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1

?-Siloxy-?-haloketones through highly diastereoselective single and double mukaiyama aldol reactions.  

PubMed

Double-action haloketones: A super silyl group enabled the first highly diastereoselective Mukaiyama aldol reactions of ?-chloro- and ?-fluoroketones with a wide range of aldehydes, providing anti-?-siloxy-?-haloketones. This process is compatible with one-pot double-aldol methodology and allows for rapid access to new halogen-modified polyketide fragments bearing up to four contiguous stereocenters. PMID:23424059

Saadi, Jakub; Yamamoto, Hisashi

2013-03-18

2

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

3

CALIX[6]ARENE DERIVATIVES BEARING SULFONATE AND ALKYL GROUPS AS SURFACTANTS IN SC(OTF)3-CATALYZED MUKAIYAMA ALDOL REACTIONS IN WATER. (R822668)  

EPA Science Inventory

Abstract Amphiphilic calix[6]arene derivatives 1a¯b were found to be efficient surfactants for Sc(OTf)3-catalyzed Mukaiyama aldol reaction of silyl enol ethers with aldehydes in water. The results indicated t...

4

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

5

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

6

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

7

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

8

N-acyl oxazolidin-2-selones promoted aldol reactions  

SciTech Connect

Selenocarbonyls that are housed in a chiral environment have been found to play a pivotal role aldol reactions. We have found that, in general,, the aldol reaction affords the non-Evans aldol syn products. However, the use of glycolate donors with glycoaldehydes, under proper conditions, gave rise to predominately the anti aldol.

Li, Zizhong; Wu, R. (Ruilian); Silks, L. A. (Louis A.), III; Michalczyk, R. (Ryszard)

2001-01-01

9

Imidazolidinone intermediates in prolinamide-catalyzed aldol reactions.  

PubMed

The reaction between acetone and 4-nitrobenzaldehyde catalyzed by aniline prolinamide 1 was studied in depth. Working in different solvents with equimolar amounts of reagents and monitoring the reaction by 1H NMR, we detected and identified several imidazolidinones, such as those of the acetone 4, the aldol products 5a and 5b, and aldehydes 10a and 10b. According to our results, these compounds could influence the reaction rate and diminish product enantioselectivity. Furthermore, acetone imidazolidinone 4 was seen to react with 4-nitrobenzaldehyde to furnish the aldol product 3. This reaction can be catalyzed by different nucleophiles and acids. In fact, strong acids such as camphorsulfonic or trifluoroacetic acid, convert imidazolidinones into iminium salts and afford more enantioselective aldol reactions when different aromatic prolinamides are used. Enantiomeric excesses of ca. 82% are reached. PMID:20461270

Fuentes de Arriba, Angel L; Simón, Luis; Raposo, César; Alcázar, Victoria; Sanz, Francisca; Muñiz, Francisco M; Morán, Joaquín R

2010-06-28

10

Enantioselective tandem O-nitroso Aldol/Michael reaction.  

PubMed

This communication presents studies that illustrated nitroso Diels-Alder adduct has been obtained in uniformly high enantioselectivity via a tandem nitroso aldol/Michael reaction using an amine catalyst. The regiochemical outcome of this construction is documented to be the opposite to that of the normal nitroso aldol reaction, which has been determined by X-ray analysis. The reaction of the enone with silver-BINAP catalyst has also been investigated in conjunction with the control of regiochemistry in a stepwise process. PMID:15137750

Yamamoto, Yuhei; Momiyama, Norie; Yamamoto, Hisashi

2004-05-19

11

Organocatalytic asymmetric aldol reaction in the presence of water.  

PubMed

Water was found to be a suitable solvent for the l-prolinethioamide catalysed aldol reaction of various cyclic ketones with aromatic aldehydes. Treatment of 4-nitrobenzaldehyde with as little as 1.2 equiv. of cyclohexanone in the presence of the protonated catalyst 1-TFA, afforded aldol products in high yields (up to 97%) with high diastereo- and enantioselectivity (up to >5 : 95 dr and 98% ee). The use of a high excess of ketone was avoided by conducting the aldol addition in the presence of water. Furthermore, different 'salting-out' and 'salting-in' salts were investigated and it was proven that the rate of acceleration and the stereochemical outcome of the reaction are affected by hydrophobic aggregation. Scope and limitation studies revealed that electron deficient aldehydes afforded aldol products with high stereoselectivity in the presence of 1-Cl(2)CHCO(2)H. It was shown that various cyclic ketones, under the conditions found, gave aldol products with fair yields, even if they are used in substoichiometric amounts (1.2 to 2.0 equiv.). PMID:17581659

Gryko, Dorota; Saletra, Wojciech J

2007-07-01

12

Functionalized multi-walled carbon nanotubes in an aldol reaction.  

PubMed

The covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with a proline-based derivative is reported. Initially, MWCNTs were oxidized in order to introduce a large number of carboxylic units on their tips followed by N-tert-butoxycarbonyl-2,2'(ethylenedioxy)bis-(ethylamine) conjugation through an amide bond. Then, a proline derivative bearing a carboxylic terminal moiety at the 4-position was coupled furnishing proline-modified MWCNTs. This new hybrid material was fully characterized by spectroscopic and microscopy means and its catalytic activity in the asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde was evaluated for the first time, showing to proceed almost quantitatively in aqueous media. Furthermore, several amino-modified MWCNTs were prepared and examined in the particular aldol reaction. These new hybrid materials exhibited an enhanced catalytic activity in water, contrasting with the pristine MWCNTs as well as the parent organic molecule, which failed to catalyze the reaction efficiently. Furthermore, the modified MWCNTs proved to catalyze the aldol reaction even after three repetitive cycles. Overall, a green approach for the aldol reaction is presented, where water can be employed as the solvent and modified MWCNTs can be used as catalysts, which can be successfully recovered and reused, while their catalytic activity is retained. PMID:25585101

Chronopoulos, D D; Kokotos, C G; Karousis, N; Kokotos, G; Tagmatarchis, N

2015-01-28

13

Anti-Selective Aldol Reactions with Titanium Enolates of  

E-print Network

Anti-Selective Aldol Reactions with Titanium Enolates of N-Glycolyloxazolidinethiones Michael T-glycolyloxazolidinethiones has been developed. Enolization of an N-glycolyloxazolidinethione with titanium (IV) chloride successful with a wide variety of aldehydes and protecting groups.2 Additionally, the titanium enolates of N

14

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

15

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

16

Investigating ionic effects applied to water based organocatalysed aldol reactions.  

PubMed

Saturated aqueous solutions of various common salts were examined for their effect on aqueous aldol reactions catalysted by a highly active C(2)-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

17

Thiazolidinedione-isatin conjugates via an uncatalyzed diastereoselective aldol reaction on water.  

PubMed

An uncatalyzed aldol reaction of N-substituted thiazolidinediones with isatin derivatives has been developed "on water" to afford a new class of pharmacologically important thiazolidinedione-isatin conjugates in excellent yields and diastereoselectivities. The isatin-thiazolidine conjugate undergoes a catalyst-free stereoselective transfer aldol reaction on water. Single-crystal X-ray studies reveal that the aldol products can self-assemble to form supramolecular DNA "zipper" like structures through intermolecular hydrogen bonds and aromatic ?-? interactions. PMID:24383887

Paladhi, Sushovan; Bhati, Meeta; Panda, Deepanjan; Dash, Jyotirmayee

2014-02-01

18

Helical polymer as mimetic enzyme catalyzing asymmetric aldol reaction.  

PubMed

This Communication reports optically active helical substituted polyacetylenes which solely catalyzed asymmetric Aldol reaction between cyclohexanone and p-nitrobenzaldehyde; more importantly the helical structures are found to play crucial roles in the asymmetric catalysis, with a remarkable yield and ee (both up to 80%). A synergic effect is observed between the helical structures in the polymer main chains and the pendent prolinamide moieties for successfully catalyzing the asymmetric reaction. The role of the helical polymer backbones is further verified by tuning the relative helical structure content. PMID:22318956

Zhang, Dongyue; Ren, Chonglei; Yang, Wantai; Deng, Jianping

2012-04-23

19

Enantioselective direct aldol reactions catalyzed by L-prolinamide derivatives.  

PubMed

l-Prolinamides 2, prepared from l-proline and simple aliphatic and aromatic amines, have been found to be active catalysts for the direct aldol reaction of 4-nitrobenzaldehyde with neat acetone at room temperature. They give moderate enantioselectivities of up to 46% enantiomeric excess (ee). The enantioselectivity increases as the amide N-H becomes a better hydrogen bond donor. l-Prolinamides 3, derived from the reaction of l-proline with alpha,beta-hydroxyamines such that there is a terminal hydroxyl group, show more efficient catalysis and higher enantioselectivities. In particular, catalyst 3h, prepared from l-proline and (1S,2S)-diphenyl-2-aminoethanol, exhibits high enantioselectivities of up to 93% ee for aromatic aldehydes and up to >99% ee for aliphatic aldehydes under -25 degrees C. Model reactions of benzaldehyde with three enamines derived from the condensation of prolinamides with acetone have been studied by quantum mechanics calculations. The calculations reveal that the amide N-H and the terminal hydroxyl groups form hydrogen bonds with the benzaldehyde substrate. These hydrogen bonds reduce the activation energy and cause high enantioselectivity. Our results suggest a new strategy in the design of new organic catalysts for direct asymmetric aldol reactions and related transformations. PMID:15079057

Tang, Zhuo; Jiang, Fan; Cui, Xin; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong; Wu, Yun-Dong

2004-04-20

20

Various polar tripeptides as asymmetric organocatalyst in direct aldol reactions in aqueous media.  

PubMed

A series of tripeptide organocatalysts containing a secondary amine group and two amino acids with polar side chain units were developed and evaluated in the direct asymmetric intermolecular aldol reaction of 4-nitrobenzaldehyde and cyclohexanone. The effectiveness of short polar peptides as asymmetric catalysts in aldol reactions to attain high yields of enantio- and diastereoselective isomers were investigated. In a comparison, glutamic acid and histidine produced higher % ee and yields when they were applied as the second amino acid in short trimeric peptides. These short polar peptides were found to be efficient organocatalysts for the asymmetric aldol addition reaction in aqueous media. PMID:23966316

Bayat, Saadi; Tejo, Bimo A; Salleh, Abu Bakar; Abdmalek, Emilia; Normi, Yahaya M; Abdul Rahman, Mohd Basyaruddin

2013-11-01

21

Accurate Reaction Enthalpies and Sources of Error in DFT Thermochemistry for Aldol, Mannich, and ?-Aminoxylation Reactions  

PubMed Central

Enthalpies for bond-forming reactions that are subject to organocatalysis have been predicted using the high-accuracy CBS-QB3 model chemistry and six DFT functionals. Reaction enthalpies were decomposed into contributions from changes in bonding and other intramolecular effects via the hierarchy of homodesmotic reactions. The order of the reaction exothermicities (aldol < Mannich ? ?-aminoxylation) arises primarily from changes in formal bond types mediated by contributions from secondary intramolecular interactions. In each of these reaction types, methyl substitution at the ?- and ?-positions stabilizes the products relative to the unsubstituted case. The performance of six DFT functionals (B3LYP, B3PW91, B1B95, MPW1PW91, PBE1PBE, and M06-2X), MP2, and SCS-MP2 has been assessed for the prediction of these reaction enthalpies. Even though the PBE1PBE and M06-2X functionals perform well for the aldol and Mannich reactions, errors roughly double when these functionals are applied to the ?-aminoxylation reactions. On the other hand, B3PW91 and B1B95, which offer modest accuracy for the aldol and Mannich reactions, yield reliable predictions for the two ?-aminoxylation reactions. The excellent performance of the M06-2X and PBE1PBE functionals for aldol and Mannich reactions stems from the cancellation of sizeable errors arising from inadequate descriptions of the underlying bond transformations and intramolecular interactions. SCS-MP2/cc-pVTZ performs most consistently across these three classes of reactions, although the reaction exothermicities are systematically underestimated by 1–3 kcal mol?1. Conventional MP2, when paired with the cc-pVTZ basis set, performs somewhat better than SCS-MP2 for some of these reactions, particularly the ?-aminoxylations. Finally, the merits of benchmarking DFT functionals for the set of simple chemically meaningful transformations underlying all bond-forming reactions are discussed. PMID:19711937

Wheeler, Steven E.; Moran, Antonio; Pieniazek, Susan N.

2009-01-01

22

A highly efficient organocatalyst for direct aldol reactions of ketones with aldehydes [corrected].  

PubMed

L-proline amides derived from various chiral beta-amino alcohols that bear substituents with various electron natures at their stereogenic centers are prepared and evaluated for catalyzing the direct Aldol reaction of 4-nitrobenzaldehyde with acetone. Catalysts with strong electron-withdrawing groups are found to exhibit higher catalytic activity and enantioselectivity than their analogues with electron-donating groups. The presence of 2 mol % catalyst 4g significantly catalyzes the direct Aldol reactions of a wide range of aldehydes with acetone and butanone, to give the beta-hydroxy ketones with very high enantioselectivities ranging from 96% to >99% ee. High diastereoselectivity of 95/5 was observed for the anti Aldol product from the reaction of cyclohexanone, and excellent enantioselectivity of 93% ee was provided for anti Aldol product from the reaction of cyclopentanone. PMID:15969611

Tang, Zhuo; Yang, Zhi-Hua; Chen, Xiao-Hua; Cun, Lin-Feng; Mi, Ai-Qiao; Jiang, Yao-Zhong; Gong, Liu-Zhu

2005-06-29

23

Functional ionic liquid from biorenewable materials: synthesis and application as a catalyst in direct aldol reactions  

Microsoft Academic Search

A new room temperature ionic liquid (IL) (2-hydroxyethyl)-trimethyl-ammonium (S)-2-pyrrolidinecarboxylic acid salt ([Choline][Pro]) has been synthesized from biorenewable and nontoxic raw materials (choline chloride and l(?)-proline) in a simple and relative green route. The IL has been demonstrated to be the efficient catalyst of the direct aldol reactions between ketones and aromatic aldehydes in water at room temperature. The aldol products

Suqin Hu; Tao Jiang; Zhaofu Zhang; Anlian Zhu; Buxing Han; Jinliang Song; Ye Xie; Wenjing Li

2007-01-01

24

A closer look at spontaneous mirror symmetry breaking in aldol reactions.  

PubMed

The aldol reaction between acetone and 4-nitrobenzaldehyde run in the nominal absence of any enantioselective catalyst was monitored by chiral HPLC with the aid of an internal standard. The collected data show the presence of a detectable initial enantiomeric excess of the aldol product in the early stages of the reaction in about 50?% of the experiments. Only a small fraction of the reaction contained the non-racemic aldol product after 24?h. This temporary emergence of natural optical activity could be the signature of a coupled reaction network that leads to a spontaneous mirror-symmetry-breaking process, which originates at very low conversions (i.e., strongly depends on events taking place at the very first stages of the process). The reaction is not autocatalytic in the aldol product, which rules out a simple Frank-type reaction network as the source of the observed symmetry breaking. On the other hand, the isolation and characterisation of a double-aldol adduct suggested a reaction network that involved both indirect autocatalysis and indirect mutual inhibition between the enantiomers of the reaction product. PMID:25346447

Valero, Guillem; Ribó, Josep M; Moyano, Albert

2014-12-22

25

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

26

Design of a binaphthyl-based axially chiral amino acid as an organocatalyst for direct asymmetric aldol reactions.  

PubMed

A novel and robust binaphthyl-based amino acid was designed and successfully applied to the direct asymmetric aldol reaction. In some cases, this catalyst leads to higher yields and selectivities than the well-known proline catalyst. For instance, the direct asymmetric aldol reaction of acetone with 4-nitrobenzaldehyde in the presence of the binaphthyl-based amino acid catalyst proceeded smoothly to give the aldol adduct in 82% yield with 95% ee. This catalyst was also found to catalyze effectively the reactions of cyclic or unsymmetrical ketones to give the corresponding aldol adducts with excellent diastereo- and enantioselectivities. PMID:17441057

Kano, Taichi; Tokuda, Osamu; Takai, Jun; Maruoka, Keiji

2006-07-17

27

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

PubMed Central

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

2011-01-01

28

Catalytic asymmetric aldol reactions in aqueous media--a 5 year update.  

PubMed

Asymmetric reactions in water and in aqueous solutions have become an area of fast growing interest recently. Although for a long time neglected as a medium for organic reactions, water has attracted attention as the most widely distributed solvent in the world. Indeed, water is the solvent used by nature for biological chemistry including aldol reactions being essential for glycolysis, gluconeogenesis and related processes. Consequently, artificial catalysts designed and used for aldol reactions in water can be promising for the synthesis of enantiopure molecules and are also important for the understanding of complex chemistry of life. This tutorial review summarizes recent developments in the area of aqueous asymmetric aldol reactions highlighting two fundamental directions--development of water compatible chiral Lewis acids and amine-based organocatalysts. PMID:24150484

Mlynarski, Jacek; Ba?, Sebastian

2014-01-21

29

Synthesis of Non-racemic ?-Hydroxy Phosphonates via Asymmetric Phospho-Aldol Reaction.  

PubMed

It has been more than 50 years since the first phospho-aldol reactions of dialkyl phosphites were reported. These efficient P-C bond-forming reactions have become the cornerstone of methods for the synthesis of ?-hydroxyphosphonates and, by numerous available substitution reactions, the synthesis of other ?- and ?-substituted phosphonates and phosphonic acids. Much of the interest in ?- and ?-substituted phosphonates and phosphonic acids has been stimulated by reports of their biological activity, which is often dependent upon their absolute and relative stereochemistry. In this chapter, we review diastereoselective and enantioselective additions of dialkyl phosphites to aldehydes and ketones, otherwise called the phospho-aldol, Pudovik or Abramov reactions. PMID:25467537

Spilling, Christopher D; Malla, Raj K

2014-12-01

30

Rapid and efficient functionalized ionic liquid-catalyzed aldol condensation reactions associated with microwave irradiation.  

PubMed

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

31

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

32

Zn-proline catalyzed direct aldol reaction in aqueous media.  

PubMed

Zn complexes of proline, lysine and arginine are efficient catalysts for the aldol addition of p-nitrobenzaldehyde and acetone in aqueous medium, giving quantitative yields and enantiomeric excesses up to 56% with 5 mol% of the catalysts at room temperature. PMID:12772917

Darbre, Tamis; Machuqueiro, Miguel

2003-05-01

33

Synthesis of ?-Hydroxy-?-haloesters through Super Silyl Ester Directed SYN-Selective Aldol Reaction  

PubMed Central

Super silyl haloesters including chloro- and bromoacetate were synthesized and utilized for aldol reactions to give SYN-?-hydroxy-?-haloacetates in good yields with high diastereoselectivities. ?-Hydroxy-?-fluoroacetate was obtained by lithiation of super silyl bromofluoroacetate. Sequential Darzens reactions provided CIS-glycidic esters in moderate yields. PMID:24205937

Oda, Susumu

2013-01-01

34

Hydrophobic Substituent Effects on Proline Catalysis of Aldol Reactions in Water  

PubMed Central

Derivatives of 4-hydroxyproline with a series of hydrophobic groups in well-defined orientations have been tested as catalysts for the aldol reactions. All of the modified proline catalysts carry out the intermolecular aldol reaction in water and provide high diastereoselectivity and enantioselectivity. Modified prolines with aromatic groups syn to the carboxylic acid are better catalysts than those with small hydrophobic groups (1a is 43.5 times faster than 1f). Quantum mechanical calculations provide transition structures, TS-1awater and TS-1fwater that support the hypothesis that a stabilizing hydrophobic interaction occurs with 1a. PMID:22500641

Zhao, Qingquan; Lam, Yu-hong; Kheirabadi, Mahboubeh; Xu, Chongsong; Houk, K. N.

2013-01-01

35

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...

36

RUTHENIUM-CATALYZED TANDEM OLEFIN MIGRATION-ALDOL AND MANNICH-TYPE REACTIONS IN IONIC LIQUID.  

EPA Science Inventory

In the presence of a catalytic amount of RuCl2(PPh3)3, a cross-coupling of 3-buten-2-ol with aldehydes and imines was developed via a tandem olefin migration--aldol--Mannich reaction in bmim[PF6]. With In(OAc)3 as a co-catalyst, a-vinylbenzyl alcohol and aldehydes underwent sim...

37

Small peptides catalyze highly enantioselective direct aldol reactions of aldehydes with hydroxyacetone: unprecedented regiocontrol in aqueous media.  

PubMed

[reaction: see text] L-Proline-based small peptides have been developed as efficient catalysts for the asymmetric direct aldol reactions of hydroxyacetone with aldehydes. Chiral 1,4-diols 7, which are disfavored products in similar aldol reactions catalyzed by either aldolases or L-proline, were obtained in high yields and enantioselectivities of up to 96% ee with peptides 3 and 4 in aqueous media. PMID:15200341

Tang, Zhuo; Yang, Zhi-Hua; Cun, Lin-Feng; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong

2004-06-24

38

A NOVEL CHIRAL GALLIUM LEWIS ACID CATALYST WITH SEMI-CROWN LIGAND IN AQUEOUS ASYMMETRIC MUKAIYAMA ALDOL REACTIONS. (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...

39

On the choice of Lewis acids for the Prins reaction; two total syntheses of (±)Civet  

Microsoft Academic Search

While developing new variations of the Prins cyclisation reaction, the effect of the choice of Lewis acid on the outcome of the reaction and the product(s) has been investigated, yielding hitherto unseen dihydropyran products in the Prins cyclisation reaction of homoallylic alcohols, and two new modifications of the reaction: the triflate-trapped Prins adduct and the Mukaiyama–Aldol–silyl-Prins reaction. Two of these

Freda K. Chio; Julie Warne; Damien Gough; Mark Penny; Simon J. Coles; Mike B. Hursthouse; Peter Jones; Lorraine Hassall; Thomas M. McGuire; Adrian P. Dobbs

2011-01-01

40

Discovery of new peptide-based catalysts for the direct asymmetric aldol reaction.  

PubMed

A series of oligo-peptide based catalysts were prepared using Fmoc solid-phase peptide synthesis. It was found that peptides with N-terminal proline residues catalyzed an aldol reaction yielding enantiomeric enriched product. Peptide H-Pro-Glu-Leu-Phe-OH catalyzed the reaction with good activity and moderate enantioselectivity (66% ee). Furthermore, it was shown that an acidic side chain and/or C-termini are essential to catalysis. PMID:12852940

Kofoed, Jacob; Nielsen, John; Reymond, Jean-Louis

2003-08-01

41

Solvent-Induced Reversal of Activities between Two Closely Related Heterogeneous Catalysts in the Aldol Reaction  

SciTech Connect

The relative rates of the aldol reaction catalyzed by supported primary and secondary amines can be inverted by 2 orders of magnitude, depending on the use of hexane or water as a solvent. Our analyses suggest that this dramatic shift in the catalytic behavior of the supported amines does not involve differences in reaction mechanism, but is caused by activation of imine to enamine equilibria and stabilization of iminium species. The effects of solvent polarity and acidity were found to be important to the performance of the catalytic reaction. This study highlights the critical role of solvent in multicomponent heterogeneous catalytic processes.

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

2013-01-11

42

Constrained beta-proline analogues in organocatalytic aldol reactions: the influence of acid geometry.  

PubMed

7-Azabicyclo[2.2.1]heptane-2-carboxylic acid 11 was prepared in enantiopure form, and its catalytic potential in the direct aldol reaction between acetone and 4-nitrobenzaldehyde was assessed. The bicyclic system was found to be more selective than its monocyclic analogue beta-proline 5b. A comparative density functional theory study of proline 1, beta-proline 5b, and 11 in the latter reaction revealed the origin of the improved enantioselectivity of 11 over 5b. The geometry of the carboxylic acid group in the transition states, which depended critically on pyrrolidine ring conformation, was found to play a key role. PMID:19485343

Armstrong, Alan; Bhonoah, Yunas; White, Andrew J P

2009-07-17

43

The effect of the hydrophobic environment on the retro-aldol reaction: Comparison to a computationally-designed enzyme  

PubMed Central

Recent work on a computationally-designed retroaldolase RA-61 suggested that most of the rate-acceleration brought about by this enzyme was due to non-specific interactions with the aromatic substrate. To provide a benchmark for the role of non-specific interactions in this system, we measured the second-order rate constant for the amine-catalysed retro-aldol reaction of methodol in the presence of non-specific hydrophobic pockets such as micelles. We found that a simple micellar system, that consists of a positively-charged surfactant and a long-chain amine, can accelerate the retro-aldol reaction of methodol by 9,500-fold. This effect rivals the 105-fold rate acceleration of RA-61. Similar results were obtained with BSA used as the catalyst, implying that the retro-aldol reaction of methodol can be greatly accelerated by non-specific hydrophobic pockets that contain an amino group. PMID:24189834

Schmidt, Joshua; Ehasz, Clayton; Epperson, Michael; Klas, Kimberly; Wyatt, Justin; Hennig, Mirko

2014-01-01

44

Diastereoselectivity in the Lewis acid mediated aldol reaction of chiral ?, ?-epoxyaldehydes with a ketene silyl acetal  

Microsoft Academic Search

The Lewis acid mediated aldol reaction of chiral a, ß-cis andtrans epoxyaldehydes1 and2 withtert-butyl ketene silyl acetal proceeds mainly withanti diastereofacial preference. The best results were obtained forcis epoxyaldehyde1 in the presence of catalytic amounts of BiCl3·1.5 eq. ZnI2 (anti:syn ~ 13:1), whereas the poorest stereoselectivity was observed when an excess of LiClO4 was used (anti:syn ~ 1:1). The more

E. Fontaine; M. Baltas; J.-M. Escudier; L. Gorrichon

1996-01-01

45

Interfacial catalysis of aldol reactions by prolinamide surfactants in reverse micelles.  

PubMed

L-Proline and their derivatives are among the most important class of organic catalysts. Three prolinamide surfactants were designed and synthesized. Although the surfactants carried identical catalytic groups, their headgroups contained different functionalities that affected their ability to self-assemble under reverse micelle conditions and hydrogen-bond with the reactants. The surfactant with a zwitterionic headgroup capable of strong aggregation was found to have the highest activity. The self-association of the surfactants played critical roles in the enhanced activity. The location of the catalytic groups at the surfactant/polar solvent interface also endowed unusual selectivity in the catalyzed aldol reactions. PMID:25387355

Arivalagan, Premkumar Rathinam; Zhao, Yan

2015-01-21

46

From allylic alcohols to aldols by using iron carbonyls as catalysts: computational study on a novel tandem isomerization-aldolization reaction.  

PubMed

The tandem isomerization-aldolization reaction between allyl alcohol and formaldehyde mediated by [Fe(CO)3] was studied with the density functional B3LYP method. Starting from the key [(enol)Fe(CO)3] complex, several reaction paths for the reaction with formaldehyde were explored. The results show that the most favorable reaction path involves first an enol/allyl alcohol ligand-exchange process followed by direct condensation of formaldehyde with the free enol. During this process, formation of the new C-C bond takes place simultaneously with a proton transfer between the enol and the aldehyde. Therefore, the role of [Fe(CO)3] is to catalyze the allyl alcohol to enol isomerization affording the free enol, which adds to the aldehyde in a carbonyl-ene type reaction. Similar results were obtained for the reaction between allyl alcohol and acetaldehyde. PMID:15472940

Branchadell, Vicenç; Crévisy, Christophe; Grée, René

2004-11-01

47

Direct asymmetric aldol reaction of aryl ketones with aryl aldehydes catalyzed by chiral BINOL-derived zincate catalyst.  

PubMed

Direct asymmetric aldol reaction of aryl ketones with aryl aldehydes catalyzed by chiral metal complex is reported for the first time herein. Two novel semicrown chiral ligands 1a and 1b were synthesized from (S)- and (R)-BINOL, respectively, and then employed to catalyze the direct asymmetric aldol addition of aryl ketones to aryl aldehydes. Introduced with 2.0 equiv of diethylzinc, 1b had higher enantioselectivity than 1a. Up to 97% yield and up to 80% enantioselectivity were achieved. PMID:18700798

Li, Hong; Da, Chao-Shan; Xiao, Yu-Hua; Li, Xiao; Su, Ya-Ning

2008-09-19

48

Noncovalently supported heterogeneous chiral amine catalysts for asymmetric direct aldol and Michael addition reactions.  

PubMed

A new strategy for the immobilization of asymmetric organocatalysts by combining polystyrene (PS)/sulfonic acids and chiral amines in situ through acid-base interactions is presented. The PS/sulfonic acids play a dual role as catalyst anchors and modulators for activity and stereoselectivity. Different types of polymeric sulfonic acids were examined and 1% divinylbenzene (DVB) cross-linked PS/sulfonic acid 1 e with a medium loading of sulfonic acid moieties was found to be the optimal support. Furthermore, the noncovalency of this system allows combinatorial screening of optimal catalysts for the targeted reactions. In this regard, highly efficient and enantioselective heterogeneous catalysts were identified for the asymmetric direct aldol and Michael addition reactions. The catalysts could be easily recovered by filtration and reused for six cycles with similar stereoselectivity but slightly decreased activity. Significantly, the deactivated catalysts could be regenerated following an acidic washing/amine recharging procedure. PMID:18000996

Luo, Sanzhong; Li, Jiuyuan; Zhang, Long; Xu, Hui; Cheng, Jin-Pei

2008-01-01

49

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

50

Design of a small-molecule catalyst using intramolecular cation-pi interactions for enantioselective Diels-Alder and Mukaiyama-Michael reactions: L-DOPA-derived monopeptide.Cu(II) complex.  

PubMed

[reaction: see text] We have designed a small-molecule artificial metalloenzyme that is prepared in situ from Cu(OTf)(2) or Cu(NTf(2))(2) (1.0 equiv) and l-DOPA-derived monopeptide (1.1 equiv). This catalyst (2-10 mol %) is highly effective for the enantioselective Diels-Alder (DA) and Mukaiyama-Michael (MM) reactions with alpha,beta-unsaturated 1-acyl-3,5-dimethylpyrazoles. The present results demonstrate that cation-pi interactions may be available for controlling the conformation of sidearms of chiral ligands, and monopeptides are readily tunable ligands that include only one chiral center. PMID:16623585

Ishihara, Kazuaki; Fushimi, Makoto

2006-04-27

51

On the mechanism of Lewis base catalyzed aldol addition reactions: kinetic and spectroscopic investigations using rapid-injection NMR.  

PubMed

The mechanistic foundations of the Lewis base catalyzed aldol addition reactions have been investigated. From a combination of low-temperature spectroscopic studies ((29)Si and (31)P NMR) and kinetic analyses using a rapid-injection NMR apparatus (RINMR), a correlation of the ground states and transition structures for the aldolization reactions has been formulated. The aldol addition of the tert-butylsilyl ketene acetal of tert-butyl propanoate with 1-naphthaldehyde is efficiently catalyzed by a combination of silicon tetrachloride and chiral phosphoramide Lewis bases. The rates and selectivities of the aldol additions are highly dependent on the structure of the Lewis bases: bisphosphoramides give the highest rate and selectivity, whereas a related monophosphoramide reacts slowly and with low selectivity. The monophosphoramide shows no nonlinear behavior. All of the additions show a first-order kinetic dependence on silyl ketene acetal and 1-naphthaldehyde and a zeroth-order dependence on silicon tetrachloride. The kinetic order in catalyst is structure dependent and is either half-, two-thirds-, or first-order. All of the phosphoramides are saturated with silicon tetrachloride in some form, and the resting-state species are mixtures of monomeric and dimeric, pentacoordinate cationic, or hexacoordinate neutral complexes. These data allow the formulation of a unified mechanistic scheme based on the postulate of a common reactive intermediate for all catalysts. PMID:19642696

Denmark, Scott E; Eklov, Brian M; Yao, Peter J; Eastgate, Martin D

2009-08-26

52

Promiscuous protease-catalyzed aldol reactions: a facile biocatalytic protocol for carbon-carbon bond formation in aqueous media.  

PubMed

Several proteases, especially pepsin, were observed to directly catalyze asymmetric aldol reactions. Pepsin, which displays well-documented proteolytic activity under acidic conditions, exhibited distinct catalytic activity in a crossed aldol reaction between acetone and 4-nitrobenzaldehyde with high yield and moderate enantioselectivity. Fluorescence experiments indicated that under neutral pH conditions, pepsin maintains its native conformation and that the natural structure plays an important role in biocatalytic promiscuity. Moreover, no significant loss of enantioselectivity was found even after four cycles of catalyst recycling, showing the high stability of pepsin under the selected aqueous reaction conditions. This case of biocatalytic promiscuity not only expands the application of proteases to new chemical transformations, but also could be developed into a potentially valuable method for green organic synthesis. PMID:20959128

Li, Chao; Zhou, Yu-Jie; Wang, Na; Feng, Xing-Wen; Li, Kun; Yu, Xiao-Qi

2010-12-01

53

Construction of contiguous tetrasubstituted chiral carbon stereocenters via direct catalytic asymmetric aldol and Mannich-type reactions.  

PubMed

Catalytic asymmetric synthesis of unnatural amino acids with vicinal tetrasubstituted chiral carbon stereocenters is described. In the first part, direct catalytic asymmetric aldol reaction of simple non-activated ketone electrophiles with ?-substituted ?-isothiocyanato ester donors was realized. A Mg/Schiff base catalyst promoted the aldol reaction, and ?-amino-?-hydroxy esters were obtained in up to 98% ee and 98:2 d.r. In the second part, the Mg/Schiff base catalyst and a Sr/Schiff base catalyst were utilized for stereodivergent direct asymmetric Mannich-type reaction of ketimines. The Mg/Schiff base catalyst gave syn-?,?-diamino esters, while the Sr/Schiff base catalyst produced anti-?,?-diamino esters in good to high enantioselectivity, up to 97% ee. PMID:21898777

Matsunaga, Shigeki; Yoshino, Tatsuhiko

2011-09-01

54

Direct Access to 6/5/7/5- and 6/7/5/5-Fused Tetracyclic Triterpenoids via Divergent Transannular Aldol Reaction of Lanosterol-Derived Diketone  

PubMed Central

In an effort to access biologically relevant chemical space, a complex natural product-derived non-symmetrical diketone was prepared as a substrate for divergent transannular aldol reactions. The use of common aldol conditions resulted in predominant syn-addition via pathway a, while the use of alumina provided access to the anti-adduct. Screening of a range of Lewis acids of varying strength unexpectedly resulted in the formation of aldol products with 6/7/5/5-fused molecular skeleton via pathway b. PMID:24161022

Ignatenko, Vasily A.; Han, Yong

2013-01-01

55

Proline-beta(3)-amino-ester dipeptides as efficient catalysts for enantioselective direct aldol reaction in aqueous medium.  

PubMed

Dipeptides obtained from l-proline and beta(3)-l-amino acids are reported to catalyze enantioselective direct aldol reaction in aqueous medium, leading to significant anti:syn diastereomeric ratios and enantiomeric excesses. The simple introduction of a polar substituent at the C-2 position of the beta(3)-l-amino acid was also found to enhance appreciably both diastereo- and enantioselectivity of the catalyst. PMID:19938836

De Nisco, Mauro; Pedatella, Silvana; Ullah, Hidayat; Zaidi, Javid H; Naviglio, Daniele; Ozdamar, Ozgür; Caputo, Romualdo

2009-12-18

56

Expedient synthesis of C-aryl carbohydrates by consecutive biocatalytic benzoin and aldol reactions.  

PubMed

The introduction of aromatic residues connected by a C?C bond into the non-reducing end of carbohydrates is highly significant for the development of innovative structures with improved binding affinity and selectivity (e.g., C?aril-sLex). In this work, an expedient asymmetric "de novo" synthetic route to new aryl carbohydrate derivatives based on two sequential stereoselectively biocatalytic carboligation reactions is presented. First, the benzoin reaction of aromatic aldehydes to dimethoxyacetaldehyde is conducted, catalyzed by benzaldehyde lyase from Pseudomonas fluorescens biovar I. Then, the ?-hydroxyketones formed are reduced by using NaBH4 yielding the anti diol. After acetal hydrolysis, the aldol addition of dihydroxyacetone, hydroxyacetone, or glycolaldehyde catalyzed by the stereocomplementary D-fructose-6-phosphate aldolase and L-rhamnulose-1-phosphate aldolase is performed. Both aldolases accept unphosphorylated donor substrates, avoiding the need of handling the phosphate group that the dihydroxyacetone phosphate-dependent aldolases require. In this way, 6-C-aryl-L-sorbose, 6-C-aryl-L-fructose, 6-C-aryl-L-tagatose, and 5-C-aryl-L-xylose derivatives are prepared by using this methodology. PMID:25640727

Hernández, Karel; Parella, Teodor; Joglar, Jesús; Bujons, Jordi; Pohl, Martina; Clapés, Pere

2015-02-16

57

Highly Stereoselective and Scalable anti-Aldol Reactions using N-(p-dodecylphenylsulfonyl)-2-Pyrrolidinecarboxamide: Scope and Origins of Stereoselectivities  

PubMed Central

A highly enantio- and diastereoselective anti-aldol process (up to >99% ee, >99:1 dr) catalyzed by a proline mimetic – N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide – has been developed. Catalyst loading as low as 2 mol% can be employed. Use of industry-friendly solvents for this transformation as well as neat reaction conditions have been demonstrated. The scope of this transformation on a range of aldehydes and ketones is explored. Density Functional Theory computations reveal that the origins of enhanced diastereoselectivity is due to the presence of non-classical hydrogen bonds between the sulfonamide, the electrophile and the catalyst enamine that favor the major Anti-Re aldol TS in the Houk-List model. PMID:20932013

Yang, Hua; Mahapatra, Subham; Cheong, Paul Ha-Yeon; Carter, Rich G.

2010-01-01

58

The mimic of type II aldolases chemistry: asymmetric synthesis of beta-hydroxy ketones by direct aldol reaction.  

PubMed

An efficient direct aldol reaction has been developed for the synthesis of chiral beta-hydroxy ketone using a combination of C(1)-symmetric chiral prolinamides based on o-phenylenediamine and zinc triflate as catalyst. The reaction was convenient to carry out in aqueous media with up to 98% chemical yields and up to 94% ee values. The current strategy can be regarded as the analogue of aldolase type II, which suggests a new pathway for the designing of new organocatalysts. PMID:20572810

Lu, Zhijin; Mei, Haibo; Han, Jianlin; Pan, Yi

2010-08-01

59

Macrophomate synthase: QM/MM simulations address the Diels-Alder versus Michael-Aldol reaction mechanism.  

PubMed

Macrophomate synthase (MPS) of the phytopathogenic fungus Macrophoma commelinae catalyzes the transformation of 2-pyrone derivatives to the corresponding benzoate analogues. The transformation proceeds through three separate chemical reactions, including decarboxylation of oxalacetate to produce pyruvate enolate, two C-C bond formations between 2-pyrone and pyruvate enolate that form a bicyclic intermediate, and final decarboxylation with concomitant dehydration. Although some evidence suggests that the second step of the reaction catalyzed by MPS is a Diels-Alder reaction, definite proof that the C-C bond formations occur via a concerted mechanism is still required. An alternative route for formation of the C-C bonds is a stepwise Michael-aldol reaction. In this work, mixed quantum and molecular mechanics (QM/MM) combined with Monte Carlo simulations and free-energy perturbation (FEP) calculations were performed to investigate the relative stabilities of the transition states (TS) for both reaction mechanisms. The key results are that the Diels-Alder TS model is 17.7 and 12.1 kcal/mol less stable than the Michael and aldol TSs in the stepwise route, respectively. Therefore, this work indicates that the Michael-aldol mechanism is the route used by MPS to catalyze the second step of the overall transformation, and that the enzyme is not a natural Diels-Alderase, as claimed by Ose and co-workers (Nature 2003, 422, 185-189; Acta Crystallogr. 2004, D60, 1187-1197). A modified link-atom treatment for the bonds at the QM/MM interface is also presented. PMID:15755179

Guimarães, Cristiano Ruch Werneck; Udier-Blagovi?, Marina; Jorgensen, William L

2005-03-16

60

Theoretical elucidation on the regio-, diastereo-, and enantio-selectivities of chiral primary-tertiary diamine catalyst for asymmetric direct aldol reactions of aliphatic ketones.  

PubMed

The asymmetric direct aldol reactions of aliphatic ketones (acetone, butanone, and cyclohexanone) with 4-nitrobenzaldehyde catalyzed by a chiral primary-tertiary diamine catalyst (trans-N,N-dimethyl diaminocyclohexane) have been investigated by performing density functional theory calculations to rationalize the experimentally observed stereoselectivities. Focused on the crucial C-C bond-forming steps, we located several low-lying transition states and predicted their relative stabilities. The calculated results demonstrate that the catalytic direct aldol reactions of acetone favors the (S)-enantiomer and that butanone prefers the branched syn-selective product, while cyclohexanone yields predominantly the opposite anti-selective product. The theoretical results are in good agreement with the experimental findings and provide a reasonable explanation for the high enantioselectivity and diastereoselectivity, as well as regioselectivity, of the aldol reactions under consideration. PMID:22642509

Sun, Xiangting; Zhu, Rongxiu; Gao, Jun; Zhang, Dongju; Feng, Dacheng

2012-07-01

61

Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis.  

PubMed

The use of protonated l-prolinethioamide instead of the free base derivative 1 as the organocatalyst for the direct aldol addition has a profound and appreciable effect on both the yield and the stereochemical course of the reaction. 4-Nitrobenzaldehyde (2) reacts with acetone in the presence of the protonated catalyst 1.TFA, affording aldol product 3 with a yield up to 99% and an ee up to 98%. The catalyst loading can be lowered to 2.5 mol %. More than 20 different acids were investigated as an additive, and its role as cocatalyst has been discussed. Furthermore, reactions of l-prolinethioamide salts with acetone have been monitored using ESI-MS and 1H NMR techniques, giving insight into the mechanism of the direct aldol reaction. The presumed formation of the iminium salt 10 has been unambiguously confirmed. PMID:17253817

Gryko, Dorota; Zimnicka, Magdalena; Lipi?ski, Rados?aw

2007-02-01

62

Antibody-catalyzed decarboxylation and aldol reactions using a primary amine molecule as a functionalized small nonprotein component.  

PubMed

Catalytic antibody 27C1 bears binding sites for both a substrate- and a functionalized small nonprotein component in the active site. We investigated the possibility of exploiting imine and enamine intermediates using a primary amine molecule into the active site of antibody 27C1. The antibody catalyzed ?-keto acid decarboxylation with a rate enhancement (kcat/Km/kuncat) of 140,000, as well as highly regioselective cross-aldol reactions of ketones and p-nitrobenzaldehyde. These studies provide new strategies for the generation of catalytic antibodies possessing binding sites for functionalized components. PMID:24094435

Ishikawa, Fumihiro; Uno, Kouki; Nishikawa, Masao; Tsumuraya, Takeshi; Fujii, Ikuo

2013-11-15

63

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

64

Synthesis of chiral 3-substituted phthalides by a sequential organocatalytic enantioselective aldol-lactonization reaction. Three-step synthesis of (S)-(-)-3-butylphthalide.  

PubMed

The development of efficient methods for the facile construction of important molecular frameworks is an important goal in organic synthesis. Chiral 3-substituted phthalides are widely distributed in a large collection of natural products with broad, potent, and potentially path-pointing biological activities. In this investigation, we have uncovered an unprecedented organocatalytic asymmetric aldol-lactonization reaction of 2-formylbenzoic esters with ketones/aldehydes for convenient construction of the enantioenriched "privileged" scaffold. As a result of the sensitive nature of substrate structures of an organocatalytic enantioselective aldol reaction, after extensive optimization of reaction conditions, catalyst L-prolinamide alcohol IV is identified as the best promoter. Interestingly, it is found that in this reaction, addition of an acid additive PhCO(2)H can significantly enhance reaction efficiency with use of only as low as 2.5 mol % IV for the process. Moreover, due to the sensitivity of reaction conditions toward a sequential aldol-lactonization process without affecting enantioselectivity and racemization, it is essential to remove the catalyst for the subsequent facile lactonization reaction in the presence of K(2)CO(3). The aldol-lactonization processes serve as a powerful approach to the preparation of synthetically and biologically important 3-substituted phthalides with a high level of enantioselectivities. A 3-step catalytic asymmetric synthesis of the natural product of 3-butylphthalide is reported. PMID:20000698

Zhang, Haoyi; Zhang, Shilei; Liu, Lu; Luo, Guangshun; Duan, Wenhu; Wang, Wei

2010-01-15

65

A highly stereoselective samarium diiodide-promoted aldol reaction with 1'-phenylseleno-2'-keto nucleosides. Synthesis of 1'alpha-branched uridine derivatives.  

PubMed

Since 1'-branched nucleosides are biologically important targets in medicinal chemistry, more efficient methods for preparing them are required. The 1'alpha-branched uridine derivatives were successfully synthesized via a samarium diiodide (SmI(2))-promoted aldol reaction. Treatment of the 1'alpha-phenylseleno-2'-ketouridine derivative 6, readily prepared from uridine, with SmI(2) at -78 degrees C in THF reductively cleaved the anomeric Se-C bond to generate the corresponding samarium enolate, which was highly stereoselectively condensed with aldehydes, such as PhCHO, MeCHO, i-PrCHO, or (CH(2)O)(n)(), to give the corresponding 1'alpha-1' 'S-branched products 12a-d. This is the first time an enolate has been generated by reductively cleaving a C-Se bond. The highly selective stereochemical results suggest that the aldol reaction proceeds via a chelation-controlled transition state. When an excess of aldehyde was used and the reaction mixture was gradually warmed, the tandem aldol-Tishchenko reaction proceeded to give the "arabino-type" nucleosides 14a-c, having a 2'-"up" hydroxyl and 1'alpha-1' 'S-branched chain. 1'alpha-Hydroxymethyluridine (21), which is the uracil version of the antitumor antibiotic angustmycin C, was synthesized from the aldol reaction product 10. PMID:12398493

Kodama, Tetsuya; Shuto, Satoshi; Ichikawa, Satoshi; Matsuda, Akira

2002-11-01

66

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

67

Three-component coupling reactions of silylglyoxylates, alkynes, and aldehydes: a chemoselective one-step glycolate aldol construction.  

PubMed

A single-pot three-component coupling reaction of silylglyoxylates (1), terminal alkynes, and aldehydes in the presence of ZnI2 and Et3N is presented. The products of the reaction, densely functionalized silyl-protected glycolate aldols (2), can be converted to the corresponding acetonides (3) in a one-pot deprotection/ketalization sequence. A variety of terminal alkynes and aldehydes can be successfully employed to give a range of highly functionalized, fully protected 1,2-diols in good yields and moderate diastereoselectivities. Mechanistic experiments suggest that the zinc acetylide reacts with the silylgyloxylate (1) in a chemoselective manner. Using an unoptimized (+)-N-methylephedrine and Zn(OTf)2 system, silyl-deprotected adduct 2 was formed in 64% ee and 89:11 dr. PMID:15853312

Nicewicz, David A; Johnson, Jeffrey S

2005-05-01

68

Aldol reactions of the trans-o-hydroxybenzylidenepyruvate hydratase-aldolase (tHBP-HA) from Pseudomonas fluorescens N3.  

PubMed

In this paper, a recombinant trans-o-hydroxybenzylidenepyruvate hydratase-aldolase (tHBP-HA) of Pseudomonas fluorescens N3 was used as a new catalyst for aldol condensation reactions. The reaction of some aldehydes with a different electronic activation catalyzed by tHBP-HA is presented and discussed together with some hints on the product structure. The enzyme is strictly pyruvate-dependent but uses different aldehydes as acceptors. The structure of the products is highly dependent on the electronic characteristics of the aldehyde. The results are interesting for both their synthetic importance and the mechanism of the formation of the products. Not only the products obtained and the recognition power are reported, but also some characteristics of its mechanism are analyzed. The results clearly show that the enzyme is efficiently prepared, purified, and stored, that it recognizes many different substrates, and that the products depend on the substrate electronic nature. PMID:23722948

Sello, Guido; Di Gennaro, Patrizia

2013-08-01

69

Poor enantioselectivity of the direct aldol reaction catalyzed by (S,S)-proline dipeptide: A density functional study  

NASA Astrophysics Data System (ADS)

Density functional theory calculations were performed to study the stereo-controlling step of the direct aldol reaction between acetone and 4-nitrobenzaldehyde catalyzed by (S,S)-proline dipeptide. Four transition state structures have been determined using B3LYP functional with the 6-31G* basis set, corresponding to the anti and syn arrangements of the methylene moiety with respect to the carbonyl group in enamine intermediate, and to the si and re attacks to the aldehyde carbonyl carbon, respectively. Solvent effects of DMSO on the stereo-controlling step were investigated with Onsager model. The energy results of the transition states reveal the origin of poor enantioselectivity for the reaction.0

Fan, Jian-Fen; Wu, Li-Fen; Tao, Fu-Ming

70

Origins of opposite syn-anti diastereoselectivities in primary and secondary amino acid-catalyzed intermolecular aldol reactions involving unmodified alpha-hydroxyketones.  

PubMed

The effects of different amino acid catalysts on the stereoselectivity of the direct intermolecular aldol reactions between alpha-hydroxyketones and isobutyraldehyde or 4-nitrobenzaldehyde have been studied with the aid of density functional theory methods. The transition states of the crucial C-C bond-forming step with the enamine intermediate addition to the aldehyde for the proline and threonine-catalyzed asymmetric aldol reactions are reported. B3LYP/6-31+G** calculations provide a good explanation for the opposite syn vs anti diastereoselectivity of these two kinds of amino acid catalysts (anti-selectivity for the secondary cyclic amino acids proline, syn-selectivity for the acyclic primary amino acids like threonine). Calculated and observed diastereomeric ratio and enantiomeric excess values are in good agreement. PMID:18549281

Fu, Aiping; Li, Hongliang; Yuan, Shuping; Si, Hongzong; Duan, Yunbo

2008-07-18

71

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

72

Total Synthesis of Auripyrone B Using a Non-Aldol Aldol-Cuprate Opening Process  

PubMed Central

A non-aldol aldol-cuprate opening generates the polypropionate 11 from the epoxy ether 14 in 8 steps as a single diastereomer. A highly stereoselective aldol reaction of 8 with 9 gives the aldol product 7 in high yield and excellent diastereoselectivity, due to double stereodifferentiation. This compound was used for an efficient synthesis of the natural product auripyrone B 2, in only 20 steps and 8% overall yield from 14, using a late stage spiroketalization onto a stable hemiketal as the final key step. PMID:20499854

Jung, Michael E.; Chaumontet, Manon; Salehi-Rad, Ramin

2012-01-01

73

Synthesis of C13-C25 fragment of 24-demethylbafilomycin C(1) via diastereoselective aldol reactions of a ketone boron enolate as the key step.  

PubMed

An efficient synthesis of the C13-C25 fragment is described for 24-demethylbafilomycin C1, a new member of the plecomacrolide family isolated from fermentation broth of Streptomyces sp. CS which is a commensal microbe of Maytenus hookeri. The targeted C13-C25 fragment possesses five oxygenated and three methyl-substituted stereogenic centers. It is obtained through formation of the C17-C18 syn aldol by using an ethyl ketone boron enolate with diastereomeric ratios of 95:5 and 83:17, respectively, for the chiral aldehydes substituted with acetoxy and methoxyacetoxy groups at C15. The results confirm the observation that the stereochemistry at C22 of the ketone is determinant to the diastereoselectivity of the aldol reaction. The synthesized C13-C25 fragment having a methoxyacetoxy group at C15 is considered as a useful precursor for construction of the 16-membered ring lactone of 24-demethylbafilomycin C1 through an aldol condensation of the methoxyacetate followed by formation of the C12-C13 double bond via a diene-ene RCM reaction. PMID:17518500

Guan, Yucui; Wu, Jinlong; Sun, Liang; Dai, Wei-Min

2007-06-22

74

The tandem chain extension aldol reaction used for synthesis of ketomethylene tripeptidomimetics targeting hPEPT1  

PubMed Central

The rationale for targeting the human di-/tripeptide transporter hPEPT1 for oral drug delivery has been well established by several drug and prodrug cases. The aim of this study was to synthesize novel ketomethylene modified tripeptidomimetics and to investigate their binding affinity for hPEPT1. Three related tripeptidomimetics of the structure H-Phe-?[COCH2]-Ser(Bz)-Xaa-OH were synthesized applying the tandem chain extension aldol reaction, where amino acid derived ?-keto imides were stereoselectively converted to ?-substituted ?-keto imides. In addition, three corresponding tripeptides, composed of amide bonds, were synthesized for comparison of binding affinities. The six investigated compounds were all defined as high affinity ligands (Ki-values <0.5 mM) for hPEPT1 by measuring the concentration dependent inhibition of apical [14C]Gly-Sar uptake in Caco-2 cells. Consequently, the ketomethylene replacement for the natural amide bond and ?-side chain modifications appears to offer a promising strategy to modify tripeptidic structures while maintaining a high affinity for hPEPT1. PMID:21703856

Thorn, Karina; Nielsen, Carsten Uhd; Jakobsen, Palle; Steffansen, Bente; Zercher, Charles K.; Begtrup, Mikael

2011-01-01

75

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

76

The Aldol Addition and Condensation: The Effect of Conditions on Reaction Pathway  

ERIC Educational Resources Information Center

The reaction of a ketone and an aldehyde in aqueous Na[subscript 2]CO[subscript 2] is described. This experiment is performed in the absence of strong bases or organic solvents and offers the opportunity for students to observe the critical role that reaction temperature and base strength have in determining the product of the base-mediated…

Crouch, R. David; Richardson, Amie; Howard, Jessica L.; Harker, Rebecca L.; Barker, Kathryn H.

2007-01-01

77

Aldol reactions catalyzed by L-proline functionalized polymeric nanoreactors in water.  

PubMed

The use of functional core-shell micelles as asymmetric catalytic nanoreactors for organic reactions in water is presented. An unprecedented increase in rate of reaction was achieved, which is proposed to be associated with the ability of the nanostructures to effectively concentrate the reagents in the catalytically active micelle core. PMID:22911135

Lu, Annhelen; Cotanda, Pepa; Patterson, Joseph P; Longbottom, Deborah A; O'Reilly, Rachel K

2012-10-01

78

Towards organo-click chemistry: development of organocatalytic multicomponent reactions through combinations of aldol, Wittig, Knoevenagel, Michael, Diels-Alder and Huisgen cycloaddition reactions.  

PubMed

Here we report on our studies on combinations of amino acids and copper(I) for catalyzing multicomponent reactions (MCRs). We aimed to prepare both diene and dienophiles simultaneously, under very mild and environmentally friendly conditions, thus giving the constituents for a stereocontrolled Diels-Alder reaction, which in turn yields compounds 4 to 8. A diversity-oriented synthesis of polysubstituted spirotriones 4 to 6 were assembled from simple substrates like 1-(triphenylphosphanylidene)-propan-2-one, two aldehydes, and cyclic-1,3-diketones through Wittig/Knoevenagel/Diels-Alder and aldol/Knoevenagel/Diels-Alder reaction sequences in one pot under stereospecific organocatalysis. Chemical diversity libraries of polysubstituted spirotrione-1,2,3-traizoles 8 were assembled from simple substrates by means of Wittig/Knoevenagel/Diels-Alder/Huisgen cycloaddition reaction sequences in one pot under stereospecific organo/Cu(I) catalysis. Functionalized dispirolactones such as 6 are biologically active antioxidants and radical scavengers, and spirotrione-1,2,3-traizoles 8 have found wide applications in chemistry, biology, and materials science. Experimentally simple and environmentally friendly, organocatalytic, asymmetric four-component Diels-Alder (AFCDA) reactions of 1-(triphenylphosphanylidene)- propan-2-one, two different aldehydes, and cyclic-1,3-diketones produced diastereospecific and highly enantioselective substituted spirotriones 4 by means of a Wittig/Knoevenagel/Diels-Alder reaction sequence in one pot. Additionally we have developed an organocatalytic, asymmetric three-component Michael (ATCM) reaction of 1-(triphenylphosphanylidene)-propan-2-one, aldehyde, and cyclic-1,3-diketones that produced Michael adducts 15, 16 through a Wittig/Michael reaction sequence in a highly enantioselective one-pot process. PMID:15390208

Ramachary, Dhevalapally B; Barbas, Carlos F

2004-10-25

79

Regioselective aldol condensations of a cholestanone-derived dialdehyde: new twists on a classic reaction  

E-print Network

reaction Scott A. Snyder and E. J. Corey* Department of Chemistry and Chemical Biology, Harvard University in Scheme 1, the test substrate 7 was pre- pared from commercially available 5a-cholestan-3-one (6) via these operations appear routine, it is worth noting that in the initial step the C-2 hydroxyl was installed

Snyder, Scott A.

80

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

81

Chemoselective Functionalization of Carboxylic Acid and Phenol Containing Natural Products and the Development and Use of a Nucleophile Catalyzed Michael Aldol Lactonization Process  

E-print Network

catalyzed aldol lactonization (NCAL) reaction for synthesizing highly substituted cyclopentane fused beta-lactones, we developed a nucleophile catalyzed, tandem Michael aldol lactonization (NCMAL) reaction. Herein, we show the synthetic utility...

McFarlin, Rae

2013-05-02

82

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) an efficient homogeneous catalyst for aldol condensation reactions. Study of the catalyst recovery and reusability using CO 2  

Microsoft Academic Search

In this work it was shown that TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), a cheap and commercially available guanidine base, efficiently catalyzes aldol condensation reactions yielding interesting products for pharmacological and fragrance industries. This methodology works under solvent-less conditions and affords with very good conversions the corresponding products. Moreover, a simple and effective separation protocol using the CO2 fixation was employed. The catalyst could

Iuliana Cota; Francisco Medina; Jesús E. Sueiras; Didier Tichit

2011-01-01

83

The first synthesis of herbicidin B, a tricyclic-sugar adenine nucleoside antibiotic, using samarium diiodide-promoted aldol-type C-glycosidation reaction as a key-step.  

PubMed

A first total synthesis of the nucleoside antibiotic herbicidin B (1) was achieved in which a novel aldol-type C-glycosidation reaction promoted by samarium diiodide (SmI2) was used as a key step. Construction of the desired stereochemistry of the tricyclic-sugar moiety was successfully achieved by conformational restriction strategy based on repulsion between adjacent bulky protecting groups on the pyranose ring. PMID:10780359

Shuto, S; Ichikawa, S; Matsuda, A

1999-01-01

84

Dynamic kinetic asymmetric transformations of ?-stereogenic ?-ketoesters by direct aldolization.  

PubMed

Dynamic kinetic asymmetric transformations (DyKAT) of racemic ?-bromo-?-keto esters by direct aldolization of nitromethane and acetone provide access to fully substituted ?-glycolic acid derivatives bearing a ?-stereocenter. The aldol adducts are obtained in excellent yield with high relative and absolute stereocontrol under mild reaction conditions. Mechanistic studies determined that the reactions proceed through a facile catalyst-mediated racemization of the ?-bromo-?-keto esters under a DyKAT Type I manifold. PMID:24222195

Corbett, Michael T; Johnson, Jeffrey S

2014-01-01

85

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

PubMed Central

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, Sh?; Ueno, Masaharu; Saito, Susumu; Mizuki, Yumiko; Ishitani, Haruro; Yamashita, Yasuhiro

2004-01-01

86

Aqueous aldol catalysis by a nicotine metabolite.  

PubMed

Nornicotine, an endogenous tobacco alkaloid and minor nicotine metabolite, can catalyze aldol reactions at physiological pH. Catalysis appears to be due to a covalent enamine mechanism, an unprecedented reaction with small organic molecule catalysts in aqueous buffer. Kinetic parameters for nornicotine as well as other related alkaloids were measured and demonstrate that both the pyrrolidine and pyridine rings are critical for optimal catalysis. Substrate compatibility of this catalyst and its implications in vivo are discussed. PMID:11916401

Dickerson, Tobin J; Janda, Kim D

2002-04-01

87

L-Selectride-Mediated Highly Diastereoselective Asymmetric Reductive Aldol Reaction: Access to an Important Subunit for Bioactive Molecules  

PubMed Central

L-Selectride reduction of a chiral or achiral enone followed by reaction of the resulting enolate with optically active ?-alkoxy aldehydes proceeded with excellent diastereoselectivity. The resulting ?,?-dimethyl-?-hydroxy ketones are inherent to a variety of biologically active natural products. PMID:18831554

Ghosh, Arun K.; Kass, Jorden; Anderson, David D.; Xu, Xiaoming; Marian, Christine

2010-01-01

88

Diastereo- and enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine: mechanistic insight into sequential nitroso Aldol/Michael reaction and application for optically pure 1-amino-3,4-diol synthesis.  

PubMed

This article presents complete diastereo- and highly enantioselective synthesis of nitroso Diels-Alder-type bicycloketones using dienamine. With the hydrogen bonding of two hydroxyls in the bulky binaphthol 1c, high enantioselectivities and complete diastereoselectivity are realized in 2-oxa-3-aza-bicycloketone synthesis. On the other hand, alpha,beta-unsaturated ketone can be employed as diene precursor, utilizing readily available tetrazole catalyst 3b, to provide the 3-oxa-2-aza-bicycloketones in moderate yields with complete enantioselectivities. Investigation into the reaction utilizing 2-morpholino-4,4-diphenylcyclohexadiene 2d clearly indicated that cyclization with the bulky binaphthol 1c is involved in the sequential process, the N-nitroso aldol reaction, followed by Michael addition. In addition, optically pure 1-amino-3,4-diol is synthesized from 2-oxa-3-aza-bicycloketones. Use of p-phenoxynitrosobenzene allows access to protected amino diol via cleavage of the N-Ph bond. PMID:17263400

Momiyama, Norie; Yamamoto, Yuhei; Yamamoto, Hisashi

2007-02-01

89

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

90

Nucleophilic Additions to 3-Azido-hexanal.  

E-print Network

??Sakurai and Mukaiyama aldol additions were carried out with 3-Azido-hexanal under chelation and non-chelation conditions. The reactions were generally found to be diastereofacially selective in… (more)

Schroeder, Chad

2009-01-01

91

Base-Catalyzed Direct Aldolization of ?-Alkyl-?-Hydroxy Trialkyl Phosphonoacetates**  

PubMed Central

Catalytic direct aldol addition of ?-hydroxy trialkyl phosphonacetates to aldehydes affords ?-hydroxy-?-phosphonyloxy ester products. The fully substituted glycolate enolate intermediate is generated in situ under mild conditions via [1,2]-phosphonate-phosphate rearrangement. High enantioselectivity and dramatic enhancement of reaction diastereocontrol is realized via the application of chiral iminophosphorane catalysts. The phosphate products undergo stereoselective nucleophilic displacement reactions. PMID:22474004

Corbett, Michael T.; Uraguchi, Daisuke; Ooi, Takashi; Johnson, Jeffrey S.

2013-01-01

92

Total Synthesis of Auripyrone A Using a Tandem Non-Aldol Aldol-Paterson Aldol Process as a Key Step**  

PubMed Central

A tandem non-aldol aldol-Paterson aldol generates the polypropionate 12 from the epoxy alcohol 8 and the ketone 9 in only two steps and 74% overall yield as a single diastereomer, due to double stereodifferentiation, where the stereoinduction from the enolate and the ?-methyl substituent of the aldehyde are reinforcing. This compound was used for an efficient synthesis of the natural product auripyrone A, 1, in only 18 steps and 17% overall yield, using a highly regioselective hemiketalization of a keto diol and a late stage spiroketalization onto a stable hemiketal as the final key steps. PMID:19824033

Salehi-Rad, Ramin

2012-01-01

93

Asymmetric aldol condensation in an ionic liquid-water system catalyzed by ( S )-prolinamide derivatives  

Microsoft Academic Search

Asymmetric aldol reaction of unmodified aldehydes with ketones catalyzed by 1(R),2(R)-bis((S)-prolinamido)cyclohexane (1) or (Rax)-2,2?-bis((S)-prolinamido)-1,1?-binaphtyl (2) proceeds with high yield (68–99%) and diastereoselectivity (dr ? 75\\/25) in the system (1-butyl-3-methylimida-zolium) tetrafluoroborate ([bmim][BF4])-water. The dependence of ee of the dominating anti-diastereomer of aldol on the percentage of water has a maximum at 50 vol.%. Catalyst 1 can be recycled 5 times without

A. S. Kucherenko; D. E. Syutkin; S. G. Zlotin

2008-01-01

94

Stereoselectivities of Histidine-Catalyzed Asymmetric Aldol Additions and Contrasts with Proline Catalysis: A Quantum Mechanical Analysis  

PubMed Central

Quantum mechanical calculations reveal the origin of diastereo- and enantioselectivities of aldol reactions between aldehydes catalyzed by histidine, and differences between related reactions catalyzed by proline. A stereochemical model that explains both the sense and the high levels of the experimentally observed stereoselectivity is proposed. The computations suggest that both the imidazolium and the carboxylic acid functionalities of histidine are viable hydrogen-bond donors that can stabilize the cyclic aldolization transition state. The stereoselectivity is proposed to arise from minimization of gauche interactions around the forming C–C bond. PMID:22458689

Lam, Yu-hong; Houk, K. N.; Scheffler, Ulf; Mahrwald, Rainer

2012-01-01

95

Progress toward the syntheses of (+)-GB 13, (+)-himgaline, and himandridine. new insights into intramolecular imine/enamine aldol cyclizations.  

PubMed

A full account of our total synthesis of the galbulimima alkaloids GB 13 and himgaline is provided. Using a strategy adapted from the proposed biosynthesis of the GB alkaloid family, a linear precursor underwent successive intramolecular Diels-Alder, Michael, and imine aldol cyclizations to form the polycyclic alkaloid core. We now show that modification of this strategy can also deliver an advanced intermediate en route to the related alkaloid himandridine. The success of the key imine aldol cyclization is acutely sensitive to substrate structure and solvent, including a case in which cyclization was spontaneous in protic solvents. A detailed computational investigation of the course of the reaction closely correlates with, and suggests a rationale for, the observed patterns of imine aldol reactivity. PMID:22533781

Evans, David A; Adams, Drew J; Kwan, Eugene E

2012-05-16

96

Light-absorbing aldol condensation products in acidic aerosols: Spectra, kinetics, and contribution to the absorption index  

NASA Astrophysics Data System (ADS)

The radiative properties of aerosols that are transparent to light in the near-UV and visible, such as sulfate aerosols, can be dramatically modified when mixed with absorbing material such as soot. In a previous work we had shown that the aldol condensation of carbonyl compounds produces light-absorbing compounds in sulfuric acid solutions. In this work we report the spectroscopic and kinetic parameters necessary to estimate the effects of these reactions on the absorption index of sulfuric acid aerosols in the atmosphere. The absorption spectra obtained from the reactions of six different carbonyl compounds (acetaldehyde, acetone, propanal, butanal, 2-butanone, and trifluoroacetone) and their mixtures were compared over 190-1100 nm. The results indicated that most carbonyl compounds should be able to undergo aldol condensation. The products are oligomers absorbing light in the 300-500 nm region where few other compounds absorb, making them important for the radiative properties of aerosols. Kinetic experiments in 96-75 wt% H 2SO 4 solutions and between 273 and 314 K gave an activation energy for the rate constant of formation of the aldol products of acetaldehyde of -(70±15) kJ mol -1 in 96 wt% solution and showed that the effect of acid concentration was exponential. A complete expression for this rate constant is proposed where the absolute value in 96 wt% H 2SO 4 and at 298 K is scaled to the Henry's law coefficient for acetaldehyde and the absorption cross-section for the aldol products assumed in this work. The absorption index of stratospheric sulfuric acid aerosols after a 2-year residence time was estimated to 2×10 -4, optically equivalent to a content of 0.5% of soot and potentially significant for the radiative forcing of these aerosols and for satellite observations in channels where the aldol products absorb.

Nozière, Barbara; Esteve, William

97

Dibenzalacetone by Aldol Condensation 45 ALDOL SYNTHESIS of DIBENZALACETONE, AN ORGANIC SUN SCREEN  

E-print Network

acetone and benzaldehyde. Acetone has -hydrogens (on both sides) and thus can be deprotonated to give sides of the ketone. Mechanism for Aldol Condensation H3C C CH3 O 1 Acetone molar mass: 58 g/mol density will be used NaOH, H2O, CH3CH2OH C CC O C H C H H H original acetone carbons Dibenzalacetone molar mass: 234 g

Jasperse, Craig P.

98

Structure of the polyketide cyclase SnoaL reveals a novel mechanism for enzymatic aldol condensation  

PubMed Central

SnoaL belongs to a family of small polyketide cyclases, which catalyse ring closure steps in the biosynthesis of polyketide antibiotics produced in Streptomyces. Several of these antibiotics are among the most used anti-cancer drugs currently in use. The crystal structure of SnoaL, involved in nogalamycin biosynthesis, with a bound product, has been determined to 1.35 Å resolution. The fold of the subunit can be described as a distorted ?+? barrel, and the ligand is bound in the hydrophobic interior of the barrel. The 3D structure and site-directed mutagenesis experiments reveal that the mechanism of the intramolecular aldol condensation catalysed by SnoaL is different from that of the classical aldolases, which employ covalent Schiff base formation or a metal ion cofactor. The invariant residue Asp121 acts as an acid/base catalyst during the reaction. Stabilisation of the enol(ate) intermediate is mainly achieved by the delocalisation of the electron pair over the extended ? system of the substrate. These polyketide cyclases thus form of family of enzymes with a unique catalytic strategy for aldol condensation. PMID:15071504

Sultana, Azmiri; Kallio, Pauli; Jansson, Anna; Wang, Ji-Shu; Niemi, Jarmo; Mäntsälä, Pekka; Schneider, Gunter

2004-01-01

99

Novel synthons from mucochloric acid: the first use of alpha,beta-dichloro-gamma-butenolides and gamma-butyrolactams for direct vinylogous aldol addition.  

PubMed

Novel 5-(1'-hydroxy)-gamma-butyrolactone and gamma-butyrolactam subunits were synthesized by direct vinylogous aldol addition of alpha,beta-dichloro gamma-butyrolactones and gamma-butyrolactams with aldehydes under basic conditions. Different bases and solvents were screened in the context of generating gamma-butyrolactones. Diastereoselectivity was observed and gamma-butenolides and gamma-butyrolactams showed opposite diastereoselectivity under the same reaction condition. PMID:17397224

Das Sarma, Koushik; Zhang, Ji; Curran, Timothy T

2007-04-27

100

The olefinic aldol reaction. Addition of zincated hydrazone to vinylsilane  

Microsoft Academic Search

A zincated N,N-dimethylhydrazone of a ketone bearing a BuZn(II) countercation undergoes intermolecular addition to a vinysilane to afford the hydrazone of a 2-(2-silylethyl)ketone in good yield, providing a new synthetic route to functionalized carbonyl compounds.

Eiichi Nakamura; Katsumi Kubota

1997-01-01

101

Intramolecular aldol cyclization of C-4-ulopyranosyl-2'-oxoalkanes controlled by steric effects. Asymmetric synthesis of substituted 8-oxabicyclo[3.2.1]octanones and -octenones and cyclopentenones.  

PubMed

Whereas C-2- and 4-ulopyranosyl compounds (C-2- and C-4-ulosides) can be converted to cyclopentenones under base conditions through beta-elimination and ring contraction, base-initiated beta-elimination of C-glycosyl 2'-aldehydes and 2'-ketones results in the formation of acyclic alpha,beta-unsaturated aldehydes or ketones. By combining both molecular features we synthesized 1-C-(4-ulopyranosyl)-2-oxoalkanes 6, 13, and 20 and investigated their reactions when they were treated with base. Both alpha- and beta-anomers of C-(4-ulopyranosyl)acetaldehydes 6 and 13 underwent a fast intramolecular aldol reaction between the C-5 enolate and 2'-aldehyde to form optically pure 8-oxabicyclo[3.2.1]octanones, which further transformed to 8-oxabicyclo[3.2.1]octenones 14 and 15 by beta-elimination. However, this aldol reaction did not occur when 1-C-(4-ulopyranosyl)propan-2-one 20 was treated with base because of steric hindrance exerted by the additional methyl group. Instead, an alternate C-3 enolization led to beta-elimination and further electro-ring opening to form an acyclic enol, which was then converted through a disrotatory intramolecular aldol cyclization to a cis-substituted cyclopentenone 21. PMID:15476708

Zou, Wei; Shao, Huawu; Wu, Shih-Hsiung

2004-10-20

102

Peculiar behavior of MWW materials in aldol condensation of furfural and acetone.  

PubMed

MWW family of different structural types (MCM-22, MCM-49, MCM-56 and MCM-36) was used as catalysts for aldol condensation of furfural and acetone studied in a batch reactor at 100 °C, autogenous pressure and a reaction time of 0-4 h. To establish a relation between physico-chemical and catalytic properties of microporous materials, the samples were characterized by XRD, SEM, N2 adsorption, FTIR and TGA. It was found that the acidic solids possessed appreciable activity in the reaction and resulted in the formation of products of aldehyde-ketone interaction. Surprisingly, MCM-22 and MCM-49, i.e. three-dimensional materials containing internal supercages, exhibited higher activity than two MCM-36 catalysts with two-dimensional character having larger accessible external surface area due to expansion of the interlayer space by swelling and pillaring treatments. Moreover, all MWW family catalysts gave higher conversion than the large-pore zeolite BEA. Nevertheless, furfural conversion decreased rapidly for all the studied materials due to coke formation. Unexpectedly, the deactivation was found to be more severe for MCM-36 catalysts than for MCM-22 and MCM-49, which was attributed to the reaction taking place also in supercages that are protected by 10-ring channels from severe coking. In contrast the cups located on the external surface were coked rapidly. PMID:24842149

Kikhtyanin, Oleg; Chlubná, Pavla; Jindrová, Tereza; Kubi?ka, David

2014-07-21

103

Diastereo- and Enantioselective Reductive Aldol Addition of Vinyl Ketones via Catalytic Hydrogenation  

PubMed Central

An overview of studies on hydrogenative reductive aldol addition is presented. By simply hydrogenating enones in the presence of aldehydes at ambient temperature and pressure, aldol adducts are generated under neutral conditions in the absence of any stoichiometric byproducts. Using cationic rhodium complexes modified by tri(2-furyl)phosphine, highly syn-diastereoselective reductive aldol additions of vinyl ketones are achieved. Finally, using novel monodentate TADDOL-like phosphonite ligands, the first highly diastereo- and enantioselective reductive aldol couplings of vinyl ketones were devised. These studies, along with other works from our laboratory, demonstrate that organometallics arising transiently in the course of catalytic hydrogenation offer byproduct-free alternatives to preformed organometallic reagents employed in classical carbonyl addition processes. PMID:21866204

Han, Soo Bong; Hassan, Abbas; Krische, Michael J.

2011-01-01

104

Diastereodivergent organocatalytic asymmetric vinylogous Michael reactions.  

PubMed

One of the major challenges of modern asymmetric catalysis is the ability to selectively control the formation of all diastereoisomers of reaction products possessing multiple stereocenters. Pioneers of such diastereodivergent catalytic asymmetric processes have focused on reactions where the newly formed stereogenic centres are proximal to the active carbonyl group. To date, however, diastereodivergent reactions at remote positions remain an unmet challenge. Herein, we describe a catalyst-controlled diastereodivergence in the formation of remote stereocenters in the direct vinylogous Michael reactions of ?, ?-unsaturated butenolides to ?, ?-unsaturated ketones. The reactions are enabled by two complementary, non-enantiomeric multifunctional catalysts, which mutually activate and organise both reactants, affording either the syn- or anti-adduct with high diastereo- and enantioselectivity. These two catalytic systems are also applicable in the Mukaiyama-Michael reactions and tandem Michael-Michael reactions. PMID:25057788

Li, Xin; Lu, Min; Dong, Yun; Wu, Wenbin; Qian, Qingqing; Ye, Jinxing; Dixon, Darren J

2014-01-01

105

Mineral catalysis of a potentially prebiotic aldol condensation  

NASA Technical Reports Server (NTRS)

Minerals may have played a significant role in chemical evolution. In the course of investigating the chemistry of phosphonoacetaldehyde (PAL), an analogue of glycolaldehyde phosphate, we have observed a striking case of catalysis by the layered hydroxide mineral hydrotalcite ([Mg2Al(OH)6][Cl.nH2O]). In neutral or moderately basic aqueous solutions, PAL is unreactive even at a concentration of 0.1 M. In the presence of a large excess of NaOH (2 M), the compound undergoes aldol condensation to produce a dimer containing a C3-C4 double-bond. In dilute neutral solutions and in the presence of the mineral, however, condensation takes place rapidly, to produce a dimer which is almost exclusively the C2-C3 unsaturated product.

De Graaf, R. M.; Visscher, J.; Xu, Y.; Arrhenius, G.; Schwartz, A. W.

1998-01-01

106

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

107

The effect of the distance between acidic site and basic site immobilized on mesoporous solid on the activity in catalyzing aldol condensation  

SciTech Connect

Acid-base bifunctional heterogeneous catalysts containing carboxylic and amine groups, which were immobilized at defined distance from one another on the mesoporous solid were synthesized by immobilizing lysine onto carboxyl-SBA-15. The obtained materials were characterized by X-ray diffraction (XRD), N{sub 2} adsorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron micrographs (SEM), transmission electron micrographs (TEM), elemental analysis, and back titration. Proximal-C-A-SBA-15 with a proximal acid-base distance was more active than maximum-C-A-SBA-15 with a maximum acid-base distance in aldol condensation reaction between acetone and various aldehydes. It appears that the distance between acidic site and basic site immobilized on mesoporous solid should be an essential factor for catalysis optimization. -- Graphical abstract: Proximal-C-A-SBA-15 with a proximal acid-base distance and maximum-C-A-SBA-15 with a maximum acid-base distance were synthesized by immobilizing lysine onto carboxyl-SBA-15. Display Omitted Research highlights: {yields} Proximal-C-A-SBA-15 with a proximal acid-base distance. {yields} Maximum-C-A-SBA-15 with a maximum acid-base distance. {yields} Compared to maximum-C-A-SBA-15, proximal-C-A-SBA-15 was more active toward aldol condensation reaction between acetone and various aldehydes.

Yu Xiaofang [College of Chemistry, Jilin University, Jiefang Road 2519, Changchun 130023 (China); Yu Xiaobo [China Pharmaceutical University, Nanjing 210009 (China); Wu Shujie; Liu Bo; Liu Heng [College of Chemistry, Jilin University, Jiefang Road 2519, Changchun 130023 (China); Guan Jingqi, E-mail: guanjq@jlu.edu.c [College of Chemistry, Jilin University, Jiefang Road 2519, Changchun 130023 (China); Kan Qiubin, E-mail: catalysischina@yahoo.com.c [College of Chemistry, Jilin University, Jiefang Road 2519, Changchun 130023 (China)

2011-02-15

108

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

E-print Network

the needed electrophilicity in order to complete the aldol; however, recent advancements have introduced ketones as a viable carbonyl. With an established protocol in hand, I set out to explore various substrates that could yield Beta-lactones in good...

Matla, Andrea Slava

2009-05-15

109

The effect of acid–base pairing on catalysis: An efficient acid–base functionalized catalyst for aldol condensation  

Microsoft Academic Search

Acid–base bifunctionalized heterogeneous catalysts may be capable of exhibiting reactivity not achievable with homogeneous catalysts. We investigated the effect of pKa of the acid component of mesoporous solids containing acid–base bifunctionality on their catalytic ability toward aldol condensation between 4-nitrobenzaldehyde and acetone. We found that higher levels of aldol product conversion were obtained when weaker acid components (phosphoric, carboxylic vs

Ryan K. Zeidan; Mark E. Davis

2007-01-01

110

Five-membered ring annelation in [2.2]paracyclophanes by aldol condensation  

PubMed Central

Summary Under basic conditions 4,5,12,13-tetraacetyl[2.2]paracyclophane (9) cyclizes by a double aldol condensation to provide the two aldols 12 and 15 in a 3:7 ratio. The structures of these compounds were obtained from X-ray structural analysis, spectroscopic data, and mechanistic considerations. On acid treatment 12 is dehydrated to a mixture of the condensed five-membered [2.2]paracyclophane derivatives 18–20, whereas 15 yields a mixture of the isomeric cyclopentadienones 21–23. The structures of these elimination products are also deduced from X-ray and spectroscopic data. The sequence presented here constitutes the simplest route so far to cyclophanes carrying an annelated five-membered ring. PMID:25246961

Narayanan, Swaminathan Vijay; Jones, Peter G

2014-01-01

111

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

112

From vinyl pyranoses to carbasugars by an iron-catalyzed reaction complementary to classical Ferrier carbocyclization.  

PubMed

Starting from vinyl pyranoses an iron-catalyzed tandem isomerization-intramolecular aldolization reaction was developed to prepare cyclohexenone derivatives bearing substituents on the double bond, and it has been applied in a short synthesis of 4-epi-gabosines A and B, from d-glucose. PMID:19641820

Mac, Dinh Hung; Samineni, Ramesh; Petrignet, Julien; Srihari, Pabbaraja; Chandrasekhar, Srivari; Yadav, Jhillu Singh; Grée, René

2009-08-21

113

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

114

Gold (III) Chloride-Catalyzed 6-endo-trig Oxa-Michael Addition Reactions for Diastereoselective Synthesis of Fused Tetrahydropyranones  

PubMed Central

Alkynones were treated with boron trifluoride diethyl etherate to generate ?-iodoallenolates, which underwent intramolecular aldol reactions to produce cycloalkenyl alcohols. Diastereoselective oxa-Michael ring closure could then be induced by treatment with a catalytic amount of gold(III) chloride, affording highly functionalized tetrahydropyran-containing ring systems. PMID:24032002

Ciesielski, Jennifer; Lebœuf, David; Stern, Harry A.

2013-01-01

115

Synthesis of novel long wavelength cationic chlorins via stereoselective aldol-like condensation.  

PubMed

Using stereoselective aldol-like condensation as a key methodology, a series of chlorophyll a-based long wavelength cationic chlorins were synthesized using methyl pyropheophorbide a (MPPa) and purpurin-18-N-methoxylimide methyl ester as starting materials. Such long wavelength cationic chlorins possess covalently linked cationic moieties (pyridinium or quinolinium) on the peripheral of their tetrapyrrole macrocycles. It was found that all long wavelength cationic chlorins showed their longest absorption maxima in the range of 712-763nm, making them potential photosensitizers in photodynamic therapy. The results of preliminary experiments probing in vitro photodynamic effects showed that the purpurinimide derivatives exhibit relatively high phototoxicity in HeLa cells as compared to MPPa derivatives. PMID:22335896

Li, Jia Zhu; Wang, Jin Jun; Yoon, Il; Cui, Bing Cun; Shim, Young Key

2012-03-01

116

Preparation and characterization of Mg-Zr mixed oxide aerogels and their application as aldol condensation catalysts.  

PubMed

A series of Mg-Zr mixed oxides with different nominal Mg/(Mg+Zr) atomic ratios, namely 0, 0.1, 0.2, 0.4, 0.85, and 1, is prepared by alcogel methodology and fundamental insights into the phases obtained and resulting active sites are studied. Characterization is performed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N(2) adsorption-desorption isotherms, and thermal and chemical analysis. Cubic Mg(x)Zr(1-x)O(2-x) solid solution, which results from the dissolution of Mg(2+) cations within the cubic ZrO(2) structure, is the main phase detected for the solids with theoretical Mg/(Mg+Zr) atomic ratio ?0.4. In contrast, the cubic periclase (c-MgO) phase derived from hydroxynitrates or hydroxy precursors predominates in the solid with Mg/(Mg+Zr)=0.85. c-MgO is also incipiently detected in samples with Mg/(Mg+Zr)=0.2 and 0.4, but in these solids the c-MgO phase mostly arises from the segregation of Mg atoms out of the alcogel-derived c-Mg(x)Zr(1-x)O(2-x) phase during the calcination process, and therefore the species c-MgO and c-Mg(x)Zr(1-x)O(2-x) are in close contact. Regarding the intrinsic activity in furfural-acetone aldol condensation in the aqueous phase, these Mg-O-Zr sites located at the interface between c-Mg(x)Zr(1-x)O(2-x) and segregated c-MgO display a much larger intrinsic activity than the other noninterface sites that are present in these catalysts: Mg-O-Mg sites on c-MgO and Mg-O-Zr sites on c-Mg(x)Zr(1-x)O(2-x). The very active Mg-O-Zr sites rapidly deactivate in the furfural-acetone condensation due to the leaching of active phases, deposition of heavy hydrocarbonaceous compounds, and hydration of the c-MgO phase. Nonetheless, these Mg-Zr materials with very high specific surface areas would be suitable solid catalysts for other relevant reactions catalyzed by strong basic sites in nonaqueous environments. PMID:22855425

Sádaba, Irantzu; Ojeda, Manuel; Mariscal, Rafael; Richards, Ryan; López Granados, Manuel

2012-10-01

117

Formal carbene insertion into C-C bond: Rh(I)-catalyzed reaction of benzocyclobutenols with diazoesters.  

PubMed

A Rh(I)-catalyzed formal carbene insertion into C-C bond of benzocyclobutenols has been realized by employing diazoesters as carbene precursors. The product indanol derivatives were obtained in good yields and in diastereoselective manner under mild reaction conditions. All-carbon quaternary center is constructed at the carbenic carbon. This catalytic reaction involves selective cleavage of C-C bond, Rh(I) carbene insertion, and intramolecular aldol reaction. PMID:24512084

Xia, Ying; Liu, Zhenxing; Liu, Zhen; Ge, Rui; Ye, Fei; Hossain, Mohammad; Zhang, Yan; Wang, Jianbo

2014-02-26

118

Aldol condensation of citral with acetone on MgO and alkali-promoted MgO catalysts  

Microsoft Academic Search

The liquid-phase synthesis of pseudoionones (PSs) by cross-aldol condensation of citral with acetone was studied on alkali-promoted MgO catalysts. Alkaline metals (A), including Li, Na, K, and Cs, were added to a high-surface area MgO in A\\/Mg molar ratios of up to 0.01. Promoters of greater ionic radius than Li blocked the catalyst pores of MgO, causing a decrease in

V. K. Díez; C. R. Apesteguía; J. I. Di Cosimo

2006-01-01

119

Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products  

NASA Astrophysics Data System (ADS)

While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC-MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75-96 wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30-96 wt% sulfuric acid in water. Aerosols up to 88.4 wt% organic/11.1 wt% H 2SO 4/0.5 wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96 wt% in water.

Garland, Rebecca M.; Elrod, Matthew J.; Kincaid, Kristi; Beaver, Melinda R.; Jimenez, Jose L.; Tolbert, Margaret A.

120

Rapid Construction of the Aza-Propellane Core of Acutumine via a Photochemical [2+2] Cycloaddition Reaction  

PubMed Central

Synthetic efforts toward the chlorinated propellane alkaloid acutumine (1) are described. The key vicinal quaternary centers were constructed by a photochemical [2+2] cycloaddition reaction of a furanyl-tetrahydroindolone. Dihydroxylation of the [2+2] product enabled a tandem retro-aldol/intramolecular ketalization reaction, which revealed the aza-propellane core of 1 while generating an unusual, caged, pentacyclic hemi-ketal product. PMID:22891873

Navarro, Raul; Reisman, Sarah E.

2012-01-01

121

Crystal Structure of Reaction Intermediates in Pyruvate Class II Aldolase  

PubMed Central

Crystal structures of divalent metal-dependent pyruvate aldolase, HpaI, in complex with substrate and cleavage products were determined to 1.8–2.0 Å resolution. The enzyme·substrate complex with 4-hydroxy-2-ketoheptane-1,7-dioate indicates that water molecule W2 bound to the divalent metal ion initiates C3–C4 bond cleavage. The binding mode of the aldehyde donor delineated a solvent-filled capacious binding locus lined with predominantly hydrophobic residues. The absence of direct interactions with the aldehyde aliphatic carbons accounts for the broad specificity and lack of stereospecific control by the enzyme. Enzymatic complex structures formed with keto acceptors, pyruvate, and 2-ketobutyrate revealed bidentate interaction with the divalent metal ion by C1-carboxyl and C2-carbonyl oxygens and water molecule W4 that is within close contact of the C3 carbon. Arg70 assumes a multivalent role through its guanidinium moiety interacting with all active site enzymatic species: C2 oxygen in substrate, pyruvate, and ketobutyrate; substrate C4 hydroxyl; aldehyde C1 oxygen; and W4. The multiple interactions made by Arg70 stabilize the negatively charged C4 oxygen following proton abstraction, the aldehyde alignment in aldol condensation, and the pyruvate enolate upon aldol cleavage as well as support proton exchange at C3. This role is corroborated by loss of aldol cleavage ability and pyruvate C3 proton exchange activity and by a 730-fold increase in the dissociation constant toward the pyruvate enolate analog oxalate in the R70A mutant. Based on the crystal structures, a mechanism is proposed involving the two enzyme-bound water molecules, W2 and W4, in acid/base catalysis that facilitates reversible aldol cleavage. The same reaction mechanism promotes decarboxylation of oxaloacetate. PMID:22908224

Coincon, Mathieu; Wang, Weijun; Sygusch, Jurgen; Seah, Stephen Y. K.

2012-01-01

122

Controlling reaction specificity in pyridoxal phosphate enzymes  

PubMed Central

Pyridoxal 5'-phosphate enzymes are ubiquitous in the nitrogen metabolism of all organisms. They catalyze a wide variety of reactions including racemization, transamination, decarboxylation, elimination, retro-aldol cleavage, Claisen condensation, and others on substrates containing an amino group, most commonly ?-amino acids. The wide variety of reactions catalyzed by PLP enzymes is enabled by the ability of the covalent aldimine intermediate formed between substrate and PLP to stabilize carbanionic intermediates at C? of the substrate. This review attempts to summarize the mechanisms by which reaction specificity can be achieved in PLP enzymes by focusing on three aspects of these reactions: stereoelectronic effects, protonation state of the external aldimine intermediate, and interaction of the carbanionic intermediate with the protein side chains present in the active site. PMID:21664990

Toney, Michael D.

2012-01-01

123

Synthesis and Characterization of Aldol Condensation Products from Unknown Aldehydes and Ketones: An Inquiry-Based Experiment in the Undergraduate Laboratory  

ERIC Educational Resources Information Center

An experiment for the undergraduate chemistry laboratory in which students perform the aldol condensation on an unknown aldehyde and an unknown ketone is described. The experiment involves the use of techniques such as TLC, column chromatography, and recrystallization, and compounds are characterized by [to the first power]H NMR, GC-MS, and FTIR.…

Angelo, Nicholas G.; Henchey, Laura K.; Waxman, Adam J.; Canary, James W.; Arora, Paramjit S.; Wink, Donald

2007-01-01

124

Aldol elaboration of 4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridin-4-ones, masked precursors to acylpyridones  

PubMed Central

Summary A core 4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridine-4-one scaffold is elaborated at C-3(Me) by base-mediated aldol condensation to give new 3-alkenyl-4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridine-4-ones, which are masked forms related to the acylpyridone natural products. PMID:22423299

Choudhury, Abdul K; Iley, James N; Light, Mark E; Loizou, Georgia; Pillainayagam, Terence A

2012-01-01

125

Vinylogous aldol products from chiral crotylsilanes obtained by enantioselective Rh(II) and Cu(I) carbenoid Si-H insertion.  

PubMed

Enantioenriched homoallylic ethers containing a alpha,beta-unsaturated ester (syn-vinylogous aldol products) were directly accessed by Lewis acid catalyzed crotylation utilizing chiral silane 2. The reagents were prepared by enantioselective Si-H insertion to an alpha-diazovinylacetates using Davies' Rh(2)(DOSP)(4) catalyst or chiral Cu(I) Schiff base complex. PMID:20387893

Wu, Jie; Chen, Yu; Panek, James S

2010-05-01

126

RUTHENIUM-CATALYZED TANDEM OLEFIN MIGRATION-ALDOL AND MANNICH-TYPE REACTIONS IN WATER AND PROTIC SOLVENT. (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...

127

Isoxazole-embedded allylic zinc reagent for the diastereoselective preparation of highly functionalized aldol-type derivatives bearing a stereocontrolled quaternary center.  

PubMed

Highly functionalized aldol-type products bearing a ?-quaternary center and a stereoselectively controlled ?-hydroxy function are readily prepared by the diastereoselective addition of an allylic zinc reagent embedded in an isoxazole ring to various aromatic and heteroaromatic aldehydes, in the presence of Lewis acids, such as MgCl2 or LaCl3?2?LiCl. After reductive cleavage of the N-O bond by using Fe, NH4Cl, aldol-type products bearing a stereocontrolled ?-quaternary center and a ?-hydroxy group were observed. The benzylic reactivity of the isoxazolylmethylzinc reagent towards other electrophiles, such as acid chlorides, aryl and allylic halides, as well as aldehydes in the presence of BF3?OEt2 are also described. PMID:25204300

Klier, Lydia; Diène, Coura R; Schickinger, Manuel; Metzger, Albrecht; Wagner, Andreas J; Karaghiosoff, Konstantin; Marek, Ilan; Knochel, Paul

2014-10-20

128

Total synthesis of the protected aglycon of fidaxomicin (tiacumicin?b, lipiarmycin?a3).  

PubMed

Fidaxomicin, also known as tiacumicin?B or lipiarmycin?A3, is a novel macrocyclic antibiotic that is used in hospitals for the treatment of Clostridium difficile infections. This natural product has also been shown to have excellent bactericidal activity against multidrug-resistant Mycobacterium tuberculosis. In spite of its attractive biological activity, no total synthesis has been reported to date. The enantioselective synthesis of the central 18-membered macrolactone is reported herein. The key reactions include ring-closing metathesis between a terminal olefin and a dienoate moiety for macrocyclization, a vinylogous Mukaiyama aldol reaction, and a Stille coupling reaction of sterically demanding substrates. The retrosynthesis involves three medium-sized fragments, thus leading to a flexible yet convergent synthetic route. PMID:25431322

Miyatake-Ondozabal, Hideki; Kaufmann, Elias; Gademann, Karl

2015-02-01

129

Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1: aldehydes and ketones  

NASA Astrophysics Data System (ADS)

The term "accretion reactions" is introduced here to refer to the large collection of reactions by which atmospheric organic molecules can add mass, especially as by combination with other organic molecules. A general thermodynamic approach is developed for evaluating the tendency of atmospheric constituents (e.g., C 10 aldehydes) to undergo accretion reactions (e.g., dimerization) and thereby form less volatile molecules (e.g., aldol condensation products) that may subsequently condense and so contribute to the levels of organic particulate matter (OPM) observed in the atmosphere. As an example, gaseous compounds A and B may contribute to OPM formation by the net overall reaction A g+B g=C liq. This reaction may occur according to any of three kinetic schemes. Scheme I: (1) A g+B g=C g (accretion in the gas phase): then (2) C g=C liq (condensation of the accretion product); Scheme II: (1) B g=B liq (condensation of B); then (2) A g+B liq=C liq (heterogeneous accretion reaction of gaseous A with condensed B); or Scheme III: (1) A g+B g=A liq+B liq (condensation of A and B); then (2) A liq+B liq=C liq (accretion of A with B within the PM phase). For all three schemes, the net overall reaction remains A g+B g=C liq. The overall thermodynamic tendency of the net reaction remains the same regardless of the actual predominating kinetic mechanism. If an accretion reaction between two atmospheric components is to produce significant new OPM, appreciable amounts of the product C must form, and the vapor pressure of C must be relatively low so that a significant proportion of C can condense into the multicomponent liquid OPM phase. This study considers the thermodynamics of accretion reactions of atmospheric aldehydes including: (a) hydration, polymerization (i.e., oligomer formation), hemiacetal/acetal formation; and (b) aldol condensation. It was concluded regarding OPM formation that: (1) the reactions in the first group are not thermodynamically favored, either in the atmosphere, or in the "acid-catalyzed" chamber experiments of Jang and Kamens (Environ. Sci. Technol. 35 (2001b) 4758) with n-butanal, n-hexanal, n-octanal, and n-decanal; (2) aldol condensation is not thermodynamically favored for the conditions of the Jang and Kamens (2001b) experiments with those four aldehydes; (3) the mechanism for any observed OPM formation from n-butanal, n-hexanal, and n-octanal in those experiments remains unknown, and may also have been involved in the "acid-catalyzed" experiments with n-decanal; (4) whether Jang and Kamens (2001b) observed the consequences of aldol condensation in their n-decanal experiments remains unclear due in part to uncertainties in the free energy of formation (? Gf0) values for the aldol products of n-decanal; (5) analogous refinement in the quality of needed ? Gf0 values is required to clarify the potential importance of aldol products of pinonaldehyde in the formation of ambient OPM; and (6) the possibility that photo-assisted mechanisms may compensate for unfavorable thermodyamics in the formation of accretion products in the atmosphere should be considered.

Barsanti, Kelley C.; Pankow, James F.

130

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

131

Hydroxyapatite catalyzed aldol condensation: Synthesis, spectral linearity, antimicrobial and insect antifeedant activities of some 2,5-dimethyl-3-furyl chalcones  

NASA Astrophysics Data System (ADS)

A series of 2,5-dimethyl-3-furyl chalcones [2E-1-(2,5-dimethyl-3-furyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesized by Hydrotalcite catalyzed aldol condensation between 3-acetyl-2,5-dimethylfuron and substituted benzaldehydes. Yields of chalcones are more than 80%. These chalcones were characterized by their physical constants and spectral data. The group frequencies of infrared ?(cm-1) of CO s-cis and s-trans, CH in-plane and out of plane, CHdbnd CH out of plane, lbond2 Cdbnd Crbond2 out of plane modes, NMR chemical shifts ?(ppm) of H?, H?, CO, C? and C? of these chalcones were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analyses. From the results of statistical analyses, the effects of substituents on the group frequencies are explained. Antibacterial, antifungal and insect antifeedant activities of these chalcones have been studied.

Subramanian, M.; Vanangamudi, G.; Thirunarayanan, G.

2013-06-01

132

Cross-coupling reaction of alpha-chloroketones and organotin enolates catalyzed by zinc halides for synthesis of gamma-diketones.  

PubMed

The reaction of tin enolates 1 with alpha-chloro- or bromoketones 2 gave gamma-diketones (1,4-diketones) 3 catalyzed by zinc halides. In contrast to the exclusive formation of 1,4-diketones 3 under catalytic conditions, uncatalyzed reaction of 1 with 2 gave aldol-type products 4 through carbonyl attack. NMR study indicates that the catalyzed reaction includes precondensation between tin enolates and alpha-haloketones providing an aldol-type species and their rearrangement of the oxoalkyl group with leaving halogen to produce 1,4-diketones. The catalyst, zinc halides, plays an important role in each step. The carbonyl attack for precondensation is accelerated by the catalyst as Lewis acid and the intermediate zincate promotes the rearrangement by releasing oxygen and bonding with halogen. Various types of tin enolates and alpha-chloro- and bromoketones were applied to the zinc-catalyzed cross-coupling. On the other hand, the allylic halides, which have no carbonyl moiety, were inert to the zinc-catalyzed coupling with tin enolates. The copper halides showed high catalytic activity for the coupling between tin enolates 1 and organic halides 7 to give gamma,delta-unsaturated ketones 8 and/or 9. The reaction with even chlorides proceeded effectively by the catalytic system. PMID:12071753

Yasuda, Makoto; Tsuji, Shoki; Shigeyoshi, Yusuke; Baba, Akio

2002-06-26

133

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

2014-12-01

134

Enamine-based organocatalysis with proline and diamines: the development of direct catalytic asymmetric Aldol, Mannich, Michael, and Diels-alder reactions.  

PubMed

Enamines and imines have long been recognized as key intermediates in enzyme catalysis, particularly within a class of enzymes organic chemists would very much like to emulate, the aldolases. Here we summarize the contributions of this laboratory to converting enzymatic enamines, and in some cases imines, into a versatile catalytic asymmetric strategy powered by small organic molecules. PMID:15311957

Notz, Wolfgang; Tanaka, Fujie; Barbas, Carlos F

2004-08-01

135

Drug Reactions  

MedlinePLUS

... version Drug Reactions Drug Reactions What is an adverse drug reaction? Medicines can treat or prevent illness and ... medicines can cause problems. These problems are called adverse drug reactions. You should know what to do if ...

136

Synthesis of Substituted a-(Hydroxymethyl)-b-iodoacrylates via MgI2-Promoted Stereoselective Aldol Coupling  

E-print Network

Coupling by Han-Xun Wei*1 ), Jiali Hu, Richard L. Jasoni, Guigen Li, and Paul W. Pare¬* Department-pot coupling reaction under mild conditions, promoted by MgI2, which serves both as a Lewis acid and iodine yield (90%) and (Z)/(E) ratio (> 98 :2), when benzaldehyde was used as the electrophile. Et2O, benzene

Paré, Paul W.

137

Reaction times  

Microsoft Academic Search

Reviews 11 studies dealing with reaction times (1910-1911). Reaction time has been utilized to study a variety of problems. The studies indicate that accurate results can not be obtained without careful attention to the technique of the method of reaction time. The topics covered include effect of intensity of stimulus on reaction time, rapidity of perception of sound and light

Herbert Woodrow

1911-01-01

138

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

139

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

140

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

141

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

142

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

143

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

144

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

145

Common inorganic ions are efficient catalysts for organic reactions in atmospheric aerosols and other natural environments  

NASA Astrophysics Data System (ADS)

In this work, inorganic ammonium ions, NH4+, and carbonate ions, CO32-, are reported for the first time as catalysts for organic reactions in atmospheric aerosols and other natural environments at the Earth's surface. These reactions include the formation of C-C and C-O bonds by aldol condensation and acetal formation, and reveal a new aspect of the interactions between organic and inorganic materials in natural environments. The catalytic properties of inorganic ammonium ions, in particular, were not previously known in chemistry. The reactions were found to be as fast in tropospheric ammonium sulfate composition as in concentrated sulfuric acid. The ubiquitous presence and large concentrations of ammonium ions in tropospheric aerosols would make of ammonium catalysis a main consumption pathway for organic compounds in these aerosols, while acid catalysis would have a minor contribution. In particular, ammonium catalysis would account quantitatively for the aging of carbonyl compounds into secondary ''fulvic'' compounds in tropospheric aerosols, a transformation affecting the optical properties of these aerosols. In general, ammonium catalysis is likely to be responsible for many observations previously attributed to acid catalysis in the troposphere.

Nozière, B.; Dziedzic, P.; Córdova, A.

2009-01-01

146

The reactions of acetone with the surfaces of uranium dioxide single crystal and thin film  

NASA Astrophysics Data System (ADS)

The reaction of acetone, as an example of a carbonyl compound, is studied over UO 2 (1 1 1) single crystal and thin film surfaces. Over the stoichiometric single crystal surface, acetone is molecularly and weakly adsorbed with a computed activation energy for desorption in the range of 95-65 kJ/mol with pre-exponential factors between 10 11 and 10 13 s -1. On the contrary, acetone reacts very strongly on the O-defected single crystal and thin film surfaces. In addition to total decomposition evidence of aldolization and cyclization reactions were seen. The thin film of UO 2 was studied by synchrotron light, providing high resolution photoelectron spectroscopy in the core level, and high sensitivity in the both the core and valence band regions. The U5f line was considerably enhanced at grazing angle when compared to that obtained at normal angle for the O-defected surface, showing that the surface is more reduced than the next layers. The U 4f lines indicated the presence of U cations in lower oxidation states than +4 for the O-defected surface. These lines were considerably attenuated upon adsorption of acetone, due to surface oxidation by C dbnd O bond dissociation. The reaction pathway for acetone on the O-defected surface is presented, and compared to that of the previously studied acetaldehyde molecule.

King, R. I.; Senanayake, S. D.; Chong, S. V.; Idriss, H.

2007-12-01

147

The Reactions of Acetone with the Surfaces of Uranium Dioxide Single Crystal and Thin Film  

SciTech Connect

The reaction of acetone, as an example of a carbonyl compound, is studied over UO2 (1 1 1) single crystal and thin film surfaces. Over the stoichiometric single crystal surface, acetone is molecularly and weakly adsorbed with a computed activation energy for desorption in the range of 95-65 kJ/mol with pre-exponential factors between 1011 and 1013 s-1. On the contrary, acetone reacts very strongly on the O-defected single crystal and thin film surfaces. In addition to total decomposition evidence of aldolization and cyclization reactions were seen. The thin film of UO2 was studied by synchrotron light, providing high resolution photoelectron spectroscopy in the core level, and high sensitivity in the both the core and valence band regions. The U5f line was considerably enhanced at grazing angle when compared to that obtained at normal angle for the O-defected surface, showing that the surface is more reduced than the next layers. The U 4f lines indicated the presence of U cations in lower oxidation states than +4 for the O-defected surface. These lines were considerably attenuated upon adsorption of acetone, due to surface oxidation by C{double_bond}O bond dissociation. The reaction pathway for acetone on the O-defected surface is presented, and compared to that of the previously studied acetaldehyde molecule.

King,R.; Senanayake, S.; Chong, S.; Idriss, H.

2007-01-01

148

Mechanism for folate-independent aldolase reaction catalyzed by serine hydroxymethyltransferase.  

PubMed

Serine hydroxymethyltransferase catalyzes the cleavage of ?-hydroxyamino acids into glycine and aldehydes in the absence of tetrahydrofolate. The enzyme accepts various ?-hydroxyamino acids as the substrate of this reaction. The reaction rate varies depending on the substituent and stereochemistry at the C? atom: the erythro forms and the ?-phenyl substituent are preferred over the threo forms and the ?-methyl substituent, respectively. Although several mechanisms have been proposed, what determines the substrate preference remains unclear. We first performed quantum mechanical calculations to assess the validity of the reaction mechanisms. The results indicate that the retro-aldol mechanism starting with abstraction of the proton from the ?-hydroxyl group is plausible. This also suggests that C?-C? bond cleavage is the rate-limiting step. We next measured the dependence of the rate constants on temperature with four representative substrates and calculated the activation energies and pre-exponential factors from the Arrhenius plots. The activation energies of the erythro forms were lower than those of the threo forms. The ?-phenyl substituent lowered the activation energy in the threo form, whereas it did not alter the activation energy but increased the pre-exponential factor in the erythro form. We present a unified model to explain the origin of the substituent and stereochemical preferences by combining the theoretical and experimental results. A possible biological role of the tetrahydrofolate-independent activity in thermophiles is also discussed. PMID:22141341

Chiba, Yoko; Terada, Tohru; Kameya, Masafumi; Shimizu, Kentaro; Arai, Hiroyuki; Ishii, Masaharu; Igarashi, Yasuo

2012-02-01

149

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 ...

150

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.

Maryland Virtual High School

151

Isolation, biological activity evaluation, structure elucidation, and total synthesis of eliamid: a novel complex I inhibitor.  

PubMed

Eliamid is a secondary metabolite isolated from two bacterial strains. This molecule features a linear polyketide backbone terminated by a tetramic acid amide moiety. Among other biological activities, eliamid shows a high and specific cytostatic action on human lymphoma and cervix carcinoma cell lines. The 2,4-anti relative configuration of the C-2,C-4-dimethyl substituted amide fragment was assigned by means of Breit's rule. The absolute configuration of all stereocenters was determined by a combination of degradation methods, structural similarity analysis and total synthesis. The stereogenic centers were introduced by vinylogous Mukaiyama aldol reaction and two consecutive Myers alkylations. The use of pentafluorophenyl ester as acylation agent allowed the efficient formation of tetramic acid amide. The longest linear sequence in the synthesis consist of 13 steps and proceeds with 12% overall yield. Differential spectroscopy experiments with beef heart submitochondrial particles established that eliamid is a potent inhibitor of the NADH-ubiquinone oxidoreductase complex. Additionally, biosynthesis of eliamid was investigated by feeding experiments with (13)C-labeled precursors. PMID:22890974

Höfle, Gerhard; Gerth, Klaus; Reichenbach, Hans; Kunze, Brigitte; Sasse, Florenz; Forche, Edgar; Prusov, Evgeny V

2012-09-01

152

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

153

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

154

Reaction Time  

NSDL National Science Digital Library

In this activity, learners conduct an experiment to test how fast they can react. Learners try to catch a piece of paper with a ruler printed on it (or a ruler) as quickly as they can. Learners collect data and compare the reaction times of friends and family.

Boston, Wgbh

2003-01-01

155

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

156

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

157

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

158

Versatile One-Step One-Pot Direct Aldol Condensation Promoted by MgI2 by Han-Xun Wei*1  

E-print Network

, Qian Zhang, Richard L. Jasoni, Jiali Hu, and Paul W. Pare¬* Department of Chemistry and Biochemistry by treatment with a Lewis acid and a tertiary amine, followed by the reaction with the carbonyl acceptor. Both of the carbonyl acceptor [1][2]. Recently, we found that MgI2 is an excellent Lewis acid for C

Paré, Paul W.

159

Metal Reactions  

NSDL National Science Digital Library

This is written as a static display, but can easily be adapted to a hands-on experiment for learners to conduct. Sodium phosphate, a clear colorless solution, is combined with six different metal ion solutions. Each metal (copper, nickel, iron, silver, cobalt, and barium) forms a different color and texture precipitate. Learners discover that a chemical reaction can be identified by a color change, and formation of a precipitate. They also learn that metals can be identified by their precipitates. For safety reasons, this activity should be conducted as a demonstration for younger audiences.

2011-11-01

160

Formal total synthesis of cyanolide A.  

PubMed

Formal total synthesis of cyanolide A, aglycosidic dimeric macrolide is accomplished. The key reactions involved are asymmetric acetate aldol reaction, CBS reduction, and Shiina's lactonization. PMID:21280592

Pabbaraja, Srihari; Satyanarayana, K; Ganganna, B; Yadav, J S

2011-03-18

161

S(N)1-type substitution reactions of N-protected ?-hydroxytyrosine esters: stereoselective synthesis of ?-aryl and ?-alkyltyrosines.  

PubMed

The title compounds were prepared by aldol reaction of anisaldehyde and the respective N,N-dibenzyl glycinates. Deprotection of the nitrogen atom with Pearlman's catalyst delivered the unprotected ?-hydroxytyrosine esters, which were further N-protected as N,N-phthaloyl (Phth) and N-fluorenylmethylcarbonyloxy (Fmoc) derivatives. The Friedel-Crafts reaction with various arenes was studied employing these alcohols as electrophiles. It turned out that the facial diastereoselectivitiy depends on the nitrogen protecting group and on the ester group. The unprotected substrates (NH(2)) gave preferentially syn-products but the anti-selectivity increased when going from NHFmoc over NPhth to NBn(2). If the ester substituent was varied the syn-preference increased in the order Me < Et < iPr. The reactions were shown to be fully stereoconvergent and proceeded under kinetic product control. A model is suggested to explain the facial diastereoselectivity based on a conformationally locked benzylic cation intermediate. The reactions are preparatively useful for the N-unprotected isopropyl ester, which gave Friedel-Crafts alkylation products with good syn-selectivity (anti/syn=21:79 to 7:93), and for the N,N-dibenzyl-protected methyl ester, which led preferentially to anti-products (anti/syn=80:20 to >95:5). Upon acetylation of the latter compound to the respective acetate, Bi(OTf)(3) -catalyzed alkylation reactions became possible, in which silyl enol ethers served as nucleophiles. The respective alkylation products were obtained in high yield and with excellent anti-selectivitiy (anti/syn?95:5). PMID:22407877

Wilcke, David; Herdtweck, Eberhardt; Bach, Thorsten

2012-06-01

162

Catalysis of Photochemical Reactions.  

ERIC Educational Resources Information Center

Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

Albini, A.

1986-01-01

163

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

164

Enantioselective total synthesis of (+)-brefeldin A and 7-epi-brefeldin A.  

PubMed

A convergent enantioselective route to brefeldin A (BFA) and 7-epi-BFA was developed. The key C-4/C-5 chiral centers were established by using chiral auxiliary induced intermolecular asymmetric aldolization in the presence of TiCl(4) and TMEDA. The results with the thiazolidinethione/TiCl(4) mediated intermolecular asymmetric aldolization added some new information about the scope and limitations to the existing knowledge of that type of reactions (which so far was essentially limited to the reactions with N-propionyl thiazolidinethiones). During the course a method for protecting the liable aldol hydroxyl groups by using inexpensive TBSCl in DMF with 2,6-lutidine as the base was developed to replace the otherwise unavoidable TBSOTf procedure. Due to the excessive steric hindrance, removal of the auxiliary was much more difficult than most literature cases. Cleavage of the oxazolidinone by reduction was almost impossible. The thiazolidinethione auxiliary was relatively easier to remove. However, several reactions reported for facile removal of thiazolidinethione auxiliaries in the literature still failed. Reductive removal of the thiazolidinethione auxiliary was most effectively realized with LiBH(4) in diethyl ether in the presence of 1 equiv of MeOH (a modification of a literature procedure for removal of oxazolidinone auxiliaries in less hindered substrates). Apart from the auxiliary removal, oxidation of the alcohol into aldehyde and the deprotection of the dithiolane protecting group were also rather difficult in the present context. A range of methods were screened before final solutions were found. The five-membered ring was constructed by employing an intramolecular Mukaiyama reaction after many attempts with the intramolecular aldolization under a variety of conditions failed. The rate of elimination of the alkoxyl to form the alpha,beta-double bond of the key intermediate cyclopentenone 49 with DBU was highly solvent dependent (very sluggish in CH(2)Cl(2) but rather fast in MeOH). Introduction of the lower chain (which was synthesized by using a Jacobsen KHR to establish the C-15 chirality) was achieved through a Michael addition similar to the precedents in the literature. It has not been noticed before that the yield of this Michael reaction could be dramatically raised by using 3 equiv of the copper-lithium reagent 55. Reduction of the C-7 carbonyl was apparently more difficult than similar cases in the literature. After examination of many reagents under various conditions, it was found that the best reagent for yielding the alpha-isomer was (S)-2-methyl-CBS-borolidine/BH(3) and that for the beta-isomer was L-Selectride. The alpha- and beta-isomers were then further elaborated into (+)-brefeldin A and 7-epi-BFA, respectively. An unexpected yet very interesting solubility difference between BFA and 7-epi-BFA was also observed. PMID:15153019

Wu, Yikang; Shen, Xin; Yang, Yong-Qing; Hu, Qi; Huang, Jia-Hui

2004-05-28

165

Oxygen-dependent fragmentation reactions during the degradation of 1-deoxy-D-erythro-hexo-2,3-diulose.  

PubMed

With this work, we report on further insights into the chemistry of 1-deoxy-D-erythro-hexo-2,3-diulose (1-deoxyglucosone, 1-DG). This alpha-dicarbonyl plays an important role as a highly reactive intermediate in the Maillard chemistry of hexoses. Degradation of 1-DG in the presence of the amino acid l-alanine led to the formation of several products. Lactic acid and glyceric acid were found to be major degradation products. Their formation was dependent on the presence of oxygen. Therefore, a mechanism is postulated based on oxidation leading to a tricarbonyl intermediate. Carbonyl cleavage of this structure should then give rise to carboxylic acids. This mechanism was supported by the isotope distribution observed during degradation of different (13)C-labeled D-glucose isotopomers. Furthermore, we identified 3,5-dihydroxy-6-methyl-2,3-dihydro-4H-pyran-4-one (gamma-pyranone) to be capable of rehydration forming 1-DG to a minor extent and therefore leading to the same degradation products. The formation of carboxylic acids from gamma-pyranone was also dependent on the presence of oxygen in agreement with the postulated oxidative fragmentation. Finally, we investigated the formation of aldehydes expected as retro-aldol products formed within the degradation of 1-DG. Results seemed to rule out this reaction as an important degradation pathway under the conditions investigated herein. PMID:20441226

Voigt, Michael; Smuda, Mareen; Pfahler, Christoph; Glomb, Marcus A

2010-05-12

166

Advances in quantum and molecular mechanical (QM/MM) simulations for organic and enzymatic reactions.  

PubMed

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 for 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 semi-empirical QM method, computation of multi-dimensional 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. A comparison to 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

Acevedo, Orlando; Jorgensen, William L

2010-01-19

167

The Glyoxal Clock Reaction  

ERIC Educational Resources Information Center

Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

2007-01-01

168

Organic Reactions in Aqueous Media (by Chao-Jun Li and Tak-Hang Chan)  

NASA Astrophysics Data System (ADS)

This concise book joins the series of Wiley Interscience special topic publications. In seven chapters it selectively reviews the burgeoning literature on organic reactions conducted in water or in aqueous media as a reaction cosolvent, nicely complementing another recent book on the subject by Grieco. Following a short introduction there are six chapters that vary in length from 10 to 50 pages; they cover pericyclic reactions, nucleophilic additions and substitutions, metal-mediated reactions, transition metal-catalyzed reactions, oxidation and reduction reactions, and industrial applications. These chapters, each of which is prefaced with a short provocative quotation, also vary in depth, containing from 11 to more than 180 references. The literature is complete through 1996 and commendably includes citations of original papers by Barbier, Faraday, Frankland, Grignard, Kolbe, Lapworth, and Reformatsky as well as references to selected U.S. and foreign patents and the Russian literature. There is a subject index but no author index. This book is timely and effective. From the title, one might expect a broad discussion of the unique properties of water and water-soluble components (salts, surfactants, etc.) that would be thought to bear on organic reactivity. The first chapter opens by noting that water is the most abundant volatile material in comets and briefly describes those properties that suggest its utility as a solvent or cosolvent, summarizing the potential technical, economic, and environmental advantages. Also described are the remarkable changes in density, conductance, heat capacity, dielectric constant, and ionization constant that accompany the transition to the critical point, but the emphasis here is on the effect of water under non-critical conditions. Discussion of the structure of liquid water and the role of hydrogen bonding in mediating molecular recognition events is abbreviated. In fact, the term "hydrogen bond" is surprisingly absent from the index. The text does not explicitly include a discussion of what has come to be broadly termed biphasic reaction conditions. Understandably, enzymatic reactions are beyond the scope of the presentation. This book has a decidedly applied character with an understated environmental theme, and the authors succinctly present the extraordinary effects of water on the kinetics, efficiency, and stereoselectivity of a large number of diverse reactions. In addition to their emphasis on the historically significant aqueous Diels-Alder reaction, discovered in 1980, and the literature regarding reactions of various nucleophilic organometals, the authors are to be commended for gathering together a wide and diverse body of information: it is clear that many of the examples shown are gems buried among larger bodies of work. Thus the book does an excellent job of culling and surveying a vast amount of data. There is, however, less emphasis on organizing the mechanistic bases underlying these often dramatic effects. For example, the apparent lack of generality of the effect of water on rate and selectivity in pericyclic reactions calls for some theoretical foundation. The singularly effective use of aqueous TlOH in the Suzuki reaction is cited without comment. On the other hand, the authors' concept of a mechanistic triad that incorporates to various degrees anion, radical, or covalent character in the carbon-carbon bond-forming step between various organometals and carbonyl substrates is appealing and suggests the need for future sophisticated experimental design. The most interesting sections are those dealing with synthesis and industrial applications. Unfortunately the latter is also the shortest chapter. The synthetic examples are timely and well chosen and include water-promoted Heck, Stille, Suzuki, and aldol reactions. There is an extensive, highly informative listing and survey of the use of water-soluble phosphines (both achiral and chiral) and an excellent discussion of the diastereoselectivity that often accompanies carbonyl attack by indium, tin, and

Rosan, Reviewed Alan M.

2000-06-01

169

Formation of C-C and C-O bonds and oxygen removal in reactions of alkanediols, alkanols, and alkanals on copper catalysts.  

PubMed

This study reports evidence for catalytic deoxygenation of alkanols, alkanals, and alkanediols on dispersed Cu clusters with minimal use of external H(2) and with the concurrent formation of new C-C and C-O bonds. These catalysts selectively remove O-atoms from these oxygenates as CO or CO(2) through decarbonylation or decarboxylation routes, respectively, that use C-atoms present within reactants or as H(2)O using H(2) added or formed in situ from CO/H(2)O mixtures via water-gas shift. Cu catalysts fully convert 1,3-propanediol to equilibrated propanol-propanal intermediates that subsequently form larger oxygenates via aldol-type condensation and esterification routes without detectable involvement of the oxide supports. Propanal-propanol-H(2) equilibration is mediated by their chemisorption and interconversion at surfaces via C-H and O-H activation and propoxide intermediates. The kinetic effects of H(2), propanal, and propanol pressures on turnover rates, taken together with measured selectivities and the established chemical events for base-catalyzed condensation and esterification reactions, indicate that both reactions involve kinetically relevant bimolecular steps in which propoxide species, acting as the base, abstract the ?-hydrogen in adsorbed propanal (condensation) or attack the electrophilic C-atom at its carbonyl group (esterification). These weakly held basic alkoxides render Cu surfaces able to mediate C-C and C-O formation reactions typically catalyzed by basic sites inherent in the catalyst, instead of provided by coadsorbed organic moieties. Turnover rates for condensation and esterification reactions decrease with increasing Cu dispersion, because low-coordination corner and edge atoms prevalent on small clusters stabilize adsorbed intermediates and increase the activation barriers for the bimolecular kinetically relevant steps required for both reactions. PMID:22023723

Sad, María E; Neurock, Matthew; Iglesia, Enrique

2011-12-21

170

Cu(II)-Gd(III) cryogenic magnetic refrigerants and Cu8Dy9 single-molecule magnet generated by in situ reactions of picolinaldehyde and acetylpyridine: experimental and theoretical study.  

PubMed

A series of heterometallic [Ln(III)(x)Cu(II)(y)] complexes, [Gd2Cu2]n (1), [Gd4Cu8] (2), [Ln9Cu8] (Ln=Gd, 3·Gd; Ln=Dy, 3·Dy), were successfully synthesized by a one-pot route at room temperature with three kinds of in situ carbonyl-related reactions: Cannizzaro reaction, aldol reaction, and oxidation. This strategy led to dysprosium analogues that behaved as single-molecule magnets (SMMs) and gadolinium analogues that showed significant magnetocaloric effect (MCE). In this study a numerical DFT approach is proposed by using pseudopotentials to calculate the exchange coupling constants in three polynuclear [Gd(x)Cu(y)] complexes; with these values exact diagonalization or quantum Monte Carlo simulations have been performed to calculate the variation of the magnetic entropy involved in the MCE. For the [Dy9Cu8] complexes, local magnetic properties of the Dy(III) centers have been determined by using the CASSCF+RASSI method. PMID:24265054

Liu, Jun-Liang; Lin, Wei-Quan; Chen, Yan-Cong; Gómez-Coca, Silvia; Aravena, Daniel; Ruiz, Eliseo; Leng, Ji-Dong; Tong, Ming-Liang

2013-12-16

171

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

172

Classification of clock reactions.  

PubMed

Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. To resolve the recent dispute over the term clock reaction, we describe a new approach to classify systems featuring clock behavior into three distinct groups: substrate-depletive clock reactions, autocatalysis-driven clock reactions, and systems that have pseudo clock behavior. Many of the well-known classical and recently discovered reactions can conveniently be put into these categories. We also provide a convincing argument for classifying some autocatalytic processes as clock reactions, but it does not necessarily mean that all autocatalytic processes should be classified as autocatalysis-driven clock reactions. This classification can be conveniently performed if the kinetic nature of the given system has been completely elucidated and understood. PMID:25425415

Horváth, Attila K; Nagypál, István

2015-02-23

173

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

Chemical Reactions: this is a resource in the collection "Netorials". The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

174

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

175

Chemical Reactions and Stoichiometry  

NSDL National Science Digital Library

In this activity, students explore reactions in which chemical bonds are formed and broken. Students experiment with changing the temperature and the concentration of the atoms in order to see how these affect reaction rates. They also learn how to communicate what happens during a chemical reaction by writing the ratios of reactants and products, known as stoichiometry.

The Concord Consortium

2011-12-11

176

Reaction coordinates for electron transfer reactions  

SciTech Connect

The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

Rasaiah, Jayendran C. [Department of Chemistry, University of Maine, Orono, Maine 04469 (United States); Zhu Jianjun [Department of Chemistry, State University of New York, Stonybrook, New York 11790 (United States) and Department of Chemistry, Henan Normal University, Xinxiang, Henan (China)

2008-12-07

177

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

This activity is an inquiry-based investigation where students discover the indicators of chemical reactions (endothermic and exothermic) by collecting data and using that data to develop a testable question for further experimentation.

178

Mechanisms in Knockout Reactions  

NASA Astrophysics Data System (ADS)

We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions Be9(C9,B8+X)Y and Be9(B8,Be7+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

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

2009-06-01

179

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.

180

Sleeve reaction chamber system  

DOEpatents

A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

Northrup, M. Allen (Berkeley, CA); Beeman, Barton V. (San Mateo, CA); Benett, William J. (Livermore, CA); Hadley, Dean R. (Manteca, CA); Landre, Phoebe (Livermore, CA); Lehew, Stacy L. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

2009-08-25

181

Radical reactions of borohydrides.  

PubMed

Borohydrides are an important class of reagents in both organic and inorganic chemistry. Though popular as hydride-transfer reagents for reduction, since earlier work from the 1970s, borohydride reagents have also been known to serve as hydrogen-transfer reagents. In pursuit of greener tin hydride substitutes, recent progress has been made to mediate radical C-C bond forming reactions, including Giese reactions, radical carbonylation and addition to HCHO reactions, with borohydride reagents. This review article focuses on state-of-the-art borohydride based radical reactions, also covering earlier work, kinetics and some DFT calculations with respect to the hydrogen transfer mechanism. PMID:25349957

Kawamoto, Takuji; Ryu, Ilhyong

2014-12-28

182

Electrode kinetics: reactions  

Microsoft Academic Search

This is Volume 27 in the Comprehensive Chemical Kinetics series. The contributors are Calvo (Argentina), Hamnett (England), O'Sullivan (United States), and Weaver (United States). The book's chapters cover Redox Reactions at Metal-Solution Interfaces, Semiconductor Electrochemistry, and Reactions at Metal Oxide Electrodes. The references date from the 1960s to the mid-1980s. An index is included.

1987-01-01

183

Reactions to Attitudinal Deviancy.  

ERIC Educational Resources Information Center

This paper presents a critical review of empirical and theoretical treatments of group reaction to attitudinal deviancy. Inspired by Festinger's (1950) ideas on resolution of attitudinal discrepancies in groups, Schachter (1951) conducted an experiment that has greatly influenced subsequent research and theory concerning reaction to attitudinal…

Levine, John M.; Allen, Vernon L.

184

Clock Reaction: Outreach Attraction  

ERIC Educational Resources Information Center

Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

2010-01-01

185

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

186

Oscillating Chemical Reactions  

ERIC Educational Resources Information Center

Describes several oscillating chemical reactions which can be used in undergraduate chemistry laboratories. In one such reaction, ferroin oscillates from red (reducing solution) to blue (oxidizing solution) for about an hour at a frequency which can readily be shown to depend on such factors as the temperature, type of solvent, and concentration…

Hawkins, M. D.; And Others

1975-01-01

187

Mechanisms in knockout reactions  

NASA Astrophysics Data System (ADS)

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 ^9Be(^9C,^8B+X)Y and ^9Be(^8B,^7Be+X)Y are presented. They are compared with theoretical predictions for both the diffraction (elastic breakup) and stripping (inelastic breakup) 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. In particular, this add considerable support to the use of the eikonal model as a quantitative tool, able, for example, to determine single-particle spectroscopic strengths in rare isotopes.

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

2009-10-01

188

Oral Hypersensitivity Reactions  

MedlinePLUS

... Million NIDCR/NIH Grant 2015 AAOM Call for Abstract Submissions Upcoming Events 2015 Annual Conference Registration is Now Open 2016 Annual Meeting in Atlanta - Save the Date! Oral Hypersensitivity Reactions ...

189

Types of Allergic Reactions  

MedlinePLUS

... allergies. Substances that don't bother some people (including certain medications) can trigger allergic reactions in others. ... | Terms and Conditions © 1996-2015 Academy of General Dentistry. All Rights Reserved.

190

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

191

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...

192

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.; Idsöe, O.; Willcox, R. R.

1958-01-01

193

Polymerase Chain Reaction  

NSDL National Science Digital Library

This interactive activity adapted from the University of Nebraska's Library of Crop Technologies depicts steps in the polymerase chain reaction (PCR) technique and explains how it is used to efficiently copy sections of DNA for analysis.

WGBH Educational Foundation

2009-12-07

194

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

195

Nitropyridines: Synthesis and reactions  

Microsoft Academic Search

Reaction of pyridine and substituted pyridines with N2O5 in an organic solvent gives the N-nitropyridinium ion. When this is reacted with SO2\\/HSO3 - in water, 3-nitropyri- dine is obtained (77 % yield). With substituted pyridines, the method gives good yields for 4-substituted and moderate yields for 3-substituted pyridines. The reaction mechanism is not an electrophilic aromatic substitution, but one in

Jan M. Bakke

2003-01-01

196

Safety of chlorination reactions  

Microsoft Academic Search

Chlorination reactions are part of various processes in the chemical industry, to manufacture heavy chemicals, specialty chemicals, pesticides and pharmaceuticals, in inorganic and organic chemistry. They are a valuable tool in organic synthesis.The hazard of processing chlorine involves:u- Gas phase explosion;- Runaway reaction or thermal explosion in the condensed phase.Gas phase explosion hazard with chlorine as an oxidizer is present

Jean-Louis Gustin; Alexandre Fines

1996-01-01

197

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.

198

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

199

[Cutaneous adverse drug reactions.  

PubMed

Cutaneous adverse drug reactions (CADR) represent a heterogeneous field including various clinical patterns without specific features suggesting drug causality. Exanthematous eruptions, urticaria and vasculitis are the most common forms of CADR. Fixed eruption is uncommon in western countries. Serious reactions (fatal outcome, sequelae) represent 2% of CADR: bullous reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), DRESS (drug reaction with eosinophilia and systemic symptoms or drug-induced hypersensitivity syndrome) and acute generalized exanthematous pustulosis (AGEP). These forms must be quickly diagnosed to guide their management. The main risk factors are immunosuppression, autoimmunity and some HLA alleles in bullous reactions and DRESS. Most systemic drugs may induce cutaneous adverse reactions, especially antibiotics, anticonvulsivants, antineoplastic drugs, non-steroidal anti-inflammatory drugs, allopurinol and contrast media. Pathogenesis includes immediate or delayed immunologic mechanism, usually not related to dose, and pharmacologic/toxic mechanism, commonly dose-dependent or time-dependent. In case of immunologic mechanism, allergologic exploration is possible to clarify drug causality, with a variable sensitivity according to the drug and to the CADR type. It includes epicutaneous patch testing, prick test and intradermal test. However, no in vivo or in vitro test can confirm the drug causality. To determine the cause of the eruption, a logical approach based on clinical characteristics, chronologic factors and elimination of differential diagnosis is required, completed with a literature search. A reporting to pharmacovigilance network is essential in case of a serious CADR whatever the suspected drug and in any case if the involved drug is a newly marketed one or unusually related to cutaneous reactions. PMID:25458866

Lebrun-Vignes, B; Valeyrie-Allanore, L

2014-11-01

200

Generation of cholesterol carboxyaldehyde by the reaction of singlet molecular oxygen [O2 (1Delta(g))] as well as ozone with cholesterol.  

PubMed

A few years ago, it was reported that ozone is produced in human atherosclerotic arteries, on the basis of the identification of 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al and 3beta-hydroxy-5beta-hydroxy-B-norcholestane-6beta-carboxaldehyde (ChAld) as their 2,4-dinitrophenylhydrazones. The formation of endogenous ozone was attributed to water oxidation catalyzed by antibodies, with the formation of dihydrogen trioxide as a key intermediate. We now report that ChAld is also generated by the reaction of cholesterol with singlet molecular oxygen [O2 (1Delta(g))] that is produced by photodynamic action or by the thermodecomposition of 1,4-dimethylnaphthalene endoperoxide, a defined pure chemical source of O2 (1Delta(g)). On the basis of 18O-labeled ChAld mass spectrometry, NMR, light emission measurements, and derivatization studies, we propose that the mechanism of ChAld generation involves the formation of the well-known cholesterol 5alpha-hydroperoxide (5alpha-OOH) (the major product of O2 ((1)Delta(g))-oxidation of cholesterol) and/or a 1,2-dioxetane intermediate formed by O2 (1Delta(g)) attack at the Delta(5) position. The Hock cleavage of 5alpha-OOH (the major pathway) or unstable cholesterol dioxetane decomposition (a minor pathway, traces) gives a 5,6-secosterol intermediate, which undergoes intramolecular aldolization to yield ChAld. These results show clearly and unequivocally that ChAld is generated upon the reaction of cholesterol with O2 (1Delta(g)) and raises questions about the role of ozone in biological processes. PMID:19358613

Uemi, Miriam; Ronsein, Graziella E; Miyamoto, Sayuri; Medeiros, Marisa H G; Di Mascio, Paolo

2009-05-01

201

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.

2014-01-28

202

Proton-transfer reaction dynamics  

Microsoft Academic Search

In this article we discuss the progress made in understanding intermolecular and intermolecular reactions of proton (or hydrogen-atom) transfer. Femtosecond real-time probing, together with spectroscopic studies, in molecular beams are presented with selected examples of reactions. Reaction rates, tunneling dynamics and the nature of the reaction coordinate are examined and related to two-state multidimensional potential energy surfaces.

Abderrazzak Douhal; Françoise Lahmani; Ahmed H. Zewail

1996-01-01

203

Inorganic Reaction Mechanisms. Part I  

ERIC Educational Resources Information Center

Provides a collection of data on the mechanistic aspects of inorganic chemical reactions. Wherever possible includes procedures for classroom demonstration or student project work. The material covered includes gas phase reactions, reactions in solution, mechanisms of electron transfer, the reaction between iron III and iodine, and hydrolysis. (GS)

Cooke, D. O.

1976-01-01

204

Polarization in inclusive reactions  

Microsoft Academic Search

A formalism for discussing the spin dependence of inclusive reactions is presented. The role of various constraints following from conservation of parity and angular momentum conservation is discussed. Expressions for specific single and double polarization observables are presented. Predictions of the triple-Regge model for these observables are given.

Gary R. Goldstein; Joseph F. Owens

1976-01-01

205

The aromatic ene reaction  

PubMed Central

The ene reaction is a pericyclic process in which an alkene having 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 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: (i) hexadehydro-Diels-Alder (for aryne generation), (ii) intramolecular aromatic ene, and (iii) 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 multi-stage, reagent- and byproduct-free, single-pot transformations. PMID:24345944

Niu, Dawen; Hoye, Thomas R.

2014-01-01

206

Parallelization for reaction  

E-print Network

Parallelization for reaction waves with complex chemistry Context Application Background Numerical with complex chemistry S. Descombes 2 M. Duarte 3 T. Dumont 1 V. Louvet 1 M. Massot 3 1Camille Jordan Institute - France 3EM2C Laboratory - Ecole Centrale Paris - France Workshop on Computational and Applied Mathematics

Louvet, Violaine

207

Chemical Reactions at Surfaces  

SciTech Connect

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 program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

Michael Henderson and Nancy Ryan Gray

2010-04-14

208

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.

209

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.

210

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.

211

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

212

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

213

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

214

Photoneutron reactions in astrophysics  

NASA Astrophysics Data System (ADS)

Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing ? --decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between 74Se and 196Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in ( ?, n), ( ?, p), or ( ?, ?) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

Varlamov, V. V.; Ishkhanov, B. S.; Orlin, V. N.; Peskov, N. N.; Stopani, K. A.

2014-12-01

215

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 activated—one 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.)

Maisie Shaw

2009-01-01

216

Postmarketing adverse drug reactions  

PubMed Central

Summary Physicians play an important role in recognizing and reporting suspected adverse drug reactions (ADRs) to the Food and Drug Administration (FDA). Physicians can report suspected ADRs directly to the FDA via its MedWatch program, by contacting the manufacturer of the drug, and by publishing case reports. While this takes time, physicians have an ethical obligation to participate in recognizing and reporting ADR. PMID:24195018

Bourdette, Dennis

2013-01-01

217

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

218

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.

219

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

220

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

221

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

222

Procedures for Decomposing a Redox Reaction into Half-Reaction  

ERIC Educational Resources Information Center

A simple algorithm for a complete enumeration of the possible ways a redox reaction (RR) might be uniquely decomposed into half-reactions (HRs) using the response reactions (RERs) formalism is presented. A complete enumeration of the possible ways a RR may be decomposed into HRs is equivalent to a complete enumeration of stoichiometrically…

Fishtik, Ilie; Berka, Ladislav H.

2005-01-01

223

Reaction Extrema: Extent of Reaction in General Chemistry  

ERIC Educational Resources Information Center

Nearly 100 years ago de Donder introduced the term "extent of reaction", ?. We build on that work by defining the concept of reagent extrema for an arbitrary chemical reaction, aA + bB [reversible reaction] yY + zZ. The central equation is ?^[subscript i] = -n[subscript i,0]/?[subscript i]. The symbol ?^[subscript i] represents the…

Vandezande, Jonathon E.; Vander Griend, Douglas A.; DeKock, Roger L.

2013-01-01

224

Classes of Chemical Reactions Reactions in aqueous media  

E-print Network

acid, HBr Phosphoric acid, H3PO4 Hydroiodic acid, HI Acetic acid, CH3CO2H Nitric acid, HNO3 CarbonicClasses of Chemical Reactions Reactions in aqueous media · Precipitation reactions · Acid + electrolytes: a substance that conducts an electric current when dissolved in water Acids are donors of H

Zakarian, Armen

225

Single Replacement Micro-Reactions  

NSDL National Science Digital Library

In this chemistry activity, learners use common chemicals and metals to explore single replacement reactions. Learners will record any color changes or gas production for each reaction as well as write a balanced equation for each.

The Science House

2014-01-28

226

ChemTeacher: Combination 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 Combination Reactions page includes resources for teaching students about identifying and predicting combination reactions.

2011-01-01

227

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

228

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.

David A. Katz

2009-07-09

229

Hydrazine decomposition and other reactions  

NASA Technical Reports Server (NTRS)

This invention relates to the catalytic decomposition of hydrazine, catalysts useful for this decomposition and other reactions, and to reactions in hydrogen atmospheres generally using carbon-containing catalysts.

Armstrong, Warren E. (Inventor); La France, Donald S. (Inventor); Voge, Hervey H. (Inventor)

1978-01-01

230

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

231

More on Chemical Reaction Balancing.  

ERIC Educational Resources Information Center

A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

Swinehart, D. F.

1985-01-01

232

Double Replacement Micro-Reactions  

NSDL National Science Digital Library

In this chemistry activity, learners use common chemicals to examine reactions that occur between two aqueous solutions. Learners will record any color changes or precipitate formation for each reaction as well as write a balanced equation for each. Learners will discover that the driving force for the reaction is the formation of an insoluble product.

2014-01-28

233

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

234

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. Mancano at ISMP, 200 Lakeside Drive, Suite 200, Horsham, PA 19044 (phone: 215-707-4936; e-mail: mmancano@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:24421518

2013-01-01

235

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. Mancano at ISMP, 200 Lakeside Drive, Suite 200, Horsham, PA 19044 (phone: 215-707-4936; e-mail: mmancano@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:24421544

2013-01-01

236

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. Mancano at ISMP, 200 Lakeside Drive, Suite 200, Horsham, PA 19044 (phone: 215-707-4936; e-mail: mmancano@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:24474829

2013-01-01

237

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.

2012-08-02

238

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

239

Reactions inside nanoscale protein cages  

NASA Astrophysics Data System (ADS)

Chemical reactions are traditionally carried out in bulk solution, but in nature confined spaces, like cell organelles, are used to obtain control in time and space of conversion. One way of studying these reactions in confinement is the development and use of small reaction vessels dispersed in solution, such as vesicles and micelles. The utilization of protein cages as reaction vessels is a relatively new field and very promising as these capsules are inherently monodisperse, in that way providing uniform reaction conditions, and are readily accessible to both chemical and genetic modifications. In this review, we aim to give an overview of the different kinds of nanoscale protein cages that have been employed as confined reaction spaces.

Bode, Saskia A.; Minten, Inge J.; Nolte, Roeland J. M.; Cornelissen, Jeroen J. L. M.

2011-06-01

240

Radiation reaction in various dimensions  

Microsoft Academic Search

We discuss the radiation reaction problem for an electric charge moving in flat space-time of arbitrary dimensions. It is shown that four is the unique dimension where a local differential equation exists accounting for the radiation reaction and admitting a consistent mass-renormalization (the Dirac-Lorentz equation). In odd dimensions the Huygens principle does not hold; as a result, the radiation reaction

D. V. Gal

241

Radiation reaction in various dimensions  

Microsoft Academic Search

We discuss the radiation reaction problem for an electric charge moving in\\u000aflat space-time of arbitrary dimensions. It is shown that four is the unique\\u000adimension where a local differential equation exists accounting for the\\u000aradiation reaction and admitting a consistent mass-renormalization (the\\u000aDirac-Lorentz equation). In odd dimensions the Huygens principle does not hold;\\u000aas a result, the radiation reaction

Dmitri Gal’tsov

2002-01-01

242

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

243

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

2009-01-22

244

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

245

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

246

Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions  

ERIC Educational Resources Information Center

A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

Schultz, Emeric

2008-01-01

247

Activity : Fusion Reactions  

NSDL National Science Digital Library

This activity gives students an opportunity to learn about the elements created in the cores of high-mass stars by fusion reactions. They will discover that all stars start by burning hydrogen and end up creating many heavier elements inside their cores, elements that will be released into space when it dies in a supernova explosion. Students associate a layer with an element that is being produced by the high-mass star. This will illustrate that as the temperature of the star increases with depth, the ash of each burning stage becomes the fuel for the next stage. Surrounding the core of iron nuclei is a layer of silicon fusion, then magnesium, then neon, then oxygen, then carbon, then helium, and lastly, in the relatively cool periphery of the core, hydrogen fuses into helium. Students will draw their own version of the onion-like nature of the core of a star based on the model and explain the process that occurs at each layer.

2007-12-12

248

Two chamber reaction furnace  

DOEpatents

A vertical two chamber reaction furnace is described. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium-copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700 C and 800 C) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800 to 950 C to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product. 2 figs.

Blaugher, R.D.

1998-05-05

249

Radiation reaction in various dimensions  

Microsoft Academic Search

We discuss the radiation reaction problem for an electric charge moving in flat space-time of arbitrary dimensions. It is shown that four is the unique dimension where a local differential equation exists accounting for the radiation reaction and admitting a consistent mass renormalization (the Lorentz-Dirac equation). In odd dimensions Huygens's principle does not hold, and, as a result, the radiation

Dmitri V. Gal'Tsov

2002-01-01

250

Participants' Reactions to Assessment Centers.  

ERIC Educational Resources Information Center

A study of 37 people who have gone through a one-day assessment center measures the reactions of participants (equally divided into high and low scorers) to their experiences, and compares the reactions of high scorers with those of low scorers. Recommendations are made for the use of assessment centers. (MLF)

Teel, Kenneth S.; DuBois, Henry

1983-01-01

251

Reaction/Aggregation Clment Sire  

E-print Network

and chemistry Atoms diffusing on a surface and Diffusion Limited Aggregation Atomic clusters Chemical or even d· 4 for diffusion processes) Out of equilibrium reaction/aggregation processes can leadReaction/Aggregation Processes Clément Sire Laboratoire de Physique Théorique CNRS & Université

Giraud, Olivier

252

Pharmacogenomics of adverse drug reactions  

PubMed Central

Considerable progress has been made in identifying genetic risk factors for idiosyncratic adverse drug reactions in the past 30 years. These reactions can affect various tissues and organs, including liver, skin, muscle and heart, in a drug-dependent manner. Using both candidate gene and genome-wide association studies, various genes that make contributions of varying extents to each of these forms of reactions have been identified. Many of the associations identified for reactions affecting the liver and skin involve human leukocyte antigen (HLA) genes and for reactions relating to the drugs abacavir and carbamazepine, HLA genotyping is now in routine use prior to drug prescription. Other HLA associations are not sufficiently specific for translation but are still of interest in relation to underlying mechanisms for the reactions. Progress on non-HLA genes affecting adverse drug reactions has been less, but some important associations, such as those of SLCO1B1 and statin myopathy, KCNE1 and drug-induced QT prolongation and NAT2 and isoniazid-induced liver injury, are considered. Future prospects for identification of additional genetic risk factors for the various adverse drug reactions are discussed. PMID:23360680

2013-01-01

253

Cutaneous Manifestation Of Drug Reactions  

PubMed Central

Every drug is capable of inducing an adverse reaction in susceptible individuals, and physicians should always be on the alert for this when they prescribe a drug, or when they see unusual skin rashes. This article lists some of the more commonly seen reactions, together with the drugs which induce them. ImagesFig. 1Fig. 2Fig. 3Fig. 4 PMID:20468978

Schachter, R. K.

1973-01-01

254

Foreperiod and simple reaction time  

Microsoft Academic Search

Reviews studies of simple visual and auditory reaction processes published since W. H. Teicher (1954), with emphasis on the preparatory phase of these processes, particularly the foreperiod (FP). The 1st section consists of the analysis of actual FP variables; duration, regularity, range, distribution, and preceding FPs. The 2nd section deals with factors affecting the relation between FP and reaction time

Pekka Niemi; Risto Näätänen

1981-01-01

255

Foreign body reaction to biomaterials  

Microsoft Academic Search

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

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

2008-01-01

256

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

257

Oxide formation: reaction details studied,  

E-print Network

-nitrosohydroxylamines undergo an alternative decomposition under very similar reaction conditions to liberate nitrous oxide, N2O to human health. Investigation of the molecular basis of these alternative reactions of N recent work at Newcastle on the mechanisms of decomposition of N-nitrosohydroxylamines in which we

Johnson, Edward A.

258

Acute dystonic reaction with rivastigmine.  

PubMed

Dystonic reactions are adverse extrapyramidal side effects and are common to antipsychotics, antiemetics, and a variety of other drugs. Rivastigmine, an anticholinesterase of carbamate variety, is well tolerated. A case of acute dystonic reaction with rivastigmine patch is being reported. PMID:23561545

Dhikav, Vikas; Anand, Kuljeet Singh

2013-08-01

259

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

260

Adverse Reactions to Hallucinogenic Drugs.  

ERIC Educational Resources Information Center

This reports a conference of psychologists, psychiatrists, geneticists and others concerned with the biological and psychological effects of lysergic acid diethylamide and other hallucinogenic drugs. Clinical data are presented on adverse drug reactions. The difficulty of determining the causes of adverse reactions is discussed, as are different…

Meyer, Roger E. , Ed.

261

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

262

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

263

[Skin reactions to tattoo ink].  

PubMed

Ritual and artistic tattoos rely on the use of numerous pigments which are not all entirely inert once placed in the dermis. The compositions of some tattoo inks are identified. However, new but less well identified compounds appear on the market. Allergic reactions can be present under different aspects. They may correspond to allergic contact dermatitis or to photodermatitis. Other reactions include allergic hypersensitivity reactions as well as lichenoid, granulomatous or pseudolymphoma reactions. Pulsed light and laser are typically used for regular tattoo removal. These procedures are not indicated in inflamed tattoos. Indeed, the pigment dispersed during photolysis may perpetuate the reaction. Pseudotattoos due to the stratum corneum staining are frequently responsible for photoeczema. PMID:21942077

Piérard-Franchimont, C; Hermanns, J-F; Piérard, G E

2011-01-01

264

Eikonal reaction theory for two-neutron removal reactions  

NASA Astrophysics Data System (ADS)

The eikonal reaction theory (ERT) proposed lately is a method of calculating one-neutron removal reactions at intermediate incident energies in which Coulomb breakup is treated accurately with the continuum discretized coupled-channels method. ERT is extended to two-neutron removal reactions. ERT reproduces measured one- and two-neutron removal cross sections for He6 scattering on C12 and Pb208 targets at 240 MeV/nucleon and also on a Si28 target at 52 MeV/nucleon. For the heavier target in which Coulomb breakup is important, ERT yields much better agreement with the measured cross sections than the Glauber model.

Minomo, K.; Matsumoto, T.; Egashira, K.; Ogata, K.; Yahiro, M.

2014-08-01

265

Dynamic reaction path analysis based on an intrinsic reaction coordinate  

NASA Astrophysics Data System (ADS)

We propose two methods that may be used to describe the dynamic reaction path (DRP) based on an intrinsic reaction coordinate (IRC) or minimum energy path, to examine how the actual dynamics proceeds relative to the IRC path. In the first of these, any point on the DRP is expressed in terms of the IRC and the distance from the IRC path. In the second method, any DRP point is expressed in terms of the IRC, the curvature coordinate, and the distance from a two-dimensional ``reaction plane'' determined by the IRC path tangent and curvature vectors. The latter representation is based on the fact that the 3N-8 dimensional space orthogonal to the reaction plane is independent of an internal centrifugal force caused by the motion along the IRC path. To analyze the relation between geometrical features of the IRC path and the dynamics, we introduce a function that estimates the variation of the reaction plane along the IRC path. As demonstrations, the methods are applied to the dissociation reaction of thiofolmaldehyde (H2CS?H2+CS).

Taketsugu, Tetsuya; Gordon, Mark S.

1995-12-01

266

Reactions at supercritical conditions: Applications and fundamentals  

Microsoft Academic Search

Supercritical fluids possess properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (Solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous

Phillip E. Savage; Sudhama Gopalan; Thamid I. Mizan; Christopher J. Martino; Eric E. Brock

1995-01-01

267

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

268

Solar-thermal reaction processing  

DOEpatents

In an embodiment, a method of conducting a high temperature chemical reaction that produces hydrogen or synthesis gas is described. The high temperature chemical reaction is conducted in a reactor having at least two reactor shells, including an inner shell and an outer shell. Heat absorbing particles are included in a gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight. The inner shell re-radiates from the inner wall and heats the heat absorbing particles in the gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream, thereby heating the reactants in the gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the gas stream.

Weimer, Alan W; Dahl, Jaimee K; Lewandowski, Allan A; Bingham, Carl; Raska Buechler, Karen J; Grothe, Willy

2014-03-18

269

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

270

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

271

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

272

Bystanders' Reactions to Sexual Harassment  

E-print Network

Sexual harassment is associated with negative consequences for victims and bystanders. Because 9 in 10 victims do not report harassment, understanding bystanders' reactions to sexual harassment is important. Thus, my dissertation?s purpose...

Benavides Espinoza, Claudia

2010-07-14

273

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

274

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

275

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

276

Antidamping effect of radiation reaction  

Microsoft Academic Search

The anti-damping effect of radiation reaction, which means the radiation reaction does non-negative work on a radiating charge, is investigated at length by using the Lorentz-Dirac equation (LDE) for the motion of a point charge respectively acted on by (a) a pure electric field, (b) a pure magnetic field and (c) the fields of an electromagnetic wave. We found that

G. Wang; H. Li; Y. F. Shen; X. Z. Yuan; J. Zi

2010-01-01

277

Organocatalytic Enantioselective Synthesis of ?-Hydroxy Phosphonates  

PubMed Central

Tertiary ?-hydroxy phosphonates have been synthesized in good yields and high enantiomeric purity (up to 99% ee) through a novel L-proline-catalyzed cross aldol reaction of ?-keto phosphonates and ketones. PMID:16756289

Samanta, Sampak; Zhao, Cong-Gui

2008-01-01

278

Gold-Catalyzed Multi-Component Reactions  

NASA Astrophysics Data System (ADS)

The following sections are included: * Introduction * Gold-Catalyzed Three-Component Reactions * Gold-Catalyzed Three-Component Reactions/Tandem Cyclization * Concluding Remarks * Acknowledgments * References

Skouta, Rachid; Li, Chao-Jun

2014-04-01

279

Inorganic Reaction Mechanisms Part II: Homogeneous Catalysis  

ERIC Educational Resources Information Center

Suggests several mechanisms for catalysis by metal ion complexes. Discusses the principal factors of importance in these catalysis reactions and suggests reactions suitable for laboratory study. (MLH)

Cooke, D. O.

1976-01-01

280

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

281

Thermal reactions of brushite cements.  

PubMed

The thermal reactions of a brushite cement made of beta-tricalcium phosphate (beta-TCP), monocalcium phosphate monohydrate (MCPM), and an aqueous solution were followed in situ with an isothermal calorimeter at 37 degrees C. The investigated parameters were the beta-TCP/MCPM weight ratio, the liquid-to-powder ratio, the synthesis route and milling duration of the beta-TCP powder, as well as the presence of sulfate, citrate, and pyrophosphate ions in the mixing liquid. The thermograms were complex, particularly for mixtures containing an excess of MCPM or additives in the mixing solution. Results suggested that the endothermic MCPM dissolution and the highly exothermic beta-TCP dissolution occurred simultaneously, thereby leading to the formation of a large exothermic peak at early reaction time. Both reactions were followed by the exothermic crystallization of brushite and in the presence of an excess of MCPM by the endothermic crystallization of monetite. Additives generally widened the main exothermic reaction peak, or in some cases with pyrophosphate ions postponed the main exothermic peak at late reaction time. Generally, the results could be well explained and understood based on thermodynamic and solubility data. PMID:17618509

Bohner, M; Gbureck, U

2008-02-01

282

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,

283

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

284

Adverse reaction to intravenous gadoteridol.  

PubMed

Moderate and severe anaphylactoid reactions--while extremely rare--have been reported in association with intravenous administration of gadopentetate dimeglumine. There has been no similar experience related to use of the newly released magnetic resonance (MR) imaging contrast agent gadoteridol. The authors describe a case of vasovagal response and anaphylactoid reaction during intravenous administration of gadoteridol. MR users should be aware of the potential for adverse effects to occur in association with use of gadoteridol and be prepared by implementing appropriate observation procedures for patients receiving this as well as other MR contrast agents. In addition, physiologic monitoring devices and resuscitation equipment should be readily available in the clinical MR setting for proper treatment of patients who may experience moderate to severe adverse reactions. PMID:8372186

Shellock, F G; Hahn, H P; Mink, J H; Itskovich, E

1993-10-01

285

Radiation reaction in various dimensions  

E-print Network

We discuss the radiation reaction problem for an electric charge moving in flat space-time of arbitrary dimensions. It is shown that four is the unique dimension where a local differential equation exists accounting for the radiation reaction and admitting a consistent mass-renormalization (the Dirac-Lorentz equation). In odd dimensions the Huygens principle does not hold; as a result, the radiation reaction force depends on the whole past history of a charge (radiative tail). We show that the divergence in the tail integral can be removed by the mass renormalization only in the 2+1 theory. In even dimensions higher than four, divergences can not be removed by a renormalization.

Galtsov, D V

2002-01-01

286

Radiation reaction in various dimensions  

NASA Astrophysics Data System (ADS)

We discuss the radiation reaction problem for an electric charge moving in flat space-time of arbitrary dimensions. It is shown that four is the unique dimension where a local differential equation exists accounting for the radiation reaction and admitting a consistent mass renormalization (the Lorentz-Dirac equation). In odd dimensions Huygens's principle does not hold, and, as a result, the radiation reaction force depends on the whole past history of a charge (radiative tail). We show that the divergence in the tail integral can be removed by the mass renormalization only in the 2+1 theory. In even dimensions higher than four, divergences cannot be removed by the mass renormalization.

Gal'Tsov, Dmitri V.

2002-07-01

287

Urticarial intolerance reaction to cetirizine.  

PubMed

The paradoxical acute exacerbation of pre-existing chronic idiopathic urticaria accompanied by intense generalized pruritus, facial oedema, and dyspnoea in a 36-year-old-woman 3-4 h after a single oral dose of 10 mg cetirizine (Zyrtec tablets), suggested the presence of an underlying intolerance reaction. However, a type I hypersensitivity reaction also had to be excluded. Detailed allergy testing supported the view that the patient had suffered an intolerance reaction to cetirizine. This is the third known case of most probably a nonallergic generalized urticaria following the administration of cetirizine, a drug with extensive usage worldwide. However a type I sensitization to cetirizine is indeed possible, as has been demonstrated in this research with the verification of cetirizine-specific IgE antibodies in one of the control sera. PMID:12072003

Schröter, S; Damveld, B; Marsch, W C

2002-05-01

288

Surface reactions of natural glasses  

SciTech Connect

Reactions at natural glass surfaces are important in studies involving nuclear waste transport due to chemical control on ground water in host rocks such as basalt and tuff, to potential diffusion into natural hydrated glass surfaces and as natural analogs for waste glass stability. Dissolution kinetics can be described by linear surface reaction coupled with cation interdiffusion with resulting rates similar to those of synthetic silicate glasses. Rates of Cs diffusion into hydrated obsidian surfaces between 25{sup 0} and 75{sup 0}C were determined by XPS depth profiles and loss rates from aqueous solutions. Calculated diffusion coefficients were ten others of magnitude more rapid than predicted from an Arrhenius extrapolation of high temperature tracer diffusion data due to surface hydration reactions.

White, A.F.

1986-12-31

289

Coupled Reactions "versus" Connected Reactions: Coupling Concepts with Terms  

ERIC Educational Resources Information Center

A hallmark of living matter is its ability to extract and transform energy from the environment. Not surprisingly, biology students are required to take thermodynamics. The necessity of coupling exergonic reactions to endergonic processes is easily grasped by most undergraduate students. However, when addressing the thermodynamic concept of…

Aledo, Juan Carlos

2007-01-01

290

Internal friction in enzyme reactions.  

PubMed

The empirical concept of internal friction was introduced 20 years ago. This review summarizes the results of experimental and theoretical studies that help to uncover the nature of internal friction. After the history of the concept, we describe the experimental challenges in measuring and interpreting internal friction based on the viscosity dependence of enzyme reactions. We also present speculations about the structural background of this viscosity dependence. Finally, some models about the relationship between the energy landscape and internal friction are outlined. Alternative concepts regarding the viscosity dependence of enzyme reactions are also discussed. PMID:23281036

Rauscher, Anna; Derényi, Imre; Gráf, László; Málnási-Csizmadia, András

2013-01-01

291

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

292

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

293

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

294

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

295

Cutaneous reactions to neurologic drugs.  

PubMed

Neurologic drugs are often implicated as the causative agents producing skin eruptions. In our highly medicated society, correctly identifying the offending medication is often difficult. Determining the causative agent involves knowledge of the common offenders, their frequency of occurrence, and understanding the commonly produced reaction patterns in the skin. PMID:2957583

Ahrens, E M

1987-08-01

296

Recyclization reactions leading to benzimidazoles  

NASA Astrophysics Data System (ADS)

The published data on the recyclization reactions that afford benzimidazoles are generalized and systematized. Both classical and new methods of benzimidazole synthesis are considered. Attention is focused on the publications over the recent 10-15 years; of the earlier publications, only those unknown to the wide circle of chemists are analyzed.

Mamedov, Vakhid A.; Murtazina, Anna M.

2011-05-01

297

Runaway Reaction: Solving for X.  

ERIC Educational Resources Information Center

This article examines the runaway reaction as it was displayed by Barry, a 14-year-old eighth-grade boy with learning disabilities. It identifies some of the common characteristics of this response and proposes school intervention methods. Functional behavioral assessments and strength-based assessments are encouraged, along with using strategy…

Bartz, Solveig A.

2003-01-01

298

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

299

Theoretical studies of reaction surfaces  

NASA Astrophysics Data System (ADS)

The main goals in the previous grant period have been to develop new, more effective methods for performing accurate ab initio electronic structure calculations and to use these methods for the prediction of molecular structure, bonding and reactivity, especially for main group species and reactions of interest to the Air Force. From the theoretical point of view, the principle accomplishments have been extensive development of approaches and codes for performing electronic structure calculations in parallel, continued development of methods for interfacing electronic structure calculations with dynamics, initial studies of the possibility of splicing together different levels of electronic structure theory, and the development of a new model for treating solvation. Applications have ranged from the development of very accurate and extensive potential energy surfaces for A +HB reactions (to interface with the experiments) to the role of catalysts in the hydrosilation reaction to extensive studies of reactions involved in both main group and transition metal chemical vapor deposition (CVD) to broad-based studies of cage molecules (using our new parallel capabilities) that are potential precursors for new materials electronic and optical devices and catalysts. A new area that we have entered into is a series of systematic calculations on transition metal(TM)-main group (MG) compounds and their roles and catalysts and in such important area as CVD.

Gordon, Mark S.

1994-08-01

300

Psychophysiological Reactions to International Adjustment  

Microsoft Academic Search

Background: This controlled prospective study examines psychophysiological reactions in employees during their first and second year abroad to identify individual as well as work-related factors predictive of positive adjustment. Methods: Employees (n = 47) relocating from Sweden to a foreign country on a work-related assignment were followed. The subjects completed a questionnaire before relocation and after 1 and 2 years

Ingrid Anderzén; Bengt B. Arnetz

1999-01-01

301

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

302

Adverse drug reactions in dermatology.  

PubMed

Adverse drug reactions (ADRs) - that is, unintended and harmful responses to medicines - are important to dermatologists because many present with cutaneous signs and because dermatological treatments can cause serious ADRs. The detection of ADRs to new drugs is often delayed because they have a long latency or are rare or unexpected. This means that ADRs to newer agents emerge only slowly after marketing. ADRs are part of the differential diagnosis of unusual rashes. A good drug history that includes details of drug dose, time-course of the reaction and factors that may make the patient more susceptible, will help. For example, Stevens-Johnson syndrome with abacavir is much commoner in patients with HLA-B*5701, and has a characteristic time course. Newer agents have brought newer reactions; for example, acneiform rashes associated with epidermal growth factor receptor inhibitors such as erlotinib. Older systemic agents used to treat skin disease, including corticosteroids and methotrexate, cause important ADRs. The adverse effects of newer biological agents used in dermatology are becoming clearer; for example, hypersensitivity reactions or loss of efficacy from antibody formation and progressive multifocal leucoencephalopathy due to reactivation of latent JC (John Cunningham) virus infections during efalizumab treatment. Unusual or serious harm from medicines, including ADRs, medication errors and overdose, should be reported. The UK Yellow Card scheme is online, and patients can report their own ADRs. PMID:25622648

Ferner, R E

2015-03-01

303

Severe allergic reaction to Dermabond.  

PubMed

The use of 2-octyl cyanoacrylate (Dermabond; Ethicon, Somerville, NJ) for wound closure is increasingly popular. Problems with Dermabond are generally related to application techniques and rarely relate to the chemical nature of the adhesive. This article describes a severe allergic reaction to Dermabond following breast augmentation/mastopexy. PMID:19717065

Perry, Arthur W; Sosin, Michael

2009-01-01

304

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

305

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

306

Spin uncoupling in chemical reactions  

Microsoft Academic Search

Spin pairing is the main attribute of the covalent chemical bond. Exchange repulsion between closed shell molecules being responsible for activation barriers in bimolecular reactions can be explained by a high weight of the intermolecular triplet spin pairing. Intermolecular exchange interaction switches to a strong attraction when the molecules are in excited triplet states. This is the reason for that

Boris F. Minaev; Hans Ågren

2001-01-01

307

Binary counting with chemical reactions.  

PubMed

This paper describes a scheme for implementing a binary counter with chemical reactions. The value of the counter is encoded by logical values of "0" and "1" that correspond to the absence and presence of specific molecular types, respectively. It is incremented when molecules of a trigger type are injected. Synchronization is achieved with reactions that produce a sustained three-phase oscillation. This oscillation plays a role analogous to a clock signal in digital electronics. Quantities are transferred between molecular types in different phases of the oscillation. Unlike all previous schemes for chemical computation, this scheme is dependent only on coarse rate categories for the reactions ("fast" and "slow"). Given such categories, the computation is exact and independent of the specific reaction rates. Although conceptual for the time being, the methodology has potential applications in domains of synthetic biology such as biochemical sensing and drug delivery. We are exploring DNA-based computation via strand displacement as a possible experimental chassis. PMID:21121058

Kharam, Aleksandra; Jiang, Hua; Riedel, Marc; Parhi, Keshab

2011-01-01

308

Multifractality in intracellular enzymatic reactions.  

PubMed

Enzymatic kinetics adjust well to the Michaelis-Menten paradigm in homogeneous media with dilute, perfectly mixed reactants. These conditions are quite different from the highly structured cell plasm, so applications of the classic kinetics theory to this environment are rather limited. Cytoplasmic structure produces molecular crowding and anomalous diffusion of substances, modifying the mass action kinetic laws. The reaction coefficients are no longer constant but time-variant, as stated in the fractal kinetics theory. Fractal kinetics assumes that enzymatic reactions on such heterogeneous media occur within a non-Euclidian space characterized by a certain fractal dimension, this fractal dimension gives the dependence on time of the kinetic coefficients. In this work, stochastic simulations of enzymatic reactions under molecular crowding have been completed, and kinetic coefficients for the reactions, including the Michaelis-Menten parameter KM, were calculated. The simulations results led us to confirm the time dependence of michaelian kinetic parameter for the enzymatic catalysis. Besides, other chaos related phenomena were pointed out from the obtained KM time series, such as the emergence of strange attractors and multifractality. PMID:16256143

Aranda, Juan S; Salgado, Edgar; Muñoz-Diosdado, Alejandro

2006-05-21

309

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

310

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

311

A Synthetic Reaction Network: Chemical Amplification Using Nonequilibrium Autocatalytic Reactions Coupled in Time  

E-print Network

reaction network that performs a function: it uses autocatalysis in a time- controlled microfluidic device the reactions in space and time.1-5 An example of a chemical network is an array of 16 coupled reactionsA Synthetic Reaction Network: Chemical Amplification Using Nonequilibrium Autocatalytic Reactions

Ismagilov, Rustem F.

312

Finding reaction paths using the potential energy as reaction coordinate.  

PubMed

The intrinsic reaction coordinate curve (IRC), normally proposed as a representation of a reaction path, is parametrized as a function of the potential energy rather than the arc-length. This change in the parametrization of the curve implies that the values of the energy of the potential energy surface points, where the IRC curve is located, play the role of reaction coordinate. We use Caratheodory's relation to derive in a rigorous manner the proposed parametrization of the IRC path. Since this Caratheodory's relation is the basis of the theory of calculus of variations, then this fact permits to reformulate the IRC model from this mathematical theory. In this mathematical theory, the character of the variational solution (either maximum or minimum) is given through the Weierstrass E-function. As proposed by Crehuet and Bofill [J. Chem. Phys. 122, 234105 (2005)], we use the minimization of the Weierstrass E-function, as a function of the potential energy, to locate an IRC path between two minima from an arbitrary curve on the potential energy surface, and then join these two minima. We also prove, from the analysis of the Weierstrass E-function, the mathematical bases for the algorithms proposed to locate the IRC path. The proposed algorithm is applied to a set of examples. Finally, the algorithm is used to locate a discontinuous, or broken, IRC path, namely, when the path connects two first order saddle points through a valley-ridged inflection point. PMID:18345872

Aguilar-Mogas, Antoni; Giménez, Xavier; Bofill, Josep Maria

2008-03-14

313

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

314

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

315

Prebiotic condensation reactions using cyanamide  

NASA Technical Reports Server (NTRS)

Condensation reactions in cyanamide, 4-amino-5-imidazole-carboxamide and cyanamide, imidazole systems under dehydrating conditions at moderate temperatures (60 to 100 deg C) were investigated. The cyanamide, imidazole system was used for synthesis of palmitoylglycerols from ammonium palmitate and glycerol. With the addition of deoxythymidine to the former system, P1, P2-dideoxythymidine 5 prime-phosphate was obtained; the same cyanamide, 4-amino-5-imidazole-carboxamide system was used to synthesize deoxythymidine oligonucleotides using deoxythymidine 5 prime-phosphate and deoxythymidine 5 prime-triphosphate, and peptides using glycine, phenylalanine or isoleucine with adenosine 5 prime-triphosphate. The pH requirements for these reactions make their prebiotic significance questionable; however, it is conceivable that they could occur in stable pockets of low interlayer acidity in a clay such as montmorillonite.

Sherwood, E.; Nooner, D. W.; Eichberg, J.; Epps, D. E.; Oro, J.

1978-01-01

316

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.

Sonia Bacca; Saori Pastore

2014-07-13

317

Hypersensitivity reactions to vaccine components.  

PubMed

Vaccines are responsible for the control of many infectious diseases that were once common in the United States, including polio, measles, diphtheria, pertussis (whooping cough), rubella (German measles), mumps, tetanus, and Haemophilus influenzae type b. National efforts to generate collaboration between federal, state, and local governments and public and private health care providers have resulted in record high levels of vaccination coverage in the United States. The high rate of US vaccinations is paralleled by growing concerns about the safety of their delivery. The variety of substances used in vaccines sometimes causes the development of cutaneous reactions in susceptible adults and children. This article will review adverse cutaneous events consistent with hypersensitivity reactions to the following ingredients in vaccines: aluminum, thimerosal, 2-phenoxyethanol, formaldehyde, and neomycin. PMID:16242081

Heidary, Noushin; Cohen, David E

2005-09-01

318

The molecular dynamics of atmospheric reaction  

NASA Technical Reports Server (NTRS)

Detailed information about the chemistry of the upper atmosphere took the form of quantitative data concerning the rate of reaction into specified states of product vibration, rotation and translation for exothermic reaction, as well as concerning the rate of reaction from specified states of reagent vibration, rotation and translation for endothermic reaction. The techniques used were variants on the infrared chemiluminescence method. Emphasis was placed on reactions that formed, and that removed, vibrationally-excited hydroxyl radicals. Fundamental studies were also performed on exothermic reactions involving hydrogen halides.

Polanyi, J. C.

1971-01-01

319

Cutaneous allergic reactions to tattoo ink.  

PubMed

Tattoo artists use many compounds to create tattoo pigment and several allergic reactions can occur as a result of these additives. The compositions of many inks have been identified; however, as new mixtures are created it becomes difficult to identify the specific ingredients in a particular ink. Allergic reactions to a particular pigment can manifest in several ways including allergic contact dermatitis and photoallergic dermatitis. Subsequently, tattoo ink or pigment allergy reactions can be classified as acute inflammatory reactions, allergic hypersensitivities, and granulomatous, lichenoid, and pseudolymphomatous types of reactions. This paper will review the clinical manifestations and the most common compounds associated with cutaneous reactions to tattoo ink. PMID:19958434

Kaur, Ravneet Ruby; Kirby, William; Maibach, Howard

2009-12-01

320

Cascade reactions in multicompartmentalized polymersomes.  

PubMed

Enzyme-filled polystyrene-b-poly(3-(isocyano-L-alanyl-aminoethyl)thiophene) (PS-b-PIAT) nanoreactors are encapsulated together with free enzymes and substrates in a larger polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) polymersome, forming a multicompartmentalized structure, which shows structural resemblance to the cell and its organelles. An original cofactor-dependent three-enzyme cascade reaction is performed, using either compatible or incompatible enzymes, which takes place across multiple compartments. PMID:24254810

Peters, Ruud J R W; Marguet, Maïté; Marais, Sébastien; Fraaije, Marco W; van Hest, Jan C M; Lecommandoux, Sébastien

2014-01-01

321

Statistical Theory of Breakup Reactions  

NASA Astrophysics Data System (ADS)

We propose an alternative for Coupled-Channels calculations with looselybound exotic nuclei(CDCC), based on the the Random Matrix Model of the statistical theory of nuclear reactions. The coupled channels equations are divided into two sets. The first set, described by the CDCC, and the other set treated with RMT. The resulting theory is a Statistical CDCC (CDCCs), able in principle to take into account many pseudo channels.

Bertulani, Carlos A.; Descouvemont, Pierre; Hussein, Mahir S.

2014-04-01

322

Loudness and reaction time: I  

Microsoft Academic Search

It is widely assumed, based on Chocholle’s (1940) research, that stimuli that appear equal in loudness will generate the same\\u000a reaction times. In Experiment 1, we first obtained equal-loudness functions for five stimulus frequencies at four different\\u000a intensity levels. It was found that equal loudness produced equal RT at 80 phons and 60 phons, but not at 40 phons and

David L. Kohfeld; Jeffrey L. Santee; Norval D. Wallace

1981-01-01

323

Visual conversion reaction in children.  

PubMed

Visual conversion reaction (VCR) is a psychosomatic illness that will occasionally be seen by optometrists and ophthalmologists. This paper discusses some of the possible aetiologies and manifestations of the condition. Investigation and management of children with suspected VCR is discussed. Four case histories are presented in which signs of VCR included amblyopia, reduced accommodation and a deterioration in handwriting. The visual field defects presented include a static quantitative anomaly. Such a defect has not previously been reported. PMID:2698460

Barnard, N A

1989-10-01

324

Stickland reactions of dental plaque.  

PubMed Central

Dental plaque samples from monkeys (Macaca fascicularis) were shown to contain proline reduction activity in coupled Stickland reactions with other amino acids and also with certain end products of bacterial glucose metabolism. The unusually high concentration of bound and free proline in the oral environment may be of importance in both the production of base and in the removal of acid from the tooth surface after dietary carbohydrate ingestion. PMID:6618673

Curtis, M A; Kemp, C W; Robrish, S A; Bowen, W H

1983-01-01

325

Low-Energy Nuclear Reactions  

Microsoft Academic Search

\\u000a In 1989, two electrochemists reported anomalous laboratory findings suggestive of nuclear effects in what would normally be thought of as chemical (electron) experiments (Fleischmann and Pons, 1989). The experiments\\u000a entailed the “loading” of deuterium into Palladium electrodes and then measuring reaction products during electrolysis. The\\u000a early results indicated massive excess heat of such magnitude that nuclear involvement was suspected. Disastrously,

Norman D. Cook

326

Reaction analysis in stripline circuits  

Microsoft Academic Search

In this paper, a full-wave layered-interconnect simulator (UA-FWLIS), which is capable of simulating EM effects in packaging-interconnect problems, is introduced. Standard integral-equation-based method of moment (MoM) techniques are employed in UA-FWLIS. However, instead of using standard time-consuming numerical integration techniques, we have analytically evaluated the MoM reaction elements, thereby greatly improving the computational efficiency of the simulator. This paper illustrates

Sutirtha Kabir; Steven L. Dvorak; John L. Prince

2001-01-01

327

Radiation recall reaction causing cardiotoxicity  

PubMed Central

Radiation recall phenomenon is a tissue reaction that develops within a previously irradiated area, precipitated by the subsequent administration of certain chemotherapeutic agents. It commonly affects the skin, but can also involve internal organs with functional consequences. To our best knowledge, this phenomenon has never been reported as a complication on the heart and should be consider as a potential cause of cardiotoxicity. PMID:24755097

2014-01-01

328

Reaction Selectivity in Heterogeneous Catalysis  

SciTech Connect

The understanding of selectivity in heterogeneous catalysis is of paramount importance to our society today. In this review we outline the current state of the art in research on selectivity in heterogeneous catalysis. Current in-situ surface science techniques have revealed several important features of catalytic selectivity. Sum frequency generation vibrational spectroscopy has shown us the importance of understanding the reaction intermediates and mechanism of a heterogeneous reaction, and can readily yield information as to the effect of temperature, pressure, catalyst geometry, surface promoters, and catalyst composition on the reaction mechanism. DFT calculations are quickly approaching the ability to assist in the interpretation of observed surface spectra, thereby making surface spectroscopy an even more powerful tool. HP-STM has revealed three vitally important parameters in heterogeneous selectivity: adsorbate mobility, catalyst mobility, and selective site-blocking. The development of size controlled nanoparticles from 0.8 to 10 nm, of controlled shape, and of controlled bimetallic composition has revealed several important variables for catalytic selectivity. Lastly, DFT calculations may be paving the way to guiding the composition choice for multi-metallic heterogeneous catalysis for the intelligent design of catalysts incorporating the many factors of selectivity we have learned.

Somorjai, Gabor A.; Kliewer, Christopher J.

2009-02-02

329

Transfer reactions with heavy elements  

SciTech Connect

Transfer reactions for several transuranium elements are studied. (/sup 248/Cm, /sup 249/Bk, /sup 249/CF, /sup 254/Es), /sup 16,18/O, /sup 20,22/Ne, and /sup 40,48/Ca projectiles are used. The production of neutron-rich heavy actinides is enhanced by the use of neutron-rich projectiles /sup 18/O and /sup 22/Ne. The maxima of the isotopic distributions occur at only 2 to 3 mass numbers larger for /sup 48/Ca than for /sup 40/Ca reactions with /sup 248/Cm. The cross sections decrease rapidly with the number of nucleons transferred. The use of neutron-rich targets favors the production of neutron-rich isotopes. ''Cold'' heavy targets are produced. Comparisons with simple calculations of the product excitation energies assuming binary transfers indicate that the maxima of the isotopic distributions occur at the lightest product isotope for which the energy exceeds the reaction barrier. The cross sections for transfer of the same nucleon clusters appear to be comparable for a wide variety of systems. 23 refs., 4 figs., 4 tabs.

Hoffman, D.C.

1986-04-01

330

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

331

Effect of curvature of the reaction path on dynamic effects in endothermic chemical reactions and product energies in exothermic reactions  

Microsoft Academic Search

Collinear quasiclassical trajectories are examined for two realistic potential energy surfaces for atom?diatomic molecule reactions for two reaction attributes: (1) vibrational energy of the products of a thermal?energy exothermic reaction; (2) threshold energy for endothermic reaction of ground?state reagents. Eight different mass combinations are studied. The potential energy surfaces differ primarily in the amount of potential energy released in an

James W. Duff; Donald G. Truhlar

1975-01-01

332

Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions  

PubMed Central

Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

SUZUKI, Toshinori

2013-01-01

333

Reactions at supercritical conditions: Applications and fundamentals  

SciTech Connect

Supercritical fluids possess properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (Solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous for reactions involved in fuels processing, biomass conversion, biocatalysis, homogeneous and heterogeneous catalysis, environmental control, polymerization, materials synthesis, and chemical synthesis. Moreover, supercritical fluids can be used profitably in fundamental chemical investigations of intermolecular interactions and their influence on chemical processes. Work on chemical reactions in and with supercritical fluids is reviewed. The authors discuss both fundamental studies and applications of reactions at supercritical conditions, with focus on work published after 1985. 425 refs.

Savage, P.E.; Gopalan, S.; Mizan, T.I.; Martino, C.J.; Brock, E.E. [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.] [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.

1995-07-01

334

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.

2012-07-23

335

ChemTeacher: Double 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 Double Replacement Reactions page includes resources for teaching students about identifying and predicting double replacement reactions.

2011-01-01

336

ChemTeacher: Half-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 Half-Reactions page includes resources for teaching students about understanding half-reactions.

2012-07-24

337

A Clock Reaction Based on Molybdenum Blue  

E-print Network

Clock reactions are rare kinetic phenomena, so far limited mostly to systems with ionic oxoacids and oxoanions in water. We report a new clock reaction in cyclohexanol that forms molybdenum blue from a noncharged, yellow ...

Neuenschwander, Ulrich

338

Paradoxical reaction in HIV negative tuberculous meningitis.  

PubMed

This review focusses on paradoxical reactions occurring during the treatment of tuberculous meningitis (TBM) in human immunodeficiency virus-negative cases. A paradoxical reaction is defined as the worsening of a pre-existing lesion or the appearance of new lesion in a patient whose clinical symptoms initially improved with anti-tuberculosis treatment. A number of different paradoxical reactions have been reported in patients with TBM including expansion of existing cerebral tuberculomas, and appearance of new tuberculomas, hydrocephalus, and optochiasmatic and spinal arachnoiditis. While the exact mechanism of paradoxical reactions is uncertain, an exaggerated immune reaction against Mycobacterium tuberculosis-associated antigens is currently the most accepted theory for tuberculous paradoxical reaction. Corticosteroids are considered to have a beneficial effect in the management of paradoxical reactions. Immuno-modulatory drugs, including tumor necrosis factor-? antagonists, thalidomide and interferon-? have been used in isolated cases with more severe forms of paradoxical reactions. PMID:24680563

Garg, Ravindra Kumar; Malhotra, Hardeep Singh; Kumar, Neeraj

2014-05-15

339

Reactions : AcidBaseRxns (20 Variations)  

NSDL National Science Digital Library

In order to answer the following questions, write the net ionic equation for the reaction between equal volumes of 0.10 M solutions of the following acid and base: KOH(aq) + HBr(aq) What are the reaction products? Does the reaction yield an acidic, basic, or neutral aqueous solution?

340

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

341

Direct mechanism in solar nuclear reactions  

E-print Network

A short overview of the direct reaction mechanism and the models used for the analysis of such processes is given. Nuclear reactions proceeding through the direct mechanism and involved in solar hydrogen burning are discussed. The significance of these nuclear reactions with respect to the solar neutrino problem is investigated.

H. Oberhummer; G. Staudt

1994-04-22

342

Time uncertainty in simple reaction time  

Microsoft Academic Search

Studied the relationship between reaction time and Ss' uncertainty about the time of stimulus presentation. Reaction time increases with foreperiod variability and with mean foreperiod above an optimum value less than 1 sec. The important determiner of reaction time is not the immediate foreperiod but the distribution of foreperiods within which it is embedded.

Edmund T. Klemmer

1956-01-01

343

An Iodine Fluorescence Quenching Clock Reaction  

ERIC Educational Resources Information Center

Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock…

Weinberg, Richard B.; Muyskens, Mark

2007-01-01

344

Reaction-Map of Organic Chemistry  

ERIC Educational Resources Information Center

The Reaction-Map of Organic Chemistry lists all the most commonly studied reactions in organic chemistry on one page. The discussed Reaction-Map will act as another learning aide for the students, making the study of organic chemistry much easier.

Murov, Steven

2007-01-01

345

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

346

Stereoselective total synthesis of marine cyclodepsipeptide calcaripeptides A-C.  

PubMed

The first stereoselective total syntheses of marine cyclodepsipeptides, calcaripeptides A-C, have been accomplished. Emphasis was given particularly in identification of an efficient strategy for the macrocyclization. The notable features of our synthesis include Evans alkylation, Crimmins syn-aldol, Crimmins acetate aldol, Wittig olefination, and Shiina macrolactonization reactions. An anomaly in the (1)H NMR of the proposed calcaripeptide B has been amended during this synthetic study. PMID:25226563

Das, Sayantan; Goswami, Rajib Kumar

2014-10-17

347

Directed orthometalation and the asymmetric total synthesis of N-deoxymilitarinone A and torrubiellone B.  

PubMed

A diverted total synthesis (DTS) approach to the total synthesis of pyridone alkaloids N-deoxymilitarinone A (8) and torrubiellone B (10) has been developed. The common intermediate 14 was first assembled by a dual directed orthometalation process using a methoxymethyl group as directed metalation group. Other crucial steps include the assembly of polyenes under aldol condensation for DTS using general and concise strategy and diastereoselective synthesis of the syn-dimethyl array by an Evans aldol reaction. PMID:24295075

Ding, Feiqing; William, Ronny; Leow, Min Li; Chai, Hua; Fong, Jacqueline Zi Mei; Liu, Xue-Wei

2014-01-01

348

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

349

Dynamic Screening in Thermonuclear Reactions  

NASA Astrophysics Data System (ADS)

It has recently been argued that there are no dynamic screening corrections to Salpeter's enhancement factor in thermonuclear reactions, in the weak-screening limit. Two arguments were used: (1) the Gibbs probability distribution is factorable into two parts, one of which, exp(-?eiej/rij) (?=1/kBT), is independent of velocity space, and (2) the enhancement factor is w=1+?2e2Z1Z2 with k=k/k2 and k/(8?)=(T/2)[1-?- 1(0,k)]. We show that both of these arguments are incorrect.

Opher, Merav; Opher, Reuven

2000-05-01

350

Radiation reaction at ultrahigh intensities  

SciTech Connect

Intensities of 10{sup 22} W cm{sup -2} have been reached and it is expected that this will be increased by two orders of magnitude in the near future. At these intensities the radiation reaction force is important, especially in calculating the terminal velocity of an electron. The following briefly describes some of the problems of the existing most well-known equations and describes an approach based on conservation of energy. The resulting equation is compared to the Landau Lifshitz and Ford O'Connell equations, and laboratory tests are proposed.

Hammond, Richard T. [Department of Physics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina (United States) and Army Research Office, Research Triangle Park, North Carolina (United States)

2010-06-15

351

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

352

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

353

Factors Affecting Reaction Kinetics of Glucose Oxidase  

NASA Astrophysics Data System (ADS)

Basic principles of enzyme kinetics are demonstrated using the enzyme glucose oxidase. The glucose oxidase enzymatic reaction is coupled to horseradish peroxidase, which in turn catalyzes the oxidation of a dye to a bright blue-green color. The appearance of the blue-green dye is used to monitor the course of the reaction and is quite visible in a classroom setting. A series of reactions are arranged that vary the enzyme concentration, substrate concentration, temperature, and the substrate used in the reaction. By monitoring the rate of the color change in each beaker, the reaction kinetics of glucose oxidase in each series is observed.

Johnson, Kristin A.

2002-01-01

354

CD30+ lymphomatoid drug reactions.  

PubMed

We report 5 cases of cutaneous CD30+ lymphomatoid drug reactions that occurred shortly after the onset of drug exposure and resolved promptly upon withdrawal of the offending agents. The cases showed protean dermatologic manifestations ranging from diffuse erythema with desquamation to macules, papules, and annular plaques. The suspect drugs were amlodipine (a calcium channel blocker) for 2 cases, sertraline (a selective serotonin reuptake inhibitor) for 1 case, gabapentin for 1 case, and levofloxacin (a fluoroquinolone) versus cefepime (a fourth generation cephalosporin), and metoprolol (a beta blocker), in the fifth case. The histopathologic findings included varying combinations of spongiotic dermatitis, lichenoid infiltrates, and interface dermatitis with a dermal infiltrate of large atypical lymphocytes. Three of the 5 cases contained as much as 30% CD30+ staining of all lymphocytes, whereas the remaining 2 showed 5%-15% positivity. Three patients had a history of allergy or immune dysregulation. Increased knowledge of CD30 positivity in lymphomatoid drug reactions may be relevant in an era of targeted drug therapies. Recognition of these findings may help clinicians to tailor appropriate clinical evaluation and treatment including a review of medications and the removal of possible offending agents. PMID:23328787

Pulitzer, Melissa P; Nolan, Katherine A; Oshman, Robin G; Phelps, Robert G

2013-05-01

355

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

2014-11-25

356

Nuclear reactions from lattice QCD  

NASA Astrophysics Data System (ADS)

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 quantum chromodynamics (LQCD) provides the only reliable option for performing calculations of some of the low-energy hadronic observables. With the aim of bridging the gap between LQCD and nuclear many-body physics, the Institute for Nuclear Theory held a workshop on Nuclear Reactions from LQCD 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.

Briceño, Raúl A.; Davoudi, Zohreh; Luu, Thomas C.

2015-02-01

357

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

358

Soccer shin guard reactions: allergic and irritant reactions.  

PubMed

In spite of the worldwide popularity of soccer among youth and the common requirement of the use of protective shin guards, reports of allergy to shin guards is sparse. This is surprising in light of the fact that this equipment is often made of materials that are reported to cause allergies, and that friction and moisture from the use of these shin guards during the sport would seem to predispose soccer players to the development of an allergic response. We present eight patients that presented for evaluation of dermatitis under their shin guards--some of which had allergy to their shin guards and some of which were diagnosed as having an irritant reaction. PMID:20487661

Powell, Douglas; Ahmed, Sartaj

2010-01-01

359

Reactions of butadiyne. 1: The reaction with hydrogen atoms  

NASA Technical Reports Server (NTRS)

The reaction of hydrogen (H) atoms with butadiene (C4H2) was studied at room temperature in a pressure range between w mbar and 10 mbar. The primary step was an addition of H to C4H2 which is in its high pressure range at p 1 mbar. Under these conditions the following addition of a second H atom lies in the transition region between low and high pressure range. Vibrationally excited C4H4 can be deactivated to form buten-(1)-yne-(3)(C4H4) or decomposes into two C2H2 molecules. The rate constant at room temperature for primary step is given. The second order rate constant for the consumption of buten-(1)-yne-(3) is an H atom excess at room temperature is given.

Schwanebeck, W.; Warnatz, J.

1984-01-01

360

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

361

New types of 'combined' pericyclic reactions  

NASA Astrophysics Data System (ADS)

The review is concerned with 'combined' pericyclic reactions, i.e., multistep one-pot reactions involving a cascade of pericyclic steps, as well as concerted processes whose transition states represent superpositions of transition states of two pericyclic reactions. Some typical examples of cascade pericyclic reactions are presented, demonstrating their significance for synthetic practice. The review mainly concerns reactions with a 'combined' pericyclic transition state, e.g., dyotropic shift, bispericyclic reactions and hiscotropic rearrangements. The attention is focussed on detailed analysis of various types of coarctate reactions due to their importance for synthetic chemistry and to thorough elaboration of their theoretical basis, which is in essence a continuation and further development of the Woodward-Hoffmann theory for spirocyclic conjugated systems. The bibliography includes 115 references.

Magdesieva, Tatyana V.

2013-03-01

362

Pattern analysis of photopatch test reactions.  

PubMed

In a multicenter study, photopatch test results from more than 1500 patients were evaluated between 1985 and 1990 and from 614 patients between 1990 and 1992. Photopatch testing was conducted according to a standardized procedure. Nearly half of the photoreactions were unclassifiable according to the classic definitions of photoallergic or phototoxic reactions. To facilitate the interpretation of these remaining photopatch test reactions, we developed a computerized substance specific reaction pattern analysis. By sequential readings from immediately after irradiation up to 72 h later and by morphological qualification of the reactions, the time course and morphological changes of each individual reaction were monitored. The summation of each individual photoreaction resulted in an overall reaction pattern of a specific substance. Four main categories could be distinguished. The first category was characterized by a peak immediately after irradiation followed by a descrescendo reaction. The second category comprized reactions combining an immediate with a delayed reaction. The third category exhibited a plateau-like delayed reaction. The fourth category showed delayed reactions in a crescendo pattern. Whereas category 1 represents classic phototoxic and category 4 classic photoallergic reaction patterns, the underlying mechanisms of categories 2 and 3 remain to be investigated. Typical substances of category 1 were many of the tested systemic drugs, such as furosemide, most of which are well-known phototoxic agents. Disinfectants, nonsteroidal anti-inflammatory agents and phenothiazines showed the reaction patterns of categories 2 and 3. A delayed type reaction (category 4) could be demonstrated for well-known photoallergens such as fenticlor, musk ambrette, and ultraviolet adsorbents in sunscreens.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8043387

Neumann, N J; Hölzle, E; Lehmann, P; Benedikter, S; Tapernoux, B; Plewig, G

1994-04-01

363

Metal implants and surface reactions.  

PubMed

A metal in living tissue is prone to corrosion. The interaction of the foreign body with the tissue involves the redox reaction (an electron exchange) at the interface, the hydrolysis (a proton exchange) of oxide-hydrates as products of corrosion, and the formation of metal-organic complexes in the electrolyte. Denatured tissue in contact with the foreign body is the consequence. But behaviour of metals is variable; gold, stainless steel and most other metals react as described while few others like titanium and tantalum do not. The absence of a foreign body effect of a chemical kind is, without doubt, favorable in terms of tissue susceptibility to infection in the presence of titanium. PMID:9039349

Steinemann, S G

1996-01-01

364

The K - d? p??- reaction  

NASA Astrophysics Data System (ADS)

The ( ?p) mass distribution is calculated for the reaction K - d?? p?- at rest and in flight at 700 MeV/c, for both BDI-1 and NRS-F potentials, with results which do not discriminate strongly between them. The in flight calculations can be brought into satisfactory agreement with experiment after some modification of the ¯KN??Y amplitudes, but the ‘at rest’ calculations show a strong disagreement with experiment which is not yet resolved, but which may partly reflect the experimental procedures adopted. The discrepancy with the earlier work reported by Dalitz, Hemming and Morris is accounted for, with the conclusion that further physics input may be needed to reach agreement with the data.

Dalitz, R. H.; Deloff, A.

1982-09-01

365

Mucocutaneous reactions to antineoplastic agents.  

PubMed

Mucocutaneous reaction patterns in patients receiving cancer therapy are not only variable, but in many instances identical patterns are produced by different pathologic mechanisms. For example, patients with leukemia or lymphoma may present with nodular skin lesions that may represent malignant infiltration, septic emboli, vasculitis, or a drug eruption. The most banal skin eruption may signal an impending or ongoing catastrophe. If one is able to make some clinical evaluation regarding the likelihood of a drug being responsible for the mucocutaneous eruption, it may help avoid further clinical or laboratory investigation and patient discomfort. Unfortunately, only a few antineoplastic agents have "characteristic" skin manifestations. If, however, these are kept in mind they may be helpful in the diffential diagnosis of mucocutaneous eruptions occurring in patients treated with cancer chemotherapeutic agents. PMID:6769553

Adrian, R M; Hood, A F; Skarin, A T

1980-01-01

366

Classical Gravitational Back-Reaction  

E-print Network

The quantum gravitational back-reaction on inflation is based on the self-gravitation of infrared gravitons which are ripped out of the vacuum during inflation. The only quantum part of this process is the creation of gravitons; after they have emerged from the vacuum their behaviour is essentially classical. To test the thesis that a sufficiently dense ensemble of classical gravitons can hold the universe together in pure gravity with a positive cosmological constant, we compute the initial value and first time derivative of an invariant measure of the expansion rate for arbitrary classical initial value data. Our result is that the self-gravitation from the kinetic energy of an initial ensemble of gravitons can indeed slow expansion enough to hold the universe together.

N. C. Tsamis; R. P. Woodard

2014-05-24

367

Photo Reactions with Universal Trimers  

E-print Network

Considering one-body and two-body currents, we study the photoassociation and photodissociation of universal bosonic trimers. Analyzing the relative importance of these currents we identify two physical scenarios (i) Normal hierarchy, where naive power counting holds and the one-body current dominates, and (ii) Strong hierarchy, where the one-body current is suppressed. For both scenarios we observe that at the high frequency tail, the response function exhibits log periodic oscillations in transition to or from any continuum state regardless of the reaction partial wave channel. In contrast, near threshold log periodic oscillations appear only in the leading $s$-wave components. These oscillations are the fingerprints of universal Efimov physics. We discuss the relevance of this effect to contemporary experiments in ultracold atoms.

Betzalel Bazak; Nir Barnea

2014-02-26

368

Tracking dissipation in capture reactions  

SciTech Connect

Nuclear dissipation in capture reactions is investigated using backtracing. Combining the analysis procedure with dynamical models, the difficult and long-standing problem of competition and mixing of quasi-fission and fusion-fission is solved for the first time. At low excitation energy a new protocol able to handle low statistics data gives access to the precession neutron multiplicity in two different systems 48Ca + 208Pb, Pu. The results are in agreement with a domination of fusion-fission in the case of 256No and an equal mixing of quasi-fission and fusion-fission in the case of Z = 114. The nature of the relevant dissipation is determined as one-body dissipation.

Materna, T.; Bouchat, V.; Kinnard, V.; Hanappe, F. [PNTPM, Universite Libre de Bruxelles, Brussels (Belgium); Dorvaux, O.; Stuttge, L. [Institut de Recherches Subatomiques, Strasbourg (France); Schmitt, C. [Institut de Recherches Subatomiques, Strasbourg (France); GSI, Darmstadt (Germany); Siwek-Wilczynska, K. [Warsaw University, Warsaw (Poland); Aritomo, Y. [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna (Russian Federation); Tokyo University, Tokyo (Japan); Bogatchev, A.; Prokhorova, E. [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna (Russian Federation); Ohta, M. [Kobe University, Kobe (Japan)

2004-04-12

369

Adverse reactions of ferric carboxymaltose.  

PubMed

The author reports a 55-year-old female diagnosed of chronic kidney disease grade-5 with associated co-morbidities like type 2 diabetes mellitus, diabetic retinopathy and hypothyroidism was admitted for arteriovenous fistula construction. She was started on ferric carboxymaltose for the treatment of anaemia. She was given a test dose before administering the drug intravenously and she did not develop any reaction. The drug ferric carboxymaltose was then administered over a period of one hour. About half an hour after drug administration, the patient developed breathlessness and myalgia. After half hour of the above episode of breathlessness and myalgia she also developed vomiting (one episode). Patient was managed with oxygen therapy, IV fluids and other drugs like corticosteroids, phenaramine maleate and nalbuphine which controlled the above symptoms. PMID:25478369

Thanusubramanian, Harish; Patil, Navin; Shenoy, Smita; Bairy, K L; Sarma, Yashdeep

2014-10-01

370

Adverse Reactions of Ferric Carboxymaltose  

PubMed Central

The author reports a 55-year-old female diagnosed of chronic kidney disease grade-5 with associated co-morbidities like type 2 diabetes mellitus, diabetic retinopathy and hypothyroidism was admitted for arteriovenous fistula construction. She was started on ferric carboxymaltose for the treatment of anaemia. She was given a test dose before administering the drug intravenously and she did not develop any reaction. The drug ferric carboxymaltose was then administered over a period of one hour. About half an hour after drug administration, the patient developed breathlessness and myalgia. After half hour of the above episode of breathlessness and myalgia she also developed vomiting (one episode). Patient was managed with oxygen therapy, IV fluids and other drugs like corticosteroids, phenaramine maleate and nalbuphine which controlled the above symptoms. PMID:25478369

Patil, Navin; Shenoy, Smita; Bairy, K L; Sarma, Yashdeep

2014-01-01

371

Allergic reactions to rubber condoms.  

PubMed

With the increased use of condoms, contact dermatitis to rubber is being seen more often. To develop a rubber condom suitable for use by rubber sensitive people, a "hypoallergenic" condom, which is washed in ammonia to reduce the residues of rubber accelerators, has been manufactured. Fifty patients allergic to various rubber accelerators were patch tested with an ordinary condom and the new washed condom. Fifty patients undergoing routine patch test investigation who were not allergic to rubber were also tested as controls. Twenty two of the rubber sensitive patients had a positive reaction to the new rubber condom compared with four of the control patients. Washing rubber condoms in ammonia does not appear to reduce the residues of rubber accelerators sufficiently for their use by rubber sensitive people. A non-allergenic condom is required. PMID:2759609

Rademaker, M; Forsyth, A

1989-06-01

372

Chemical Reactions in Supercritical Carbon Dioxide  

NASA Astrophysics Data System (ADS)

Utilizing supercritical fluids as environmentally benign solvents for chemical synthesis is one of the new approaches in the "greening" of chemistry. Carbon dioxide is the most widely used gas for supercritical fluid studies because of its moderate critical constants, nontoxic nature, and availability in pure form. One unique property of supercritical carbon dioxide (sc-CO2) is its high solubility for fluorinated compounds. Thus sc-CO2 can be used to replace Freons that are conventionally used as solvents for synthesis of perfluoro-polymers. Another property of sc-CO2 is its miscibility with gases such as H2. Heterogeneous reactions involving these gases may become homogeneous reactions in sc-CO2. Reactions in sc-CO2 may offer several advantages including controlling phase behavior and products, increasing speed of reactions, and obtaining specific reaction channels. This paper describes the following nine types of chemical reactions reported in the literature utilizing sc-CO2 as a solvent to illustrate the unique properties of the supercritical fluid reaction systems: (i) hydrogenation and hydroformylation, (ii) synthesis of organometallic compounds, (iii) metal chelation and extraction, (iv) preparation of inorganic nanoparticles, (v) stereo-selectivity of lipase-catalyzed reactions, (vi) asymmetric catalytic hydrogenation, (vii) polymerization, (viii) Diels-Alder reaction, and (ix) free radical reactions.

Wai, Chien M.; Hunt, Fred; Ji, Min; Chen, Xiaoyuan

1998-12-01

373

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

374

Surface reactions in microelectronics process technology.  

PubMed

Current integrated circuit (IC) manufacturing consists of more than 800 process steps, nearly all of which involve reactions at surfaces that significantly impact device yield and performance. From initial surface preparation through film deposition, patterning, etching, residue removal, and metallization, an understanding of surface reactions and interactions is critical to the successful continuous scaling, yield, and reliability of electronic devices. In this review, some of the most important surface reactions that drive the development of microelectronic device fabrication are described. The reactions discussed do not constitute comprehensive coverage of this topic in IC manufacture but have been selected to demonstrate the importance of surface/interface reactions and interactions in the development of new materials, processing sequences, and process integration challenges. Specifically, the review focuses on surface reactions related to surface cleaning/preparation, semiconductor film growth, dielectric film growth, metallization, and etching (dry and wet). PMID:22432621

Levitin, Galit; Hess, Dennis W

2011-01-01

375

Z dependence of the ( ?, ?) reaction yield  

NASA Astrophysics Data System (ADS)

Reactions induced by photons may be used as a probe for bonds and correlations of nucleons inside a heavy target nucleus. In contrast to strongly interacting particles, electromagnetic radiation perturbs nucleons only slightly. The yield of ( ?, ?) reactions could be used to test theoretical models that assume complete alpha-particle clustering or the presence of multiquark objects in heavy nuclei. The relative yields of ( ?, n), ( ?, p), and ( ?, ?) reactions were measured at the bremsstrahlung endpoint energy of 23 MeV for several targets. A much lower probability of ( ?, ?) in relation to ( ?, p) reactions was proved despite very close threshold and spin factors for the two reaction types being considered. Therefore, alpha-particle clustering in heavy targets was not confirmed. The mechanism of particle release in nuclear reactions is discussed, and some details are clarified.

Karamian, S. A.

2014-11-01

376

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

377

Controlling chemical reactions of a single particle  

NASA Astrophysics Data System (ADS)

Traditionally, chemical reactions have been investigated by tuning thermodynamic parameters, such as temperature or pressure. More recently, laser or magnetic field control methods have emerged to provide new experimental possibilities, in particular in the realm of cold collisions. The control of reaction pathways is also a critical component to implement molecular quantum information processing. For these studies, single particles provide a clean and well-controlled experimental system. Here, we report on the experimental tuning of the exchange reaction rates of a single trapped ion with ultracold neutral atoms by exerting control over both their quantum states. We observe the influence of the hyperfine interaction on chemical reaction rates and branching ratios, and monitor the kinematics of the reaction products. These investigations advance chemistry with single trapped particles towards achieving quantum-limited control of chemical reactions and indicate limits for buffer-gas cooling of single-ion clocks.

Ratschbacher, Lothar; Zipkes, Christoph; Sias, Carlo; Köhl, Michael

2012-09-01

378

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

379

Catalytic reactions in heavy-ion collisions  

SciTech Connect

We discuss a new type of reactions of a {phi}-meson production on hyperons, {pi}Y {yields} {phi}Y and antikaons -KN {yields} {phi}Y. These reactions are not suppressed according to Okubo-Zweig-Iizuka rule and can be a new efficient source of {phi} mesons in a nucleus-nucleus collision. We discuss how these reactions can affect the centrality dependence and the rapidity distributions of the {phi} yield.

Kolomeitsev, E. E., E-mail: e.kolomeitsev@gsi.de; Tomasik, B. [Matej Bel University (Slovakia)

2012-06-15

380

PHYSICAL ORGANIC STUDIES OF ORGANOMETALLIC REACTIONS  

SciTech Connect

The mechanisms of reactions of organotransition metal complexes have only begun to be understood in detail during the last ten years. The complementary interaction of techniques and concepts developed earlier in studies of organic reaction mechanisms, with those commonly used in inorganic chetnistry, has played a crucial role in helping to elucidate organor.1etall.ic reaction mechanisms. A few systems in which this interaction has proved especially fruitful are discussed in this article.

Bergman, Robert G.

1980-09-01

381

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

382

AMSD Reaction Structure Cryo Deformation Test Plan  

NASA Technical Reports Server (NTRS)

The method developed for measuring both in-plane & out-of-plane cryo deformations of AMSD reaction structures at the XRCF will be presented. For in-plane measurements, a theodolite is used to track the positions of several (up to ten) targets on the reaction structure. For out-of-plane measurements, the Leica ADM is used to measure the change in distance to several (up to ten) corner cubes attached to the reaction structure.

Eng, Ron; Hraba, John; Thornton, Gary; Baker, Mark; Haight, Harlan; Hadaway, James; Blackwell, Lisa; Stahl, Phil (Technical Monitor)

2002-01-01

383

Hot-spot reaction in unsustained shocks  

SciTech Connect

Shock waves in reactive media create hot spots which undergo further temperature change (following creation) by means of (1) chemical reaction, (2) thermal conduction, and (3) adiabatic effects resulting from pressure variation. A thermodynamic description of exothermic reaction under conditions of variable pressure is presented here. The reaction rate is assumed to be a function of temperature only, and of the Arrhenius form: the effect of variable pressure enters through its influence on temperature. Decreasing pressure significantly alters adiabatic thermal explosion times, and can, under nominal conditions, completely inhibit hot-spot reaction. This effect is discussed in terms of explosive initiation by unsustained shock waves. 7 refs., 2 figs.

Johnson, J.N.

1987-01-01

384

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

385

A Lewis acid-promoted Pinner reaction  

PubMed Central

Summary Carbonitriles and alcohols react in a Lewis acid-promoted Pinner reaction to carboxylic esters. Best results are obtained with two equivalents of trimethylsilyl triflate as Lewis acid. Good yields are achieved with primary alcohols and aliphatic or benzylic carbonitriles, but the straightforward synthesis of acrylates and benzoates starting with acrylonitrile and benzonitrile, respectively, is similarly possible. Phenols are not acylated under these reaction conditions. The method has been used for the first total synthesis of the natural product monaspilosin. In the reaction of benzyl alcohols variable amounts of amides are formed in a Ritter-type side reaction. PMID:23946857

Pfaff, Dominik; Nemecek, Gregor

2013-01-01

386

Modeling Enzymatic Reactions in Proteins.  

NASA Astrophysics Data System (ADS)

We will discuss application of our density functional (DFT)-based QM/MM methodology to modeling a variety of protein active sites, including methane monooxygenase, myoglobin, and cytochrome P450. In addition to the calculation of intermediates, transition states, and rate constants, we will discuss modeling of reactions requiring protein conformational changes. Our methodology reliably achieves small errors as a result of imposition of the QM/MM boundary. However, the accuracy of DFT methods can vary significantly with the type of system under study. We will discuss a novel approach to the reduction of errors in gradient corrected and hybrid DFT functionals, using empirical localized orbital corrections (DFT-LOC), which addresses this problem effectively. For example, the mean unsigned error in atomization energies for the G3 data set using the B3LYP-LOC model is 0.8 kcal/mole, as compared with 4.8 kcal/mole for B3LYP and 1.0 kcal/mole for G3 theory.

Friesner, Richard

2007-03-01

387

Vertical two chamber reaction furnace  

DOEpatents

A vertical two chamber reaction furnace is disclosed. The furnace comprises a lower chamber having an independently operable first heating means for heating the lower chamber and a gas inlet means for admitting a gas to create an ambient atmosphere, and an upper chamber disposed above the lower chamber and having an independently operable second heating means for heating the upper chamber. Disposed between the lower chamber and the upper chamber is a vapor permeable diffusion partition. The upper chamber has a conveyor means for conveying a reactant there through. Of particular importance is the thallinating of long-length thallium-barium-calcium copper oxide (TBCCO) or barium-calcium-copper oxide (BCCO) precursor tapes or wires conveyed through the upper chamber to thereby effectuate the deposition of vaporized thallium (being so vaporized as the first reactant in the lower chamber at a temperature between about 700 and 800 C) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800 to 950 C to thereby replace thallium oxide lost from TBCCO tape or wire because of the high annealing temperature or to deposit thallium on BCCO tape or wire. Continuously moving the tape or wire provides a single-step process that effectuates production of long-length TBCCO superconducting product. 2 figs.

Blaugher, R.D.

1999-03-16

388

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

389

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

390

The Reaction Rolodex; A Web-Based System for Learning Reactions in Organic Chemistry  

NSDL National Science Digital Library

This Web-based system of note cards has been developed to aid students in learning the vast number of reactions encountered in organic chemistry. A thorough knowledge of these reactions is essential for success in first- and second-semester organic chemistry courses. The reactions are organized by functional group and can be chosen from a menu at the left side of the Web page. Once a particular reaction has been selected, the main frame displays the reactant(s) and reagent(s) along with a question mark in place of the product. After considering the reaction as long as needed, the user can click the question mark to reveal the reaction product. Clicking the product will again hide the answer and regenerate the question mark so that the reaction can be practiced again. Selecting other reactions from the menu on the left allows them to be practiced in the same manner.

391

Complicated Grief Reactions in Children and Adolescents  

Microsoft Academic Search

An understanding of complicated grief in youth is incomplete, because the full range of observed, theorized, and studied symptoms and reactions has not yet been examined in different age groups. Until recently, scales to assess complicated grief in youth were based on adult constructs of complicated grief and did not include many of the symptoms and reactions proposed for posttrauma

Kathleen Nader; Alison Salloum

2011-01-01

392

Catalysis and Multi-Component Reactions  

NASA Astrophysics Data System (ADS)

We have been studying the development of new asymmetric two-center catalysis using rare earth alkoxides and bifunctional sugar and related ligands. In The Fourth International Conference on Multi-Component Reactions and Related Chemistry (MCR 2009), new catalytic asymmetric reactions using catalysts 1 and 2 and catalytic asymmetric syntheses of ranirestat 3 and tamiflu 4 will be presented.

Shibasaki, Masakatsu; Yus, Miguel; Bremner, Stacy; Comer, Eamon; Shore, Gjergji; Morin, Sylvie; Organ, Michael G.; van der Eycken, Erik; Merkul, Eugen; Dorsch, Dieter; Müller, Thomas J. J.; Ryabukhin, Sergey V.; Ostapchuk, Eugeniy N.; Plaskon, Andrey S.; Volochnyuk, Dmitriy M.; Shivanyuk, Alexander N.; Tolmachev, Andrey A.; Sheibani, Hassan; Babaie, Maryam; Behzadi, Soheila; Dabiri, Minoo; Bahramnejad, Mahboobeh; Bashiribod, Sahareh; Hekmatshoar, Rahim; Sadjadi, Sodeh; Khorasani, Mohammad; Polyakov, Anatoliy I.; Eryomina, Vera A.; Medvedeva, Lidiya A.; Tihonova, Nadezhda I.; Listratova, Anna V.; Voskressensky, Leonid G.; Merkul, Eugen; Dorsch, Dieter; Müller, Thomas J. J.; Sheibani, Hassan; Esfandiarpoor, Zeinab; Behzadi, Soheila; Titova, Julia A.; Fedorova, Olga V.; Ovchinnikova, Irina G.; Valova, Marina S.; Koryakova, Olga V.; Rusinov, Gennady L.; Charushin, Valery N.; Hekmatshoar, Rahim; Sadjadi, Sodeh

393

A Warning About Median Reaction Time  

Microsoft Academic Search

When used with positively skewed reaction time distributions, sample medians tend to over-estimate population medians. The extent of overestimation is related directly to the amount of skew in the reaction time distributions and inversely to the size of the sample over which the median is computed. Simulations indicate that overestimation could approach 50 ms with small samples and highly skewed

Jeff Miller

1988-01-01

394

CEMENTING REACTIONS IN THE HAZARDOUS WASTE ENVIRONMENT  

EPA Science Inventory

The use of chemical grout for bottom sealing waste sites requires careful consideration of interfering reactions from contaminated soil or ground water. The cementing reactions in the acrylates and urethanes are very specific. The presence of reducers, oxidizers and complexors ca...

395

Hypersensitivity reactions to beta-lactams.  

PubMed

Beta-lactam antibiotics (BLs) are the most frequent cause of hypersensitivity reactions mediated by specific immunological mechanisms, with two main types, IgE reactions or T-cell-dependent responses. From a practical point of view, these reactions can be classified into immediate, for those appearing within 1 h after drug intake, and non-immediate, for those appearing at least 1 h after and usually within 24 h of BL administration. The clinical symptoms differ according to this classification. Urticaria and anaphylaxis are the most frequently recorded symptoms in immediate reactions and maculopapular exanthema and delayed urticaria in non-immediate reactions. Although the exact diagnostic approach differs depending on the underlying mechanism, it is based on the performance of skin testing, laboratory tests, and drug provocation tests.T cells are a key factor in all types of hypersensitivity reactions to BLs, regulating both IgE production or acting as effector cells, with a different profile of cytokine production. A Th1 pattern is observed in both CD4(+) and CD8(+) peripheral T cells in non-immediate reactions, whereas a Th2 pattern is expressed in CD4(+) T cells in immediate reactions. PMID:24214624

Torres, Maria J; Mayorga, Cristobalina; Blanca-López, Natalia; Blanca, Miguel

2014-01-01

396

Resonant structures in heavy-ion reactions  

SciTech Connect

An investigation of heavy-ion resonance structures using the /sup 24/Mg(/sup 16/O, /sup 12/C)/sup 28/Si reaction is presented. The data are analyzed in the context of Breit-Wigner resonances added to a direct-reaction background.

Sanders, S.J.; Henning, W.; Ernst, H.; Geesaman, D.F.; Jachcinski, C.; Kovar, D.G.; Paul, M.; Schiffer, J.P.

1980-01-01

397

Dynamic Phase Transition, Enhanced Reaction Rate, and  

E-print Network

reactions, biological populations, growth- deposition, economics, etc. Catalytic processes have many-reaction model that describes kinetics aspects of the gas- phase catalytic oxidation of carbon monoxide arriving to the surface is CO. Proportional to partial pressure of CO. #12;Two kinetic phase transitions

Rikvold, Per Arne

398

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

Tykodi, R. J.

1987-01-01

399

SULFUR DIOXIDE OXIDATION REACTIONS IN AQUEOUS SOLUTIONS  

EPA Science Inventory

This is the final report on a three year project to study the kinetics and mechanisms of some 105 reactions involving the aqueous oxidation of sulfur dioxide and nitrogen oxides in mixed catalyst-oxidant systems at low pH (0-3). The 105 systems involve six redox reaction types: S...

400

Catalytic enantioselective Conia-ene reaction.  

PubMed

An enantioselective intramolecular Conia-ene reaction of beta-dicarbonyl compounds and alkynes to afford methylene cyclopentanes is described. The reaction employs a DTBMSegphos-Pd(II)/Yb(III) dual catalyst system that allows for the asymmetric synthesis of all-carbon quaternary centers and generates a product containing an alkene that can be further manipulated. PMID:16332048

Corkey, Britton K; Toste, F Dean

2005-12-14

401

Pentoxifylline Suppresses Irritant and Contact Hypersensitivity Reactions  

Microsoft Academic Search

Pharmacologic suppression of the effector phase ot contact hypersensitivity appears to have major relevance with regard to treatment of type IV reactions like contact dermatitis. Recently, tumor necrosis factor ? has been shown to be a critical mediator in hapten-induced irritant and contact hypersensitivity reactions, thus offering new possibilities, for therapeutic intervention. Pentoxifylline, a methylxanthine derivative used in the treatment

Agatha Schwarz; Christine Krone; Franz Trautinger; Yoshinori Aragane; Peter Neuner; Thomas A. Luger; Thomas Schwarz

1993-01-01

402

Ambulatory measurement of ground reaction forces  

Microsoft Academic Search

The measurement of ground reaction forces is important in the biomechanical analysis of gait and other motor activities. Many applications require full ambulatory measurement of these forces, but this is not supported by current measurement systems. We propose the use of two six-degrees-of-freedom force and moment sensors under each shoe, which enables the ambulatory measurement of ground reaction forces and

Peter H. Veltink; Christian Liedtke; Ed Droog; Kooij van der Herman

2005-01-01

403

Laws of visual choice reaction time  

Microsoft Academic Search

Reviews 59 visual choice reaction time studies to determine the most significant independent variables and to develop empirical functions for them. The functions were then applied in conjunction with a proposed modification of F. C. Donders's law to isolate the relative temporal contributions to choice reaction time of 4 stages of information processing identified as stimulus coding, stimulus-stimulus translation, stimulus-response

Warren H. Teichner; Marjorie J. Krebs

1974-01-01

404

Reliability of a Shuttle reaction timer  

NASA Technical Reports Server (NTRS)

Reaction, movement, and task times refer to the times needed to initially respond to a stimulus, make the specific movement, and complete the entire task. This study evaluated the reliability of a simple reaction timer designed to mimic a Space Shuttle task (turning on an overhead switch).

Hays, Russell D.; Mazzocca, Augustus D.; Rashid, Michael; Siconolfi, Steven F.

1992-01-01

405

ChemTeacher: Balancing Redox 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 Balancing Redox Reactions page includes resources for teaching students about the steps needed to balance oxidation-reduction reactions.

2012-07-24

406

Ruthenium-catalyzed regioselective allylic trifluoromethylthiolation reaction.  

PubMed

An efficient Ru-catalyzed regioselective allylic trifluoromethylthiolation reaction of allylic carbonates was developed. The linear allylic trifluoromethyl thioethers were obtained in 52-91% yields. Mechanistic investigation revealed that this reaction proceeds via a double allylic trifluoromethylthiolation sequence. PMID:25203498

Ye, Ke-Yin; Zhang, Xiao; Dai, Li-Xin; You, Shu-Li

2014-12-19

407

Transport model of nucleon-nucleus reaction  

NASA Technical Reports Server (NTRS)

A simplified model of nucleon-nucleus reaction is developed and some of its properties are examined. Comparisons with proton production measured for targets of Al-27, Ni-58, Zr-90, and Bi-209 show some hope for developing an accurate model for these complex reactions. It is suggested that binding effects are the next step required for further development.

Wilson, J. W.; Townsend, L. W.; Cucinotta, F. A.

1986-01-01

408

Photosynthetic reaction center complexes from heliobacteria  

NASA Technical Reports Server (NTRS)

The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus of this project is the family of newly discovered strictly anaerobic photosynthetic organisms known as Heliobacteria. These organisms are the only known photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reaction centers suggest that they might be the decendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes have been isolated from the photosynthetic bacteria Heliobacillus mobilis and Heliobacterium gestii. The absorption and fluorescence properties of membranes and reaction centers are almost identical, suggesting that a single pigment-protein complex serves as both antenna and reaction center. Experiments in progress include sequence determination of the 48,000 Mr reaction center protein, and evolutionary comparisons with other reaction center proteins.

Trost, J. T.; Vermaas, W. F. J.; Blankenship, R. E.

1991-01-01

409

A reusable prepositioned ATP reaction chamber  

NASA Technical Reports Server (NTRS)

Luminescence biometer detects presence of life by means of light-emitting chemical reaction of luciferin and luciferase with adenosine triphosphate (ATP) that occurs in all living cells. Amount of light in reaction chamber is measured to determine presence and extent of life.

Hoffman, D. G.

1972-01-01

410

Theory of Low Energy Nuclear Reactions  

Microsoft Academic Search

The principal features of the theory of resonance reactions are ; described in terms of simple examples. A straightforward derivation is given of ; the particular result for the collision matrix found recently to be most useful ; for the description of low energy nuclear reactions. This result is expressed in ; terms of the potential scattering phase shifts and

Erich Vogt

1962-01-01

411

The Science of Low Energy Nuclear Reactions  

Microsoft Academic Search

The large literature describing the anomalous behavior attributed to cold fusion or low energy nuclear reactions has been critically described in a recently published book. Over 950 publications are evaluated allowing the phenomenon to be understood. A new class of nuclear reactions has been discovered that are able to generate practical energy without significant radiation or radioactivity. Edmund K Storms,

Edmund Storms

2007-01-01

412

3-haloquinolines by Friedländer reaction of ?-haloketones.  

PubMed

A general approach to 3-fluoro-, 3-chloro-, and 3-bromoquinolines which relies on organosilane-promoted Friedla?nder reaction of ?-haloketones is described. The scope of the methylene component as well as influence of the organosilane component on the outcome of the reaction is studied. The method can be used under parallel synthesis conditions. PMID:21627119

Ryabukhin, Sergey V; Naumchik, Vasiliy S; Plaskon, Andrey S; Grygorenko, Oleksandr O; Tolmachev, Andrey A

2011-07-15

413

Chemistry and shock initiation of intermetallic reactions  

Microsoft Academic Search

Shock initiation of pyrotechnic mixtures is a relatively new discipline. In earlier studies, the estimation of the Hugoniots of porous mixtures had been described (1) and application of experimental results to pyrotechnic mixtures was reported (2). In this investigation the shocked reaction mixture was recovered in order to determine whether or not reaction took place. The mixture hafnium-platinum was chosen

A. P. Hardt; S. L. McHugh; S. L. Weinland

1986-01-01

414

Chemistry and shock initiation of intermetallic reactions  

Microsoft Academic Search

Shock initiation of pyrotechnic mixtures is a relatively new discipline. In earlier studies, the estimation of the Hugoniots of porous mixtures had been described and application of experimental results to pyrotechnic mixtures was reported. In this investigation, the shocked reaction mixture was recovered in order to demonstrate that reaction took place. The mixture hafnium-platinum was chosen for its low thermal

A. P. Hardt; S. L. McHugh; S. L. Weinland

1986-01-01

415

A Hierarchy of Homodesmotic Reactions for Thermochemistry  

PubMed Central

Chemical equations that balance bond types and atom hybridization to different degrees are often used in computational thermochemistry, for example, to increase accuracy when lower levels of theory are employed. We expose the widespread confusion over such classes of equations and demonstrate that the two most widely used definitions of “homodesmotic” reactions are not equivalent. New definitions are introduced and a consistent hierarchy of reaction classes (RC1 – RC5) for hydrocarbons is constructed: isogyric (RC1) ? isodesmic (RC2) ? hypohomodesmotic (RC3) ? homodesmotic (RC4) ? hyperhomodesmotic (RC5). Each of these successively conserves larger molecular fragments. The concept of isodesmic bond separation reactions is generalized to all classes in this hierarchy, providing a unique sectioning of a given molecule for each reaction type. Several ab initio and density functional methods are applied to the bond separation reactions of 38 hydrocarbons containing five or six carbon atoms. RC4 and RC5 reactions provide bond separation enthalpies with errors consistently less than 0.4 kcal mol?1 across a wide range of theoretical levels, performing significantly better than the other reaction types and far superior to atomization routes. Our recommended bond separation reactions were demonstrated by determining the enthalpies of formation (at 298 K) of 1,3,5-hexatriyne (163.7 ± 0.4 kcal mol?1), 1,3,5,7-octatetrayne (217.6 ± 0.6 kcal mol?1), the larger polyynes C10H2 through C26H2, and an infinite acetylenic carbon chain. PMID:19182999

Schleyer, Paul v. R.

2009-01-01

416

Cysteine-selective reactions for antibody conjugation.  

PubMed

Moving tracks from maleimide: New site-selective protein modification reactions at cysteine have been developed. Unlike conventional maleimide conjugation, which results in a labile thioether succinimide, the new bioconjugation reactions result in stable conjugates and provide opportunities to develop a new generation of homogeneous, stable, and therapeutically useful conjugates. PMID:25070879

Cal, Pedro M S D; Bernardes, Gonçalo J L; Gois, Pedro M P

2014-09-26

417

Organic Reaction Mechanisms at A-Level.  

ERIC Educational Resources Information Center

Advocates teaching of organic reaction mechanisms through the methods which are used in elucidating them. This also provides a useful way of illustrating the theories and methods of physical chemistry. Describes an approach to teaching three reaction mechanisms: substitution in alkanes; addition to alkenes; and ester hydrolysis. (Author/GA)

Norman, R. O. C.; Waddington, D. J.

1979-01-01

418

Enantioselective Catalytic Transannular Ketone-Ene Reactions  

PubMed Central

Highly enantio- and diastereoselective transannular ketone-ene reactions are catalyzed by a new chromium(III) triflate tridentate Schiff-base complex. Electronically unactivated keto-olefins undergo hetero-ene reactions at ambient temperature to afford enantioenriched bicyclic alcohols, common structural motifs in natural products. The kinetic resolution of a configurationally stable planar-chiral cyclodecenone is also described. PMID:23923982

Rajapaksa, Naomi S.

2013-01-01

419

A modification of the thiobarbituric acid reaction.  

PubMed

A simple modification of the thiobarbituric acid reaction, which removes nonspecific chromogenic reaction products, involves incubation at room temperature for 16-20 hr and a column chromatographic step. The chromogen-concentrating capacity of the latter step is useful for determination of low concentrations of thiobarbituric acid-reactive materials in biological preparations. PMID:2779371

Bidder, T G; Sipka, B M

1989-07-01

420

Cutaneous allergic reactions to tattoo ink  

Microsoft Academic Search

Summary Tattoo artists use many compounds to create tattoo pigment and several allergic reactions can occur as a result of these additives. The compositions of many inks have been identified; however, as new mixtures are created it becomes difficult to identify the specific ingredients in a particular ink. Allergic reactions to a particular pigment can manifest in several ways including

Ravneet Ruby Kaur; William Kirby; Howard Maibach

2009-01-01

421

TRIMOLECULAR REACTIONS OF URANIUM HEXAFLUORIDE WITH WATER  

SciTech Connect

The hydrolysis reaction of uranium hexafluoride (UF{sub 6}) is a key step in the synthesis of uranium dioxide (UO{sub 2}) powder for nuclear fuels. Mechanisms for the hydrolysis reactions are studied here with density functional theory and the Stuttgart small-core scalar relativistic pseudopotential and associated basis set for uranium. The reaction of a single UF{sub 6} molecule with a water molecule in the gas phase has been previously predicted to proceed over a relatively sizeable barrier of 78.2 kJ {center_dot} mol{sup -1}, indicating this reaction is only feasible at elevated temperatures. Given the observed formation of a second morphology for the UO{sub 2} product coupled with the observations of rapid, spontaneous hydrolysis at ambient conditions, an alternate reaction pathway must exist. In the present work, two trimolecular hydrolysis mechanisms are studied with density functional theory: (1) the reaction between two UF{sub 6} molecules and one water molecule, and (2) the reaction of two water molecules with a single UF{sub 6} molecule. The predicted reaction of two UF{sub 6} molecules with one water molecule displays an interesting 'fluorine-shuttle' mechanism, a significant energy barrier of 69.0 kJ {center_dot} mol{sup -1} to the formation of UF{sub 5}OH, and an enthalpy of reaction ({Delta}H{sub 298}) of +17.9 kJ {center_dot} mol{sup -1}. The reaction of a single UF{sub 6} molecule with two water molecules displays a 'proton-shuttle' mechanism, and is more favorable, having a slightly lower computed energy barrier of 58.9 kJ {center_dot} mol{sup -1} and an exothermic enthalpy of reaction ({Delta}H{sub 298}) of -13.9 kJ {center_dot} mol{sup -1}. The exothermic nature of the overall UF{sub 6} + 2 {center_dot} H{sub 2}O trimolecular reaction and the lowering of the barrier height with respect to the bimolecular reaction are encouraging; however, the sizable energy barrier indicates further study of the UF{sub 6} hydrolysis reaction mechanism is warranted to resolve the remaining discrepancies between the predicted mechanisms and experimental observations.

Westbrook, M.; Becnel, J.; Garrison, S.

2010-02-25

422

Direct Monte Carlo simulation of chemical reaction systems: Simple bimolecular reactions  

E-print Network

Direct Monte Carlo simulation of chemical reaction systems: Simple bimolecular reactions Shannon D and understanding the behavior of gas phase chemical reaction systems. This Monte Carlo method, originated by Bird useful, and the gas dynamics of many systems is more easily predicted and understood by using Monte Carlo

Anderson, James B.

423

A Green Multicomponent Reaction for the Organic Chemistry Laboratory: The Aqueous Passerini Reaction  

ERIC Educational Resources Information Center

Water is the ideal green solvent for organic reactions. However, most organic molecules are insoluble in it. Herein, we report a laboratory module that takes advantage of this property. The Passerini reaction, a three-component coupling involving an isocyanide, aldehyde, and carboxylic acid, typically requires [similar to] 24 h reaction times in…

Hooper, Matthew M.; DeBoef, Brenton

2009-01-01

424

Some Concepts in Reaction Dynamics  

NASA Technical Reports Server (NTRS)

In 1929 London 1 published a very approximate solution of the Schroedinger equation for a system of chemical interest: H3. To the extent that chemistry can be regarded as existing separately from physics, this was a landmark in the history of chemistry, comparable in importance to the landmark in the history of physics marked by the appearance of the Heitler-London equation for H2. The expression for H3, was, of necessity, even less accurate than that for H2, but chemists, like the habitual poor, were accustomed to this sort of misfortune. Together with the physicists they enjoyed the sensation of living in a renaissance. The physicists still could not calculate a great deal that was of interest to them, and the chemists could calculate less, but both could now dream. It would be too easy to say that their dreams were dreams of unlimited computer time. Their dreams were a lot more productive than that. Two years after London published his equation, H. Eyring and M. Polanyi obtained the first numerical energy surface for H3. They infused the London equation with a measure of empiricism to produce an energy surface which, whether or not it was correct in its details, provided a basis for further speculations of an important sort. The existence of a tangible energy surface in 1931 stimulated speculation along two different lines. The following year Pelzer and Wigner used this London-Eyring-Polanyi (LEP) energy surface for a thermodynamic treatment of the reaction rate in H + H2. This important development reached its full flowering a few years later. In these remarks I shall be concerned with another line of development. A second more-or-less distinct category of speculation that began with (and, indeed, in) the 1931 paper has to do with the dynamics of individual reactive encounters under the influence of specified interaction potentials.

Polannyi, John C.

1972-01-01

425

Nurses must report adverse drug reactions.  

PubMed

There is renewed determination throughout the European Union (EU) to reduce the economic cost and high death rate associated with adverse drug reactions through better pharmacovigilance. Timely reporting and sharing of information concerning adverse drug reactions is vital to the success of this initiative. In the UK, the reporting of serious adverse drug reactions is facilitated by the Yellow Card Scheme, yet despite being well placed to monitor the effect of medicines on patients, nurses do not make full use of the scheme. This article sets out the impact of adverse drug reactions in the EU and argues that it is essential that nurses must be at the vanguard of adverse reaction reporting if the EU's pharmacovigilance initiative is to be a success. PMID:23905231

Griffith, Richard

426

Magnetic trap of a reaction zone  

NASA Astrophysics Data System (ADS)

The reaction of ethylene glycol oxidation catalyzed by a colloidal suspension of iron oxide nanoparticles was monitored by IR thermography under an inhomogeneous magnetic field (with a spatial gradient ˜50T2/m). The interaction of a reaction zone with the gradient magnetic field, in a way that the reaction zone could be trapped and manipulated at a desired position with the aid of the magnetic field effect, has been discovered. We explain this phenomenon by the magnetic buoyancy force arising from the variation in the magnetic susceptibility between the reaction zone and rest solution during the catalyzed redox process. These observations suggest the potential use magnetic fields for controlling chemical processes by the long-time localization of the reaction zone from the environment and enables complex problem solving to be performed in physics, chemistry, biology, chemical engineering, nanotechnology, and medicine.

Digilov, Rafael M.; Sheintuch, M.

2005-02-01

427

Low energy ion-molecule reactions  

SciTech Connect

This project is concerned with elucidating the dynamics of elementary ion-molecule reactions at collision energies near and below 1 eV. From measurements of the angular and energy distributions of the reaction products, one can infer intimathe details about the nature of collisions leading to chemical reaction, the geometries and lifetimes of intermediate complexes that govern the reaction dynamics, and the collision energy dependence of these dynamical features. The author employs crossed-beam low energy mass spectrometry technology developed over the last several years, with the focus of current research on proton transfer and hydrogen atom transfer reactions of te O{sup {minus}} ion with species such as HF, H{sub 2}O, and NH{sub 3}.

Farrar, J.M. [Univ. of Rochester, NY (United States)

1993-12-01

428

Endothermic photo-catalytic reactions. Final report  

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

429

[Hip surgery: local tissue reactions].  

PubMed

Present extent of total hip prostheses, protracted course of first operations lead to pathological studies on local tissue reactions, sign of the failure or of the damaging of the artificial hip. Another pathology, often as intricate, is observed after more conservative surgery: high femoral osteotomies, cup arthroplasties, femoral metallic prostheses. Failure of an high femoral osteotomy shows a running of osteoarthritic lesions the topography of which is always modified by the new orientation of the articular bearing segment. Osteosclerosis, osteoarthritic cysts may develop on a preexisting osteophytosis. Osteonecrosis or bone resorption are sometimes found. Anatomical results in case of a successful osteotomy are scarce. Fibrous layer eventually quoted as a guide to the development of fibrocartilage is more often associated with osteoclast mediated bone loss. Efficient bone remodelling is assumed only, today, by radiological proof. Failures of cup arthroplasties induce femoral bone or acetabular cartilage lesions which are different according to the surgical technic. Some are marked by cartilage destruction of the acetabula or by a cup dislodgement. Bone structure in those cases shows under the cup a good remodelling with a fibrous or fibrocartilaginous mantle originating from the bone marrow spaces and the capsular attachment. In other cases, the femoral head presents areas of superficial or total osteonecrosis, signs of intense osteoclastic activity, cleaving of the fibrous surface and eventually metallic debris or cement induced histiocytic granuloma. A fibrous layer may develop between the cup and the acetabula. Femoral metallic prostheses may damage in some years cartilage of the acetabula. Osteoarthritic bone remodelling is sometimes observed in close contact with the metallic collar. Lesions of capsular tissues are eventually represented by metallic debris or an histiocytic granuloma due to cement anchorage. Material received at the time of surgical revision on total hip arthroplasties concerns chiefly the newly formed capsular and synovial tissues. Their appearance is quite similar to the tissular layers found between prosthetic material and bone or cement. For the pathologist, main inquiries are the rule out of an infection, the extent and course of the macrophage or giant cell response, the nature of wear debris or of the products of corrosion and the histological factors contributing to the loosening of the prosthetic components. It should be stressed that any physiopathological schedule of an artificial hip failure is a topographical and dynamic problem only partly resolved by studying autopsy material. PMID:3893449

Forest, M; Courpied, J P; Lefloch, P; Carlioz, A; Abelanet, R; Postel, M

1985-01-01

430

DTP-associated reactions: an analysis by injection site, manufacturer, prior reactions, and dose.  

PubMed

Local and less serious systemic reactions are frequent following immunization with diphtheria-tetanus-pertussis (DTP) vaccine. The effects of injection site, manufacturer, previous reactions, and dosage reduction upon subsequent reactions to DTP immunization were investigated. Local reactions, notably pain and swelling, were less common when the immunization was given in the buttocks than in the thigh. No injection site was consistently associated with lower systemic reaction rates. There was no significant difference in the rate of more serious reactions by vaccine manufacturer. Differences in rates of less serious reactions by manufacturer were observed but seemed to be related to vaccine lot differences rather than the specific vaccines. In a subset of 772 children, in whom data regarding sequential reactions were available, it was noted that all three reactions investigated--local redness, temperature greater than or equal to 39 degrees C, and persistent crying longer than one-half hour--were two to three times more frequent on a subsequent immunization when present on a prior vaccination than if not present on a prior vaccination than if not present previously. One hundred children received a half dose of DTP vaccine because of a less serious reaction associated with prior immunization. In all instances, they had significantly less serious local reactions as well as notable differences in temperature, drowsiness, and persistent crying. PMID:6606797

Baraff, L J; Cody, C L; Cherry, J D

1984-01-01

431

STUDIES ON THE GENERALIZED SHWARTZMAN REACTION  

PubMed Central

Lesions indistinguishable from those of the generalized Shwartzman reaction occured in rabbits when a single intravenous injection of Gram-negative bacterial endotoxin was accompanied, or followed, by an injection of one of the following synthetic, heparin-like, acidic polymers-sodium polyanethol sulfonate, dextran sulfate, or sodium polyvinyl alcohol sulfonate. These reactions were produced by doses of polymer or of endotoxin which were without demonstrable effect when given singly. Heparin, in those similar to those previously shown to protect rabbits against the lesions of the generalized Shwartzman reaction, prevented the reaction to the combined injection of endotoxin and acidic polymers. Nitrogen mustard, which was previously shown to prevent the lesions of the generalized Shwartzman reaction from occurring after two intravenous injections of endotoxin, had no protective action against the lesions produced by the combined injection of endotoxin and polymer. Cortisone did not affect the reaction to endotoxin and polymer. The role of fibrinogen in the reaction under study is discussed in the paper which follows. PMID:13252181

Thomas, Lewis; Brunson, Joel; Smith, Richard T.

1955-01-01

432

The hydroarylation reaction--scope and limitations.  

PubMed

The synthetic potential of stereoselective, palladium-catalyzed hydro(het)arylation reactions of bi-, tri- and tetracyclic (hetero)alkenes in the presence of phospines and arsines as highly efficient ligands was studied. The mechanism of this reductive Heck reaction becomes more complex in the case of benzonorbornenes. Hydroarylation of diazabicyclo-[2.2.1]heptenes provides a stereoselective access to aryldiaminocyclopentanes. Electron-deficient arylpalladium complexes shift the reaction towards the product of a formal 1,2-hydrazidoarylation reaction of 1,3-cyclopentadiene by a stereoselective C-N cleavage. Due to steric reasons, rigid bicyclo[2.2.2]octenes react slower in hydroarylation reactions than the corresponding bicyclo[2.2.1]heptenes. The more flexible bicyclo[4.2.2]decene system already tends to undergo domino-Heck reactions, even under reductive conditions. When a tetracyclic cis-allylcyclopropane is carbopalladated in the presence of formates, the neighboring cyclopropane ring is attacked in the first reported example of a pi,sigma domino-Heck reaction. PMID:20657489

Namyslo, Jan C; Storsberg, Jörg; Klinge, Jens; Gärtner, Christian; Yao, Min-Liang; Ocal, Nuket; Kaufmann, Dieter Eckhard

2010-05-01

433

Transport-theoretical Description of Nuclear Reactions  

E-print Network

In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30 AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100 MeV to a few 100 GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion-nucleus interactions, nuclear fragmentation, heavy ion reactions, hyper nucleus formation, hadronization, color transparency, electron-nucleus collisions and neutrino-nucleus interactions are all possible applications of GiBUU and are discussed in this article.

O. Buss; T. Gaitanos; K. Gallmeister; H. van Hees; M. Kaskulov; O. Lalakulich; A. B. Larionov; T. Leitner; J. Weil; U. Mosel

2012-02-02

434

Enzyme Reaction Annotation Using Cloud Techniques  

PubMed Central

An understanding of the activities of enzymes could help to elucidate the metabolic pathways of thousands of chemical reactions that are catalyzed by enzymes in living systems. Sophisticated applications such as drug design and metabolic reconstruction could be developed using accurate enzyme reaction annotation. Because accurate enzyme reaction annotation methods create potential for enhanced production capacity in these applications, they have received greater attention in the global market. We propose the enzyme reaction prediction (ERP) method as a novel tool to deduce enzyme reactions from domain architecture. We used several frequency relationships between architectures and reactions to enhance the annotation rates for single and multiple catalyzed reactions. The deluge of information which arose from high-throughput techniques in the postgenomic era has improved our understanding of biological data, although it presents obstacles in the data-processing stage. The high computational capacity provided by cloud computing has resulted in an exponential growth in the volume of incoming data. Cloud services also relieve the requirement for large-scale memory space required by this approach to analyze enzyme kinetic data. Our tool is designed as a single execution file; thus, it could be applied to any cloud platform in which multiple queries are supported. PMID:24222895

Huang, Chuan-Ching

2013-01-01

435

Dehydriding reactions of mixed complex hydrides  

NASA Astrophysics Data System (ADS)

Dehydriding reactions of the mixtures LiBH 4 + 2LiNH 2 and LiAlH 4 + 2LiNH 2 were investigated. The new pathways confirmed for the dehydriding reactions were LiBH 4 + 2LiNH 2 ? Li 3BN 2 + 4H 2 and LiAlH 4 + 2LiNH 2 ? Li 3AlN 2 + 4H 2 in which 11.9 and 9.6 mass% of hydrogen can be desorbed theoretically. The quantities of desorbed hydrogen were deduced experimentally to be approximately 7.9-9.5 and 4.1 mass% for the mixtures of LiBH 4 + 2LiNH 2 and LiAlH 4 + 2LiNH 2, respectively. The dehydriding temperature of LiBH 4 reduces by 150 K by mixing 2 M LiNH 2. An exothermic peak was observed at a slightly higher temperature of the dehydriding reaction; however, this peak might be due to the solidification of the product after the dehydriding reaction and not due to the exothermic dehydriding reaction. Although the first-step dehydriding reaction of LiAlH 4 is exothermic, the mixture of LiAlH 4 + 2LiNH 2 exhibits an endothermic dehydriding reaction. These results suggest that the stability of the dehydriding reactions of complex hydrides can be controlled by introducing new pathways that are produced by mixing. Two criteria for selecting complex hydrides that are mixed together for producing new pathways were proposed from the viewpoints of both the melting/dehydriding temperatures and the products of the dehydriding reactions.

Nakamori, Y.; Ninomiya, A.; Kitahara, G.; Aoki, M.; Noritake, T.; Miwa, K.; Kojima, Y.; Orimo, S.

436

Violent Reactions from Non-Shock Stimuli  

NASA Astrophysics Data System (ADS)

Most reactions are thermally initiated, whether from direct heating or dissipation of energy from mechanical, shock, or electrical stimuli. For other than prompt shock initiation, the reaction must be able to spread through porosity or over large surface area to become more violent than just rupturing any confinement. While burning rates are important, high-strain mechanical properties are nearly so, either by reducing existing porosity or generating additional surface area through fracture. The first example is deflagration-to-detonation transition (DDT) in porous beds. During the early stages, weak compressive waves ahead of the convective ignition front will reduce porosity, thereby restricting the spread of combustion and the pressure buildup. If, however, pressure increases faster than can be relieved by loss of confinement, coalescing compressive waves can initiate reaction at hot spots from rapid pore collapse. This compressive reaction can drive a shockwave that transits to detonation, the most violent reaction in any scenario. It has been shown that reaction violence is reduced in DDT experiments if the binder is softened, either by raising the initial temperature or adding a solvent. An example of the role of mechanical properties in enhancing reaction violence through fracturing occurs when cavities in projectile fills collapse during acceleration in the gun barrel, which is referred to as setback. Explosives with soft rubber binders will deform and undergo mild reaction from shear heating within the explosive and adiabatic compression of any gas in the cavity. Stiff explosives are similarly ignited, but also fracture and generate additional surface area for a violent event. The last example to be considered is slow cook-off, where thermal damage can increase burning rate as well as provide porosity to enhance the pressure buildup. As reaction spreads from the zone of thermal run-away, an explosive binder that resists breakup will limit the violence.

Sandusky, Harold

2007-06-01

437

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

NASA Technical Reports Server (NTRS)

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 species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

438

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

NASA Astrophysics Data System (ADS)

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 species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2011-05-01

439

Stepwise acid-promoted double-Michael process: an alternative to Diels-Alder cycloadditions for hindered silyloxydiene-dienophile pairs.  

PubMed

The hindered diene 1 reacts with 3-methylcyclohexenone 6 catalyzed by triflimide to produce the Mukaiyama Michael product 7 (low-temperature quenching) or the [4+2] cycloadduct 8 (quenching at 0 degrees C). Reaction of the hindered diene 23 with 2-methylcyclohexenone 12 with 5:1 AlBr3:AlMe3 afforded a 71% yield of a 1.9:1 mixture of two cycloadducts. Hydrolysis of the major isomer gave the dione 27', a model for the BCD ring system of pentacyclic triterpenes. [reaction: see text]. PMID:17217308

Jung, Michael E; Ho, David G

2007-01-18

440

Polar reactions of acyclic conjugated bisallenes  

PubMed Central

Summary The chemical behaviour of various alkyl-substituted, acyclic conjugated bisallenes in reactions involving polar intermediates and/or transition states has been investigated on a broad scale for the first time. The reactions studied include lithiation, reaction of the thus formed organolithium salts with various electrophiles (among others, allyl bromide, DMF and acetone), oxidation to cyclopentenones and epoxides, hydrohalogenation (HCl, HBr addition), halogenation (Br2 and I2 addition), and [2 + 2] cycloaddition with chlorosulfonyl isocyanate. The resulting adducts were fully characterized by spectroscopic and analytical methods; they constitute interesting substrates for further organic transformations. PMID:23400309

Stamm, Reiner

2013-01-01

441

Reaction-diffusion in the NEURON simulator  

PubMed Central

In order to support research on the role of cell biological principles (genomics, proteomics, signaling cascades and reaction dynamics) on the dynamics of neuronal response in health and disease, NEURON's Reaction-Diffusion (rxd) module in Python provides specification and simulation for these dynamics, coupled with the electrophysiological dynamics of the cell membrane. Arithmetic operations on species and parameters are overloaded, allowing arbitrary reaction formulas to be specified using Python syntax. These expressions are then transparently compiled into bytecode that uses NumPy for fast vectorized calculations. At each time step, rxd combines NEURON's integrators with SciPy's sparse linear algebra library. PMID:24298253

McDougal, Robert A.; Hines, Michael L.; Lytton, William W.

2013-01-01

442

Nonlinear reaction-diffusion: a microscopic approach  

NASA Astrophysics Data System (ADS)

A microscopic theory for reaction-difusion (R-D) processes is developed from Einstein's master equation including a reactive term. The mean field formulation leads to a generalized R-D equation for the n-th order annihilation reaction A + A + A + ... + A ? 0, and the steady state solutions exhibit long range power law behavior showing the relative dominance of sub-diffusion over reaction effects in constrained systems, or conversely short range concentration distribution with finite support describing situations where diffusion is slow and extinction is fast. We apply the theory to analyze experimental data for morphogen gradient formation in the wing disc of the Drosophila embryo.

Boon, Jean Pierre; Lutsko, James F.; Lutsko, Christopher

2012-06-01

443

Physiological aspects of free-radical reactions.  

PubMed Central

Enzymes which catalyze the formation of free radicals in vitro will catalyze similar reactions in vivo. We believe that the formation of some kinds of free radicals has definite physiological meanings in metabolism. In this sense, the enzymes forming such free radicals are concluded to be in evolutionally advanced states. Elaborated structure and function of enzymes such as horseradish peroxidase and microsomal flavoproteins support the idea. Deleterious and side reactions caused by free radicals are assumed to be minimized in vivo by localizing the reactions, but this assumption should be verified by future studies. PMID:3007098

Yamazaki, I; Tamura, M; Nakajima, R; Nakamura, M

1985-01-01

444

Cutaneous drug reactions in the pediatric population.  

PubMed

Cutaneous adverse drug reactions (ADRs) constitute a major pediatric health problem frequently encountered in clinical practice, and represent a diagnostic challenge. Children are more susceptible than adults to errors in drug dosage because of their smaller body size; moreover, ADRs can mimic other skin diseases of children, especially viral exanthems. Most ADRs with cutaneous involvement are mild and resolve on withdrawal of the causative drug. The most common forms of cutaneous ADRs, maculopapular exanthems and urticarial reactions, have excellent outcomes. Less frequent but more severe reactions may incur a risk of mortality. PMID:24636653

Noguera-Morel, Lucero; Hernández-Martín, Ángela; Torrelo, Antonio

2014-04-01

445

On the Violence of High Explosive Reactions  

SciTech Connect

High explosive reactions can be caused by three general energy deposition processes: impact ignition by frictional and/or shear heating; bulk thermal heating; and shock compression. The violence of the subsequent reaction varies from benign slow combustion to catastrophic detonation of the entire charge. The degree of violence depends on many variables, including the rate of energy delivery, the physical and chemical properties of the explosive, and the strength of the confinement surrounding the explosive charge. The current state of experimental and computer modeling research on the violence of impact, thermal, and shock-induced reactions is reviewed.

Tarver, C M; Chidester, S K

2004-02-09

446

Reaction kinetics, geospeedometry, and relaxation theory  

NASA Astrophysics Data System (ADS)

This paper explores the application of homogeneous reaction kinetics to geospeedometry and to structural relaxation theory. Numerical simulations of reaction kinetics during cooling for some first- and second-order elementary reactions have been carried out to systematically examine the effects of kinetic parameters and cooling histories on the final speciation. An analytical solution for a special case of first-order reaction A ? B has also been obtained. On the basis of both the analytical solution and the numerical simulation, the cooling rate ( -dT/dt) at the apparent equilibrium temperature ( T ae, obtained by measuring 'quenched' speciation) and the relaxation time scale ( ? r, the time for the departure from equilibrium to decrease to 1/e of the initial departure) at T ae can be approximately related as follows: (-dT/dt)| T=T ae ? 2RT ae/max( E f, E b) where R is the gas constant, and max( E f, E b) is the greater of E f and E b, which are the activation energies of the forward and backward reactions. This approximation works well when the initial temperature ( T 0) is high such that ? r(T 0) is small compared to the cooling time scale. Using the above relation, the cooling rate at T ae can be estimated easily and the cooling history of a natural assemblage can be inferred if enough homogeneous reactions are characterized. Relaxation of homogeneous reactions during the quench of a silicate melt into a glass can be studied quantitatively using the above method if the kinetic parameters are known. Melt-glass transitions probably involve the quenching of many homogeneous reactions that may have different T ae for a given quench rate, and are thus complicated. Authors have previously discussed relaxation of a reaction during cooling using the idea of a melt-glass transition. Because glass relaxation is complicated and the theory is still in its infancy, whereas reaction kinetics can be understood and quantified, it may be more productive to study the relaxation of homogeneous reactions directly and to study glass relaxation using the concept of reaction kinetics instead.

Zhang, Youxue

1994-04-01

447

Serpentinization reaction pathways: implications for modeling approach  

SciTech Connect

Experimental seawater-peridotite reaction pathways to form serpentinites at 300/sup 0/C, 500 bars, can be accurately modeled using the EQ3/6 codes in conjunction with thermodynamic and kinetic data from the literature and unpublished compilations. These models provide both confirmation of experimental interpretations and more detailed insight into hydrothermal reaction processes within the oceanic crust. The accuracy of these models depends on careful evaluation of the aqueous speciation model, use of mineral compositions that closely reproduce compositions in the experiments, and definition of realistic reactive components in terms of composition, thermodynamic data, and reaction rates.

Janecky, D.R.

1986-01-01

448

Polyneutrons as agents for cold nuclear reactions  

SciTech Connect

In this paper new nuclear reactions are described where polyneutrons exchange neutron pairs with charged nuclides, liberating substantial energy with only minor production of neutrons and tritium. It is postulated that polyneutrons are bound in a totally paired collective phase analogous to the Bardeen-Cooper-Schrieffer superconducting phase, that massive precursor hydrogen nuclides are bound in the same collective phase, and the polyneutrons are generated from precursor hydrogen by reaction with neutrons. The concentration and disposition of precursor hydrogen, of lithium, and of neutron-moderating and neutron-absorbing materials in the reactor environment emerge as key variables in cold nuclear reaction processes.

Fisher, J.C. (Thomas Paine Associates, Carpinteria, CA (United States))

1992-12-01

449

Low-energy proton capture reactions  

SciTech Connect

An overview of experimental problems in measuring the cross sections for (p,?) and (p,n) reactions at low energies is given with a specific emphasis on electron screening in metallic targets. Thick target ?-ray and neutron yields are compared for Ni and NiO targets, V and VO{sub 2} targets and Mn and MnO targets. The {sup 1}H({sup 7}Li,?){sup 4}He reaction was studied in inverse kinematics with hydrogen loaded into Pd and PdAg alloy foils from gas phase. Based on these results, a new approach to electron screening in nuclear reactions is suggested.

Lipoglavsek, M.; Cvetinovic, A.; Gajevic, J.; Likar, A.; Vavpetic, P. [Jozef Stefan Institute, Jamova ulica 39, Ljubljana (Slovenia); Petrovic, T. [Jozef Stefan Institute, Jamova ulica 39, Ljubljana, Slovenia and Cosylab d.d., Teslova ulica 30, Ljubljana (Slovenia)

2014-05-09

450

Relativisitic hydrodynamics and heavy ion reactions  

SciTech Connect

The author discusses a hydrodynamic model for describing heavy ion reactions in which the three dimensional relativistic Euler equations are solved numerically using the particle in cell method. This method allows for calculations in cases of extreme distortion and shear and provides a means for presenting graphical representations of the reaction process. The techniques are illustrated by considering the /sup 20/Ne + /sup 238/U and the /sup 238/U + /sup 238/u reactions at 393 MeV and 800 MeV laboratory energies, respectively. 16 refs., 4 figs.

Strottman, D.

1987-01-01

451

Supercritical Fluid Reactions for Coal Processing  

SciTech Connect

Exciting opportunities exist for the application of supercritical fluid (SCF) reactions for the pre-treatment of coal. Utilizing reactants which resemble the organic nitrogen containing components of coal, we developed a method to tailor chemical reactions in supercritical fluid solvents for the specific application of coal denitrogenation. The tautomeric equilibrium of a Schiff base was chosen as one model system and was investigated in supercritical ethane and cosolvent modified supercritical ethane. The Diels-Alder reaction of anthracene and 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) was selected as a second model system, and it was investigated in supercritical carbon dioxide.

Charles A. Eckert

1997-11-01

452

Reaction synthesis of heat-resistant materials  

SciTech Connect

Exothermicity associated with the synthesis of aluminides can be utilized to obtain aluminides of transition metals. Combustion synthesis, extrusion, and hot pressing were utilized to obtain dense intermetallics and their composites. Composites were analyzed by X- ray diffraction and microscopy techniques, and tensile properties were measured on button-head and sheet specimens of intermetallics and their composites. Mechanical properties of intermetallics obtained by reaction synthesis and densification compare well with conventionally processed materials. Reaction-synthesis principles were also extended to weld overlays. Possible approaches to obtaining dense products by reaction synthesis and densification are summarized in a schematic illustration. 19 refs., 14 figs., 3 tabs.

Deevi, S.C.; Sikka, V.K.

1995-12-31

453

Silicon-based 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 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); Mariella, Jr., Raymond P. (Danville, CA); Carrano, Anthony V. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

1996-01-01

454

A Case of a Generalized Lichenoid Tattoo Reaction  

PubMed Central

Cutaneous reactions to tattoos have been increasing in conjunction with the rise in popularity of tattoos. While localized lichenoid reactions to tattoo inks are fairly common, generalized lichenoid reactions are relatively rare. Herein the authors present a case of a generalized lichenoid reaction to a tattoo containing only black ink. They also present a brief discussion of tattoo reactions and treatment options. PMID:25161761

Zirwas, Matthew J.; Mosser, Joy L.

2014-01-01

455

A case of a generalized lichenoid tattoo reaction.  

PubMed

Cutaneous reactions to tattoos have been increasing in conjunction with the rise in popularity of tattoos. While localized lichenoid reactions to tattoo inks are fairly common, generalized lichenoid reactions are relatively rare. Herein the authors present a case of a generalized lichenoid reaction to a tattoo containing only black ink. They also present a brief discussion of tattoo reactions and treatment options. PMID:25161761

Jacks, Stephanie K; Zirwas, Matthew J; Mosser, Joy L

2014-08-01

456

Method for predicting enzyme-catalyzed reactions  

DOEpatents

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

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

2013-03-19

457

Design of Multi-Component Reactions  

NASA Astrophysics Data System (ADS)

Multi-component reactions (MCRs) have now been well established as a powerful synthetic tool for creating molecular complexity and diversity and are undoubtedly well suited for the drug discovery program. Another potential that has probably received less attention among synthetic chemists is the opportunity offered by MCRs for the development of new fundamentally important transformations (reactions). Indeed, although an MCR is composed of a series of known bimolecular reactions, the overall transformation could be novel. Consequently, it provides chemists the opportunities to uncover transformations that were otherwise difficult to realize. In this talk, we will present our recent work in this field, including: (1) the oxidative homologation of aldehydes to amides, (2) the oxidative coupling of aldehydes and isocyanides to ?-ketoamides, (3) oxidative isocyanide-based MCRs, and (4) the enantioselective Passerini reaction.

Zhu, Jieping; Kaïm, Laurent El; Tron, Gian Cesare; Lavilla, Rodolfo; Banfi, Luca; Basso, Andrea; Cerulli, Valentina; Guanti, Giuseppe; Lecinska, Paulina; Riva, Renata; Arévalo, M. J.; Kielland, N.; Masdeu, C.; Miguel, M.; Isambert, N.; Lavilla, R.; Medvedeva, Alevtina S.; Novokshonov, Vladimir V.; Novokshonova, Irina A.; Demina, Maria M.; Kon'kova, Tatyana V.; Shklyaev, Yurii V.; Rozhkova, Yulia S.; Vshivkova, Tatiana S.; Stryapunina, Olga G.; Glushkov, Vladimir A.; Kharitonova, Anastasia V.; Fisyuk, Alexander S.; Mukanov, Aleksey Y.; Poendaev, Nicolay V.; Gulevich, Anton V.; Nenajdenko, Valentine G.; Ivantsova, Maria N.; Tokareva, Maria I.; Mironov, Maxim A.; Mokrushin, Vladimir S.; Pirali, Tracey; Tron, Gian Cesare; Zhu, Jieping; Rozentsveig, Igor B.; Popov, Aleksandr V.; Levkovskaya, Galina G.; Chernyshev, Kirill A.; Krivdin, Leonid B.; Tomilov, Yury V.; Platonov, Dmitry N.; Rulev, Alexander Y.; Ushakov, Igor A.; Vorobyeva, Alexandra; Ilyin, Alexey; Kysil, Volodimir; Ivachtchenko, Alexandre

458

Dynamical dipole mode in fusion reactions  

SciTech Connect

We investigated the dynamical dipole mode, related with entrance channel charge asymmetry effects, in the {sup 40}Ar+{sup 92}Zr and {sup 36}Ar+{sup 96}Zr fusion reactions at E{sub lab} = 15.1 A and 16 A MeV, respectively. These reactions populate, through entrance channels having different charge asymmetries, a compound nucleus in the A = 126 mass energy region, identical spin distribution at an average excitation energy of about 280 MeV. The compound nucleus average excitation energy and average mass were deduced by the analysis of the light charged particle energy spectra. By studying the {gamma}-ray energy spectra and the {gamma}-ray angular distributions of the considered reactions, the dynamical nature of the prompt radiation related to the dynamical dipole mode was evidenced. The data are compared with calculations based on a collective bremsstrahlung analysis of the reaction dynamics.

Pierroutsakou, D.; Boiano, A.; Romoli, M. [INFN, Sezione di Napoli, Napoli (Italy); Martin, B.; Inglima, G.; La Commara, M.; Sandoli, M. [INFN, Sezione di Napoli, Napoli (Italy); Dipartimento di Scienze Fisiche, Universita di Napoli Federico II, Napoli (Italy); Agodi, C.; Alba, R.; Coniglione, R.; Zoppo, A. Del; Maiolino, C.; Piattelli, P.; Santonocito, D.; Sapienza, P. [INFN-Laboratori Nazionali del Sud, Catania (Italy); Baran, V.; Glodariu, T. [NIPNE-HH and Bucarest University (Romania); Cardella, G.; De Filippo, E.; Pagano, A. [INFN, Sezione di Catania, Catania (Italy)] (and others)

2009-05-04

459

Adsorption Isotherms and Surface Reaction Kinetics  

ERIC Educational Resources Information Center

Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

Lobo, L. S.; Bernardo, C. A.

1974-01-01

460

Reaction patterns in a blinking vortex flow  

NASA Astrophysics Data System (ADS)

We study the patterns formed by the excitable Belousov-Zhabotinsky reaction in a blinking vortex flow produced by magnetohydrodynamic forcing. Mixing in this flow is chaotic, as has been documented extensively in previous studies. The reaction is triggered by a silver wire, and the result is a pulse (``trigger wave'') that propagates through the system. We investigate the patterns formed by the propagating pulse and compare them with theoriesootnotetextT. Tel, A. de Moura, C. Grebogi and G. Karolyi, Phys. Rep. 413, 91 (2005). that predict fractal patterns determined by the unstable manifolds of the flow. We also consider ``burn-like'' reaction fronts, and compare the results with previous experiments for patterns of oscillatory reactions in this flow.

Nugent, Carolyn

2005-11-01

461

Individual Reactions to Failure in Virtual Teams  

E-print Network

This project examines the relationship between team identification and collaboration configuration and how they affect attributions to failure. In a sample of 110 participants, we examined reactions to failure. We manipulated perceptions...

Diaz, Ismael

2012-02-14

462

Chemistry: Principles and Reactions, 6th Edition  

NSDL National Science Digital Library

Finds ChemEd DL resources related to the sections of the General Chemistry textbook, Chemistry: Principles and Reactions, 6th Edition, by William L. Masterton and Cecile N. Hurley published by Brooks/Cole, 2009.

463

Newton's Third Law: Action–Reaction  

NSDL National Science Digital Library

In this lesson designed to enhance literacy skills, an early astronaut's experiences teach students that Newton's third law of motion—for every action, there is an equal and opposite reaction—applies both on Earth and in outer space.

2010-11-17

464

Micelle Catalysis of an Aromatic Substitution Reaction  

ERIC Educational Resources Information Center

Describes an experiment in which the iodonation of aniline reaction is shown to undergo catalysis in solution of sodium lauryl sulfate which forms micelles with negatively charged pseudo surfaces. (MLH)

Corsaro, Gerald; Smith J. K.

1976-01-01

465

Immune Reactions Among Marine and Other Invertebrates  

ERIC Educational Resources Information Center

Discusses the defense mechanisms and immune reaction found in invertebrates, and examines the wealth of related biological problems that need study and many of the leads that have recently been developed. (JR)

Bang, Frederik B.

1973-01-01

466

Contact-Allergic Reactions to Cosmetics  

PubMed Central

Contact-allergic reactions to cosmetics may be delayed-type reactions such as allergic and photo-allergic contact dermatitis, and more exceptionally also immediate-type reactions, that is, contact urticaria. Fragrances and preservative agents are the most important contact allergens, but reactions also occur to category-specific products such as hair dyes and other hair-care products, nail cosmetics, sunscreens, as well as to antioxidants, vehicles, emulsifiers, and, in fact, any possible cosmetic ingredient. Patch and prick testing to detect the respective culprits remains the golden standard for diagnosis, although additional tests might be useful as well. Once the specific allergens are identified, the patients should be informed of which products can be safely used in the future. PMID:21461388

Goossens, An

2011-01-01

467

Using Reaction Mechanism to Measure Enzyme Similarity  

PubMed Central

Summary The concept of reaction similarity has been well-studied in terms of the overall transformation associated with a reaction, but not in terms of mechanism. We present the first method to give a quantitative measure of the similarity of reactions based upon their explicit mechanisms. Two approaches are presented to measure the similarity between individual steps of mechanisms: a fingerprint-based approach which incorporates relevant information on each mechanistic step, and an approach based only on bond formation, cleavage and changes in order. The overall similarity for two reaction mechanisms is then calculated using the Needleman-Wunsch alignment algorithm. An analysis of MACiE, a database of enzyme mechanisms, using our measure of similarity identifies some examples of convergent evolution of chemical mechanism. In many cases mechanism similarity is not reflected by similarity according to the EC system of enzyme classification. In particular, little mechanistic information is conveyed by the class level of the EC. PMID:17400244

O’Boyle, Noel M.; Holliday, Gemma L.; Almonacid, Daniel E.; Mitchell, John B.O.

2012-01-01

468

Nucleon exchange in damped nuclear reactions  

SciTech Connect

Starting from the general context of one-body nuclear dynamics, the nucleon-exchange mechanism in damped nuclear reactions is discussed. Some of its characteristic effects on various dinuclear observables are highlighted and a few recent advances are described.

Randrup, J.

1986-04-01

469

Stochastic Analysis of Reaction–Diffusion Processes  

PubMed Central

Reaction and diffusion processes are used to model chemical and biological processes over a wide range of spatial and temporal scales. Several routes to the diffusion process at various levels of description in time and space are discussed and the master equation for spatially discretized systems involving reaction and diffusion is developed. We discuss an estimator for the appropriate compartment size for simulating reaction–diffusion systems and introduce a measure of fluctuations in a discretized system. We then describe a new computational algorithm for implementing a modified Gillespie method for compartmental systems in which reactions are aggregated into equivalence classes and computational cells are searched via an optimized tree structure. Finally, we discuss several examples that illustrate the issues that have to be addressed in general systems. PMID:23719732

Hu, Jifeng; Kang, Hye-Won

2013-01-01

470

Catalytic Friedel-Crafts reaction of aminocyclopropanes.  

PubMed

A Lewis acid catalyzed Friedel-Crafts reaction between donor-acceptor aminocyclopropanes and indoles and other electron-rich aromatic compounds is reported. Indole alkylation at the C3 position was generally obtained for a broad range of functional groups and substitution patterns. In the case of C3-substituted indoles, C2 alkylation was observed. The reaction gives a rapid access to gamma amino acid derivatives present in numerous bioactive molecules. PMID:23815365

de Nanteuil, Florian; Loup, Joachim; Waser, Jérôme

2013-07-19

471

Aluminum/water reactions under extreme conditions  

NASA Astrophysics Data System (ADS)

We discuss mechanisms that may control the reaction of aluminum and water under extreme conditions. We are particularly interested in the high-temperature, high-strain regime where the native oxide layer is destroyed and fresh aluminum is initially in direct contact with liquid or supercritical water. Disparate experimental data over the years have suggested rapid oxidation of aluminum is possible in such situations, but no coherent picture has emerged as to the basic oxidation mechanism or the physical processes that govern the extent of reaction. We present theoretical and computational analysis of traditional metal/water reaction mechanisms that treat diffusion through a dynamic oxide layer or reaction limited by surface kinetics. Diffusion through a fresh solid oxide layer is shown to be far too slow to have any effect on the millisecond timescale (even at high temperatures). Quantum molecular dynamics simulations of liquid Al and water surface reactions show rapid water decomposition at the interface, catalyzed by adjacent water molecules in a Grotthus-like relay mechanism. The surface reaction barriers are far too low for this to be rate-limiting in any way. With these straightforward mechanisms ruled out, we investigate two more complex possibilities for the rate-limiting factor; first, we explore the possibility that newly formed oxide remains a metastable liquid well below its freezing point, allowing for diffusion-limited reactions through the oxide shell but on a much faster timescale. The extent of reaction would then be controlled by the solidification kinetics of alumina. Second, we discuss preliminary analysis on surface erosion and turbulent mixing, which may play a prominent role during hypervelocity penetration of solid aluminum projectiles into water.

Hooper, Joseph

2013-03-01

472

The reaction time to vestibular stimuli  

Microsoft Academic Search

The problem of this study was to determine the reaction time of voluntary response to the perception of passive rotary motion of the body with visual and auditory cues either masked or removed. Results are summarized as follows: (1) The average vestibular reaction time to passive body motion was 0.598 second, and the range from 0.190 to 1.79 second. (2)

B. Baxter; R. C. Travis

1938-01-01

473

Electron Transfer in Photosynthetic Reaction Centers  

Microsoft Academic Search

The central importance of (bacterio)chlorophyll as a major photosynthetic pigment arises from its ability to both harvest\\u000a the sunlight and perform ultrafast electron transfer (ET) reactions. The main function of the reaction center (RC) is to convert\\u000a the photoexcitation in order to generate a trans-membrane potential in a series of ET steps. In bacterial RCs it is possible\\u000a to relate

Josef Wachtveitl; Wolfgang Zinth

474

Reaction of synthetic corundum with orthophosphoric acid  

Microsoft Academic Search

Conclusions It was shown in an Investigation of mixtures of fine-ground electrofused corundum with orthophosphoric acid that at 20–25°C the degree of the reaction of the components is highest during the first four days. During this period only water-soluble acid aluminum phosphates are formed and a significant proportion of the orthophosphoric acid remains uncombined. The reaction rate is low and

L. A. Tseitlin; A. K. Mendelenko; S. T. Balyuk; Z. D. Zhukova

1975-01-01

475

Kinetics of Chemical Reactions in Flames  

NASA Technical Reports Server (NTRS)

In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

Zeldovich, Y.; Semenov, N.

1946-01-01

476

OH + HONO reaction: A theoretical study  

Microsoft Academic Search

The reaction of OH radical with nitrous acid HONO is investigated by ab initio quantum chemistry methods. The doublet potential energy surfaces are calculated at the CCSD(T)\\/aug-cc-pVDZ\\/\\/UMP2\\/6-311++G(d,p) levels. Various possible reaction pathways are considered. Among them, the most feasible pathway should be the OH radical attacking on the hydrogen of cis-HONO to form a 6-member-ring complex C2 barrierlessly, followed by

De-Quan Wang; Ji-Lai Li; Xu-Ri Huang; Cai-Yun Geng; Chia-Chung Sun

2007-01-01

477

The Reaction Specificity of Nanoparticles in Solution  

SciTech Connect

Iron-based metallic and oxide nanoparticles have been shown to have enhanced reactivity towards a variety of chemical species, including chlorinated hydrocarbons and reducible oxyanions, which frequently contaminate ground water at DOE and other government and industrial sites. Possibly of greater importance is the ability of these nanoparticles to select specific reaction pathways, potentially facilitating the formation of the most environmentally acceptable reaction products.

Baer, Donald R.

2006-06-01

478

Photosensitivity reactions: a case report involving NSAIDs.  

PubMed

Photosensitivity reactions associated with the use of prescription or over-the-counter drugs may be classified as phototoxic (caused by potentiation of solar energy by a drug) or photoallergic (in which the combination of a photosensitizing agent and light evokes a true cell-mediated hypersensitivity response). A case of a photoallergic response related to the use of piroxicam is included to illustrate the presentation and management of photosensitivity reactions to nonsteroidal anti-inflammatory drugs. PMID:7625330

Mammen, L; Schmidt, C P

1995-08-01

479

Recuperative coupling of exothermic and endothermic reactions  

Microsoft Academic Search

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions improves the thermal efficiency of processes and reduces the size of the reactors. One type of reactor suitable for such a type of coupling is the heat exchanger reactor. In this work, a one-dimensional pseudo-homogeneous plug flow model is used to analyze and compare the performance of co-current and counter-current

R. C. Ramaswamy; P. A. Ramachandran; M. P. Dudukovi?

2006-01-01

480

Pharmacogenetics of Idiosyncratic Adverse Drug Reactions  

Microsoft Academic Search

Idiosyncratic adverse drug reactions are unpredictable and thought to have an underlying genetic etiology. With the completion\\u000a of the human genome and HapMap projects, together with the rapid advances in genotyping technologies, we have unprecedented\\u000a capabilities in identifying genetic predisposing factors for these relatively rare, but serious, reactions. The main roadblock\\u000a to this is the lack of sufficient numbers of

Munir Pirmohamed

481

Cyclic Peptidomimetics and Pseudopeptides from Multicomponent Reactions  

NASA Astrophysics Data System (ADS)

Multicomponent reactions (MCRs) that provide in the final product amides are suitable to produce peptides and peptide-like moieties. The Passerini and Staudinger reactions provide one amide bond, and the Ugi-four-component reaction generates two amides from three or even four (or more) components, respectively. The Ugi-reaction thus is most important to produce peptides and peptoids while the Passerini reaction is useful to generate depsipeptoid moieties. In order to produce cyclic peptides and pseudopeptides, the linear peptidic MCR products have to be cyclized, usually with the help of bifunctional or activatable building blocks. Orthogonal but cyclizable secondary functionalities that need no protection in isonitrile MCRs commonly include alkenes (for ring closing metathesis), azide/alkyne (for Huisgen click reactions) or dienes and enoates (Diels-Alder) etc. If MCR-reactive groups are to be used also for the cyclisation, monoprotected bifunctional building blocks are used and deprotected after the MCR, e.g. for Ugi reactions as Ugi-Deprotection-Cyclisation (UDC). Alternatively one of the former building blocks or functional groups generated by the MCR can be activated. Most commonly these are activated amides (from so-called convertible isonitriles) which can be used e.g. for Ugi-Activation-Cyclisation (UAC) protocols, or most recently for a simultaneous use of both strategies Ugi-Deprotection/Activation-Cyclisation (UDAC). These methods mostly lead to small, medicinally relevant peptide turn mimics. In an opposing strategy, the MCR is rather used as ring-closing reaction, thereby introducing a (di-)peptide moiety. Most recently these processes have been combined to use MCRs for both, linear precursor synthesis and cyclisation. These multiple MCR approaches allow the most efficient and versatile one pot synthesis of macrocyclic pseudopeptides known to date.

Wessjohann, Ludger A.; Rhoden, Cristiano R. B.; Rivera, Daniel G.; Vercillo, Otilie Eichler

482

Serious allergic reaction to administration of epirubicin.  

PubMed

A 47-year old woman was admitted for adjuvant treatment with chemotherapy consisting of epirubicin and cyclophosphamide. During the second course of chemotherapy an allergic reaction occurred after administration of epirubicin. Treatment with clemastine 2 mg iv caused a quick recovery and after 24 hours there was only a slight redness of the face. A discussion follows on allergic reactions to antracyclines and the literature is updated. PMID:12948166

Oltmans, R; van der Vegt, S G L

2003-06-01

483

Studies of chemiluminescence in boron atom reactions  

SciTech Connect

Chemiluminescence has been observed in the single collision reactions of boron atoms with O/sub 2/, SO/sub 2/, N/sub 2/O, NO/sub 2/, and H/sub 2/O/sub 2/. The experiments were performed in a beam-gas apparatus using photon counting to detect the optical signals. The electronically excited A/sup 2/pi state of BO was observed in all the reactions. In addition the BO/sup -/ excited state, B/sup 2/..sigma../sup +/, was observed in the reaction of boron with N/sub 2/O. Excited BO/sub 2/ (A/sup 2/pi/sub u/) was observed in the reaction with SO/sub 2/ and excited OH (A/sup 2/..sigma../sup +/) was observed in the reaction with H/sub 2/O/sub 2/. Cross sections for the production of electronically excited molecules were determined. These cross sections for the reactions with O/sub 2/, SO/sub 2/, N/sub 2/O, NO/sub 2/, and H/sub 2/O/sub 2/ are, respectively, 0.048 A/sup 2/, 0.078 A/sup 2/, 0.011 A/sup 2/, 0.19 A/sup 2/, and 0.0058 A/sup 2/. In those reactions involving more than one chemiluminescent product channel, branching ratios were obtained for the observed products. The vibrational distributions in the electronically excited states of BO were determined for all the reactions and were analyzed using information theory. Some implications of the results are discussed.

DeHaven, J.J.

1982-01-01

484

Exclusive Reactions Involving Pions and Nucleons  

NASA Technical Reports Server (NTRS)

The HZETRN code requires inclusive cross sections as input. One of the methods used to calculate these cross sections requires knowledge of all exclusive processes contributing to the inclusive reaction. Conservation laws are used to determine all possible exclusive reactions involving strong interactions between pions and nucleons. Inclusive particle masses are subsequently determined and are needed in cross-section calculations for inclusive pion production.

Norbury, John W.; Blattnig, Steve R.; Tripathi, R. K.

2002-01-01

485

Reactions of halogen-pyridine systems  

SciTech Connect

The combination of halogens (acceptors) with pyridine derivatives (donors) produces, initially, charge transfer complexes with conductivities useful as depolarizers in lithium-halogen power cell cathodes. The complex most often employed in pacemaker batteries is I/sub 2//P2VP. Pyridines and halogens undergo additional reactions of consequence to cell performance. Such side reactions include: Alkyl group substitution, ring coupling, polymer molecular weight degradation, olefin addition and ring substitution. Instrumental analysis of model systems and the commercial iodine/poly-2-vinylpyridine (I/sub 2//P2VP) system provided evidence for alkyl group substitution, coupling and molecular weight degradation. The addition reaction was inferred from the presence of the needed reactants and their facile reactivity. Halogenation of the pyridine ring was not found. Side reactions cause reduced cathode capacity. Hydrogen halides generated by such side reactions may cause corrosion, but may enhance conductivity properties. Deleterious pressure buidup or dimensional changes may result from side reactions occurring within sealed battery cans. 7 refs.

Coury, A.J.; Cahalan, P.T.

1980-01-01

486

Stellar evolution and the triple-? reactions  

SciTech Connect

Nuclear reaction rates play a crucial role in the evolution of stars. For low-mass stars, the triple-? reaction controls the helium burning stars in the red giant and asymptotic giant branch (AGB) phase. More importantly, the cross section of the triple-? reaction has a great impact on the helium ignition at the center of the electron degenerate helium core of red giants and on the helium shell flashes of AGB stars. It is to be noted that stellar evolution models are influenced not only by the value of the cross section, but also by the temperature dependence of the reaction rate. In this paper, I present the impact of the triple-? reaction rates on the evolution of low-mass metal-free stars and intermediate-mass AGB stars. According to the previous study, the constraint on the triple-? reaction rate is derived based on stellar evolution theory. It is found that the recent revisions of the rate proposed by nuclear physics calculations satisfy the condition for the ignition of the helium core flash in low-mass stars.

Suda, Takuma [Osawa 2-21-1, Mitaka, Tokyo, 181-8588 (Japan)

2014-05-02

487

Cascade reactions catalyzed by metal organic frameworks.  

PubMed

Cascade or tandem reactions where two or more individual reactions are carried out in one pot constitute a clear example of process intensification, targeting the maximization of spatial and temporal productivity with mobilization of minimum resources. In the case of catalytic reactions, cascade processes require bi-/multifunctional catalysts that contain different classes of active sites. Herein, we show that the features and properties of metal-organic frameworks (MOFs) make these solids very appropriate materials for the development of catalysts for cascade reactions. Due to composition and structure, MOFs can incorporate different types of sites at the metal nodes, organic linkers, or at the empty internal pores, allowing the flexible design and synthesis of multifunctional catalysts. After some introductory sections on the relevance of cascade reactions from the point of view of competitiveness, sustainability, and environmental friendliness, the main part of the text provides a comprehensive review of the literature reporting the use of MOFs as heterogeneous catalysts for cascade reactions including those that combine in different ways acid/base, oxidation/reduction, and metal-organic centers. The final section summarizes the current state of the art, indicating that the development of a first commercial synthesis of a high-added-value fine chemical will be a crucial milestone in this area. PMID:25082205

Dhakshinamoorthy, Amarajothi; Garcia, Hermenegildo

2014-09-01

488

Reaction cycle and thermodynamics in bacteriorhodopsin  

NASA Technical Reports Server (NTRS)

Light causes the all-trans to 13-cis isomerization of the retinal in bacteriorhodopsin; the thermal relaxation leading back to the initial state drives proton transport first via proton transfer between the retinal Schiff base and D85 and then between the Schiff base and D96. The reaction sequence and thermodynamics of this photocycle are described by measuring time-resolved absorption changes with a gated multichannel analyzer between 100 ns and 100 ms, at six temperatures between 5 degrees C and 30 degrees C. Analysis of the energetics of the chromophore reaction sequence is on the basis of a recently proposed model (Varo & Lanyi, Biochemistry 30, 5016-5022, 1991) which consists of a single cycle and many reversible reactions: BR -hv-->K<==>L<==>M1-->M2<==>N<==>O-->BR. The existence of the M1-->M2 reaction, which functions as the switch in the proton transfer, is confirmed by spectroscopic evidence. The calculated thermodynamic parameters indicate that the exchange of free energy between the protein and the protons is at the switch step. Further, a large entropy decrease at this reaction suggests a protein conformation change which will conserve delta G for driving the completion of the reaction cycle. The results provide insights to mechanism and energy coupling in this system, with possible relevance to the general question of how ion pumps function.

Lanyi, J. K.

1992-01-01

489

Overcharge reaction of lithium-ion batteries  

NASA Astrophysics Data System (ADS)

Overcharge reaction was studied in detail using 650 mAh prismatic hermetically sealed lithium-ion batteries with LiCoO 2 cathodes, graphitic carbon anodes and ethylene carbonate/ethyl methyl carbonate (EC/EMC) electrolytes. Several varieties of gases (CO 2, CO, H 2, CH 4, C 2H 6 and C 2H 4) were evolved in the overcharge reaction. The amount of gas increased with the increase in the cell temperature and rose rapidly at the end of the overcharge. In particular, the amount of CO 2 gas produced by the oxidation of the electrolyte at the cathode increased markedly. The exothermic oxidation reaction of the electrolyte was accelerated at the temperature above 60 °C, causing the cell temperature to increase rapidly thereafter. The heating tests of the overcharged anode samples enclosed in cylindrical cell cases with EC/EMC electrolytes resulted in thermal runaways. In contrast, the overcharged cathodes tested in the same manner showed no thermal runaway. The thermal runaway reaction during overcharge was caused by the violent reaction between the overcharged anode (deposited lithium) and the electrolyte solvent at high temperature that was the result of the rapid exothermic reaction of the delithiated cathode and the electrolyte.

Ohsaki, Takahisa; Kishi, Takashi; Kuboki, Takashi; Takami, Norio; Shimura, Nao; Sato, Yuichi; Sekino, Masahiro; Satoh, Asako

490

Proton transfer in the photosynthetic reaction center of Blastochloris viridis  

E-print Network

Proton transfer in the photosynthetic reaction center of Blastochloris viridis Maria A. Kozlovaa reaction center; Ubiquinone; Proton transfer; Capacitive potentiometry; Blastochloris viridis; Rhodobacter Abstract Photosynthetic reaction centers of Blastochloris viri- dis require two quanta of light to catalyse

Steinhoff, Heinz-Jürgen

491

SHORT COMMUNICATION Multiplex Polymerase Chain Reaction Diagnostics of Bed Bug  

E-print Network

SHORT COMMUNICATION Multiplex Polymerase Chain Reaction Diagnostics of Bed Bug (Hemiptera. A molecular diagnostic technique applying multiplex polymerase chain reaction (PCR) was developed, molecular