized 1,3,5-triarylpyrrolidin-2-ones bearing three contiguous stereocenters through an aza-Michael/aldol domino reaction of ?-ketoamides with ?,?-unsaturated aldehydes is described. The domino products were further derivatized by aldehyde olefination under one-pot conditions. The reaction proceeds with excellent diastereoselectivities (>20:1) and good to excellent enantioselectivities (60–96% ee).

Joie, Celine; Deckers, Kristina; Enders, Dieter

2014-01-01

71

Highly enantioselective aldol reactions between acetaldehyde and activated acyclic ketones catalyzed by chiral primary amines.  

PubMed

Highly enantioselective cross-aldol reactions between acetaldehyde and activated acyclic ketones are reported for the first time. Various acyclic ketones, such as saturated and unsaturated keto esters, reacted with acetaldehyde in the presence of a chiral primary amine and a Brønsted acid to afford optically enriched tertiary alcohols in good yields and with excellent enantioselectivities. Trifluoromethyl ketones were tolerable under the reaction conditions, thereby affording the trifluoromethyl carbinol in good-to-excellent yields and enantioselectivities. Structural modification of the chiral amines from the same chiral source switched the stereoselectivity of the products. The utility of aldol chemistry was demonstrated in the brief synthesis of functionally enriched ?-lactones. Theoretical calculations on the transition-state structure indicated that the protonated tertiary amine could effectively activate the carbonyl group of a keto ester to promote the addition process through hydrogen-bonding interaction and, simultaneously, provide an appropriate attacking pattern for the approach of the keto ester to the enamine, which is formed from acetaldehyde and the chiral catalyst, on a particular face, resulting in high enantioselectivity. PMID:23559455

Deng, Yu-Hua; Chen, Jin-Quan; He, Long; Kang, Tai-Ran; Liu, Quan-Zhong; Luo, Shi-Wei; Yuan, Wei-Chen

2013-05-27

72

Lanthanide triflates as water-tolerant Lewis acids. Activation of commercial formaldehyde solution and use in the aldol reaction of silyl enol ethers with aldehydes in aqueous media  

Microsoft Academic Search

The catalytic effects of lanthanide triflates in the hydroxymethylation and the aldol reaction of silyl enol ethers (w\\/aldehydes). The rare earth triflates served as Lewis acid catalysts in the aqueous reaction medium.

Shue Kobayashi; Iwao Hachiya

1994-01-01

73

Lanthanide triflates as water-tolerant Lewis acids. Activation of commercial formaldehyde solution and use in the aldol reaction of silyl enol ethers with aldehydes in aqueous media  

SciTech Connect

The catalytic effects of lanthanide triflates in the hydroxymethylation and the aldol reaction of silyl enol ethers (w/aldehydes). The rare earth triflates served as Lewis acid catalysts in the aqueous reaction medium.

Kobayashi, Shue; Hachiya, Iwao [Univ. of Tokyo (Japan)

1994-07-01

74

Direct enantioselective vinylogous aldol-cyclization cascade reaction of allyl pyrazoleamides with isatins: asymmetric construction of spirocyclic oxindole-dihydropyranones.  

PubMed

The first enantioselective vinylogous aldol-cyclization cascade reaction of allyl pyrazoleamides with isatins is reported. With 1 mol% of Takemoto catalyst, optically active spirocyclic oxindole-dihydropyranones were obtained in excellent yields (93-99%) and good-to-excellent enantioselectivities (82-97% ee). PMID:25019965

Li, Tian-Ze; Jiang, Yu; Guan, Yu-Qing; Sha, Feng; Wu, Xin-Yan

2014-09-25

75

Organocatalytic cascade sulfa-Michael/aldol reaction of ?,?-disubstituted enones: enantioselective synthesis of tetrahydrothiophenes with a trifluoromethylated quaternary center.  

PubMed

A bifunctional squaramide-catalyzed sulfa-Michael/aldol cascade reaction initiated by sulfa-Michael addition of mercaptoacetaldehyde to ?-aryl-?-trifluoromethylated enones is successfully developed. The functionalized tetrahydrothiophenes with three continuous stereocenters including a trifluoromethylated quaternary carbon are readily obtained with moderate to good yields and high enantioselectivities. PMID:24079617

Su, Yu; Ling, Jun-Bing; Zhang, Shuang; Xu, Peng-Fei

2013-11-01

76

Asymmetric Michael-aldol tandem reaction of 2-substituted benzofuran-3-ones and enones: a facile synthesis of griseofulvin analogues.  

PubMed

A highly enantioselective Michael-aldol tandem reaction with respect to prochiral 2-substituted benzofuran-3-ones and enones by a facile primary amine catalyst was investigated. The approach provides rapid access to the desired pharmaceutically active griseofulvin analogues. PMID:24001214

Dong, Nan; Li, Xin; Wang, Feng; Cheng, Jin-Pei

2013-09-20

77

Toward the combinatorial synthesis of polyketide libraries: asymmetric aldol reactions with alpha-chiral aldehydes on solid support.  

PubMed

[reaction: see text] The viability of performing stereocontrolled aldol additions with alpha-chiral aldehydes attached by a silyl linker to a hydroxymethylpolystyrene resin is demonstrated for boron and titanium enolates. Subsequent ketone reduction and manipulation on the solid support leads to elaborate stereopentad sequences, as occur in 6-deoxyerythronolide B and discodermolide. PMID:12123354

Paterson, Ian; Temal-Laïb, Taoues

2002-07-25

78

L-Proline/CoCl2-catalyzed highly diastereo- and enantioselective direct aldol reactions.  

PubMed

The CoCl(2)/L-proline (1:2) system was found to be an excellent catalyst for direct aldol reactions. Excellent yields (up to 93%) and a significant improvement in diastereoselectivity (anti/syn up to 45:1) as well as enantioselectivity (up to more than 99% ee) compared with using proline as the sole catalyst were observed. This catalyst system was successfully applied to both cyclic and acyclic ketones in combination with aromatic and aliphatic aldehydes. In situ chelation of CoCl(2) and proline (1:2) is proposed to promote the reaction through a six-membered Zimmermann-Traxler type transition state involving the positioning of proline-enamine and the aldehyde through chelation to Co(II). PMID:21932236

Karmakar, Ananta; Maji, Tapan; Wittmann, Sebastian; Reiser, Oliver

2011-09-19

79

Tandem Aldol-Michael Reactions in Aqueous Diethylamine Medium: A Greener and Efficient Approach to Bis-Pyrimidine Derivatives  

PubMed Central

A simple protocol, involving the green synthesis for the construction of novel bis-pyrimidine derivatives, 3a–i and 4a–e are accomplished by the aqueous diethylamine media promoted tandem Aldol-Michael reaction between two molecules of barbituric acid derivatives 1a,b with various aldehydes. This efficient synthetic protocol using an economic and environmentally friendly reaction media with versatility and shorter reaction time provides bis-pyrimidine derivatives with high yields (88%–99%). PMID:24317435

Al-Majid, Abdullah M.; Barakat, Assem; AL-Najjar, Hany J.; Mabkhot, Yahia N.; Ghabbour, Hazem A.; Fun, Hoong-Kun

2013-01-01

80

Organocatalyzed enantioselective aldol reaction of 1H-pyrrole-2,3-diones.  

PubMed

The enantioselective cross aldol reaction of 1-benzyl 4,5-dioxo-2-aryl-4,5-dihydro-1H-pyrrole-3-carboxylates and ketones was studied with proline derivatives or cinchona alkaloid-derived primary amines as the catalysts for the first time. trans-4-Benzoyloxy-L-proline (15) was found to be the best catalyst for acyclic ketones. For cyclohexanone, the best results were achieved with 9-deoxy-9-epi-aminoquinine (18) as the catalyst in the presence of racemic 1,1'-binaphthyl-2,2'-diyl hydrogen phosphate (19) as the cocatalyst. Using these protocols, 3-alkyl-3-hydroxy-1H-pyrrol-2(3H)-one derivatives were obtained in excellent yields and good to high ee values (up to 94% ee). PMID:22544980

Bhanushali, Mayur; Zhao, Cong-Gui

2012-01-18

81

Ionic nucleophilic catalysis of chiral ammonium betaines for highly stereoselective aldol reaction from oxindole-derived vinylic carbonates.  

PubMed

A new strategy for developing stereoselective bond-forming reactions is introduced; it takes advantage of the ionic nucleophilic catalysis of chiral ammonium betaines to utilize vinylic esters simultaneously as the enolate precursor and the acylating agent for coupling with electrophiles. Its synthetic utility is clearly demonstrated by the realization of a highly diastereo- and enantioselective aldol reaction from oxindole-derived vinylic carbonates. PMID:22482889

Uraguchi, Daisuke; Koshimoto, Kyohei; Ooi, Takashi

2012-04-25

82

Proline-tetrazole-catalyzed enantioselective N-nitroso aldol reaction of aldehydes with in situ generated nitrosocarbonyl compounds.  

PubMed

A highly enantioselective method (up to 98% ee) for the preparation of ?-amino alcohols was achieved by using the readily available proline-tetrazole as the catalyst for the N-nitroso aldol reaction of aldehydes with in situ generated nitrosocarbonyl compounds. The key to success of this reaction is the use of MnO2 as an oxidant and catechol as a Brønsted acid additive. PMID:24554628

Maji, Biplab; Yamamoto, Hisashi

2014-08-11

83

A cascade Heck-Aldol-Heck reaction by a combination of transition-metal catalysis and aminocatalysis.  

PubMed

An unprecedented cascade Heck-Aldol-Heck reaction was developed to form two C-C single bonds and one C=C double bond in one process by a combination of palladium(0) catalysis and aminocatalysis. Various aryl iodides could perform the cascade reaction with readily available propenol and formaldehyde to afford novel (E)-trisubstituted alkenes in 66-81% yields. PMID:21331414

Guo, Chang-Shan; Du, Yu-Han; Huang, Zhi-Zhen

2011-04-01

84

The direct catalytic asymmetric aldol reaction of ?-substituted nitroacetates with aqueous formaldehyde under base-free neutral phase-transfer conditions.  

PubMed

Enantioselective direct aldol reaction of ?-substituted nitroacetates with aqueous formaldehyde for the synthesis of ?-alkyl serines has been achieved under base-free neutral phase-transfer conditions with a bifunctional chiral phase-transfer catalyst. PMID:22349720

Shirakawa, Seiji; Ota, Kensuke; Terao, Shogo J; Maruoka, Keiji

2012-08-14

85

A highly efficient asymmetric organocatalytic aldol reaction in a ball mill.  

PubMed

Anti-aldol products with up to >99 % enantiomeric excess (ee) have been obtained by proline catalysis in excellent yields under experimentally simple solvent-free conditions. Efficient mixing of all the components is accomplished by applying a mechanochemical technique (ball milling). The catalysis is air and moisture tolerant and can be performed with non-purified starting materials. Even mixtures of solely solid compounds react, giving (mostly solid) products through a partially homogeneous (honey-like) intermediate melt. Since the reactant ratio is almost 1:1 (avoiding the common excess of ketone), the product isolation is easy leading to high aldol product yields. PMID:17506051

Rodríguez, Belén; Bruckmann, Angelika; Bolm, Carsten

2007-01-01

86

A convenient enantioselective decarboxylative aldol reaction to access chiral ?-hydroxy esters using ?-keto acids.  

PubMed

We show a convenient decarboxylative aldol process using a scandium catalyst and a PYBOX ligand to generate a series of highly functionalized chiral ?-hydroxy esters. The protocol tolerates a broad range of ?-keto acids with inactivated aromatic and aliphatic ?-keto esters. The possible mechanism is rationalized. PMID:24991246

Duan, Zhiqiang; Han, Jianlin; Qian, Ping; Zhang, Zirui; Wang, Yi; Pan, Yi

2014-01-01

87

A convenient enantioselective decarboxylative aldol reaction to access chiral ?-hydroxy esters using ?-keto acids  

PubMed Central

Summary We show a convenient decarboxylative aldol process using a scandium catalyst and a PYBOX ligand to generate a series of highly functionalized chiral ?-hydroxy esters. The protocol tolerates a broad range of ?-keto acids with inactivated aromatic and aliphatic ?-keto esters. The possible mechanism is rationalized. PMID:24991246

Duan, Zhiqiang; Han, Jianlin; Qian, Ping; Zhang, Zirui; Pan, Yi

2014-01-01

88

Highly enantioselective cross-aldol reactions of acetaldehyde mediated by a dual catalytic system operating under site isolation.  

PubMed

Polystyrene-supported (PS) diarylprolinol catalysts 1?a (Ar = phenyl) and 1?b (Ar = 3,5-bis(trifluoromethyl)phenyl) have been developed. Operating under site-isolation conditions, PS-1?a/1?b worked compatibly with PS-bound sulfonic acid catalyst 2 to promote deoligomerization of paraldehyde and subsequent cross-aldol reactions of the resulting acetaldehyde in one pot, affording aldol products in high yields with excellent enantioselectivities. The effect of water on the performance of the catalytic system has been studied and its optimal amount (0.5?equiv) has been determined. The dual catalytic system (1/2) allows repeated recycling and reuse (10 cycles). The potential of this methodology is demonstrated by a two-step synthesis of a phenoperidine analogue (68% overall yield; 98%?ee) and by the preparation of highly enantioenriched 1,3-diols 4 and 3-methylamino-1-arylpropanols 5, key intermediates in the synthesis of a variety of druglike structures. PMID:25168085

Fan, Xinyuan; Rodríguez-Escrich, Carles; Wang, Shoulei; Sayalero, Sonia; Pericàs, Miquel A

2014-10-01

89

Brønsted acid/rhodium(II) cooperative catalytic asymmetric three-component aldol-type reaction for the synthesis of 3-amino oxindoles.  

PubMed

Cooperation is key! Chiral Brønsted acid/rhodium(II) cooperative catalysis enabled an enantioselective three-component aldol-type reaction of 3-diazo oxindoles and anilines with glyoxylates to give highly functionalized and structurally diverse 3-amino oxindoles in high stereoselectivity (>20:1 d.r., 99?% ee; see scheme). PMID:23401186

Ren, Lei; Lian, Xiao-Lei; Gong, Liu-Zhu

2013-03-01

90

Substrate control in enantioselective and diastereoselective aldol reaction by memory of chirality: a rapid access to enantiopure ?-hydroxy quaternary ?-amino acids.  

PubMed

An asymmetric aldol reaction by memory of chirality is reported with a substrate control of stereoselectivity by aldehyde and rationalized. Starting from l-alanine, several diastereopure and enantioenriched ?-hydroxy quaternary ?-amino acids have been obtained in three steps. The initial chirality of l-alanine is memorized through the dynamic axial chirality of tertiary aromatic amide. PMID:24432786

Viswambharan, Baby; Gori, Didier; Guillot, Régis; Kouklovsky, Cyrille; Alezra, Valérie

2014-02-01

91

Enantioselective direct aldol reaction of ?-keto esters catalyzed by (S(a))-binam-D-prolinamide under quasi solvent-free conditions.  

PubMed

(S(a))-Binam-D-prolinamide (20 mol%), instead of (S(a))-binam-L-prolinamide, in combination with chloroacetic acid (100 mol%) is an efficient organocatalyst for the direct aldol reaction between ?-keto esters as electrophiles and alkyl and ?-functionalised ketones, under quasi solvent-free conditions, providing access to highly functionalised chiral quaternary ?-keto ?-hydroxyesters with up to 92% ee. PMID:22514086

Viózquez, Santiago F; Bañón-Caballero, Abraham; Guillena, Gabriela; Nájera, Carmen; Gómez-Bengoa, Enrique

2012-05-28

92

Dynamic kinetic asymmetric synthesis of five contiguous stereogenic centers by sequential organocatalytic stetter and Michael-aldol reaction: enantioselective synthesis of fully substituted cyclopentanols bearing a quaternary stereocenter.  

PubMed

A synthesis of fully substituted cyclopentanes bearing a quaternary carbon center and five contiguous stereogenic centers has been achieved by sequential organocatalyzed Stetter and Michael-Aldol reactions of heteroaromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with dynamic kinetic asymmetric transformation and excellent enantioselectivities (up to >99% ee). PMID:21348455

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou; Lee, Gene-Hsiang

2011-03-18

93

TANDEM BIS-ALDOL REACTION OF KETONES: A FACILE ONE-POT SYNTHESIS OF 1,3-DIOXANES IN AQUEOUS MEDIUM  

EPA Science Inventory

A novel tandem bis-aldol reaction of ketone with paraformaldehyde catalyzed by polystyrenesulfonic acid in aqueous medium delivers 1,3-dioxanes in high yield. This one pot, operationally simple microwave-assisted synthetic protocol proceeds efficiently in water in the absence of ...

94

Organocatalyzed aldol reaction between pyridine-2-carbaldehydes and ?-ketoacids: a straightforward route towards indolizidines and isotetronic acids.  

PubMed

Enantioselective aldol reactions between substituted pyridine carbaldehydes and ?-ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate-to-good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst. Hydrogenation of the resulting pyridinium salts led to new indolizidines with high ee values and diastereocontrol. X-ray diffraction studies allowed the determination of the relative configuration of the products. Finally, DFT calculations were performed to rationalize the divergent pathway as a function of the pyridine substituents. PMID:24038579

Liautard, Virginie; Jardel, Damien; Davies, Clotilde; Berlande, Muriel; Buffeteau, Thierry; Cavagnat, Dominique; Robert, Frédéric; Vincent, Jean-Marc; Landais, Yannick

2013-10-18

95

A Combined DFT and NMR Investigation of the Zinc Organometallic Intermediate Proposed in the Syn-Selective Tandem Chain Extension-Aldol Reaction of ?-Keto Esters  

PubMed Central

The tandem chain extension-aldol (TCA) reaction of ?-keto esters provides a ?-substituted ?-keto ester with an average syn:anti selectivity of 10:1. It is proposed that the reaction proceeds via a carbon-zinc bound organometallic intermediate potentially bearing mechanistic similarity to the Reformatsky reaction. Evidence, derived from control Reformatsky reactions and a study of the structure of the TCA intermediate utilizing DFT methods and NMR-spectroscopy, suggests the ?-keto group of the TCA intermediate plays a significant role in diastereoselectivity observed in this reaction. Such coordination effects have design implications for future zinc mediated reactions. PMID:22703563

Aiken, Karelle S.; Eger, Wilhelm A.; Williams, Craig M.; Spencer, Carley M.

2012-01-01

96

A secondary kinetic isotope effect study of the 1-deoxy-D-xylulose-5-phosphate reductoisomerase-catalyzed reaction: evidence for a retroaldol-aldol rearrangement.  

PubMed

1-Deoxy-d-xylulose 5-phosphate (DXP) reductoisomerase (DXR, also known as methyl-d-erythritol 4-phosphate (MEP) synthase) is a NADPH-dependent enzyme, which catalyzes the conversion of DXP to MEP in the nonmevalonate pathway of isoprene biosynthesis. Two mechanisms have been proposed for the DXR-catalyzed reaction. In the alpha-ketol rearrangement mechanism, the reaction begins with deprotonation of the C-3 hydroxyl group followed by a 1,2-migration to give methylerythrose phosphate, which is then reduced to MEP by NADPH. In the retroaldol/aldol rearrangement mechanism, DXR first cleaves the C3-C4 bond of DXP in a retroaldol manner to generate a three-carbon and a two-carbon phosphate bimolecular intermediate. These two species are then reunited by an aldol reaction to form a new C-C bond, yielding an aldehyde intermediate. Subsequent reduction by NADPH affords MEP. To differentiate these mechanisms, we have prepared [3-(2)H]- and [4-(2)H]-DXP and carried out a competitive secondary kinetic isotope effect (KIE) study of the DXR reaction. The normal 2 degrees KIEs observed for [3-(2)H]- and [4-(2)H]-DXP provide compelling evidence supporting a retroaldol/aldol mechanism for the rearrangement catalyzed by DXR, with the rate-limiting step being cleavage of the C3-C4 bond of DXP. PMID:19159292

Munos, Jeffrey W; Pu, Xiaotao; Mansoorabadi, Steven O; Kim, Hak Joong; Liu, Hung-wen

2009-02-18

97

One-pot organocatalytic enantioselective Michael-Michael-aldol-Henry reaction cascade. A facile entry to the steroid system with six contiguous stereogenic centers.  

PubMed

An expedited method has been developed for the enantioselective synthesis of highly functionalized steroid systems containing six contiguous stereogenic centers with high enantioselectivities (99% ee). The one-pot methodology comprises a cascade of organocatalytic Michael-Michael-aldol-Henry reactions of 7-nitrohept-3-en-2-one and 5-(1-methyl-2,5-dioxocyclopentyl)pent-2-enal. The structure and absolute configuration of the products were confirmed by X-ray analyses of appropriate products. PMID:24796861

Jhuo, Dai-Huei; Hong, Bor-Cherng; Chang, Chun-Wei; Lee, Gene-Hsiang

2014-05-16

98

Highly diastereo- and enantioselective organocatalytic domino Michael/aldol reaction of acyclic 3-halogeno-1,2-diones to ?,?-unsaturated aldehydes.  

PubMed

The first organocatalytic diastereo- and enantioselective domino Michael/aldol reaction of 3-halogeno-1,2-diones to ?,?-unsaturated aldehydes has been achieved. This transformation tolerates a large variety of electronically different substituents on both reactive partners and allows the synthesis of challenging cyclopentanone derivatives with four contiguous stereogenic centers in excellent diastereoselectivities (>20:1 dr) as well as good yields (69-97%), and enantioselectivities (up to 94% ee). PMID:23607321

Lefranc, Alice; Guénée, Laure; Alexakis, Alexandre

2013-05-01

99

Enantioselective organocatalytic domino Michael/aldol reactions: an efficient procedure for the stereocontrolled construction of 2H-thiopyrano[2,3-b]quinoline scaffolds.  

PubMed

An efficient procedure for the stereocontrolled construction of 2H-thiopyrano[2,3-b]quinoline scaffolds has been developed, starting from simple compounds. The domino Michael/aldol reactions between 2-mercaptobenzaldehydes and enals, promoted by chiral diphenylprolinol TMS ether, proceed with excellent chemo- and enantioselectivity to give the corresponding synthetically useful and pharmaceutically valuable 2H-thiopyrano[2,3-b]quinolines in high yields with 90-99?% ee. PMID:23728825

Wu, Lulu; Wang, Youming; Song, Haibin; Tang, Liangfu; Zhou, Zhenghong; Tang, Chuchi

2013-09-01

100

Tandem Aldol-Michael reactions in aqueous diethylamine medium: a greener and efficient approach to dimedone-barbituric acid derivatives  

PubMed Central

Background Green chemistry is a rapidly developing new field that provides us with a proactive avenue for the sustainable development of future science and technologies. Green chemistry uses highly efficient and environmentally benign synthetic protocols to deliver lifesaving medicines, accelerating lead optimization processes in drug discovery, with reduced unnecessary environmental impact. From this view point, it is desirable to use water instead of organic solvents as a reaction medium, since water is safe, abundant and an environmentally benign solvent. Results A convenient one-pot method for the efficient synthesis of the novel Zwitterion derivatives 4a-pvia a three-component condensation reaction of barbituric acid derivatives 1a,b, dimedone 2, and various aldehydes 3 in the presence of aqueous diethylamine media is described. This new approach is environmentally benign, with clean synthetic procedure, short reaction times and easy work-up procedure which proceeded smoothly to provide excellent yield (88-98%). The synthesized products were characterized by elemental analysis, IR, MS, NMR and CHN analysis. The structure of 4a was further confirmed by single crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pbca with ??=?14.6669 (5) Å, b?=?18.3084 (6) Å, c?=?19.0294 (6) Å, ??=?90°, ??=?90°, = 90°, V?=?5109.9 (3) Å3, and Z?=?8. The molecules are packed in crystal structure by weak intermolecular C–H? ? ?O hydrogen bonding interactions. Conclusions An environmentally benign Aldol-Michael protocol for the synthesis of dimedone-barbituric derivatives using aqueous diethylamine medium is achieved. PMID:24485059

2014-01-01

101

BF?·Et?O-induced stereoselective aldol reaction with benzaldehyde, and steroid sapogenins and its application to a convenient synthesis of dinorcholanic lactones.  

PubMed

Treatment of steroid sapogenins with benzaldehyde and BF(3)·Et(2)O cleanly produces E-23(23')-benzylidenspirostanes in good yields in a reaction pathway which consists on an aldol reaction followed by a dehydration step. The obtained E-23(23')-benzylidenspirostanes can be easily converted to dinorcholanic lactones by treatment with CrO(3) in acetic acid. The synthetic sequence to dinorcholanic lactones is compatible with the presence of double bonds and carbonyl groups in the steroid framework. PMID:22449388

Ruíz-Pérez, Karen M; Romero-Ávila, Margarita; Tinajero-Delgado, Verónica; Flores-Álamo, Marcos; Iglesias-Arteaga, Martín A

2012-06-01

102

LETTER 1371 An Improved Procedure for Asymmetric Aldol Additions with N-Acyl  

E-print Network

: Asymmetric aldol additions using chlorotitanium eno- lates of N-acyl oxazolidinones, oxazolidinethiones reactions, asymmetric synthesis, titanium eno- lates, imides, glycolates The chiral auxiliary mediated found increasingly wider use as an eno- lization method for asymmetric aldol reactions.10 However

103

Enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates via boron-mediated asymmetric aldol reaction.  

PubMed

A reagent-controlled, diastereo- and enantioselective synthesis of anti- and syn-?-hydroxy-?-phenyl carboxylates has been achieved by the proper choice of solvent, temperature, alkoxy group, and amine for the diisopinocampheylboron-mediated asymmetric enolization-aldolization of phenylacetates. The pure diastereomers can be readily separated by column chromatography. PMID:23478288

Ramachandran, P Veeraraghavan; Chanda, Prem B

2013-04-18

104

Iterative direct aldol strategy for polypropionates: enantioselective total synthesis of (-)-membrenone a and B.  

PubMed

An iterative direct aldol reaction using a C3 propionate unit as an aldol donor offers expeditious access to polyketide assembly in a highly diastereo- and enantioselective manner. An all-syn polyketide array with four consecutive stereogenic centers was efficiently constructed by an aldol reaction of thiopropionamide via soft Lewis acid/hard Brønsted base cooperative catalysis. This iterative aldol strategy led to an enantioselective synthesis of (-)-membrenone A and B. PMID:25259628

Alagiri, Kaliyamoorthy; Lin, Shaoquan; Kumagai, Naoya; Shibasaki, Masakatsu

2014-10-17

105

Asymmetric aldol reactions between acetone and benzaldehydes catalyzed by chiral Zn2+ complexes of aminoacyl 1,4,7,10-tetraazacyclododecane: fine-tuning of the amino-acid side chains and a revised reaction mechanism.  

PubMed

We previously reported that chiral Zn(2+) complexes that were designed to mimic the actions of class-I and class-II aldolases catalyzed the enantioselective aldol reactions of acetone and its analogues thereof with benzaldehyde derivatives. Herein, we report the synthesis of new chiral Zn(2+) complexes that contain Zn(2+)-tetraazacyclododecane (Zn(2+)-[12]aneN4) moieties and amino acids that contain aliphatic, aromatic, anionic, cationic, and dipeptide side chains. The chemical and optical yields of the aldol reaction were improved (up to 96?% ee) by using ZnL complexes of L-decanylglycyl-pendant [12]aneN4 (L-ZnL(7)), L-naphthylalanyl-pendant [12]aneN4 (L-ZnL(10)), L-biphenylalanyl-pendant [12]aneN4 (L-ZnL(11)), and L-phenylethylglycyl-pendant [12]aneN4 ligands (L-ZnL(12)). UV/Vis and circular dichroism (CD) titrations of acetylacetone (acac) with ZnL complexes confirmed that a ZnL-(acac)(-) complex was exclusively formed and not the enaminone of ZnL and acac, as we had previously proposed. Moreover, the results of stopped-flow experiments indicated that the complexation of (acac)(-) with ZnL was complete within milliseconds, whereas the formation of an enaminone required several hours. X-ray crystal-structure analysis of L-ZnL(10) and the ZnL complex of L-diphenylalanyl-pendant [12]aneN4 (L-ZnL(13)) shows that the NH2 groups of the amino-acid side chains of these ligands are coordinated to the Zn(2+) center as the fourth coordination site, in addition to three nitrogen atoms of the [12]aneN4 rings. The reaction mechanism of these aldol reactions is discussed and some corrections are made to our previous mechanistic hypothesis. PMID:23780779

Itoh, Susumu; Tokunaga, Takuya; Sonoike, Shotaro; Kitamura, Masanori; Yamano, Akihito; Aoki, Shin

2013-09-01

106

Towards catalyst compartimentation in combined chemo- and biocatalytic processes: immobilization of alcohol dehydrogenases for the diastereoselective reduction of a ?-hydroxy ketone obtained from an organocatalytic aldol reaction.  

PubMed

The alcohol dehydrogenases (ADHs) from Lactobacillus kefir and Rhodococcus sp., which earlier turned out to be suitable for a chemoenzymatic one-pot synthesis with organocatalysts, were immobilized with their cofactors on a commercially available superabsorber based on a literature known protocol. The use of the immobilized ADH from L. kefir in the reduction of acetophenone as a model substrate led to high conversion (>95%) in the first reaction cycle, followed by a slight decrease of conversion in the second reaction cycle. A comparable result was obtained when no cofactor was added although a water rich reaction media was used. The immobilized ADHs also turned out to be suitable catalysts for the diastereoselective reduction of an organocatalytically prepared enantiomerically enriched aldol adduct, leading to high conversion, diastereomeric ratio and enantioselectivity for the resulting 1,3-diols. However, at a lower catalyst and cofactor amount being still sufficient for biotransformations with "free" enzymes the immobilized ADH only showed high conversion and >99% ee for the first reaction cycle whereas a strong decrease of conversion was observed already in the second reaction cycle, thus indicating a significant leaching effect of catalyst and/or cofactor. PMID:24036136

Rulli, Giuseppe; Heidlindemann, Marcel; Berkessel, Albrecht; Hummel, Werner; Gröger, Harald

2013-11-01

107

Aldol-Promoted Reaction of R106-Sarcosine: Synthesis and Conformational Analysis of Novel R106 Analogs.  

PubMed

A unique semisynthetic pathway has been used as a route to novel R106 derivatives. R106-sarcosine, 2, was discovered to be a key intermediate to obtain these derivatives using classical aldol alkylation conditions. Surprisingly, the site of alkylation on 2 was found to be conformationally hindered which yielded both the D and L isomers of R106-1 (aureobasidin A), 1, and other new R106 derivatives. The scope of the alkylation was found to be highly dependent upon the reactivity potential of the electrophile. Semiempirical calculations on R106-1 and 8-(N-methylthrenonine)aureobasidin A, 7, were performed to investigate the thermodynamic stabilities of the D and L isomers. By contrast to stable conformations observed by two X-ray crystal structures of aureobasidins, the calculations indicated that the D isomers were significantly more stable. Furthermore, model semiempirical calculations to probe facial selecitivty were consistent with results obtained experimentally. PMID:11667021

Rodriguez, Michael J.; Zweifel, Mark J.; Loncharich, Richard J.

1996-03-01

108

Enantio- and Diastereoselective Synthesis of syn-?-Hydroxy-?-Vinyl Carboxylic Esters via Reductive Aldol Reactions of Ethyl Allenecarboxylate with 10-TMS-9-Borabicyclo[3.3.2]decane and DFT Analysis of the Hydroboration Pathway  

PubMed Central

An enantio- and diastereoselective synthesis of syn-?-hydroxy-?-vinyl carboxylate esters 3 via the reductive aldol reaction of ethyl allenecarboxylate (2) with 10-trimethylsilyl-9-borabicyclo[3.3.2]decane (1R, Soderquist’s borane) has been developed. Density functional theory calculations suggest that the allene hydroboration involves the 1,4-reduction of 2 with the chiral borane 1R, leading directly to dienolborinate Z-(O)-8a. PMID:24138187

Kister, Jeremy; Ess, Daniel H.

2013-01-01

109

One-pot chemoenzymatic synthesis of chiral 1,3-diols using an enantioselective aldol reaction with chiral Zn2+ complex catalysts and enzymatic reduction using oxidoreductases with cofactor regeneration.  

PubMed

We previously reported on enantioselective aldol reactions of acetone and some aldehydes catalyzed by chiral Zn(2+) complexes of L-prolyl-pendant [12]aneN(4) (L-ZnL(1)) and L-valyl-pendant [12]aneN(4) (L-ZnL(2)) in aqueous solution. Here, we report on the one-pot chemoenzymatic synthesis of chiral 1,3-diols in an aqueous solvent system at room temperature by a combination of enantioselective aldol reactions catalyzed by Zn(2+) complexes of L- and D-phenylalanyl-pendant [12]aneN(4) (L-ZnL(3) and D-ZnL(3) ) and the successive enantioselective reduction of the aldol products using oxidoreductases with the regeneration of the NADH (reduced form of nicotinamine adenine dinucleotide) cofactor. The findings indicate that all four stereoisomers of 1,3-diols can be produced by appropriate selection of a chiral Zn(2+)-complex and an oxidoreductase commercially available from the "Chiralscreen OH" kit. PMID:22174123

Sonoike, Shotaro; Itakura, Toshinari; Kitamura, Masanori; Aoki, Shin

2012-01-01

110

Air-stable, storable, and highly efficient chiral zirconium catalysts for enantioselective Mannich-type, aza Diels-Alder, aldol, and hetero Diels-Alder reactions.  

PubMed

For the synthesis of optically active compounds, chiral catalysts have attracted much attention because large quantities of optically active molecules can be prepared from a small amount of a chiral source. However, many chiral catalysts are often unstable in air (oxygen) and/or in the presence of water. This is especially the case in chiral Lewis acid catalysis, because most Lewis acids are air- and moisture-sensitive. Therefore, many catalysts are prepared in situ in an appropriate solvent just before use, and they cannot be stored for extended periods. We have developed air-stable, storable, and highly efficient chiral zirconium Lewis acids. The catalysts promoted asymmetric Mannich-type, aza Diels-Alder, aldol, and hetero Diels-Alder reactions efficiently with high enantioselectivities. A key to stabilizing the catalysts is an appropriate combination of chiral zirconium Lewis acids with molecular sieves, and the zirconium-molecular sieves-combined catalysts can be stored for extended periods in air at room temperature without loss of activity. Moreover, it has been demonstrated that the catalysts can be recovered and reused. PMID:15067139

Kobayashi, Shu; Ueno, Masaharu; Saito, Susumu; Mizuki, Yumiko; Ishitani, Haruro; Yamashita, Yasuhiro

2004-04-13

111

Bimorpholine-mediated enantioselective intramolecular and intermolecular aldol condensation.  

PubMed

Monosalts of N-substituted bimorpholine derivatives are efficient organocatalysts in intramolecular and intermolecular aldol reactions. The properties of the catalysts can be tuned either by the selection of an appropriate acid for the salt formation or by the change of a substituent at the nitrogen atom. In aldol condensation, i-Pr-substituted bimorpholine is the most stereoselective catalyst affording products in high yield with enantioselectivities up to 95% ee. PMID:17567073

Kanger, Tõnis; Kriis, Kadri; Laars, Marju; Kailas, Tiiu; Müürisepp, Aleksander-Mati; Pehk, Tõnis; Lopp, Margus

2007-07-01

112

Sequential organocatalytic Stetter and Michael-Aldol condensation reaction: asymmetric synthesis of fully substituted cyclopentenes via a [1 + 2 + 2] annulation strategy.  

PubMed

A stereoselective synthesis of fully substituted cyclopentenes has been achieved by a sequential organocatalyzed Stetter and Michael-aldol condensation of aromatic aldehydes, nitroalkenes, and ?,?-unsaturated aldehydes via the [1 + 2 + 2] annulation strategy with excellent diastereoselectivities and enantioselectivities (up to >99% ee). PMID:20936853

Hong, Bor-Cherng; Dange, Nitin S; Hsu, Che-Sheng; Liao, Ju-Hsiou

2010-11-01

113

Enantioselective organocatalytic one-pot amination/aza-Michael/aldol condensation reaction sequence: synthesis of 3-pyrrolines with a quaternary stereocenter.  

PubMed

Primary amine-catalyzed direct conversion of ?,?-disubstituted aldehydes into 3-pyrrolines with a quaternary stereocenter is reported. The one-pot enantioselective sequence is based on a ?-amination, an aza-Michael addition of hydrazine, an aldol condensation dehydratation and proceeds with good yields and excellent levels of enantioselectivity. Synthetically attractive applications including the formation of aziridinopyrrolidine or epoxypyrrolidine derivatives with good yields and selectivities are also described. PMID:22927036

Desmarchelier, Alaric; Coeffard, Vincent; Moreau, Xavier; Greck, Christine

2012-10-01

114

Chiral catalysts dually functionalized with amino acid and Zn2+ complex components for enantioselective direct aldol reactions inspired by natural aldolases: design, synthesis, complexation properties, catalytic activities, and mechanistic study.  

PubMed

Aldolases are enzymes that catalyze stereospecific aldol reactions in a reversible manner. Naturally occurring aldolases include class I aldolases, which catalyze aldol reactions via enamine intermediates, and class II aldolases, in which Zn(2+) enolates of substrates react with acceptor aldehydes. In this work, Zn(2+) complexes of L-prolyl-pendant[15]aneN(5) (ZnL(3)), L-prolyl-pendant[12]aneN(4) (ZnL(4)), and L-valyl-pendant[12]aneN(4) (ZnL(5)) were designed and synthesized for use as chiral catalysts for enantioselective aldol reactions. The complexation constants for L(3) to L(5) with Zn(2+) [logK(s)(ZnL)] were determined to be 14.1 (for ZnL(3)), 7.6 (for ZnL(4)), and 9.6 (for ZnL(5)), indicating that ZnL(3) is more stable than ZnL(4) and ZnL(5). The deprotonation constants of Zn(2+)-bound water [pK(a)(ZnL) values] for ZnL(3), ZnL(4), and ZnL(5) were calculated to be 9.2 (for ZnL(3)), 8.2 (for ZnL(4)), and 8.6 (for ZnL(5)), suggesting that the Zn(2+) ions in ZnL(3) is a less acidic Lewis acid than in ZnL(4) and ZnL(5). These values also indicated that the amino groups on the side chains weakly coordinate to Zn(2+). We carried out aldol reactions between acetone and 2-chlorobenzaldehyde and other aldehydes in the presence of catalytic amounts of the chiral Zn(2+) complexes in acetone/H(2)O at 25 and 37 degrees C. Whereas ZnL(3) yielded the aldol product in 43% yield and 1% ee (R), ZnL(4) and ZnL(5) afforded good chemical yields and high enantioselectivities of up to 89% ee (R). UV titrations of proline and ZnL(4) with acetylacetone (acac) in DMSO/H(2)O (1:2) indicate that ZnL(4) facilitates the formation of the ZnL(4)(acac)(-) complex (K(app)=2.1x10(2) M(-1)), whereas L-proline forms a Schiff base with acac with a very small equilibrium constant. These results suggest that the amino acid components and the Zn(2+) ions in ZnL(4) and ZnL(5) function in a cooperative manner to generate the Zn(2+)-enolate of acetone, thus permitting efficient enantioselective C-C bond formation with aldehydes. PMID:19746465

Itoh, Susumu; Kitamura, Masanori; Yamada, Yasuyuki; Aoki, Shin

2009-10-12

115

Synthesis of novel chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives via domino aldol-type/hetero Diels-Alder reaction and their cytotoxicity evaluation.  

PubMed

New chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives have been synthesized by domino aldol-type reaction/hetero Diels-Alder reaction generated from o-quinone methide in situ from 7-O-prenyl derivatives of 8-formyl-2,3-disubstituted chromenones with resorcinols/naphthols in the presence of 20 mol% ethylenediamine diacetate (EDDA), triethylamine (2 mL) as co-catalyst in CH3CN under reflux conditions in good yields. The structures were established based on spectroscopic data, and further confirmed by X-ray diffraction analysis. The results showed that compounds 4h and 4j exhibited very potent cytotoxicity against human cervical cancer cell line (HeLa). Compound 4h displayed good inhibitory activity against both breast cancer cell lines, MDA-MB-231 and MCF-7. Further, the compound 4i exhibited good cytotoxicity against only MDA-MB-231, and compound 4j showed promising activity against human lung cancer cell line, A549 with IC50 value of 2.53±0.07 ?M, which was comparable to the standard doxorubicin (IC50=1.21±0.1 ?M). PMID:25172420

Madda, Jyothi; Venkatesham, Akkaladevi; Naveen Kumar, Bejjanki; Nagaiah, Kommu; Sujitha, Pombala; Ganesh Kumar, C; Rao, Tadikamalla Prabhakar; Jagadeesh Babu, Nanubolu

2014-09-15

116

Catalytic Enantioselective Quick Route to Aldol-Tethered 1,6- and 1,7-Enynes from ?-Unsaturated Aldehydes.  

PubMed

An effective asymmetric route to functionalized 1,6- and 1,7-enynes has been developed based on a direct cross-aldol reaction between ?-unsaturated aldehydes and propargylic aldehydes (?,?-ynals) promoted by combined ?,?-dialkylprolinol ether/Brønsted acid catalysis. This synergistic activation strategy is key to accessing the corresponding aldol adducts with high stereoselectivity, both enantio- and diastereoselectivity. The aldol reaction also proceeds well with propargylic ketones (?,?-ynones) thus enabling a stereocontrolled access to the corresponding tertiary alcohols. The utility of these adducts, which are difficult to prepare through standard methodology, is demonstrated by their transformation into trisubstituted bicyclic enones using standard Pauson-Khand conditions. PMID:25283152

García, Jesús M; Odriozola, José M; Razkin, Jesús; Lapuerta, Irati; Odriozola, Amaiur; Urruzuno, Iñaki; Vera, Silvia; Oiarbide, Mikel; Palomo, Claudio

2014-11-17

117

Hybrid gold/chiral Brønsted acid relay catalysis allows an enantioselective synthesis of (-)-5-epi-eupomatilone-6.  

PubMed

An enantioselective synthesis of (-)-5-epi-eupomatilone-6 has been accomplished by using relay catalytic cascade intramolecular hydrosiloxylation and Mukaiyama aldol reaction of 2,3,4-trimethoxy-6-(phenylethynyl)phenyl dimethylsilanol with fluorenylglyoxylate. PMID:24328038

Wu, Xiang; Li, Ming-Li; Wang, Pu-sheng

2014-01-01

118

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step.  

PubMed

The first organocatalytic asymmetric synthesis of smyrindiol, by using an (S)-proline catalyzed enantioselective intramolecular aldol reaction as the key step, is described. Smyrindiol was synthesized from commercially available 2,4-dihydroxybenzaldehyde in 15 steps, with excellent stereoselectivity (de = 99%, ee = 99%). In the course of this total synthesis a new and mild coumarin assembly was developed. PMID:23019438

Enders, Dieter; Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

2012-01-01

119

Domino hydroformylation/aldol condensation/hydrogenation catalysis: highly selective synthesis of ketones from olefins.  

PubMed

A general and highly chemo- and regioselective synthesis of ketones from olefins by domino hydroformylation/aldol condensation/hydrogenation reaction has been developed. A variety of olefins are efficiently converted into various ketones in good to excellent yields and regioselectivities in the presence of a specific rhodium phosphine/base-acid catalyst system. PMID:25331557

Fang, Xianjie; Jackstell, Ralf; Börner, Armin; Beller, Matthias

2014-11-24

120

Neighboring Group Effects in Intramolecular Aldol Condensations. Rate Enhancement by gamma Substituents(1).  

PubMed

The O-acetyl dieneol 1b, obtained from the Grignard addition of 2-(2-bromoethyl)-1,3-dioxolane to 2,4-hexadienal via 1a, and followed by an acetylation, was treated with maleic anhydride to give the crystalline Diels-Alder adduct 2b with good stereoselectivity. The acetal of 2b was selectively hydrolyzed to the acetoxy aldehyde 3b. This was treated with potassium hydride in tetrahydrofuran. A stereoselective intramolecular Aldol reaction resulted in the formation of the tricyclic lactone 4b. However, attempts to achieve an Aldol condensation under similar reaction conditions with the analogous aldehyde 3c, lacking the acetoxy group, failed, giving back the starting material 3c. On the other hand, the methoxy aldehyde 3d was cyclized to the tricyclic compound 4d. PMID:11667238

Eberle, Marcel K.

1996-05-31

121

Synthesis of the Cores of Hypocrellin and Shiraiachrome: Diastereoselective 1,8-Diketone Aldol Cyclization  

PubMed Central

Intramolecular 1,8-diketone aldol reactions were studied as a tool for the construction of the 7-membered rings of hypocrellin and shiraiachrome. Conditions were identified to obtain the relative stereochemistries present in the two natural products with excellent diastereoselectivity. In addition, a nine-membered ring congener, which has yet to be observed in nature, formed with high selectivity when a hindered amine was used in conjunction with silazide bases. PMID:19894740

O'Brien, Erin M.; Li, Jingxian; Carroll, Patrick J.

2009-01-01

122

A diastereoselective, nucleophile-promoted aldol-lactonization of ketoacids leading to bicyclic-?-lactones.  

PubMed

An improved, tandem acid activation/aldol-lactonization process is described. This more practical protocol shortens reaction times for the construction of bicyclic ?-lactones from ketoacids and implements the use of commercially available reagents p-toluenesulfonyl chloride (p-TsCl) as activator and 4-dimethylaminopyridine (4-DMAP) as nucleophilic promoter (Lewis base). Substrates with ?-substituents, with respect to the carboxylic acid, consistently showed excellent levels of diastereoselectivity during the bis-cyclization event. PMID:22260519

Liu, Gang; Shirley, Morgan E; Romo, Daniel

2012-03-01

123

From amino alcohol to aminopolyol: one-pot multienzyme oxidation and aldol addition.  

PubMed

In this work, the successful coupling of enzymatic oxidation and aldol addition reactions for the synthesis of a Cbz-aminopolyol from a Cbz-amino alcohol was achieved for the first time in a multienzymatic one-pot system. The two-step cascade reaction consisted of the oxidation of Cbz-ethanolamine to Cbz-glycinal catalyzed by chloroperoxidase from the fungus Caldariomyces fumago and aldol addition of dihydroxyacetone phosphate to Cbz-glycinal catalyzed by rhamnulose-1-phosphate aldolase expressed as a recombinant enzyme in Escherichia coli, yielding (3R,4S)-5-{[(benzyloxy)carbonyl]amino}-5-deoxy-1-O-phosphonopent-2-ulose. Tools of enzymatic immobilization, reactor configurations, and modification of the reaction medium were applied to highly increase the production of the target compound. While the use of soluble enzymes yielded only 23.6 % of Cbz-aminopolyol due to rapid enzyme inactivation, the use of immobilized ones permitted an almost complete consumption of Cbz-ethanolamine, reaching Cbz-aminopolyol yields of 69.1 and 71.9 % in the stirred-tank and packed-bed reactor, respectively. Furthermore, the reaction production was 18-fold improved when it was catalyzed by immobilized enzymes in the presence of 5 % (v/v) dioxane, reaching a value of 86.6 mM of Cbz-aminopoliol (31 g/L). PMID:23749229

Peši?, Milja; López, Carmen; López-Santín, Josep; Alvaro, Gregorio

2013-08-01

124

Domino-Hydroformylation/Aldol Condensation Catalysis: Highly Selective Synthesis of ?,?-Unsaturated Aldehydes from Olefins.  

PubMed

A general and highly chemo-, regio-, and stereoselective synthesis of ?,?-unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted ?,?-unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid-base catalyst system. In view of the easy availability of the substrates, the high atom-efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of ?,?-unsaturated aldehydes. PMID:25179918

Fang, Xianjie; Jackstell, Ralf; Franke, Robert; Beller, Matthias

2014-10-01

125

A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

A number of laboratory exercises for the organic chemistry curriculum that emphasize enantioselective synthesis of the aldol condensation which involves the proline-catalyzed condensation between acetone and isobutyraldehyde are explored. The experiment illustrates some of the trade-offs involved in green chemistry like the use of acetone in large…

Bennett, George D.

2006-01-01

126

Highly efficient aldol additions of DHA and DHAP to N-Cbz-amino aldehydes catalyzed by L-rhamnulose-1-phosphate and L-fuculose-1-phosphate aldolases in aqueous borate buffer.  

PubMed

Aldol addition reactions of dihydroxyacetone (DHA) to N-Cbz-amino aldehydes catalyzed by L-rhamnulose-1-phosphate aldolase (RhuA) in the presence of borate buffer are reported. High yields of aldol adduct (e.g. 70-90%) were achieved with excellent (>98?:?2 syn/anti) stereoselectivity for most S or R configured acceptors, which compares favorably to the reactions performed with DHAP. The stereochemical outcome was different and depended on the N-Cbz-amino aldehyde enantiomer: the S acceptors gave the syn (3R,4S) aldol adduct whereas the R ones gave the anti (3R,4R) diastereomer. Moreover, the tactical use of Cbz protecting group allows simple and efficient elimination of borate and excess of DHA by reverse phase column chromatography or even by simple extraction. This, in addition to the use of unphosphorylated donor nucleophile, makes a useful and expedient methodology for the synthesis of structurally diverse iminocyclitols. The performance of aldol additions of dihydroxyacetone phosphate (DHAP) to N-Cbz-amino aldehydes using RhuA and L-fuculose-1-phosphate aldolase (FucA) catalyst in borate buffer was also evaluated. For FucA catalysts, including FucA F131A, the initial velocity of the aldol addition reactions using DHAP were between 2 and 10 times faster and the yields between 1.5 and 4 times higher than those in triethanolamine buffer. In this case, the retroaldol velocities measured for some aldol adducts were lower than those without borate buffer indicating some trapping effect that could explain the improvement of yields. PMID:22042499

Garrabou, Xavier; Calveras, Jordi; Joglar, Jesús; Parella, Teodor; Bujons, Jordi; Clapés, Pere

2011-12-21

127

Aldol Reactions - Isotope Effects, Mechanism and Dynamic Effects  

E-print Network

S KCal/Mol Cal/Mol-Kelvin Cal/Mol-Kelvin Total 67.836 27.746 86.642 C,0,0.0635074983,0.,-0.0605631261 C,0,0.0137883836,0.,1.3444347379 C,0,1.1745729015,0.,2.1060260578 C,0... S KCal/Mol Cal/Mol-Kelvin Cal/Mol-Kelvin Total 67.596 27.866 86.994 C,0,0.0603668497,0.,-0.0574078273 C,0,0.0124120185,0.,1.348903725 C,0,1.1762556373,0.,2.1088773404 C,0...

Vetticatt, Mathew J.

2011-02-22

128

An Aldol-based Build/Couple/Pair Strategy for the Synthesis of Medium- and Large-Sized Rings: Discovery of Macrocyclic Histone Deacetylase Inhibitors  

PubMed Central

An aldol-based ‘build/couple/pair’ (B/C/P) strategy was applied to generate a collection of stereochemically and skeletally diverse small molecules. In the build phase, a series of asymmetric syn- and anti- aldol reactions were performed to produce four stereoisomers of a Boc protected ?-amino acid. In addition both stereoisomers of O-PMB-protected alaninol were generated to provide a chiral amine coupling partner. In the couple step, eight stereoisomeric amides were synthesized by coupling the chiral acid and amine building blocks. The amides were subsequently reduced to generate the corresponding secondary amines. In the pair phase, three different reactions were employed to enable intramolecular ring-forming processes, namely: nucleophilic aromatic substitution (SNAr), Huisgen [3+2] cycloaddition and ring-closing metathesis (RCM). Despite some stereochemical dependencies, the ring-forming reactions were optimized to proceed with good to excellent yields providing a variety of skeletons ranging in size from 8- to 14-membered rings. Scaffolds resulting from the RCM pairing reaction were diversified on solid-phase to yield a 14,400-membered library of macrolactams. Screening of this library led to the discovery of a novel class of histone deacetylase inhibitors, which display mixed enzyme inhibition and led to increased levels of acetylation in a primary mouse neuron culture. The development of stereo-structure/activity relationships (SSAR) was made possible by screening all 16 stereoisomers of the macrolactams produced through the aldol-based B/C/P strategy. PMID:21067169

Marcaurelle, Lisa A.; Comer, Eamon; Dandapani, Sivaraman; Duvall, Jeremy R.; Gerard, Baudouin; Kesavan, Sarathy; Lee, Maurice D.; Liu, Haibo; Lowe, Jason T.; Marie, Jean-Charles; Mulrooney, Carol A.; Pandya, Bhaumik A.; Rowley, Ann; Ryba, Troy D.; Suh, Byung-Chul; Wei, Jingqiang; Young, Damian W.; Akella, Lakshmi B.; Ross, Nathan T.; Zhang, Yan-Ling; Fass, Daniel M.; Reis, Surya A.; Zhao, Wen-Ning; Haggarty, Stephen J.; Palmer, Michelle; Foley, Michael A.

2010-01-01

129

One-pot Aldol Condensation and Hydrodeoxygenation of Biomass-derived Carbonyl Compounds for Biodiesel Synthesis.  

PubMed

Integrating reaction steps is of key interest in the development of processes for transforming lignocellulosic materials into drop-in fuels. We propose a procedure for performing the aldol condensation (reaction between furfural and acetone is taken as model reaction) and the total hydrodeoxygenation of the resulting condensation adducts in one step, yielding n-alkanes. Different combinations of catalysts (bifunctional catalysts or mechanical mixtures), reaction conditions, and solvents (aqueous and organic) have been tested for performing these reactions in an isothermal batch reactor. The results suggest that the use of bifunctional catalysts and aqueous phase lead to an effective integration of both reactions. Therefore, selectivities to n-alkanes higher than 50?% were obtained using this catalyst at typical hydrogenation conditions (T=493?K, P=4.5?MPa, 24?h reaction time). The use of organic solvent, carbonaceous supports, or mechanical mixtures of monofunctional catalysts leads to poorer results owing to side effects; mainly, hydrogenation of reactants and adsorption processes. PMID:25088473

Faba, Laura; Díaz, Eva; Ordóñez, Salvador

2014-10-01

130

Substrate inhibition in the heterogeneous catalyzed aldol condensation: A mechanistic study of supported organocatalysts  

SciTech Connect

In this study, we demonstrate how materials science can be combined with the established methods of organic chemistry to find mechanistic bottlenecks and redesign heterogeneous catalysts for improved performance. By using solid-state NMR, infrared spectroscopy, surface and kinetic analysis, we prove the existence of a substrate inhibition in the aldol condensation catalyzed by heterogeneous amines. We show that modifying the structure of the supported amines according to the proposed mechanism dramatically enhances the activity of the heterogeneous catalyst. We also provide evidence that the reaction benefits significantly from the surface chemistry of the silica support, which plays the role of a co-catalyst, giving activities up to two orders of magnitude larger than those of homogeneous amines. This study confirms that the optimization of a heterogeneous catalyst depends as much on obtaining organic mechanistic information as it does on controlling the structure of the support.

Kandel, Kapil; Althaus, Stacey M.; Peeraphatdit, Chorthip; Kobayashi, Takeshi; Trewyn, Brian G.; Pruski, Marek; Slowing, Igor I.

2012-05-23

131

Synthesis of aza-fused isoquinolines through domino cross-aldol condensation and palladium-catalyzed intramolecular direct arylation.  

PubMed

A straightforward method has been developed for the synthesis of aroyl-substituted imidazo-/benzimidazo-fused isoquinolines. The cascade reaction proceeds via a cross-aldol condensation of 2-(1H-imidazol-1-yl/benzimidazolyl-1-yl)-1-arylethanones and 2-bromobenzaldehyde followed by palladium-catalyzed intramolecular C-H functionalization. This approach offers a simple and efficient alternative one-pot protocol for the assembly of imidazo/benzimidazo[2,1-a]isoquinolines in moderate to good yields. PMID:25046002

Dhiman, Shiv; Pericherla, Kasiviswanadharaju; Nandwana, Nitesh K; Kumar, Dalip; Kumar, Anil

2014-08-15

132

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s as high-efficiency catalysts for carbonyl-group transformation reactions.  

PubMed

Strong Lewis acids of air-stable metallocene bis(perfluorooctanesulfonate)s [M(Cp)(2)][OSO(2)C(8)F(17)](2)?nH(2)O?THF (M = Zr (2?a?3?H(2)O?THF), M = Ti (2?b?2?H(2)O?THF)) were synthesized by the reaction of [M(Cp)(2)]Cl(2) (M = Zr (1?a), M = Ti (1?b)) with nBuLi and C(8)F(17)SO(3)H (2?equiv) or with C(8)F(17)SO(3)Ag (2?equiv). The hydrate numbers (n) of these complexes were variable, changing from 0 to 4 depending on conditions. In contrast to well-known metallocene triflates, these complexes suffered no change in open air for a year. thermogravimetry-differential scanning calorimetry (TG-DSC) analysis showed that 2?a and 2?b were thermally stable at 300 and 180?°C, respectively. These complexes exhibited unusually high solubility in polar organic solvents. Conductivity measurement showed that the complexes (2?a and 2?b) were ionic dissociation in CH(3)CN solution. X-ray analysis result confirmed 2?a?3?H(2)O?THF was a cationic organometallic Lewis acid. UV/Vis spectra showed a significant red shift due to the strong complex formation between 10-methylacridone and 2?a. Fluorescence spectra showed that the Lewis acidity of 2?a fell between those of Sc(3+) (?(em)=474?nm) and Fe(3+) (?(em)=478?nm). ESR spectra showed the Lewis acidity of 2?a (0.91?eV) was at the same level as that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV), while the Lewis acidity of 2?b (1.06?eV) was larger than that of Sc(3+) (1.00?eV) and Y(3+) (0.85?eV). They showed high catalytic ability in carbonyl-compound transformation reactions, such as the Mannich reaction, the Mukaiyama aldol reaction, allylation of aldehydes, the Friedel-Crafts acylation of alkyl aromatic ethers, and cyclotrimerization of ketones. Moreover, the complexes possessed good reusability. On account of their excellent catalytic efficiency, stability, and reusability, the complexes will find broad catalytic applications in organic synthesis. PMID:22504964

Qiu, Renhua; Xu, Xinhua; Peng, Lifeng; Zhao, Yalei; Li, Ningbo; Yin, Shuangfeng

2012-05-14

133

Enantioselective total synthesis of (+)-galbulin via organocatalytic domino Michael-Michael-aldol condensation.  

PubMed

A concise and practical enantioselective synthesis of (+)-galbulin has been achieved using organocatalytic domino Michael-Michael-aldol condensation and organocatalytic kinetic resolution as the key steps. PMID:22179766

Hong, Bor-Cherng; Hsu, Che-Sheng; Lee, Gene-Hsiang

2012-02-28

134

Total synthesis of virgatolide B via exploitation of intramolecular hydrogen bonding.  

PubMed

A full account of the enantioselective total synthesis of virgatolide B is reported. Key features of the synthesis include an sp(3)-sp(2) Suzuki-Miyaura cross-coupling of a ?-trifluoroboratoamide with an aryl bromide, regioselective intramolecular carboalkoxylation, and a 1,3-anti-selective Mukaiyama aldol reaction. Intramolecular hydrogen bonding governed the regioselectivity of the key spiroketalization step, affording the natural product as a single regioisomer. PMID:24836848

Hume, Paul A; Furkert, Daniel P; Brimble, Margaret A

2014-06-01

135

Assignment of Absolute Configuration to SCH 351448 via Total Synthesis?  

PubMed Central

The synthesis and absolute configuration of SCH 351448, an interesting ionophoric natural product, are reported herein. Mukaiyama aldol-Prins and segment-coupling Prins reactions were employed to construct the constituent tetrahydropyrans of SCH 351448. Efforts to assemble the C2-symmetric core of the natural product by a templated olefin metathesis strategy are described, however, a stepwise fragment assembly was ultimately utilized to complete the target molecule. PMID:18543942

Cheung, Lael L.; Marumoto, Shinji; Anderson, Christopher D.

2008-01-01

136

Employing crude glycerol from biodiesel production as an alternative green reaction medium  

Microsoft Academic Search

Crude glycerol from triglyceride alcoholysis has successfully been employed as a green solvent in base catalyzed aldol condensation and palladium catalyzed Heck carbon–carbon coupling without any purification. The oil source did not affect reaction performance, yet the reactions in crude glycerol usually showed lower conversions than the reactions in pure glycerol. However, the residual base, which was used as a

Adi Wolfson; Gustabo Litvak; Christina Dlugy; Yoram Shotland; Dorith Tavor

2009-01-01

137

Mathematical model for aldol addition catalyzed by two D-fructose-6-phosphate aldolases variants overexpressed in E. coli.  

PubMed

Two D-fructose-6-phosphate aldolase variants namely, single variant FSA A129S and double variant FSA A129S/A165G, were used as catalysts in the aldol addition of dihydroxyacetone (DHA) to N-Cbz-3-aminopropanal. Mathematical model for reaction catalyzed by both enzymes, consisting of kinetic and mass balance equations, was developed. Kinetic parameters were estimated from the experimental data gathered by using the initial reaction rate method. The model was validated in the batch and continuously operated ultrafiltration membrane reactor (UFMR). The same type of kinetic model could be applied for both enzymes. The operational stability of the aldolases was assessed by measuring enzyme activity during the experiments. FSA A129S/A165G had better operational stability in the batch reactor (half-life time 26.7 h) in comparison to FSA A129S (half-life time 5.78 h). Both variants were unstable in the continuously operated UFMR in which half-life times were 1.99 and 3.64 h for FSA A129S and FSA A129S/A165G, respectively. PMID:23876482

Sudar, Martina; Findrik, Zvjezdana; Vasi?-Ra?ki, Dur?a; Clapés, Pere; Lozano, Carles

2013-09-10

138

A DFT analysis of thermal decomposition reactions important to natural products.  

PubMed

The thermal decomposition reactions of several important natural flavor and fragrance chemicals have been investigated using density functional theory (DFT, B3LYP/6-31G*). Retro-aldol reactions of glucose, fructose, hernandulcin, epihernandulcin, [3]-gingerol, and [4]-isogingerol; retro-carbonyl-ene reactions of isopulegol, lavandulol, isolyratol, and indicumenone; and pyrolytic syn elimination reactions of linalyl acetate, alpha-terpinyl acetate, and bornyl acetate, have been carried out. The calculations indicate activation enthalpies of around 30 kcal/mol for the retro-aldol reactions and for retro-carbonyl-ene reactions, comparable to pericyclic reactions such as the Cope rearrangement and electrocyclic reactions, and therefore important reactions at elevated temperatures (e.g., boiling aqueous solutions, gas-chromatograph injection ports). Activation enthalpies for pyrolytic eliminations are around 40 kcal/mol and are unlikely to occur during extraction or GC analysis. PMID:20734926

Setzer, William N

2010-07-01

139

Recent progress in lanthanide-catalyzed organic reactions in protic media  

Microsoft Academic Search

Lanthanide triflates are stable in water. It is possible for lanthanides to undergo many organic reactions in environmentally\\u000a friendly solvents. This makes lanthanides very promising in the field of green chemistry. This review describes the recent\\u000a development of the lanthanidecatalyzed organic reactions in protic solvents. Those reactions include Diels-Alder, Aldol, Allylation,\\u000a acetalization, pericyclization, radical reactions as well as some newlydeveloped

Luo Sanzhong; Zhang Baolian; Xian Ming; Adam JaÑczuk; Xie Wenhua; Cheng Jinpei; Peng George Wang

2001-01-01

140

Amberlyst-15 and Amberlite-200C: efficient catalysts for aldol and cross-aldol condensation under ultrasound irradiation.  

PubMed

This paper presents an improved synthesis of trans-chalcones and ?,?'-bis(arylmethylidene) cycloalkanones under ultrasound irradiation in the presence of commercial acid-resins as catalysts in solvent free conditions. Several trans-chalcones and ?,?'-bis(arylmethylidene) cycloalkanones were synthesized in good yields and excellent selectivity in a short reaction time. PMID:23490314

Lahyani, Achraf; Chtourou, Manef; Frikha, Mohamed Hédi; Trabelsi, Mahmoud

2013-09-01

141

Synthesis of 2,6-disubstituted dihydropyrans via an efficient BiBr3-initiated three component, one-pot cascade  

PubMed Central

The rapid synthesis of cis-2,6-disubstituted dihydropyrans is achieved in a three-component, one-pot cascade reaction. BiBr3-ediated addition of ketene silyl acetals or silyl enol ethers to ?,?-unsaturated cis-4-trimethylsilyl-3-butenal provides a Mukaiyama aldol adduct containing a vinylsilane moiety tethered to a silyl ether. Addition of a second aldehyde initiates a domino sequence involving intermolecular addition followed by an intramolecular silyl-modified Sakurai (ISMS) reaction. Isolated yields of this one-pot reaction vary from 44 to 80% and all compounds were isolated as the cis-diastereomers (10 examples). PMID:20161364

Lian, Yajing; Speight, Lee C.; Stevenson, Heather E.; Sprachman, Melissa M.; Katkish, Lauren A.; Mattern, M. Christa

2009-01-01

142

ALDOL- AND MANNICH-TYPE REACTIONS VIA IN SITU OLEFIN MIGRATION IN IONIC LIQUID. (R828129)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

143

An Exercise on Structure Elucidation Based on a Tricky Aldol Reaction  

ERIC Educational Resources Information Center

An exercise on structure elucidation for advanced undergraduate students is described. To determine the structure of an unknown product, students are required to use spectra together with an organic chemistry mechanism. This exercise exemplifies the procedure commonly used in research, thus helping students develop problem-solving skills. In…

Sierra, Manuel Gonzalez; Pellegrinet, Silvina C.; Colombo, Maria I.; Ruveda, Edmundo A.

2008-01-01

144

Highly enantioselective organocatalytic trifluoromethyl carbinol synthesis--a caveat on reaction times and product isolation.  

PubMed

Aldol reactions with trifluoroacetophenones as acceptors yield chiral ?-aryl, ?-trifluoromethyl tertiary alcohols, valuable intermediates in organic synthesis. Of the various organocatalysts examined, Singh's catalyst [(2S)-N-[(1S)-1-hydroxydiphenylmethyl-3-methylbutyl]-2-pyrrolidinecarboxamide] was found to efficiently promote this organocatalytic transformation in a highly enantioselective manner. Detailed reaction monitoring ((19)F-NMR, HPLC) showed that, up to full conversion, the catalytic transformation proceeds under kinetic control and affords up to 95% ee in a time-independent manner. At longer reaction times, the catalyst effects racemization. For the product aldols, even weak acids (such as ammonium chloride) or protic solvents, can induce racemization, too. Thus, acid-free workup, at carefully chosen reaction time, is crucial for the isolation of the aldols in high (and stable) enantiomeric purity. As evidenced by (19)F-NMR, X-ray structural analysis, and independent synthesis of a stable intramolecular variant, Singh's catalyst reversibly forms a catalytically inactive ("parasitic") intermediate, namely a N,O-hemiacetal with trifluoroacetophenones. X-ray crystallography also allowed the determination of the product aldols' absolute configuration (S). PMID:22631871

Duangdee, Nongnaphat; Harnying, Wacharee; Rulli, Giuseppe; Neudörfl, Jörg-M; Gröger, Harald; Berkessel, Albrecht

2012-07-11

145

Enantioselective reactions catalyzed by synthetic enzymes. A model for chemical evolution  

Microsoft Academic Search

Polyleucines of various lengths act as enantioselective catalysts in the aldol condensation between cyclohexanone and various aromatic aldehydes. Polyleucine and other polyamino acids behave as synthetic enzymes in the epoxidation of chalcone and other electron-deficient alkenes. Both reactions are of considerable prebiotic significance.

Stefano Colonna; Dario Perdicchia; Ernesto Di Mauro

2009-01-01

146

Synthetic Strategies Toward Tetrahydrofurans Involving Double Diastereoselective Nucleophile-Promoted Aldol-Lactonizations and Subsequent Applications to Bioactive Natural Products  

E-print Network

of tetrahydrofuran-fused ?-lactones through nucleophile-catalyzed aldol-lactonization (NCAL) has been developed. By employing a chiral catalyst, such as OTMS-quinidine or OTMS-quinine, coupled with a chiral aldehyde acid substrate, we have been able to successfully...

Arendt, Kevin M.

2011-08-08

147

Development of asymmetric reactions catalyzed by chiral organotin-alkoxide reagents.  

PubMed

Asymmetric catalysis under almost-neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)-BINOL-derived chiral tin-dibromide reagent that possesses a bulky aryl group at the 3 or 3' position as the chiral pre-catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three-component Mannich-type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N-nitroso aldol reaction of unsaturated lactones with nitrosoarenes. PMID:23424074

Yanagisawa, Akira; Yoshida, Kazuhiro

2013-02-01

148

Stereoselective redox transformations of phosphorus heterocycles  

Microsoft Academic Search

Chiral ?3-diazaphospholidine heterocycles of the form {(5R,4S)-N?R-ephedrine}P[N(SiMe3)2] have been demonstrated to undergo clean redox addition reactions with aldehydes (R?CHO) to afford ?-imino-?5-oxazaphospholidines of the general form {(5R,4S)-N?R-ephedrine}P(?NSiMe3)CHR?(OSiMe3); potential precursors of ?-hydoxyphosphonate esters of a type with proven medicinal application. Of crucial importance in these close relatives of the Mukaiyama aldol reaction is the ability to control stereochemistry at the newly

Mark J. Cain; Anthony Cawley; Vivienne Sum; Dearg Brown; Mark Thornton-Pett; Terence P. Kee

2003-01-01

149

A microreactor functionalized with acoustic wave effects and a liquid phase catalytic reaction.  

PubMed

In a microreactor functionalized with the effects of acoustic waves such as surface acoustic waves (SAWs) and resonance oscillations (ROs) that can be generated on ferroelectric crystals by applying rf electric power, the acoustic wave-induced dynamic lattice displacement vertical to surface significantly enhanced the catalysis of Sc(OTf)(3) in aldol condensation reaction of benzaldehyde and acetophenone to chalcone, demonstrating that the functionalization provided the microreactor with reaction-controllable functions of promoting liquid phase catalytic reactions. PMID:20386801

Nishiyama, Hiroshi; Asari, Ryusuke; Inoue, Yasunobu

2010-06-21

150

Flexible protocol for the chemo- and regioselective building of pyrroles and pyrazoles by reactions of Danishefsky's dienes with 1,2-diaza-1,3-butadienes.  

PubMed

The versatility of the Mukaiyama-Michael-type addition/heterocyclization of Danishefsky's diene with 1,2-diaza-1,3-butadienes was applied to the synthesis of both 4 H-1-aminopyrroles and 4,5 H-pyrazoles. Thus, the same reagents furnished different types of highly functionalized azaheterocycles essentially depending on their structure: as a matter of fact, R1 = COOR or CONR 2 differently affects the acidity of the proton at the adjacent carbon. An unexpected formation of 5 H-1-aminopyrroles from the reactions carried out in water was also observed. PMID:18426219

Attanasi, Orazio A; Favi, Gianfranco; Filippone, Paolino; Giorgi, Gianluca; Mantellini, Fabio; Moscatelli, Giada; Spinelli, Domenico

2008-05-15

151

Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis.  

PubMed

The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1. PMID:19006391

Evans, David A; Kvaernø, Lisbet; Dunn, Travis B; Beauchemin, André; Raymer, Brian; Mulder, Jason A; Olhava, Edward J; Juhl, Martin; Kagechika, Katsuji; Favor, David A

2008-12-01

152

Enantioselective total syntheses and absolute configuration of JBIR-02 and Mer-A2026B.  

PubMed

The first total syntheses of the piericidin related natural products Mer-A2026B and JBIR-02 are reported. Key features of the synthetic approach involve an Ir-catalyzed one-pot C-H activation/oxidation procedure for the preparation of the hydroxypyridine, a vinylogous Mukaiyama aldol reaction, and a final Negishi cross-coupling of an advanced pyridine derivative with an allylic side chain precursor. In addition, the absolute configuration of Mer-A2026B (9R,10R) and JBIR-02 (9R,10R) was established. PMID:23330661

Hoecker, Johannes; Gademann, Karl

2013-02-01

153

A general and enantioselective approach to pentoses: a rapid synthesis of PSI-6130, the nucleoside core of sofosbuvir.  

PubMed

An efficient route towards biologically relevant pentose derivatives is described. The de novo synthetic strategy features an enantioselective ?-oxidation reaction enabled by a chiral amine in conjunction with copper(II) catalysis. A subsequent Mukaiyama aldol coupling allows for the incorporation of a wide array of modular two-carbon fragments. Lactone intermediates accessed via this route provide a useful platform for elaboration, as demonstrated by the preparation of a variety of C-nucleosides and fluorinated pentoses. Finally, this work has facilitated expedient syntheses of pharmaceutically active compounds currently in clinical use. PMID:24670208

Peifer, Manuel; Berger, Raphaëlle; Shurtleff, Valerie W; Conrad, Jay C; MacMillan, David W C

2014-04-23

154

Synthesis, spectroscopic characterization, and reactivity of water-tolerant Eu3+-based precatalysts.  

PubMed

We report the synthesis, spectroscopic characterization, and reactivity of Eu(3+) in the presence of a new set of chiral ligands designed for the aqueous, enantioselective Mukaiyama aldol reaction. Luminescence and NMR measurements were used to characterize the coordination environments of the Eu(3+)-based precatalysts, and this data is compared with yields and stereoselectivities. In addition to structure-function relationships, we found that, in the presence of excess hexadentate ligands, Eu(3+) is coordinatively saturated, and subsequently, the reactivity of the precatalysts is reduced. These findings are helpful for the design of new ligands that bind Eu(3+) without saturating the Eu(3+) coordination sphere. PMID:24874180

Averill, Derek J; Allen, Matthew J

2014-06-16

155

Synthesis of 8-desmethoxy psymberin: a putative biosynthetic intermediate towards the marine polyketide psymberin.  

PubMed

The synthesis of a putative biosynthetic precursor of psymberin including a formal synthesis of the natural product is described. The key step towards the densely functionalized tetrahydropyran core was an enantioselective catalytic Mukaiyama aldol reaction using a titanium(IV)-BINOL catalyst system. syn-Selective reduction followed by ozonolysis led to a rapid assembly of the tetrahydropyran ring. This flexible approach also allows the synthesis of similar fragments of other complex molecules such as bryostatins and pederins. The syn-selective coupling between the tetrahydropyran and the aromatic aldehyde was achieved using a boron-mediated aldol reaction which was followed by further transformations to complete the synthesis of the precursor as well as the formal synthesis of the natural product. PMID:23606588

Bielitza, Max; Pietruszka, Jörg

2013-06-17

156

Chiral BINOL-derived phosphoric acids: privileged Brønsted acid organocatalysts for C-C bond formation reactions.  

PubMed

BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene-type, Diels-Alder, as well as cascade and multi-component reactions. PMID:20820680

Zamfir, Alexandru; Schenker, Sebastian; Freund, Matthias; Tsogoeva, Svetlana B

2010-12-01

157

Asymmetric synthesis of congested spiro-cyclopentaneoxindoles via an organocatalytic cascade reaction.  

PubMed

Starting from simple alkylidene oxindoles and nitroketones, a highly stereoselective methodology was developed for the synthesis of spiro-cyclopentaneoxindoles with four consecutive stereogenic centers. Using an organocatalytic cascade of Michael and aldol reactions in the presence of a chiral thiourea catalyst products were obtained in moderate to high yields and excellent enantioselectivities. Nitro, ester, and hydroxyl groups were introduced to the spiro ring, which could be used to facilitate further functionalization of the products. PMID:23879690

Noole, Artur; Ilmarinen, Kaja; Järving, Ivar; Lopp, Margus; Kanger, Tõnis

2013-08-16

158

An expeditious synthesis of tamoxifen, a representative SERM (selective estrogen receptor modulator), via the three-component coupling reaction among aromatic aldehyde, cinnamyltrimethylsilane, and ?-chlorophenetole  

Microsoft Academic Search

Two new synthetic pathways to the anti-cancer agent tamoxifen and its derivatives were developed. The first route involved the aldol reaction of benzyl phenyl ketone with acetaldehyde followed by Friedel–Crafts substitution with anisole in the presence of Cl2Si(OTf)2 to produce 1,1,2-triaryl-3-acetoxybutane, a precursor of the tamoxifen derivatives. The second one utilized the novel three-component coupling reaction among aromatic aldehydes, cinnamyltrimethylsilane,

Isamu Shiina; Yoshiyuki Sano; Masahiko Suzuki; Toshikazu Yokoyama; Akane Sasaki; Tomoko Orikasa; Tomomi Miyamoto; Masahiko Ikekita; Yukitoshi Nagahara; Yoshimune Hasome

2007-01-01

159

Selective 1,5-alkylidenecarbene insertion reactions on [3.2.1] oxabicyclic ethers: a new approach toward the AB ring system of ingenol.  

PubMed

Two methods to achieve the formal aldol reaction between acetone and two oxabicyclic [3.2.1] ketones are reported. The trimethylsilyl-protected beta-hydroxy ketones are converted by a Wittig reaction into vinyl chlorides as synthetic precursors to alkylidenecarbenes. Selective 1,5 C-H over 1,5 O-Si insertion has been applied to the synthesis of a model for the ABC ring system of ingenol. PMID:15330658

Grainger, Richard S; Owoare, Richard B

2004-08-19

160

Studies on self-assembly phenomena of hydrophilization of microporous polypropylene membrane by acetone aldol condensation products: New separator for high-power alkaline batteries  

Microsoft Academic Search

Commercial hydrophobic polypropylene (PP) membranes were modified by a novel chemical method. This procedure consists of two steps. In the first step, the virgin hydrophobic PP membrane is saturated with acetone; in the second step, the filled membrane is dipped in aqueous KOH solution (d=1.28gcm?3), i.e. in the electrolyte typical for the nickel–cadmium cell. This two-step procedure starts the aldol

Aleksander Ciszewski; Bo?ena Rydzy?ska

2007-01-01

161

Silyloxyazadienes: one intermediate and two competitive pericyclic reactions.  

PubMed

The two competing mechanisms in the reaction of 3-trialkylsilyloxy-2-aza-1,3 dienes to form beta-lactams through a [2+2] electrocyclic ring closure or tetrahydrooxazinan-4-ones via a [4+2] hetero-Diels-Alder reaction were studied using Density Functional computations. Although the [2+2] and [4+2] mechanisms are typical of dienes, their competition, starting from the same diene intermediate, has not yet been observed and analyzed. This competition is governed by a delicate interplay between temperature and substituents at the diene and dienophile, respectively. Clearly, entropy tends to favor the [4+2] hetero-Diels-Alder at low temperatures and the [2+2] electrocyclic ring closure at high temperatures, but simple substituent modifications at the diene and dienophile, can make the [4+2] competitive at high temperatures and sometimes even transform the [4+2] concerted mechanism into a two-step Mukaiyama-type process. Moreover, a study of the global electrophilicity values showed that charge transfer in the hetero-Diels-Alder transition states is driven by chemical hardness rather than by chemical potential. PMID:20445910

Bongini, Alessandro; Panunzio, Mauro; Venturini, Alessandro

2010-05-21

162

A base-free neutral phase-transfer reaction system.  

PubMed

Although phase-transfer reactions catalyzed by using quaternary ammonium salts are generally believed to require base additives, we discovered that, even without any base additives, conjugate additions of 3-substituted oxindoles to nitroolefins proceeded smoothly in the presence of lipophilic quaternary ammonium bromide under water-organic biphasic conditions. The mechanism of this novel base-free neutral phase-transfer reaction system is investigated and the assumed catalytic cycle is presented together with interesting effects of water and lipophilicity of the phase-transfer catalyst. The base-free neutral phase-transfer reaction system can be applied to highly enantioselective conjugate addition and aldol reactions under the influence of chiral bifunctional ammonium bromides as key catalysts. The structure of the chiral ammonium enolate intermediate is discussed based on the single-crystal X-ray structures of relevant ammonium salts and the importance of bifunctional design of catalyst is clearly explained in the model of intermediate. PMID:24737616

Shirakawa, Seiji; Wang, Lijia; He, Rongjun; Arimitsu, Satoru; Maruoka, Keiji

2014-06-01

163

Montmorillonite clay-promoted, solvent-free cross-aldol condensations under focused microwave irradiation.  

PubMed

An environmentally benign, clean and general protocol was developed for the synthesis of aryl and heteroaryl trans-chalcones. This method involved solvent-free reaction conditions under microwave irradiation in the presence of a clay-based catalyst, and afforded the target compounds in good yields and short reaction times. Furthermore, the same conditions allowed the synthesis of symmetrical, diarylmethylene-?,?-unsaturated ketones from aromatic aldehydes and ketones. PMID:24901834

Rocchi, Damiano; González, Juan F; Menéndez, J Carlos

2014-01-01

164

Enantioselective Henry reaction catalyzed by "ship in a bottle" complexes.  

PubMed

Two chiral Schiff-base complexes of copper(II) have been successfully encapsulated inside the cavity of zeolite-NaY via a "ship in a bottle" synthesis method. The presence of the two complexes inside the cages of zeolite-Y has been confirmed based on various spectrochemical and physicochemical techniques, viz. FTIR, UV-vis/DRS, ESR, XPS, CV, EDX, SEM, and TGA. Zeolite-encapsulated chiral copper(II) Schiff-base complexes are found to give a high-enantioselective (84% ee, R conformation) nitro-aldol product at -20 °C. The encapsulated copper complexes are found to show higher catalytic efficiency than their homogeneous counterparts under identical conditions. Density functional theory (DFT) calculation has been implemented to understand the effect of the zeolite matrix on structural, electronic, and reactivity properties of the synthesized complexes. Theoretical calculation predicts that upon encapsulation into the zeolite matrix the Cu center becomes more susceptible to nucleophilic attack, favoring a nitro-aldol reaction. A plausible mechanism is suggested based on the experimental and theoretical results. The structures of reaction intermediates and transition state(s) involved in the catalytic cycle are derived using DFT. PMID:23848182

Bania, Kusum K; Karunakar, Galla V; Goutham, Kommuru; Deka, Ramesh C

2013-07-15

165

Linked strategy for the production of fuels via formose reaction.  

PubMed

Formose reaction converts formaldehyde to carbohydrates. We found that formose reaction can be used linking the biomass gasification with the aqueous-phase processing (APP) to produce liquid transportation fuel in three steps. First, formaldehyde from syn-gas was converted to triose. This was followed by aldol condensation and dehydration to 4-hydroxymethylfurfural (4-HMF). Finally, 4-HMF was hydrogenated to produce 2,4-dimethylfuran (2,4-DMF) or C(9)-C(15) branched-chain alkanes as liquid transportation fuels. In the linked strategy, high energy-consuming pretreatment as well as expensive and polluting hydrolysis of biomass were omitted, but the high energy recovery of APP was inherited. In addition, the hexoketoses via formose reaction could be converted to HMFs directly without isomerization. A potential platform molecule 4-HMF was formed simultaneously in APP. PMID:23393625

Deng, Jin; Pan, Tao; Xu, Qing; Chen, Meng-Yuan; Zhang, Ying; Guo, Qing-Xiang; Fu, Yao

2013-01-01

166

Total synthesis of (R)-sarkomycin via asymmetric rhodium-catalyzed conjugate addition.  

PubMed

(R)-Sarkomycin was prepared using a five-step total synthesis. Key steps in the enantioselective construction of the targeted scaffold were a rhodium-catalyzed asymmetric conjugate alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol reaction with aqueous formaldehyde. Protection of the hydroxy group as a THP acetal and oxidative cleavage of the C,C-double bond provided a stable direct precursor to the natural product. The final liberation was carried out under slightly acidic conditions in a microwave-assisted reaction, resulting in a high yield of the "deceptive" sarkomycin. This represents the shortest enantioselective synthesis of this rather unstable compound to date and the first to employ asymmetric catalysis to introduce the stereogenic center. PMID:24079484

Westmeier, Johannes; Kress, Steffen; Pfaff, Christopher; von Zezschwitz, Paultheo

2013-11-01

167

Asymmetric total synthesis of 1-deoxy-7,8-di-epi-castanospermine.  

PubMed

An efficient, stereocontrolled synthesis of (6S,7S,8S,8aR)-6,7,8-trihydroxyindolizidine (alias 1-deoxy-7,8-di-epi-castanospermine) (14) has been developed, which exploits an asymmetric vinylogous Mukaiyama aldol reaction (VMAR) between N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsilyloxy)pyrrole (1) and 2,3-O-isopropylidene-D-glyceraldehyde (2) to construct the initial pyrrolidine building block 3, and an ene-ene ring closing metathesis reaction (RCM) (9 to 10) to install the indolizidine skeleton. The synthetic sequence was 13 steps, proceeding in 19.5% overall yield. The configurational and conformational structure of 14 was ascertained unambiguously and confronted to previously published assignments of rac-14 and ent-14. PMID:20237688

Zambrano, Vincenzo; Rassu, Gloria; Roggio, Annamaria; Pinna, Luigi; Zanardi, Franca; Curti, Claudio; Casiraghi, Giovanni; Battistini, Lucia

2010-04-01

168

Metal-Catalyzed Carbon-Carbon Bond Forming Reactions for the Synthesis of Significant Chiral Building Blocks  

E-print Network

the process through getting this degree. I?m very proud of her. vii NOMENCLATURE COD Cyclooctadiene EtOAc Ethyl Acetate DABCO 1,4-diazabicyclic[2.2.2]octane DBU 1,8-diazabicyclic[5.4.0]undec-7-ene DMAP 4-N,N-dimethylaminopyridine DMF N... such as aldol, Michael, and Diels-Alder reactions, or 1,2- additions, among others. This in turn can lead to the synthesis of complex molecules including natural products and other biologically important materials. The mechanism of the MBH reaction is believed...

Bugarin Cervantes, Alejandro

2011-08-08

169

A new pyridine-2,6-bis(oxazoline) for efficient and flexible lanthanide-based catalysts of enantioselective reactions with 3-alkenoyl-2-oxazolidinones.  

PubMed

A new pyridine-2,6-bis(oxazoline) (4) has been easily synthesised from the reaction of (1S,2S)-2-amino-1-phenylpropane-1,3-diol (1) and dimethyl pyridine-2,6-dicarboximidate (2), followed by TIPS (TIPS=triisopropylsilyl) protection of the 4'-CH2OH group. The catalysts derived from 4 and eight lanthanide(III) triflates have been tested over three reactions involving 3-acryloyl- and 3-crotonoyloxazolidinones (5 a,b): the Diels-Alder (DA) reaction with cyclopentadiene, the 1,3-dipolar cycloaddition with diphenyl nitrone and the Mukaiyama-Michael reaction with 2-trimethylsilyloxyfuran. Several reactions exhibit very good enantioselectivity (ee>90 %), and the opposite enantiomers can be easily obtained simply by changing the cation. This specific feature of the ligand can be appreciated in the DA reaction of 5 a, since the catalyst [Sc(III)4] gives the adduct (2'S)-9 a with 99 % ee, whereas the catalyst [Y(III)4] gives the opposite enantiomer with 95 % ee. A rationale of the enantioselectivity is proposed on the basis of the NMR spectra of La-based complexes involving 4 and 5 as ligands. PMID:15827979

Desimoni, Giovanni; Faita, Giuseppe; Guala, Matilde; Laurenti, Anna; Mella, Mariella

2005-06-20

170

Synthesis, double-helix formation, and higher-assembly formation of chiral polycyclic aromatic compounds: conceptual development of polyketide aldol synthesis.  

PubMed

Polycyclic aromatic compounds are an important group of substances in chemistry, and the study of their properties is a subject of interest in the development of drugs and materials. We have been conducting studies to develop chiral polycyclic aromatic compounds, i.e., helicenes and equatorenes. These helical molecules showed notable aggregate-forming properties and the capability for chiral recognition exerted by noncovalent bond interactions, which were not observed in compounds with central chirality. Homo- and hetero-double-helix-forming helicene oligomers were developed, and the latter self-assembled to form gels and vesicles. In this article, we describe such hierarchical studies of polycyclic aromatic compounds, which were started from polyketide aldol synthesis. PMID:24343866

Yamaguchi, Masahiko; Shigeno, Masanori; Saito, Nozomi; Yamamoto, Koji

2014-02-01

171

Hydrogenolysis of cellulose over Cu-based catalysts-analysis of the reaction network.  

PubMed

A series of polyols, carbohydrates, and cellulose were tested in the aqueous, CuO/ZnO/Al2O3-catalyzed hydrogenolysis reaction at 245?°C and 50?bar H2. The compositions of liquid-phase products were analyzed; based on these results a unified reaction mechanism is proposed that accounts for the observed product distribution. Elementary transformations such as dehydration, dehydrogenation/hydrogenation, Lobry?de?Bruyn-van?Ekenstein isomerization and retro-aldol cleavage were identified as most important for controlling the selectivity of simple polyols and carbohydrates. For cellulose the product distribution is considerably different than for glucose or sorbitol, indicating a change in the reaction pathway. Therefore, next to the traditional hydrolysis of the glycosidic bond, an additional depolymerization mechanism involving only the reducing ends of cellulose oligomers is proposed to account for this observation. PMID:24596082

Tajvidi, Kameh; Hausoul, Peter J C; Palkovits, Regina

2014-05-01

172

An advanced and novel one-pot synthetic method for diverse benzo[c]chromen-6-ones by transition-metal free mild base-promoted domino reactions of substituted 2-hydroxychalcones with ?-ketoesters and its application to polysubstituted terphenyls.  

PubMed

Novel and efficient one-pot syntheses of a variety of benzo[c]chromen-6-one derivatives were accomplished using Cs2CO3-promoted reactions between substituted 2-hydroxychalcones and ?-ketoesters. These reactions involved domino Michael addition/intramolecular aldol/oxidative aromatization/lactonization and provided a rapid synthetic route for the production of biologically interesting novel benzo[c]chromen-6-one molecules bearing several different substituents on benzene rings. As an application of this methodology, several synthesized benzo[c]chromen-6-ones were transformed into highly functionalized novel terphenyls. PMID:24357122

Poudel, Tej Narayan; Lee, Yong Rok

2014-02-14

173

Total Synthesis of the Anti-inflammatory and Pro-resolving Lipid Mediator MaR1n-3 DPA Utilizing an sp(3) -sp(3) Negishi Cross-Coupling Reaction.  

PubMed

The first total synthesis of the lipid mediator MaR1n-3 DPA (5) has been achieved in 12?% overall yield over 11?steps. The stereoselective preparation of 5 was based on a Pd-catalyzed sp(3) -sp(3) Negishi cross-coupling reaction and a stereocontrolled Evans-Nagao acetate aldol reaction. LC-MS/MS results with synthetic material matched the biologically produced 5. This novel lipid mediator displayed potent pro-resolving properties stimulating macrophage efferocytosis of apoptotic neutrophils. PMID:25225129

Tungen, Jørn Eivind; Aursnes, Marius; Dalli, Jesmond; Arnardottir, Hildur; Serhan, Charles Nicholas; Hansen, Trond Vidar

2014-11-01

174

Studies in asymmetric ?-lactone synthesis: extensions of the chiral nucleophile catalyzed aldol-lactonization (NCAL) reaction and new transformations of chlorinated ?-lactones  

E-print Network

-lactones were accomplished to further extend the utility of these products. In addition, 4-(trichloromethyl)-2-oxetanone was transformed into a variety of amino acid precursors. The first synthesis of the natural amino acid, 2-amino-5-methyl-6-hydroxyhex-4...

Tennyson, Reginald L.

2012-06-07

175

Lewis acid promoted construction of chromen-4-one and isoflavone scaffolds via regio- and chemoselective domino Friedel-Crafts acylation/Allan-Robinson reaction.  

PubMed

A facile and efficient synthesis of chromen-4-one and isoflavone frameworks is achieved by the domino C-acylation/O-acylation/aldolization sequence. This operationally simple one-pot elegant strategy provides structurally unique chromen-4-ones and isoflavones directly from phenols via concomitant formation of multiple C-C and C-O bonds in a single operation. The outcomes of the buttressing effect, substituent dependence, and catalyst and solvent specificity during the course of the Friedel-Crafts acylation reactions are demonstrated and supported by fitting experiments. PMID:25299841

Chanda, Tanmoy; Chowdhury, Sushobhan; Koley, Suvajit; Anand, Namrata; Singh, Maya Shankar

2014-10-29

176

Reactions & Rates  

NSDL National Science Digital Library

Explore what makes a reaction happen by colliding atoms and molecules. Design experiments with different reactions, concentrations, and temperatures. When are reactions reversible? What affects the rate of a reaction?

Simulations, Phet I.; Koch, Linda; Lemaster, Ron; Loeblein, Trish; Perkins, Kathy; Gratny, Mindy

2006-12-01

177

Investigation of thermochemistry associated with the carbon-carbon coupling reactions of furan and furfural using ab initio methods.  

PubMed

Upgrading furan and small oxygenates obtained from the decomposition of cellulosic materials via formation of carbon-carbon bonds is critical to effective conversion of biomass to liquid transportation fuels. Simulation-driven molecular level understanding of carbon-carbon bond formation is required to design efficient catalysts and processes. Accurate quantum chemical methods are utilized here to predict the reaction energetics for conversion of furan (C4H4O) to C5-C8 ethers and the transformation of furfural (C5H6O2) to C13-C26 alkanes. Furan can be coupled with various C1 to C4 low molecular weight carbohydrates obtained from the pyrolysis via Diels-Alder type reactions in the gas phase to produce C5-C8 cyclic ethers. The computed reaction barriers for these reactions (?25 kcal/mol) are lower than the cellulose activation or decomposition reactions (?50 kcal/mol). Cycloaddition of C5-C8 cyclo ethers with furans can also occur in the gas phase, and the computed activation energy is similar to that of the first Diels-Alder reaction. Furfural, obtained from biomass, can be coupled with aldehydes or ketones with ?-hydrogen atoms to form longer chain aldol products, and these aldol products can undergo vapor phase hydrocycloaddition (activation barrier of ?20 kcal/mol) to form the precursors of C26 cyclic hydrocarbons. These thermochemical studies provide the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to longer chain hydrocarbons. PMID:24902118

Liu, Cong; Assary, Rajeev S; Curtiss, Larry A

2014-06-26

178

Ternary copper(II)-polypyridyl enantiomers: aldol-type condensation, characterization, DNA-binding recognition, BSA-binding and anticancer property.  

PubMed

Chiral enantiomers [Cu(phen)(L-threo)(H2O)]NO3 1 and [Cu(phen)(D-threo)(H2O)]NO3 2 (threo = threoninate) underwent aldol-type condensation with formaldehyde, with retention of chirality, to yield their respective enantiomeric ternary copper(II) complexes, viz. L- and D-[Cu(phen)(5MeOCA)(H2O)]NO3·xH2O (3 and 4; phen = 1,10-phenanthroline; 5MeOCA = 5-methyloxazolidine-4-carboxylate; x = 0-3) respectively. These chiral complexes were characterized by FTIR, elemental analysis, circular dichroism, UV-Visible spectroscopy, fluorescence spectroscopy (FL), molar conductivity measurement, ESI-MS and X-ray crystallography. Analysis of restriction enzyme inhibition by these four complexes revealed modulation of DNA binding selectivity by the type of ligand, ligand modification and chirality. Their interaction with bovine serum albumin was investigated by FL and electronic spectroscopy. With the aid of the crystal structure of BSA, spectroscopic evidence suggested their binding at the cavity containing Trp134 with numerous Tyr residues in subdomain IA. The products were more antiproliferative than cisplatin against cancer cell lines HK-1, MCF-7, HCT116, HSC-2 and C666-1 except HL-60, and were selective towards nasopharyngeal cancer HK-1 cells over normal NP69 cells of the same organ type. PMID:23728518

Ng, Chew-Hee; Wang, Wai-San; Chong, Kok-Vei; Win, Yip-Foo; Neo, Kian-Eang; Lee, Hong-Boon; San, Swee-Lan; Raja Abd Rahman, Raja Noor Zaliha; Leong, Weng Kee

2013-07-28

179

Expanding the scope of the nucleophile catalyzed aldol lactonization (NCALl) process and transformations of the resulting beta-lactones  

E-print Network

by 1H NMR of crude product mixtures. d 90% ee using TMSq as catalyst. e 95% ee using TMSq as catalyst. f 96% ee using TMSq as catalyst. Two years later, Nelson expanded upon his own studies to provide a general methodology applicable towards... of entry 4's ?-lactone and comparison of 1H coupling constants. c Diastereomeric ratios determined by HPLC or 1H-NMR analysis of crude reaction mixtures. Similar to Nelson's studies, Calter has also used a combination of cinchona alkaloids...

Matla, Andrea Slava

2009-05-15

180

Enzyme Reactions  

NSDL National Science Digital Library

This video shows an enzyme reaction lab. The teacher demonstrates how the enzyme, catalase, reacts with hydrogen peroxide (a substrate found in cells). The teacher first demonstrates a normal enzyme reaction. He or she then goes on to show how manipulating temperature and pH will affect the reaction of an enzyme.

School, Minerva D.

2011-10-03

181

Reversible Reactions  

NSDL National Science Digital Library

Watch a reaction proceed over time. How does total energy affect a reaction rate? Vary temperature, barrier height, and potential energies. Record concentrations and time in order to extract rate coefficients. Do temperature dependent studies to extract Arrhenius parameters. This simulation is best used with teacher guidance because it presents an analogy of chemical reactions.

Simulations, Phet I.; Barbera, Jack; Koch, Linda; Lemaster, Ron; Adams, Wendy

2005-09-01

182

Nuclear Reactions  

Microsoft Academic Search

Nuclear reactions generate energy in nuclear reactors, in stars, and are responsible for the existence of all elements heavier than hydrogen in the universe. Nuclear reactions denote reactions between nuclei, and between nuclei and other fundamental particles, such as electrons and photons. A short description of the conservation laws and the definition of basic physical quantities is presented, followed by

C. A. Bertulani

2009-01-01

183

Chemical Reactions  

NSDL National Science Digital Library

We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

National Science Teachers Association (NSTA)

2009-05-01

184

Special Reactions  

NSDL National Science Digital Library

The basics of chemical reactions were covered in the first chemistry book, including how to write and balance chemical equations that represent those reactions. There is also a quick review of chemical reactions in Chapter 1 of this book. We're going to d

Robertson, William C.

2010-03-01

185

Design and Synthesis of Chiral Zn2+ Complexes Mimicking Natural Aldolases for Catalytic C-C Bond Forming Reactions in Aqueous Solution  

PubMed Central

Extending carbon frameworks via a series of C–C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C–C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective C–C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented. PMID:24481060

Itoh, Susumu; Sonoike, Shotaro; Kitamura, Masanori; Aoki, Shin

2014-01-01

186

Design and synthesis of chiral Zn2+ complexes mimicking natural aldolases for catalytic C-C bond forming reactions in aqueous solution.  

PubMed

Extending carbon frameworks via a series of C-C bond forming reactions is essential for the synthesis of natural products, pharmaceutically active compounds, active agrochemical ingredients, and a variety of functional materials. The application of stereoselective C-C bond forming reactions to the one-pot synthesis of biorelevant compounds is now emerging as a challenging and powerful strategy for improving the efficiency of a chemical reaction, in which some of the reactants are subjected to successive chemical reactions in just one reactor. However, organic reactions are generally conducted in organic solvents, as many organic molecules, reagents, and intermediates are not stable or soluble in water. In contrast, enzymatic reactions in living systems proceed in aqueous solvents, as most of enzymes generally function only within a narrow range of temperature and pH and are not so stable in less polar organic environments, which makes it difficult to conduct chemoenzymatic reactions in organic solvents. In this review, we describe the design and synthesis of chiral metal complexes with Zn2+ ions as a catalytic factor that mimic aldolases in stereoselective C-C bond forming reactions, especially for enantioselective aldol reactions. Their application to chemoenzymatic reactions in aqueous solution is also presented. PMID:24481060

Itoh, Susumu; Sonoike, Shotaro; Kitamura, Masanori; Aoki, Shin

2014-01-01

187

Nuclear Reactions  

Microsoft Academic Search

Nuclear reactions generate energy in nuclear reactors, in stars, and are\\u000aresponsible for the existence of all elements heavier than hydrogen in the\\u000auniverse. Nuclear reactions denote reactions between nuclei, and between nuclei\\u000aand other fundamental particles, such as electrons and photons. A short\\u000adescription of the conservation laws and the definition of basic physical\\u000aquantities is presented, followed by

C. A. Bertulani; B. Kinematics

2009-01-01

188

Key reaction for formation of isobutene over ZrO{sub 2} and isoprene over CeO{sub 2} in CO hydrogenation  

SciTech Connect

CO hydrogenation over ZrO{sub 2} at 623 and 673 K selectively forms isobutene. {sup 13}C tracer experiment with {sup 13}CO showed that carbon of surface methoxide species is incorporated in central carbon of isobutene. CeO{sub 2} forms 2-methylpropanal and diisopropyl ketone at 523 K and isobutene and isoprene with high selectivities in C{sub 4} and C{sub 5} hydrocarbons, respectively, at 673 K. Addition of H{sub 2}O to a mixture of CO H{sub 2} at 583 and 653 K led to formation of ketones and secondary alcohol`s. These suggest that there is acyl species as a common intermediate, which converts to isobutene via aldol-condensation with formaldehyde and to isoprene via acetone formed from its reaction with H{sub 2}O or bulk oxygen followed by ketonization reaction.

Maruya, K.; Hara, M.; Kondo, J.; Domen, K. [Tokyo Inst. of Technology, Yokohama (Japan); Onishi, T. [Advance Polytechnic Center, Chiba (Japan)

1996-12-31

189

Reaction Time  

NSDL National Science Digital Library

In this activity, learners explore reaction time and challenge themselves to improve their coordination. Do you want to move faster? Catch that ball that you never seem to see in time? Use a simple test to help you improve your reaction (or response) time.

Science, New Y.

1999-01-01

190

Chemical Reactions  

NSDL National Science Digital Library

We are going go over a general view of reactions to prepare us for our unit on Chemical Reactions! Have fun learning! WARNING: If you are caught looking at ANY other site, without permission, you will be sent to the ALC, and you will not participate in any other computer activities for the rest of the year. Get your worksheet and begin! Overview Take this quiz and have me come over and sign off on your worksheet when you have completed the quiz! Overview Quiz Next let's take a look at what effect the rate of a chemical reaction. Rates of Reactions Another quiz, another check off by me! Rates of Reactions Quiz Now how do we measure how fast a ...

Hicken, Mrs.

2009-05-04

191

Total synthesis and structure revision of didemnaketal B.  

PubMed

Didemnaketal?B, a structurally complex spiroacetal that exhibits potent HIV-1 protease inhibitory activity, was originally discovered by Faulkner and his colleagues from the ascidian Didemnum sp. collected at Palau. Its absolute configuration was proposed on the basis of degradation/derivatization experiments of the authentic sample. However, our total synthesis of the proposed structure of didemnaketal?B questioned the stereochemical assignment made by Faulkner et?al. Here we describe in detail our first total synthesis of the proposed structure 2 of didemnaketal?B, which features 1)?a convergent synthesis of the C7-C21 spiroacetal domain by means of a strategy exploiting Suzuki-Miyaura coupling, 2)?an Evans syn-aldol reaction and a vinylogous Mukaiyama aldol reaction for the assembly of the C1-C7 acyclic domain, and 3)?a Nozaki-Hiyama-Kishi reaction for the construction of the C21-C28 side chain domain. The NMR spectroscopic discrepancies observed between synthetic 2 and the authentic sample as well as careful inspection of the Faulkner's stereochemical assignment led us to postulate that the absolute configuration of the C10-C20 domain of 2 has been erroneously assigned. Accordingly, the total synthesis of the revised structure 65 was achieved to show that the NMR spectroscopic properties of synthetic 65 were in good agreement with those of the authentic sample. Furthermore, application of the phenylglycine methyl ester (PGME) method to the C7-C21 spiroacetal domain enabled us to establish the absolute configuration of didemnaketal?B. PMID:24431266

Fuwa, Haruhiko; Muto, Takashi; Sekine, Kumiko; Sasaki, Makoto

2014-02-10

192

Drug Reactions  

MedlinePLUS

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions. One problem is ...

193

Allergic Reactions  

MedlinePLUS

... For instance, if you have an allergy to pollen, your immune system identifies pollen as an invader or allergen . Your immune system ... it can affect a child's speech and language development. Diagnosing and Treating Allergic Reactions An allergist / immunologist, ...

194

Enzyme Reactions  

NSDL National Science Digital Library

The enzyme reaction rate activity allows students to simulate the effects of variables such as temperature and pH on the reaction rate of the enzyme catalase. This computer simulation is best used after the students have done a wet lab experiment. The value of the simulation is that it requires the students to interpret and analyze the graphical representation of data and it enables the running of mutiple experiments in a short amount of time.

School, Maryland V.

195

Wittig Reaction 33 Reaction: Synthesis of Alkenes  

E-print Network

elimination reactions (E1 or E2 reactions from alcohols or alkyl halides, for example), in eliminationWittig Reaction 33 The Wittig Reaction: Synthesis of Alkenes Intro The "Wittig Reaction" is one reactions the carbon skeleton is already pre-assembled. In the Wittig reaction, however, two smaller carbon

Jasperse, Craig P.

196

Taxol reactions.  

PubMed

Paclitaxel (Taxol) a taxane antineoplastic agent causing irreversible microtubule aggregation with activity against breast, ovarian, lung, head and neck, bladder, testicular, esophageal, endometrial and other less common tumors was derived from the bark of the Pacific yew (Taxus brevifolia). Phase I trials conducted in the late 1980s were almost halted because of the high frequency of hypersensitivity-like reactions. Respiratory distress (dyspnea and/or bronchospasm), hypotension, and angioedema were the major manifestations, but flushing, urticaria, chest, abdomen, and extremity pains were described also. Reactions occurred on first exposure in the majority of cases raising etiologic questions. The vehicle for paclitaxel Cremophor EL (polyoxyethylated castor oil in 50% ethanol) was strongly suspect as a direct (non-immunoglobulin E dependent) histamine releaser. Premedication regimens and longer infusion times lowered the incidence of reactivity allowing phase II and III trials to progress through the early 1990s. The mechanism(s) underlying paclitaxel hypersensitivity-like reactions is still unknown, and clinical data on probable complement and mast cell activation are lacking. The original clinical trial protocols for paclitaxel required discontinuation of therapy for patients who experienced hypersensitivity-like reactions. Here, we review the current etiologic knowledge of these reactions and describe our clinical approach to allow completion of chemotherapy with this powerful plant-derived agent. PMID:12125509

Price, Kursteen S; Castells, Mariana C

2002-01-01

197

Glucose and fructose decomposition in subcritical and supercritical water: Detailed reaction pathway, mechanisms, and kinetics  

SciTech Connect

The authors are developing a new catalyst-free process of cellulose decomposition in supercritical water. In their initial study on the cellulose decomposition in supercritical water, the main products of cellulose decomposition were found to be oligomers of glucose (cellobiose, cellotriose, etc.) and glucose at short residence times (400 C, 25 MPa, 0.05 s). The kinetics of glucose at these conditions can be useful in understanding the reaction pathways of cellulose. Experiments were performed on the products of glucose decomposition at short residence times to elucidate the reaction pathways and evaluate kinetics of glucose and fructose decomposition in sub- and supercritical water. The conditions were a temperature of 300--400 C and pressure of 25--40 MPa for extremely short residence times between 0.02 and 2 s. The products of glucose decomposition were fructose, a product of isomerization, 1,6-anhydroglucose, a product of dehydration, and erythrose and glyceraldehyde, products of C-C bond cleavage. Fructose underwent reactions similar to glucose except that it did not form 1,6-anhydroglucose and isomerization to glucose is negligible. The mechanism for the products formed from C-C bond cleavage could be explained by reverse aldol condensation and the double-bond rule of the respective enediols formed during the Lobry de Bruyn Alberda van Ekenstein transformation. The differential equations resulting from the proposed pathways were fit to experimental results to obtain the kinetic rate constants.

Kabyemela, B.M.; Adschiri, T.; Malaluan, R.M.; Arai, K. [Tohoku Univ., Sendai (Japan). Dept. of Chemical Engineering] [Tohoku Univ., Sendai (Japan). Dept. of Chemical Engineering

1999-08-01

198

Reaction Time  

NSDL National Science Digital Library

This lab is not an inquiry activity. There are some students whose reaction times will not allow them to catch a 12 inch ruler. They may use a dowel, stick, strip of cardboard, etc. Although the students are led to believe that the point of the lab is to

Horton, Michael

2009-05-30

199

Asymmetric Friedel-Crafts alkylation of indoles with methyl (E)-2-oxo-4-aryl-3-butenoates catalyzed by Sc(OTf)3/pybox.  

PubMed

The asymmetric Friedel-Crafts reaction between a series of substituted indoles 2 a-l and methyl (E)-2-oxo-4-aryl-3-butenoates 3 a-c has been efficiently catalyzed by the scandium(III) triflate complex of (4'S,5'S)-2,6-bis[4'-(triisopropylsilyl)oxymethyl-5'-phenyl-1',3'-oxazolin-2'-yl]pyridine (pybox; 1). Substituted 4-(indol-3-yl)-2-oxo-4-arylbutyric acid methyl esters 4 a-n were usually formed in excellent yields and the enantioselectivity was up to 99 % ee, irrespective of the electronic character of the substituent and its location on the indole ring, albeit with the exclusion of position 2. The adducts could be obtained as stable enol tautomers and the equilibrium with the keto structure is discussed. The X-ray crystal structure determination of 4 m indicated the 4R absolute configuration, thus confirming the proposal of Jørgensen for 4 i. The sense of the stereoinduction can be rationalized by the same octahedral complex 5 between 3, pybox 1, and scandium triflate already proposed for the Diels-Alder/hetero-Diels-Alder and the Mukaiyama-aldol reactions of pyruvates. PMID:18306268

Desimoni, Giovanni; Faita, Giuseppe; Toscanini, Marco; Boiocchi, Massimo

2008-01-01

200

A recyclable bifunctional acid-base organocatalyst with ionic liquid character. The role of site separation and spatial configuration on different condensation reactions.  

PubMed

A series of bifunctional organic catalysts containing acid and basic sites with ionic liquid characteristics have been prepared and their catalytic activity and reaction coordinate for aldol and Knoevenagel condensations have been compared. While the only factor controlling catalyst activity for the Knoevenagel condensation was the distance between the acid and base sites, the spatial orientation of the organocatalyst is also key to achieve high activity and selectivity in the Claisen-Schmidt condensation. Mechanistic studies based on theoretical DFT calculations show that the acid-base bifunctional organocatalyst follows a mechanism inspired in natural aldolases for the synthesis of trans-chalcones, being able to produce a large variety of these compounds of industrial interest. The combination of the acid-base pairs within the proper geometry and the ionic liquid nature makes this catalyst active, selective and recyclable. PMID:21879067

Corma, Avelino; Boronat, Mercedes; Climent, María José; Iborra, Sara; Montón, Raquel; Sabater, María J

2011-10-14

201

Enantioselective Synthesis of anti- and syn-homopropargyl alcohols via Chiral Br?nsted Acid Catalyzed asymmetric Allenylboration reactions  

PubMed Central

Chiral Brønsted acid catalyzed asymmetric allenylboration reactions are described. Under optimized conditions, anti-homopropargyl alcohols 2 are obtained in high yields with excellent diastereo- and enantioselectivities from stereochemically matched aldehyde allenylboration reactions with (M)-1 catalyzed by the chiral phosphoric acid (S)-4. The syn-isomers 3 can also be obtained in good diastereoselectivities and excellent enantioselectivities from the mismatched allenylboration reactions of aromatic aldehydes using (M)-1 in the presence of the enantiomeric phosphoric acid (R)-4. The stereochemistry of the methyl group introduced into 2 and 3 is controlled by the chirality of the allenylboronate (M)-1, whereas the configuration of the new hydroxyl stereocenter is controlled by the enantioselectivity of the chiral phosphoric acid catalyst used in these reactions. The synthetic utility of this methodology was further demonstrated in triple asymmetric syntheses of a variety of anti,anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R.

2012-01-01

202

Advances in QM/MM Simulations for Organic and Enzymatic Reactions  

PubMed Central

CONSPECTUS Application of combined quantum and molecular mechanical (QM/MM) methods focuses on predicting activation barriers and the structures of stationary points for organic and enzymatic reactions. Characterization of the factors that stabilize transition structures in solution and in enzyme active sites provides a basis for design and optimization of catalysts. Continued technological advances allowed expansion from prototypical cases to mechanistic studies featuring detailed enzyme and condensed-phase environments with full integration of the QM calculations and configurational sampling. This required improved algorithms featuring fast QM methods, advances in computing changes in free energies including free-energy perturbation (FEP) calculations, and enhanced configurational sampling. In particular, the present Account highlights development of the PDDG/PM3 semiempirical QM method, computation of multidimensional potentials of mean force (PMF), incorporation of on-the-fly QM in Monte Carlo (MC) simulations, and a polynomial quadrature method for efficient modeling of proton-transfer reactions. The utility of this QM/MM/MC/FEP methodology is illustrated for a variety of organic reactions including substitution, decarboxylation, elimination, and pericyclic reactions. Comparison with experimental kinetic results on medium effects has verified the accuracy of the QM/MM approach in the full range of solvents from hydrocarbons to water to ionic liquids. Corresponding results from ab initio and density functional theory (DFT) methods with continuum-based treatments of solvation reveal deficiencies, particularly for protic solvents. Also summarized in this Account are three specific QM/MM applications to biomolecular systems: (1) a recent study that clarified the mechanism for the reaction of 2-pyrone derivatives catalyzed by macrophomate synthase as a tandem Michael-aldol sequence rather than a Diels-Alder reaction; (2) elucidation of the mechanism of action of fatty acid amide hydrolase (FAAH), an unusual Ser-Ser-Lys proteolytic enzyme; and, (3) the construction of enzymes for Kemp elimination of 5-nitrobenzisoxazole that highlights the utility of QM/MM in the design of artificial enzymes. PMID:19728702

2010-01-01

203

Early stage composition of SOA produced by ?-pinene/ozone reaction: ?-Acyloxyhydroperoxy aldehydes and acidic dimers  

NASA Astrophysics Data System (ADS)

Composition of the freshly formed secondary organic aerosol (SOA) generated by ozonolysis of cyclohexene, cyclohexene-d10 (model precursors) and ?-pinene was studied using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-ESI/MS2). SOA was generated in the flow-tube reactor under the following conditions: 22 ± 2 °C, 1 atm and reaction time was approx. 30 s. In an attempt to resolve the current ambiguities, regarding the structure of ?-pinene SOA nucleating agents, analytical methods for analysis of ?-acyloxyhydroperoxy aldehydes and oligomers containing carboxylic group were developed to study the potential nucleating agents. Negatively charged m/z 351, 341, 337, 357 and 367 ions corresponding to the acidic oligomers were detected in freshly formed ?-pinene SOA. For the first time, structures and formation mechanism for compounds detected as m/z 337 and 351 ions were proposed. Based on the model precursor analysis (cyclohexene and cyclohexene-d10) it was concluded that these compounds were most likely formed via aldol reaction of the lower molecular weight aerosol components. ?-Acyloxyhydroperoxy aldehydes were studied in the SOA samples using previously developed, novel method, based on the prediction of fragmentation spectrum for the compounds of interest. It was concluded that ?-acyloxyhydroperoxy aldehydes were not formed in significant quantities. Based on the obtained results, possible SOA formation and growth mechanism is discussed.

Witkowski, Bart?omiej; Gierczak, Tomasz

2014-10-01

204

Formamidine Reactions  

E-print Network

.36$, 8.44$ Calculated for C ^ O ^ B r , nitrogen = 3.16$. METHYL IS0XAZ0L0N DERIVATIVES. The amido methylene derivatives of methyl lsoxazolon should be obtainable by the same methods as those of phenyl lsoxazolon. There are however, two practical... hydrochloid is neutralized. If it is neutralized with pyirldene the following reaction takes place. CH3 0 -==-C 'COHHR H«C - 0 * COINHR ' 1 II /I 0 CH v " " 1 - = N-O-O-OH, + H,0 f-R UH- H * flTO 3 HO- JT/Ha I t This gives the aMde of 5-methyl...

Griffin, E. L.

1913-05-15

205

Highly Selective Claisen–Schmidt Condensation Catalyzed by Silica Chloride Under Solvent-Free Reaction Conditions  

Microsoft Academic Search

Silica chloride serves as a useful catalyst in the cross-aldol condensation, leading to the synthesis of a wide variety of bisarylidene cycloalkanones and chalcones. The catalyst showed high selectivity; self-condensation of ketones was not observed.

Hassan Hazarkhani; Pradeep Kumar; Kadam Sachin Kondiram; Ikhlas M. Shafi Gadwal

2010-01-01

206

The effects of interactions between proline and carbon nanostructures on organocatalysis in the Hajos-Parrish-Eder-Sauer-Wiechert reaction  

NASA Astrophysics Data System (ADS)

The non-covalent interactions of S-(-)-proline with the surfaces of carbon nanostructures (fullerene, nanotubes and graphite) change the nucleophilic-electrophilic and acid-base properties of the amino acid, thus tuning its activity and selectivity in the organocatalytic Hajos-Parrish-Eder-Sauer-Wiechert (HPESW) reaction. Whilst our spectroscopy and microscopy measurements show no permanent covalent bonding between S-(-)-proline and carbon nanostructures, a systematic investigation of the catalytic activity and selectivity of the organocatalyst in the HPESW reaction demonstrates a clear correlation between the pyramidalisation angle of carbon nanostructures and the catalytic properties of S-(-)-proline. Carbon nanostructures with larger pyramidalisation angles have a stronger interaction with the nitrogen atom lone pair of electrons of the organocatalyst, thereby simultaneously decreasing the nucleophilicity and increasing the acidity of the organocatalyst. These translate into lower conversion rates but higher selectivities towards the dehydrated product of Aldol addition.The non-covalent interactions of S-(-)-proline with the surfaces of carbon nanostructures (fullerene, nanotubes and graphite) change the nucleophilic-electrophilic and acid-base properties of the amino acid, thus tuning its activity and selectivity in the organocatalytic Hajos-Parrish-Eder-Sauer-Wiechert (HPESW) reaction. Whilst our spectroscopy and microscopy measurements show no permanent covalent bonding between S-(-)-proline and carbon nanostructures, a systematic investigation of the catalytic activity and selectivity of the organocatalyst in the HPESW reaction demonstrates a clear correlation between the pyramidalisation angle of carbon nanostructures and the catalytic properties of S-(-)-proline. Carbon nanostructures with larger pyramidalisation angles have a stronger interaction with the nitrogen atom lone pair of electrons of the organocatalyst, thereby simultaneously decreasing the nucleophilicity and increasing the acidity of the organocatalyst. These translate into lower conversion rates but higher selectivities towards the dehydrated product of Aldol addition. Electronic supplementary information (ESI) available: Control experiments in the absence of carbon nanostructures and additional spectroscopic measurements and titrations are described in the ESI. See DOI: 10.1039/c4nr04009k

Rance, G. A.; Khlobystov, A. N.

2014-09-01

207

Reaction of arylethanals with boron tribromide  

Microsoft Academic Search

Treatment of arylethanals 1 with boron tribromide give 2-phenylnaphthalenes 2 or 1,2,9,10-tetrahydro-1,9-epoxydibenzo[a,e]cyclooctenes 3 by a tandem aldol condensation-intramolecular Friedel-Crafts cyclization or a condensation at the O-position followed by a double Friedel-Crafts alkylation respectively. In all cases, a total demethylation of the methoxy groups occurs.

Romain Dupont; Philippe Cotelle

1998-01-01

208

Asymmetric Catalysis Special Feature Part I: Air-stable, storable, and highly efficient chiral zirconium catalysts for enantioselective Mannich-type, aza Diels-Alder, aldol, and hetero Diels-Alder reactions  

Microsoft Academic Search

For the synthesis of optically active compounds, chiral catalysts have attracted much attention because large quantities of optically active molecules can be prepared from a small amount of a chiral source. However, many chiral catalysts are often unstable in air (oxygen) and\\/or in the presence of water. This is especially the case in chiral Lewis acid catalysis, because most Lewis

Shu Kobayashi; Masaharu Ueno; Susumu Saito; Yumiko Mizuki; Haruro Ishitani; Yasuhiro Yamashita

2004-01-01

209

Proline catalyzed ?-aminoxylation reaction in the synthesis of biologically active compounds.  

PubMed

The search for new and efficient ways to synthesize optically pure compounds is an active area of research in organic synthesis. Asymmetric catalysis provides a practical, cost-effective, and efficient method to create a variety of complex natural products containing multiple stereocenters. In recent years, chemists have become more interested in using small organic molecules to catalyze organic reactions. As a result, organocatalysis has emerged both as a promising strategy and as an alternative to catalysis with expensive proteins or toxic metals. One of the most successful and widely studied secondary amine-based organocatalysts is proline. This small molecule can catalyze numerous reactions such as the aldol, Mannich, Michael addition, Robinson annulation, Diels-Alder, ?-functionalization, ?-amination, and ?-aminoxylation reactions. Catalytic and enantioselective ?-oxygenation of carbonyl compounds is an important reaction to access a variety of useful building blocks for bioactive molecules. Proline catalyzed ?-aminoxylation using nitrosobenzene as oxygen source, followed by in situ reduction, gives enantiomerically pure 1,2-diol. This molecule can then undergo a variety of organic reactions. In addition, proline organocatalysis provides access to an assortment of biologically active natural products including mevinoline (a cholesterol lowering drug), tetrahydrolipstatin (an antiobesity drug), R(+)-?-lipoic acid, and bovidic acid. In this Account, we present an iterative organocatalytic approach to synthesize both syn- and anti-1,3-polyols, both enantio- and stereoselectively. This method is primarily based on proline-catalyzed sequential ?-aminoxylation and Horner-Wadsworth-Emmons (HWE) olefination of aldehyde to give a ?-hydroxy ester. In addition, we briefly illustrate the broad application of our recently developed strategy for 1,3-polyols, which serve as valuable, enantiopure building blocks for polyketides and other structurally diverse and complex natural products. Other research groups have also applied similar strategies to prepare such bioactive molecules as littoralisone, brasoside and (+)-cytotrienin A. Among the various synthetic approaches reported for 1,3-polyols, our organocatalytic iterative approach appears to be very promising and robust. This method combines the merit of organocatalytic reaction with an easy access to both enantiomerically pure forms of proline, mild reaction conditions, and tolerance to both air and moisture. In this Account, we present the latest applications of organocatalysis and how organic chemists can use this new tool for the total synthesis of complex natural products. PMID:23148510

Kumar, Pradeep; Dwivedi, Namrata

2013-02-19

210

IC ................................... ... Reaction Product Imaging  

E-print Network

offers two modes of operation. One mode involves imaging of the atomic fragment or reaction productIC ................................... ... Reaction Product Imaging: The H + D2 Reaction Theofanis reaction product imaging. In this experiment, a photolytically produced beam of hydrogen (H) atoms crossed

Zare, Richard N.

211

Iodine Clock Reaction  

NSDL National Science Digital Library

This site allows the user to vary initial solution concentration and temperature for the iodine clock reaction. A simulation of the reaction lets reaction times be measured. The data can then be used to determine the order of reaction for the various components.

212

Microscale Thermite Reactions.  

ERIC Educational Resources Information Center

Describes the adaptation of thermite (aluminum with metal oxides) reactions from whole-class demonstrations to student-run micro-reactions. Lists detailed directions and possible variations of the experiment. (WRM)

Arnaiz, Francisco J.; Aguado, Rafael; Arnaiz, Susana

1998-01-01

213

Treatment and Managing Reactions  

MedlinePLUS

Treatment & Managing Reactions Currently, the only way to prevent a food-allergic reaction is to avoid the problem food. ... treatment plan includes all of the following: Strict avoidance of problem foods Working with your doctor to ...

214

Passivation of Anodic Reactions.  

National Technical Information Service (NTIS)

Extending the Wagner definition of passivity to anodic reactions of chemical species on inert electrodes, passivation of a Pt electrode for the hydrogen oxidation reaction can be explained as being caused by small amounts (fraction of a monolayer) of adso...

S. Schuldiner

1968-01-01

215

Microfluidic chemical reaction circuits  

DOEpatents

New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

Lee, Chung-cheng (Irvine, CA); Sui, Guodong (Los Angeles, CA); Elizarov, Arkadij (Valley Village, CA); Kolb, Hartmuth C. (Playa del Rey, CA); Huang, Jiang (San Jose, CA); Heath, James R. (South Pasadena, CA); Phelps, Michael E. (Los Angeles, CA); Quake, Stephen R. (Stanford, CA); Tseng, Hsian-rong (Los Angeles, CA); Wyatt, Paul (Tipperary, IE); Daridon, Antoine (Mont-Sur-Rolle, CH)

2012-06-26

216

Microscale Thermite Reactions  

NASA Astrophysics Data System (ADS)

The reaction of aluminum with the oxides of a variety of elements (aluminothermy, or the Goldschmidt process) illustrates exothermic reactions that require a high activation energy. It is also an appropriate experiment with regard to the discussion of Ellingham diagrams. Because it is spectacular, this reaction is a favorite for demonstrations. When drama is not the main objective, conducting these reactions at microscale level offers numerous advantages over the usual scale.

Arnáiz, Francisco J.; Aguado, Rafael; Arnáiz, Susana

1998-12-01

217

Nuclear Reactions Some Basics  

E-print Network

Q in a reaction ­ Definition: Q = masses BEFORE the reaction ­ masses AFTER the reaction ­ Example: e + 3He e + p + d: Q = (Me + M3He) - (Me + Mp + Md) ­ Q may be >0 (exothermic) or ?) measurements made in a nuclear physics lab experiment. #12;Formal Definition of Cross Section · Consider a beam

Gilfoyle, Jerry

218

Chemical Reactions at Surfaces  

Microsoft Academic Search

Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The

Nancy Ryan Gray Michael Henderson

2010-01-01

219

Mechanisms in knockout reactions  

E-print Network

We report on the first detailed study of the mechanisms involved in knockout reactions, via a coincidence measurement of the residue and fast proton in one-proton knockout reactions, using the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results on the reactions $^9$Be($^9$C,$^8$B+X)Y and $^9$Be($^8$B,$^7$Be+X)Y are presented. They are compared with theoretical predictions for both the diffraction and stripping reaction mechanisms, as calculated in the eikonal model. The data shows a clear distinction between the two reaction mechanisms, and the observed respective proportions are very well reproduced by the reaction theory. This agreement supports the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

D. Bazin; R. J. Charity; R. T. de Souza; M. A. Famiano; A. Gade; V. Henzl; D. Henzlova; S. Hudan; J. Lee; S. Lukyanov; W. G. Lynch; S. McDaniel; M. Mocko; A. Obertelli; A. M. Rogers; L. G. Sobotka; J. R. Terry; J. A. Tostevin; M. B. Tsang; M. S. Wallace

2009-02-16

220

Weathering Reactions and Soil-Groundwater Reactions  

NSDL National Science Digital Library

This 11-page PDF document is part of an environmental geochemistry course taught by Dr. David Sherman at the University of Bristol. The lecture explores the weathering reactions that convert primary minerals into quartz or phyllosilicate clays and iron oxide hydroxides, and the mineral-water reactions that buffer pH and the dissolved ion concentration of groundwater. Also discussed is the manner in which phyllosilicate clays, iron oxides and hydroxides sorb pollutants via ion exchange and adsorption. Helpful diagrams and illustrations accompany the text.

Sherman, David M.; Bristol, University O.

221

Noncanonical Reactions of Flavoenzymes  

PubMed Central

Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates. PMID:23203060

Sobrado, Pablo

2012-01-01

222

Reaction-diffusion textures  

Microsoft Academic Search

We present a method for texture synthesis based on the simulation of a process of local nonlinear interaction, called reaction-diffusion, which has been proposed as a model of biological pattern formation. We extend traditional reaction-diffusion systems by allowing anisotropic and spatially non-uniform diffusion, as well as multiple competing directions of diffusion. We adapt reaction-diffusion system to the needs of computer

Andrew P. Witkin; Michael Kass

1991-01-01

223

Classic Organic Reactions  

NSDL National Science Digital Library

Despite the fact that the Classic Organic Reactions Page was designed for commercial purposes, to demonstrate the capabilities of ChemPen chemical structure drawing software for Windows, the page offers a useful resource for chemistry students and professionals. The creator of this page, and author and proprietor of ChemPen, Dr. Hilton Evans, has cited the literature for each reaction. The site contains drawings for over 300 alphabetically listed classic organic reactions. The list begins with the Acetoacetic Ester Condensation and ends with the Zinke-Suhl Reaction.

2007-05-12

224

High resolution reaction intermediates of rabbit muscle fructose-1,6-bisphosphate aldolase: substrate cleavage and induced fit.  

PubMed

Crystal structures were determined to 1.8 A resolution of the glycolytic enzyme fructose-1,6-bis(phosphate) aldolase trapped in complex with its substrate and a competitive inhibitor, mannitol-1,6-bis(phosphate). The enzyme substrate complex corresponded to the postulated Schiff base intermediate and has reaction geometry consistent with incipient C3-C4 bond cleavage catalyzed Glu-187, which is adjacent by to the Schiff base forming Lys-229. Atom arrangement about the cleaved bond in the reaction intermediate mimics a pericyclic transition state occurring in nonenzymatic aldol condensations. Lys-146 hydrogen-bonds the substrate C4 hydroxyl and assists substrate cleavage by stabilizing the developing negative charge on the C4 hydroxyl during proton abstraction. Mannitol-1,6-bis(phosphate) forms a noncovalent complex in the active site whose binding geometry mimics the covalent carbinolamine precursor. Glu-187 hydrogen-bonds the C2 hydroxyl of the inhibitor in the enzyme complex, substantiating a proton transfer role by Glu-187 in catalyzing the conversion of the carbinolamine intermediate to Schiff base. Modeling of the acyclic substrate configuration into the active site shows Glu-187, in acid form, hydrogen-bonding both substrate C2 carbonyl and C4 hydroxyl, thereby aligning the substrate ketose for nucleophilic attack by Lys-229. The multifunctional role of Glu-187 epitomizes a canonical mechanistic feature conserved in Schiff base-forming aldolases catalyzing carbohydrate metabolism. Trapping of tagatose-1,6-bis(phosphate), a diastereoisomer of fructose 1,6-bis(phosphate), displayed stereospecific discrimination and reduced ketohexose binding specificity. Each ligand induces homologous conformational changes in two adjacent alpha-helical regions that promote phosphate binding in the active site. PMID:15870069

St-Jean, Miguel; Lafrance-Vanasse, Julien; Liotard, Brigitte; Sygusch, Jurgen

2005-07-22

225

Nuclear Reaction Data Centers  

SciTech Connect

The cooperating Nuclear Reaction Data Centers are involved in the compilation and exchange of nuclear reaction data for incident neutrons, charged particles and photons. Individual centers may also have services in other areas, e.g., evaluated data, nuclear structure and decay data, reactor physics, nuclear safety; some of this information may also be exchanged between interested centers. 20 refs., 1 tab.

McLane, V.; Nordborg, C.; Lemmel, H.D.; Manokhin, V.N.

1988-01-01

226

Smell the Maillard Reaction  

NSDL National Science Digital Library

In this activity, learners cook amino acids and sugar to explore the range of aromas released. When amino acids and sugars are heated, learners will observe a phenomenon known as the Maillard reaction, also known as the browning reaction. Caution!: Kids, please don't try this at home without the help of an adult. The corn syrup can get very hot, very quickly.

Exploratorium

2012-10-03

227

Reactions of alkyl radicals  

Microsoft Academic Search

Recent investigations into the reactions of alkyl radicals are reviewed. Reactions discussed are: heats of formation, association, addition, dissociation, hydrogen atom transfer and oxidation. A trend towards the greater use of direct time-resolved methods for measuring rate coefficients is noted and future developments, based on the availability of high-quality ab initio potential energy surfaces, are anticipated.

Michael J. Pilling; V. Kay Proudler

1990-01-01

228

Fractal reaction kinetics.  

PubMed

Classical reaction kinetics has been found to be unsatisfactory when the reactants are spatially constrained on the microscopic level by either walls, phase boundaries, or force fields. Recently discovered theories of heterogeneous reaction kinetics have dramatic consequences, such as fractal orders for elementary reactions, self-ordering and self-unmixing of reactants, and rate coefficients with temporal "memories." The new theories were needed to explain the results of experiments and supercomputer simulations of reactions that were confined to low dimensions or fractal dimensions or both. Among the practical examples of "fractal-like kinetics" are chemical reactions in pores of membranes, excitation trapping in molecular aggregates, exciton fusion in composite materials, and charge recombination in colloids and clouds. PMID:17820893

Kopelman, R

1988-09-23

229

Organocatalytic High Enantioselective Synthesis of ?-Formyl-?-hydroxyphosphonates.  

PubMed

The cross aldol reaction between enolizable aldehydes and ?-ketophosphonates was achieved for the first time by using 9-amino-9-deoxy-epi-quinine as the catalyst. ?-Formyl-?-hydroxyphosphonates were obtained in high to excellent enantioselectivities. The reaction works especially well with acetaldehyde, which is a tough substrate for organocatalyzed cross aldol reactions. The products were demonstrated to have anticancer activities. PMID:21918646

Perera, Sandun; Naganaboina, Vijaya Kumar; Wang, Long; Zhang, Bin; Guo, Qunsheng; Rout, Laxmidhar; Zhao, Cong-Gui

2011-06-30

230

Cycloaddition reactions of ICNO  

NASA Astrophysics Data System (ADS)

The mechanism and selectivity of cycloaddition reactions of iodonitrile oxide, ICNO, have been studied with theoretical methods for the first time using MR-AQCC coupled-cluster and B3LYP DFT methods. Calculations have predicted that the favoured ICNO dimerisation process is a multi-step reaction to diiodofuroxan involving dinitrosoethylene-like intermediates. The ICNO cycloaddition with nitriles and ethynyl derivatives is a synchronous process favouring the formation of 1,2,4-oxadiazole and 1,2-oxazole derivatives, respectively. The cycloaddition reactions of ICNO have been studied experimentally by generating ICNO from AgCNO and iodine. Diiodofuroxan is obtained, however, even at the presence of nitriles.

Pasinszki, Tibor; Krebsz, Melinda; Hajgató, Balázs

2009-05-01

231

Chemisorption And Precipitation Reactions  

EPA Science Inventory

The transport and bioavailability of chemical components within soils is, in part, controlled by partitioning between solids and solution. General terms used to describe these partitioning reactions include chemisorption and precipitation. Chemisorption is inclusive of the suit...

232

Autocatalysis in reaction networks.  

PubMed

The persistence conjecture is a long-standing open problem in chemical reaction network theory. It concerns the behavior of solutions to coupled ODE systems that arise from applying mass-action kinetics to a network of chemical reactions. The idea is that if all reactions are reversible in a weak sense, then no species can go extinct. A notion that has been found useful in thinking about persistence is that of "critical siphon." We explore the combinatorics of critical siphons, with a view toward the persistence conjecture. We introduce the notions of "drainable" and "self-replicable" (or autocatalytic) siphons. We show that: Every minimal critical siphon is either drainable or self-replicable; reaction networks without drainable siphons are persistent; and nonautocatalytic weakly reversible networks are persistent. Our results clarify that the difficulties in proving the persistence conjecture are essentially due to competition between drainable and self-replicable siphons. PMID:25245394

Deshpande, Abhishek; Gopalkrishnan, Manoj

2014-10-01

233

Reactor for exothermic reactions  

DOEpatents

A liquid phase process is described for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, L.A. Jr.; Hearn, D.; Jones, E.M. Jr.

1993-03-02

234

Bad Reaction to Cosmetics?  

MedlinePLUS

... for the person who had the reaction; the age, gender, and ethnicity of the product’s user; the name ... was purchased. And be sure to give the age, gender, and ethnicity of the person who had the ...

235

Oral Hypersensitivity Reactions  

MedlinePLUS

... a hypersensitivity reaction in the mouth? A: A large number of substances. The most common causes are food, ... What is the “Latex-Fruit Syndrome”? A: A large number of individuals who are allergic to latex products ...

236

Iodine Clock Reaction.  

ERIC Educational Resources Information Center

Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)

Mitchell, Richard S.

1996-01-01

237

Untoward penicillin reactions  

PubMed Central

The literature on untoward reactions following the administration of penicillin is reviewed. These reactions, including a certain number of deaths which have been reported, are of particular interest to health administrations and to WHO in view of the large-scale programmes for controlling the treponematoses which are now under way—programmes affecting millions of people in many parts of the world. The most serious problems are anaphylactic sensitivity phenomena and superinfection or cross-infection with penicillin-resistant organisms, and the reactions involved range in intensity from the mildest to the fatal; the incidence of the latter is estimated at 0.1-0.3 per million injections. The authors point out that with increasing use of penicillin, more persons are likely to become sensitized and the number of reactions can therefore be expected to rise. The best prevention against such an increase is the restriction of the unnecessary use of penicillin. PMID:13596877

Guthe, T.; Idsoe, O.; Willcox, R. R.

1958-01-01

238

An Illuminating Reaction.  

ERIC Educational Resources Information Center

Describes the use of carbide lights as an excellent mechanism for introducing or reviewing many basic chemistry concepts including elements and compounds, endothermic and exothermic reactions, physical and chemical changes, and balancing chemical equations. (JRH)

Matthews, Catherine E.

1996-01-01

239

Solvent-free Reactions  

Microsoft Academic Search

For reasons of economy and pollution, solvent-free methods are of great interest in order to modernize classical procedures\\u000a making them more clean, safe and easy to perform. Reactions on solid mineral supports, reactions without any solvent\\/support\\u000a or catalyst, and solid-liquid phase transfer catalysis can be thus employed with noticeable increases in reactivity and selectivity.\\u000a A comprehensive review of these techniques

André Loupy

240

Phototoxic and Photoallergic Reactions  

Microsoft Academic Search

\\u000a Phototoxic and photoallergic reactions represent skin reactions to the sun, in the presence of photoactive chemicals applied\\u000a on the skin or taken systemically. They have a highly polymorphic clinical presentation – photocontact urticaria, eczema on\\u000a sun-exposed areas sometimes with erythema multiforme, exaggerated sunburn, linear phytophotodermatitis, pseudoporphyria, photoonycholysis,\\u000a dyschromia, and lupus erythematosus. Also, skin cancers are increasingly associated with exposure to

Margarida Gonçalo

241

Reaction imaging with interferometry.  

PubMed

We analyze scattering into a double-slit interferometer with target-fragment recoil detection as a monitor of quantum correlation and entanglement in few-body reaction amplitudes. We thus investigate two-slit interference with which-way information as an enhancement to modern reaction-fragment detection. We briefly consider charged-particle scattering with recoil-ion detection from the point of view of quantum information. PMID:11384415

Feagin, J M; Han, S

2001-05-28

242

Polymerase Chain Reaction  

NSDL National Science Digital Library

Polymerase chain reaction (PCR) enables researchers to produce millions of copies of a specific DNA sequence in approximately two hours. This automated process bypasses the need to use bacteria for amplifying DNA. This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents Polymerase Chain Reaction through a series of illustrations of the processes involved. Users may view the animation online (Flash is required) or download it for PC or Mac.

2013-07-09

243

Bereavement: Reactions, Consequences, and Care.  

National Technical Information Service (NTIS)

Contents: PART I. BEREAVEMENT: REACTIONS AND CONSEQUENCES--Epidemiologic Perspectives on the Health Consequences of Bereavement; Adults' Reactions to Bereavement; Reactions to Particular Types of Bereavement; Bereavement During Childhood and Adolescence; ...

M. Osterweis, M. Green

1984-01-01

244

Silver Crystals Through Tollen's Reaction.  

National Technical Information Service (NTIS)

A method for the formation of regular-shaped silver crystals through a wet chemical reaction (Tollen's reaction) is presented. The growth of the Ag crystals (size, morphology and aggregation) can be controlled via adjusting reaction conditions such as tem...

D. Fries, X. Ding

2005-01-01

245

Diels-Alder Reaction 91 Diels-Alder Reaction  

E-print Network

Diels-Alder Reaction 91 Diels-Alder Reaction General Diels-Alder Reaction: A conjugated "diene as a student-friendly low-smell Diels- Alder diene, with the labeled carbons functioning as the reactive diene/reactivity principle). The "cyclohexene" ring produced in every Diels-Alder reaction is hard to visualize, but consists

Jasperse, Craig P.

246

Velocity pump reaction turbine  

DOEpatents

An expanding hydraulic/two-phase velocity pump reaction turbine including a dual concentric rotor configuration with an inter-rotor annular flow channel in which the inner rotor is mechanically driven by the outer rotor. In another embodiment, the inner rotor is immobilized and provided with gas recovery ports on its outer surface by means of which gas in solution may be recovered. This velocity pump reaction turbine configuration is capable of potential energy conversion efficiencies of up to 70%, and is particularly suited for geothermal applications.

House, Palmer A. (Walnut Creek, CA)

1984-01-01

247

Uptake and Reactions of Formaldehyde, Acetaldehyde, Acetone, Propanal and Ethanol in Sulfuric Acid solutions at 200-240 K: Implications for upper tropospheric aerosol composition  

NASA Astrophysics Data System (ADS)

The production of light absorbing, organic material in aerosol that is normally considered to be transparent in the UV and visible wavelength regions has significant implications for biogeochemical cycling and climate modelling. Production mechanisms likely involve carbonyl compounds such as formaldehyde, acetone, acetaldehyde and propanal that are present in significant quantities in the upper troposphere (UT). In this study, we have performed experiments focusing on a class of acid catalyzed carbonyl reactions, the formation of acetals. R2C=O + 2R'OH --> R2C(OR')2 + H2O Using a Knudsen cell apparatus, we have measured the rate of uptake of formaldehyde, acetaldehyde, acetone, propanal, and ethanol into sulfuric acid solutions ranging between 40-70 wt% of acid, containing 0-0.1 M of ethanol, acetone or formaldehyde at temperatures of 220-250 K. For all reactant pairs, the aldol condensation path, including self reaction, should be insignificant at the acidities studied. Evidence for reaction between organics was observed for all pairs, except those involving propanal which were likely limited by the very low solubility. We attribute enhanced uptake to the formation of acetals, such as 1,1-diethoxyethane and 2,2- diethoxypropane, among others. Enhanced uptake was observed to proceed on timescales > 1 hour and sometimes shows complex dependence on acidity that is likely related to speciation of the individual carbonyls in acidic solution. The acetal products do not absorb in the visible but are less volatile than parent molecules, allowing for accumulation in sulfuric acid particles, and enhanced uptake. Cross reactions of carbonyls with alcohols in sulfuric acid medium have not been previously measured, yet methanol and ethanol show high solubility and are present at significant concentrations in the UT. Thus even at slow reaction rates, the acetal reaction has ample starting material and proceeds under conditions common to the UT. We will present results for the enhanced uptake of carbonyls in the presence of alcohols, derive rate constants, and discuss the atmospheric impact of the acetal reaction path.

Iraci, L. T.; Williams, M. B.; Axson, J.; Michelsen, R.

2007-12-01

248

Gas Producing Micro-Reaction  

NSDL National Science Digital Library

In this chemistry activity, learners use common chemicals and metals to examine reactions that produce gaseous substances. Learners will identify the gases produced and write a balanced equation for each reaction. Use this activity to also introduce learners to single displacement and double displacement reactions, two types of chemical reactions.

House, The S.

2014-01-28

249

Reaction Formulation: A Bibliography.  

ERIC Educational Resources Information Center

Reaction formation was studied by Sigmund Freud. This defense mechanism may be related to repression, substitution, reversal, and compensation (or over-compensation). Alfred Adler considered compensation a basic process in his individual psychology. Anna Freud discussed some defense mechanisms, and Bibring, Dwyer, Huntington, and Valenstein…

Pedrini, D. T.; Pedrini, Bonnie C.

250

Azoxy rearrangement reactions  

NASA Astrophysics Data System (ADS)

The mechanisms of several types of azoxy compound (XN(O)NY) rearrangement reactions have been studied using density functional theory (DFT) with the B3LYP exchange-correlation potential. The substituents X and Y are taken from the set H, CH , F, C H , Cl and CN. The 6-311 + G(d,p) basis set was used to optimize up to ten equilibrium and transition state structures for a given pair of X and Y substituents; except for azoxybenzene where a 6- 311(+)G(d) basis set was used. All geometric structures were characterized by a frequency calculation. The reaction path for converting XN (O)N Y to XN N (O)Y via a concerted intramolecular shift of the oxygen atom from N to N involves three equilibrium and two saddle-point structures. The relatively high (about 70-80 kcalmol1) calculated barrier height to reaction and its independence of the nature of the X and Y substituents is attributed to characteristic orbital, atomic charge and structural factors along the reaction path. Cis trans isomerization across N-- N in the NH(O)NH azoxy compound and across N-N in the ring XNONY oxadiaziridine intermediate is found to have a barrier height of at least - 1 about 30 kcalmol . Single-point CCSD(T)/DFT energy differences are found to be somewhat smaller than the DFT calculated values. 3 6 5

Basch, Harold; Hoz, Tova

251

Reaction Time Sound Explanation  

NSDL National Science Digital Library

This experiment presents auditory stimuli and requires the participant to respond after hearing target stimuli under different conditions. This experiment gives students the opportunity to determine whether their reaction times are reliably different for tasks that require slightly different decisions. This page provides guidance for faculty who wish to incorporate this activity into their classroom.

252

A Principal's Reaction  

ERIC Educational Resources Information Center

This article presents a principal's reaction to Catherine Marshall and Michael Ward's article on research on social justice and training for leadership. The author applauds Marshall and Ward's efforts to address what is undoubtedly among the most fundamentally important issues facing principals today. Marshall and Ward illuminate the importance of…

Zaretsky, Lindy

2004-01-01

253

The aromatic ene reaction  

NASA Astrophysics Data System (ADS)

The ene reaction is a pericyclic process in which an alkene with an allylic hydrogen atom (the ene donor) reacts with a second unsaturated species (the enophile) to form a new product with a transposed ?-bond. The aromatic ene reaction, in which the alkene component is embedded in an aromatic ring, has only been reported in a few (four) instances and has proceeded in low yield (?6%). Here, we show efficient aromatic ene reactions in which a thermally generated aryne intermediate engages a pendant m-alkylarene substituent to produce a dearomatized isotoluene, itself another versatile but rare reactive intermediate. Our experiments were guided by computational studies that revealed structural features conducive to the aromatic ene process. We proceeded to identify a cascade comprising three reactions: (1) hexadehydro-Diels-Alder (for aryne generation), (2) intramolecular aromatic ene and (3) bimolecular Alder ene. The power of this cascade is evident from the structural complexity of the final products, the considerable scope, and the overall efficiency of these multistage, reagent- and by-product-free, single-pot transformations.

Niu, Dawen; Hoye, Thomas R.

2014-01-01

254

Radical-Radical Reactions  

Microsoft Academic Search

Radical-radical reactions generally proceed on potential energy surfaces that have no maximum. Collisional deactivation leads to a stable molecular product; alternatively, radical or molecular products can be formed via dissociation channels additional to those regenerating the reactants. Models of the transition states must take into account the loose internal motion of the fragments, and a variational approach is necessary. The

M. J. Pilling

1996-01-01

255

Asymmetric reactions in sonochemistry  

Microsoft Academic Search

Sonochemical processes involved in asymmetric synthesis are reviewed. The goal of this overview is to provide a comprehensive picture about the fields of both enantioselective and diastereoselective reactions accelerated or initiated by ultrasounds. Since the most, in many cases comparative, data are available in heterogeneous metal catalysis, the emphasis will be placed on these enantioselective hydrogenations, however, other applications such

Béla Török; Katalin Balázsik; Károly Felföldi; Mihály Bartók

2001-01-01

256

Organic Reactions and Biofuels  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) provides this classroom activity on organic reactions and biofuels. The goal of the lesson is to react methanol with waste oil to synthesize biodiesel. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

2011-02-16

257

Exocharmic Reactions up Close  

ERIC Educational Resources Information Center

The exocharmic reactions that can be observed microscopically are discussed. The students can discover the optimal concentration of an acidic lead nitrate solution, so that a crystal of potassium iodide, nudged to the edge of a drop, results in glinting golden hexagons of lead iodide.

Ramette, R. W.

2007-01-01

258

Reaction product imaging  

SciTech Connect

Over the past few years the author has investigated the photochemistry of small molecules using the photofragment imaging technique. Bond energies, spectroscopy of radicals, dissociation dynamics and branching ratios are examples of information obtained by this technique. Along with extending the technique to the study of bimolecular reactions, efforts to make the technique as quantitative as possible have been the focus of the research effort. To this end, the author has measured the bond energy of the C-H bond in acetylene, branching ratios in the dissociation of HI, the energetics of CH{sub 3}Br, CD{sub 3}Br, C{sub 2}H{sub 5}Br and C{sub 2}H{sub 5}OBr dissociation, and the alignment of the CD{sub 3} fragment from CD{sub 3}I photolysis. In an effort to extend the technique to bimolecular reactions the author has studied the reaction of H with HI and the isotopic exchange reaction between H and D{sub 2}.

Chandler, D.W. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

259

A World of Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the first of four Science Objects in the Chemical Reactions SciPack. It explains tha

National Science Teachers Association (NSTA)

2009-07-10

260

Categorizing Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the second of four Science Objects in the Chemical Reactions SciPack. It provides an

National Science Teachers Association (NSTA)

2009-07-10

261

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

262

The aromatic ene reaction.  

PubMed

The ene reaction is a pericyclic process in which an alkene with an allylic hydrogen atom (the ene donor) reacts with a second unsaturated species (the enophile) to form a new product with a transposed ?-bond. The aromatic ene reaction, in which the alkene component is embedded in an aromatic ring, has only been reported in a few (four) instances and has proceeded in low yield (?6%). Here, we show efficient aromatic ene reactions in which a thermally generated aryne intermediate engages a pendant m-alkylarene substituent to produce a dearomatized isotoluene, itself another versatile but rare reactive intermediate. Our experiments were guided by computational studies that revealed structural features conducive to the aromatic ene process. We proceeded to identify a cascade comprising three reactions: (1) hexadehydro-Diels-Alder (for aryne generation), (2) intramolecular aromatic ene and (3) bimolecular Alder ene. The power of this cascade is evident from the structural complexity of the final products, the considerable scope, and the overall efficiency of these multistage, reagent- and by-product-free, single-pot transformations. PMID:24345944

Niu, Dawen; Hoye, Thomas R

2014-01-01

263

Optimization and extensions of the nucleophile catalyzed aldol-lactonization (NCAL) process for bicyclic beta-lactone synthesis: applications to piperidine, pyrrolidine, and gamma-lactam-fused beta-lactones  

E-print Network

Summary of Attempted Amide Coupling of Amine 260 and Acid 242.................. 98 20 a-Cylopropylated g-Lactam Fused b-Lactone (272) with NCAL Reaction...........103 21 Work-up Conditions after NCAL Reaction... ketene dimmers, b-lactones or b-lactams (Scheme 7). 8 Scheme 7 C O R1 R2 NR3 R3 NR 3 O -H O NR3 R4Base 31 32 33 O C N H O H R5 O O N O R4 R5 O O R4 Ketene dimer 33a b-Lactam 33b b-Lactone 33c 1.3.1 Enantioselective Nucleophile Catalyzed Additions From...

Oh, Seongho

2006-08-16

264

Laser Induced Nuclear Reactions  

NASA Astrophysics Data System (ADS)

In the last decade the intensities of light fields which can be produced in a laser focus increased by four orders of magnitude from 1016 to 1020 W/cm2. Intensities exceeding 1018 W/cm2 allow for the production of relativistic laser plasmas, that is the quiver energy of plasma electrons reaches the electron rest mass. These plasmas are sources of a whole spectrum of energetic particles, such as highly relativistic electrons, hard bremsstrahlung [13], protons with energies up to a few hundred MeV [7,14], neutrons [4,11,13] and deuterons [4, 17]. These particles can be used to induce nuclear reactions like photo-fission (?,f) [3,6,8,12], neutron generation by (?,n)- (p,n)- or (d,n)-reactions, neutron capture or fusion [4, 17].

Ewald, Friederike; Schwoerer, Heinrich; Magill, Joseph; Galy, Jean; Schenkel, Roland; Sauerbrey, Roland

265

Magnetically suspended reaction wheels  

NASA Technical Reports Server (NTRS)

Magnetic suspensions offer several advantages over conventional bearings, arising because of the contactless nature of the load support. In application to spacecraft reaction wheels, the advantages are low drag torque, wearfree, unlubricated, vacuum-compatible operation, and unlimited life. By the provision of redundancy in the control electronics, single-point failures are eliminated. The rational for selection of a passive radial, active axial, dc magnetic suspension is presented, and the relative merits of 3-loop and single-loop magnetic suspensions are discussed. The design of a .678 N-m-sec (.5 ft-lb-sec) reaction wheel using the single loop magnetic suspension was developed; the design compares favorably with current ball bearing wheels in terms of weight and power.

Sabnis, A. V.; Stocking, G. L.; Dendy, J. B.

1975-01-01

266

Reaction chemistry of cerium  

SciTech Connect

It is truly ironic that a synthetic organic chemist likely has far greater knowledge of the reaction chemistry of cerium(IV) than an inorganic colleague. Cerium(IV) reagents have long since been employed as oxidants in effecting a wide variety of organic transformations. Conversely, prior to the late 1980s, the number of well characterized cerium(IV) complexes did not extend past a handful of known species. Though in many other areas, interest in the molecular chemistry of the 4f-elements has undergone an explosive growth over the last twenty years, the chemistry of cerium(IV) has for the most part been overlooked. This report describes reactions of cerium complexes and structure.

NONE

1997-01-01

267

Heat Speeds Up Reactions  

NSDL National Science Digital Library

In this activity, learners investigate the effect of heat on a reaction. Learners first model molecular motion by moving their bodies (running, moving slowly) and pretending to be molecules at different temperatures, then by using groups of cut-out shapes (not provided) which get rearranged when they collide. After this introduction, three glow sticks are activatedâone is put in ice water, one in warm water, and one left at room temperature for 15 minutes. A comparison of which glow stick gives off the most light gives an indication of the speed of the molecules and the number of reactions occurring. (The activity was originally written as part of a kit to be checked out of the library, but the kit is not required.)

Shaw, Maisie; Gomez, Maria

2009-01-01

268

Reaction Time 2: Zap!  

NSDL National Science Digital Library

This Science NetLinks lesson is the second of a two-part series that encourages students to think about their own learning and the strategies that best help them learn new skills and ideas. In this lesson, students build upon what they have already learned by participating in another online reaction-time activity--this one testing their visual and auditory abilities, both separately and together.

Science Netlinks;

2003-06-19

269

Polymerase Chain Reaction  

NSDL National Science Digital Library

Teachers' Domain presents this interactive, adapted from the University of Nebraska's Library of Crop Technologies, with reading material and animations to help students learn the basic steps of polymerase chain reaction. Following the introduction, the lesson is divided four parts: Finding and Isolating DNA, Creating the DNA Solution, Begin Thermal Cycling, and Replication. Animations help students visualize each step of the processes described. On the site, visitors will also find a supplemental background essay, discussion questions, and standards alignment from Teachers' Domain.

2010-10-05

270

Photochemical reaction dynamics  

SciTech Connect

The purpose of the program is to develop a fundamental understanding of unimolecular and bimolecular reaction dynamics with application in combustion and energy systems. The energy dependence in ketene isomerization, ketene dissociation dynamics, and carbonyl substitution on organometallic rhodium complexes in liquid xenon have been studied. Future studies concerning unimolecular processes in ketene as well as energy transfer and kinetic studies of methylene radicals are discussed.

Moore, B.C. [Lawrence Berkeley Laboratory, Livermore, CA (United States)

1993-12-01

271

Chemical Reactions in DSMC  

SciTech Connect

DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

Bird, G. A. [GAB Consulting Pty Ltd, 144/110 Sussex Street, Sydney NSW 2000 (Australia)

2011-05-20

272

Factors augmenting allergic reactions.  

PubMed

Elicitors of anaphylactic reactions are any sources of protein with allergenic capacity. However, not all allergic reactions end up in the most severe form of anaphylaxis. Augmenting factors may explain why certain conditions lead to anaphylaxis. Augmenting factors may exhibit three effects: lowering the threshold, increasing the severity, and reversing acquired clinical tolerance. Common augmenting factors are physical exercise, menstruation, NSAIDs, alcohol, body temperature, acute infections, and antacids. Therapeutic options may address causative, preventive, pragmatic, or symptomatic considerations: avoid the eliciting food, take an antihistamine before any situation with a possible risk of augmentation, separate food and sport (at least for 2 h), and carry an adrenaline autoinjector at all times. Individual patterns include summation effects and specific patterns. In conclusion, in the case of a suggestive history but a negative oral challenge, one should consider the possible involvement of augmenting factors; after anaphylactic reactions, always ask for possible augmentation and other risk factors during the recent past; if augmentation is suspected, oral food challenges should be performed in combination with augmenting factors; and in the future, standardized challenge protocols including augmenting factors should be established. PMID:25306896

Niggemann, B; Beyer, K

2014-12-01

273

A concise approach to (+)-1- epi-castanospermine  

Microsoft Academic Search

A concise enantioselective synthesis of (+)-1-epi-castanospermine (2) is described, which featured the use of chiral non-racemic tetramic acid derivative 5 as a synthetic equivalent of the challenging synthon A through a highly diastereoselective vinylogous Mukaiyama type reaction.

Tian-Jun Wu; Pei-Qiang Huang

2008-01-01

274

Rapid biocatalytic polytransesterification: Reaction kinetics in an exothermic reaction  

Microsoft Academic Search

Biocatalytic polytransesterification at high concentrations of monomers proceeds rapidly and is accompanied by an increase in the temperature of the reaction mixture due to liberation of heat of reaction during the initial phase. The authors have used principles of reaction calorimetry to monitor the kinetics of polymerization during this initial phase, thus relating the temperature to the extent of polymerization.

A. K. Chaudhary; E. J. Beckman; A. J. Russell

1998-01-01

275

Zip-lock Bag Reactions  

NSDL National Science Digital Library

Students conduct and observe a chemical reaction in a sealable plastic bag. Students then devise and conduct their own experiments to determine the identity of two unknown substances used in the reaction.

Katz, David A.

2009-07-09

276

ChemTeacher: Decomposition Reactions  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Decomposition Reactions page includes resources for teaching students about identifying and predicting decomposition reactions.

2011-01-01

277

Coping with Traumatic Stress Reactions  

MedlinePLUS

... Guidelines Hospital Quality Data Medical Inspector Patient Safety Organizations Administrative Clinical Quick Links Enter ZIP code here Enter ZIP code here Coping with Traumatic Stress Reactions Coping with Traumatic Stress Reactions Available in ...

278

Laser induced nuclear reactions  

NASA Astrophysics Data System (ADS)

Dramatic improvements in laser technology since 1984 have revolutionised high power laser technology. Application of chirped-pulse amplification techniques has resulted in laser intensities in excess of 1019W/cm2. In the mid to late eighties, C. K. Rhodes and K. Boyer discussed the possibility of shining laser light of this intensity onto solid surfaces and to cause nuclear transitions. In particular, irradiation of a uranium target could induce electro- and photofission in the focal region of the laser. In this paper it is shown that ?Ci of 62Cu can be generated via the (?,n) reaction by a laser with an intensity of about 1019Wcm-2.

Ledingham, Ken; McCanny, Tom; Graham, Paul; Fang, Xiao; Singhal, Ravi; Magill, Joe; Creswell, Alan; Sanderson, David; Allott, Ric; Neely, David; Norreys, Peter; Santala, Marko; Zepf, Matthew; Watts, Ian; Clark, Eugene; Krushelnick, Karl; Tatarakis, Michael; Dangor, Bucker; Machecek, Antonin; Wark, Justin

1998-12-01

279

Reactions of the Formamidines  

E-print Network

correct is furnished by the fact that a secondary product, methyl-bis- methylphenylpyrazolone, according to this reaction. N = C - CH3 I / CH c+ RII: CHNHR Mt==== Ph N - CO Me N = C I Q . JJ I 0 - CH( ' + 2RNH Ph B - GOH CO — NPh This is the first... FOR THE DEGREE OF MASTER OF SCIENCE BY TENNYSON MYERS JUNE 1 1912 Page 1. Pormainidines are substituted formic acids * Thus aim- pie formamidine HC is formic acid with the hydroxyl nNH 0 group replaced by an &mido and the oxygen replaced by an imido group...

Myers, Tennyson

1912-06-01

280

Low Energy Nuclear Reactions?  

E-print Network

After an introduction to the controversial problem of Low Energy Nuclear Reactions (LENR) catalyzed by neutrons on metallic hydride surfaces we present the results of an experiment, made in collaboration with ENEA Labs in Frascati, to search neutrons from plasma discharges in electrolytic cells. The negative outcome of our experiment goes in the direction of ruling out those theoretical models expecting LENR to occur in condensed matter systems under specific conditions. Our criticism on the theoretical foundations of such models will also be presented.

CERN. Geneva; Faccini, R.

2014-01-01

281

The Vitamin C Clock Reaction.  

ERIC Educational Resources Information Center

Describes an iodine clock reaction that produces an effect similar to the Landolt clock reaction. This reaction uses supermarket chemicals and avoids iodate, bisulfite, and mercury compounds. Ascorbic acid and tincture of iodine are the main reactants with alternate procedures provided for vitamin C tablets and orange juice. (DDR)

Wright, Stephen W.

2002-01-01

282

The classification of chemical reactions  

Microsoft Academic Search

The classification and shorthand designation of chemical reactions are considered. It is concluded that single-step reactions can be divided into a finite number of types, each of which could be represented by an unambiguous symbol. The various types are listed and illustrated. Multi-step reactions, however, cannot be classified (in any detail) in a limited number of ways and for such

D. P. N. Satchell

1977-01-01

283

Mass Transfer with Chemical Reaction.  

ERIC Educational Resources Information Center

Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

DeCoursey, W. J.

1987-01-01

284

Polymerase Chain Reaction Assay and  

E-print Network

Polymerase Chain Reaction Assay and Bacterial Meningitis Surveillance in Remote Areas, Niger Fati reference laboratory for meningitis in Niger used polymerase chain reaction (PCR) to enhance) and the national reference center for menin- gitis in Niger. The polymerase chain reaction (PCR) method

Paris-Sud XI, Université de

285

Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru{sub 3}(CO){sub 12} (or RuCl{sub 3}) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline  

SciTech Connect

Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru [as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}] and Mo [as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)] decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

Koo, Sang-Man; Ryan, D.; Laine, R.M.

1992-09-01

286

Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru sub 3 (CO) sub 12 (or RuCl sub 3 ) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline  

SciTech Connect

Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru (as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}) and Mo (as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)) decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

Koo, Sang-Man; Ryan, D.; Laine, R.M.

1992-01-01

287

Subdiffusion-reaction processes with A ?B reactions versus subdiffusion-reaction processes with A +B?B reactions  

NASA Astrophysics Data System (ADS)

We consider the subdiffusion-reaction process with reactions of a type A +B?B (in which particles A are assumed to be mobile, whereas B are assumed to be static) in comparison to the subdiffusion-reaction process with A ?B reactions which was studied by Sokolov, Schmidt, and Sagués [Phys. Rev. E 73, 031102 (2006), 10.1103/PhysRevE.73.031102]. In both processes a rule that reactions can only occur between particles which continue to exist is taken into account. Although in both processes a probability of the vanishing of particle A due to a reaction is independent of both time and space variables (assuming that in the system with the A +B?B reactions, particles B are distributed homogeneously), we show that subdiffusion-reaction equations describing these processes as well as their Green's functions are qualitatively different. The reason for this difference is as follows. In the case of the former reaction, particles A and B have to meet with some probability before the reaction occurs in contradiction with the case of the latter reaction. For the subdiffusion process with the A +B?B reactions we consider three models which differ in some details concerning a description of the reactions. We base the method considered in this paper on a random walk model in a system with both discrete time and discrete space variables. Then the system with discrete variables is transformed into a system with both continuous time and continuous space variables. Such a method seems to be convenient in analyzing subdiffusion-reaction processes with partially absorbing or partially reflecting walls. The reason is that within this method we can determine Green's functions without a necessity of solving a fractional differential subdiffusion-reaction equation with boundary conditions at the walls. As an example, we use the model to find the Green's functions for a subdiffusive reaction system (with the reactions mentioned above), which is bounded by a partially absorbing wall. This example shows how the model can be used to analyze the subdiffusion-reaction process in a system with partially absorbing or reflecting thin membranes. Employing a simple phenomenological model, we also derive equations related to the reaction parameters used in the considered models.

Koszto?owicz, Tadeusz; Lewandowska, Katarzyna D.

2014-09-01

288

ISMP Adverse Drug Reactions  

PubMed Central

The purpose of this feature is to heighten awareness of specific adverse drug reactions (ADRs), discuss methods of prevention, and promote reporting of ADRs to the US Food and Drug Administration’s (FDA’s) MedWatch program (800-FDA-1088). If you have reported an interesting, preventable ADR to MedWatch, please consider sharing the account with our readers. Write to Dr. Shuster at ISMP, 200 Lakeside Drive, Suite 200, Horsham, PA 19044 (phone: 215-947-7797; fax: 215-914-1492; e-mail: joel.shuster@temple.edu). Your report will be published anonymously unless otherwise requested. This feature is provided by the Institute for Safe Medication Practices (ISMP) in cooperation with the FDA’s MedWatch program and Temple University School of Pharmacy. ISMP is an FDA MedWatch partner. PMID:24421415

2013-01-01

289

Fission in Spallation Reactions  

NASA Astrophysics Data System (ADS)

Some properties of fission in spallation reactions in the GeV range are examined. It is shown on theoretical grounds that the charge, mass and excitation energy are strongly fluctuating. The range of accessible excitation energies is determined. The ability of a particular intranuclear plus evaporation model, namely the INCL4+ABLA model to describe the existing data is demonstrated. In view of the numerous parameters used in the fission model, the sensitivity of the results to these parameters is investigated. It is shown that, due to the complexity of the fission modeling, it is hard to get reliable information on the level density parameters at high excitation energy. Finally the influence of the nature of the incident projectile is shortly discussed.

Cugnon, J.; Aoust, Th.; Boudard, A.

2008-04-01

290

Polymerase chain reaction  

SciTech Connect

This paper discusses the polymerase chain reaction (PCR) an in-vitro method of amplifying DNA sequences. Beginning with DNA of any origin- bacterial, viral, plant, or animal- PCR can increase the amount of a DNA sequence hundreds of millions to billions of times. The procedure can amplify a targeted sequence even when it makes up less than one part in a million of the total initial sample. PCR is an enzymatic process that is carried out in discrete cycles of amplification, each of which can double the amount of target DNA in the sample. Thus, n cycles can produce 2{sup n} times as much target as was present to begin with. This paper discusses how PCR has had an impact on molecular biology, human genetics, infectious and genetic disease diagnosis, forensic science, and evolutionary biology.

Arnhelm, N. (Univ. of Southern California, CA (US)); Levenson, C.H. (Cetus Corp. (US))

1990-10-01

291

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ab initio potential energy surfaces. We will also describe results from recent studies on the kinetics of transition metal catalyzed reactions, including the importance of vibrational coupling to the reaction coordinate and the role of this coupling in catalytic rate enhancement.

Hratchian, Hrant P.

2011-06-01

292

Rapid biocatalytic polytransesterification: Reaction kinetics in an exothermic reaction  

SciTech Connect

Biocatalytic polytransesterification at high concentrations of monomers proceeds rapidly and is accompanied by an increase in the temperature of the reaction mixture due to liberation of heat of reaction during the initial phase. The authors have used principles of reaction calorimetry to monitor the kinetics of polymerization during this initial phase, thus relating the temperature to the extent of polymerization. Rate of polymerization increases with the concentration of monomers. This is also reflected by the increase in the temperature of the reaction mixture. Using time-temperature-conversion contours, a differential method of kinetic analysis was used to calculate the energy of activation ({approximately} 15.1 Kcal/mol).

Chaudhary, A.K.; Beckman, E.J.; Russell, A.J. [Univ. of Pittsburgh, PA (United States)] [Univ. of Pittsburgh, PA (United States)

1998-08-20

293

Formaldehyde reactions in dark clouds  

NASA Technical Reports Server (NTRS)

The low-pressure reactions of formaldehyde (H2CO) with D(+), D2(+), D3(+), and He(+) are studied by the ion-cyclotron resonance technique. These reactions are potential loss processes for formaldehyde in cores of dark interstellar clouds. The deuterated reactants represent direct analogs for protons. Rate coefficients and branching ratios of product channels have been measured. Charge transfer is observed to be the dominant reaction of H2CO with D(+), D2(+), and He(+) ions. Only the D3(+) reaction exhibits a proton-transfer channel. All reactions proceed at rate coefficients near the collision limit. Proton-deuteron exchange reactions are found to be inefficient processes in the formaldehyde system.

Sen, A. D.; Anicich, V. G.; Federman, S. R.

1992-01-01

294

EXPERIMENTAL BONE MARROW REACTIONS  

PubMed Central

1. The effect produced by intravenous administration of gum shellac solution varied directly with the strength of the solution and the amount injected. (a) Strong solutions were intensely toxic and fatal to all the animals injected. Toxicity was abolished by the presence of carbon particles in the solution. (b) Medium strength solutions produced a marked normoblastosis followed by an erythroblastosis if injections were continued, accompanied either by an initial rise of red blood cells and hemoglobin followed by a decrease or an initial decline followed by an increase. The decrease of erythrocytes and hemoglobin did not amount to an actual anemia, and was usually concomitant with the greatest outpouring of nucleated red cells. (c) Small doses elicited the same kind of response except that the normoblastosis was less marked, the decrease of red cells and hemoglobin minimal or absent, the increase of red blood cells and hemoglobin marked in most instances. (d) Minimal doses elicited no appreciable reaction. 2. The bone marrow in animals killed after a course of injections showed intense erythrocytic hyperplasia. This disappeared after a variable length of time with a return of the bone marrow to apparently normal condition. 3. Toxic effects with non-fatal doses in form of hemorrhages were produced mainly in the bone marrow and occasionally in the kidney under the following conditions. (a) After one injection in an animal with hyperplastic marrow (hemorrhages ih the bone marrow only). (b) After the fourth and fifth dose when administered at long intervals (4 to 19 day intervals). (c) After one injection given 40 days after several successive injections (one animal only). 4. Small and divided doses administered at long intervals produced no apparent ill effect. 5. Subcutaneous administrations did not elicit any marked systemic reactions. Locally there was induration and edema. 6. The conclusion was drawn that gum shellac solution stimulates markedly the production of erythrocytes in the bone marrow. The mechanism of stimulation is not clear, but it seems unlikely that it is due to destruction of red blood cells in the peripheral blood stream. PMID:19869286

Muller, Gulli Lindh

1927-01-01

295

Accurate determinations of the extent to which the SE2' reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti.  

PubMed

The allylsilanes, (R)-E- and (R)-Z-4-trimethylsilylpent-2-ene 16, were prepared in essentially an enantiomerically and geometrically pure state (er >99.95 : 0.05, E : Z and Z : E >99.95 : 0.05) by, successively, conjugate addition of lithium dimethylcuprate to N-[(E)-3'-trimethylsilylpropenoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide 13, to give N-[(E)-(3'R)-3'-trimethylsilylbutanoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide, removal of the chiral auxiliary with bromomagnesium benzyloxide, aldol reaction with acetaldehyde, and decarboxylative elimination, to give either the Z- or E-isomer. Both the E- and Z-allylsilanes 16 reacted with the adamantyl cation to give mixtures of E- and Z-4-adamantylpent-2-enes 17. The E-allylsilane gave the E- and Z-products in a ratio of 40 : 60, and the Z-allylsilane gave the E- and Z-products in a ratio of 99.8:0.02. The enantiomer ratio was >99:1 for the reaction of the E-allylsilane giving the Z-product, 90:10 for the E-allylsilane giving the E-product, and 95 : 5 for the Z-allylsilane giving the E-product, showing that the reactions were stereospecific to a high degree, but not always quite completely so. The allenylsilane, 2-trimethylsilylpenta-2,3-diene 29, was prepared enantiomerically highly enriched (er 99:1) by copper-catalysed reaction of methylmagnesium chloride with (S)-4-trimethylsilylbut-3-yn-2-yl camphor-10-sulfonate 28. The allenylsilane 29 reacted with the adamantyl cation to give (S)-4-adamantylpent-2-yne (S)-30 with the same level of enantiomeric purity, showing that the reaction was, as accurately as can be measured, completely stereospecific. The allenylsilane 29 also reacted with isobutanal in the presence of titanium tetrachloride to give 2,4-dimethylhept-5-yn-3-ol as a mixture of diastereoisomers, syn 31 and anti 32, in a ratio of 95:5, with the major diastereoisomer present as a mixture of enantiomers (4R,5R):(4S,5S) in a ratio of 99:1, showing that the reaction was, as accurately as can be measured, completely stereospecific in the anti sense. The corresponding propargylsilane, 4-trimethylsilylpent-2-yne 37, reacted with the adamantyl cation to give dienes assigned the structures 2,3-diadamantyl-1,3-pentadiene 42 and 2,4-diadamantyl-1,3-pentadiene 43, and reacted with isobutanal in the presence of titanium tetrachloride to give 2-(1-hydroxy-2-methylpropyl)-3-trimethylsilylpenta-1,3-dienes 45 and 2,4-dimethyl-5-trimethylsilylhept-5-en-3-one 46. The enantiomerically enriched propargylsilane (R)-1,3-bis(trimethylsilyl)but-1-yne (er >99.7:0.3) was prepared from the sultam 13, by removal of the chiral auxiliary with lithium ethoxide, reduction of the ethyl ester to give (R)-3-trimethylsilylbutanal 60, enol triflate formation, beta-elimination and C-silylation. The propargylsilane reacted with 2,4-dinitrobenzaldehyde in the presence of titanium tetrachloride to give the allenes, 1-(2,4-dinitrophenyl)-2-trimethylsilylpenta-2,3-dienols 63-66, as two diastereoisomers in a ratio of 2 : 1, each of which was a pair of enantiomers in a ratio of approximately 3:1, showing that there was considerable loss of stereospecificity, but that what there was was in the anti sense. A similar reaction with isobutanal gave a similar set of four allenes, 2-methyl-4-trimethylsilylhepta-4,5-dien-3-ol 73-76, but with a negligible degree of stereospecificity. PMID:14985816

Buckle, Michael J C; Fleming, Ian; Gil, Salvador; Pang, Kah Ling Christine

2004-03-01

296

Enzymatic reactions on immobilised substrates.  

PubMed

This review gives an overview of enzymatic reactions that have been conducted on substrates attached to solid surfaces. Such biochemical reactions have become more important with the drive to miniaturisation and automation in chemistry, biology and medicine. Technical aspects such as choice of solid surface and analytical methods are discussed and examples of enzyme reactions that have been successful on these surfaces are provided. PMID:23579870

Gray, Christopher J; Weissenborn, Martin J; Eyers, Claire E; Flitsch, Sabine L

2013-08-01

297

Drug Hypersensitivity Reactions Involving Skin  

Microsoft Academic Search

Immune reactions to drugs can cause a variety of diseases involving the skin, liver, kidney, lungs, and other organs. Beside\\u000a immediate, IgE-mediated reactions of varying degrees (urticaria to anaphylactic shock), many drug hypersensitivity reactions\\u000a appear delayed, namely hours to days after starting drug treatment, showing a variety of clinical manifestations from solely\\u000a skin involvement to fulminant systemic diseases which may

Oliver Hausmann; Benno Schnyder; Werner J. Pichler

298

Nuclear astrophysics from direct reactions  

E-print Network

Accurate nuclear reaction rates are needed for primordial nucleosynthesis and hydrostatic burning in stars. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies. In recent years direct reactions have been developed and applied to extract low-energy astrophysical S-factors. These methods require a combination of new experimental techniques and theoretical efforts, which are the subject of this presentation.

C. A. Bertulani

2008-02-23

299

Change in Temperature: Exothermic Reaction  

NSDL National Science Digital Library

Learners add calcium chloride to a baking soda solution and observe an increase in temperature along with the production of a gas and a white precipitate. These are all signs of a chemical reaction. Learners can quantify the results of the reaction by using a thermometer to measure the temperature change. Learners also design their own experiment to alter the reaction and measure how it affects the change in temperature.

Kessler, James H.; Galvan, Patricia M.

2007-01-01

300

ChemTeacher Resource: Oxidation Reduction Reactions  

NSDL National Science Digital Library

This computer resource goes over oxidation reduction reactions and how they are broken down into half reactions. It explains which half reaction is the oxidation reaction and which one is the reduction, then has some summary questions at the end.

Dr. Martin McClinton, Debbie McClinton, Dr. Miriam Douglass

2011-01-01

301

Catalytic enantioselective decarboxylative reactions using organocatalysts.  

PubMed

Catalytic decarboxylative reactions are attractive as biomimetic reactions and environmentally friendly reaction processes. In this review, the origin and recent development of organocatalytic enantioselective decarboxylative reactions of malonic acid half oxy- or thioesters, or ?-ketoacids are summarized. PMID:24270735

Nakamura, Shuichi

2014-01-21

302

Radiation reaction in fusion plasmas.  

PubMed

The effects of a radiation reaction on thermal electrons in a magnetically confined plasma, with parameters typical of planned burning plasma experiments, are studied. A fully relativistic kinetic equation that includes the radiation reaction is derived. The associated rate of phase-space contraction is computed and the relative importance of the radiation reaction in phase space is estimated. A consideration of the moments of the radiation reaction force show that its effects are typically small in reactor-grade confined plasmas, but not necessarily insignificant. PMID:15600530

Hazeltine, R D; Mahajan, S M

2004-10-01

303

Recent advances in Sonogashira reactions.  

PubMed

The coupling of aryl or vinyl halides with terminal acetylenes catalysed by palladium and other transition metals, commonly termed as Sonogashira cross-coupling reaction, is one of the most important and widely used sp(2)-sp carbon-carbon bond formation reactions in organic synthesis, frequently employed in the synthesis of natural products, biologically active molecules, heterocycles, molecular electronics, dendrimers and conjugated polymers or nanostructures. This critical review focuses on developments in the Sonogashira reaction achieved in recent years concerning catalysts, reaction conditions and substrates (352 references). PMID:21655588

Chinchilla, Rafael; Nájera, Carmen

2011-10-01

304

Kinematically complete chemical reaction dynamics  

NASA Astrophysics Data System (ADS)

Kinematically complete studies of molecular reactions offer an unprecedented level of insight into the dynamics and the different mechanisms by which chemical reactions occur. We have developed a scheme to study ion-molecule reactions by velocity map imaging at very low collision energies. Results for the elementary nucleophilic substitution (SN2) reaction Cl- + CH3I ? ClCH3 + I- are presented and compared to high-level direct dynamics trajectory calculations. Furthermore, an improved design of the crossed-beam imaging spectrometer with full three-dimensional measurement capabilities is discussed and characterization measurements using photoionization of NH3 and photodissociation of CH3I are presented.

Trippel, S.; Stei, M.; Otto, R.; Hlavenka, P.; Mikosch, J.; Eichhorn, C.; Lourderaj, U.; Zhang, J. X.; Hase, W. L.; Weidemüller, M.; Wester, R.

2009-11-01

305

Charge Transfer Reactions  

NASA Astrophysics Data System (ADS)

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

Dennerl, Konrad

2010-12-01

306

Effective reaction parameters for mixing controlled reactions in heterogeneous media  

Microsoft Academic Search

Sound understanding of mixing-controlled reactions in heterogeneous media is needed for the realistic modeling of contaminant transport in aquifers and is a precondition for the evaluation of natural attenuation processes, the design of nuclear waste disposal, and the engineered remediation of contaminated sites. In this work, we study the bimolecular dissolution-precipitation equilibrium reaction, adapted after De Simoni et al. (2005).

Jian Luo; Marco Dentz; Jesus Carrera; Peter Kitanidis

2008-01-01

307

Nuclear Reactions & Scaling Arguments 11 October 2011  

E-print Network

Nuclear Reactions & Scaling Arguments 11 October 2011 Goals · Review nuclear reaction rates · Practice using scaling arguments Nuclear Reactions 1. Consider the simple reaction A k1 ---- B k2 ---- C = 3. #12;nuclear reactions & scaling arguments 2 3. Frequently, we approximate nuclear reaction rates

Militzer, Burkhard

308

Understanding the novolak synthesis reaction  

Microsoft Academic Search

We describe new tools for the characterization of novolac resins, for the understanding of the novolac synthesis reaction, and for the prediction of resin structures. These tools have been used to optimize the performance of photoresists for microlithography. The current state-of- the-art describes novolac copolymer compositions as the ratio of monomers charged in the reaction, even though it is well

Leonard E. Bogan

1993-01-01

309

Theory of hybrid nuclear reactions  

SciTech Connect

A theory of hybrid nuclear reactions, which are partially direct and partially compound, is presented. We review first the formulation of the theory, based on the optical theorem, and then its applications to a few example reactions. Discussions will be given on the physical picture (deep peripheral nature) of such hybrid processes emerging from the numerical studies. 25 references, 10 figures.

Udagawa, T.

1983-01-01

310

Semiclassical aspects of transfer reactions  

SciTech Connect

Semiclassical analysis of heavy ion induced transfer reactions are discussed for the quasielastic region. Some unique aspects of these reactions are shown, the variety of features which can be understood semiclassically is demonstrated, and some open problems are indicated. 28 refs., 16 figs. (LEW)

Bond, P.D.

1985-01-01

311

Reciprocity theory of homogeneous reactions  

Microsoft Academic Search

The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to various classes of dissociation, recombination, rearrangement, ionizing, and photochemical reactions. It is shown that for the principle of reciprocity to be

Adolf A. Agbormbai

1990-01-01

312

PHENOTHIAZINE ATARAXICS--Extrapyramidal Reactions  

PubMed Central

Thirty-nine cases of extrapyramidal reactions caused by seven chemically different phenothiazine medications are presented. Historical, pharmacological, diagnostic, and therapeutic factors are considered. It is important that the physician prescribing phenothiazines be well aware of the reactions which may occur so that therapy may be discontinued at the first untoward signs. PMID:13806816

Cain, Harvey D.; Malcolm, Mary

1960-01-01

313

Allergic reactions to insect secretions.  

PubMed

Some products derived from insects can induce allergic reactions. The main characteristics of some products from honeybees, cochineal and silkworms are summarised here. We review allergic reactions from honey-derived products (propolis, wax, royal jelly), from cochineal products (shellac and carmine) and from silk : clinical features, allergological investigations and allergens if they are known. PMID:24449611

Pecquet, Catherine

2013-01-01

314

Chemistry of heavy ion reactions  

SciTech Connect

The use of heavy ions to induce nuclear reactions was reported as early as 1950. Since that time it has been one of the most active areas of nuclear research. Intense beams of ions as heavy as uranium with energies high enough to overcome the Coulomb barriers of even the heaviest elements are available. The wide variety of possible reactions gives rise to a multitude of products which have been studied by many ingenious chemical and physical techniques. Chemical techniques have been of special value for the separation and unequivocal identification of low yield species from the plethora of other nuclides present. Heavy ion reactions have been essential for the production of the trans-Md elements and a host of new isotopes. The systematics of compound nucleus reactions, transfer reactions, and deeply inelastic reactions have been elucidated using chemical techniques. A review of the variety of chemical procedures and techniques which have been developed for the study of heavy ion reactions and their products is given. Determination of the chemical properties of the trans-Md elements, which are very short-lived and can only be produced an ''atom-at-a-time'' via heavy ion reactions, is discussed. 53 refs., 19 figs.

Hoffman, D.C.

1988-10-01

315

Granulomatous Reaction to Descemet'S Membrane.  

National Technical Information Service (NTIS)

A granulomatous reaction to Descemet's membrane was found in 28 of 298 consecutive eyes with corneal ulcer or keratitis. The reaction was seen in a variety of corneal conditions but most frequently in eyes with a disciform keratitis, either with or withou...

W. R. Green, L. E. Zimmerman

1967-01-01

316

The Variance Reaction Time Model  

ERIC Educational Resources Information Center

The variance reaction time model (VRTM) is proposed to account for various recognition data on reaction time, the mirror effect, receiver-operating-characteristic (ROC) curves, etc. The model is based on simple and plausible assumptions within a neural network: VRTM is a two layer neural network where one layer represents items and one layer…

Sikstrom, Sverker

2004-01-01

317

REACTION OF URANIUM WITH NITROGEN  

Microsoft Academic Search

Studies of U reactions with nitrogen at 400 to 920 deg C and 200 mm Hg ; nitrogen pressure indicated no nitriding below 400 deg . The reaction rate at ; 590 and 710 deg C and 20 to 600 mm Hg pressure is directly proportional to the ; square root of the pressure and is not influenced by nitrogen

A. F. Bessonov; V. G. Vlasov

1962-01-01

318

Free Radical Reactions in Food.  

ERIC Educational Resources Information Center

Discusses reactions of free radicals that determine the chemistry of many fresh, processed, and stored foods. Focuses on reactions involving ascorbic acid, myoglobin, and palmitate radicals as representative radicals derived from a vitamin, metallo-protein, and saturated lipid. Basic concepts related to free radical structure, formation, and…

Taub, Irwin A.

1984-01-01

319

Endothermic photo-catalytic reactions  

SciTech Connect

The overall objective of this report is to present the results of an investigation to provide guidelines for future experimental work, on solar energy driven endothermic photo-catalytic reactions, and primarily to select candidate synthesis reactions which lead to high $-value products. An intensive literature search was conducted to find properties, market demand, and prices of pertinent chemicals; meeting four criteria: (1) the reaction must be endothermic and favorable; (2) the reaction must be catalytic; (3) the product must be produced from low cost feedstocks; and (4) the product must have a sales price >$1.00/lb. Initial examination of low cost feedstocks to high value products lead to consideration of n-paraffins to aromatics and substituted aromatics. Fifteen candidate endothermic synthesis reactions, meeting the above criteria, are suggested. The ratio of product price by reactant cost indicates {approximately}5--8 for the best possibilities; all can be visualized as starting with low cost paraffin and methanol feedstocks.

Prengle, H.W. Jr.; Wentworth, W.E.; Polonczyk, K.C.; Saghafi, M.; Wilking, J.A.; Kramer, K.S. (Houston Univ., TX (United States))

1992-04-01

320

Fundamental reaction pathways during coprocessing  

SciTech Connect

The objective of this research was to investigate the fundamental reaction pathways in coal petroleum residuum coprocessing. Once the reaction pathways are defined, further efforts can be directed at improving those aspects of the chemistry of coprocessing that are responsible for the desired results such as high oil yields, low dihydrogen consumption, and mild reaction conditions. We decided to carry out this investigation by looking at four basic aspects of coprocessing: (1) the effect of fossil fuel materials on promoting reactions essential to coprocessing such as hydrogen atom transfer, carbon-carbon bond scission, and hydrodemethylation; (2) the effect of varied mild conditions on the coprocessing reactions; (3) determination of dihydrogen uptake and utilization under severe conditions as a function of the coal or petroleum residuum employed; and (4) the effect of varied dihydrogen pressure, temperature, and residence time on the uptake and utilization of dihydrogen and on the distribution of the coprocessed products. Accomplishments are described.

Stock, L.M.; Gatsis, J.G. [Chicago Univ., IL (United States). Dept. of Chemistry

1992-12-01

321

Sodium concrete reaction: structural considerations  

SciTech Connect

An overview of the sodium concrete reaction phenomenon, with emphasis on structural considerations, is presented. Available test results for limestone, basalt, and magnetite concrete with various test article configurations are reviewed. Generally, tests indicate reaction is self limiting before all sodium is used. Uncertainties, however, concerning the mechanism for penetration of sodium into concrete have resulted in different theories about a reaction model. Structural behavior may be significant in the progression of the reaction due to thermal-structural-chemical interactions involving tensile cracking, compressive crushing, or general deterioration of concrete and the exposure of fresh concrete surfaces to react with sodium. Structural behavior of test articles and potential factors that could enhance the progression of the reaction are discussed.

Freskakis, G.N.

1984-09-01

322

Construction of the reaction networks for heterogeneous catalytic reactions: Fischer—Tropsch synthesis and related reactions  

Microsoft Academic Search

The key approaches to the generation of reaction networks for the synthesis of products from CO and H2 are considered. The selection rules for the elementary steps on the surface of heterogeneous catalysts are formulated. Data on the surface compounds and steps related to reactions of CO and H2 are analyzed and a set of transforms (models of elementary steps)

O. N. Temkin; A. V. Zeigarnik; A. E. Kuz\\; L. G. Bruk; E. V. Slivinskii

2002-01-01

323

Atomic effects in nuclear reactions  

SciTech Connect

The dependence of nuclear reaction observables on excitation of the surrounding atom is developed in a systematic way. Considerations are confined to those excitations of the atomic electrons arising from changes in the nuclear charge and velocity as a result of the nuclear reaction. The analysis is divided into two distinct parts. In the first, a general time-dependent semiclassical formalism of atomic excitation as a result of a nuclear reaction is derived and sum rules for the moments of the electron excitation-energy distribution are obtained. Reasonable procedures for modifying nuclear reaction observables by atomic transition amplitudes and energies are applied to calculate atomic corrections to Q values in ..beta../sup +/ decay, (p,n) threshold, and (/sup 3/He,t) reactions, as well as to an analysis of a nuclear resonance reaction. In the second part, a time-independent R-matrix theory is developed and the dependence on atomic excitation of quantities characterizing a nuclear reaction is derived. The R-matrix formalism, generalized to include atomic excitation, retains all the utility of the usual nuclear R-matrix theory. The results of the second part are applied to an analysis of resonant elastic scattering in /sup 4/He(..cap alpha..,..cap alpha..)/sup 4/He.

Feagin, J.M.

1980-01-01

324

Gray Scott Reaction Diffusion Model  

NSDL National Science Digital Library

The Gray-Scott Reaction Diffusion Model displays the spatial concentration of chemical species U and V under the influence of the reaction U+2V->3V and V->P. The simulation models this reaction in an open system with a constant addition of U and removal of V due to a flow rate f and with the removal of V by the reaction V->P with reaction rate k. Combining this autocatalytic process with diffusion results in pattern formation that depends on the f and k rates and on the U and V diffusivities Du and Dv. This reaction diffusion system has a surprising variety of spatiotemporal patterns when starting in the initial state U=1 and V=0 except for a square grid at the center where U=1/2 and V=1/4. The Gray-Scott Reaction Diffusion Model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Christian, Wolfgang

2012-05-26

325

Nuclear Structure and Reaction Mechanism Studies with Multinucleon Reactions  

SciTech Connect

This contribution reports on the results of an experiment to study the near-yrast states in selenium- and osmium-like nuclei, following their population in thick-target, multinucleon transfer reactions between an 82Se beam and a 192Os target. The experimental results for the level scheme for 84Se are presented together with investigations into the use of multi-dimensional gamma-ray energy gating to investigate angular momentum population in such heavy-ion binary reactions.

Regan, P. H.; Jones, G. A.; Podolyak, Zs.; Abdullah, M.; Gelletly, W.; Langdown, S. D.; Wollel, G. [Dept. of Physics, School of Electronics and Physical Sciences, Guildford, Surrey, GU2 7XH (United Kingdom); De Angelis, G.; Gadea, A.; Kroell, Th.; Marginean, N.; Martinez, T.; Napoli, D. R.; Rusu, C.; Tonev, D. [INFN Laboratori Nazionali di Legnaro, Legnaro (Italy); Zhang, Y. H. [INFN Laboratori Nazionali di Legnaro, Legnaro (Italy); Institute of Modern Physics, CAS, Lanzhou (China); Ur, C. A.; Axiotis, M.; Bazzacco, D.; Farnea, E. [INFN, Sezione di Padova, Padova (Italy)] (and others)

2006-08-14

326

Magnetically suspended reaction wheel assembly  

NASA Technical Reports Server (NTRS)

The magnetically suspended reaction wheel assembly (MSRWA) is the product of a development effort funded by the Air Force Materials Laboratory (AFML) at Wright Patterson AFB. The specific objective of the project was to establish the manufacturing processes for samarium cobalt magnets and demonstrate their use in a space application. The development was successful on both counts. The application portion of the program, which involves the magnetically suspended reaction wheel assembly, is emphasized. The requirements for the reaction wheel were based on the bias wheel requirements of the DSP satellite. The tasks included the design, fabrication, and test of the unit to the DSP program qualification requirements.

Stocking, G.

1984-01-01

327

Bioluminescent Reaction by Immobilized Luciferase  

NASA Astrophysics Data System (ADS)

We have investigated an effect of immobilization of luciferase molecules at the optical fiber end on a bioluminescent reaction. The time dependence of measured count rates of emitted photons has been analyzed by fitting with numerical solution of differential equations including the effect of the product-inhibitor and the deactivation of the luciferase. Through the analysis, we have successfully extracted kinetic constants such as, reaction rate, number of active luciferase molecules, etc. Ratio of active molecules to total luciferase molecules in immobilization was one order of magnitude lower than that in solution. The reaction rate of the bioluminescent process was also different from the one of free luciferase in solution.

Tanaka, Ryuta; Takahama, Eriko; Iinuma, Masataka; Ikeda, Takeshi; Kadoya, Yutaka; Kuroda, Akio

328

Experimental Study of Serpentinization Reactions  

NASA Technical Reports Server (NTRS)

Current carbonaceous chondrite parent-body thermal models [1-3] produce scenarios that are inconsistent with constraints on aqueous alteration conditions based on meteorite mineralogical evidence, such as phase stability relationships within the meteorite matrix minerals [4] and isotope equilibration arguments [5, 6]. This discrepancy arises principally because of the thermal runaway effect produced by silicate hydration reactions (here loosely called serpentinization, as the principal products are serpentine minerals), which are so exothermic as to produce more than enough heat to melt more ice and provide a self-sustaining chain reaction. One possible way to dissipate the heat of reaction is to use a very small parent body [e.g., 2] or possibly a rubble pile model. Another possibility is to release this heat more slowly, which depends on the alteration reaction path and kinetics.

Cohen, B. A.; Brearley, A. J.; Ganguly, J.; Liermann, H.-P.; Keil, K.

2004-01-01

329

Positive reaction to allergen (image)  

MedlinePLUS

... a sensitivity to a specific substance, called an allergen, that is contacted through the skin, inhaled into ... swallowed or injected. The body's reaction to an allergen can be mild, such as a localized rash, ...

330

Reaction Rates, Catalysis, and Pasteurization  

NSDL National Science Digital Library

In this activity, by the Concord Consortium's Molecular Literacy project, students are introduced to "key ideas of chemistry, including reaction rates, bond strength, activation energy, catalysis, and equilibrium." Upon completion of this activity students should be able to describe and manipulate models to discover how reaction rates, energy, bond strength, catalysis, and equilibrium are related; manipulate reaction rates by changing temperature and concentration; demonstrate their understanding by creating an endothermic reaction that releases a lot of heat energy, one that requires a catalyst, and one that reaches equilibrium between reactants and products. The activity itself is a java-based interactive resource built upon the free, open source Molecular Workbench software. In the activity, students are allowed to explore at their own pace in a digital environment full of demonstrations, illustrations, and models they can manipulate. In addition to the activity, visitors will find an overview of the activity, a test and rubric, central concepts, and their correlation to AAAS standards.

2008-10-23

331

Energy partitioning in elementary reactions  

SciTech Connect

In the past year three photodissociation projects were completed on acetylene, ethylene and the pair of molecules, cyclopentadiene and indene and an experiment begun on an interesting reaction of excited rare gas atoms and hydrogen molecules.

Bersohn, R.

1990-01-01

332

Medications and Drug Allergic Reactions  

MedlinePLUS

... detaches like in a patient who has suffered burns, is another type of severe cutaneous adverse reaction. ... you may develop a cough or facial and tongue swelling. Some people are sensitive to aspirin, ibuprofen ...

333

Method for conducting exothermic reactions  

DOEpatents

A liquid phase process for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, L. Jr.; Hearn, D.; Jones, E.M. Jr.

1993-01-05

334

Severe cutaneous adverse drug reactions  

PubMed Central

Severe cutaneous drug reactions are one of the commonest medical challenges presenting to an emergency room in any hospital. The manifestations range from maculopapular rash to severe systemic symptoms like renal failure and cardiovascular compromise. Toxic epidermal necrolysis, erythroderma, drug rash with eosinophilia and systemic symptoms, acute generalised exanthematous pustulosis and drug induced vasculitis are the common cutaneous drug reactions which can have severe morbidity and even mortality. Careful history taking of the lag period after drug intake and associated symptoms, along with detailed examination of the skin, mucosa and various systems, help in early diagnosis of these reactions. Early stoppage of the incriminating drug, specific therapy including corticosteroids, cyclosporine and intravenous immunoglobulin depending on the case along with supportive therapy and local measures help in salvaging most patients. An overview of these important cutaneous drug reactions along with their management is being reviewed in this article. PMID:24600147

Verma, Rajesh; Vasudevan, Biju; Pragasam, Vijendran

2013-01-01

335

Nanoplasmonic probes of catalytic reactions.  

PubMed

Optical probes of heterogeneous catalytic reactions can be valuable tools for optimization and process control because they can operate under realistic conditions, but often probes lack sensitivity. We have developed a plasmonic sensing method for such reactions based on arrays of nanofabricated gold disks, covered by a thin (approximately 10 nanometer) coating (catalyst support) on which the catalyst nanoparticles are deposited. The sensing particles monitor changes in surface coverage of reactants during catalytic reaction through peak shifts in the optical extinction spectrum. Sensitivities to below 10(-3) monolayers are estimated. The capacity of the method is demonstrated for three catalytic reactions, CO and H2 oxidation on Pt, and NO(x) conversion to N2 on Pt/BaO. PMID:19933104

Larsson, Elin M; Langhammer, Christoph; Zori?, Igor; Kasemo, Bengt

2009-11-20

336

Pericyclic reactions in organic synthesis  

E-print Network

Part I of this thesis describes a formal, metal-free, [2 + 2 + 2] cycloaddition strategy based on a cascade of two pericyclic processes. An intramolecular propargylic ene reaction of a 1,6-diyne is used to generate a ...

Robinson-Surry, Julia M. (Julia Mae)

2011-01-01

337

Radiation Reaction in Quantum Vacuum  

E-print Network

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model named "radiation reaction". P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the run-away solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. Therefore, it is desirable to stabilize this model of the radiation reaction for estimations. Via my recent research, I found a stabilized model of radiation reaction in quantum vacuum. This leads us to an updated Fletcher-Millikan's charge to mass ratio including radiation, de/dm, derived as the 4th order tensor measure. In this paper, I will discuss the latest update of the model and the ability of the equation of motion with radiation reaction in quantum vacuum via photon-photon scatterings.

Seto, Keita

2014-01-01

338

Radiation Reaction in Quantum Vacuum  

E-print Network

From the development of the electron theory by H. A. Lorentz in 1906, many authors have tried to reformulate this model named "radiation reaction". P. A. M. Dirac derived the relativistic-classical electron model in 1938, which is now called the Lorentz-Abraham-Dirac model. But this model has the big difficulty of the run-away solution. Recently, this equation has become important for ultra-intense laser-electron (plasma) interactions. Therefore, it is desirable to stabilize this model of the radiation reaction for estimations. Via my recent research, I found a stabilized model of radiation reaction in quantum vacuum. This leads us to an updated Fletcher-Millikan's charge to mass ratio including radiation, de/dm, derived as the 4th order tensor measure. In this paper, I will discuss the latest update of the model and the ability of the equation of motion with radiation reaction in quantum vacuum via photon-photon scatterings.

Keita Seto

2014-05-26

339

Reactions of Mustard on Concrete.  

National Technical Information Service (NTIS)

The reactions of the blister agent mustard, (bis(2- chloroethyl) sulfide, HD), and chloroethyl phenyl sulfide, CEPS*, a simulants, were monitored on concrete. asphalt and sand substrates. The CDC13 extract of concrete monoliths was analyzed using both NMR...

C. A. Brevett, G. W. Wagner, K. Sumpter, J. Rice, M. Hall

2004-01-01

340

Adalimumab induced pulmonary sarcoid reaction  

PubMed Central

Sarcoidosis is a multisystem granulomatous inflammatory disease of unknown etiology. There is evidence that Tumor Necrosis Factor alpha (TNF-?) antagonists are useful in the treatment of advanced or refractory disease. However, sarcoidosis-like reaction has been reported with TNF-? blockade in other inflammatory conditions. Here we report a case of sarcoid-like reaction in a patient with psoriatic arthritis shortly after initiation of adalimumab therapy. Stopping adalimumab and systemic anti-inflammatory therapy with corticosteroids resulted in resolution of pulmonary symptoms and chest radiographic findings. Though TNF-? plays a critical role in pathogenesis of sarcoidosis, the development of sarcoid reaction with TNF-? blockade is paradoxical and the mechanism of this response remains unknown. TNF-? induced sarcoid-reaction could involve multiple organs. Its development with one agent does not preclude therapy with other TNF-? blockers.

Bhargava, S.; Perlman, D.M.; Allen, T.L.; Ritter, J.H.; Bhargava, M.

2013-01-01

341

Nuclear Reactions & Scaling Arguments 11 October 2011  

E-print Network

Nuclear Reactions & Scaling Arguments 11 October 2011 Goals · Review nuclear reaction rates · Practice using scaling arguments Nuclear Reactions 1. Consider the simple reaction A k1 ---- B k2 ---- C rate for something like p + p D scales like n2 p. Think in microscopic terms. #12;nuclear reactions

Militzer, Burkhard

342

Thermal explosion of autocatalytic reaction  

Microsoft Academic Search

Analytical and numerical solutions are used to determine the critical conditions for thermal explosion of autocatalytic reaction. The solutions covers both the reaction governed by the Arrhenius kinetics equation and the Frank-Kamenetskii approximation for that equation. The definition of criticality as the point at which d2?\\/d?2=0, d3?\\/d?3=0 and d?\\/d??0 is used here. The study is dealt with low and high

Saad A. El-Sayed

2003-01-01

343

Psychosocial reactions to physical illness.  

PubMed Central

Recently medical educators have emphasized the need for physicians to acquire the skills to deal with psychologic aspects of patient care. To facilitate this task a descriptive schema is presented for use in evaluating patients' psychosocial reactions to physical illness. Three core components of such reactions are: the personal meaning of illness, emotional responses to illness and modes of coping with illness. Clinical application of this schema may help with patient management and prevent psychiatric complications of physical illness. PMID:6839255

Lipowski, Z. J.

1983-01-01

344

Bystanders' Reactions to Sexual Harassment  

E-print Network

? was never included in the study. They were then asked to complete a questionnaire in which they provided their demographics and responded to items concerning their 14 reactions to the harassment. Before the questionnaires were distributed, three...? was never included in the study. They were then asked to complete a questionnaire in which they provided their demographics and responded to items concerning their 14 reactions to the harassment. Before the questionnaires were distributed, three...

Benavides Espinoza, Claudia

2010-07-14

345

Kinetics of actinide complexation reactions  

SciTech Connect

Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions.

Nash, K.L.; Sullivan, J.C.

1997-09-01

346

Asymmetric synthesis of chiral dihydrothiopyrans via an organocatalytic enantioselective formal thio [3 + 3] cycloaddition reaction with binucleophilic bisketone thioethers.  

PubMed

An unprecedented organocatalytic highly enantioselective approach to a 3,4-dihydro-2H-thiopyran scaffold with two contiguous stereogenic centers has been implemented through a formal thio [3 + 3] cycloaddition process involving a Michael-aldol condensation cascade sequence. Notably, a new class of binucleophilic bisketone thioethers is designed for the process. Furthermore, the fine-tuning of their reactivity enables the cascade process to proceed with highly regioselectively. PMID:24152030

Wang, Shengzheng; Zhang, Yongqiang; Dong, Guoqiang; Wu, Shanchao; Zhu, Shiping; Miao, Zhenyuan; Yao, Jianzhong; Li, Hao; Li, Jian; Zhang, Wannian; Sheng, Chunquan; Wang, Wei

2013-11-01

347

Streamlined catalytic asymmetric synthesis of atorvastatin.  

PubMed

An efficient enantioselective synthetic route to atorvastatin was developed based on a direct catalytic asymmetric aldol reaction. The expensive chiral ligand used in the initial aldol reaction was readily recovered (91 %) and reused. Implementation of an oxy-Michael reaction for the construction of the syn-1,3-diol unit eliminated several redundant steps, allowing for rapid access to the common intermediate in six steps. PMID:23436316

Kawato, Yuji; Chaudhary, Sandeep; Kumagai, Naoya; Shibasaki, Masakatsu

2013-03-18

348

Silyl-substituted 1,3-butadienes for Diels-Alder reaction, ene reaction and allylation reaction.  

PubMed

Silyl-substituted 1,3-butadienes are useful building blocks and are readily applied in several types of reactions such as Diels-Alder reaction, ene reaction and allylation. They can also participate in different tandem reactions such as Diels-Alder/allylation, ene/allylation, ene/allylation/Diels-Alder reaction, ene/allylation/ene reaction and ene/allylation/Diels-Alder/allylation reaction. This feature article reviews the synthesis of silyl-substituted 1,3-butadienes, and their applications in the reaction types mentioned above, involving a tandem Diels-Alder/ene/allylation process. This article also introduces some reactions of alkenylsilanes and allylsilanes for comparison and discussion about the tandem reaction. The tandem reactions described in this article are a powerful tool to construct complicated multicyclic compounds with high selectivity and high efficiency. PMID:21336391

Zhao, Fei; Zhang, Shaoguang; Xi, Zhenfeng

2011-04-21

349

Chemical ReactionsChemical Reactions between the Componentsbetween the Components  

E-print Network

products, one the result of an SN2 reaction, the other an E2 reaction. P O O- OH OP O HO OP O O HO + N(C6H.Abundance 700600500400300200100 m/z negative MS 2 610 m/z 256.82 E2 340.83 SN2 609.93 Triphosphate DianionTriphosphate Dianion SN2: Hexyl triphosphate (m/z 341) is produced E2: Triphosphate anion (m/z 257) is produced P O O- OH

Beauchamp, Jack

350

Combustion kinetics and reaction pathways  

SciTech Connect

This project is focused on the fundamental chemistry of combustion. The overall objectives are to determine rate constants for elementary reactions and to elucidate the pathways of multichannel reactions. A multitechnique approach that features three independent experiments provides unique capabilities in performing reliable kinetic measurements over an exceptionally wide range in temperature, 300 to 2500 K. Recent kinetic work has focused on experimental studies and theoretical calculations of the methane dissociation system (CH{sub 4} + Ar {yields} CH{sub 3} + H + Ar and H + CH{sub 4} {yields} CH{sub 3} + H{sub 2}). Additionally, a discharge flow-photoionization mass spectrometer (DF-PIMS) experiment is used to determine branching fractions for multichannel reactions and to measure ionization thresholds of free radicals. Thus, these photoionization experiments generate data that are relevant to both reaction pathways studies (reaction dynamics) and fundamental thermochemical research. Two distinct advantages of performing PIMS with high intensity, tunable vacuum ultraviolet light at the National Synchrotron Light Source are high detection sensitivity and exceptional selectivity in monitoring radical species.

Klemm, R.B.; Sutherland, J.W. [Brookhaven National Laboratory, Upton, NY (United States)

1993-12-01

351

Reaction Exposed: The Big Chill!  

NSDL National Science Digital Library

Students investigate the endothermic reaction involving citric acid, sodium bicarbonate and water to produce carbon dioxide, water and sodium citrate. In the presence of water [H2O], citric acid [C6H8O7] and sodium bicarbonate [NaHCO3] (also known as baking soda) react to form sodium citrate [Na3C6H5O7], water [H2O], and carbon dioxide [CO2]. Students test a stoichiometric version of the reaction followed by testing various perturbations on the stoichiometric version in which each reactant (citric acid, sodium bicarbonate, and water) is strategically doubled or halved to create a matrix of the effect on the reaction. By analyzing the test matrix data, they determine the optimum quantities to use in their own production companies to minimize material cost and maximize CO2 production. They use their test data to "scale-up" the system from a quart-sized ziplock bag to a reaction tank equal to the volume of their classroom. They collect data on reaction temperature and CO2 production.

CREAM GK-12 Program, Engineering Education Research Center, College of Engineering and Architecture,

352

Nonlocality in deuteron stripping reactions.  

PubMed

We propose a new method for the analysis of deuteron stripping reactions, A(d,p)B, in which the nonlocality of nucleon-nucleus interactions and three-body degrees of freedom are accounted for in a consistent way. The model deals with equivalent local nucleon potentials taken at an energy shifted by ?40??MeV from the "E(d)/2" value frequently used in the analysis of experimental data, where E(d) is the incident deuteron energy. The "E(d)/2" rule lies at the heart of all three-body analyses of (d, p) reactions performed so far with the aim of obtaining nuclear structure properties such as spectroscopic factors and asymptotic normalization coefficients that are crucial for our understanding of nuclear shell evolution in neutron- and proton-rich regions of the nuclear periodic table and for predicting the cross sections of stellar reactions. The large predicted shift arises from the large relative kinetic energy of the neutron and proton in the incident deuteron in those components of the n+p+A wave function that dominate the (d, p) reaction amplitude. The large shift reduces the effective d-A potentials and leads to a change in predicted (d, p) cross sections, thus affecting the interpretation of these reactions in terms of nuclear structure. PMID:25166525

Timofeyuk, N K; Johnson, R C

2013-03-15

353

Programmable reaction-diffusion fronts  

E-print Network

Morphogenesis is central to biology but remains largely unexplored in chemistry. Reaction-diffusion (RD) mechanisms are, however, essential to understand how shape emerges in the living world. While numerical methods confirm the incredible potential of RD mechanisms to generate patterns, their experimental implementation, despite great efforts, has yet to surpass the paradigm of stationary Turing patterns achieved 25 years ago. The principal reason for our difficulty to synthesize arbitrary concentration patterns from scratch is the lack of fully programmable reaction-diffusion systems. To solve this problem we introduce here a DNA-based system where kinetics and diffusion can be individually tuned. We demonstrate the capability to precisely control reaction-diffusion properties with an autocatalytic network that propagates in a one-dimensional reactor with uniform velocity, typically 100 {\\mu}m min-1. The diffusion coefficient of the propagating species can be reduced up to a factor 2.7 using a species-speci...

Zadorin, Anton S; Galas, Jean-Christophe; Estevez-Torres, André

2014-01-01

354

Ionic reactions of atmospheric importance  

NASA Astrophysics Data System (ADS)

A variable-temperature flowing afterglow/Langmuir probe (VT-FALP) apparatus has been used to study several electron-ion dissociative recombination reactions and several electron attachment reactions. Thus the variation with temperature of the respective dissociative recombination coefficients, alpha and electron attachment coefficients, beta have been determined. The recombination studies have included the species O2+, NO+, NH4+, H3, HC0+, N2H+ and CH5+, and the attachment studies have included the species CC14, CC13F, CC12F2, CHC13, C12, SF6, C-C7F14, CH3Br, CF3Br, CH2Br2 and CH3I. Some ion molecule reactions have also been studied as a function of temperature and of ion-molecule center-of mass energy using a variable-temperature selective ion flow drift tube (VT-SIFDT).

Smith, D.; Adams, N.

1984-08-01

355

Understanding the novolak synthesis reaction  

NASA Astrophysics Data System (ADS)

We describe new tools for the characterization of novolac resins, for the understanding of the novolac synthesis reaction, and for the prediction of resin structures. These tools have been used to optimize the performance of photoresists for microlithography. The current state-of- the-art describes novolac copolymer compositions as the ratio of monomers charged in the reaction, even though it is well known that the actual product composition is quite different. Quantitative 13C NMR spectroscopy provides a direct method for accurately determining copolymer composition by integrating methyl carbon resonances. By using this method to analyze the results of competition reactions, relative monomer and site reactivities for phenol and the cresols with formaldehyde have been determined. These observed reactivities have been used in a simple, kinetic model to accurately predict copolymer composition, branch density, and molecular weight.

Bogan, Leonard E., Jr.

1993-09-01

356

Unraveling reaction pathways and specifying reaction kinetics for complex systems.  

PubMed

Many natural and industrial processes involve a complex set of competing reactions that include several different species. Detailed kinetic modeling of such systems can shed light on the important pathways involved in various transformations and therefore can be used to optimize the process conditions for the desired product composition and properties. This review focuses on elucidating the various components involved in modeling the kinetics of pyrolysis and oxidation of polymers. The elementary free radical steps that constitute the chain reaction mechanism of gas-phase/nonpolar liquid-phase processes are outlined. Specification of the rate coefficients of the various reaction families, which is central to the theme of kinetics, is described. Construction of the reaction network on the basis of the types of end groups and reactive moieties in a polymer chain is discussed. Modeling frameworks based on the method of moments and kinetic Monte Carlo are evaluated using illustrations. Finally, the prospects and challenges in modeling biomass conversion are addressed. PMID:22468596

Vinu, R; Broadbelt, Linda J

2012-01-01

357

Reversal reaction to Hansen's disease.  

PubMed

A 25-year-old man with a history of mid-borderline (BB) Hansen's disease developing a reversal reaction after starting dapsone and rifampin therapy is presented. His clinical features included erythematous, edematous plaques and peripheral neuropathy. Reversal reactions are caused immunologically by enhanced cell-mediated (Th-1) immunity to Mycobacterium leprae, resulting in inflammation of infected tissues, such as skin and nerves. Acute neuritis can lead to permanent nerve damage and necessitate prompt treatment with prednisone and/or clofazamine. PMID:12847760

Jih, Ming H; Kimyai-Asadi, Arash; Levis, William R

2002-07-01

358

Reaction Dynamics and Multifragmentation in Fermi Energy Heavy Ion Reactions  

E-print Network

The reaction systems, 64Zn + 58Ni, 64Zn + 92Mo, 64Zn + 197Au, at 26A, 35A and 47A MeV, have been studied both in experiments with a 4$\\pi$ detector array, NIMROD, and with Antisymmetrized Molecular Dynamics model calculations employing effective interactions corresponding to soft and stiff equations of state (EOS). Direct experimental observables, such as multiplicity distributions, charge distributions, energy spectra and velocity spectra, have been compared in detail with those of the calculations and a reasonable agreement is obtained. The velocity distributions of $\\alpha$ particles and fragments with Z >= 3 show distinct differences in calculations with the soft EOS and the stiff EOS. The velocity distributions of $\\alpha$ particle and Intermediate Mass Fragments (IMF's) are best described by the stiff EOS. Neither of the above direct observables nor the strength of the elliptic flow are sensitive to changes in the in-medium nucleon-nucleon (NN) cross sections. A detailed analysis of the central collision events calculated with the stiff EOS revealed that multifragmentation with cold fragment emission is a common feature predicted for all reactions studied here. A possible multifragmentation scenario is presented; after the preequilibrium emission ceases in the composite system, cold light fragments are formed in a hotter gas of nucleons and stay cold until the composite system underdoes multifragmentation. For reaction with 197Au at 47A MeV a significant radial expansion takes place. For reactions with 58Ni and 92Mo at 47A MeV semi-transparency becomes prominent. The differing reaction dynamics drastically change the kinematic characteristics of emitted fragments. This scenario gives consistent explanations for many existing experimental results in the Fermi energy domain.

R. Wada; T. Keutgen; K. Hagel; Y. G. Ma; J. Wang; M. Murray; L. Qin; P. Smith; J. B. Natowitz; R. Alfarro; J. Cibor; M. Cinausero; Y. El Masri; D. Fabris; E. Fioretto; A. Keksis; M. Lunardon; A. Makeev; N. Marie; E. Martin; A. Martinez-Davalos; A. Menchaca-Rocha; G. Nebbia; G. Prete; V. Rizzi; A. Ruangma; D. V. Shetty; G. Souliotis; P. Staszel; M. Veselsky; G. Viesti; E. M. Winchester; S. J. Yennello; Z. Majka; A. Ono

2003-08-27

359

Annulation reactions of allenyl esters: an approach to bicyclic diones and medium-sized rings.  

PubMed

A flexible approach to construct sterically congested bicyclo-alkenedione frameworks is reported. Under the action of potassium carbonate, ?-sulphonyl cycloalkanones are added to functionalized allenyl esters, leading to a lactone intermediate that is subsequently reduced to initiate an intramolecular aldol cyclization to [3.2.1], [3.3.1], and [4.3.1] bicycles. Oxidation then affords bicyclic diones in good three-step yields. Under exceptionally mild conditions, these bicycles are converted to highly functionalized medium-sized rings through a Grob-type fragmentation. PMID:25184784

Bhat, Bilal A; Maki, Samantha L; St Germain, Elijah J; Maity, Pradip; Lepore, Salvatore D

2014-10-01

360

USING NPS CHROMATOGRAPHY TO MONITOR MESYLATION REACTIONS  

Microsoft Academic Search

Using nonporous silica (NPS) chromatography, mesylation reactions with unhindered and hindered amines were studied as proton scavengers. During reaction monitoring it is important to conduct sensitive and fast analyses. To optimally control the reaction quick feedback is necessary. The NPS proved to be highly suitable. When unhindered amines are used to remove the proton, the SN2 mesylate reaction was observed

Charles J. Shaw; Helen Chao; James E. Hanson

2001-01-01

361

An Iodine Fluorescence Quenching Clock Reaction  

Microsoft Academic Search

A fluorescent clock reaction is described that is based on the principles of the Landolt iodine reaction but uses the potent fluorescence quenching properties of triiodide to abruptly extinguish the ultraviolet fluorescence of optical brighteners present in liquid laundry detergents. The reaction uses easily obtained household products. One variation illustrates the sequential steps and mechanisms of the reaction; other variations

Richard B. Weinberg

2007-01-01

362

Laser-initiated chemical chain reactions  

Microsoft Academic Search

A detailed kinetic and experimental analysis is presented for chemical chain reaction processes initiated by well-controlled, low power laser pulses. Realtime evolution of the chain reaction is followed by direct detection of infrared chemiluminescence from vibrationally excited HCl product molecules produced by one of the propagation reactions in the chain. By appropriate choice of conditions, the chain reactions may be

David J. Nesbitt; Stephen R. Leone

1980-01-01

363

Adverse Drug Reactions in Dental Practice  

PubMed Central

Adverse reactions may occur with any of the medications prescribed or administered in dental practice. Most of these reactions are somewhat predictable based on the pharmacodynamic properties of the drug. Others, such as allergic and pseudoallergic reactions, are less common and unrelated to normal drug action. This article will review the most common adverse reactions that are unrelated to drug allergy. PMID:24697823

Becker, Daniel E.

2014-01-01

364

Temperature dependence of phytochrome dark reactions  

Microsoft Academic Search

The dark reversion and the destruction reaction of the phytochrome of squash (Cucurbita pepo L.) cotyledons show different temperature behaviour in the temperature range 15–35°. The Arrhenius activation energy of the destruction reaction is temperature independent whereas that of the reversion reaction shows a jump at 20°. This indicates an interaction of phytochrome molecules with membranes. A reaction scheme is

E. Schäfer; W. Schmidt

1974-01-01

365

Cold fusion reaction products and their measurement  

Microsoft Academic Search

The major reaction products that have been possibly associated with cold fusion reactions are neutrons, protons, tritium, He-3, He-4, internal conversion electrons, and gamma radiation. The branching ratios and relative reaction rates for these products are examined for consistency with cold fusion experiments. Both theoretical calculations and experimental data are examined and presented. The He-4 plus internal conversion reaction has

Vern C. Rogers; Gary M. Sandquist

1990-01-01

366

Reaction of Organoboranes with iodine  

Microsoft Academic Search

The reaction of organoboranes with iodine is an efficient method for synthesizing alkyl iodides. Unfortunately the earlier methods employed sodium methoxide as a reactant which is a potential problem when theorganoborane contians reactive functional groups. We recently reported that organoboranes readily react with iodine monochloride in the presence of sodium acetate, a mild base..

George W. Kabalka; K. A. R. Sastry; K. Usha Sastry

1982-01-01

367

Hydrothermal reactions under mechanochemical treating  

Microsoft Academic Search

The mechanochemical treating of solids containing some amount of free or chemically bound water in high-energetic activators enable the hydrothermal processes (as in autoclaves). Estimations of the optimal value of the water content were carried out. The data on the investigation of the mechanochemical reaction between calcium hydroxide and hydrated silica are presented as the experimental confirmation of the hydrothermal

N. V. Kosova; A. Kh. Khabibullin; V. V. Boldyrev

1997-01-01

368

Anaphylactic reactions to tolperisone (Mydocalm).  

PubMed

Four patients with anaphylaxis attributed to the intake of the centrally acting muscle relaxant tolperisone hydrochloride (Mydocalm) were observed at the Emergency Department of the Geneva University Hospital between November 2001 and March 2003. All patients were middle-aged women who took tolperisone for chronic muscular pain. All reactions occurred within an hour after oral intake of this drug frequently prescribed in Switzerland. The severity of anaphylaxis ranged from urticarial reactions to shock with arterial hypotension. Prick-to-prick skin testing performed in one patient with a tablet of tolperisone diluted in water was negative. Its globally restricted commercialisation may explain the lack of reports on such adverse effects in the MedLine database. Anaphylactic reactions to this drug, however, are mentioned in other sources such as the Swiss Drug Compendium and the WHO drug reaction database. Together, these findings suggest that anaphylaxis to tolperisone is not uncommon and should be known to physicians in countries where this drug is available. PMID:12947534

Ribi, Camillo; Vermeulen, Christophe; Hauser, Conrad

2003-06-28

369

Insect Bite Reactions: An Update  

Microsoft Academic Search

Contact with insects may induce cutaneous or systemic reactions, ranging from little more than annoying to life threatening. The diagnosis depends on maintaining a high index of suspicion and being familiar with the insect fauna of the patient’s environment and area of travel.

Adam S. Stibich; Paul A. Carbonaro; Robert A. Schwartz

2001-01-01

370

Alief in Action (and Reaction)  

Microsoft Academic Search

I introduce and argue for the importance of a cognitive state that I call alief. An alief is, to a reasonable approximation, an innate or habitual propensity to respond to an apparent stimulus in a particular way. Recognizing the role that alief plays in our cognitive repertoire provides a framework for understanding reactions that are governed by non- conscious or

TAMAR SZABÓ GENDLER

2008-01-01

371

Exotic Food Allergy: Anaphylactic Reaction  

Microsoft Academic Search

? Abstract There are very few reports on allergic reactions to lychee fruit in the literature. We describe the case of a 26-year-old man who developed pruritus, generalized urticaria, and severe angioedema of his lips and tongue with dyspnea within 15 minutes after lychee fruit intake. Although we found no lychee-specifi c immunoglobulin E antibodies, a basophil activation test (BAT)

T Schaefer; A Kapp; B Wedi

372

ORGANIC REACTIONS, INC. PREVIOUS LECTURERS  

E-print Network

it from other review vehicles include exhaustive literature surveys, complete compilation of extant. It is remarkable that Adams' legacy of interest in organic chemistry, in organic chemists, and in students still motivates those who carry this important resource forward. Scott E. Denmark Organic Reactions, Inc. Previous

Charette, André

373

Interfacial Reaction Studies Using ONIOM  

NASA Technical Reports Server (NTRS)

In this report, we focus on the calculations of the energetics and chemical kinetics of heterogeneous reactions for Organometallic vapor phase epitaxy (OMVPE). The work described in this report builds upon our own previous thermochemical and chemical kinetics studies. The first of these articles refers to the prediction of thermochemical properties, and the latter one deals with the prediction of rate constants for gaseous homolytic dissociation reactions. The calculations of this investigation are at the microscopic level. The systems chosen consisted of a gallium nitride (GaN) substrate, and molecular nitrogen (N2) and ammonia (NH3) as adsorbants. The energetics for the adsorption and the adsorbant dissociation processes were estimated, and reaction rate constants for the dissociation reactions of free and adsorbed molecules were predicted. The energetics for substrate decomposition was also computed. The ONIOM method, implemented in the Gaussian98 program, was used to perform the calculations. This approach has been selected since it allows dividing the system into two layers that can be treated at different levels of accuracy. The atoms of the substrate were modeled using molecular mechanics6 with universal force fields, whereas the adsorbed molecules were approximated using quantum mechanics, based on density functional theory methods with B3LYP functionals and 6-311G(d,p) basis sets. Calculations for the substrate were performed in slabs of several unit cells in each direction. The N2 and NH3 adsorbates were attached to a central location at the Ga-lined surface.

Cardelino, Beatriz H.

2003-01-01

374

Photosynthesis-The Light Reactions  

Microsoft Academic Search

During the past three or four years there has been a substantial advance in our knowledge of the light reactions in photosynthesis. This comes at a time of heightened interest in sunlight as a source of energy for our daily needs. The exploration of potential practical applications in this area will be helped by identifying the common features of the

K. Sauer

1979-01-01

375

Homeostasis in Chemical Reaction Pathways  

E-print Network

We consider stochastic models of chemical reaction networks with time dependent input rates and several types of molecules. We prove that, in despite of strong time dependence of input rates, there is a kind of homeostasis phenomenon: far away from input nodes the mean numbers of molecules of each type become approximately constant (do not depend on time).

V. A. Malyshev; A. D. Manita; A. A. Zamyatin

2011-12-25

376

Homeostasis in Chemical Reaction Pathways  

E-print Network

We consider stochastic models of chemical reaction networks with time dependent input rates and several types of molecules. We prove that, in despite of strong time dependence of input rates, there is a kind of homeostasis phenomenon: far away from input nodes the mean numbers of molecules of each type become approximately constant (do not depend on time).

Malyshev, V A; Zamyatin, A A

2011-01-01

377

Matter and Energy in Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the final of four Science Objects in the Chemical Reactions SciPack. It explains how

National Science Teachers Association (NSTA)

1900-01-01

378

The Pitfalls of Precipitation Reactions.  

ERIC Educational Resources Information Center

Described are some of the difficulties presented in these reactions by competing equilibria that are usually ignored. Situations involving acid-base equilibria, solubility product calculations, the use of ammonia as a complexing agent, and semiquantitative comparisons of solubility product values are discussed. (CW)

Slade, Peter W.; Rayner-Canham, Geoffrey W.

1990-01-01

379

Reactions of cells to topography  

Microsoft Academic Search

Though contact guidance has been known since the very early days of cell culture very little quantitative examination of the reaction of cells to topography has been made. Exceptions to this subjective approach are given prominence below. Yet if we are to understand how cells react and if we are to be able to design ideal substrata for particular cells

Adam S. G. Curtis; Chris D. W. Wilkinson

1998-01-01

380

FOREIGN BODY REACTION TO BIOMATERIALS  

PubMed Central

The foreign body reaction composed of macrophages and foreign body giant cells is the end-stage response of the inflammatory and wound healing responses following implantation of a medical device, prosthesis, or biomaterial. A brief, focused overview of events leading to the foreign body reaction is presented. The major focus of this review is on factors that modulate the interaction of macrophages and foreign body giant cells on synthetic surfaces where the chemical, physical, and morphological characteristics of the synthetic surface are considered to play a role in modulating cellular events. These events in the foreign body reaction include protein adsorption, monocyte/macrophage adhesion, macrophage fusion to form foreign body giant cells, consequences of the foreign body response on biomaterials, and cross-talk between macrophages/foreign body giant cells and inflammatory/wound healing cells. Biomaterial surface properties play an important role in modulating the foreign body reaction in the first two to four weeks following implantation of a medical device, even though the foreign body reaction at the tissue/material interface is present for the in vivo lifetime of the medical device. An understanding of the foreign body reaction is important as the foreign body reaction may impact the biocompatibility (safety) of the medical device, prosthesis, or implanted biomaterial and may significantly impact short- and long-term tissue responses with tissue-engineered constructs containing proteins, cells, and other biological components for use in tissue engineering and regenerative medicine. Our perspective has been on the inflammatory and wound healing response to implanted materials, devices, and tissue-engineered constructs. The incorporation of biological components of allogeneic or xenogeneic origin as well as stem cells into tissue-engineered or regenerative approaches opens up a myriad of other challenges. An in depth understanding of how the immune system interacts with these cells and how biomaterials or tissue-engineered constructs influences these interactions may prove pivotal to the safety, biocompatibility, and function of the device or system under consideration. PMID:18162407

Anderson, James M.; Rodriguez, Analiz; Chang, David T.

2008-01-01

381

Astronomy with Radioactivities: Chapter 9, Nuclear Reactions  

E-print Network

Nuclear reaction rates determine the abundances of isotopes in stellar burning processes. A multitude of reactions determine the reaction flow pattern which is described in terms of reaction network simulations. The reaction rates are determined by laboratory experiments supplemented by nuclear reaction and structure theory. We will discuss the experimental approach as well as the theoretical tools for obtaining the stellar reaction rates. A detailed analysis of a reaction is only possible for a few selected cases which will be highlighted in this section. The bulk of nuclear reaction processes is however described in terms of a statistical model approach, which relies on global nuclear structure and reaction parameters such as level density and mass and barrier penetration, respectively. We will discuss a variety of experimental facilities and techniques used in the field, this includes low energy stable beam experiments, measurements at radioactive beam accelerators, and neutron beam facilities.

M. Wiescher; T. Rauscher

2010-11-01

382

Rational design of asymmetric organocatalysts––increased reactivity and solvent scope with a tetrazolic acid  

Microsoft Academic Search

Replacement of the carboxylic acid functionality in the widely used organocatalyst proline with a tetrazolic acid leads to a catalyst with increased reactivity and solvent scope, as demonstrated in the direct catalytic asymmetric aldol reaction.

Antti Hartikka; Per I Arvidsson

2004-01-01

383

Reactions of arsine with hemoglobin  

SciTech Connect

The mechanism of arsine (AsH{sub 3}) induced hemolysis was studied in vitro using isolated red blood cells (RBCs) from the rat or dog. AsH{sub 3}-induced hemolysis of dog red blood cells was completely blocked by carbon monoxide (CO) preincubation and was reduced by pure oxygen (O{sub 2}) compared to incubations in air. Since CO and O{sub 2} bind to heme and also reduced hemolysis, these results suggested a reaction between AsH{sub 3} and hemoglobin in the hemeligand binding pocket or with the heme iron. Further, sodium nitrite induction of methemoglobin (metHb) to 85% and 34% of total Hb in otherwise intact RBCs resulted in 56% and 16% decreases in hemolysis, respectively, after incubation for 4 h. This provided additional evidence for the involvement of hemoglobin in the AsH{sub 3}-induced hemolysis mechanism. Reactions between AsH{sub 3} and hemoglobin were studied in solutions of purified dog hemoglobin. Spectrophotometric studies of the reaction of AsH{sub 3} with various purified hemoglobin species revealed that AsH{sub 3} reacted with HbO{sub 2} to produce metHb and, eventually, degraded Hb characterized by gross precipitation of the protein. AsH{sub 3} did not alter the spectrum of deoxyHb and did not cause degradation of metHb in oxygen, but bound to and reduced metHb in the absence of oxygen. These data indicate that a reaction of AsH{sub 3} with oxygenated hemoglobin, HbO{sub 2}, may lead to hemolysis, but there are reactions between AsH{sub 3} and metHb that may not be directly involved in the hemolytic process. 17 refs., 6 figs.

Hatlelid, K.M.; Brailsford, C.; Carter, D.E. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States)

1996-02-09

384

Carbene reactions produced by recoil excitation methods  

E-print Network

and CTCT. Reactions of CTF with 1, 3-butadiene, aliene, and cyclohexene were studied. Also, products of the Diels-Alder retrogression reaction of cyclohexene were observed when high energy tritium atoms reacted with cyclohexene. A qualitative discussion.... Experimental III. 'Reaction of Tritium-Labeled Monofluorocarbene with Higher Olefins 31 IV. Reactions of F -La'baled Monofluorocarbene V. Formation of Monochlorocarbene-Clgg VI. Formation of Monobromoc"rbene-Br VII. Diels-Alder Retrogression Reaction...

Lowery, Kirby

2012-06-07

385

Lowering barriers in surface reactions through concerted reaction mechanisms Sung Sakong,1  

E-print Network

simultaneously, for example in the so-called SN 2 reactions [3]. Yet, there are usually severe symmetryLowering barriers in surface reactions through concerted reaction mechanisms Sung Sakong,1 technologically important chemical reaction typically involves a number of different elemen- tary reaction steps

Ulm, Universität

386

Late reaction to ustekinumab infusion.  

PubMed

Psoriasis is a chronic inflammatory disease that directly affects the quality of life. Biologics are prescribed for patients unresponsive to conventional treatments and with severe forms of the disease. Ustekinumab is a fully human monoclonal antibody against the p40 subunit of interleukins 12/23 that is being used with satisfactory responses, achieving an improvement in the baseline Psoriasis Area and Severity Index of approximately 75% after 12 weeks of treatment. It has few side effects, including grater susceptibility to infections and development of reactions to the drug. Our report discusses a case of a cutaneous reaction to the use of ustekinumab in a 27 year-old male patient after the third dose of the medication. No similar case has been reported in the literature. PMID:25386321

Morais, Marina Resener; Meneghello, Luana Pizarro; de Oliveira, Carina Flores; Carvalho, André Vicente Esteves

2013-07-29

387

Reaction mechanisms of pair transfer  

E-print Network

The mechanisms of nuclear transfer reactions are described for the transfer of two nucleons from one nucleus to another. Two-nucleon overlap functions are defined in various coordinate systems, and their transformation coefficients given between coordinate systems. Post and prior couplings are defined for sequential transfer mechanisms, and it is demonstrated that the combination of `prior-post' couplings avoids non-orthogonality terms, but does not avoid couplings that do not have good zero-range approximations. The simultaneous and sequential mechanisms are demonstrated for the $^{124}$Sn(p,t)$^{122}$Sn reaction at 25 MeV using shell-model overlap functions. The interference between the various simultaneous and sequential amplitudes is shown.

Ian J. Thompson

2012-04-13

388

Investigating Reaction-Driven Cracking  

NASA Astrophysics Data System (ADS)

Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required for constant volume replacement. Natural examples have fracture energy densities due to strain energy density of 100's of MPa [2]. Despite theory and observation, until now lab experiments on peridotite hydration and carbonation have not produced reaction-driven cracking. Slow kinetics and limited reactive surface area in low porosity samples may be the cause. Also, maximum stress may be limited by 'disjoining pressure', above which nano-films along grain boundaries collapse, and crystal growth essentially ceases [7]. To address these issues, we've begun experiments on analog materials with fast reaction rates, e.g., CaO + H2O = Ca(OH)2, to efficiently investigate the role of confining pressure and other factors on reaction-driven fracture events. Intriguingly, commercially available 'demolition mortar', largely CaO, produces stresses of 70 MPa or more around 1 inch bore holes at room T and P [8], even though there is a free surface at the top of the borehole, and hydration in a 'closed' system creates ~ 40% air-filled pore space. [1] Jamtveit et al EPSL 08 [2] Kelemen & Hirth EPSL 12 [3] Kelemen et al AREPS 11 [4] Aharonov et al JGR 98 [5] Fletcher & Merino GCA 01 [6] Macdonald & Fyfe T'phys 85 [7] Espinosa-Marzal & Scherer GSL Special Papers 10 [8] Laefer et al Mag Concrete Res 10

Kelemen, P. B.; Hirth, G.; Savage, H. M.

2013-12-01

389

Nuclear Reactions from Lattice QCD  

E-print Network

One of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculations of some of the low- energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path ...

Briceño, Raúl A; Luu, Thomas C

2014-01-01

390

Electroweak reactions with light nuclei  

E-print Network

The investigation of light nuclei with ab-initio methods provides an optimal setting to probe our knowledge on nuclear forces, because the few-nucleon problem can be solved accurately. Nucleons interact not only in pairs but also via many-body forces. Theoretical efforts need to be taken towards the identification of nuclear observables sensitive to the less known many-nucleon forces. Electromagnetic reactions can potentially provide useful information on this. We present results on photo-absorption and electron scattering off light nuclei, emphasizing the role of three-body forces and the comparison with experimental data. On the other hand, reactions induced by weak probes, like neutrino interactions with nucleonic matter, are relevant to astrophysics and can be calculated with few-body techniques. In this case, since often no experiment is possible, ab-initio predictions provide valuable input for astrophysical simulations.

Sonia Bacca

2010-06-01

391

Electromagnetic reactions on light nuclei  

E-print Network

Electromagnetic reactions on light nuclei are fundamental to advance our understanding of nuclear structure and dynamics. The perturbative nature of the electromagnetic probes allows to clearly connect measured cross sections with the calculated structure properties of nuclear targets. We present an overview on recent theoretical ab-initio calculations of electron-scattering and photonuclear reactions involving light nuclei. We encompass both the conventional approach and the novel theoretical framework provided by chiral effective field theories. Because both strong and electromagnetic interactions are involved in the processes under study, comparison with available experimental data provides stringent constraints on both many-body nuclear Hamiltonians and electromagnetic currents. We discuss what we have learned from studies on electromagnetic observables of light nuclei, starting from the deuteron and reaching up to nuclear systems with mass number A=16.

Bacca, Sonia

2014-01-01

392

Electrochemical promotion of catalytic reactions  

NASA Astrophysics Data System (ADS)

The electrochemical promotion of heterogeneously catalyzed reactions (EPOC) became feasible through the use of porous metal electrodes interfaced to a solid electrolyte. With the O 2- conducting yttrium stabilized zirconia (YSZ), the Na + conducting ??-Al 2O 3 (?-alumina), and several other types of solid electrolytes the EPOC effect has been demonstrated for about 100 reaction systems in studies conducted mainly in the mbar range. Surface science investigations showed that the physical basis for the EPOC effect lies in the electrochemically induced spillover of oxygen and alkali metal, respectively, onto the surface of the metal electrodes. For the catalytic promotion effect general concepts and mechanistic schemes were proposed but these concepts and schemes are largely speculative. Applying surface analytical tools to EPOC systems the proposed mechanistic schemes can be verified or invalidated. This report summarizes the progress which has been achieved in the mechanistic understanding of the EPOC effect.

Imbihl, R.

2010-05-01

393

Modelling reaction kinetics inside cells  

PubMed Central

In the past decade, advances in molecular biology such as the development of non-invasive single molecule imaging techniques have given us a window into the intricate biochemical activities that occur inside cells. In this article we review four distinct theoretical and simulation frameworks: (1) non-spatial and deterministic, (2) spatial and deterministic, (3) non-spatial and stochastic and (4) spatial and stochastic. Each framework can be suited to modelling and interpreting intracellular reaction kinetics. By estimating the fundamental length scales, one can roughly determine which models are best suited for the particular reaction pathway under study. We discuss differences in prediction between the four modelling methodologies. In particular we show that taking into account noise and space does not simply add quantitative predictive accuracy but may also lead to qualitatively different physiological predictions, unaccounted for by classical deterministic models. PMID:18793122

Grima, Ramon; Schnell, Santiago

2009-01-01

394

Microfabricated electrochemiluminescence cell for chemical reaction detection  

DOEpatents

A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA); Hsueh, Yun-Tai (Davis, CA); Smith, Rosemary L. (Davis, CA)

2003-01-01

395

SPIRULINA PLATENSIS INHIBITS ANAPHYLACTIC REACTION  

Microsoft Academic Search

We investigated the effects of the powders of Spirulina platensis (SPP) on anaphylactic reactions. SPP inhibited compound 4880-induced anaphylactic shock 100% with doses of 0.5, and 1.0 mg\\/g body weight (BW). SPP significantly inhibited serum histamine levels induced by compound 4880 in rats. SPP (0.5 mg\\/g BW) inhibited to 68.7% passive cutaneous anaphylaxis activated by antidinitrophenyl (DNP) IgE. SPP dose-dependently

Huh-Nam Yang; Eun-Hee Lee; Hyung-Min Kim

1997-01-01

396

Strain-induced chemical reactions  

SciTech Connect

The uniaxial displacements at leading edges of detonation fronts in solids create large shear-strains. These bend the covalent bonds, and cause piezoelectric effects, thereby closing the HOMO-LUMO energy gaps, and leading to ultra-fast athermal chemical reactions. Specific examples are discussed: ammonium, azide, and nitrate ions; and PETN. It is shown that their properties are consistent with the proposed mechanism. [copyright]American Institute of Physics

Gilman, J.J. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1994-07-10

397

Chemical Reactions Among Indoor Pollutants  

Microsoft Academic Search

\\u000a Chemistry takes place all around us, regulating the intensity and nature of our exposure to pollutants in water, air and soil.\\u000a In indoor environments, chemistry can significantly alter the composition of the air we breathe. Transformations reduce our\\u000a exposure to reactants and increase our exposure to products. If this reaction takes place on or in a surface, the relative\\u000a exposure

Glenn Morrison

398

Management of cutaneous drug reactions  

Microsoft Academic Search

Drugs are potent chemicals that often have effects in the body beyond the desired action. These effects may range from mild\\u000a and expected side effects to dramatic and lifethreatening anaphylaxis. Adverse drug reactions account for between 2% and 6%\\u000a of hospital admissions and may prevent administration of otherwise effective therapeutic agents. Cutaneous and mucocutaneous\\u000a eruptions are the most common adverse

K. S. Babu; Geeta Belgi

2002-01-01

399

Bystanders’ Reactions to Sexual Harassment  

Microsoft Academic Search

The purpose of this investigation was to examine bystanders’ reactions to observing sexual harassment. Undergraduate students\\u000a (n?=?107 and n?=?122, respectively) in the Southwest U.S. participated in two experiments in which they read about cases of sexual harassment\\u000a and responded with their preferred punishment for the offenses. Findings from both studies demonstrate the importance of (a)\\u000a a proactive organizational culture, (b)

Claudia Benavides-Espinoza; George B. Cunningham

2010-01-01

400

Variable expansion ratio reaction engine  

SciTech Connect

A variable expansion ratio reaction rocket engine for producing a mainstream of hot combustion gases is described comprising: a reaction chamber including a thrust nozzle portion formed by converging and diverging wall portions in which the diverging portion terminates in a gas discharge and through which the combustion gases pass; a nozzle throat section at the juncture of the convergent-divergent wall portions; rows of circumferentially and axially spaced injection ports formed within the wall portions and communicating therethrough and into the reaction chamber; fluid conduit means in communication with the injection ports; at least one high pressure pump in communication with the fluid conduit means; a fluid containing storage tank including a conduit in communication with the high pressure pump; and means for selectively controlling a flow of fluid out of the tank, through the pump and to the fluid conduit means and the injection ports for controlling a cross-sectional area of the mainstream combustion gases passing through the thrust nozzle.

Wagner, W.R.

1987-11-24

401

Reactions of alkenes on lanthana  

SciTech Connect

Reactions of ethene, propene, butenes, 2-methylpropene, cyclopentene, 2,3-dimethylbut-1-ene, and 3,3-dimethylbut-1-ene have been studied with hydrogen, and sometimes deuterium, on lanthana catalysts. Many alkene/lanthana systems show evidence of self-poisoning which is more marked with straight-chain hydrocarbons than with branched hydrocarbons and at higher temperatures; the catalysts are also highly sensitive to impurities. The temperature required to attain a fixed rate of hydrogenation (10/sup 16/ molecules s/sup -1/ m/sup -2/) varied from 220 K for ethene to over 373 K for the 2,3-dimethylbutenes. Fast hydrogenation without accompanying deuterium exchange was observed with alkenes which cannot form allylic species. The ability to form such species led to rapid isomerization of the butenes below 273 K and of 2-3-dimethylbut-1-ene at 373 K, and to exchange rates with deuterium which were comparable to (propene) or faster than (2-methylpropene) addition reactions at 380 K. Deuterium NMR spectroscopy was used for analysis of the products from the reactions with deuterium. Although the hydrogenation of 3,3-dimethylbut-1-ene occurred readily at 245 K, no isomerization was detected even at 510 K.

Bird, R.; Kemball, C.; Leach, H.F.

1987-05-01

402

Precolumn fluorescence tagging reagent for carboxylic acids in high-performance liquid chromatography: 4-substituted-7-aminoalkylamino-2,1,3-benzoxadiazoles.  

PubMed

Four new 2,1,3-benzoxadiazole amine reagents having different functional groups at the 4- and 7-positions, [4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ), 4-(N,N-dimethylaminosulphonyl)-7-N-piperazino-2,1,3-benzoxad iazole (DBD-PZ), 4-(N,N-dimethylaminosulphonyl)-7-N-cadaverino-2,1,3-benzoxad iazole (DBD-CD) and ammonium 7-N-piperazino-2,1,3-benzoxadiazole-4-sulphonate (SBD-PZ)] were synthesized as fluorogenic tagging reagents for carboxylic acids in high-performance liquid chromatography. The reagents, except SBD-PZ, reacted with carboxylic acid at room temperature in the presence of activation agents to produce fluorescent adducts. The maximum wavelengths of arachidic acid tagged with DBD-PZ, DBD-CD and NBD-PZ were 569 nm (excitation, 440 nm), 561 nm (excitation, 437 nm) and 541 nm (excitation, 470 nm), respectively. Among various activation agents tested [diethyl phosphorocyanidate (DEPC), diphenyl phosphoroyl azide (DPPA), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-pyridine, 2.2'-dipyridyl disulphide-triphenylphosphine (Mukaiyama A) and 2-chloro-1-methylpyridinium iodide-triethylamine (Mukaiyama B)], DEPC and Mukaiyama A were more effective than the others. When the piperazino reagents (DBD-PZ and NBD-PZ) were used as the tagging reagents, the derivatization reaction in the presence of Mukaiyama A was faster than that in the presence of DEPC. Although the reaction in the presence of Mukaiyama A was completed after 30 min, an unknown peak derived from the activation agent appeared on the chromatograms. The fluorescence peak intensities were compared in the presence of DEPC. The order of the fluorescence peak areas obtained after reaction for 6 h in the presence of DEPC was DBD-PZ greater than DBD-CD greater than NBD-PZ. Thirteen saturated free fatty acids (FFAs) derivatized with DBD-PZ (or DBD-CD) and DEPC (or Mukaiyama A) in acetonitrile were separated completely by linear gradient elution on a reversed-phase ODS column. Eight drugs (ibuprofen, indomethacin, dinoprost, prostaglandin E1, dehydrocholic acid, ursodesoxycholic acid, hydrocartisone succinate and prednisolone succinate) were also tagged with DBD-PZ in the presence of DEPC and separated by isocratic elution. The detection limits (signal-to-noise ratio = 3) of FFAs tagged with DBD-PZ were in the range 3.2-4.7 fmol, whereas those of drugs were in the range 3.9-14 fmol. PMID:1818086

Toyo'oka, T; Ishibashi, M; Takeda, Y; Nakashima, K; Akiyama, S; Uzu, S; Imai, K

1991-12-27

403

Microfabricated sleeve devices for chemical reactions  

DOEpatents

A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

Northrup, M. Allen (Berkeley, CA)

2003-01-01

404

ChemTeacher: Single Replacement Reactions  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Single Replacement Reactions page includes resources for teaching students about identifying and predicting single replacement reactions.

2011-01-01

405

Heavy atom isotope effects on enzymatic reactions  

NASA Astrophysics Data System (ADS)

The theory of isotope effects, which has proved to be extremely useful in providing geometrical details of transition states in a variety of chemical reactions, has recently found an application in studies of enzyme-catalyzed reactions. These reactions are multistep in nature with few steps being partially rate-limiting, thus interpretation of these isotope effects is more complex. The theoretical framework of heavy-atom isotope effects on enzymatic reactions is critically analyzed on the basis of recent results of: carbon kinetic isotope effects on carbonic anhydrase and catalytic antibodies; multiple carbon, deuterium isotope effects on reactions catalyzed by formate decarboxylase; oxygen isotope effects on binding processes in reactions catalyzed by pyruvate kinase; and equilibrium oxygen isotope effect on binding an inhibitor to lactate dehydrogenase. The advantages and disadvantages of reaction complexity in learning details of formal and molecular mechanisms are discussed in the examples of reactions catalyzed by phosphoenolpyruvate carboxylase, orotidine decarboxylase and glutamine synthetase.

Paneth, Piotr

1994-05-01

406

Reaction of steam with molybdenum is studied  

NASA Technical Reports Server (NTRS)

Comprehensive report studies the reaction of flowing steam with refractory metals /in particular molybdenum/, in the temperature range of 1100 degrees C. The reaction products are hydrogen gas and molybdenum oxide vapor.

Kilpatrick, M.; Lott, S.

1967-01-01

407

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

This activity is a lab investigation in which students observe the rate of generation of hydrogen gas from a reaction, and then modify the procedure to compare another variable affecting the rate of this reaction.

Derickson, Paula

408

Kinetics of reactions occurring during polyurethane synthesis  

NASA Astrophysics Data System (ADS)

We have used Fourier transform IR spectroscopy to study the kinetics of reaction between phenylisocyanate and oligomeric polyols at room temperature. We have determined the degree of conversion and the reaction rate constants for urethane formation.

Volkova, E. R.; Tereshatov, V. V.; Karmanov, V. I.

2010-11-01

409

Reaction of lithium peroxide with ethane  

Microsoft Academic Search

1.The reaction of lithium peroxide with ethane was studied in the temperature range 250–300°. The end reaction products are Li2CO3 and LiOH. The activation energy of the reaction is 27 kcal\\/mole.2.The thermal decomposition of Li2O2 goes in parallel with the oxidation reaction. The activation energy of the decomposition is 50 kcal\\/mole.

A. B. Tsentsiper; Z. I. Kuznetsova

1965-01-01

410

Fronts in anomalous diffusion-reaction systems.  

PubMed

A review of recent developments in the field of front dynamics in anomalous diffusion-reaction systems is presented. Both fronts between stable phases and those propagating into an unstable phase are considered. A number of models of anomalous diffusion with reaction are discussed, including models with Lévy flights, truncated Lévy flights, subdiffusion-limited reactions and models with intertwined subdiffusion and reaction operators. PMID:23185056

Volpert, V A; Nec, Y; Nepomnyashchy, A A

2013-01-13

411

Sonochemical reactions with mesoporous alumina  

Microsoft Academic Search

Herein, we report the sonochemical reactions with MSU-X mesoporous alumina (m-Al2O3) in aqueous solutions. Sonication (f=20kHz, I=30Wcm?2, Waq=0.67WmL?1, T=36–38°C, Ar) causes significant acceleration of m-Al2O3 dissolution in the pH range of 4–11. Moreover, power ultrasound has a dramatic effect on the textural properties and phase composition of m-Al2O3. Short-time sonication at pH = 4 leads to the formation of nanorods

Tony Chave; Sergei I. Nikitenko; Dominique Granier; Thomas Zemb

2009-01-01

412

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

Vecitis, Chad David

413

Photochemical reactions for commercial synthesis  

SciTech Connect

Photochemical reactions are conducted using floating polymer beads on the surface of a moving body of water. The polymer bead is impregnated with a reactant, floated on the water in direct sunlight so as to expose the reactant to solar radiation, collected at a downstream location, treated to remove product from the polymer, and then the bead can be recycled. The process can be used to collect and store solar energy in chemical form, or for conducting photochemical synthesis to produce useful chemical products.

Guillet, J. E.

1985-06-25

414

NTNU Java: Reaction time measurement  

NSDL National Science Digital Library

This Java applet measures braking distance and reaction time for stopping a car. Initial velocity is controlled by the user, and the coefficient of friction can be set from 0 to 1.5 to simulate varying road conditions. Once initial parameters are set, click "Start", then click "Brake" when you see the light turn yellow. Did you set a safe speed for the road conditions, or did you run the red light? Editor's Note: This simulation can be adapted for a wide range of age groups and course levels since its pre-set parameters include constant initial velocity.

Hwang, Fu-Kwun

2008-07-11

415

Rate constant for OH,,2 ... reaction  

E-print Network

. The title reaction is exothermic by 16.7 kcal/mol and its rate constant is decidedly nonRate constant for OH,,2 ...+O,,3 P...\\H,,2 S...+O2,,3 g - ... reaction on an improved ab initio and the rate constant for the title reaction was obtained using a J-shifting method. The calculated rate

Honvault, Pascal

416

Thermodynamic criteria of homogeneous reaction rates  

Microsoft Academic Search

A theoretical analysis of the restrictions imposed by macroscopic equilibrium thermodynamics on rate theories for homogeneous chemical reactions is described. Elementary gas-phase, constant pressure, exothermic reactions are used throughout this rate study. Reaction path, based on the experimental results from combustion processes in flames, is outlined. The sequence of the availability function is studied along this path, subject to the

F. L. Lansing

1975-01-01

417

Radicals and Hydroxy Radical Reactions in Troposphere  

E-print Network

with same molecule? { Which dominates? Depends on reaction rates-details of conditions and molecule. The art that OH can abstract in an exothermic reaction, this generally occurs #15; Bond strengths important: O HRadicals and Hydroxy Radical Reactions in Troposphere Examples of ground state radicals: 1. H atom

Schofield, Jeremy

418

New reaction tester accurate within 56 microseconds  

NASA Technical Reports Server (NTRS)

Testing device measures simple and disjunctive reaction time of human subject to light stimuli. Tester consists of reaction key, logic card, panel mounted neon indicators, and interconnecting wiring. Device is used for determining reaction times of patients undergoing postoperative neurological therapy.

Brown, H.

1972-01-01

419

Severe photosensitivity reaction induced by topical diclofenac  

PubMed Central

Albeit uncommon, photosensitivity reaction induced by diclofenac can be an unfortunate adverse reaction complicating its use as a topical analgesic. We here present a case of a patient who suffered such a reaction as a result of exposure to diclofenac, employed as a topical analgesic for low backache. The lesions healed with conservative management without extensive scarring or other complications. PMID:24014923

Akat, Pramod B.

2013-01-01

420

'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

421

A novel capillary polymerase chain reaction machine  

E-print Network

I built a novel prototype capillary polymerase chain reaction machine. The purpose was to perform a single reaction as fast as possible with a reaction volume - 100 nl. The PCR mix is in the form of a 1 /1 droplet that ...

Chiou, Jeffrey Tsungshuan

2001-01-01

422

?-Facial Selectivity of Diels-Alder Reactions  

NASA Astrophysics Data System (ADS)

Diels-Alder reaction is one of the most fundamental and important reactions for organic synthesis. In this chapter we review the studies of the ?-facial selectivity in the Diels-Alder reactions of the dienes having unsymmetrical ?-plane. The theories proposed as the origin of the selectivity are discussed.

Ishida, Masaru; Inagaki, Satoshi

423

Relay cross metathesis reactions of vinylphosphonates.  

PubMed

Dimethyl (?-substituted) vinylphosphonates do not readily undergo cross metathesis reactions with Grubbs catalyst and terminal alkenes. However, the corresponding mono- or diallyl vinylphosphonate esters undergo facile cross metathesis reactions. The improved reactivity is attributed to a relay step in the cross metathesis reaction mechanism. PMID:25246952

Malla, Raj K; Ridenour, Jeremy N; Spilling, Christopher D

2014-01-01

424

Good vibrations in enzyme-catalysed reactions  

Microsoft Academic Search

Fast motions (femtosecond to picosecond) and their potential involvement during enzyme-catalysed reactions have ignited considerable interest in recent years. Their influence on reaction chemistry has been inferred indirectly from studies of the anomalous temperature dependence of kinetic isotope effects and computational simulations. But can such motion reduce the width and height of energy barriers along the reaction coordinate, and contribute

Sam Hay; Nigel S. Scrutton

2012-01-01

425

Global reaction schemes for hydrocarbon combustion  

Microsoft Academic Search

Global reaction schemes for the combustion of alkane hydrocarbons up to butane in mixtures with air in premixed and diffusion flames have been derived using analysis of flame structures. The schemes include two competing fuel breakdown reactions, and equilibrium assumptions have been used to derive initial estimates of the forms of the rate expressions. The deduced four-step reaction mechanism is

W. P. Jones; R. P. Lindstedt

1988-01-01

426

Method of controlling fusion reaction rates  

DOEpatents

A method of controlling the reaction rates of the fuel atoms in a fusion reactor comprises the step of polarizing the nuclei of the fuel atoms in a particular direction relative to the plasma confining magnetic field. Fusion reaction rates can be increased or decreased, and the direction of emission of the reaction products can be controlled, depending on the choice of polarization direction.

Kulsrud, Russell M. (Princeton, NJ); Furth, Harold P. (Princeton, NJ); Valeo, Ernest J. (Princeton Junction, NJ); Goldhaber, Maurice (Bayport, NY)

1988-01-01

427

The Spinning World of Spacecraft Reaction Wheels  

NSDL National Science Digital Library

This is a activity about how reaction wheels affect spacecraft orientation (attitude). Learners will observe Newton's Third Law (action-reaction) in the changes caused by a reaction wheel acting upon a spacecraft suspended from a support wire and in the ensuing interfering forces from the wire support. The experiment includes an option for demonstration and for learner investigation. Notes about gyroscopes are included.

428

Competing reaction channels in IR-laser-induced unimolecular reactions  

SciTech Connect

The competing reaction channels in the unimolecular decomposition of two molecules, formaldehyde and tetralin were studied. A TEA CO/sub 2/ laser was used as the excitation source in all experiments. The dissociation of D/sub 2/CO was studied by infrared multiphoton dissociation (MPD) and the small-molecule nature of formaldehyde with regard to MPD was explored. The effect of collisions in MPD were probed by the pressure dependence of the MPD yield and ir fluorescence from multiphoton excited D/sub 2/CO. MPD yield shows a near cubic dependence in pure D/sub 2/CO which is reduced to a 1.7 power dependence when 15 torr of NO is added. The peak amplitude of 5 ..mu..m ir fluorescence from D/sub 2/CO is proportional to the square of the D/sub 2/CO pressure in pure D/sub 2/CO or in the presence of 50 torr of Ar. Results are explained in terms of bottlenecks to excitation at the v = 1 level which are overcome by a combination of vibrational energy transfer and rotational relaxation. The radical/molecule branching ratio in D/sub 2/CO MPD was 0.10 +- 0.02 at a fluence of 125 J/cm/sup 2/ at 946.0 cm/sup -1/. The barrier height to molecular dissociation was calculated to be 3.6 +- 2.0 kcal/mole below the radical threshold or 85.0 +- 3.0 kcal/mole above the ground state of D/sub 2/CO. In H/sub 2/CO, this corresponds to 2.5 +- 2.0 kcal/mole below the radical threshold or 83.8 +- 3.0 kcal/mole above the ground state. Comparison with uv data indicate that RRKM theory is an acceptable description of formaldehyde dissociation in the 5 to 10 torr pressure range. The unimolecular decomposition of tetralin was studied by MPD and SiF/sub 4/ - sensitized pyrolysis. Both techniques induce decomposition without the interference of catalytic surfaces. Ethylene loss is identified as the lowest energy reaction channel. Dehydrogenation is found to result from step-wise H atom loss. Isomerization via disproportionation is also identified as a primary reaction channel.

Berman, M.R.

1981-01-01

429

Radiation Reaction and Thomson Scattering  

SciTech Connect

In recent years high power high irradiance lasers of peta-watt order have been or are under construction. In addition, in the next 10 years lasers of unprecedented powers, exa-watt, could be built If lasers such as these are focused to very small spot sizes, extremely high laser irradiances will be achieved. When electrons interact with such a laser, they become highly relativistic over very short time and spatial scales. Usually the motion of an electron under the influence of electromagnetic fields is influenced to a small extent by radiation emission from acceleration. However, under such violent acceleration the amount of radiation emitted by electrons can become so large that significant damping of the electron motion by the emission of this radiation can occur. In this lecture note we will study this problem of radiation reaction by first showing how the equations of motion are obtained. Then, we will examine the problems with such equations and what approximations are made. We will specifically examine the effects of radiation reaction on the Thomson scattering of radiation from counter-streaming laser pulses and high energy electrons through the numerical integration of the equations of motion. We will briefly address the fundamental physics, which can be addressed by using such high irradiance lasers interacting with high energy electrons.

Koga, James [Advanced Photon Research Center Japan Atomic Energy Agency Umemidai 8-1, Kizugawa City, Kyoto 619-0215 (Japan)

2007-07-11

430

Combined model of photonucleon reactions  

SciTech Connect

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range E{sub {gamma}} Less-Than-Or-Equivalent-To 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E{sub {gamma}} Greater-Than-Or-Equivalent-To 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the {sup 40,48}Ca, {sup 90}Zr, {sup 139}La, {sup 142}Nd, and {sup 181}Ta nuclei, as well as difference (E{sub {gamma}max} = 85-55 MeV) bremsstrahlung photoneutron spectra for the {sup 63}Cu, {sup 115}In, {sup 118}Sn, {sup 181}Ta, {sup 207}Pb, {sup 209}Bi, and {sup 235}U nuclei and bremsstrahlung photoproton spectra for the {sup 90}Zr nucleus at the energies of E{sub {gamma}max} = 22, 25, and 34 MeV.

Ishkhanov, B. S.; Orlin, V. N., E-mail: orlinvn@yandex.ru [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation)

2011-01-15

431

Transfusion reactions: the changing priorities.  

PubMed

Over the last dozen years the relative frequencies of specific transfusion reactions have markedly altered, in general for the better. Although AIDS remains the Public's primary concern, the risk of AIDS from a transfusion is extremely low at this point. Hepatitis remains the most common infectious complication of blood transfusion, but only 1 in 6,000 units now carry a risk, whereas in the early 1980's the risk is believed to have been close to 10% per patient. Transmission of HTLV-I/II has also been markedly reduced by tests of donor sera. In contrast, cytomegalovirus has become of increased importance in view of the large number of patients immunosuppressed for transplantation and cancer therapy; bacterial growth in blood components appears to be increasingly common; and Chagas disease is likely to become a serious transfusion problem in this country. More widespread use of filters which remove three logs or more of white blood cells from components should play a major role in reducing transfusion reactions further. PMID:7713589

Perkins, H

1995-01-01

432

Nuclear Reactions from Lattice QCD  

E-print Network

One of the overarching goals of nuclear physics is to rigorously compute properties of hadronic systems directly from the fundamental theory of strong interactions, Quantum Chromodynamics (QCD). In particular, the hope is to perform reliable calculations of nuclear reactions which will impact our understanding of environments that occur during big bang nucleosynthesis, the evolution of stars and supernovae, and within nuclear reactors and high energy/density facilities. Such calculations, being truly ab initio, would include all two-nucleon and three- nucleon (and higher) interactions in a consistent manner. Currently, lattice QCD provides the only reliable option for performing calculations of some of the low- energy hadronic observables. With the aim of bridging the gap between lattice QCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from Lattice QCD on March 2013. In this review article, we report on the topics discussed in this workshop and the path planned to move forward in the upcoming years.

Raúl A. Briceño; Zohreh Davoudi; Thomas C. Luu

2014-06-22

433

Surface catalyzed mercury transformation reactions  

NASA Astrophysics Data System (ADS)

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/m 3 using a diffusion tube as the source of Hg0(g). All experiments were conducted using 4% O2 in nitrogen mix as a reaction gas, and other reactants (HCl, H2O and SO2, NO 2, Br2) were added as required. The fixed bed reactor was operated over a temperature range of 200 to 400°C. In each experiment, the reactor effluent was analyzed using the modified Ontario-Hydro method. After each experiment, fly ash particles were also analyzed for mercury. The results show that the ability of fly ash to adsorb and/or oxidize mercury is primarily dependent on its carbon, iron and calcium content. There can be either one or more than one key component at a particular temperature and flue gas condition. Surface area played a secondary role in effecting the mercury transformations when compared to the concentration of the key component in the fly ash. Amount carbon and surface area played a key important role in the adsorption of mercury. Increased concentration of gases in the flue gas other than oxygen and nitrogen caused decreased the amount of mercury adsorbed on carbon surface. Mercury adsorption by iron oxide primarily depended on the crystalline structure of iron oxide. alpha-iron oxide had no effect on mercury adsorption or oxidation under most of the flue gas conditions, but gamma-iron oxide adsorbed mercury under most of the flue gas conditions. Bromine is a very good oxidizing agent for mercury. But in the presence of calcium oxide containing fly ashes, all the oxidized mercury would be reduced to elemental form. Among the catalysts, it was observed that presence of free lattice chlorine in the catalyst was very important for the oxidation of mercury. But instead of using the catalyst alone, using it along with carbon may better serve the purpose by providing the adsorption surface for mercury and also some extra surface area for the reaction to occur (especially for fly ashes with low surface area).

Varanasi, Patanjali

434

Incidents of chemical reactions in cell equipment  

SciTech Connect

Strongly exothermic reactions can occur between equipment structural components and process gases under certain accident conditions in the diffusion enrichment cascades. This paper describes the conditions required for initiation of these reactions, and describes the range of such reactions experienced over nearly 50 years of equipment operation in the US uranium enrichment program. Factors are cited which can promote or limit the destructive extent of these reactions, and process operations are described which are designed to control the reactions to minimize equipment damage, downtime, and the possibility of material releases.

Baldwin, N.M.; Barlow, C.R. [Uranium Enrichment Organization, Oak Ridge, TN (United States)

1991-12-31

435

Kinetic studies of elementary chemical reactions  

SciTech Connect

This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

Durant, J.L. Jr. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

436

Unusual reaction paths of SN2 nucleophile substitution reactions CH4+H-  

E-print Network

Unusual reaction paths of SN2 nucleophile substitution reactions CH4+H- CH4+H- and CH4+F- CH3F for the SN2 nucleophile substitution reactions CH4+H- CH4+H- and CH4+F- CH3F+H- . The calculated gradient the reaction path branches. 1. Introduction Mechanisms of a gas-phase bimolecular nucleophilic substitution

Quapp, Wolfgang

437

Epidemiology of cutaneous drug-induced reactions.  

PubMed

Cutaneous reactions represent in many surveillance systems, the most frequent adverse events attributable to drugs. The spectrum of clinical manifestations is wide and virtually encompasses any known dermatological disease. The introduction of biological agents and so-called targeted therapies has further enlarged the number of reaction patterns especially linked with cytokine release or in balance. The frequency and clinical patterns of cutaneous reactions are influenced by drug use, prevalence of specific conditions (e.g., HIV infection) and pharmacogenetic traits of a population, and they may vary greatly among the different populations around the world. Studies of reaction rates in cohorts of hospitalized patients revealed incidence rates ranging from, 1 out 1000 to 2 out 100 of all hospitalized patients. For drugs such as aminopenicillines and sulfamides the incidence of skin reactions is in the order of 3-5 cases out of 100 exposed people. Although the majority of cutaneous reactions are mild and self-limiting, there are reactions such as Stevens Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS) which are associated with significant morbidity and mortality. Surveillance systems routed on sound epidemiologic methodology, are needed to raise signals and to assess risks associated with specific reactions and drug exposures. Identification of risk factors for adverse reactions and appropriate genetic screening of groups at higher risk may improve the outcomes of skin reactions. PMID:24819642

Naldi, L; Crotti, S

2014-04-01

438

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

Walch, Stephen P.

1990-01-01

439

An Iodine Fluorescence Quenching Clock Reaction  

NASA Astrophysics Data System (ADS)

A fluorescent clock reaction is described that is based on the principles of the Landolt iodine reaction but uses the potent fluorescence quenching properties of triiodide to abruptly extinguish the ultraviolet fluorescence of optical brighteners present in liquid laundry detergents. The reaction uses easily obtained household products. One variation illustrates the sequential steps and mechanisms of the reaction; other variations maximize the dramatic impact of the demonstration; and a variation that uses liquid detergent in the Briggs Rauscher reaction yields a striking oscillating luminescence. The iodine fluorescence quenching clock reaction can be used in the classroom to explore not only the principles of redox chemistry and reaction kinetics, but also the photophysics of fluorescent pH probes and optical quenching.

Weinberg, Richard B.

2007-05-01

440

The Ozone-Iodine-Chlorate Clock Reaction  

PubMed Central

This work presents a new clock reaction based on ozone, iodine, and chlorate that differs from the known chlorate-iodine clock reaction because it does not require UV light. The induction period for this new clock reaction depends inversely on the initial concentrations of ozone, chlorate, and perchloric acid but is independent of the initial iodine concentration. The proposed mechanism considers the reaction of ozone and iodide to form HOI, which is a key species for producing non-linear autocatalytic behavior. The novelty of this system lies in the presence of ozone, whose participation has never been observed in complex systems such as clock or oscillating reactions. Thus, the autocatalysis demonstrated in this new clock reaction should open the possibility for a new family of oscillating reactions. PMID:24386257

Sant'Anna, Rafaela T. P.; Monteiro, Emily V.; Pereira, Juliano R. T.; Faria, Roberto B.

2013-01-01

441

The OH + HBr reaction revisited  

NASA Technical Reports Server (NTRS)

Variable-temperature measurements of the rate coefficient /k(1)/ for the reaction OH + HBr yield Br + H2O are presented. The measurements are verified by two techniques: one involved a 266-nm pulsed-laser photolysis of O3/H2O/HBr/He mixtures in conjunction with time-resolved resonance fluorescence detection of OH, the second comprised pulsed laser-induced fluorescence detection of OH following 248-nm pulsed-laser photolysis of H2O2/HBr/Ar mixtures. It is reported that k(1) = (11.9 + or -1.4 x 10 to the -12th (cu cm)/(molecule)(s) independent of temperature. The measurements are compared with other available results.

Ravishankara, A. R.; Wine, P. H.; Wells, J. R.

1985-01-01

442

Coulomb excitation and transfer reactions  

NASA Astrophysics Data System (ADS)

Using the ?-spectrometer GASP and the PYRAMID array of position sensitive particle counters enabled improved nuclear structure studies employing direct reactions. Coulomb excitation of 232Th by 58Ni at a beam energy of 265 MeV was used to investigate multi-phonon surface vibrations. For 232Th a new band has been found which is interpreted as harmonic two-phonon octupole vibrational band with K ?=0 +. The system 110Pd + 52Cr was chosen to study the mechanism of multinucleon transfer at energies in the vicinity of the Coulomb barrier. It was possible to identify 10 different transfer channels by their characteristic ?-decay. The total excitation energy versus ?-multiplicity correlations for the most prominent even-even transfer channels show a ‘cold’ component which is a strong indication for correlated pair transfer. For the 2n and 2p channel this fraction is 30(4)%, respectively 16(8)%.

Gerl, J.; Bazzacco, D.; Elze, Th. W.; Happ, T.; Härtlein, T.; Korten, W.; Kröll, T.; Napoli, D.; Alvarez, C. Rossi; Schubert, R.; Vetter, K.; Wollersheim, H. J.

443

Nuclear structure and pion reactions  

SciTech Connect

Shell model analyses of inelastic pion and electron scattering are used to derive many body wave functions suitable for DCX studies of masses 14 and 18. These calculations show clear evidence for the need to include core-excitations in the wave functions of the ground and excited states of these nuclei. The appropriate enhancement and quenching of the isoscalar and isovector one-body density matrix elements are deduced, and their possible effects on DCX cross-sections discussed. Effective (q-dependent) transitions, obtained from microscopic core-polarization calculations, are found to give an excellent description of the pion angular distributions and {pi}{sup {plus}}/{pi}{sup {minus}} ratios in this mass region, justifying the use of effective charges in shell model studies of pion reactions. 13 refs., 12 figs.

Hayes, A.C.

1989-01-01

444

Picosecond Dynamics Of Solution Reactions  

NASA Astrophysics Data System (ADS)

There is now a four order of magnitude time range (?100 fs to 1 ns) over which molecular dynamic calculations can overlap short light pulse experimental measurements to probe the microscopic nature of chemical processes. In this paper we combine theoretical molecular dynamics calculations of picosecond transient spectra with experimental measurements of such spectra to probe the molecular dynamics of a chemical reaction in solution. The example illustrated is the photodissociation of ?2 followed by solvent caging, radical recombination to form a new highly vibra-tionally excited ?2 molecule, and the subsequent decay of this vibrational energy to the solvent. We suggest, as Nes-bitt and Hynes do also, that the lifetimes observed in ?2 picosecond absorption experiments may not be due to gem-inate recombination times, but perhaps to the time necessary for the recombined ?2 molecules to vibrationally decay to levels with high Franck-Condon factors for absorption.

Bado, Philippe; Berens, Peter H.; Wilson, Kent R.

1982-04-01

445

Tandem Reactions for Streamlining Synthesis  

PubMed Central

CONSPECTUS In 1980 Sharpless and Katsuki introduced the asymmetric epoxidation of prochiral allylic alcohols (the Sharpless-Katsuki Asymmetric Epoxidation), which enabled the rapid synthesis of highly enantioenriched epoxy alcohols. This reaction was a milestone in the development of asymmetric catalysis because it was the first highly enantioselective oxidation reaction. Furthermore, it provided access to enantioenriched allylic alcohols that are now standard starting materials in natural product synthesis. In 1981 Sharpless and coworkers made another seminal contribution by describing the kinetic resolution (KR) of racemic allylic alcohols. This work demonstrated that small-molecule catalysts could compete with enzymatic catalysts in KRs. For these pioneering works, Sharpless was awarded the 2001 Nobel Prize with Knowles and Noyori. Despite these achievements, the Sharpless KR is not an efficient method to prepare epoxy alcohols with high enantiomeric excess (ee). First, the racemic allylic alcohol must be prepared and purified. KR of the racemic allylic alcohol must be stopped at low conversion, because the ee of the product epoxy alcohol decreases as the KR progresses. Thus, better methods to prepare epoxy alcohols containing stereogenic carbinol carbons are needed. This Account summarizes our efforts to develop one-pot methods for the synthesis of various epoxy alcohols and allylic epoxy alcohols with high enantio-, diastereo-, and chemoselectivity. Our laboratory developed titanium-based catalysts for use in the synthesis of epoxy alcohols with tertiary carbinols. The catalysts are involved in the first step, which is an asymmetric alkyl or allyl addition to enones. The resulting intermediates are then subjected to a titanium-directed diastereoselective epoxidation to provide tertiary epoxy alcohols. Similarly, the synthesis of acyclic epoxy alcohols begins with asymmetric additions to enals and subsequent epoxidation. The methods described here enable the synthesis of skeletally diverse epoxy alcohols. PMID:18710197

HUSSAIN, MAHMUD M.; WALSH, PATRICK J.

2009-01-01

446

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

Microsoft Academic Search

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized

Derek S. Liechty; Mark J. Lewis

2011-01-01

447

Palladium-catalyzed oxidative carbonylation reactions.  

PubMed

Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions. PMID:23307763

Wu, Xiao-Feng; Neumann, Helfried; Beller, Matthias

2013-02-01

448

Charge exchange reactions and applications to astrophysics  

SciTech Connect

Neutrino-induced reactions have been known to play important roles as the neutrino process on the nucleosynthesis in core collapsing supernovae (SNe) explosions because expected neutrino flux and energy are sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. However, we do not have enough data for the neutrino reaction to be exploited in the network calculation. Only a sparse data in the relevant energy range is known, in specific, for {sup 12}C. Therefore we have to rely on theoretical estimation of the reaction, which has two different modes, charge current (CC) and neutral current (NC). In particular, CC reactions are closely related to charge exchange reactions (CEXRs) which are feasible in the experiment, such as, (p,n) or (n,p) reactions. These CEXRs are usually dominated by the Gamow-Teller (GT) transition in the lower energy region. In this respect, any theoretical approaches for the neutrino reaction should be investigated for the CEXR because we have and expect more useful experimental data. After confirming our models to the GT strength deduced from the CEXR, we calculated neutrino-induced reactions in the energy range below the quasielastic region for nuclei of astrophysical importance. Our calculations are carried out with the Quasi-particle Random Phase Approximation (QRPA), which successfully described the nuclear beta decays of relevant nuclei. To describe neutrino-nucleus reactions, general multipole transitions by the weak interaction are considered for CC and NC reactions. Both reactions are described in a theoretical framework. Our results are shown to well reproduce the data from CEXRs and the sparse experimental data related to the neutrino-induced reaction, and further extended for neutrino reactions on various nuclear targets. Parts of the results are reported in this talk.

Cheoun, Myung-Ki; Ha, Eunja; Kajino, T. [Department of Physics, Soongsil University, Seoul, 156-743 (Korea, Republic of); National Astronomical Observatory, Mitaka, Tokyo 181-8589 (Japan) and Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan)

2012-11-12

449

Neutron Halo and Breakup Reactions  

NASA Astrophysics Data System (ADS)

Characteristic features of neutron halos in the context of breakup experiments at intermediate/high energies are discussed. Neutron halos have been found for light neutron rich nuclei along the neutron drip line, as intense radioactive nuclear beams have become available in recent years. A neutron halo nucleus is composed of a tightly bound core surrounded by one or two neutrons which extend outside of the mean field potential due to quantum tunneling. Coulomb breakup of halo nuclei shows extremely enhanced cross sections for such systems, originating from the characteristic electric dipole response of halo nuclei at low excitation energies, called soft E1 excitation. Such features are shown for one-neutron halo nuclei by Coulomb breakup experiments of {}^{11}Be on Pb at about 70 MeV/nucleon, performed at RIKEN, where it was found that the direct breakup mechanism is responsible for this excitation. We then show how the E1 excitation spectrum can be related to properties of the halo distribution, and hence that the method of Coulomb breakup is a powerful spectroscopic tool. As such, applications of the Coulomb breakup of {}^{15}C and {}^{19}C are shown. The {}^{19}C case is valuable for extracting the microscopic structure of {}^{19}C, which has only recently been clarified. The {}^{15}C case can be used to extract the radiative capture cross section of the {}^{14}C(n,?)^{15}C reaction. We then demonstrate recent applications of the "inclusive" Coulomb breakup method to a new-region of loosely bound nuclei near the island of inversion (N˜20). There, evidence obtained, of the 1n halo structure in {}^{31}Ne, is presented. In the 2n halo case the Coulomb breakup of {}^{11}Li at 70 MeV/nucleon, measured at RIKEN, is shown. This reaction has provided evidence of dineutron-like structure, revealed by the strong enhancement of the soft E1 excitation. For nuclear dominated breakup, where a light target is used, the momentum distribution of the core fragment has key information on the halo distribution, and the single-particle properties of the valence neutron. Here we show an example of a spectroscopic study of {}^{13}Be, populated by removing one neutron from the two neutron halo nucleus {}^{14}Be. These results show that the breakup reactions play significant roles in elucidating the structures along the neutron drip line. This feature will be very important for further investigations of the drip-line nuclei towards the heavier region, as will be produced using the new-generation RI (Rare-Isotope) beam facilities, as has just been completed in RIKEN (RIBF) in Japan. Such enhanced RI-beam facilities are soon to be commissioned in Europe (SPIRAL2, FAIR etc.), in Asia (KoRIA), and in the US (FRIB).

Nakamura, T.; Kondo, Y.

450

Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft  

NASA Technical Reports Server (NTRS)

A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

Rizvi, Farheen

2013-01-01

451

Disulfiram-like reaction with ornidazole.  

PubMed

Many drugs are implicated in causation of disulfiram-like reaction. The disulfiram-like reaction can vary in severity and can occasionally be fatal. The reaction is believed to result from inhibition of metabolism of acetaldehyde to acetate by inhibition of aldehyde dehydrogenase. The increase in serum acetaldehyde results in unpleasant clinical manifestations. Metronidazole is known to cause disulfiram-like reaction. Although no previous report has implicated ornidazole in causation of disulfiram-like reaction, caution has been advised with the use of all imidazoles. We report the case of a 48-year-old male, who was taking ornidazole and developed features of disulfiram-like reaction after taking alcohol. The patient was managed with supportive measures and improved. The report highlights the need for clinicians to advise patients to restrict intake of alcohol if they are being prescribed imidazole derivatives. PMID:20083883

Sharma, V; Sharma, A; Kumar, V; Aggarwal, S

2009-01-01

452

Studying Reaction Intermediates Formed at Graphenic Surfaces  

NASA Astrophysics Data System (ADS)

We report in-situ production and detection of intermediates at graphenic surfaces, especially during alcohol oxidation. Alcohol oxidation to acid occurs on graphene oxide-coated paper surface, driven by an electrical potential, in a paper spray mass spectrometry experiment. As paper spray ionization is a fast process and the time scale matches with the reaction time scale, we were able to detect the intermediate, acetal. This is the first observation of acetal formed in surface oxidation. The process is not limited to alcohols and the reaction has been extended to aldehydes, amines, phosphenes, sugars, etc., where reaction products were detected instantaneously. By combining surface reactions with ambient ionization and mass spectrometry, we show that new insights into chemical reactions become feasible. We suggest that several other chemical transformations may be studied this way. This work opens up a new pathway for different industrially and energetically important reactions using different metal catalysts and modified substrate.

Sarkar, Depanjan; Sen Gupta, Soujit; Narayanan, Rahul; Pradeep, Thalappil

2014-03-01

453

Rat tissue reaction to MTA FILLAPEX®.  

PubMed

The aim of this study was to evaluate the rat subcutaneous tissue reaction to implanted polyethylene tubes filled with mineral trioxide aggregate (MTA) FILLAPEX® compared to the reaction to tubes filled with Sealapex® or Angelus MTA® . These materials were placed in polyethylene tubes and implanted into the dorsal connective tissue of Wistar rats for 7, 15, 30, 60, and 90?days. The specimens were stained with hematoxylin and eosin or Von Kossa or left unstained for examination under polarized light. Qualitative and quantitative evaluations of the reaction were performed. All materials caused moderate reactions after 7 days, which decreased with time. The reactions were moderate and similar to that evoked by the control and Sealapex® on the 15th day. MTA FILLAPEX(®) and Angelus MTA caused mild reactions beginning after 15?days. Mineralization and granulation birefringent to polarized light were observed with all materials. It was concluded that MTA FILLAPEX® was biocompatible and stimulated mineralization. PMID:22151741

Gomes-Filho, João Eduardo; Watanabe, Simone; Lodi, Carolina Simonetti; Cintra, Luciano Tavares Angelo; Nery, Mauro Juvenal; Filho, José Arlindo Otoboni; Dezan, Elói; Bernabé, Pedro Felício Estrada

2012-12-01

454

Antibody-mediated cofactor-driven reactions  

DOEpatents

Chemical reactions capable of being rate-enhanced by auxiliary species which interact with the reactants but do not become chemically bound to them in the formation of the final product are performed in the presence of antibodies which promote the reactions. The antibodies contain regions within their antigen binding sites which recognize the auxiliary species in a conformation which promotes the reaction. The antigen binding site frequently recognizes a particular transition state complex or other high energy complex along the reaction coordinate, thereby promoting the progress of the reaction along the desired route as opposed to other less favorable routes. Various classes of reaction together with appropriate antigen binding site specificities tailored for each are disclosed.

Schultz, Peter G. (Oakland, CA)

1993-01-01

455

Neutrino nuclear response and photo nuclear reaction  

E-print Network

Photo nuclear reactions are shown to be used for studying neutrino/weak nuclear responses involved in astro-neutrino nuclear interactions and double beta decays. Charged current weak responses for ground and excited states are studied by using photo nuclear reactions through isobaric analog states of those states, while neutral current weak responses for excited states are studied by using photo nuclear reactions through the excited states. The weak interaction strengths are studied by measuring the cross sections of the photo nuclear reactions, and the spin and parity of the state are studied by measuring angular correlations of particles emitted from the photo nuclear reactions. Medium-energy polarized photons obtained from laser photons scattered off GeV electrons are very useful. Nuclear responses studied by photo nuclear reactions are used to evaluate neutrino/weak nuclear responses, i.e. nuclear beta and double beta matrix elements and neutrino nuclear interactions, and to verify theoretical calculations for them.

H. Ejiri; A. I. Titov; M. Boswell; A. Young

2013-11-10

456

Reactions of Organic Halides in Solution  

Microsoft Academic Search

REACTIONS of organic halides in solution which involve substitution by a nucleophilic reagent at a saturated carbon atom have been extensively studied by Hughes, Ingold and co-workers1. These authors conclude that reactions of this type may occur by two possible mechanisms, a unimolecular mechanism SN1 or a bimolecular mechanism SN2. The increase in the unimolecular SN1 reaction-rate of the halide

Alwyn G. Evans

1946-01-01

457

Charge Transfer Reactions and Solvation Dynamics  

Microsoft Academic Search

\\u000a In this article, we offer a perspective on solvation dynamics from the point of view of chemical reactions, and in particular\\u000a from an initial viewpoint of heavy particle charge transfer reactions. These reactions include SN2 nucleophilic displacements —, SN1 unimolecular ionizations —, dipolar isomerizations, and (with a certain elasticity of definition) ion pair interconversion.\\u000a Here the solvation dynamics act to

James T. Hynes

458

Kinetics of reaction of cyclopentadiene with sodium  

SciTech Connect

The kinetics of the topochemical reaction of cyclopentadiene with metallic sodium were studied in a toluene medium. It was found that the observed rate of the first-order reaction is proportional to the surface of sodium and the cyclopentadiene concentration. The values of the energy of activation and reaction-rate constants are: E = 31 kJ/mole; k = 7.4 x 10/sup -4/ liter/m/sup 2/ x sec at 40/sup 0/C.

Koshkina, S.B.; Krylov, A.V.; Rozovskii, V.Ya.; Zhitkov, I.V.

1987-08-01

459

Dinuclear systems in complete fusion reactions  

NASA Astrophysics Data System (ADS)

Formation and evolution of dinuclear systems in reactions of complete fusion are considered. Based on the dinuclear system concept, the process of compound nucleus formation is studied. Arguments confirming the validity of this concept are given. The main problems of describing the complete fusion in adiabatic approximation are listed. Calculations of evaporation residue cross sections in complete fusion reactions leading to formation of superheavy nuclei are shown. Isotopic trends of the cross sections of heavy nuclei formation in complete fusion reactions are considered.

Adamian, G. G.; Antonenko, N. V.; Zubov, A. S.

2014-09-01

460

A Unified Theory of Chemical Reactions  

E-print Network

We propose a new and general formalism for elementary chemical reactions where quantum electronic variables are used as reaction coordinates. This formalism is in principle applicable to all kinds of chemical reactions ionic or covalent. Our theory reveals the existence of an intermediate situation between ionic and covalent which may be almost barrierless and isoenegetic and which should be of high interest for understanding biochemistry.

Aubry, S

2014-01-01

461

Hymenoptera-Induced Hypersensitivity Reactions and Anaphylaxis  

Microsoft Academic Search

\\u000a Most Hymenoptera (honeybees, bumblebees, yellow jackets, hornets, wasps and fire ants) stings lead to a local reaction. Up\\u000a to 7% of population develops systemic allergic reaction to the constituents of venom. Up to 0.5 per one million people die\\u000a per year due to Hymenoptera venom allergy. Risk factors for the most severe reactions are advanced age, concomitant cardiovascular\\u000a diseases, concomitant

Mitja Kosnik; Peter Korosec

462

Reductive bromine atom-transfer reaction.  

PubMed

Atom-transfer radical (ATR) reactions of alkenes with R-X usually give products having new C-C and C-X bonds at the adjacent carbons. However, when the reaction was carried out under irradiation using a low-pressure Hg lamp, addition/reduction products were obtained in good yield. Hydrogen bromide, formed by H-abstraction of a bromine radical from alkenes, is likely to play a key role in the reductive ATR reaction. PMID:23697921

Sumino, Shuhei; Fusano, Akira; Ryu, Ilhyong

2013-06-01

463

Habituation of orienting reaction in night terrors  

Microsoft Academic Search

A polygraphic study on resistance to habituation of the somatic (EMG), autonomic (finger vasoconstriction, galvanic skin reaction,\\u000a respiration, pulse) and EEG (acoustic-evoked potential, EEG-blocking reaction) components of the orienting reaction elicited\\u000a by a repetitive auditory stimulus was performed in 36 patients with night terrors and in 72 matched subjects in two control\\u000a groups. The study evidenced a significantly higher resistance

R. Rogozea; V. Florea-Ciocoiu

1985-01-01

464

On Nuclear Transmutation Reactions in Solids  

Microsoft Academic Search

Research on transmutation reactions in solids heavily loaded with H or D( high H\\/D atoms\\/metal atom) is rapidly growing. Previously it was thought that reactant energies were too low to overcome the coulombic field barrier. However, such reactions have been reported by a number of researchers. Earlier Miley, et al. studied multi-layer thin-film Ni\\/Pd electrodes loaded electrolytically Reaction products exhibited

George H. Miley; Heinz Hora; Nie Luo

2004-01-01

465

Organic syntheses employing supercritical carbon dioxide as a reaction solvent  

NASA Technical Reports Server (NTRS)

Chemical reactions are readily carried out using supercritical carbon dioxide as the reaction medium. Supercritical carbon dioxide is of special value as a reaction medium in reactions for synthesizing polypeptides, for sequencing polypeptides, or for amino acid analysis.

Barstow, Leon E. (Inventor); Ward, Glen D. (Inventor); Bier, Milan (Inventor)

1993-01-01

466

Organic syntheses employing supercritical carbon dioxide as a reaction solvent  

NASA Technical Reports Server (NTRS)

Chemical reactions are readily carried out using supercritical carbon dioxide as the reaction medium. Supercritical carbon dioxide is of special value as a reaction medium in reactions for synthesizing polypeptides, for sequencing polypeptides, or for amino acid analysis.

Barstow, Leon E. (Inventor); Ward, Glen D. (Inventor); Bier, Milan (Inventor)

1991-01-01

467

Energy distribution among reaction products. V.  

NASA Technical Reports Server (NTRS)

Discussion of three reactions, one point of theoretical interest being the predicted correlation between barrier height and barrier location. The H + Br 2 reaction having a lower activation barrier than H + Cl 2, should have an earlier barrier, and hence a greater percentage attractive energy release and higher efficiency of vibrational excitation. Information is developed concerning the effect of isotopic substitution in the pair of reactions H + Cl 2 and D + Cl 2. The 'arrested relaxation' method was used. Essentially, the method involves reacting two diffuse reagent beams in a reaction vessel with background pressure less than 0.001 torr, and with walls cooled by liquid nitrogen or liquid helium.

Anlauf, K. G.; Horne, D. S.; Macdonald, R. G.; Polanyi, J. C.; Woodall, K. B.

1972-01-01

468

Process for operating equilibrium controlled reactions  

DOEpatents

A cyclic process for operating an equilibrium controlled reaction in a plurality of reactors containing an admixture of an adsorbent and a reaction catalyst suitable for performing the desired reaction which is operated in a predetermined timed sequence wherein the heating and cooling requirements in a moving reaction mass transfer zone within each reactor are provided by indirect heat exchange with a fluid capable of phase change at temperatures maintained in each reactor during sorpreaction, depressurization, purging and pressurization steps during each process cycle.

Nataraj, Shankar (Allentown, PA); Carvill, Brian Thomas (Orefield, PA); Hufton, Jeffrey Raymond (Fogelsville, PA); Mayorga, Steven Gerard (Allentown, PA); Gaffney, Thomas Richard (Allentown, PA); Brzozowski, Jeffrey Richard (Bethlehem, PA)

2001-01-01

469

Direct reactions in/for astrophysics  

E-print Network

Precise nuclear reaction rates are needed for a detailed description of the production of elements in primordial nucleosynthesis and during the hydrostatic burning of stars to constrain the astrophysical models. The relevant reactions are extremely difficult to measure directly in the laboratory at the small astrophysical energies. In recent years direct reactions methods have been developed and applied to extract low-energy astrophysical S factors. The application of these methods requires a combination of experimental and theoretical efforts. This contribution focuses on the underlying reaction theories that have to be well understood in order to assess the precision and limitations of the various approaches.

C. A. Bertulani

2006-07-10

470

Demisable Reaction-Wheel Assembly  

NASA Technical Reports Server (NTRS)

A document discusses the concept of a demisable motor-drive-and-flywheel assembly [reaction-wheel assembly (RWA)] used in controlling the attitude of a spacecraft. Demisable as used here does not have its traditional legal meaning; instead, it signifies susceptible to melting, vaporizing, and/or otherwise disintegrating during re-entry of the spacecraft into the atmosphere of the Earth so as not to pose a hazard to anyone or anything on the ground. Prior RWAs include parts made of metals (e.g., iron, steel, and titanium) that melt at high temperatures and include structures of generally closed character that shield some parts (e.g., magnets) against re-entry heating. In a demisable RWA, the flywheel would be made of aluminum, which melts at a lower temperature. The flywheel web would not be a solid disk but would have a more open, nearly-spoke-like structure so that it would disintegrate more rapidly; hence, the flywheel rim would separate more rapidly so that parts shielded by the rim would be exposed sooner to re-entry heating. In addition, clearances between the flywheel and other components would be made greater, imparting a more open character and thus increasing the exposure of those components.

Roder, Russell; Ahronovich, Eliezer; Davis, Milton C., III

2008-01-01

471

Sonochemical reactions with mesoporous alumina.  

PubMed

Herein, we report the sonochemical reactions with MSU-X mesoporous alumina (m-Al(2)O(3)) in aqueous solutions. Sonication (f=20 kHz, I=30 Wcm(-2), W(aq)=0.67 WmL(-1), T=36-38 degrees C, Ar) causes significant acceleration of m-Al(2)O(3) dissolution in the pH range of 4-11. Moreover, power ultrasound has a dramatic effect on the textural properties and phase composition of m-Al(2)O(3). Short-time sonication at pH = 4 leads to the formation of nanorods and nanofibers of boehmite, AlO(OH). Prolonged ultrasonic treatment causes high aspect morphology transformation to aggregated nanosheets in weakly acid solutions or plated nanocrystals in alkaline solutions. Sonochemical products in alkaline medium are composed principally from boehmite and small amounts of bayerite, Al(OH)(3). Silent hydrolysis of m-Al(2)O(3) yields boehmite at pH = 4 and bayerite at pH = 11. The effect of ultrasound on the textural properties of mesoporous alumina as well as on the transformation of nanosized bayerite to boehmite can be consistently attributed to the transient strong heating of the liquid shell surrounding the cavitation bubble which caused the chemical processes similar to those occurred during hydrothermal treatment. PMID:19211292

Chave, Tony; Nikitenko, Sergei I; Granier, Dominique; Zemb, Thomas

2009-04-01

472

Allergic reactions to food proteins.  

PubMed

Four to eight percent of the population are estimated to be food-allergic. Most food allergies in adolescents and adults are acquired on the basis of cross-reaction to pollen allergens. Theses allergens are ubiquitous in the plant kingdom. Therefore pollen-allergic patients might acquire a multitude of different plant food allergies, and even react to novel foods to which they have never previously been exposed. A curative therapy for food allergy does not yet exist. Food-allergic patients have to rely on strict avoidance diets, The widespread use of industrially processed foods poses a general problem for food-allergic patients. Although the most frequent allergens must be declared openly in the list of ingredients, involuntary contamination with allergy-provoking compounds can occur. The precautionary labelling "may contain" is sometimes applied even if the chance of contamination is very low; on the other hand, foods not declared to contain possible traces of allergenic components may actually contain relevant amounts of allergenic proteins. Switzerland is the only country in Europe with legal regulations on contamination by allergenic food; however, the allowance of 1 g/kg is too high to protect a relevant proportion of food-allergic individuals. PMID:22139568

Ballmer-Weber, Barbara K

2011-03-01

473

Reaction products of chlorine dioxide.  

PubMed Central

Inspection of the available literature reveals that a detailed investigation of the aqueous organic chemistry of chlorine dioxide and systematic identification of products formed during water disinfection has not been considered. This must be done before an informed assessment can be made of the relative safety of using chlorine dioxide as a disinfectant alternative to chlorine. Although trihalomethanes are generally not formed by the action of chlorine dioxide, the products of chlorine dioxide treatment of organic materials are oxidized species, some of which also contain chlorine. The relative amounts of species types may depend on the amount of chlorine dioxide residual maintained and the concentration and nature of the organic material present in the source water. The trend toward lower concentrations of chlorinated by-products with increasing ClO2 concentration, which was observed with phenols, has not been observed with natural humic materials as measured by the organic halogen parameter. Organic halogen concentrations have been shown to increase with increasing chlorine dioxide dose, but are much lower than those observed when chlorine is applied. Aldehydes have been detected as apparent by-products of chlorine dioxide oxidation reactions in a surface water that is a drinking water source. Some other nonchlorinated products of chlorine dioxide treatment may be quinones and epoxides. The extent of formation of these moieties within the macromolecular humic structure is also still unknown. PMID:7151750

Stevens, A A

1982-01-01

474

FERMENTATION REACTIONS OF ERYSIPELOTHRIX RHUSIOPATHIAE  

PubMed Central

White, Thomas G. (U. S. Department of Agriculture, Ames, Iowa), and Richard D. Shuman. Fermentation reactions of Erysipelothrix rhusiopathiae. J. Bacteriol. 82:595–599. 1961.—A study was made to determine the effect of four different basal media, to which fermentable carbon compounds had been added, upon 22 selected strains of Erysipelothrix rhusiopathiae (insidiosa). Acid production was measured by (i) chemical indicator, (ii) change in pH, and (iii) production of titrable acidity. At least two determinations, usually four, were made for each test on each strain. The fermentation pattern varied according to the medium, the indicator, and the method of measuring acid production. Andrade's base plus serum was the most dependable medium because it permitted the least variation in the total number of different patterns. Of the three methods used to measure acid production, the chemical indicator gave the most valid and reproducible results. The within-strain variation was not extreme and most strains persisted in a given fermentation pattern under like conditions of growth and acid production. Results of the study indicated that, regardless of the medium and indicator routinely used, one should be familiar with the fermentation pattern of known strains of the erysipelas organism. PMID:14006576

White, Thomas G.; Shuman, Richard D.

1961-01-01

475

Ionic reactions of atmospheric importance  

NASA Astrophysics Data System (ADS)

A variable-temperature flowing afterglow/Langmuir probe (FALP) apparatus has been used to study the temperature dependence of a number of electron-ion dissociative recombination coefficients, alpha e, and electron attachment coefficients, Beta, over the temperature range 200-600 K. Thus alpha e(02(+)), alpha e(NO+)) and alpha e(NH4+)) have been shown to vary inversely with temperature, T, as alpha e approximately T to the -n power with n = 0.7, 0.9 and 0.6 respectively. Alpha e(H30+)) was found to be independent of temperature. Beta(CC14), Beta(CC13F) and Beta (SF6) were all very large, close to their theoretical maximum values (approximately .0000004 cc/s at 300 K) and varied only very slowly with temperature over the available range, whereas Beta(CC12F2), Beta(CHC13) and Beta(C12) were smaller and increased appreciably with temperature. From the data, activation energies, Ea, were obtained for the dissociative attachment reactions of CC13F, CC12F2, CHC13 and C12. Thus Ea(CC13F) approximately 0.02eV, Ea(CC12F2) approximately 0.15eV, Ea(CHC13) approximately 0.12 eV and Ea(C12) approximately 0.05 eV.

Smith, D.; Adams, N. G.

1983-11-01

476

2005 Chemical Reactions at Surfaces  

SciTech Connect

The Gordon Research Conference (GRC) on 2005 Chemical Reactions at Surfaces was held at Ventura Beach Marriott, Ventura California from February 13, 2005 through February 18, 2005. The Conference was well-attended with 124 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

Cynthia M. Friend

2006-03-14

477

Mediating chemical reactions using polysaccharides  

NASA Astrophysics Data System (ADS)

We have studied the NaBH4-mediated hydrogenation of select alkenes catalyzed by polysaccharide-stabilized nanoparticles. We compared the catalytic properties of Ni-based nanoparticles or Au/Co-based nanoparticles on the hydrogenation of cinnamic acid, cinnamide, cinnamyl alcohol, and ethyl cinnamate. We evaluated the possibility that the type of stabilizing polysaccharide surrounding the nanoparticle may affect the selectivity towards the alkene compounds that undergo the hydrogenation reaction. We found that the hydrogenation of cinnamide or ethyl cinnamate proceeded readily to 100% completion independent of the type of polysaccharide stabilizing the nanoparticle. However, the extent of the hydrogenation of cinnamyl alcohol and cinnamic acid varied greatly depending on the type of polysaccharide stabilizing the nanoparticle. In the course of these studies, we observed that some polysaccharides by themselves promoted the hydrolysis of ethyl cinnamate. Thus, we have raised the hypothesis that some polysaccharides may act as "esterases" and explored the interaction between select polysaccharides and a variety of ester compounds.

Tyler, Lauren E.

478

Defensive Physiological Reactions to Rejection  

PubMed Central

We examined the hypothesis that rejection automatically elicits defensive physiological reactions in people with low self-esteem (SE) but that attentional control moderates this effect. Undergraduates (N = 67) completed questionnaire measures of SE and attentional control. Their eye-blink responses to startle probes were measured while they viewed paintings related to rejection and acceptance themes. The stimuli also included positive-, negative-, and neutral-valence control paintings unrelated to rejection. As predicted, compared with people high in SE, those low in SE showed stronger startle eye-blink responses to paintings related to rejection, but not to negative paintings. Paintings related to acceptance did not attenuate their physiological reactivity. Furthermore, attentional control moderated their sensitivity to rejection, such that low SE was related to greater eye-blink responses to rejection only among individuals who were low in attentional control. Implications of the role of attentional control as a top-down process regulating emotional reactivity in people with low SE are discussed. PMID:17894606

Gyurak, Anett; Ayduk, Ozlem

2014-01-01

479

Reaction energetics on long-range corrected density functional theory: Diels-Alder reactions.  

PubMed

The possibility of quantitative reaction analysis on the orbital energies of long-range corrected density functional theory (LC-DFT) is presented. First, we calculated the Diels-Alder reaction enthalpies that have been poorly given by conventional functionals including B3LYP functional. As a result, it is found that the long-range correction drastically improves the reaction enthalpies. The barrier height energies were also computed for these reactions. Consequently, we found that dispersion correlation correction is also crucial to give accurate barrier height energies. It is, therefore, concluded that both long-range exchange interactions and dispersion correlations are essentially required in conventional functionals to investigate Diels-Alder reactions quantitatively. After confirming that LC-DFT accurately reproduces the orbital energies of the reactant and product molecules of the Diels-Alder reactions, the global hardness responses, the halves of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, along the intrinsic reaction coordinates of two Diels-Alder reactions were computed. We noticed that LC-DFT results satisfy the maximum hardness rule for overall reaction paths while conventional functionals violate this rule on the reaction pathways. Furthermore, our results also show that the HOMO-LUMO gap variations are close to the reaction enthalpies for these Diels-Alder reactions. Based on these results, we foresee quantitative reaction analysis on the orbital energies. PMID:23037888

Singh, Raman K; Tsuneda, Takao

2013-02-15

480

[Life-threatening drug reactions in children].  

PubMed

Adverse drug reactions in children are serious public health problem. The overall incidence of ADRs is estimated at about 9.5% in hospitalized children and about 1.5% for outpatient children. ADRs have very diverse manifestations from minor skin rashes to potentially life-threatening severe skin reactions such as: acute generalized exanthematous pustulosis, Stevens-Johnson syndrome, toxic epidermal necrolysis and anaphylactic reactions. The aim of the study was to analyze the results of ADRs monitoring with particular regard to life-threatening reactions in the pediatric population in Poland. We analyzed spontaneous reports of ADRs in Poland in patients aged 0-18 years in the period 01.01.2004-31.03.2013. Each reported case was evaluated and classified by a clinical pharmacologist and an allergologist. Analysis of the data showed the occurrence of ADR in 846 pediatric patients including one case of Stevens-Johnson syndrome, and 90 (10.6% ADR) drug reactions classified as anaphylactic reactions (44 responses (5.2% ADR)) and non-immune anaphylaxis (46 responses (5.4% ADR)). Classes of drugs most frequently causing anaphylactic reactions were: anti-inflammatory and antipyretic (31%), antibiotics (19%) and drugs used in anesthesia (16%). The substances most commonly causing anaphylactic reactions/non-immune anaphylaxis were: paracetamol and lidocaine (with 8 responses). The most common clinical manifestations of ADRs are skin reactions (402 responses, 47.5%). Acute drug reactions in the pediatric population may have life-threatening clinical manifestations. Drugs that most commonly cause anaphylaxis are: anti-inflammatory/ antipyretic drugs (acetaminophen, aspirin, ibuprofen), antibiotics (cephalosporins, amoxicillin, sulfonamides), local anesthetics (lidocaine). Early diagnosis of allergy and choice of safe product can prevent life-threatening drug reactions. PMID:24720116

Le?niak, Ma?gorzata; Woron, Jaros?aw; Czarnobilska, Ewa

2013-01-01

481

Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions  

EPA Science Inventory

Magnetite-sulfonic acid (NanocatFe-OSO3H), prepared by wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter reaction which can be used in several reaction cycles without any loss of activity....

482

The isothermal sulphation reactions of natural sorbents  

Microsoft Academic Search

The chemical reaction between sulphur dioxide and calcined limestone and dolomite particles was investigated using a thermogravimetric analyser. The samples used in this study originated from different parts of Turkey. Sulphation reactions w