Note: This page contains sample records for the topic mukaiyama aldol reactions from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Mukaiyama Aldol Reactions in Aqueous Media  

PubMed Central

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

Kitanosono, Taku; Kobayashi, Shu

2013-01-01

2

Catalyzed vinylogous Mukaiyama aldol reactions with controlled enantio- and diastereoselectivities.  

PubMed

In control: A new catalytic vinylogous Mukaiyama aldol reaction provides products with high diastereo- and enantioselectivities (up to 99 % de and ee; see scheme). The relative and absolute stereochemistry of a representative product was rigorously assigned by NMR and CD spectroscopies (measured and calculated), X-ray diffraction, and quantum-chemical calculations. PMID:19123229

Frings, Marcus; Atodiresei, Iuliana; Runsink, Jan; Raabe, Gerhard; Bolm, Carsten

2009-01-01

3

Indium-trichloride catalyzed mukaiyama-aldol reaction in water: Solubility, aggregation and internal pressure effect  

Microsoft Academic Search

Studies on the effects of water and the binding characteristic of InCl3 in the Mukaiyama-aldol reaction with an in depth mechanistic probe on the probable internal pressure and aggregation effects exerted in this media.

Teck-Peng Loh; Jian Pei; Kevin Siong-Ve Koh; Guo-Qiang Cao; Xu-Ran Li

1997-01-01

4

Iron- and bismuth-catalyzed asymmetric Mukaiyama aldol reactions in aqueous media.  

PubMed

We have developed asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral Fe(II) and Bi(III) complexes. Although previous reactions often required relatively harsh conditions, such as strictly anhydrous conditions, very low temperatures (-78 °C), etc., the reactions reported herein proceeded in the presence of water at 0 °C. To find appropriate chiral water-compatible Lewis acids for the Mukaiyama aldol reaction, many Lewis acids were screened in combination with chiral bipyridine L1, which had previously been found to be a suitable chiral ligand in aqueous media. Three types of chiral catalysts that consisted of a Fe(II) or Bi(III) metal salt, a chiral ligand (L1), and an additive have been discovered and a wide variety of substrates (silicon enolates and aldehydes) reacted to afford the desired aldol products in high yields with high diastereo- and enantioselectivities through an appropriate selection of one of the three catalytic systems. Mechanistic studies elucidated the coordination environments around the Fe(II) and Bi(III) centers and the effect of additives on the chiral catalysis. Notably, both Brønsted acids and bases worked as efficient additives in the Fe(II) -catalyzed reactions. The assumed catalytic cycle and transition states indicated important roles of water in these efficient asymmetric Mukaiyama aldol reactions in aqueous media with the broadly applicable and versatile catalytic systems. PMID:24101589

Kitanosono, Taku; Ollevier, Thierry; Kobayashi, Sh?

2013-12-01

5

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

PubMed Central

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

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

2008-01-01

6

A new Brønsted acid derived from squaric acid and its application to Mukaiyama aldol and Michael reactions  

Microsoft Academic Search

Bis-N-trifluoromethanesulfonyl squaramide was prepared as a new bench-stable strong Brønsted acid and applied to the Brønsted acid-catalyzed Mukaiyama aldol and Michael reactions with silyl enol ethers. The resulting Mukaiyama aldol products of aldehydes were obtained in quantitative yields, whereas expansion of the utility of this Brønsted acid to ketones was limited to electron-deficient ketones presumably due to lower reactivity of

Cheol Hong Cheon; Hisashi Yamamoto

2009-01-01

7

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

PubMed Central

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

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

2012-01-01

8

C1-symmetric aminosulfoximines in copper-catalyzed asymmetric vinylogous Mukaiyama aldol reactions.  

PubMed

Vinylogous Mukaiyama-type aldol reactions have been catalyzed by a combination of Cu(OTf)2 and readily available C1-symmetric aminosulfoximines. After a fine-tuning of the reaction conditions and an optimization of the modularly assembled ligand structure, high stereoselectivities and excellent yields have been achieved in catalyzed reactions involving various electrophile/nucleophile combinations. The relative and absolute configurations of two products were assigned by X-ray single crystal structure analysis and a comparison of calculated and experimental CD spectra. PMID:20229533

Frings, Marcus; Atodiresei, Iuliana; Wang, Yutian; Runsink, Jan; Raabe, Gerhard; Bolm, Carsten

2010-04-19

9

Asymmetric Mukaiyama aldol reaction of silyl enol ethers with aldehydes using a polymer-supported chiral Lewis acid catalyst  

Microsoft Academic Search

Chiral N-sulfonylated ?-amino acid monomer (5) derived from (S)-tryptophan was copolymerized with styrene and divinylbenzene under radical polymerization conditions to give a polymer-supported N-sulfonyl-(S)-tryptophan (6). Treatment of the polymer-supported chiral ligand with 3,5-bis(trifluoromethyl)phenyl boron dichloride afforded a polymeric Lewis acid catalyst (16) effective for asymmetric Mukaiyama aldol reaction of silyl enol ethers and aldehydes. Various aldehydes were allowed to react

Shinichi Itsuno; Shinnosuke Arima; Naoki Haraguchi

2005-01-01

10

Iron(II) and zinc(II) complexes with designed pybox ligand for asymmetric aqueous Mukaiyama-aldol reactions.  

PubMed

An iron(II) complex with a hindered hydroxyethyl-pybox (he-pybox) ligand shows improved catalytic activity and enantioselectivity for asymmetric Mukaiyama-aldol reactions in aqueous media. This water-stable chiral Lewis acid promotes condensation of aromatic silyl enol ethers with a range of aldehydes with good yields, excellent syn-diastereoselectivity and up to 92% ee. The combination of the same ligand with ZnII salt is also demonstrated as a remarkably efficient and water-compatible chiral Lewis acid. PMID:17315931

Jankowska, Joanna; Paradowska, Joanna; Rakiel, Bartosz; Mlynarski, Jacek

2007-03-16

11

Calix[6]arene derivatives bearing sulfonate and alkyl groups as surfactants in Sc(OTf) 3-catalyzed Mukaiyama aldol reactions in water  

Microsoft Academic Search

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 that a hydrophobic microenvironment was formed in the reaction system, which is favorable to stabilize some labile silyl enol ethers and thus promotes the reactions.

Hong-Yu Tian; Yong-Jun Chen; Dong Wang; Cheng-Chu Zeng; Chao-Jun Li

2000-01-01

12

Reexamination of CeCl3 and InCl3 as activators in the diastereoselective Mukaiyama aldol reaction in aqueous media.  

PubMed

A search for suitable reaction conditions in Mukaiyama-type aldol condensations activated by CeCl(3) and InCl(3) revealed that the reaction proceeds best in i-PrOH/H(2)O (95:5). Contrary to literature precedent, no reaction was observed in pure water, and the encountered destruction of the starting silyl enol ether can be ascribed to initial hydrolysis of the Lewis acid. As anticipated from the dual parameter (pK(h), WERC value) characteristics of CeCl(3) and InCl(3), the former proved more efficient as Lewis acid-promoter, in terms of reaction speed and yield. Nevertheless, InCl(3) was a superior catalyst during evaluation of the diastereoselectivity of the process. In this regard, determination of diastereoselectivity as a function of time showed that the InCl(3)-catalyzed reaction is irreversible, whereas the CeCl(3)-catalyzed reaction is a reversible process. In both cases, formation of the syn product is kinetically preferred, although DeltaDeltaG(++)273K(InCl(3)) = 1.50 kcal/mol versus DeltaDeltaG(++)273K (CeCl(3)) = 0.38 kcal/mol. Molecular modeling (semiempirical PM3, ab initio HF/3-21G*, hybrid B3LYP/3-21G*, and B3LYP/LANL2DZ) of the diastereoselective aldol reaction promoted by InCl(3) supports a "closed", Zimmermann-Traxler transition state. PMID:12585921

Muñoz-Muñiz, Omar; Quintanar-Audelo, Martina; Juaristi, Eusebio

2003-02-21

13

Mechanistic investigations of the ZnCl2-mediated tandem Mukaiyama aldol lactonization: evidence for asynchronous, concerted transition states and discovery of 2-oxopyridyl ketene acetal variants.  

PubMed

The ZnCl(2)-mediated tandem Mukaiyama aldol lactonization (TMAL) reaction of aldehydes and thiopyridyl ketene acetals provides a versatile, highly diastereoselective approach to trans-1,2-disubstituted ?-lactones. Mechanistic and theoretical studies described herein demonstrate that both the efficiency of this process and the high diastereoselectivity are highly dependent upon the type of ketene acetal employed but independent of ketene acetal geometry. Significantly, we propose a novel and distinct mechanistic pathway for the ZnCl(2)-mediated TMAL process versus other Mukaiyama aldol reactions based on our experimental evidence to date and further supported by calculations (B3LYP/BSI). Contrary to the commonly invoked mechanistic extremes of [2+2] cycloaddition and aldol lactonization mechanisms, investigations of the TMAL process suggest a concerted but asynchronous transition state between aldehydes and thiopyridyl ketene acetals. These calculations support a boat-like transition state that differs from commonly invoked Mukaiyama "open" or Zimmerman-Traxler "chair-like" transition-state models. Furthermore, experimental studies support the beneficial effect of pre-coordination between ZnCl(2) and thiopyridyl ketene acetals prior to aldehyde addition for optimal reaction rates. Our previously proposed, silylated ?-lactone intermediate that led to successful TMAL-based cascade sequences is also supported by the described calculations and ancillary experiments. These findings suggested that a similar TMAL process leading to ?-lactones would be possible with an oxopyridyl ketene acetal, and this was confirmed experimentally, leading to a novel TMAL process that proceeds with efficiency comparable to that of the thiopyridyl system. PMID:22239064

Zhao, Cunxiang; Mitchell, T Andrew; Vallakati, Ravikrishna; Pérez, Lisa M; Romo, Daniel

2012-02-15

14

Tetrahydropyran rings from a Mukaiyama-Michael cascade reaction.  

PubMed

A new annulation reaction leading to tetrahydropyrans has been discovered. The reaction of homoallylic enol ethers (e.g., 1) with alpha,beta-unsaturated ketones or esters begins with a Mukaiyama-Michael addition. The intermediate oxocarbenium ion undergoes a rapid 2-oxonia-Cope rearrangement, and the resulting zwitterion collapses to form a tetrahydropyran. The reaction is stereoselective with 3-butene-2-one, but leads to diastereomeric mixtures with ethyl acrylate. More complex enones, such as cyclohexenone, also undergo the reaction to produce fused ring products. The optical activity of the substrates is relayed in the tetrahydropyran products. PMID:16287289

Bolla, Megan L; Patterson, Brian; Rychnovsky, Scott D

2005-11-23

15

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

Brindle, Cheyenne S.

2013-01-01

16

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

17

Diastereoselective Synthesis of Tetrahydrofurans via Mead Reductive Cyclization of Keto-?-Lactones Derived from the Tandem Mukaiyama Aldol Lactonization (TMAL) Process  

PubMed Central

The development of a diastereoselective, three-step strategy for the construction of substituted tetrahydrofurans from alkenyl aldehydes based on the tandem Mukaiyama aldol-lactonization process and Mead reductive cyclization of keto ?-lactones is reported. Stereochemical outcomes of the TMAL process are consistent with models established for Lewis acid-mediated additions to ?-benzyloxy and ?-silyloxy aldehydes while reductions of the five-membered oxocarbenium ions are consistent with Woerpel’s models. Further rationalization for observed high diastereoselectivity in reductions of ?-silyloxy 5-membered oxocarbenium ions based on stereoelectronic effects are posited. A diagnostic trend for coupling constants of ?-benzyloxy ?-lactones was observed that should enable assignment of the relative configuration of these systems.

Mitchell, T. Andrew; Romo, Daniel

2008-01-01

18

Mukaiyama-Michael reactions with acrolein and methacrolein: a catalytic enantioselective synthesis of the C17-C28 fragment of pectenotoxins.  

PubMed

Enantioselective iminium-catalyzed reactions with acrolein and methacrolein are rare. A catalytic enantioselective Mukaiyama-Michael reaction that readily accepts acrolein or methacrolein as substrates, affording the products in good yields and 91-97% ee, is presented. As an application of the methodology, an enantioselective route to the key C17-C28 segment of the pectenotoxin using the Mukaiyama-Michael reaction as the key step is described. PMID:22296172

Kemppainen, Eeva K; Sahoo, Gokarneswar; Valkonen, Arto; Pihko, Petri M

2012-02-17

19

Chlorine, an atom economical auxiliary for asymmetric aldol reactions.  

PubMed

An auxiliary strategy has been developed for asymmetric reactions of aldehydes in which the auxiliary itself is not chiral, but a single chlorine atom introduced via organocatalytic ?-chlorination. The stereodirecting influence of the chlorine atom is then exploited prior to its removal by radical reduction. This strategy is demonstrated in the synthesis of several aldols (92-99% ee) and the natural products (+)-dihydroyashabushiketol and (+)-solistatin. PMID:23370443

Halperin, Shira D; Britton, Robert

2013-02-13

20

One-pot Synthesis of Lactams Using Domino Reactions: Combination of Schmidt Reaction with Sakurai and Aldol Reactions  

PubMed Central

A series of domino reactions in which the intramolecular Schmidt reaction is combined with either a Sakurai reaction, an aldol reaction, or both is reported. The Sakurai reaction of an allylsilane with an azido-containing enone under Lewis acidic conditions followed by protonation of the resulting titanium enolate species allowed for a subsequent intramolecular Schmidt reaction. Alternatively, the intermediate titanium enolate could undergo an aldol reaction, followed by the intramolecular Schmidt reaction to form lactam products with multiple stereogenic centers. The stereochemical features of the titanium enolate aldol reaction with several 3-azidoaldehyde substrates during this domino process is discussed.

Huh, Chan Woo; Somal, Gagandeep K.; Katz, Christopher E.; Pei, Huaxing; Zeng, Yibin; Douglas, Justin T.; Aube, Jeffrey

2009-01-01

21

Development of N, Nbis(perfluoroalkanesulfonyl)squaramides as new strong Brønsted acids and their application to organic reactions  

Microsoft Academic Search

New strong Brønsted acids derived from a squaric acid scaffold bearing different perfluoroalkanesulfonyl groups have been developed and applied to several organic reactions. These squaramides are bench-stable and exhibit much higher reactivities in several organic reactions than squaric acid itself. N,N-Bis(trifluoromethanesulfonyl)squaramide 2a was applied to the Mukaiyama aldol reaction and Mukaiyama Michael reaction. Mechanistic studies revealed that the Brønsted acid

Cheol Hong Cheon; Hisashi Yamamoto

2010-01-01

22

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.

Bhanushali, Mayur; Zhao, Cong-Gui

2011-01-01

23

Method of carbon chain extension using novel aldol reaction  

DOEpatents

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

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

2013-08-13

24

Method of carbon chain extension using novel aldol reaction  

DOEpatents

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

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

2013-07-30

25

Diastereoselective reductive aldol reactions of Boc-protected electron deficient pyrroles  

Microsoft Academic Search

An anti-selective reductive aldol reaction of a Boc-protected, 2-substituted pyrrole is reported. Reduction with LiDBB generates an exocyclic lithium enolate, but optimal stereoselectivity is obtained by transmetallation to magnesium with MgBr2·OEt2. The corresponding syn-aldols can easily be obtained (protected as carbamates) by subsequent inversion.

Timothy J. Donohoe; David House

2003-01-01

26

Spontaneous Mirror Symmetry Breaking in the Aldol Reaction and its Potential Relevance in Prebiotic Chemistry  

Microsoft Academic Search

The origin of the single chirality of most biomolecules is still a great puzzle. Carbohydrates could form in the formose reaction,\\u000a which is proposed to be autocatalytic and contains aldol reaction steps. Based on our earlier observation of organoautocatalysis\\u000a and spontaneous enantioenrichment in absence of deliberate chiral influences in the aldol reaction of acetone and p-nitrobenzaldehyde\\u000a we suggest that a

Michael Mauksch; Shengwei Wei; Matthias Freund; Alexandru Zamfir; Svetlana B. Tsogoeva

2010-01-01

27

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

28

Aldol Reactions in MCR-Based Domino Pathways: a Multipurpose Enabling Tool in Heterocyclic Chemistry  

PubMed Central

The aldol reaction has been evaluated in combination with the Ugi multicomponent reaction to assemble richly decorated mono- and polycyclic systems via expeditious cascade pathways. A small collection of pyrrolinones was generated thereof, and the scarcely accessible pyridoquinoxalinedione scaffold was also prepared by designing an additional nucleophilic substitution step in this domino sequence requiring minimal operational effort.

Xu, Zhigang; De Moliner, Fabio; Cappelli, Alexandra P.

2013-01-01

29

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

PubMed Central

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

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

2010-01-01

30

Effects of magnesium salts and amines on the stereoselectivity in the imine aldol reaction.  

PubMed

In the imine aldol reactions of 1 with aromatic aldehydes using magnesium salts in the presence of amines, the threo/erythro ratios of products increased in the order Mg(ClO4)2>MgI2>MgBr2>MgCl2>Mg(OTf)2 and N,N,N',N'-tetramethylethylenediamine (TMEDA)>Et3N. This increase in the threo/erythro ratios of products was estimated to be caused by a retro-imine aldol reaction under thermodynamic control. PMID:18057758

Hayashi, Kazuhiko; Kujime, Eiko; Katayama, Hajime; Sano, Shigeki; Nagao, Yoshimitsu

2007-12-01

31

Hammett correlation of nornicotine analogues in the aqueous aldol reaction: implications for green organocatalysis.  

PubMed

[reaction: see text] A series of meta- and para-substituted 2-arylpyrrolidines were synthesized and examined for their ability to catalyze an aqueous aldol reaction under buffered conditions. Kinetic analysis of arylpyrrolidine-catalyzed reactions displayed a linear Hammett correlation with rho = 1.14 (R(2) = 0.996), indicating that the reaction is accelerated by electron-withdrawing aryl rings. These results show promise for the development of a synthetically viable aqueous organo-catalyst. PMID:15845010

Rogers, Claude J; Dickerson, Tobin J; Brogan, Andrew P; Janda, Kim D

2005-04-29

32

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...

33

Stereoselective titanium-mediated aldol reactions of a chiral isopropyl ketone.  

PubMed

A novel substrate-controlled aldol reaction of a chiral isopropyl ketone is reported. The outstanding regioselective enolization by TiCl4-i-Pr2NEt provides a chelated enolate that can participate in highly diastereoselective additions to a wide array of aldehydes favouring the corresponding 2,5-syn adducts. PMID:23576096

Zambrana, Joana; Romea, Pedro; Urpí, Fèlix

2013-05-18

34

Tandem Aldol Condensation - Platinacycle-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids  

PubMed Central

Tandem aldol condensation of aldehydes with methyl ketones followed by anionic four-electron donor-based (Type I) platinacycle-catalyzed addition reactions of arylboronic acids to form ?-arylated ketones is described. Good to excellent yields of ?-arylated ketones were obtained for the tandem reactions of aromatic/aliphatic aldehydes, methyl ketones and arylboronic acids, and moderate yields were observed for the tandem reaction with ?, ?-unsaturated aldehydes as the aldehyde source.

Liao, Yuan-Xi; Hu, Qiao-Sheng

2013-01-01

35

Magnesium halide-catalyzed anti-aldol reactions of chiral N-acylthiazolidinethiones.  

PubMed

[reaction: see text] Diastereoselective direct aldol reactions of chiral N-acylthiazolidinethiones occur in high yield with preference for the illustrated anti diastereomer. This reaction is catalyzed by 10% MgBr2.OEt2 in the presence of triethylamine and chlorotrimethylsilane. Yields range from 56 to 93% with diastereoselectivity up to 19:1 for a variety of N-acylthiazolidinethiones and unsaturated aldehydes. PMID:11922799

Evans, David A; Downey, C Wade; Shaw, Jared T; Tedrow, Jason S

2002-04-01

36

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...

37

Stereoselective titanium-mediated aldol reactions of a chiral lactate-derived ethyl ketone with ketones.  

PubMed

Aldol reactions of titanium enolates of lactate-derived ethyl ketone 1 with other ketones proceed in a very efficient and stereocontrolled manner provided that a further equivalent of TiCl4 is added to the reacting mixture. The scope of these reactions encompasses simple ketones such as acetone or cyclohexanone as well as other ketones that contain potential chelating groups such as pyruvate esters or ?- and ?-hydroxy ketones. PMID:24372372

Alcoberro, Sandra; Gómez-Palomino, Alejandro; Solà, Ricard; Romea, Pedro; Urpí, Fèlix; Font-Bardia, Mercè

2014-01-17

38

Proline and benzylpenicillin derivatives grafted into mesoporous MCM-41: Novel organic-inorganic hybrid catalysts for direct aldol reaction  

Microsoft Academic Search

New organic-inorganic hybrid catalysts were synthesized by covalent grafting of proline and benzylpenicillin derivatives into\\u000a mesoporous MCM-41. These catalysts were extensively characterized using FT-IR,13C CP MAS solid stateNMR, XRD and TEM techniques. These were used as catalysts for direct, asymmetric aldol reaction between\\u000a acetone and activated aromatic aldehydes. In the reaction of 4-nitro and 4-fluoro benzaldehyde, the aldol products were

Dwairath Dhar; Ian Beadham; Srinivasan Chandrasekaran

2003-01-01

39

Direct synthesis of ?-hydroxy-?-amino acids via diastereoselective decarboxylative aldol reaction.  

PubMed

A straightforward metal-free synthesis of anti-?-hydroxy-?-amino acids is described. The organic base-mediated decarboxylative aldol reaction of cheap, readily available ?-amidohemimalonates with various aldehydes afforded under very mild conditions anti-?-hydroxy-?-amido esters in high yields and complete diastereoselectivity. Simple one-pot subsequent transformations enabled the corresponding anti-?-hydroxy-?-amino acids or in a few examples their syn diastereomers to be obtained directly using epimerization conditions. PMID:24188057

Singjunla, Yuttapong; Baudoux, Jérôme; Rouden, Jacques

2013-11-15

40

Sequential Aldol Condensation - Transition Metal-Catalyzed Addition Reactions of Aldehydes, Methyl Ketones and Arylboronic Acids  

PubMed Central

Sequential aldol condensation of aldehydes with methyl ketones followed by transition metal-catalyzed addition reactions of arylboronic acids to form ?-substituted ketones is described. By using the 1,1?-spirobiindane-7,7?-diol (SPINOL)-based phosphite, an asymmetric version of this type of sequential reaction, with up to 92% ee, was also realized. Our study provided an efficient method to access ?-substituted ketones and might lead to the development of other sequential/tandem reactions with transition metal-catalyzed addition reactions as the key step.

Liao, Yuan-Xi; Xing, Chun-Hui; Israel, Matthew; Hu, Qiao-Sheng

2011-01-01

41

Practical asymmetric synthesis of ?-hydroxy ?-amino acids via complimentary aldol reactions  

PubMed Central

Orthogonally protected chiral ?-hydroxy-?-amino acids can be accessed in >100 g quantities from readily available starting materials and reagents in 3–4 steps. These chiral synthons contain two adjacent stereocenters along with suitably protected functional groups (O-TBS, N-Boc) for downstream reactivity. Implementation of two existing aldol technologies allows rapid access to all possible stereoisomers of 1. The guiding principles during reaction optimization were reaction scalability and operational efficiency. Conversion of the amino acids to a variety of chiral building blocks in 1–2 steps demonstrates their synthetic utility.

Pandya, Bhaumik A.; Dandapani, Sivaraman; Duvall, Jeremy R.; Rowley, Ann; Mulrooney, Carol A.; Ryba, Troy; Dombrowski, Michael; Harton, Marie; Young, Damian W.; Marcaurelle, Lisa A.

2011-01-01

42

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

PubMed

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

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

2014-06-01

43

Density functional theory study of the mechanism of the proline-catalyzed intermolecular aldol reaction  

Microsoft Academic Search

.   Transition structures associated with the C-C bond-formation step of the proline-catalyzed intermolecular aldol reaction\\u000a between acetone and isobutyraldehyde have been studies using density functional theory methods at the B3LYP\\/6-31G** computational\\u000a level. A continuum model has been selected to represent solvent effects. For this step, which is the stereocontrolling and\\u000a rate-determining step, four reactive channels corresponding to the syn and

Manuel Arnó; Luis R. Domingo

2002-01-01

44

"Supersilyl" Group as Novel Carboxylic Acid Protecting Group: Application to Highly Stereoselective Aldol and Mannich Reactions  

PubMed Central

“Super Power”: The application of the "supersilyl” group as carboxylic acid protecting group has been investigated. The unique properties of the “supersilyl” group enabled it to outperform typical carboxyl protecting groups, conferring extraordinary protection upon the carboxyl functionality. “Supersilyl” esters were also utilized for the first time as stable carboxylic acid synthetic equivalents in highly stereoselective aldol and Mannich reactions. The value of this methodology has been further described by the easy photo-deprotection protocol and its applications in rapid synthesis of polyketide subunits.

Tan, Jiajing; Akakura, Matsujiro

2013-01-01

45

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

PubMed

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

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

2013-11-01

46

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%).

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

2013-01-01

47

On indium(III) chloride-catalyzed aldol reactions of silyl enol ethers with aldehydes in water  

Microsoft Academic Search

Contrary to previous reports, it was found that hydrolysis of silyl enol ethers is superior to the desired condensation in InCl3-catalyzed aldol reactions of silyl enol ethers with aldehydes in water. The reactions were found to proceed in certain amounts in the presence of a catalytic amount of a Lewis acid under neat (solvent-free) conditions, while substrate limitation was observed

Sh? Kobayashi; Tsuyoshi Busujima; Satoshi Nagayama

1998-01-01

48

Tin or magnesium-mediated diastereoselective aldol-type reactions for the asymmetric synthesis of ?-substituted serines  

Microsoft Academic Search

Diastereoselective aldol-type reactions of ethyl (5S)-3,6-diethoxy-2,5-dihydro-5-isopropyl-2-pyrazinecarboxylate (5S)-3 with achiral aldehydes 8a–d was investigated by using Sn(OSO2CF3)2–N-ethylpiperizine and MgBr2–triethylamine. The reaction with Sn(II) between (5S)-3 and aliphatic aldehydes 8a,b proved to be quite different from that with Mg(II). On the other hand, Sn(II)- or Mg(II)-mediated aldol-type reactions of (5S)-3 with benzaldehyde 8c and 3-methyl-2-butenal 8d each afforded the same diastereomer as

Shigeki Sano; Toshio Miwa; Xiao-Kai Liu; Takahiro Ishii; Tomoka Takehisa; Motoo Shiro; Yoshimitsu Nagao

1998-01-01

49

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.

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

2010-01-01

50

Highly stereoselective and scalable anti-aldol reactions using N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide: scope and origins of stereoselectivities.  

PubMed

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 are due to the presence of nonclassical 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

2010-11-01

51

Asymmetric direct aldol reaction catalyzed by an L-prolinamide derivative: considerable improvement of the catalytic efficiency in the ionic liquid.  

PubMed

The asymmetric direct aldol reactions of a wide scope of aldehydes with unmodified ketones in the presence of 20 mol%(S,S,S)-pyrrolidine-2-carboxylic acid (2'-hydroxyl-1',2'-diphenyl-ethyl)-amine (1) were performed in ionic liquids; aldol products with 91 to >99% ees for aromatic aldehydes and 99% ees for alphatic aldehydes were offered by the present procedure. PMID:15756332

Guo, Hai-Ming; Cun, Lin-Feng; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong

2005-03-21

52

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.

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

2014-01-01

53

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

PubMed

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

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

2014-01-01

54

L-prolinamide-catalyzed direct nitroso aldol reactions of alpha-branched aldehydes: a distinct regioselectivity from that with L-proline.  

PubMed

The first direct enantioselective N-nitroso aldol reaction of aldehyde with nitrosobenzene catalyzed by an L-prolinamide derivative is presented; the reactions proceed smoothly furnishing the -hydroxyamino carbonyl compounds, the otherwise disfavored products, in good yields with up to 64% ee. PMID:16493825

Guo, Hai-Ming; Cheng, Li; Cun, Lin-Feng; Gong, Liu-Zhu; Mi, Ai-Qiao; Jiang, Yao-Zhong

2006-01-28

55

Lewis acid catalysis in micellar systems. Sc(OTf) 3-Catalyzed aqueous aldol reactions of silyl enol ethers with aldehydes in the presence of a surfactant  

Microsoft Academic Search

Scandium triflate (Sc(OTf)3)-catalyzed aldol reactions of silyl enol ethers with aldehydes were successfully carried out in micellar systems. While the reactions proceeded sluggishly in water, remarkable enhancement of the reactivity was observed in the presence of a small amount of a surfactant. In these systems, versatile carbon-carbon bond-forming reactions proceeded in water without using any organic solvents.

Sh? Kobayashi; Takeshi Wakabayashi; Satoshi Nagayama; Hidekazu Oyamada

1997-01-01

56

Development of highly diastereo- and enantioselective direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes catalyzed by chiral quaternary ammonium salts.  

PubMed

A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention of an unfavorable yet inevitable retro aldol process involving the chiral catalyst. On the basis of this information, a reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-beta-hydroxy-alpha-amino esters almost exclusively in an essentially optically pure form. PMID:15291572

Ooi, Takashi; Kameda, Minoru; Taniguchi, Mika; Maruoka, Keiji

2004-08-11

57

Water as dual functional cocatalyst: A theoretical study on the mechanism of direct aldol reaction on water catalyzed by a leucine derivative  

Microsoft Academic Search

The role of water and stereoselectivity in the direct syn-aldol reaction involving 3-pentanone and 4-nitrobenzaldehyde catalyzed by amino acid derivatives on water has been investigated\\u000a by density functional theory. Calculations indicate that the formation of intermediate enamine is the rate determining step\\u000a via a three-step process with activation enthalpies of 50 kcal\\/mol in the gas phase and 21 kcal\\/mol in

QinQuan Rao; ShiWei Luo; LiuZhu Gong

2010-01-01

58

Access to polyfunctionalized diquinanes, hydrindanes, and decalines via TiCl4 promoted Michael-aldol and Baylis-Hillman reactions.  

PubMed

The addition of 0.5 equiv of TiCl(4) to (cyclo)alkanones tethered to ?,?-unsaturated ketones afforded polyfunctionalized diquinanes, hydrindanes, and decalines. These products, resulting from a Michael-aldol or a Baylis-Hillman reaction, can be obtained with high or total diastereoselectivity in moderate to high yields. These scaffolds represent interesting building blocks for the synthesis of complex natural products. PMID:22149721

Ressault, Blandine; Jaunet, Alexis; Geoffroy, Philippe; Goudedranche, Sébastien; Miesch, Michel

2012-01-01

59

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.

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

2012-01-01

60

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.

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

2011-01-01

61

Formal Homologous Aldol Reactions: Interrupting the Nazarov Cyclization via Carboalkoxylation of Alkynes.  

PubMed

Reactions between 1,4-pentadien-3-ones and aryl acetylenes in the presence of BF3·OEt2 furnish ?-phenacyl cyclopentanones via a domino electrocyclization/carboalkoxylation reaction sequence. The overall process underscores a new mode of interrupted Nazarov trapping, where two new carbon-carbon bonds are installed with concomitant formation of carbonyl functionality. PMID:24735109

Wu, Yen-Ku; West, F G

2014-05-01

62

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

63

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

64

Asymmetric synthesis of ?-amino acids via homologation of Ni(II) complexes of glycine Schiff bases. Part 2: aldol, Mannich addition reactions, deracemization and (S) to (R) interconversion of ?-amino acids.  

PubMed

This review provides a comprehensive treatment of literature data dealing with asymmetric synthesis of ?-amino-?-hydroxy and ?,?-diamino acids via homologation of chiral Ni(II) complexes of glycine Schiff bases using aldol and Mannich-type reactions. These reactions proceed with synthetically useful chemical yields and thermodynamically controlled stereoselectivity and allow direct introduction of two stereogenic centers in a single operation with predictable stereochemical outcome. Furthermore, new application of Ni(II) complexes of ?-amino acids Schiff bases for deracemization of racemic ?-amino acids and (S) to (R) interconversion providing additional synthetic opportunities for preparation of enantiomerically pure ?-amino acids, is also reviewed. Origin of observed diastereo-/enantioselectivity in the aldol, Mannich-type and deracemization reactions, generality and limitations of these methodologies are critically discussed. PMID:24043459

Sorochinsky, Alexander E; Aceña, José Luis; Moriwaki, Hiroki; Sato, Tatsunori; Soloshonok, Vadim

2013-11-01

65

A novel aldol-type C-glycosidation reaction promoted by samarium diiodide. Regioselective generation of a ulose-1-enolate from phenyl 3,4,6-tri-O-benzyl-1-thio-?- d-arabino-hexopyranosid-2-ulose  

Microsoft Academic Search

A novel aldol-type C-glycosidation reaction promoted by samarium diiodide (SmI2) was developed. Treatment of phenyl 3,4,6-tri-o-benzyl-1-thio-?-d-arabino-hexopyranosid-2-ulose (6) with SmI2 in THF regioselectively gave the corresponding 1-enolate, which was readily trapped with ketones or aldehydes to afford various C-glycosides in high yields.

Satoshi Ichikawa; Satoshi Shuto; Akira Matsuda

1998-01-01

66

Enantio- and diastereoselective synthesis of syn-?-hydroxy-?-vinyl carboxylic esters via reductive aldol reactions of ethyl allenecarboxylate with 10-TMS-9-Borabicyclo[3.3.2]decane and DFT analysis of the hydroboration pathway.  

PubMed

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

Kister, Jeremy; Ess, Daniel H; Roush, William R

2013-11-01

67

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.

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

2004-01-01

68

An Aldol-Based Synthesis of (+)-Peloruside A, A Potent Microtubule Stabilizing Agent  

PubMed Central

A convergent synthesis of the marine natural product (+)-peloruside has been reported. This target has been assembled through the successive application of two methyl ketone boron aldol addition reactions to the latent C7–C11 dialdehyde synthon. This approach afforded a 22-step synthesis of this natural product. The influence of resident stereocenters on aldol reaction diastereoselection has been examined in detail.

Evans, David A.; Welch, Dennie S.; Speed, Alexander W. H.; Moniz, George A.; Reichelt, Andreas; Ho, Stephen

2010-01-01

69

Development of new iron catalysts for the tandem isomerization–aldol condensation of allylic alcohols  

Microsoft Academic Search

(bda)Fe(CO)3 and (COT)Fe(CO)3 are shown to be excellent catalysts for the tandem isomerization–aldol reaction of allylic alcohols with aldehydes and to significantly increase the scope of this aldolization process, especially, in the case of sterically hindered aldehydes.

Ramalinga Uma; Nicolas Gouault; Christophe Crévisy; René Grée

2003-01-01

70

Aldol condensation reactions of tricarbonyliron complexes. Towards building blocks for the synthesis of carbomycin B\\/tylosin macrolide antibiotics and fluorinated analogs  

Microsoft Academic Search

Tricarbonyliron complexes of ?-methoxyheptadienone 3 and octadienone 8 were reacted as silyl enol ethers with protected ?-hydroxypropanal and TiCl4, to give the syn–syn aldol condensation products 4 and 11 as major, isolated diastereomers (61 and 45%). Products 4 and 11 were converted into key intermediates of previous total syntheses of carbonolide B and tylonide, in a few steps, including the

Michel Franck-Neumann; Philippe Geoffroy; Fabien Gumery

2000-01-01

71

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.

Salehi-Rad, Ramin

2012-01-01

72

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.

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

2013-01-01

73

Synthesis of (-)-stemoamide using a stereoselective anti-aldol step.  

PubMed

The synthesis of (-)-stemoamide was achieved in 11 steps from 5-acetoxy-N-crotyl pyrrolidinone. A chiral N-acyl thiazolidinethione was employed in a stereoselective addition to a cyclic N-acyl iminium ion to install the required stereochemistry of carbon C9a. This iminium ion addition product was employed in a stereoselective MgBr2-catalyzed anti-aldol reaction to install the required stereochemistry of carbons C8 and C9. The X-ray crystal analysis of (-)-stemoamide confirmed the structure and the stereochemical outcome of these selective reactions. PMID:16599632

Olivo, Horacio F; Tovar-Miranda, Ricardo; Barragán, Efraín

2006-04-14

74

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers.  

PubMed

The relative configurations of tert-butyldimethylsilyl (TBDMS) ethers of all four diastereomers of the aldols of tropinone (8-methyl-8-azabicyclo[3.2.1]octan-3-one), as well as of granatanone (9-methyl-9-azabicyclo[3.3.1]nonan-3-one), were determined from NMR data, and from the observed interconversion of the diastereomers (exo,anti to endo,syn and exo,syn to endo,anti). The exo forms invert to endo isomers in the presence of silica gel. The relative configuration of a new isomer of tropinone aldol accessible synthetically through the direct solventless reaction of tropinone and benzaldehyde in the presence of water was determined as exo,syn by comparison of NMR data of the aldol isomers, in particular vicinal coupling constants and shifts corresponding to the side-chain CH group, with data of related TBDMS derivatives and confirmed by single-crystal X-ray diffraction. PMID:23209525

Lazny, Ryszard; Nodzewska, Aneta; Sidorowicz, Katarzyna; Kalicki, Przemyslaw

2012-01-01

75

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers  

PubMed Central

Summary The relative configurations of tert-butyldimethylsilyl (TBDMS) ethers of all four diastereomers of the aldols of tropinone (8-methyl-8-azabicyclo[3.2.1]octan-3-one), as well as of granatanone (9-methyl-9-azabicyclo[3.3.1]nonan-3-one), were determined from NMR data, and from the observed interconversion of the diastereomers (exo,anti to endo,syn and exo,syn to endo,anti). The exo forms invert to endo isomers in the presence of silica gel. The relative configuration of a new isomer of tropinone aldol accessible synthetically through the direct solventless reaction of tropinone and benzaldehyde in the presence of water was determined as exo,syn by comparison of NMR data of the aldol isomers, in particular vicinal coupling constants and shifts corresponding to the side-chain CH group, with data of related TBDMS derivatives and confirmed by single-crystal X-ray diffraction.

Nodzewska, Aneta; Sidorowicz, Katarzyna; Kalicki, Przemyslaw

2012-01-01

76

Asymmetric total synthesis of smyrindiol employing an organocatalytic aldol key step  

PubMed Central

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

Fronert, Jeanne; Bisschops, Tom; Boeck, Florian

2012-01-01

77

Study on the base-catalyzed reverse vinylogous aldol reaction of (4abeta,5beta)-4,4a,5,6,7,8-hexahydro-5-hydroxy-1,4a-dimethylnaphthalen-2(3H)-one under Robinson annulation conditions.  

PubMed

[reaction: see text] We have proposed a pathway for the base-catalyzed reverse vinylogous aldol reaction of (-)-(4abeta,5beta)-4,4a,5,6,7,8-hexahydro-5-hydroxy-1,4a-dimethylnaphthalen-2(3H)-one [(-)-8] under Robinson annulation conditions. For confirmation, 4-(2,6-dimethyl-3-oxocyclohex-1-enyl)butanal (11) and 4-(2,6-dimethyl-5-oxocyclohex-1-enyl)butanal (12), both of which potentially produce enolate I, were synthesized regioselectively. Unexpectedly, 11 gave a complex mixture, including only a trace amount of (+/-)-8 (less than 5% yield), under these basic conditions. To the contrary, 12 cleanly afforded (+/-)-8 in 66% yield. This result provides evidence for our proposed mechanism of the above reaction. PMID:16388674

Payette, Joshua N; Honda, Tadashi; Yoshizawa, Hidenori; Favaloro, Frank G; Gribble, Gordon W

2006-01-01

78

Stereoselective synthesis of the monomeric unit of actin binding macrolide rhizopodin.  

PubMed

An efficient, scalable, and stereocontrolled synthesis of the entire carbon framework of an actin binding dimeric macrolide rhizopodin has been accomplished in its protected form. The key features of our synthesis include a titanium catalyzed anti acetal aldol reaction, a substrate controlled diastereoslelective prenyl stannylation, a Mukaiyama aldol reaction, an indium mediated diastereoselective propargylation, and an advanced stage Stille coupling reaction. PMID:22594399

Pulukuri, Kiran Kumar; Chakraborty, Tushar Kanti

2012-06-01

79

Method for the preparation of aldol product 7B  

US Patent & Trademark Office Database

A method of preparing (.+-.)-calanolide A, 1, a potent HIV reverse transcriptase inhibitor, from chromene 4 is provided. Useful intermediates for preparing (+)-calanolide A and its derivatives are also provided. According to the disclosed method, chromene 4 intermediate was reacted with acetaldehyde diethyl acetal or paraldehyde in the presence of an acid catalyst with heating, or a two-step reaction including an aldol reaction with acetaldehyde and cyclization either under acidic conditions or neutral Mitsunobu conditions, to produce chromanone 7. Reduction of chromanone 7 with sodium borohydride, in the presence of cerium trichloride, produced (.+-.)-calanolide A. A method for resolving (.+-.)-calanolide A into its optically active forms by a chiral HPLC system or by enzymatic acylation and hydrolysis is also disclosed. Finally, a method for treating or preventing viral infections using (.+-.)-calanolide A or (-)-calanolide A is provided.

1998-11-24

80

NMR investigations on the proline-catalyzed aldehyde self-condensation: Mannich mechanism, dienamine detection, and erosion of the aldol addition selectivity.  

PubMed

The proline-catalyzed self-condensation of aliphatic aldehydes in DMSO with varying amounts of catalyst was studied by in situ NMR spectroscopy. The reaction profiles and intermediates observed as well as deuteration studies reveal that the proline-catalyzed aldol addition and condensation are competing, but not consecutive, reaction pathways. In addition, the rate-determining step of the condensation is suggested to be the C-C bond formation. Our findings indicate the involvement of two catalyst molecules in the C-C bond formation of the aldol condensation, presumably by the activation of both the aldol acceptor and donor in a Mannich-type pathway. This mechanism is shown to be operative also in the oligomerization of acetaldehyde with high proline amounts, for which the first in situ detection of a proline-derived dienamine was accomplished. In addition, the diastereoselectivity of the aldol addition is evidenced to be time-dependent since it is undermined by the retro-aldolization and the competing irreversible aldol condensation; here NMR reaction profiles can be used as a tool for reaction optimization. PMID:21446689

Schmid, Markus B; Zeitler, Kirsten; Gschwind, Ruth M

2011-05-01

81

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

PubMed Central

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

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

2009-01-01

82

Trisannulated benzene derivatives by Acid catalyzed aldol cyclotrimerizations of cyclic ketones. Methodology development and mechanistic insight.  

PubMed

Several factors that contribute to the success of aldol cyclotrimerizations have been clarified as part of an effort to shed light on the inner workings of this century old reaction. The use of 4,7-di-tert-butylacenaphthenone (11) as a mechanistic probe molecule has led to intriguing discoveries about temperature, solvent, and solubility effects. Solvents that are both polarizable and somewhat polar, e.g., o-dichlorobenzene (ODCB), work best for the aromatic ketones examined. Certain Brønsted acids were found to work better than Lewis acids as catalysts for the archetypal aldol cyclotrimerization of indanone (2) in aprotic solvents, and a strong dependence on the pKa of the acid was observed. A standardized protocol, using p-toluenesulfonic acid monohydrate, is shown to work well in a number of test cases. PMID:17381158

Amick, Aaron W; Scott, Lawrence T

2007-04-27

83

Symbiotic reagent activation: Oppenauer oxidation of magnesium alkoxides by silylglyoxylates triggers second-stage aldolization.  

PubMed

The treatment of silylglyoxylates with magnesium alkoxides at ambient temperature results in symbiotic Oppenauer oxidation of the alkoxide and Meerwein-Ponndorf-Verley reduction of the silylglyoxylate. The reduced silylglyoxylate undergoes subsequent [1,2]-Brook rearrangement and aldol reaction with the carbonyl oxidation product. The magnesium alkoxide may be accessed via deprotonation of primary or secondary alcohols with EtMgBr, via addition of Grignard reagents to aldehydes, or via CuI-catalyzed alkylation of epoxides. For aliphatic primary alkoxides, moderate levels of anti diastereoselection are observed. A crossover experiment reveals that dissociation of the nascent aldehyde from the magnesium center is faster than [1,2]-Brook rearrangement and aldolization. PMID:16848444

Linghu, Xin; Satterfield, Andrew D; Johnson, Jeffrey S

2006-07-26

84

NHC-catalyzed spiro bis-indane formation via domino Stetter-aldol-Michael and Stetter-aldol-aldol reactions.  

PubMed

Two novel domino NHC-catalyzed spirocyclizations are described herein, enabling the rapid construction of three new carbon-carbon bonds and a quaternary center with high diastereoselectivity. A variety of spiro bis-indane structures are assembled in a single step from simple o-phthaldialdehyde derivatives. PMID:21090705

Sánchez-Larios, Eduardo; Holmes, Janice M; Daschner, Crystal L; Gravel, Michel

2010-12-17

85

Catalytic Redox-Initiated Glycolate Aldol Additions of Silyl Glyoxylates  

PubMed Central

Lanthanide triisopropoxides catalyze a rapid, tandem MPV reduction/Brook rearrangement/aldol sequence between silyl glyoxylates and aldehydes that achieves catalytic turnover through alkoxide transfer from a strain-release Lewis acidic silacycle.

Greszler, Stephen N.; Johnson, Jeffrey S.

2009-01-01

86

Organocatalytic enantioselective domino Michael-aldol condensation of 5-oxoalkanal and alpha,beta-unsaturated aldehydes. Efficient assembly of densely functionalized cyclohexenes.  

PubMed

Organocatalytic Michael reaction of glutaraldehyde and 3-arylpropenal followed by the subsequent intramolecular aldol condensation provided 2-arylcyclohex-3-ene-1,3-dicarbaldehydes. Reactions with the 5-oxohexanal variant afforded the highly functionalized cyclohexenedicarbaldehydes in high diastereoselectivity and high enantioselectivity (>99% ee). Structure of the adduct 3j was confirmed unambiguously by X-ray analysis. PMID:18484729

Hong, Bor-Cherng; Nimje, Roshan Y; Sadani, Amit A; Liao, Ju-Hsiou

2008-06-19

87

Organocatalytic atroposelective aldol condensation: synthesis of axially chiral biaryls by arene formation.  

PubMed

Axially chiral compounds are of significant importance in modern synthetic chemistry and particularly valuable in drug discovery and development. Nonetheless, current approaches for the preparation of pure atropisomers often prove tedious. We demonstrate here a synthetic method that efficiently transfers the stereochemical information of a secondary amine organocatalyst into the axial chirality of tri-ortho-substituted biaryls. An aromatic ring is formed during the dehydration step of the described aldol condensation cascade, leading to highly enantioenriched binaphthyl derivatives. The fundamental course of the reaction is related to the biosynthesis of aromatic polyketides. PMID:24757165

Link, Achim; Sparr, Christof

2014-05-19

88

A Green Enantioselective Aldol Condensation for the Undergraduate Organic Laboratory  

ERIC Educational Resources Information Center

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

Bennett, George D.

2006-01-01

89

Asymmetric total synthesis of (-)-azaspirene, a novel angiogenesis inhibitor.  

PubMed

The asymmetric total synthesis of (-)-azaspirene, an angiogenesis inhibitor, has been accomplished, establishing its absolute stereochemistry. The key steps are a MgBr2.OEt2-mediated, diastereoselective Mukaiyama aldol reaction, a NaH-promoted, intramolecular cyclization of an alkynylamide, and the aldol reaction of a ketone containing functionalized gamma-lactam moiety without protection of tert-alcohol and amide functionalities. PMID:12371831

Hayashi, Yujiro; Shoji, Mitsuru; Yamaguchi, Junichiro; Sato, Kenji; Yamaguchi, Shinpei; Mukaiyama, Takasuke; Sakai, Ken; Asami, Yukihiro; Kakeya, Hideaki; Osada, Hiroyuki

2002-10-16

90

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.

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

2004-01-01

91

Lewis acid catalysis by lanthanide complexes with tris(perfluorooctanesulfonyl)methide ponytails in fluorous recyclable phase  

Microsoft Academic Search

Scandium and ytterbium tris(perfluorooctanesulfonyl)methide complexes are shown to be immobilized in fluorous recyclable phase and extremely efficient Lewis acid catalysts for alcohol acylation, Friedel–Crafts acylation, Diels–Alder reaction, and Mukaiyama aldol reaction by virtue of the highly electron-withdrawing effect of tris(perfluorooctanesulfonyl)methide ponytails without any hydrocarbon spacer.

Koichi Mikami; Yutaka Mikami; Yousuke Matsumoto; Joji Nishikido; Fumihiko Yamamoto; Hitoshi Nakajima

2001-01-01

92

A Hetero-Diels-Alder Approach to Complex Pyrones: An Improved Synthesis of the Spongistatin AB Spiroketal  

PubMed Central

The conversion of a substituted dioxinone to a pyrone was used in an improved synthesis of the AB spiroketal subunit of the spongistatins. This transformation occurred via a hetero-Diels-Alder reaction of an acyl ketene with butyl vinyl ether. A double diastereoselective Mukaiyama aldol reaction is used to provide the hetero-Diels-Alder precursor.

Crimmins, Michael T.; Smith, Aaron C.

2008-01-01

93

A hetero-Diels-Alder approach to complex pyrones: an improved synthesis of the spongistatin AB spiroketal.  

PubMed

The conversion of a substituted dioxinone to a pyrone was used in an improved synthesis of the AB spiroketal subunit of the spongistatins. This transformation occurred via a hetero-Diels-Alder reaction of an acyl ketene with butyl vinyl ether. A double diastereoselective Mukaiyama aldol reaction is used to provide the hetero-Diels-Alder precursor. PMID:16494495

Crimmins, Michael T; Smith, Aaron C

2006-03-01

94

Highly stereoselective oxazaborolidinium ion catalyzed synthesis of (Z)-silyl enol ethers from alkyl aryl ketones and trimethylsilyldiazomethane.  

PubMed

Highly stereoselective (Z)-silyl enol ethers were prepared from alkyl aryl ketones and trimethylsilyldiazomethane (TMSD) using an oxazaborolidinium ion catalyst. In addition, ring-expanded silyl enol ethers were successfully constructed from cyclic ketones. Their synthetic utilities were shown by sequential Mukaiyama aldol and [2 + 2]-cycloaddition reactions. PMID:24670001

Kang, Byung Chul; Shim, Su Yong; Ryu, Do Hyun

2014-04-18

95

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

PubMed Central

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

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

2010-01-01

96

Enantioselective construction of multifunctionalized spirocyclohexaneoxindoles through organocatalytic Michael-Aldol cyclization of isatin derived alkenes with linear dialdehydes.  

PubMed

Optically active spirocyclohexaneoxindole motifs are very important building blocks for preparations of biologically active complexes, natural products, and pharmaceutical compounds. Herein, we report the syntheses of enantiopure spirocyclohexaneoxindoles through domino Michael-Aldol reactions between isatin derived alkenes and pentane-1,5-dial in the presence of diphenylprolinol silyl ether as an aminocatalyst. As a result, a series of multistereogenic and functionalized spirocyclohexaneoxindoles have been obtained in good yields with moderate diastereoselectivities and excellent enantioselectivities. In addition, electronic circular dichroism (ECD) spectroscopy and time-dependent density functional theory (TD-DFT) were used to investigate the rational structures of spirocyclohexaneoxindoles. PMID:23044749

Huang, Xiao-Fei; Liu, Zhao-Min; Geng, Zhi-Cong; Zhang, Shao-Yun; Wang, Yong; Wang, Xing-Wang

2012-11-28

97

Copper-Catalyzed One-Pot Denitrogenative-Dehydrogenative-Decarboxylative Coupling of ?-Ketoacids with Trifluorodiazoethane: Facile Access to Trifluoromethylated Aldol Products.  

PubMed

A novel copper-catalyzed one-pot cross-coupling of ?-ketoacids with in situ generated trifluorodiazoethane has been developed. This reaction provides a direct and efficient method, in which one C?C bond and one C?O bond were formed in a carbenoid center with concomitant denitrogenation-dehydrogenation-decarboxylation, to afford trifluoromethylated aldol products. In several preliminary experiments, good to high enantioselectivities were also obtained. PMID:24889186

Xiong, Heng-Ying; Yang, Zhen-Yan; Chen, Zhen; Zeng, Jun-Liang; Nie, Jing; Ma, Jun-An

2014-07-01

98

Total Synthesis of the Spirocyclic Imine Marine Toxin (-)-Gymnodimine and an Unnatural C4-Epimer  

PubMed Central

The first total synthesis of the marine toxin (?)-gymnodimine (1) has been accomplished in a convergent manner. A highly diastereo- and enantioselective exo-Diels–Alder reaction catalyzed by a bis-oxazoline Cu(II) catalyst enabled rapid assembly of the spirocyclic core of gymnodimine. The preparation of the tetrahydrofuran fragment utilized a chiral auxiliary based anti-aldol reaction. Two major fragments, spirolactam 56 and tetrahydrofuran 55, were then coupled through an efficient Nozaki–Hiyama–Kishi reaction. An unconventional, ambient temperature t-BuLi-initiated intramolecular Barbier reaction of alkyl iodide 64 was employed to form the macrocycle. A late stage vinylogous Mukaiyama aldol addition of a silyloxyfuran to a complex cyclohexanone 83 appended the butenolide and a few additional steps provided (?)-gymnodimine (1). A diastereomer of the natural product was also synthesized, C4-epi-gymnodimine (90), derived from the vinylogous Mukaiyama aldol addition.

Kong, Ke; Moussa, Ziad; Lee, Changsuk

2011-01-01

99

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

100

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.

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

2011-01-01

101

Synthesis of six-membered spirocyclic oxindoles with five consecutive stereocenters in an asymmetric organocatalytic one-pot Michael/Michael/aldol addition sequence.  

PubMed

An asymmetric organocatalytic one-pot synthesis of six-membered spirocyclic oxindoles has been successfully developed through a relay Michael/Michael/aldol addition reaction catalyzed by the combination of readily available diphenylprolinol silyl ether and bifunctional quinine thiourea. The one-pot protocol affords the highly substituted spirocyclic oxindoles in high yields and perfect enantioselectivities. More importantly, through judicious choice of the organocatalysts employed, this reaction could be readily adapted to predominantly afford an alternative major diastereomer of the product. PMID:23469872

Zhou, Bing; Yang, Yaxi; Shi, Jingjing; Luo, Zhi; Li, Yuanchao

2013-04-01

102

Organolanthanide-induced C-C bond formation. Preparation and properties of monomeric lanthanide aldolates and enolates  

SciTech Connect

The reactivity of early-lanthanide carbyls Cp* {sub 2}LnCH(SiMe{sub 3}){sub 2} (1, Ln = La; 2, Ln = Ce) toward ketones has been studied. No reaction was observed with the bulky di-tert-butyl ketone. The corresponding lanthanum hydride [Cp* {sub 2}LaH]{sub 2} (3) is more reactive and afforded the addition product Cp*{sub 2}LaOCH(t-Bu){sub 2}{sup center-dot}O=C(t-Bu){sub 2} (4). Hydrogen transfer and formation of lanthanide aldolates Cp* {sub 2}LnOCMe{sub 2}C(=O)Me (5, Ln = Ce; 6, Ln =La) together with the protonated carbyl CH{sub 2}(SiMe{sub 3}){sub 2} were observed when 1 or 2 was treated with acetone. The molecular structure of the cerium analogue 5 was determined by X-ray diffraction and was found to be a monomeric bent metallocene compound with a {eta}{sup 2}-coordinated aldol fragment. Addition of 3-pentanone to the carbyls 1 and 2 did not result in C-C coupling but provided enolate-ketone adducts Cp*{sub 2}LnOC(Et)=C(H)MeO=CEt{sub 2} (7, Ln = La; 8, Ln = Ce). Reactions of the carbyls 1 and 2 with 4-methyl-5-hydroxy-5ethyl-3-heptanone yielded the enolate-ketone adducts as well and suggest that the differences in reactivity between acetone and 3-pentanone are thermodynamic and not kinetic in origin. 32 refs., 2 figs., 5 tabs.

Heeres, H.J.; Maters, M.; Teuben, J.H. [Univ. of Groningen (Netherlands)] [and others

1992-01-01

103

Total synthesis of the proposed structure of didemnaketal B.  

PubMed

Total synthesis of the proposed structure of didemnaketal B has been accomplished. The C7-C21 spiroacetal domain was synthesized by exploiting our Suzuki-Miyaura coupling/spiroacetalization strategy. The C1-C7 acyclic domain was constructed via an Evans syn-aldol reaction and a vinylogous Mukaiyama aldol reaction. Finally, the C22-C28 side chain was introduced by means of a Nozaki-Hiyama-Kishi reaction. Comparison of the NMR spectroscopic data of our synthetic material with those of the authentic sample revealed that the proposed structure requires stereochemical reassignment. PMID:23875682

Fuwa, Haruhiko; Sekine, Kumiko; Sasaki, Makoto

2013-08-01

104

Formal synthesis of actin binding macrolide rhizopodin.  

PubMed

Formal synthesis of an actin binding macrolide rhizopodin was achieved in 19 longest linear steps. The key features of the synthesis include a stereoselective Mukaiyama aldol reaction, dual role of a Nagao auxiliary (first, as a chiral auxiliary of choice for installing hydroxy centers and, later, as an acylating agent to form an amide bond with an amino alcohol), late stage oxazole formation, and Stille coupling reactions. PMID:24742162

Pulukuri, Kiran Kumar; Chakraborty, Tushar Kanti

2014-04-18

105

Diastereoselective reactions of enolates  

Microsoft Academic Search

Triphenylglycol-derived esters 2 and 8a have been applied in asymmetric aldol reactions. The homochiral propionates 7 and 8a,b react with imines in a stereodivergent manner: Doubly deprotonated 7 delivers anti-fklactams 14 whereas the lithium enolates of %ah afford ciS-f)-lactams 15 in 87-9796 e.e. Diastereoselective carbon silylation occurs when deprotonated 8a is treated with chlorotrimethylsilane. Approaches towards the construction of quaternary

M. Braun; H. Sacha; D. Galle; S. Baskaran

1996-01-01

106

Diastereo- and enantioselective hydrogenative aldol coupling of vinyl ketones: design of effective monodentate TADDOL-like phosphonite ligands.  

PubMed

We report the first enantioselective reductive aldol couplings of vinyl ketones, which were achieved through the design of a novel monodentate TADDOL-like phosphonite ligand. Specifically, hydrogenation of commercially available methyl vinyl ketone (MVK) or ethyl vinyl ketone (EVK) in the presence of aldehydes 1a-7a using cationic rhodium catalysts modified by chiral TADDOL-like phosphonite ligands AP-I and AP-IV produces aldol adducts 1b-7b and 1c-7c with excellent control of relative and absolute stereochemistry. The absolute stereochemical assignments of the aldol adducts are made in analogy to that determined for the 5-bromophthalimido derivative of aldol adduct 1b and the 2-bromo-5-nitrobenzoate of 3b, which were established by single-crystal X-ray diffraction analysis using the anomalous dispersion method. PMID:18266373

Bee, Cisco; Han, Soo Bong; Hassan, Abbas; Iida, Hiroki; Krische, Michael J

2008-03-01

107

D-Aminoacylase-initiated cascade Aldol condensation/Robinson annulation for synthesis of substituted cyclohex-2-enones from simple aldehydes and acetone.  

PubMed

As an important building block, developing efficient and green synthesis strategy of cyclohex-2-enones is of great importance. In this present work, a general approach to the mild synthesis of substituted cyclohex-2-enones derivatives starting fro m simple aldehydes and acetone have been achieved via D-aminoacylase-initiated Aldol condensation/Robinson annulation cascade reaction using imidazole as an additive in organic media. The influences of reaction conditions including solvents, enzyme concentration, additives type, molar ratio of enzyme to additive, and substrate scopes were systematically investigated. Furthermore, some experiments were designed to explore the catalytic roles of D-aminoacylase and imidazole in the multistep cascade process, and one possible mechanism was proposed. PMID:24770961

Xiang, Ziwei; Liang, Yiru; Chen, Xiang; Wu, Qi; Lin, Xianfu

2014-08-01

108

Stereocontrolled Synthesis of syn-?-Hydroxy-?-Amino Acids by Direct Aldolization of Pseudoephenamine Glycinamide.  

PubMed

?-Hydroxy-?-amino acids figure prominently as chiral building blocks in chemical synthesis and serve as precursors to numerous important medicines. Reported herein is a method for the synthesis of ?-hydroxy-?-amino acid derivatives by aldolization of pseudoephenamine glycinamide, which can be prepared from pseudoephenamine in a one-flask protocol. Enolization of (R,R)- or (S,S)-pseudoephenamine glycinamide with lithium hexamethyldisilazide in the presence of LiCl followed by addition of an aldehyde or ketone substrate affords aldol addition products that are stereochemically homologous with L- or D-threonine, respectively. These products, which are typically solids, can be obtained in stereoisomerically pure form in yields of 55-98?%, and are readily transformed into ?-hydroxy-?-amino acids by mild hydrolysis or into 2-amino-1,3-diols by reduction with sodium borohydride. This new chemistry greatly facilitates the construction of novel antibiotics of several different classes. PMID:24692320

Seiple, Ian B; Mercer, Jaron A M; Sussman, Robin J; Zhang, Ziyang; Myers, Andrew G

2014-04-25

109

Sequential Aldol Condensation Catalyzed by Hyperthermophilic 2-Deoxy-D-Ribose-5Phosphate Aldolase  

Microsoft Academic Search

Genes encoding 2-deoxy-D-ribose-5-phosphate aldolase (DERA) homologues from two hyperthermophiles, the archaeon Pyrobaculum aerophilum and the bacterium Thermotoga maritima, were expressed individually in Escherichia coli, after which the structures and activities of the enzymes produced were characterized and compared with those of E. coli DERA. To our surprise, the two hyperthermophilic DERAs showed much greater catalysis of sequential aldol condensation using

Haruhiko Sakuraba; Kazunari Yoneda; Kumiko Yoshihara; Kyoko Satoh; Ryushi Kawakami; Yoshihiro Uto; Hideaki Tsuge; Katsuyuki Takahashi; Hitoshi Hori; Toshihisa Ohshima

2007-01-01

110

Boron enolate chemistry toward the syntheses of polyketide stereotetrads.  

PubMed

In 1976 Mukaiyama published a paper that was to make a major impact on the development of the aldol reaction in the future. Mild enolate formation by treatment of a ketone with dibutylboron triflate in the presence of a tertiary amine generates a relatively stable boron enolate, which can subsequently react with an aldehyde to give the cross-aldol product in good yields. This reaction has become a reliable tool for the practicing synthetic chemist. Nearly 10000 polyketides are known, and of these about 600 contain the tripropionate unit with a stereotetrad, four contiguous stereocenters with alternating methyl and hydroxyl substituents in the main chain. The versatility of the boron enolate aldol reaction is showcased with selected applications in the synthesis of these structural motifs. PMID:24420331

Koskinen, Ari M P

2014-02-01

111

Asymmetric induction in hydrogen-mediated reductive aldol additions to alpha-amino aldehydes catalyzed by rhodium: selective formation of syn-stereotriads directed by intramolecular hydrogen-bonding.  

PubMed

Rhodium-catalyzed hydrogenation of methyl vinyl ketone and ethyl vinyl ketone in the presence of N-Boc-alpha-aminoaldehydes 3a-8a at ambient temperature and pressure results in reductive C-C coupling to furnish aldol adducts 3b-8b and 3c-8c, respectively, which incorporate stereotriads that embody high levels of syn-aldol selectivity accompanied by high levels of anti-Felkin-Anh control. The collective data are consistent with a catalytic mechanism involving addition of the Z(O)-rhodium enolate to the sterically less-encumbered aldehyde pi-face of an intramolecularly hydrogen-bonded chelate through a Zimmerman-Traxler type transition structure. Stereochemical assignments are supported by single-crystal X-ray diffraction analysis of 5b-O-3,5-dinitrobenzoate, iso-5b, N-Me-iso-5b-O-3,5-dinitrobenzoate, and 7b. As revealed by HPLC analysis, optical purity of the stereochemically labile alpha-aminoaldehydes is completely preserved under the conditions of hydrogen-mediated aldol coupling. Deletion of the intramolecular hydrogen bond, as in the case of N-methyl-N-Boc-l-leucinal N-Me-5a, inverts stereoselectivity to furnish the Felkin-Anh product N-Me-iso-5b in 17% yield. Additionally, reactions performed in the presence of tert-amyl alcohol (10 equiv) exhibit markedly lower levels of anti-Felkin-Anh control (7:1 versus > or = 20:1). The collective studies suggest that intramolecular hydrogen bonding plays a key role in both activating the alpha-aminoaldehyde toward addition and directing facial selectivity. PMID:17177457

Jung, Cheol-Kyu; Krische, Michael J

2006-12-27

112

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

EPA Science Inventory

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

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

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

PubMed

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

Setzer, William N

2010-07-01

115

Double Diastereoselective, Nucleophile-Catalyzed Aldol Lactonizations (NCAL) Leading to ?-Lactone Fused Carbocycles and Extensions to ?-Lactone Fused Tetrahydrofurans  

PubMed Central

A double diastereoselective variant of the nucleophile catalyzed aldol-lactonization (NCAL) process is described. This strategy delivers ?-lactone-fused carbocycles with good to excellent diastereoselectivities using cinchona alkaloid catalysts with enantioenriched aldehyde acids, which gave low diastereoselectivity based on substrate control alone. ?-Lactone fused tetrahydrofurans are also prepared for the first time via the NCAL process, however diastereoselectivity was only modestly improved when applying double diastereodifferentiation to these systems.

Morris, Kay A.; Arendt, Kevin M.; Oh, Seong Ho; Romo, Daniel

2010-01-01

116

Synthesis of the C(29)-C(45) bis-pyran subunit (E-F) of spongistatin 1 (Altohyrtin A).  

PubMed

A synthesis of the C(29)-C(45) bis-pyran subunit 2 of spongistatin 1 (1a) is described. The synthesis proceeds in 19 steps from the chiral aldehyde ent-7, and features highly diastereoselective alpha-alkoxyallylation reactions using the gamma-alkoxy substituted allylstannanes 17 and 19, as well as a thermodynamically controlled intramolecular Michael addition to close the F-ring pyran. The E ring was assembled via the Mukaiyama aldol reaction of F-ring methyl ketone 3 and the 2,3-syn aldehyde 4. PMID:11112596

Micalizio, G C; Pinchuk, A N; Roush, W R

2000-12-15

117

Improvement on the catalytic performance of Mg-Zr mixed oxides for furfural-acetone aldol condensation by supporting on mesoporous carbons.  

PubMed

A new procedure for improving the performance of the most common catalysts used in aqueous-phase aldol condensation (Mg-Zr mixed oxides) reactions is presented. This reaction is of interest for upgrading carbohydrate feedstocks. The procedure involves supporting Mg-Zr oxides on non-microporous carbonaceous materials, such as carbon nanofibers (CNFs) or high-surface-area graphites (HSAGs), using either incipient wetness or coprecipitation procedures. The use of HSAGs together with the coprecipitation method provides the best performance. Results obtained for the cross-condensation of acetone and furfural at 323?K reveal that the catalyst performance is greatly improved compared to the bulk oxides (96.5?% conversion vs. 81.4?% with the bulk oxide; 87.8?% selectivity for C13 and C8 adducts vs. 76.2?% with the bulk oxide). This difference is even more prominent in terms of rates per catalytically active basic site (four and seven times greater for C8 and C13 adducts, respectively). The improved performance is explained in terms of a more appropriate basic site distribution and by greater interaction of the reactants with the carbon surface. In addition, deactivation behavior of the catalyst is improved by tuning the morphology of the carbonaceous support. An important enhancement of the catalytic stability can be obtained selecting a HSAG with an appropriate pore diameter. With HSAG100 the activity decreased by less than 20?% between successive reaction cycles and the selectivity for the condensation products remained almost unaltered. The decrease is greater than 80?% for the bulk oxides tested at these conditions, with important increases in the selectivity for by-product formation. PMID:23362138

Faba, Laura; Díaz, Eva; Ordóñez, Salvador

2013-03-01

118

Tandem application of C-C bond-forming reactions with reductive ozonolysis  

PubMed Central

Several variants of reductive ozonolysis, defined here as the in situ generation of aldehydes or ketones during ozonolytic cleavage of alkenes, are demonstrated to work effectively in tandem with a number of C-C bond-forming reactions. For reactions involving basic nucleophiles (1,2-addition of Grignard reagents, Wittig or Horner-Emmons olefinations, and directed Aldol reactions of lithium enolates) the one-pot process offers a rapid and high-yielding alternative to traditional two-step protocols.

Willand-Charnley, Rachel; Dussault, Patrick H.

2012-01-01

119

A General and Enantioselective Approach to Pentoses: A Rapid Synthesis of PSI-6130, the Nucleoside Core of Sofosbuvir.  

PubMed

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

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

2014-04-23

120

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.

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

2013-01-01

121

Quantum mechanical investigations on the role of neutral and negatively charged enamine intermediates in organocatalyzed reactions  

NASA Astrophysics Data System (ADS)

The proline-catalyzed aldol reaction is the seminal example of asymmetric organocatalysis. Previous theoretical and experimental studies aimed at identifying its mechanism in order to rationalize the outcome of this reaction. Here, we focus on key steps with modern first principle methods, i.e. the M06-2X hybrid exchange-correlation functional combined to the solvation density model to account for environmental effects. In particular, different pathways leading to the formation of neutral and negatively charged enamine intermediates are investigated, and their reactivity towards two electrophiles, i.e. an aldehyde and a benzhydrylium cation, are compared. Regarding the self-aldol reaction, our calculations confirm that the neutral enamine intermediate is more reactive than the negatively charged one. For the reaction with benzhydrylium cations however, the negatively charged enamine intermediate is more reactive.

Hubin, Pierre O.; Jacquemin, Denis; Leherte, Laurence; Vercauteren, Daniel P.

2014-04-01

122

Hydrogen-bond-mediated cascade reaction involving chalcones: facile synthesis of enantioenriched trisubstituted tetrahydrothiophenes.  

PubMed

A bifunctional squaramide catalyzed sulfa-Michael/aldol cascade reaction between 1,4-dithiane-2,5-diol and chalcones with a low catalyst loading has been developed. Trisubstituted tetrahydrothiophenes with three contiguous stereogenic centers are obtained in a highly stereocontrolled manner. Additionally, a remarkable temperature effect on reaction efficiency was observed and a synthetically potential gram-synthesis was also conducted. PMID:22313116

Ling, Jun-Bing; Su, Yu; Zhu, Hai-Liang; Wang, Guan-Yu; Xu, Peng-Fei

2012-02-17

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

Desymmetrization of enone-diones via rhodium-catalyzed diastereo- and enantioselective tandem conjugate addition-aldol cyclization.  

PubMed

Catalytic tandem conjugate addition-enolate trapping represents an effective strategy for the design of catalytic transformations that enable formation of multiple C-C bonds. Recently, using enantioselective rhodium-catalyzed conjugate addition methodology, we developed a catalytic tandem conjugate addition-aldol cyclization of keto-enones. Here, we report related desymmetrizations and parallel kinetic resolutions involving the use of diones as terminal electrophiles. The Rh-enolate generated on enone carbometallation effectively discriminates among four diastereotopic pi-faces of the appendant dione, ultimately providing products that embody four contiguous stereocenters, including two adjacent quaternary centers, with quantitative diastereoselection and high levels of enantiomeric excess. This methodology allows concise entry to optically enriched seco-B ring steroids possessing a 14-hydroxy cis-fused C-D ring junction, as found in naturally occurring cardiotonic steroids derived from digitalis. PMID:15024093

Bocknack, Brian M; Wang, Long-Cheng; Krische, Michael J

2004-04-13

125

Desymmetrization of enone-diones via rhodium-catalyzed diastereo- and enantioselective tandem conjugate addition-aldol cyclization  

PubMed Central

Catalytic tandem conjugate addition-enolate trapping represents an effective strategy for the design of catalytic transformations that enable formation of multiple C—C bonds. Recently, using enantioselective rhodium-catalyzed conjugate addition methodology, we developed a catalytic tandem conjugate addition-aldol cyclization of keto-enones. Here, we report related desymmetrizations and parallel kinetic resolutions involving the use of diones as terminal electrophiles. The Rh-enolate generated on enone carbometallation effectively discriminates among four diastereotopic ?-faces of the appendant dione, ultimately providing products that embody four contiguous stereocenters, including two adjacent quaternary centers, with quantitative diastereoselection and high levels of enantiomeric excess. This methodology allows concise entry to optically enriched seco-B ring steroids possessing a 14-hydroxy cis-fused C-D ring junction, as found in naturally occurring cardiotonic steroids derived from digitalis.

Bocknack, Brian M.; Wang, Long-Cheng; Krische, Michael J.

2004-01-01

126

Rasta resin-PPh3-NBniPr2 and its use in one-pot Wittig reaction cascades.  

PubMed

A new triarylphosphine-tertiary amine bifunctional polymeric reagent has been prepared and used effectively in a variety of one-pot Wittig reactions. The design of this reagent resolved a deficiency of a previously reported related material, and allowed it to perform more efficiently in such reactions. Furthermore, it was readily recyclable, and was also successfully applied in cascade processes involving one-pot Wittig reactions followed by either a conjugate reduction or a reductive aldol reaction. In these reaction cascades, the phosphine oxide groups generated in the Wittig reaction served as the catalyst for the subsequent reaction. PMID:22162318

Teng, Yan; Lu, Jinni; Toy, Patrick H

2012-02-01

127

Rapid construction of the aza-propellane core of acutumine via a photochemical [2 + 2] cycloaddition reaction.  

PubMed

Synthetic efforts toward the chlorinated aza-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 hemiketal product. PMID:22891873

Navarro, Raul; Reisman, Sarah E

2012-09-01

128

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.

Navarro, Raul; Reisman, Sarah E.

2012-01-01

129

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.

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

2012-01-01

130

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

PubMed

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

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

2014-01-01

131

Stabilization of ketone and aldehyde enols by formation of hydrogen bonds to phosphazene enolates and their aldol products.  

PubMed

Solution properties of enolates generated using the phosphazene (Schwesinger) base P4-tBu were investigated by NMR spectroscopy. With a full equivalent of base the benzyl ketones 1a and 1b, the acetophenone 2, the arylacetaldehyde 1c, and the methyl arylacetate 1d formed the expected "naked" (P4H+) enolates 3 and 7. However, at a half-equivalent of base the ketones 1a and 1b as well as the aldehyde 1c formed solutions of stable hydrogen-bonded dimeric (enol-enolate) structures (4). The acetophenone 2, on the other hand, forms only traces of the H-bonded dimer 8 during deprotonation of 2. The thermodynamic product was the isomeric self-aldol condensation product 12. The mechanism of this condensation was elucidated by low temperature rapid-injection (RI) NMR spectroscopy. Solutions of 8 stable enough for NMR characterization could be transiently generated by semiprotonation of the enolate 7 with HCl.OEt2 at -130 degrees C using RINMR. The ester enolate 1d gave no trace of 4d even on a time scale as short as a few seconds at -130 degrees C either during the semideprotonation of 1d, or during semiprotonation of the enolate 3d. Long-lived solutions of the enols derived from 1a, 1b, 1c, and 2 (but not 1d) could be produced by full protonation of the phosphazene enolates with HCl.OEt2 at low temperature. PMID:18593122

Kolonko, Kristopher J; Reich, Hans J

2008-07-30

132

An Entry to Curcuphenol/Elvirol Core Structures via a Retro-Aldol Procedure  

PubMed Central

Curcuphenol/elvirol analogues, the naturally occurring bisabolane sesquiterpenes were prepared in six steps from alkyl ?-tetralones employing an aromatization reaction of cyclic dienone precursors and olefination of the key aldehyde intermediates. The in vitro antifungal activities of 6a, 6b, 6d and 6g are also reported.

Plano, Maria F.; Labadie, Guillermo R.; Jacob, Melissa R.; Tekwani, Babu L.; Cravero, Raquel M.

2013-01-01

133

Overcoming the limitations of the Morita-Baylis-Hillman reaction: a rapid and general synthesis of alpha-alkenyl-beta'-hydroxy thioesters.  

PubMed

Acryloyl chlorides, aldehydes, and PhSLi undergo a direct aldol cascade sequence in the presence of MgBr2 x OEt2 via in situ derived thioester enolates, which is followed by oxidative elimination to give alpha-alkenyl-beta'-hydroxy thioesters. Overall, the procedure is rapid, efficient, and generally applicable, even to beta-substituted acryloyl chlorides, thus providing an alternative to the Morita-Baylis-Hillman reaction with substantially greater synthetic scope and utility. PMID:18844367

Tarsis, Emily; Gromova, Anna; Lim, Daniel; Zhou, Guoqiang; Coltart, Don M

2008-11-01

134

Efficient entry to the [2.2.2]-diazabicyclic ring system via diastereoselective domino reaction sequence.  

PubMed

A domino reaction sequence involving aldol condensation, alkene isomerization, and intramolecular hetero-Diels-Alder cycloaddition for the synthesis of [2.2.2]-diazabicyclic structures is reported. Excellent diastereofacial control during the cycloaddition is enforced with a removable chiral phenyl aminal diketopiperazine substituent. The reaction sequence rapidly generates molecular complexity and is competent with both enolizable and nonenolizable aldehyde substrates (nine examples total). Progress toward the synthesis of malbrancheamide B, a protypical member of the [2.2.2]-diazabicyclic natural product family, is also disclosed. PMID:22571782

Margrey, Kaila A; Chinn, Alex J; Laws, Stephen W; Pike, Robert D; Scheerer, Jonathan R

2012-05-18

135

A base-free neutral phase-transfer reaction system.  

PubMed

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

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

2014-06-01

136

TiCl4-promoted Baylis-Hillman reaction: mechanistic rationale toward product distribution and stereoselectivity.  

PubMed

The mechanism of TiCl(4)-promoted Baylis-Hillman reaction between methyl vinyl ketone (MVK) and acetaldehyde, in the absence of any base, is studied using the mPW1K density functional theory. The study focuses on several mechanistic intricacies as well as selectivity issues at each step of the reaction. The minimum energy pathway for this reaction involves three major steps such as a chloride transfer resulting in a chloro-enolate, titanium-mediated aldol reaction, and elimination of HCl or HOTiCl(3). Both s-cis and s-trans conformers of MVK are considered along with various modes of chloride transfer involving different complexes between TiCl(4), aldehyde, and MVK. Chloride transfer is found to be kinetically more favored for s-cis-MVK than for s-trans-MVK. The diastereoselectivity in the next step, i.e., Ti-mediated aldol reaction between the enolate and aldehyde, is found to be dependent on the geometry of the enolate, wherein anti and syn BH products are predicted for Z and E enolates, respectively. An interesting secondary orbital interaction between the oxygen atoms of the enolate and aldehyde moieties in the transition states for the C-C bond formation is identified as one of the contributing factors toward the predicted diastereoselectivity in the formation of the alpha-chloromethyl aldol product (P2). It has earlier been reported that under different experimental conditions, any of the three products such as (i) a normal BH product (P1), (ii) 2-(chloromethyl)vinyl ketones (P3), and (iii) alpha-chloro methyl aldol could be generated (Scheme 1 ). The present study offers valuable insights toward rationalizing the observed product distribution as well as diastereoselectivity in TiCl(4)-promoted BH reaction under base-free conditions. The computed energetics indicate that when MVK is employed as the Michael acceptor, the formation of 2-(choromethyl)vinyl ketone is the preferred product rather than the corresponding normal BH product, consistent with the known experimental reports. PMID:20000733

Patel, Chandan; Sunoj, Raghavan B

2010-01-15

137

Linked strategy for the production of fuels via formose reaction  

PubMed Central

Formose reaction converts formaldehyde to carbohydrates. We found that formose reaction can be used linking the biomass gasification with the aqueous-phase processing (APP) to produce liquid transportation fuel in three steps. First, formaldehyde from syn-gas was converted to triose. This was followed by aldol condensation and dehydration to 4-hydroxymethylfurfural (4-HMF). Finally, 4-HMF was hydrogenated to produce 2,4-dimethylfuran (2,4-DMF) or C9-C15 branched-chain alkanes as liquid transportation fuels. In the linked strategy, high energy-consuming pretreatment as well as expensive and polluting hydrolysis of biomass were omitted, but the high energy recovery of APP was inherited. In addition, the hexoketoses via formose reaction could be converted to HMFs directly without isomerization. A potential platform molecule 4-HMF was formed simultaneously in APP.

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

2013-01-01

138

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

PubMed

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

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

2014-02-01

139

A modular approach to marine macrolide construction. 4. Assembly of C36-C51 and C29-C44 building blocks and evaluation of key coupling reactions targeting spongistatin 1 (altohyrtin A).  

PubMed

Routes have been developed for the stereocontrolled elaboration of two highly functionalized sectors of spongistatin 1. The approach to ring F takes advantage of B-alkyl Suzuki-Miyaura coupling to install the C44-C45 bond. The E-ring pyran moiety was generated by acylation of an alpha-sulfonyl carbanion, the stereogenic centers of which were incorporated by sequential asymmetric aldol reactions. [structure: see text]. PMID:17286379

Ciblat, Stephane; Kim, Jungchul; Stewart, Catherine A; Wang, Jizhou; Forgione, Pat; Clyne, Dean; Paquette, Leo A

2007-02-15

140

Et3B-mediated radical-polar crossover reaction for single-step coupling of O,Te-acetal, ?,?-unsaturated ketones, and aldehydes/ketones.  

PubMed

Et3B-mediated three-component coupling reactions between O,Te-acetal, ?,?-unsaturated ketones, and aldehydes/ketones were developed. Et3B promoted the generation of the potently reactive bridgehead radical from the O,Te-acetal of the trioxaadamantane structure and converted the ?-carbonyl radical of the resultant two-component adduct to the boron enolate, which then underwent a stereoselective aldol reaction with the aldehyde/ketone. This powerful, yet mild, radical-polar crossover reaction efficiently connected the hindered linkages between the three units and selectively introduced three new stereocenters. PMID:24066907

Kamimura, Daigo; Urabe, Daisuke; Nagatomo, Masanori; Inoue, Masayuki

2013-10-01

141

Effects of water on reactions for waste treatment, organic synthesis, and bio-refinery in sub- and supercritical water.  

PubMed

Current research analyzing the effects of water in the field of homogeneous and heterogeneous reactions of organics in sub- and supercritical water are reviewed in this article. Since the physical properties of water (e.g., density, ion product and dielectric constants) can affect the reaction rates and mechanisms of various reactions, understanding the effects that water can have is important in controlling reactions. For homogeneous reactions, the effects of water on oxidation, hydrolysis, aldol condensation, Beckman rearrangement and biomass refining were introduced including recent experimental results up to 100 MPa using special pressure-resistance equipment. For heterogeneous reactions, the effects of ion product on acid/base-catalyzed reactions, such as hydrothermal conversion of biomass-related compounds, organic synthesis in the context of bio-refinery, and hydration of olefins were described and how the reaction paths are controlled by the concentration of water and hydrogen ions was summarized. PMID:23867097

Akizuki, Makoto; Fujii, Tatsuya; Hayashi, Rumiko; Oshima, Yoshito

2014-01-01

142

Understanding solid/solid organic reactions.  

PubMed

The concept of an organic reaction between two macroscopic solid particles is investigated. Thus, we study several reactions that have been recently reported to proceed "in the solid phase" and clearly show that, in most cases, grinding the two solid reactants together results in the formation of a liquid phase. This is true both for catalytic transformations (e.g., aldol condensations and oligomerization of benzylic compounds) and for noncatalytic reactions (Baeyer-Villiger oxidations, oxidative coupling of naphthols using iron chloride, condensation of amines and aldehydes to form azomethines, homo-etherification of benzylic alcohols using p-toluenesulfonic acid, and nuclear aromatic bromination with NBS). This liquefaction implies the existence of a eutectic mixture with T(fusion) below ambient temperature (although both reagents have higher than ambient melting points). In cases where heating is required, it is again clear that a phase change (from solid to liquid) occurs, explaining the observed reaction kinetics. On the basis of 19 experimental examples, we discuss the possibility of solid-phase organic reactions and the implications of these findings to the reaction between two solid reagents. A general description of such reactive systems is proposed, based on a consideration of the potential for eutectic (or peritectic) formation between the constituents of the liquid phases that arise during the process of mechanical mixing of the solid reagents and products. PMID:11535074

Rothenberg, G; Downie, A P; Raston, C L; Scott, J L

2001-09-12

143

H2SO4-Promoted Synthesis of (E)-Stilbenes from Substituted Phenylacetones and Substituted Benzaldehydes Through Tandem Aldol–Grob Reaction  

Microsoft Academic Search

Stilbene derivates (stilbenoids) are present in plants and show a wide range of biological activities and potential therapeutic value. In continuation of our natural product synthesis program, an efficient, simple, and practical method has been developed to regioselectively synthesize (E)-stilbenes using H2SO4 as a catalyst in a short time (30–60 s) at room temperature in good to excellent yields.

T. Narender; K. Papi Reddy; Sriniwas Tiwari

2011-01-01

144

Three-Component Glycolate Michael Reactions of Enolates, Silyl Glyoxylates, and ?,?-Enones  

PubMed Central

Silyl glyoxylates react with enolates and enones to afford either glycolate aldol or Michael adducts. Product identity is controlled by the countercation associated with the enolate. Reformatsky nucleophiles in the presence of additional Zn(OTf)2 result in aldol coupling (A), while lithium enolates provide the Michael coupling (B). Deprotonation of the aldol product A with LDA induces equilibration to form the minor diastereomer of Michael product B. This observation suggests that formation of the major diastereomer of Michael product B does not occur via an aldol/retro-aldol/Michael sequence.

Schmitt, Daniel C.; Malow, Ericka J.; Johnson, Jeffrey S.

2012-01-01

145

Microwave-assisted four-component, one-pot condensation reaction: an efficient synthesis of annulated pyridines.  

PubMed

A one-pot, effective synthesis of pyridines by a modified Kröhnke procedure is described. Polysubstituted annulated pyridines were synthesized in high yields by four-component, one-pot cyclocondensation reactions of N-phenacylpyridinium bromide, aromatic aldehydes, acetophenones or cyclic ketones in the presence of ammonium acetate and acetic acid, assisted by microwave irradiation. In this procedure, cyclic ketones with two alpha-CH(2) groups yield annulated pyridines with additional alpha-benzylidene groups, which are derived in situ from double aldol condensation of cyclic ketones with two moles of aromatic aldehydes. PMID:17340010

Yan, Chao-Guo; Cai, Xi-Mei; Wang, Qi-Fang; Wang, Ting-Yu; Zheng, Ming

2007-03-21

146

Guerbet reaction of primary alcohols leading to beta-alkylated dimer alcohols catalyzed by iridium complexes.  

PubMed

[IrCl(cod)]2 and [Cp*IrCl2]2 complexes catalyzed efficiently the Guerbet reaction of primary alcohols to beta-alkylated dimer alcohols in good yields. For instance, the reaction of 1-butanol in the presence of [Cp*IrCl2]2 (1 mol %), t-BuOK (40 mol %), and 1,7-octadiene (10 mol %) produced 2-ethyl-1-hexanol in 93% yield. Various primary alcohols undergo the Guerbet reaction under the influence of Ir complexes to give the corresponding dimer alcohols in good yields. This method provides an alternative direct route to beta-alkylated primary alcohols which are prepared by aldol condensation of aldehydes followed by hydrogenation. PMID:17025333

Matsu-ura, Toyomi; Sakaguchi, Satoshi; Obora, Yasushi; Ishii, Yasutaka

2006-10-13

147

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

PubMed

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

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

2014-05-01

148

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

PubMed

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

Poudel, Tej Narayan; Lee, Yong Rok

2014-02-14

149

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

PubMed Central

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

Chen, Ming; Roush, William R.

2012-01-01

150

Uptake and reaction kinetics of acetone, 2-butanone, 2,4-pentanedione, and acetaldehyde in sulfuric acid solutions.  

PubMed

This work presents a study of the uptake of acetone, 2-butanone (methyl ethyl ketone), 2,4-pentanedione, and acetaldehyde by sulfuric acid solutions with an aim at understanding the reactivity of carbonyl compounds present in the atmosphere toward acidic aerosols. Experiments were performed in a rotating wetted-wall reactor coupled to a mass spectrometer at room temperature (298 +/- 3 K) with 0-96 wt % H(2)SO(4) solutions. For all compounds, a reactive uptake was observed at high acidity (>or=64 wt % H(2)SO(4)). The corresponding reactions were found to follow a second-order kinetics, and their rate constants, k (M(-1) s(-1)) were found to increase exponentially with acidity. These rate constants and their variations with acid concentration were in good agreement with the kinetic behavior of acid-catalyzed aldol condensation reported in the organic chemical literature, except for 2,4-pentanedione. The results of this work suggest that aldol condensation should be too slow to account for the enhanced organic aerosol mass observed in smog chamber studies and should have an even smaller contribution under atmospheric conditions. The rate constants of other compounds, such as large aldehydes, remain however to be measured. However, in order to contribute significantly to organic aerosol formation, a liquid phase reaction would have to result in an uptake coefficient of the order of 10(-2). PMID:16331936

Esteve, Williams; Nozière, Barbara

2005-12-01

151

Investigation of Thermochemistry Associated with the Carbon-Carbon Coupling Reactions of Furan and Furfural Using ab Initio Methods.  

PubMed

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

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

2014-06-26

152

Drug Reactions  

MedlinePLUS

... adverse drug reaction. One medicine might cause an adverse reaction if it’s taken with another medicine. One way ... reaction. Are prescription medicines the only cause of adverse reactions? No. Even medicines that you don't need ...

153

Microwave-assisted, rhodium(III)-catalyzed N-annulation reactions of aryl and ?,?-unsaturated ketones with alkynes.  

PubMed

New Rh(III)-catalyzed, one-pot N-annulation reactions of aryl and ?,?-unsaturated ketones with alkynes in the presence of ammonium acetate have been developed. Under microwave irradiation conditions, the processes lead to rapid formation of the respective isoquinoline and pyridine derivatives with efficiencies that are strongly dependent on the steric nature of the aryl ring and enone substituents. By employing this protocol, a variety of isoquinoline and pyridine derivatives were prepared in high yields. In addition, a new one-pot approach to the synthesis of pyridines, involving four-component reactions of ketones, formaldehyde, NH(4)OAc, and alkynes, has been uncovered. This process takes place through a route involving initial aldol condensation of the ketone with formaldehyde to generate a branched ?,?-unsaturated ketone that then undergoes Rh(III)-catalyzed N-annulation with NH(4)OAc and the alkyne PMID:24516891

Lee, Hyejeong; Sim, Yong-Kyun; Park, Jung-Woo; Jun, Chul-Ho

2014-01-01

154

Total synthesis and structure revision of didemnaketal B.  

PubMed

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

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

2014-02-10

155

Understanding the mechanism of stereoselective synthesis of cyclopentenes via N-heterocyclic carbene catalyzed reactions of enals with enones.  

PubMed

The N-heterocyclic carbene (NHC) catalyzed addition of enals to enones to yield trans-cyclopentenes has been investigated using DFT methods at B3LYP/6-31G** computational level. This NHC catalyzed reaction comprises several steps. The first one is the formation of a Breslow intermediate, which nucleophilically attacks to the conjugated position of the enone to yield an enol-enolate. This second step is responsible for the trans relationship at the final cyclopentene. An intramolecular aldolic condensation allows for the formation of the alkoxy cyclopentane intermediate, that by intramolecular nucleophilic attack on the carbonyl group yields a bicyclic ether. The extrusion of the NHC catalyst affords a bicyclic lactone, yielding by CO(2) elimination, the final trans-cyclopentene. PMID:20740249

Domingo, Luis R; Zaragozá, Ramón J; Arnó, Manuel

2010-11-01

156

Stereocontrolled total synthesis of polygalolide?A.  

PubMed

The total synthesis of polygalolide?A, a secondary metabolite that was isolated from a Chinese medicinal plant, is reported. A key issue in this synthesis was construction of an oxabicyclo[3.2.1] skeleton, which was solved by the development of an intramolecular Ferrier-type C-glycosylation of a glucal with siloxyfuran as an internal nucleophile. The substrate was prepared from D-glucal by the introduction of trimethylsilylacetylene and siloxyfuran groups. Although C-glycosylation did not occur under the conditions found from model experiments, further examination revealed that the combination of trimethylsilyl trifluoromethanesulfonate (TMSOTf) and 2,4,6-collidine successfully afforded the desired product as a single diastereomer. The siloxy group at the C3 position played a crucial role in the stereocontrol of this reaction. The product was further transformed into a tetracyclic compound as follows: The vinyl ether and acetylenic moieties were reduced and the siloxy group was removed with a Barton-McCombie reaction. The construction of the six-membered ether and the ?-lactone provided the tetracyclic compound. Finally, a phenolic moiety was introduced by using a Mukaiyama aldol reaction to furnish polygalolide?A. PMID:23670825

Yamada, Hitomi; Adachi, Masaatsu; Isobe, Minoru; Nishikawa, Toshio

2013-07-01

157

Epoxide Reactions  

NASA Astrophysics Data System (ADS)

This puzzle presents 16 numbered reactions of epoxides and 11 possible products designated by letters. The reactions are matched with the letters corresponding to the products to answer a playful question.

Bertolini, Thomas

2002-07-01

158

Reaction time  

Microsoft Academic Search

Reviews five studies of reaction time published during 1917-1918. The Studies pertain to (a) effect of continuous, intermittent, continuous-intermittent auditory distraction upon sensory reactions to auditory stimuli (b) processes involved in the fore-period, main period and after-period of the controlled associative reaction with special reference to the analysis of fore-period (c) use of reaction key suspended as a pendulum and

V. A. C. Henmon

1918-01-01

159

Special Reactions  

NSDL National Science Digital Library

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

Robertson, William C.

2010-03-01

160

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

161

Enantioselective palladium-catalyzed total synthesis of vitamin e by employing a domino Wacker-Heck reaction.  

PubMed

An enantioselective total synthesis of vitamin E in which a novel palladium-catalyzed domino reaction was employed as the key step is described. This reaction allows the formation of the chiral chroman framework and the concurrent introduction of part of the side chain of vitamin E. The sequence comprises an enantioselective Wacker cyclization and a subsequent Heck reaction. Accordingly, reaction of alkenylphenol 12 with methyl vinyl ketone (13) in the presence of catalytic amounts of Pd(OTFA)(2) (TFA = trifluoroacetate), the enantiopure ligand (S,S)-Bn-BOXAX (8 b; Bn = benzyl, BOXAX = 2,2'-bis(oxazolyl)-1,1'-binaphthyl, and p-benzoquinone (9) as an oxidant gives access to chiral chroman 10 with an enantioselectivity of 97 % ee in 84 % yield. Chroman 10 is then converted into 24 by an aldol condensation reaction with (3R)-3,7-dimethyloctanal (11). Subsequent 1,2-addition of methyllithium, elimination of water, and hydrogenation yields vitamin E. PMID:17001611

Tietze, Lutz F; Stecker, Florian; Zinngrebe, Julia; Sommer, Konrad M

2006-11-24

162

Highly stereoselective synthesis of 3-amino-3,6-dideoxy-aldohexoses by tin triflate mediated aldol condensation reaction of tricarbonyl iron ?-aminodienone complexes. Total synthesis of multiprotected mycosamine  

Microsoft Academic Search

The divalent tin enol ether of the racemic N-BOC ?-aminodienone tricarbonyliron complex 4 reacts with both enantiomers of protected lactaldehydes to predominantly yield one optically active ketol diastereoisomer (45 %). From the enantiomerically pure complex (S)-(+)-4 and (R)-(+) tert butyldimethylsilyloxylactaldehyde this ketol is obtained almost alone (isolated 86 %). From there, the multi-protected 3-amino-3,6-dideoxy-d-aldohexose mycosamine is obtained in a few

Michel Franck-Neumann; Laurence Miesch-Gross; Christelle Gateau

1999-01-01

163

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

164

Reaction Kinetics  

NASA Astrophysics Data System (ADS)

Detonation, which is the result of a reacting high explosive, is not a simple chemical reaction. Instead it is a complex process of rapid chemical changes that give rise to equally rapid mechanical and physical changes. Initially, as the explosive is initiated or Subscriptjected to a stimulus such as a shock wave, energy is transferred to the material causing mechanical deformation and heating. The transferred energy and heating produce chemically excited species, leading to initial bond-breaking or reaction initiation. These processes are thought to occur in a Hot-Molecule Zone (HMZ). Once reaction is initiated, sequences of chemical reactions follow resulting in the liberation of chemical energy and the production of gaseous reaction products.

Peiris, Suhithi M.

165

[Periosteal reaction].  

PubMed

The periosteal membrane covers the cortical bone except for the articular surface. The deep layer of the periosteum contains bone-forming mesenchymal cells, capillaries, and nerves. This layer is more active in infants than in adults. Prostaglandin osteopathy, infantile cortical hyperostosis, hypervitaminosis A, and congenital syphilis are examples of periostitis in infants. Incidental asymptomatic periosteal reactions are usually either physiological changes or cortical bone irregularities simulating periostitis. On the other hand, symptomatic periosteal reactions of single bone, such as bone tumor, tumor-like lesion, infection, and trauma, are always pathologic. Careful radiological analysis of periosteal reactions is needed to evaluate the activity and aggressiveness of the lesions. Periosteal reactions of multiple bones usually show solid smooth or undulating patterns. They include pachydermoperiostosis, secondary hypertrophic osteoarthropathy, vascular insufficiency, renal osteodystrophy, and thyroid acropachy. These are usually skeletal manifestations of systemic disorders. PMID:10429428

Fukuda, K

1999-06-01

166

Drug Reactions  

MedlinePLUS

... can also cause unwanted reactions. One problem is interactions, which may occur between Two drugs, such as ... and diseases, such as aspirin and peptic ulcers Interactions can change the actions of one or both ...

167

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

168

Reaction time  

Microsoft Academic Search

Reviews the studies on RT by H. E. Burtt, A. T. Poffenberger, T. Topciu, and H. Woodrow (1915-1916). It was found that the with shorter intervals, the time of the 1st reaction was lengthened through the inhibiting and distracting influence of the 2nd stimulus. The RT to the cessation of sound and light stimuli and to beginning of the stimuli

V. A. C. Henmon

1916-01-01

169

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.

Industry, Oregon M.

1997-01-01

170

Organic reaction pathways in the nonaqueous synthesis of metal oxide nanoparticles.  

PubMed

Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods. PMID:16927442

Niederberger, Markus; Garnweitner, Georg

2006-09-25

171

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

172

Nuclear Chain Reaction  

NSDL National Science Digital Library

This simulation shows a chain reaction. The visitor can introduce a neutron and observe how it produces an additional reaction or escapes. The chain reaction can be paused in order to analyze the process.

Bauer, W. (Wolfgang), 1959-

2011-11-29

173

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

174

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

175

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

176

High Resolution Reaction Intermediates of rabbit Muscle Fructose-1,6-bisphosphate Aldolase: Substrate Cleavage and Induced Fit  

SciTech Connect

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

St-Jean,M.; Lafrance-Vanasse, J.; Liotard, B.; Sygusch, J.

2005-01-01

177

gem-Difluoroolefination of Diaryl Ketones and Enolizable Aldehydes with Difluoromethyl 2-Pyridyl Sulfone: New Insights into the Julia-Kocienski Reaction.  

PubMed

The direct conversion of diaryl ketones and enolizable aliphatic aldehydes into gem-difluoroalkenes has been a long-standing challenge in organofluorine chemistry. Herein, we report efficient strategies to tackle this problem by using difluoromethyl 2-pyridyl sulfone as a general gem-difluoroolefination reagent. The gem-difluoroolefination of diaryl ketones proceeds by acid-promoted Smiles rearrangement of the carbinol intermediate; the gem-difluoroolefination is otherwise difficult to achieve through a conventional Julia-Kocienski olefination protocol under basic conditions due to the retro-aldol type decomposition of the key intermediate. Efficient gem-difluoroolefination of aliphatic aldehydes was achieved by the use of an amide base generated in situ (from CsF and tris(trimethylsilyl)amine), which diminishes the undesired enolization of aliphatic aldehydes and provides a powerful synthetic method for chemoselective gem-difluoroolefination of multi-carbonyl compounds. Our results provide new insights into the mechanistic understanding of the classical Julia-Kocienski reaction. PMID:24807811

Gao, Bing; Zhao, Yanchuan; Hu, Mingyou; Ni, Chuanfa; Hu, Jinbo

2014-06-16

178

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

179

Oral Hypersensitivity Reactions  

MedlinePLUS

... although it is rare. Only 1% of the adverse reactions due to local anesthetics are considered truly allergic, ... an allergic response to the vast majority of adverse reactions attributed to local anesthetics are in reality caused ...

180

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.

181

Alkali-hydrogen reactions  

Microsoft Academic Search

Highly endoergic alkali-hydrogen reactions are usually initiated by electronic excitation of the alkali atom. This implies that non-adiabatic couplings take place along the reaction path, the collision mechanism being dominated by the electron transfer jump that occurs between the alkali atom and the hydrogen molecule. Since electronic excitation can be selectively achieved over many atomic states, these reactions constitute good

King-Chuen Lin; Raymond Vetter

2002-01-01

182

[Adverse reactions to vaccines].  

PubMed

Adverse reactions to vaccines are highly varied, ranging from mild local reactions to fatal outcomes. In the last few years many adverse reactions have been attributed to vaccines, often without justification. In agreement with the World Health Organization, these reactions can be classified as follows, depending on the cause: vaccination-induced reactions (due to an effect of the vaccine itself or to an idiosyncrasy); reactions due to errors in storage, manipulation and/or administration; and coincidental reactions (no causal relationship with the vaccine). Hypersensitivity reactions fall into six categories, depending on the causative agent: reactions due to some component of the infectious agent or one of its products; reactions due to adjuvants: aluminium hydroxide; reactions due to stabilizers: gelatin; reactions due to preservatives: thiomersal; reactions due to antibiotics: neomycin; and reactions due to a biological culture medium: chicken embryo cells. Allergic children should not be excluded from the normal vaccine calendar. Immunologically, allergic individuals are more susceptible to infection and to microbial and viral diseases, which often play an aggravating role. Rubella, whooping cough, and influenza usually exacerbate respiratory allergies. Non-vaccination carries a marked risk of contracting serious diseases such as poliomyelitis, tetanus, and diphtheria, etc. In a not too distant future, the techniques of genetic recombination and monoclonal antibody production will allow the creation of vaccines from organisms that cannot be cultivated in the laboratory or that produce small quantities of antigen. These techniques will also lead to identification of the antigens with the greatest immunogenic power and, consequently, to extremely pure vaccines. The adverse reactions to vaccines referred to our service account for between 0.59 % and 1.27 % of first visits in the last three years. We recorded a total of 48 adverse reactions to vaccines. Of these, 44 were attributed to the tetanus vaccine (92 %), 2 to the measles-mumps-rubella vaccine (4 %) and 2 to the meningitis A and C vaccine (4 %). Clinical features consisted of urticaria (11 cases), urticaria with angioedema (7 cases), pseudo-shock (5 cases), fever and urticaria (4 cases), local reactions (4 cases), persistent crying with exanthema (3 cases), giant local reactions with angioedema of the limb (3 cases), anaphylaxis (3 cases), fever > 39.5 C (2 cases), bronchospasm (1 case), and severe atopic dermatitis (1 case).A regimen of hyposensitization to tetanus toxoid was required in 20 patients (45 %); in three, this could not be completed due to generalized urticaria but all the patients presented protective titers with diluted vaccine. PMID:12783762

Eseverri, J L; Ranea, S; Marin, A

2003-01-01

183

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.

184

Noncanonical Reactions of Flavoenzymes  

PubMed Central

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

Sobrado, Pablo

2012-01-01

185

Immediate Contact Reactions  

Microsoft Academic Search

\\u000a Immediate contact reactions comprise a diverse spectrum of inflammatory skin reactions of both immune and nonimmune origin\\u000a and involving several often poorly characterized mechanisms and which can be caused by an enormous variety of chemicals and\\u000a proteins. Reactions range from sensory effects through local weal and flare to a more generalized response, but all generally\\u000a characterized by a rapid onset

David Basketter; Arto Lahti

186

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

187

New Serological Reactions in Syphilis.  

National Technical Information Service (NTIS)

The Nelson test was compared to the following reactions: the reactions to the lipidic antigens; the complement fixation reactions to the treponemic antigens, both pathogenic and nonpathogenic; and the immunofluorescence reaction. The sensitivity and respe...

M. E. Hadida M. Allinne J. Orfila

1966-01-01

188

Marketing Mix Reactions to Entry  

Microsoft Academic Search

Initial product, distribution, marketing expenditure, and price reactions by incumbents are examined for 115 entrants into oligopolistic markets. The most common reaction pattern is either no reaction or only a single reaction. It is very unusual for entrants to face reactions across the entire marketing mix. Reactions in the first two years after entry are explained as a function of

William T. Robinson

1988-01-01

189

Applications of Reaction Rate  

ERIC Educational Resources Information Center

This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

Cunningham, Kevin

2007-01-01

190

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

191

Thiol-catalysed radical-chain redox rearrangement reactions of benzylidene acetals derived from terpenoid diols.  

PubMed

The thiol-catalysed radical-chain redox rearrangement of cyclic benzylidene acetals derived from 1,2- and 1,3-diols of terpene origin has been investigated from both synthetic and mechanistic standpoints. The redox rearrangement was carried out either at ca. 70 degrees C (using Bu(t)ON=NOBu(t) as initiator) or at ca. 130 degrees C (using Bu(t)OOBu(t) as initiator) in the presence of triisopropylsilanethiol or methyl thioglycolate as catalyst; the silanethiol was usually more effective. This general reaction affords the benzoate ester of the monodeoxygenated diol, unless rearrangement of intermediate carbon-centred radicals takes place prior to final trapping by the thiol to give the product, in which case structurally rearranged esters are obtained. For the benzylidene acetals of 1,2-diols prepared by vicinal cis-dihydroxylation of 2-carene, alpha-pinene or beta-pinene, intermediate cyclopropylcarbinyl or cyclobutylcarbinyl radicals are involved and ring opening of these leads ultimately to unsaturated monocyclic benzoates. 1,2-Migration of the benzoate group in the intermediate beta-benzoyloxyalkyl radical sometimes also competes with thiol trapping during the redox rearrangement of benzylidene acetals derived from 1,2-diols. Redox rearrangement of the benzylidene acetal from carane-3,4-diol, obtained by cis-dihydroxylation of 3-carene, does not involve intermediate cyclopropylcarbinyl radicals and leads to benzoate ester in which the bicyclic carane skeleton is retained. The inefficient redox rearrangement of the relatively rigid benzylidene acetal from exo,exo-norbornane-2,3-diol is attributed to comparatively slow chain-propagating beta-scission of the intermediate 2-phenyl-1,3-dioxolan-2-yl radical, probably caused by the development of adverse angle strain in the transition state for this cleavage. Similar angle strain effects are thought to influence the regioselectivities of redox rearrangement of bicyclic [4.4.0]benzylidene acetals resulting from selected 1,3-diols, themselves prepared by reduction of aldol adducts derived from reactions of aldehydes with the kinetic lithium enolates obtained from menthone and from isomenthone. PMID:14664397

Dang, Hai-Shan; Roberts, Brian P; Tocher, Derek A

2003-11-21

192

[Allergic reactions to vaccines].  

PubMed

Allergic reactions after vaccination are very rare. Even if the vaccine is not clearly the cause of possible side effects, including possible allergic reactions occurring after vaccine administration, they should be reported to the appropriate authorized body. Allergic reaction occuring to other vaccine components are more likely than to the active agent, for instance to gelatine, egg protein, chicken protein, dextran, thimerosal, antimicrobials, etc. All patients with suspected allergy to vaccine components should be evaluated by an allergist. Immediate-type allergy skin testing should be performed in patients who appear to have had an allergic reaction after vaccination. This testing should help confirm that the reaction was IgE mediated and identify the responsible vaccine component. If the skin test result is negative, it is extremely unlikely that the patient will develop an allergic reaction and the patient can be vaccinated. In patients with suggestive history and positive skin tests results to vaccine components, the clinician can consider administering the alternative vaccine or the same vaccine in graded doses while observing the patient. Mild local reactions, fever, and other constitutional symptoms after vaccinations are not contraindications to subsequent doses. PMID:22930937

Turkalj, Mirjana; Erceg, Damir

2012-01-01

193

Chemical reactions with aerosols  

NASA Astrophysics Data System (ADS)

Chemical reactions of aerosol droplets with vapors are discussed. Examples are given in which liquid aerosols of 1-octadecene of narrow size distribution are converted to 1,2-dibromooctadecane with bromine vapor. It was shown that the chemical reaction in the droplet controls the kinetics of this process. The application of chemical reactions with aerosols to the formation of pure, uniform spherical particles of metal oxides is also described. Droplets of metal alkoxides rapidly react with water vapor to yield well-defined powders. The technique was used to prepare titanium dioxide, aluminum oxide, and particles consisting of both metal oxides. This procedure allows generation of powders of predetermined size and composition.

Matijevi?, Egon

194

Reaction interface in reduction  

SciTech Connect

When an oxide such as cobalt ferrite is reacted with hydrogen, a porous metal scale will form topochemically from its surface. The pores in the metal scale permit the reducing gas to reach the reaction interface directly. At the pore bottoms the parent oxide is then destroyed by the reduction process, the oxygen is removed in the form of water vapor, and the cations that are produced at the pore bottoms are transported to the adjacent metal phase. The purpose of the present paper is to clarify the processes occurring at the metal/oxide reaction interface, and to determine which subprocesses are most important in determining the interface reaction rates.

Chang, M.; De Jonghe, L.C.

1980-07-01

195

Anaphylaxis-Like Reactions  

MedlinePLUS

... Like Reactions Reviewed on 7/12 By Dr. Alam Rafeul Alam, MD, PhD Dept. of Medicine Chief, Division of ... Doctors Who Treat Anaphlyaxis Rohit K. Katial Rafeul Alam Donna L. Bratton Michael Miller Tho Q. Truong ...

196

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

197

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...

198

Translated chemical reaction networks.  

PubMed

Many biochemical and industrial applications involve complicated networks of simultaneously occurring chemical reactions. Under the assumption of mass action kinetics, the dynamics of these chemical reaction networks are governed by systems of polynomial ordinary differential equations. The steady states of these mass action systems have been analyzed via a variety of techniques, including stoichiometric network analysis, deficiency theory, and algebraic techniques (e.g., Gröbner bases). In this paper, we present a novel method for characterizing the steady states of mass action systems. Our method explicitly links a network's capacity to permit a particular class of steady states, called toric steady states, to topological properties of a generalized network called a translated chemical reaction network. These networks share their reaction vectors with their source network but are permitted to have different complex stoichiometries and different network topologies. We apply the results to examples drawn from the biochemical literature. PMID:24610094

Johnston, Matthew D

2014-05-01

199

[Paranoid reactions and culture].  

PubMed

Paranoid Reaction (or bouffée délirante) according to the french classification was the basic psychosis of primitive societies. It corresponds to a need of defense of restructuration or restitution according to a pattern of "misconduction" admitted by the cultural environment. Paranoid reaction, in this respect, offers some relative good pronostic as soon as the goal is reached even if the previous personality remains modified. Paranoid reaction may get closer to hysterical crepuscular states. Some symptoms may also evoke schizophrenias. Evolution toward a lasting psychosis may be considered only in case the process of deculturation/acculturation is already engaged in an irreversible way and the defensive mode presented in the new cultural system shows schizophrenic patterns. Quick transformations and strong cultural pressures, trough that primitive societies are going, might increase dramatically chronic evolution of paranoid reactions. A case has been related to illustrate those considerations. PMID:3448958

Sizaret, P; Degiovanni, A; Faure, M

1987-09-01

200

Iodine Clock Reaction.  

ERIC Educational Resources Information Center

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

Mitchell, Richard S.

1996-01-01

201

Chemical Reactions and Pancakes  

NSDL National Science Digital Library

Students will compare ingredients in two different pancake recipes, then taste the difference. We will talk about the chemical reaction that happened when the recipes are mixed and why there are bubbles in the pancakes.

202

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.

Foundation, Wgbh E.

2009-12-07

203

Jets in hadronic reactions  

SciTech Connect

Recent experimental data on the properties of jets in hadronic reactions are reviewed and compared with theoretical expectations. Jets are clearly established as the dominant process for high E/sub T/ events in hadronic reactions. The cross section and the other properties of these events are in qualitative and even semiquantitative agreement with expectations based on perturbative QCD. However, we can not yet make precise tests of QCD, primarily because there are substantial uncertainties in the theoretical calculations. 45 references. (WHK)

Paige, F.E.

1983-01-01

204

Predicting Idiosyncratic Drug Reactions  

Microsoft Academic Search

Idiosyncratic drug reactions (IDR) remain an important cause of late development program failure or drug withdrawal. They\\u000a represent a significant economic cost and patient burden. Although our understanding of IDR continues to grow, our ability\\u000a to predict and avoid these reactions remains unacceptably poor. The intent of this chapter is to review approaches that may\\u000a be used during lead optimization

Alastair Cribb

205

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

206

Ligase Chain Reaction  

Microsoft Academic Search

\\u000a Nucleic acid amplification technologies have greatly facilitated medical diagnostics for genetic and infectious diseases through\\u000a the exquisite sensitivity and specificity associated with these methods. Polymerase chain reaction (PCR) (see\\u000a Chapter 6) ushered in these technologies and was soon accompanied by numerous newly developed amplification techniques, including\\u000a ligase chain reaction (LCR). These nucleic acid amplification techniques result in the exponential increase

Carla Osiowy

207

Phototoxic and Photoallergic Reactions  

Microsoft Academic Search

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

Margarida Gonçalo

208

Immediate reaction to clarithromycin.  

PubMed

We present the case of bronchospastic reaction to clarithromycin had during a drug challenge test. Personal allergic history was negative for respiratory allergies and positive for adverse drug reactions to general and regional anesthesia and to ceftriaxone. After the administration of 1/4 of therapeutic dose of clarithromycin the patient showed dyspnea, cough and bronchospasm in all the lung fields. The positivity of the test was confirmed by the negativity to the administration of placebo. The quickness and the clinical characteristic of the adverse reaction suggest a pathogenic mechanism of immediate-type hypersensitivity. On reviewing the literature we have found no reports of bronchospastic reaction to clarithromycin. Macrolides are a class of antibiotics mainly used in the last years in place of beta-lactams because of a broad spectrum of action and a low allergic power. In fact, there are few reports on allergic reactions to these molecules. Clarithromycin is one of the latest macrolides, characterised by the presence of a 14-carbon-atom lactone ring as erythromycin, active on a wide spectrum of pathogens. PMID:11449533

Gangemi, S; Ricciardi, L; Fedele, R; Isola, S; Purello-D'Ambrosio, F

2001-01-01

209

Transfer reactions with HELIOS  

NASA Astrophysics Data System (ADS)

Nucleon-transfer reactions have formed the backbone of nuclear- structure studies for several decades, providing a wealth of information about the energies, quantum numbers, and wave functions of single-particle states in nuclei throughout the nuclear chart. Current trends in nuclear-structure physics and the modern emphasis on properties of neutron-rich nuclei far from stability have renewed interest in such transfer reactions with radioactive beams. Here, the usual combination of light beam and heavy target cannot be used, and measurements must be performed in "inverse kinematics," with a heavy, unstable beam incident on a light target. This arrangement introduces several technical difficulties, including the identification of the reaction products and the resolution of the states of interest in the residual nuclei. A new device, HELIOS (the HELIcal Orbit Spectrometer) at the ATLAS facility at Argonne National Laboratory, solves many of the problems encountered with inverse kinematics including particle identification and energy resolution in the center-of-mass frame. The device utilizes the uniform magnetic field of a large, superconducting solenoid to transport light reaction products from the target to a linear array of position-sensitive silicon detectors. The properties of HELIOS will be described, and examples from the initial research program that focuses on neutron transfer with the (d,p) reaction, using both stable and unstable beams with mass A=11 to 136, will be presented.

Wuosmaa, Alan H.

2011-04-01

210

Reaction/Momentum Wheel  

NASA Technical Reports Server (NTRS)

CTA Space Systems, Inc. has been licensed to sell commercially a reaction/momentum wheel originally developed for NASA's scientific satellites. NASA originally identified a need for the wheel in its Small Explorer program. The Submillimeter Wave Astronomy Satellite required extremely low jitter and a reaction/momentum wheel with a torque greater than any comparably sized commercially available wheel to keep the instrument pointed at celestial objects to a high degree of precision. After development, a market assessment by Research Triangle Institute was completed, showing commercial potential for the flywheel technology. A license was granted to CTA in the fall of 1996. The company currently uses the technology in its complete spacecraft fabrication services and has built over 10 reaction/momentum wheels for commercial, scientific, and military customers.

1997-01-01

211

Nanoparticle Reactions on Chip  

NASA Astrophysics Data System (ADS)

The handling of heterogenous systems in micro reactors is difficult due to their adhesion and transport behaviour. Therefore, the formation of precipitates and gas bubbles has to be avoided in micro reaction technology, in most cases. But, micro channels and other micro reactors offer interesting possibilities for the control of reaction conditions and transport by diffusion and convection due to the laminar flow caused by small Reynolds numbers. This can be used for the preparation and modification of objects, which are much smaller than the cross section of microchannels. The formation of colloidal solutions and the change of surface states of nano particles are two important tasks for the application of chip reactors in nanoparticle technology. Some concepts for the preparation and reaction of nanoparticles in modular chip reactor arrangements will be discussed.

Köhler, J. M.; Kirner, Th.; Wagner, J.; Csáki, A.; Möller, R.; Fritzsche, W.

212

Hypersensitivity reaction to desipramine.  

PubMed

Adverse reactions to the tricyclic antidepressant drugs imipramine and desipramine have been described and include eosinophilia, pulmonary infiltrates with eosinophilia, and elevated total serum IgE levels. The immunologic mechanism accounting for these adverse reactions has not been elucidated. This article describes a patient manifesting bronchospasm, profound eosinophilia, and elevated serum IgE levels after therapy with desipramine that resolved rapidly after withdrawal of the drug. Immunologic investigations failed to demonstrate specific IgE directed against a protein conjugate of desipramine but demonstrated the ability of desipramine to induce mast cell degranulation with direct intradermal skin challenges. PMID:3598027

Panuska, J R; King, T R; Korenblat, P E; Wedner, H J

1987-07-01

213

Velocity pump reaction turbine  

DOEpatents

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

House, Palmer A. (Walnut Creek, CA)

1982-01-01

214

Velocity pump reaction turbine  

DOEpatents

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

House, Palmer A. (Walnut Creek, CA)

1984-01-01

215

Foreign Media Reaction  

NSDL National Science Digital Library

This Daily Digest of foreign media reaction, prepared Monday through Friday by the United States Information Agency, is a valuable addition to any course that discusses US foreign policy or current events. "Each Digest provides a global round-up of editorial and op-ed reaction to a major foreign policy issue or event. The reports include commentary--sorted by country and region--from major newspapers, magazines and broadcast media around the world." The searchable archive section contains all Daily Digests published since November 1994.

Agency., United S.

1994-01-01

216

Reaction Time and Intelligence.  

ERIC Educational Resources Information Center

Measurements of various parameters derived from different reaction time (RT) paradigms are found to be correlated with psychometric measurements of general mental ability. Such RT-derived measurements, when combined in a multiple regression equation, predict some 50 percent or more of the variance in intelligence. This relationship of intelligence…

Jensen, Arthur R.

217

Reactions to Others' Intimacy.  

ERIC Educational Resources Information Center

Research using behavioral measures has indicated that men react less positively to the touch of a same sex individual than women, that both men and women react more positively to the touch of an opposite sex individual than to the touch of a same sex individual, and that men and women do not differ in their reactions to opposite sex touch. This…

Neufeldt, David E.; Olinger, Evanelle J.

218

Lithium Cell Reactions.  

National Technical Information Service (NTIS)

The objectives of Part 1 of this program were to (i) investigate reactions occurring in the Li/SOCl2 cell for a range of specified test conditions and (ii) to perform analyses to identify reactants, intermediates and products generated by the chemical and...

W. Clark F. Dampier R. McDonald A. Lombardi D. Batson

1985-01-01

219

Types of Allergic Reactions  

MedlinePLUS

... teeth and mouth change in every stage of life. More RSS Feeds Get dental news feeds delivered directly to your desktop! more... ... are mild, while others can be severe and life-threatening. Allergic reactions often occur more frequently in people with ... Have an Allergy-Free Dental Visit What is Latex Allergy?

220

Quinoprotein-catalysed reactions.  

PubMed Central

This review is concerned with the structure and function of the quinoprotein enzymes, sometimes called quinoenzymes. These have prosthetic groups containing quinones, the name thus being analogous to the flavoproteins containing flavin prosthetic groups. Pyrrolo-quinoline quinone (PQQ) is non-covalently attached, whereas tryptophan tryptophylquinone (TTQ), topaquinone (TPQ) and lysine tyrosylquinone (LTQ) are derived from amino acid residues in the backbone of the enzymes. The mechanisms of the quinoproteins are reviewed and related to their recently determined three-dimensional structures. As expected, the quinone structures in the prosthetic groups play important roles in the mechanisms. A second common feature is the presence of a catalytic base (aspartate) at the active site which initiates the reactions by abstracting a proton from the substrate, and it is likely to be involved in multiple reactions in the mechanism. A third common feature of these enzymes is that the first part of the reaction produces a reduced prosthetic group; this part of the mechanism is fairly well understood. This is followed by an oxidative phase involving electron transfer reactions which remain poorly understood. In both types of dehydrogenase (containing PQQ and TTQ), electrons must pass from the reduced prosthetic group to redox centres in a second recipient protein (or protein domain), whereas in amine oxidases (containing TPQ or LTQ), electrons must be transferred to molecular oxygen by way of a redox-active copper ion in the protein.

Anthony, C

1996-01-01

221

High Temperature Reaction Calorimetry.  

National Technical Information Service (NTIS)

A hot-zone reaction calorimeter is described and tested by measuring the enthalpies of reduction of copper and lead oxides by hydrogen gas. The heats of formation of these oxides, in various modifications and crystal structures, were determined. The therm...

G. Pilcher H. A. Skinner L. Espada L. Nunez

1970-01-01

222

Exocharmic Reactions up Close  

ERIC Educational Resources Information Center

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

Ramette, R. W.

2007-01-01

223

Lithium Cell Reactions.  

National Technical Information Service (NTIS)

The objectives of this program were: (1) investigate reactions occurring in the Li/SOCL2 cell for a range of specified test conditions and (2) perform detailed analyses for impurities present in cell components, assess the impact of each impurity on cell ...

W. Clark F. Dampier A. Lombardi T. Cole

1983-01-01

224

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

225

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.

226

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

227

Organic Reactions and Biofuels  

NSDL National Science Digital Library

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

2011-02-16

228

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.

229

Online Access: User Reaction.  

ERIC Educational Resources Information Center

Surveys reactions of students and faculty to the online circulation system at University of Guelph Library, Ontario. Findings concerning status of users, frequency of use, effectiveness of instructions on screen, convenience of terminal locations, type of information required by user, and general comments are noted. Four references are provided.…

Pawley, Carolyn

1982-01-01

230

Gas Producing Micro-Reaction  

NSDL National Science Digital Library

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

House, The S.

2014-01-28

231

What Is a Reaction Rate?  

ERIC Educational Resources Information Center

The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

Schmitz, Guy

2005-01-01

232

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

233

Magnetically suspended reaction wheels  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

234

Heat Speeds Up Reactions  

NSDL National Science Digital Library

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

Shaw, Maisie; Gomez, Maria

2009-01-01

235

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

236

Hypersensitivity reactions to fluoroquinolones  

Microsoft Academic Search

Fluoroquinolone antibiotics cause immediate and delayed hypersensitivity reactions, and may also affect internal organs and\\u000a circulating blood cells. The underlying pathomechanisms are only partly understood. The extent of cross-reactivity among different\\u000a quinolones depends on the type of clinical manifestation and its underlying mechanism. Despite recent advances, reliable diagnostic\\u000a tests are still lacking. Recent studies have shown quinolone-specific IgE in vitro

Kathrin Scherer; Andreas J. Bircher

2005-01-01

237

The Gewald multicomponent reaction  

Microsoft Academic Search

The Gewald reaction of sulfur, cyanoacetic acid derivatives, and oxo-component (G-3CR) yielding highly substituted 2-aminothiophene\\u000a derivatives has seen diverse applications in combinatorial and medicinal chemistry. Its products are of great use in pharmaceutical\\u000a industry mainly as small molecular weight inhibitors. We herein review synthetic scope and variations, usage, and structural\\u000a biology of Gewald products.

Yijun Huang; Alexander Dömling

2011-01-01

238

Allergic reactions to fish  

Microsoft Academic Search

A wide variety of fish are known to induce allergic reactions following ingestion or inhalation of vapors by sensitized individuals.\\u000a Although the exact prevalence of fish sensitivity is not known, fish are among the most important food allergens; and as consumption\\u000a of fish increases, rates of sensitization are expected to increase. Diagnosis of fish allergy is aided by clinical history,

Carol O’Neil; Arthur A. Helbling; Samuel B. Lehrer

1993-01-01

239

Chemical reaction dynamics  

PubMed Central

Understanding the motions of the constituent atoms in reacting molecules lies at the heart of chemistry and is the central focus of chemical reaction dynamics. The most detailed questions one can ask are about the evolution of molecules prepared in a single quantum state to products in individual states, and both calculations and experiments are providing such detailed understanding of increasingly complex systems. A central goal of these studies is uncovering the essential details of chemical change by removing the averaging over the initial conditions that occurs in many cases. Such information provides an exquisite test of theory and helps paint pictures of complicated chemical transformations. The goal of this Special Feature is to provide a snapshot of a portion of the field of chemical reaction dynamics. Much of the work presented here emphasizes a close interplay of experiment and theory in ways that sharpen the conclusions of both and animate future studies. The articles do not completely cover the rich field of chemical reaction dynamics but rather provide a glimpse of some of the emerging insights.

Crim, F. Fleming

2008-01-01

240

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

241

The heterogeneous explosive reaction zone  

SciTech Connect

The calculated reaction zone of PBX-9404 using solid HMX Arrhenius kinetics is stable to perturbations. The calculated reaction zone Von Neumann spike pressure agrees with the experimental observations within experimental uncertainty associated with different experimental techniques. The calculated homogengeous explosive reaction zone thickness is larger than observed for the heterogeneous explosive. The effect of two volume percent air holes on the reaction zone was modeled using the three-dimensional Eulerian reactive hydrodynamic code, 3DE. The air holes perturb the reaction zone. A complicated, time-dependent, multidimensional reaction region proceeds through the heterogeneous explosive. The experimentally observed reaction zone characteristic of heterogeneous explosives are mean values of an irregular, three-dimensional reaction region. 20 refs., 6 figs.

Mader, C.L.; Kershner, J.D.

1989-01-01

242

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.

House, The S.

2014-01-28

243

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

244

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

245

Demonstration of the Fenton Reaction  

ERIC Educational Resources Information Center

The study demonstrates the Fenton reaction, which is carried out using the Fenton reagent that is used for groundwater and soil remediation. The Fenton reaction can be implicated in DNA damage, Alzheimer's disease, cardiovascular disease and ageing in general.

Luehrs, Dean C.; Roher, Alex E.

2007-01-01

246

Filtering Crucible-Reaction Vessel.  

National Technical Information Service (NTIS)

A brief description is given of the conversion of a filtering crucible to a reaction vessel in order to eliminate the need for transfering reaction products when performing gravimetric quantitative determinations with sub-milligram quantities.

T. McCullough

1967-01-01

247

Insect bite reactions.  

PubMed

Insects are a class of living creatures within the arthropods. Insect bite reactions are commonly seen in clinical practice. The present review touches upon the medically important insects and their places in the classification, the sparse literature on the epidemiology of insect bites in India, and different variables influencing the susceptibility of an individual to insect bites. Clinical features of mosquito bites, hypersensitivity to mosquito bites Epstein-Barr virus NK (HMB-EBV-NK) disease, eruptive pseudoangiomatosis, Skeeter syndrome, papular pruritic eruption of HIV/AIDS, and clinical features produced by bed bugs, Mexican chicken bugs, assassin bugs, kissing bugs, fleas, black flies, Blandford flies, louse flies, tsetse flies, midges, and thrips are discussed. Brief account is presented of the immunogenic components of mosquito and bed bug saliva. Papular urticaria is discussed including its epidemiology, the 5 stages of skin reaction, the SCRATCH principle as an aid in diagnosis, and the recent evidence supporting participation of types I, III, and IV hypersensitivity reactions in its causation is summarized. Recent developments in the treatment of pediculosis capitis including spinosad 0.9% suspension, benzyl alcohol 5% lotion, dimethicone 4% lotion, isopropyl myristate 50% rinse, and other suffocants are discussed within the context of evidence derived from randomized controlled trials and key findings of a recent systematic review. We also touch upon a non-chemical treatment of head lice and the ineffectiveness of egg-loosening products. Knockdown resistance (kdr) as the genetic mechanism making the lice nerves insensitive to permethrin is discussed along with the surprising contrary clinical evidence from Europe about efficacy of permethrin in children with head lice carrying kdr-like gene. The review also presents a brief account of insects as vectors of diseases and ends with discussion of prevention of insect bites and some serious adverse effects of mosquito coil smoke. PMID:23442453

Singh, Sanjay; Mann, Baldeep Kaur

2013-01-01

248

Reactions among indoor pollutants.  

PubMed

This paper reviews recent studies in the field of "indoor chemistry"--reactions among indoor pollutants. Advances have occurred in a number of areas. A mouse bioassay procedure has shown that ozone/terpene reactions produce products that are more irritating than their precursors, although the agents responsible for the deleterious effects remain to be determined. Indoor ozone/terpene reactions have been demonstrated to produce hydroxyl radicals, hydrogen peroxide, sub-micron particles, and ultrafine particles. New analytical techniques such as LC/MS and thermal desorption mass spectrometry have greatly improved our knowledge of the condensed-phase species associated with such particles. Indeed, the latter approach has identified a number of short-lived or thermally labile species, including organic hydroperoxides, peroxy-hemiacetals, and secondary ozonides, which would be missed by more conventional techniques. Investigators are making inroads into the poorly understood area of indoor heterogeneous chemistry. Systems studied include ozone/HVAC components, ozone/paint, and ozone/carpets. Another heterogeneous process that has been further examined is the indoor formation of nitrous acid through NO2/surface chemistry. Emissions from indoor sources that contribute to, or are altered by, indoor chemistry have also received attention. Researchers have expanded our awareness of reactive chemicals that can emanate from wood coatings and other products commonly used indoors. In a related vein, a number of recent investigations have shown that emissions from materials can be significantly altered by indoor chemistry. On the theoretical side, an outdoor atmospheric chemistry model has been modified for use as an indoor air model, the effects of ventilation rates on indoor chemistry have been simulated, and initial steps have been taken in applying computational fluid dynamics (CFD) methods to indoor chemistry. PMID:12806061

Weschler, C J

2001-09-13

249

Laser induced nuclear reactions  

NASA Astrophysics Data System (ADS)

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

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

1998-12-01

250

Ionic Reactions in Gaseous Acetylene.  

National Technical Information Service (NTIS)

Mass spectrometric studies of ionic reactions in acetylene have been made which gave rate constants of .9 and 1.3 x 10 to the -9th power cc/molecule-sec. for reaction of C2H2(+) and C2H(+). Consecutive ionic reactions were observed giving ionic species up...

M. S. B. Munson

1964-01-01

251

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.

House, The S.

2014-01-28

252

Mass Transfer with Chemical Reaction.  

ERIC Educational Resources Information Center

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

DeCoursey, W. J.

1987-01-01

253

Monotonicity in chemical reaction systems  

Microsoft Academic Search

This article discusses the question of when the dynamical systems arising from chemical reaction networks are monotone, preserving an order induced by some proper cone. The reaction systems studied are defined by the reaction network structure while the kinetics is only constrained very weakly. Necessary and sufficient conditions on cones preserved by these systems are presented. Linear coordinate changes which

Murad Banaji

2009-01-01

254

Nucleophilic Substitution and Elimination Reactions  

NSDL National Science Digital Library

These pages show the basic mechanism for nucleophilic substition and elimination reactions of alkyl halides. The mechanisms for alcohols are similar. Animated GIFs and controllable Flash animations illustrate SN1, SN2, E1 and E2 reactions. The Flash animations were constructed using AM1 reaction path calculations.

Berger, Dan

255

The redox-Mannich reaction.  

PubMed

A complement to the classic three-component Mannich reaction, the redox-Mannich reaction, utilizes the same starting materials but incorporates an isomerization step that enables the facile preparation of ring-substituted ?-amino ketones. Reactions occur under relatively mild conditions and are facilitated by benzoic acid. PMID:24857691

Chen, Weijie; Seidel, Daniel

2014-06-01

256

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

257

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

258

Multisite reversible geminate reaction.  

PubMed

We provide an analytic solution for diffusion-influenced geminate reaction with multiple (N) reversible binding sites (of which one may be irreversible). The solution obtained in the Laplace domain, for two different initial conditions, is valid for the case when the sites are overlapping spheres with no long-range interactions with the diffusing particle. The possibility to invert into the time domain is determined by a characteristic polynomial. When all its roots are distinct, it is possible to apply the Lagrange interpolation formula and obtain a partial-fraction expansion that can be termwise inverted. At long times the occupancy of all sites, and for all initial conditions, decays as t(-3/2). The behavior at short times depends on the initial condition: when starting from contact, the binding probability rises as t(1/2), but if the particle is initially bound to one of the sites, the occupancy of the others rises as t(3/2). In between these two power laws we observe an intermediate-time kinetics consisting of N decaying exponentials. Those which are slower than a characteristic diffusion time are in the reaction-control regime and fit a discrete-state kinetic approximation with no adjustable parameters, whereas the faster kinetic steps are diffusion controlled. The model solved herein may depict a wide range of physical situations, from multisite proton transfer kinetics to hydrogen-bond dynamics of liquid water. PMID:19239302

Park, Soohyung; Agmon, Noam

2009-02-21

259

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.

2013-01-01

260

Polymerase chain reaction  

SciTech Connect

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

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

1990-10-01

261

Laser induced nuclear reactions  

SciTech Connect

Dramatic improvements in laser technology since 1984 have revolutionised high power laser technology. Application of chirped-pulse amplification techniques has resulted in laser intensities in excess of 10{sup 19} W/cm{sup 2}. In the mid to late eighties, C. K. Rhodes and K. Boyer discussed the possibility of shining laser light of this intensity onto solid surfaces and to cause nuclear transitions. In particular, irradiation of a uranium target could induce electro- and photofission in the focal region of the laser. In this paper it is shown that {mu}Ci of {sup 62}Cu can be generated via the ({gamma},n) reaction by a laser with an intensity of about 10{sup 19} Wcm{sup -2}.

Ledingham, Ken; McCanny, Tom; Graham, Paul; Fang Xiao; Singhal, Ravi; Magill, Joe; Creswell, Alan; Sanderson, David; Allott, Ric; Neely, David; Norreys, Peter; Santala, Marko; Zepf, Matthew; Watts, Ian; Clark, Eugene; Krushelnick, Karl; Tatarakis, Michael; Dangor, Bucker; Machecek, Antonin; Wark, Justin [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); European Commission, Institute for Transuranic Elements, Karlsruhe, Postfach 2340, D-76125 (Germany); Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU (United Kingdom); Rutherford Appleton Laboratory, Chilton, Didcot (United Kingdom); Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom); Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU (United Kingdom)

1998-12-16

262

OH + HBr reaction revisited  

SciTech Connect

Variable-temperature measurements of the rate coefficient /k(1)/ for the reaction OH + HBr yield Br + H2O are presented. The measurements are verified by two techniques: one involved a 266-nm pulsed-laser photolysis of O3/H2O/HBr/He mixtures in conjunction with time-resolved resonance fluorescence detection of OH, the second comprised pulsed laser-induced fluorescence detection of OH following 248-nm pulsed-laser photolysis of H2O2/HBr/Ar mixtures. It is reported that k(1) = (11.9 + or -1.4 x 10 to the -12th (cu cm)/(molecule)(s) independent of temperature. The measurements are compared with other available results. 6 references.

Ravishankara, A.R.; Wine, P.H.; Wells, J.R.

1985-07-01

263

Reactions to community noise  

NASA Technical Reports Server (NTRS)

Most of the research on reactions of people to community noise is divided into studies of annoyance as measured by attitude surveys and annoyance as measured by complaint behavior, including legal actions. This research has provided means of testing the concept promulgated over 20 years ago that the average amount of noise energy from significant sources that intrudes daily into houses and living areas can be used to predict the impact of the noise on people in a community. However, research data on annoyance and complaint behavior collected over the past 10 to 20 years have shown that there are significant limitations and variables that must be considered in the fair application of the noise energy concept in its simplest form.

1984-01-01

264

Adverse reactions to vaccines.  

PubMed

(The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.) Immunization healthcare is becoming increasingly complex as the number and types of vaccines have continued to expand. Like all prescription drugs, vaccines may be associated with adverse events. The majority of these reactions are self-limited and not associated with prolonged disability. The media, Internet and public advocacy groups have focused on potentially serious vaccine-associated adverse events with questions raised about causal linkages to increasing frequencies of diseases such as autism and asthma. Despite a lack of evidence of a causal relationship to a variety of vaccine safety concerns, including extensive reviews by the Institute of Medicine, questions regarding vaccine safety continue to threaten the success of immunization programs. Risk communication arid individual risk assessment is further challenged by the public health success of vaccine programs creating the perception that certain vaccines are no longer necessary or justified because of the rare reaction risk. There is a need for improved understanding of true vaccine contraindications and precautions as well as host factors and disease threat in order to develop a patient specific balanced risk communication intervention. When they occur, vaccine related adverse events must be treated, documented and reported through the VAERS system. The increasing complexity of vaccination health care has led the Center of Disease Control and Prevention (CDC) to identify Vaccine Safety Assessment and Evaluation as a potential new specialty. PMID:12721397

Martin, Bryan L; Nelson, Michael R; Hershey, Joyce N; Engler, Renata J M

2003-06-01

265

Rapid biocatalytic polytransesterification: Reaction kinetics in an exothermic reaction  

SciTech Connect

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

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

1998-08-20

266

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

267

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

268

NIF Gamma Reaction History  

NASA Astrophysics Data System (ADS)

The primary objective of the NIF Gamma Reaction History (GRH) diagnostics is to provide bang time and burn width information based upon measurement of fusion gamma-rays. This is accomplished with energy-thresholded Gas Cherenkov detectors that convert MeV gamma-rays into UV/visible photons for high-bandwidth optical detection. In addition, the GRH detectors can perform ?-ray spectroscopy to explore other nuclear processes from which additional significant implosion parameters may be inferred (e.g., plastic ablator areal density). Implementation is occurring in 2 phases: 1) four PMT-based channels mounted to the outside of the NIF target chamber at ˜6 m from TCC (GRH-6m) for the 3e13-3e16 DT neutron yield range expected during the early ignition-tuning campaigns; and 2) several channels located just inside the target bay shield wall at ˜15 m from TCC (GRH-15m) with optical paths leading through the wall into well-shielded streak cameras and PMTs for the 1e16-1e20 yield range expected during the DT ignition campaign. This suite of diagnostics will allow exploration of interesting ?-ray physics well beyond the ignition campaign. Recent data from OMEGA and NIF will be shown.

Herrmann, H. W.; Kim, Y.; Young, C. S.; Mack, J. M.; McEvoy, A. M.; Hoffman, N. M.; Wilson, D. C.; Langenbrunner, J. R.; Evans, S.; Batha, S. H.; Stoeffl, W.; Lee, A.; Horsfield, C. J.; Rubery, M.; Miller, E. K.; Malone, R. M.; Kaufman, M. I.

2010-11-01

269

Two chamber reaction furnace  

DOEpatents

A vertical two chamber reaction furnace. 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.degree. and 800.degree. C.) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800.degree. to 950.degree. 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.

Blaugher, Richard D. (Evergreen, CO)

1998-05-05

270

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

271

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

272

SABIO Reaction Kinetics Database (Homepage)  

NSDL National Science Digital Library

The SABIO-RK (System for the Analysis of Biochemical Pathways - Reaction Kinetics) is a web-based application based on the SABIO relational database that contains information about biochemical reactions, their kinetic equations with their parameters, and the experimental conditions under which these parameters were measured. It aims to support modellers in the setting-up of models of biochemical networks, but it is also useful for experimentalists or researchers with interest in biochemical reactions and their kinetics. Information about reactions and their kinetics can be exported in SBML (Systems Biology Mark-Up Language) format.

Scientific Databases And Visualization Group At The Eml Research In Heidelberg, Germany

273

Reaction surface array diagnostic apparatus  

US Patent & Trademark Office Database

A reaction surface array diagnostic apparatus and method of making the same includes a substrate carrying a plurality of reaction surfaces and a gasket having a plurality of through bores, each alignable with one of the reaction surfaces and forming a fluid tight well about each reaction surface when the gasket is sealingly affixed to the substrate. In one aspect, the gasket and the substrate are mounted in a support. In another aspect, a plate having a plurality of through bores is mountable on the gasket and substrate. Clamp members engage opposite side edges of the plate, the gasket and the substrate.

2010-06-15

274

Speeding chemical reactions by focusing  

NASA Astrophysics Data System (ADS)

We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system parameters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate ~t-1/2 to very close to the perfect mixing rate, ~t-1.

Lacasta, A. M.; Ramírez-Piscina, L.; Sancho, J. M.; Lindenberg, K.

2013-04-01

275

ChemTeacher Resource: Oxidation Reduction Reactions  

NSDL National Science Digital Library

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

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

2011-01-01

276

Electrochemical Aspects of the Maillard Reaction and Related Reactions  

Microsoft Academic Search

The Maillard reaction of amino acids and reducing sugars is important for food flavor formation and for the biological ageing of living organisms. The redox nature of the reaction is examined by measurement of open-circuit galvanic cell potentials and by electrolytic methods including polarography and amperometry. Electrochemical detectors (ECD) designed on the basis of voltammetric principles are employed as useful

George P. Rizzi

2012-01-01

277

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

278

Stereoselective synthesis of protected threo-?-hydroxy- l-glutamic acid using a chiral aziridine  

Microsoft Academic Search

Threo-?-hydroxy-l-glutamic acid derivatives with different carboxylic acid protecting groups were stereoselectively prepared from a chiral aziridine-2-carboxylate using an aldol reaction, stereoselective ketone reduction, and aziridine ring transformation.

Chan Sun Park; Hawn Geun Choi; Hyunjoo Lee; Won Koo Lee

2000-01-01

279

Magnesium bromide mediated highly diastereoselective heterogeneous hydrogenation of olefins.  

PubMed

Palladium on carbon combined with magnesium bromide catalyzed hydrogenation of Baylis-Hillman olefins to afford the corresponding aldol derivatives in a highly syn-diastereoselective manner is described. [reaction: see text] PMID:11950359

Bouzide, Abderrahim

2002-04-18

280

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

Microsoft Academic Search

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

Antti Hartikka; Per I Arvidsson

2004-01-01

281

Predisposing Factors in Adverse Reactions to Drugs  

Microsoft Academic Search

Predisposing factors were sought in 118 patients who developed adverse drug reactions in hospital. Significantly more patients of 60 years and over, and more women than men, developed adverse drug reactions. Patients with reactions had more drugs before the development of the reaction than patients who did not develop reactions. A previous adverse drug reaction and a history of allergic

Natalie Hurwitz

1969-01-01

282

Isosinglet approximation for nonelastic reactions  

NASA Technical Reports Server (NTRS)

Group theoretic relations are derived between different combinations of projectile and secondary particles which appear to have a broad range of application in spacecraft shielding or radiation damage studies. These relations are used to reduce the experimental effort required to obtain nuclear reaction data for transport calculations. Implications for theoretical modeling are also noted, especially for heavy-heavy reactions.

Wilson, J. W.

1972-01-01

283

The Variance Reaction Time Model  

ERIC Educational Resources Information Center

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

Sikstrom, Sverker

2004-01-01

284

Theory of hybrid nuclear reactions  

SciTech Connect

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

Udagawa, T.

1983-01-01

285

Participants' Reactions to Computerized Testing.  

ERIC Educational Resources Information Center

This study investigated participants' reactions to computerized testing and assessed the practicability of this testing method in the classroom. A sample of 315 secondary-level students took a computerized and a printed version of a standardized aptitude test battery and a survey assessing their reactions to the computerized testing. Overall…

Moe, Kim C.; Johnson, Marilyn F.

286

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

287

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

288

Surrogate Nuclear Reactions using STARS  

SciTech Connect

The results from two surrogate reaction experiments using the STARS (Silicon Telescope Array for Reaction Studies) spectrometer are presented. The surrogate method involves measuring the particle and/or {gamma}-ray decay probabilities of excited nuclei populated via a direct reaction. These probabilities can then be used to deduce neutron-induced reaction cross sections that lead to the same compound nuclei. In the first experiment STARS coupled to the GAMMASPHERE {gamma}-ray spectrometer successfully reproduce surrogate (n,{gamma}) (n,n'{gamma}) and (n,2n{gamma}) cross sections on 155,156Gd using 3He-induced reactions. In the second series of experiments an energetic deuteron beam from the ESTU tandem at the Wright Nuclear Structure Lab at Yale University was used to obtain the ratio of fission probabilities for 238U/236U and 237U/239U populated using the 236,238U(d,d'f) and 236,238U(d,pf) reactions. Results from these experiments are presented and the implications for the surrogate reaction technique are discussed.

Bernstein, L.A.; Burke, J.T.; Church, J.A.; Ahle, L.; Cooper, J.R.; Hoffman, R.D.; Punyon, J.; Schiller, A.; Algin, E. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Plettner, C.; Ai, H.; Beausang, C.W.; Casten, R.F.; Hughes, R.; Ricard-McCutchan, E.; Meyer, D.; Ressler, J.J.; Caggiano, J.A.; Zamfir, N.V.; Amro, H. [A.W. Wright Nuclear Structure Laboratory, Yale University New Haven, CT 06520 (United States)] [and others

2005-05-24

289

Surrogate Nuclear Reactions using STARS  

SciTech Connect

The results from two surrogate reaction experiments using the STARS (Silicon Telescope Array for Reaction Studies) spectrometer are presented. The surrogate method involves measuring the particle and/or {gamma}-ray decay probabilities of excited nuclei populated via a direct reaction. These probabilities can then be used to deduce neutron-induced reaction cross sections that lead to the same compound nuclei. In the first experiment STARS coupled to the GAMMASPHERE {gamma}-ray spectrometer successfully reproduce surrogate (n,{gamma}), (n,n'{gamma}) and (n,2n{gamma}) cross sections on {sup 155,156}Gd using Gd {sup 3}He-induced reactions. In the second series of experiments an energetic deuteron beam from the ESTU tandem at the Wright Nuclear Structure Lab at Yale University was used to obtain the ratio of fission probabilities for {sup 238}U/ {sup 236}U and {sup 237}U/ {sup 239}U populated using the {sup 236,238}U(d,d'f) and {sup 236,238}U(d,pf) reactions. Results from these experiments are presented and the implications for the surrogate reaction technique are discussed.

Bernstein, L A; Burke, J T; Church, J A; Ahle, L; Cooper, J R; Hoffman, R D; Moody, K; Punyon, J; Schiller, A; Algin, E; Plettner, C; Ai, H; Beausang, C W; Casten, R F; Hughes, R; Ricard-McCutchan, E; Meyer, D; Ressler, J J; Caggiano, J A; Zamfir, N V; Amro, H; Heinz, A; Fallon, P; McMahan, M A; Macchiavelli, A O; Phair, L W

2004-10-26

290

Nuclear Structure and Reaction Mechanism Studies with Multinucleon Reactions  

SciTech Connect

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

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

2006-08-14

291

Magnetically suspended reaction wheel assembly  

NASA Technical Reports Server (NTRS)

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

Stocking, G.

1984-01-01

292

Catalytic Organometallic Reactions of Ammonia  

PubMed Central

Until recently, ammonia had rarely succumbed to catalytic transformations with homogeneous catalysts, and the development of such reactions that are selective for the formation of single products under mild conditions has encountered numerous challenges. However, recently developed catalysts have allowed several classes of reactions to create products with nitrogen-containing functional groups from ammonia. These reactions include hydroaminomethylation, reductive amination, alkylation, allylic substitution, hydroamination, and cross-coupling. This Minireview describes examples of these processes and the factors that control catalyst activity and selectivity.

Klinkenberg, Jessica L.

2012-01-01

293

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

294

Review of Tritium Conversion Reactions.  

National Technical Information Service (NTIS)

The chemical processes by which elemental tritium can be converted to tritiated water have been examined by reviewing the available literature on these processes. It would appear that gas phase conversion reactions at room temperature are slow and that th...

J. R. Robins F. E. Bartoszek K. B. Woodall

1984-01-01

295

Cellular Reactions Due to Infections.  

National Technical Information Service (NTIS)

Among the organism's defense mechanisms against bacterial and viral infections, those present in the secretions (liquids) seem to play a preeminent role; but it is nevertheless a good idea to consider here all of those cell reactions which constitute the ...

G. M. Pontiera

1967-01-01

296

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

297

Inclusive Tritium Stripping Reaction Theory  

NASA Astrophysics Data System (ADS)

The angular and energy distributions and the integrated cross-section of the inclusive two-nucleon transfer reaction with the participation of three-nucleon nucleus were calculated at intermediate energies.

Akhiezer, A. I.; Soznik, A. P.; Berezhnoy, Yu. A.

298

Color Changes Mark Polymer Reactions.  

ERIC Educational Resources Information Center

Describes how polydiacetylenes can be used as educational aids. These polymers have conjugated backbones, which cause changes in color when the polydiacetylenes undergo various chemical and physical processes. Diagrams summarize all chemical reactions and their associated color changes. (CS)

Krieger, James H.

1980-01-01

299

Computational perspectives in nuclear reactions  

NASA Astrophysics Data System (ADS)

Nuclear reactions are crucial to probe the structure of nuclei, in particular for unstable systems. They can also provide important astrophysical information. However, it is only in the last decade, as a wider variety of mechanisms are consistently included in the reaction model and more structure information is taken into account, that modelling nuclear reactions has become computationally intensive. In this talk I will give a snapshot of the state of the art calculations including some results on breakup and transfer reactions with light exotic nuclei. I will show some results on performance and will discuss the degree of parallelism in the codes as well as the bottlenecks we need to resolve when scaling up to Petaflops machines. Finally, I will conclude with a vision of where we would like to be in a decade.

Nunes, Filomena

2008-10-01

300

Hot-Water Reaction Turbine.  

National Technical Information Service (NTIS)

Under simplifying assumptions, the operation of a hot-water reaction turbine, based on the principle of Segner's waterwheel, was investigated theoretically. Its application as a temporary drive for a high-power generator and the possibilities for regulati...

J. Reinkenhof

1964-01-01

301

Adverse reactions to food additives  

Microsoft Academic Search

There are thousands of additives used by the food industry for a variety of purposes in the foods we eat. However, only a\\u000a small number have been implicated in causing adverse reactions in humans. Although there are reported cases of individuals\\u000a who have reactions to single additives, most of the medical literature involves patients with asthma or chronic idiopathic\\u000a urticaria\\/angioedema

Ronald A. Simon

2003-01-01

302

LATE REACTION, PERSISTENT REACTION AND DOUBTFUL ALLERGIC REACTION: THE PROBLEMS OF INTERPRETATION  

PubMed Central

The standard method of patch test reading is to read the test site for any positive allergy at 48 hr and then again at 72/96 hr. A late reading on the seventh day is also advised to exclude the irritant reaction (IR) and to notice some delayed development of allergic reaction. However, multiple visits are often difficult for the patient; therefore, this late reading is sometimes omitted. Here a case of plantar hyperkeratosis, due to allergic contact dermatitis, is reported with some insight into interpretation of the patch test. The patient showed delayed patch test reaction to formaldehyde and colophony, which has never been reported before.

Sarma, Nilendu

2009-01-01

303

Late reaction, persistent reaction and doubtful allergic reaction: the problems of interpretation.  

PubMed

The standard method of patch test reading is to read the test site for any positive allergy at 48 hr and then again at 72/96 hr. A late reading on the seventh day is also advised to exclude the irritant reaction (IR) and to notice some delayed development of allergic reaction. However, multiple visits are often difficult for the patient; therefore, this late reading is sometimes omitted. Here a case of plantar hyperkeratosis, due to allergic contact dermatitis, is reported with some insight into interpretation of the patch test. The patient showed delayed patch test reaction to formaldehyde and colophony, which has never been reported before. PMID:20049272

Sarma, Nilendu

2009-01-01

304

Reactions in microemulsions: Effect of thermal fluctuations on reaction kinetics  

NASA Astrophysics Data System (ADS)

In this paper we address the generic effects arising from the interplay of thermal fluctuations and reactions. This is accomplished by considering specifically the kinetics of reactions effected in microemulsion media. In the first part of this paper we consider the kinetics of the reaction A+B-->Ø in bicontinuous microemulsion media, wherein the solutes A and B are assumed to be preferentially attracted to water and oil, respectively, and Ø constitutes an inert product. We formulate the diffusion and reaction of these solutes in a field-theoretical framework within which the fluctuations of the background microemulsion are embedded. We then employ mean-field arguments and a perturbative Wilson-type renormalization group (RG) approach to discern the relevance, at long length scales, of the background fluctuations. Our analysis indicates that the dynamic fluctuations of the microemulsion prove irrelevant in impacting the asymptotic kinetics of the reaction. In view of the fact that our field-theoretic approach enables us to probe only the long time characteristics, moreover, only in the weak-coupling limit, in the second part of this paper we analyze similar issues in the context of the droplet phase of microemulsions. This enables us to surmount some of the restrictions placed upon the results of the first part of this paper. In the second part, our analysis focuses upon a simpler reaction, viz., A-->Ø, wherein the solute A which is present only in the water phase is anhiliated upon contact with the fluctuating interfaces of the droplets. We employ a standard diffusion equation framework to formulate the transport and reaction of A. The fluctuations of the microemulsion are manifest in the boundary condition positing the vanishing concentration of A. We then employ a perturbation scheme to the solution of the diffusion equation, and thereby discern the explicit effects of the fluctuations of the sinks. Our formulation enables, in a sequentially improvable asymptotic manner, the explicit computation of the time-dependent and the steady state fluctuation contributions to the reaction rate.

Ganesan, Venkat; Fredrickson, Glenn H.

2000-08-01

305

Nonlocality in Deuteron Stripping Reactions  

NASA Astrophysics Data System (ADS)

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

Timofeyuk, N. K.; Johnson, R. C.

2013-03-01

306

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,

307

Understanding the novolak synthesis reaction  

NASA Astrophysics Data System (ADS)

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

Bogan, Leonard E., Jr.

1993-09-01

308

Two Paired "Le Chatelier" Reactions  

NASA Astrophysics Data System (ADS)

We have created a two-week, two hour-per-week cyclic experiment, which pairs two reactions. These reactions, the acid catalyzed esterification to yield n-amyl acetate and the base catalyzed hydrolysis of n-amyl acetate are intended to serve as a first and last experiment respectively, of the second-semester laboratory for liberal arts students. Because of time constraints, we have modified these experiments so that no distillation is performed as a purification step. The notion of achieving yields beyond the equilibrium value is discussed in terms of the pragmatics of removing one of the products of an equilibrium. Because of this "Le Chatelier" aspect of each reaction, each of them may be pushed in practicality to completion, which is well beyond the equilibrium value expectation. Because of the cycle, the chemistry may be done on a scale well beyond the microscale approach with little loss of material.

Cawley, John J.

1995-07-01

309

Diffusion and Heterogeneous Reaction X. Kinetic Considerations of Surface Reactions.  

National Technical Information Service (NTIS)

A theoretical analysis is presented of the influence of the kinetic order of the heterogeneous surface reaction on the diffusive mass transport of the reactant through a cylinder with catalytic walls and catalytic end plate. Because of the relevance to ex...

C. M. Ablow H. Wise

1967-01-01

310

THE CALORIMETRY OF COMBUSTIONS AND RELATED REACTIONS: INORGANIC REACTIONS  

Microsoft Academic Search

A review is presented of calorimetric measurements of the heats of ; combustion and other reactions. The precision of the measurements is discussed, ; and possible sources of error in combustion calorimetry are considered. ; Measurement of the heats of formation of the oxides and other compounds is also ; discussed. Recent developments in calorimetry are described briefly, including ;

Holley; C. E. Jr

1962-01-01

311

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

312

Learning to Predict Chemical Reactions  

PubMed Central

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal (http://cdb.ics.uci.edu) under the Toolkits section.

Kayala, Matthew A.; Azencott, Chloe-Agathe; Chen, Jonathan H.

2011-01-01

313

Learning to predict chemical reactions.  

PubMed

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

2011-09-26

314

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

315

Chlorhexidine: uses and adverse reactions.  

PubMed

Chlorhexidine is increasingly being used not only as an antiseptic to prevent hospital infections and an adjuvant in oral hygiene but also as a preservative in personal care products. As exposure to the agent becomes more widespread, reports of adverse reactions to it are increasing. Complications range from mild irritant contact dermatitis to life-threatening anaphylaxis. Allergic contact dermatitis in some cases precedes anaphylaxis. It is imperative that physicians be aware of the many possible sources of contact with this antiseptic and be alert to recognize the potentially debilitating and catastrophic reactions that may occur because of chlorhexidine sensitization. PMID:23665831

Silvestri, Dianne L; McEnery-Stonelake, Melissa

2013-01-01

316

Selective Reaction Times and Intelligence.  

ERIC Educational Resources Information Center

The relationship between psychometric intelligence and 2 selective reaction time (RT) tasks was determined for 81 university students (27 males and 54 females). Results generally support the paradigm of W. E. Hick (1952). Some surprising findings are discussed with respect to the specific demands of selective RT tasks. (SLD)

Neubauer, Aljoscha C.

1990-01-01

317

Reactions of Gaseous Bronsted Acids.  

National Technical Information Service (NTIS)

Gaseous ionic reactions have been observed for a series of oxygenated compounds in the source of a mass spectrometer at pressures up to a few tenths of a torr. The major produce ions were the solvated protons. Major differences in relative abundances were...

M. S. B. Munson

1965-01-01

318

Retest Reaction in Tuberculous Monkeys.  

National Technical Information Service (NTIS)

Retest tuberculin reactions in rhesus (Macaca mulatta) monkeys to 0.2 ml of 1:10 dilution of veterinary-type old tuberculin given intradermally into the eyelid produced responses as seen by eye closure at 6 hours. With readings made at 1/4, 6, 24, and 48 ...

J. T. Sinski W. L. Pannier

1965-01-01

319

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

320

Teachers' Reactions to Children's Aggression  

ERIC Educational Resources Information Center

Drawing on social schema theory (Fiske & Taylor, 1991) and social identity theory (Tajfel & Turner, 1979), this study examined the impact on teachers' reactions to children's aggression of three variables, two of which were related to the aggressors and one was related to the teachers. Experienced female elementary school teachers (N=90) each read…

Nesdale, Drew; Pickering, Kaye

2006-01-01

321

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

322

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

323

Employer Reactions to Job Development.  

ERIC Educational Resources Information Center

Surveys of Portland and San Francisco employers about their reactions to job development activity found most were favorable or indifferent to being contacted by representatives serving the disabled. The hiring of state vocational rehabilitation agency clients increased with the number of employees and the number of positions filled. (Author)

Zadny, Jerry J.

1980-01-01

324

Ground reaction forces on stairs  

Microsoft Academic Search

The goal of this study was to compare selected parameters of vertical ground reaction forces (GRF) of good outcome patients with different prosthesis designs with a matched control group during level walking, stair ascent and descent. Forty subjects, 29 with three main implant designs (including four subjects with a passive knee flexion restriction), and 11 healthy controls were measured with

Alex Stacoff; Inès A. Kramers-de Quervain; Gerhard Luder; Renate List; Edgar Stüssi

2007-01-01

325

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

326

Polarization phenomena in hadronic reactions  

NASA Astrophysics Data System (ADS)

Predictions are made in the framework of the effective color field ( ECF) model for polarization observables in , A + A ? ? X and p + Pb ? pX reactions. The predictions can be checked in the polarization experiments at IHEP (SPASCHARM), JINR (NICA) and BNL (RHIC). Estimates of quark masses and anamolous chromomagnetic quark moments are given.

Abramov, V. V.

2014-01-01

327

Change in Temperature: Endothermic Reaction  

NSDL National Science Digital Library

Learners investigate signs of a chemical reaction when they mix vinegar and baking soda. In addition to a gas being produced, learners also notice the temperature decreases. Learners can quantify the experiment by using a thermometer to measure the temperature change.

Kessler, James H.; Galvan, Patricia M.

2007-01-01

328

Microwave Irradiation and Multicomponent Reactions  

Microsoft Academic Search

A common theme throughout drug discovery and process development is speed. With the emergence of combinatorial chemistry and high-speed parallel synthesis, multicomponent reactions (MCRs) have seen a resurgence of interest. MCRs are therefore becoming increasingly popular since they provide the possibility to introduce a large degree of chemical diversity in only one step! Microwave irradiation under controlled conditions has been

Jitender B. Bariwal; Jalpa C. Trivedi; Erik V. van der Eycken

2010-01-01

329

Quantum back-reaction problems  

Microsoft Academic Search

The macroscopic behavior of many physical systems can be approximately described by classical quantities. However, quantum theory demands the existence of omnipresent quantum fluctuations on top of this classical background -- which, albeit small, should have some impact onto its dynamics. The correct treatment of this quantum back-reaction is one of the main problems in quantum gravity and related to

Ralf Schützhold

2007-01-01

330

Hysterical Conversion Reactions in Childhood.  

ERIC Educational Resources Information Center

Retrospective analysis indicated hysterical conversion reactions are uncommon prior to age five, uncommon in in-patient psychiatric practice, and are more common among girls than among boys. The frequency of previous psychiatric difficulties in both the child and his/her family suggests that symptom formation is but one component in ongoing…

Goodyear, Ian

1981-01-01

331

Anomalous thresholds of reaction amplitudes  

Microsoft Academic Search

Summary  Anomalous thresholds of reaction amplitudes are studied without recourse to a partial wave expansion. Ft is shown that the\\u000a behavior of the amplitudes is quite similar to that of the partial wave projections even though the Legendre series does not\\u000a converge near the anomalous threshold.

P. G. O. Freund; R. Karplus

1961-01-01

332

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.

2014-01-01

333

Catalytic, enantioselective vinylogous Michael reactions.  

PubMed

Recent progress in the field of catalytic, enantioselective vinylogous Michael reactions of latent dienolates is described which furnish optically highly enriched chiral 1,7-dioxo compounds of great utility in one synthetic operation. Emphasis is given to new catalysis modes which realise this challenging transformation with high regio- as well as enantioselectivity. PMID:24760480

Schneider, Christoph; Abels, Falko

2014-06-14

334

Reactions of cells to topography  

Microsoft Academic Search

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

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

1998-01-01

335

Atmospheric Atomic Sulfur Ion Reactions.  

National Technical Information Service (NTIS)

The apparent observation of atomic sulfur ions below 86 km in the ionosphere stimulates an interest in their possible production and loss processes. Toward this end we have measured the following reactions at 300K: S(+) + NO goes to NO(+) + S, for k = 4.2...

F. C. Fehsenfeld E. E. Ferguson

1972-01-01

336

Validating Adverse Drug Reaction Cases.  

National Technical Information Service (NTIS)

Difficulties in evaluating drug-reaction cases have arisen from failure to study time relationships between drugs and disease makers, failure to rule out other-than-drug causes, failure to use clinical-laboratory data, and lack of communication between cl...

N. S. Irey

1973-01-01

337

Reaction modeling in geothermal systems  

NASA Astrophysics Data System (ADS)

Natural volcanic geothermal systems are open systems in term of matter and energy. Such systems are complex to model in terms of fluid chemistry, fluid flow and energy budget. Reaction modeling may be used to gain insight and possibly quantify chemical processes occurring within a system, for example fluid-fluid and fluid-rock interaction. Methods have been developed within the WATCH (Bjarnason, 1994; Arnórsson et al., 2007) and PHREEQC (Parkhurst and Appelo, 1999) programs to simulate reactions of multicomponent and multiphase systems to 300°C. The models include boiling and phase segregation (open system boiling), fluid-fluid mixing and fluid-rock interaction (gas-water-rock interaction). The models have been applied to quantify processes within the Hellisheidi geothermal system, Iceland. Open system boiling and fluid-rock interaction were simulated as a function of temperature, initial fluid composition and extent of reaction (T-X-?). In addition the interactions of magmatic gases with geothermal fluids and rocks were modeled. In this way various component behavior has been traced within the geothermal system and compared with observations of fluid composition and mineralogy. In addition, the reaction models have been used to evaluate the geochemical feasibility and best conditions of gas (CO2 and H2S) and waste water injection into geothermal system.

Stefansson, A.

2012-12-01

338

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

339

Complexation reactions in aquatic systems  

Microsoft Academic Search

This book discusses the properties, reactivities, and ecological implications of all chemically ill-defined natural complexants in aquatic systems. Analytical and theoretical aspects are presented simultaneously, covering speciation parameters, nature, and properties of organic and inorganic ligands in natural waters, their reactions with inorganic elements (particularly metals), and methods of measurement of speciation parameters.

J. Buffle; R. A. Chalmers

1988-01-01

340

Reaction kinetics, geospeedometry, and relaxation theory  

Microsoft Academic Search

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

Youxue Zhang

1994-01-01

341

Reaction Kinetics of Nanostructured Silicon Carbide  

Microsoft Academic Search

Nanostructured silicon carbide (SiC) is of interest particularly for use in nanocomposites that demonstrate high hardness as well as for use in semiconductor applications. Reaction kinetics studies of solid-solid reactions are relatively recent and present a method of determining the reaction mechanism and activation energy by measuring reaction rates. We have used induction heating to heat quickly, thus reducing the

Kendra Wallis; T. W. Zerda

2006-01-01

342

Reactions and interactions in liquid crystalline media  

Microsoft Academic Search

This chapter discusses critically the most representative examples of reactions performed both in low molar mass and polymeric liquid crystals. Examples of reactions whose pathway is affected when they are performed in low molar mass liquid crystals, as well as reactions performed on polymeric liquid crystals whose phase behavior is affected whether the reaction takes place in the isotropic or

V. Percec; H. Jonsson; D. Tomazos

1991-01-01

343

Thermochemical Modeling of Thermite-Type Reactions.  

National Technical Information Service (NTIS)

Purpose of this work was to use thermodynamic modeling to study the chemistry associated with the synthesis of TiB sub 2 , SiC, and TiC by thermite-type reactions. Side reactions (including vaporization reactions) compete with the primary reaction and thu...

R. G. Behrens G. P. Hansen

1985-01-01

344

Reaction of alkylcobalamins with thiols  

SciTech Connect

Carbon-13 NMR spectroscopy and phosphorus-31 NMR spectroscopy have been used to study the reaction of several alkylcobalamins with 2-mercaptoethanol. At alkaline pH, when the thiol is deprotonated, the alkyl-transfer reactions involve a nucleophilic attack of the thiolate anion on the Co-methylene carbon of the cobalamins, yielding alkyl thioethers and cob(II)alamin. In these nucleophilic displacement reactions cob(I)alamin is presumably formed as an intermediate. The higher alkylcobalamins react more slowly than methylcobalamin. The lower reactivity of ethyl- and propylcobalamin is probably the basis of the inhibition of the corrinoid-dependent methyl-transfer systems by propyl iodide. The transfer of the upper nucleoside ligand of adenosylcobalamin to 2-mercaptoethanol is a very slow process; S-adenosylmercaptoethanol and cob(II)alamin are the final products of the reaction. The dealkylation of (carboxymethyl)cobalamin is a much more facile reaction. At alkaline pH S-(carboxymethyl)mercaptoethanol and cob(II)alamin are produced, while at pH values below 8 the carbon-cobalt bond is cleaved reductively to acetate and cob(II)alamin. The reductive cleavage of the carbon-cobalt bond of (carboxymethyl)cobalamin by 2-mercaptoethanol is extremely fast when the cobalamin is in the base-off form. Because the authors have been unable to detect trans coordination of 2-mercaptoethanol, they favor a mechanism that involves a hydride attack on the Co-methylene carbon of (carboxymethyl) rather than a trans attack of the thiol on the cobalt atom.

Hogenkamp, H.P.C.; Bratt, G.T.; Kotchevar, A.T.

1987-07-28

345

Thermodynamics of Enzyme-Catalyzed Reactions Database  

National Institute of Standards and Technology Data Gateway

SRD 74 Thermodynamics of Enzyme-Catalyzed Reactions Database (Web, free access)   The Thermodynamics of Enzyme-Catalyzed Reactions Database contains thermodynamic data on enzyme-catalyzed reactions that have been recently published in the Journal of Physical and Chemical Reference Data (JPCRD). For each reaction the following information is provided: the reference for the data, the reaction studied, the name of the enzyme used and its Enzyme Commission number, the method of measurement, the data and an evaluation thereof.

346

Thermochemical modeling of thermite-type reactions  

Microsoft Academic Search

Purpose of this work was to use thermodynamic modeling to study the chemistry associated with the synthesis of TiBâ, SiC, and TiC by thermite-type reactions. Side reactions (including vaporization reactions) compete with the primary reaction and thus decrease the yield of a desired product. The relative importance of side reactions is governed in part by the thermodynamic stabilities of byproducts

R. G. Behrens; G. P. Hansen

1985-01-01

347

Effect of pozzolanic reaction products on alkali-silica reaction  

Microsoft Academic Search

The effect of fly ash on controlling alkali-silica reaction (ASR) in simulated alkali solution was studied. The expansion\\u000a of mortar bars and the content of Ca (OH)2 in cement paste cured at 80°C for 91 d were measured. Transmission electron microscopy (TEM) and high-resolution transmission\\u000a electron microscopy (HRTEM) were employed to study the microstructure of C-S-H. TEM\\/energy dispersive spectroscopy (EDS)

Wei Fengyan; Lan Xianghui; Lv Yinong; Xu Zhongzi

2006-01-01

348

Finding reaction paths using the potential energy as reaction coordinate  

NASA Astrophysics Data System (ADS)

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 Carathéodory's relation to derive in a rigorous manner the proposed parametrization of the IRC path. Since this Carathéodory'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.

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

2008-03-01

349

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

350

Investigation of early tailoring reactions in the oxytetracycline biosynthetic pathway.  

PubMed

Tetracyclines are aromatic polyketides biosynthesized by bacterial type II polyketide synthases. The amidated tetracycline backbone is biosynthesized by the minimal polyketide synthases and an amidotransferase homologue OxyD. Biosynthesis of the key intermediate 6-methylpretetramid requires two early tailoring steps, which are cyclization of the linearly fused tetracyclic scaffold and regioselective C-methylation of the aglycon. Using a heterologous host (CH999)/vector pair, we identified the minimum set of enzymes from the oxytetracycline biosynthetic pathway that is required to afford 6-methylpretetramid in vivo. Only two cyclases (OxyK and OxyN) are necessary to completely cyclize and aromatize the amidated tetracyclic aglycon. Formation of the last ring via C-1/C-18 aldol condensation does not require a dedicated fourth-ring cyclase, in contrast to the biosynthetic mechanism of other tetracyclic aromatic polyketides, such as daunorubicin and tetracenomycin. Acetyl-derived polyketides do not undergo spontaneous fourth-ring cyclization and form only anthracene carboxylic acids as demonstrated both in vivo and in vitro. OxyF was identified to be the C-6 C-methyltransferase that regioselectively methylates pretetramid to yield 6-methylpretetramid. Reconstitution of 6-methylpretetramid in a heterologous host sets the stage for a more systematic investigation of additional tetracycline downstream tailoring enzymes and is a key step toward the engineered biosynthesis of tetracycline analogs. PMID:17631493

Zhang, Wenjun; Watanabe, Kenji; Wang, Clay C C; Tang, Yi

2007-08-31

351

Propulsive Reaction Control System Model  

NASA Technical Reports Server (NTRS)

This software models a propulsive reaction control system (RCS) for guidance, navigation, and control simulation purposes. The model includes the drive electronics, the electromechanical valve dynamics, the combustion dynamics, and thrust. This innovation follows the Mars Science Laboratory entry reaction control system design, and has been created to meet the Mars Science Laboratory (MSL) entry, descent, and landing simulation needs. It has been built to be plug-and-play on multiple MSL testbeds [analysis, Monte Carlo, flight software development, hardware-in-the-loop, and ATLO (assembly, test and launch operations) testbeds]. This RCS model is a C language program. It contains two main functions: the RCS electronics model function that models the RCS FPGA (field-programmable-gate-array) processing and commanding of the RCS valve, and the RCS dynamic model function that models the valve and combustion dynamics. In addition, this software provides support functions to initialize the model states, set parameters, access model telemetry, and access calculated thruster forces.

Brugarolas, Paul; Phan, Linh H.; Serricchio, Frederick; San Martin, Alejandro M.

2011-01-01

352

[Adverse drug reactions on hair].  

PubMed

Adverse drug reactions on the hair are common side effects. The spectrum of loss of hair reaches from diffuse telogen effluvium up to circumscribed or diffuse alopecia on the scalp, sometimes also including other body areas. Other side effects observed are the stimulation of hair growth with hypertrichosis and induction or worsening of hirsutism, as well as changes of the structure or color of the hair. In most cases--other than those treated with cytostatics, androgens, or hormonal contraceptives with some androgenic effect--it is rather difficult to determine the time of onset and primary cause, since the diffuse types often start subclinically, and other factors may play an additional part. As a rule, adverse drug reactions are reversible provided the causative drug is avoided. PMID:2087842

Gollnick, H; Blume, U; Orfanos, C E

1990-12-01

353

Kinetics of Polymer Interfacial Reaction  

NASA Astrophysics Data System (ADS)

Germanium crystals modified with high quality azide functional monolayers are used to directly monitor in situ the kinetics of interfacial ``click'' reactions with complementary alkyne end-functional poly(n-butyl acrylate) (PnBA) and polystyrene (PS) by attenuated total reflectance infrared spectroscopy (ATR-IR). In the presence of copper (I), the azide-modified Ge substrates react quantitatively with PnBA and PS via a 1,3-dipolar cycloaddition reaction. Time-resolved ATR-IR measurements show two regimes of kinetic behavior, as predicted by theory. In the first regime the rate is rapid and is controlled by diffusion of the polymer through the solvent, scaling with the square root of time. The rate slows considerably in the second regime, limited by penetration of the reacting polymer through the covalently bound polymer brush layer, scaling with the natural logarithm of time. The influence of polymer size and solvent quality are reported.

Zhang, Shuo; Koberstein, Jeffrey

2012-02-01

354

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

355

Microwave Irradiation and Multicomponent Reactions  

NASA Astrophysics Data System (ADS)

A common theme throughout drug discovery and process development is speed. With the emergence of combinatorial chemistry and high-speed parallel synthesis, multicomponent reactions (MCRs) have seen a resurgence of interest. MCRs are therefore becoming increasingly popular since they provide the possibility to introduce a large degree of chemical diversity in only one step! Microwave irradiation under controlled conditions has been shown to be an invaluable technology since it often allows to dramatically reduce reaction times from days or hours to minutes or even seconds. Compound libraries can be rapidly synthesized in either a parallel or sequential way using this new, enabling technology. The current chapter highlights the application of microwave irradiation for MCRs during the last 4 years. More than 110 recent literature reports have been covered.

Bariwal, Jitender B.; Trivedi, Jalpa C.; van der Eycken, Erik V.

356

Cefuroxime induced lymphomatoid hypersensitivity reaction  

PubMed Central

An 84 year old women developed erythematous blotchy erythema and purpuric rashes over the lower limbs three days after being started on intravenous cefuroxime for acute diverticulitis. A skin biopsy specimen showed a mixed infiltrate of lymphoid cells and eosinophils; many of the lymphocytes were large, pleomorphic, and showed a raised mitotic rate. Immunohistochemistry showed the infiltrate to be T cell rich, with all the large cells being CD30 positive. Typical mycosis fungoides cells, marked epidermotropism, and Pautrier's abscesses were not seen. The rash disappeared 10 days after cessation of cefuroxime and the patient remained asymptomatic 15 months later. This apparent cutaneous T cell lymphoma-like reaction is best described as lymphomatoid vascular reaction. The drug induced immune response with an atypical cutaneous lymphoid infiltrate mimics a cutaneous pseudolymphoma.???Keywords: cefuroxime; atypical cutaneous lymphomatoid infiltrate; cutaneous T cell lymphoma

Saeed, S; Bazza, M; Zaman, M; Ryatt, K

2000-01-01

357

Programmability of Chemical Reaction Networks  

NASA Astrophysics Data System (ADS)

Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

358

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

359

The alkali-silica reaction  

Microsoft Academic Search

Electrical double-layer theory has been used successfully to explain the expansion caused by the alkali-silica reaction. The net proton surface charge density of the reactive aggregate is a critical parameter for this approach. However, little work has been done to measure the surface charge density of silica as a function of pH at background electrolyte concentrations that are relevant to

Flávio A. Rodrigues; Paulo J. M. Monteiro; Garrison Sposito

1999-01-01

360

The alkali–silica reaction  

Microsoft Academic Search

The degree of expansion of alkali–silica reaction (ASR) gel is dependent on the valence and relative concentrations of cations present in the ASR gel. The electrical double-layer (EDL) model can predict which gel will be more expansive. If double-layer models are applied in a complex system, as in concrete, it is necessary to characterize the surface charge density of amorphous

Flávio A. Rodrigues; Paulo J. M. Monteiro; Garrison Sposito

2001-01-01

361

Atypical Reaction to Inhaled Silica  

Microsoft Academic Search

THE classical reaction of the lung to the deposition of airborne silica is the formation of discrete nodules, which in man exhibit a characteristic disposition of dust and connective tissue fibres1,2. Although the experimental lesion does not reproduce all the human features3, I have confirmed that it remains focal and discrete4,5. In recent experiments on the disposal of inhaled particles

A. G. Heppleston

1967-01-01

362

Strain-induced chemical reactions  

SciTech Connect

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

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

1994-07-10

363

Microwave Irradiation and Multicomponent Reactions  

Microsoft Academic Search

\\u000a \\u000a Abstract  A common theme throughout drug discovery and process development is speed. With the emergence of combinatorial chemistry and\\u000a high-speed parallel synthesis, multicomponent reactions (MCRs) have seen a resurgence of interest. MCRs are therefore becoming\\u000a increasingly popular since they provide the possibility to introduce a large degree of chemical diversity in only one step!\\u000a Microwave irradiation under controlled conditions has been

Jitender B. Bariwal; Jalpa C. Trivedi; Erik V. Van der Eycken

364

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

365

SPIRULINA PLATENSIS INHIBITS ANAPHYLACTIC REACTION  

Microsoft Academic Search

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

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

1997-01-01

366

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

367

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

368

Hydroxylapatite and titanium: interfacial reactions.  

PubMed

The chemical reactions between hydroxylapatite (HA) and titanium were studied in three different kinds of experiments to increase understanding of how to bond HA to titanium for implant materials. HA powder was bonded to a titanium rod with hot isostatic pressing. Interdiffusion of the HA elements and titanium was found in concentration profiles measured in the electron microprobe. Titanium was vapor-deposited on sintered HA discs and heated in air; perovskite (CaTiO(3)) was found on the HA surface with Rutherford backscattering and X-ray diffraction measurements. Powder composites of HA and titanium and TiO(2) were sintered at 1100 degrees C; again, perovskite was a reaction product, as well as beta-Ca(3)(PO(4))(2), from decomposition of the HA. These results demonstrate chemical reactions and interdiffusion between HA and TiO(2) during sintering, resulting in chemical bonding between HA and titanium. Thus, cracks and weakness at HA-titanium interfaces probably result from mismatch between the coefficients of thermal expansion of these materials. HA composites with other ceramics and different alloys should lead to better thermal matching and better bonding at the interface. PMID:12746880

Ergun, Celaletdin; Doremus, Robert; Lanford, William

2003-06-01

369

Primary reactions of sensory rhodopsins  

PubMed Central

The first steps in the photocycles of the archaeal photoreceptor proteins sensory rhodopsin (SR) I and II from Halobacterium salinarum and SRII from Natronobacterium pharaonis have been studied by ultrafast pump/probe spectroscopy and steady-state fluorescence spectroscopy. The data for both species of the blue-light receptor SRII suggests that their primary reactions are nearly analogous with a fast decay of the excited electronic state in 300–400 fs and a transition between two red-shifted product states in 4–5 ps. Thus SRII behaves similarly to bacteriorhodopsin. In contrast for SRI at pH 6.0, which absorbs in the orange part of the spectrum, a strongly increased fluorescence quantum yield and a drastically slower and biexponential decay of the excited electronic state occurring on the picosecond time scale (5 ps and 33 ps) is observed. The results suggest that the primary reactions are controlled by the charge distribution in the vicinity of the Schiff base and demonstrate that there is no direct connection between absorption properties and reaction dynamics for the retinal protein family.

Lutz, I.; Sieg, A.; Wegener, A. A.; Engelhard, M.; Boche, I.; Otsuka, M.; Oesterhelt, D.; Wachtveitl, J.; Zinth, W.

2001-01-01

370

Photosynthetic reaction centers in bacteria  

SciTech Connect

The photochemistry of photosynthesis begins in complexes called reaction centers. These have become model systems to study the fundamental process by which plants and bacteria convert and store solar energy as chemical free energy. In green plants, photosynthesis occurs in two systems, each of which contains a different reaction center, working in series. In one, known as photosystem 1, oxidized nicotinamide adenine dinucleotide phosphate (NADP[sup +]) is reduced to NADPH for use in a series of dark reactions called the Calvin cycle, named for Nobel Laureate Melvin Calvin, by which carbon dioxide is converted into useful fuels such as carbohydrates and sugars. In the other half of the photosynthetic machinery of green plants, called photosystem 2, water is oxidized to produce molecular oxygen. A different form of photosynthesis occurs in photosynthetic bacteria, which typically live at the bottom of ponds and feed on organic debris. Two main types of photosynthetic bacteria exist: purple and green. Neither type liberates oxygen from water. Instead, the bacteria feed on organic media or inorganic materials, such as sulfides, which are easier to reduce or oxidize than carbon dioxide or water. Perhaps in consequence, their photosynthetic machinery is simpler than that of green, oxygen-evolving plants and their primary photochemistry is better understood.

Norris, J.R. (Argonne National Lab., IL (United States) Univ. of Chicago, IL (United States)); Schiffer, M. (Argonne National Lab., IL (United States))

1990-07-30

371

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

372

[Injectable fillers: adverse reactions and their management].  

PubMed

Injectable fillers are one of the corner stones of aesthetic medicine. In general they are safe to use. However, adverse reactions may occur. These reactions may be acute, subacute or delayed, e.g. after decades. It is important to know these reactions and to be prepared so that they can be adequately treated, in view of the clinical symptoms, the injected material and if applicable other diseases/treatments that might trigger these reactions. Last but not least, all reactions should be reported either to specialized registries or regulatory agencies. Only then we are able to learn more about these reactions and their best possible treatment. PMID:23407758

Rzany, B; Bachmann, F; Nast, A

2013-02-01

373

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.

SUZUKI, Toshinori

2013-01-01

374

Secondary reactions from fast particles formed through thermonuclear reactions in stellar interiors  

Microsoft Academic Search

The influence of excess high-energy particles formed in thermonuclear reactions upon the rates of secondary reactions is discussed. Fast particles will make the dominant contribution for reactions having a high Coulomb barrier.

V. M. Kontorovich; V. N. Melnik

1980-01-01

375

Secondary reactions from fast particles formed through thermonuclear reactions in stellar interiors  

SciTech Connect

The influence of excess high-energy particles formed in thermonuclear reactions upon the rates of secondary reactions is discussed. Fast particles will make the dominant contribution for reactions having a high Coulomb barrier.

Kontorovich, V.M.; Mel'nik, V.N.

1980-05-01

376

Microfabricated sleeve devices for chemical reactions  

DOEpatents

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

Northrup, M. Allen (Berkeley, CA)

2003-01-01

377

Nuclear reactions triggered by relativistic electron jets  

Microsoft Academic Search

Laser generated, highly collimated multi-MeV electron jets were used to induce nuclear reactions in high-Z materials like 197Au, 181Ta and in 129I. Applications of laser-induced nuclear reactions are presented

B. Liesfeld; K.-U. Amthor; F. Ewald; H. Schwoerer; R. Sauerbrey; J. Magill; J. Galy; R. Schenkel

2004-01-01

378

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.

2011-01-01

379

ChemTeacher: Single Replacement Reactions  

NSDL National Science Digital Library

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

2011-01-01

380

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

381

Heat Transfer Characteristics of SHS Reactions.  

National Technical Information Service (NTIS)

The program consisted of two inter-related tasks: Theoretical modeling and experimental verification. Task I of the effort focused on thermodynamic modeling of the SHS reactions, and modeling of the heat transfer efficiency between the SHS reaction and th...

K. V. Logan G. R. Villalobos J. N. Harris P. Mackle S. C. Neel

1990-01-01

382

Study of Chemiluminescent Reactions of Metal Atoms.  

National Technical Information Service (NTIS)

Laser vaporization of thin metal films has been used as the metal atom beam source for the study of chemiluminescent oxidation reactions. Techniques have been developed and demonstrated to experimentally determine the chemiluminescent reaction stoichiomet...

J. F. Friichtenicht, S. P. Tang, B. G. Wicke

1977-01-01

383

A Study of Oxalic Ester Chemiluminescent Reactions.  

National Technical Information Service (NTIS)

The effects of a number of reaction variables and additives on the kinetics and quantum yields of oxalic ester chemiluminescent reactions were investigated. The experiments were successfully designed to distinguish variable effects on processes leading to...

M. M. Rauhut A. M. Semsel

1974-01-01

384

Anomalous subdiffusion with multispecies linear reaction dynamics.  

PubMed

We have introduced a set of coupled fractional reaction-diffusion equations to model a multispecies system undergoing anomalous subdiffusion with linear reaction dynamics. The model equations are derived from a mesoscopic continuous time random walk formulation of anomalously diffusing species with linear mean field reaction kinetics. The effect of reactions is manifest in reaction modified spatiotemporal diffusion operators as well as in additive mean field reaction terms. One consequence of the nonseparability of reaction and subdiffusion terms is that the governing evolution equation for the concentration of one particular species may include both reactive and diffusive contributions from other species. The general solution is derived for the multispecies system and some particular special cases involving both irreversible and reversible reaction dynamics are analyzed in detail. We have carried out Monte Carlo simulations corresponding to these special cases and we find excellent agreement with theory. PMID:18351991

Langlands, T A M; Henry, B I; Wearne, S L

2008-02-01

385

Production and Reactions of Negative Ions.  

National Technical Information Service (NTIS)

Negative ions play a role in photophysics and photochemistry. This review discusses only negative ion properties and reactions in the gas phase. Electron affinities, photoabsorption by negative ions, production of negative ions by photon reactions, and co...

R. N. Compton

1982-01-01

386

Laser Studies of Gas Phase Radical Reactions.  

National Technical Information Service (NTIS)

A series of measurements on free radicals produced by chemical reaction and photodissociation has been made, using laser methods for formation and in some cases, detection. Highly exothermic reactions between oxygen atoms and both CF2 and CHF radicals hav...

G. Hancock

1989-01-01

387

Latest Research on the Hydrosilylation Reaction  

Microsoft Academic Search

The latest (1964-1974) literature data on the hydrosilylation reaction are surveyed and the results of studies on hydrosilylation, the possibility of using new catalysts, new applications, and the commonest side reactions are considered. The bibliography includes 428 references.

E. Lukevics

1977-01-01

388

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

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

Derickson, Paula

389

Stereochemical control of the Passerini reaction.  

PubMed

A catalytic asymmetric Passerini reaction using tridentate indan (pybox) Cu(II) Lewis acid complex 4 with substrates capable of bidentate coordination has been achieved. The reaction occurs via ligand-accelerated catalysis. PMID:15524450

Andreana, Peter R; Liu, Chang C; Schreiber, Stuart L

2004-11-11

390

Chemoselective Reactions of a-Aminonitriles.  

National Technical Information Service (NTIS)

A carbocyclic model for 4-anilino-4-cyano-l-benzylpiperidine was used to elucidate the chemistry of the reaction with diisobutylaluminum hydride. Reactions with alkaline hydrogen peroxide, triethyloxonium tetrafluoroborate and boron trifluoroetherate in m...

M. A. Waugh H. D. Banks

1994-01-01

391

Heavy atom isotope effects on enzymatic reactions  

NASA Astrophysics Data System (ADS)

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

Paneth, Piotr

1994-05-01

392

Analysis of Symmetry in Chemical Reactions.  

National Technical Information Service (NTIS)

The authors investigated the effect of the symmetry of the electronic and nuclear motion in chemical reactions. The analysis focuses on concerted reactions which are defined to be describable by a single transition matrix. The transition matrix for rearra...

T. F. George J. Ross

1971-01-01

393

Reaction of steam with molybdenum is studied  

NASA Technical Reports Server (NTRS)

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

Kilpatrick, M.; Lott, S.

1967-01-01

394

Investigation of Seminal Plasma Hypersensitivity Reactions.  

National Technical Information Service (NTIS)

Since returning from the Persian Gulf War (PGW) veterans and/or their wives have reported burning after contact with their semen. This has been called Burning Semen Syndrome (BSS). These reactions bear striking resemblance to reactions experienced by wome...

J. A. Bernstein

1997-01-01

395

Kinetics of resid hydrodesulfurization reactions  

SciTech Connect

In this article the authors examine the results obtained in hydrodesulfurizing an atmospheric resis from Bai-Hassan crude on Ni-Mo/Al/sub 2/O/sub 3/ catalyst at 320-420/sup 0/C, feedstock space velocity 0.37-2.6 h/sup -1/, pressure 6.1 MPa, and hydrogen/feed ratio 300 liters/liter, in a single-pass downflow reactor with a stationary bed of catalyst. Also, they give certain thermodynamic characteristics for desulfurization, demetalization, and deasphalting of this resid. The kinetic model describing most accurately the kinetics of the different reactions will be examined.

Mohammed, A.H.A.K.; Abbas, A.A.A.; Al'-Maiya, A.S.K.

1987-07-01

396

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

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

Vecitis, Chad David

397

Microbial analysis using Sharma's reaction  

NASA Astrophysics Data System (ADS)

The photoreaction of thionine with NAD(P)H leads to the formation of non-fluorescent semi and lecuothionine. This has been previously used for the development of enzymatic assays. We show that the fluorescence of thionine is quenched in the presence of Nocardia corallin. We ascribe this decrease in fluorescence to the presence of NAD(P)H present on the walls and in the body of the cells as described by Sharma. We therefore demonstrate that it is possible to measure, in situ, NAD(P)H in Nocardia corallin in a simple and inexpensive manner and that this finding extends the analytical application of Sharma's reaction to other organisms.

Ali, Zulfiqur; Hodson, Bruce; Timmins, James; Keith, Stephen

1999-02-01

398

Pathology Case Study: Transfusion Reaction  

NSDL National Science Digital Library

This is a case study presented by the University of Pittsburgh Department of Pathology in which a young woman experienced vomiting, dizziness, headaches, and change of mental status due to conjunctival petechiae. Visitors are given the transfusion reaction investigation, and have the opportunity to diagnose the patient. This is an excellent resource for students in the health sciences to familiarize themselves with using patient history and laboratory results to diagnose disease. It is also a helpful site for educators to use to introduce or test student learning in transfusion pathology.

Johnson, Douglas R.; Triulzi, Darrell

2008-09-02

399

Emergent computation by catalytic reactions  

NASA Astrophysics Data System (ADS)

Recently, biochemical systems have been shown to possess interesting computational properties. In a parallel development, the chemical computation metaphor is becoming more and more frequently used as part of the emergent computation paradigm in computer science. We review in this contribution the idea behind the chemical computational metaphor and outline its relevance for nanotechnology. We set up a simulated reaction system of mathematical objects and examine its dynamics by computer experiments. Typical problems of computer science, such as sorting, parity checking or prime number computation are placed within this context. The implications of this approach for nanotechnology, parallel computers based on molecular devices and DNA-RNA-protein information processing are discussed.

Banzhaf, Wolfgang; Dittrich, Peter; Rauhe, Hilmar

1996-12-01

400

Control Electronics For Reaction Wheel  

NASA Technical Reports Server (NTRS)

Bidirectional operation achieved with single-polarity main power supply. Control circuitry generates pulse-width-modulated 800-Hz waveforms to drive two-phase ac motor and reaction wheel. Operates partly in response to digital magnitude-and-direction torque command generated by external control subsystem and partly in response to tachometric feedback in form of two once-per-revolution sinusoids with amplitudes proportional to speed. Operation in either of two modes called "normal" and "safehold." In normal mode, drive pulses timed so that, on average over one or few cycles, motor applies commanded torque. In safehold mode, pulses timed to keep motor running at set speed in one direction.

Chamberlin, Keith

1995-01-01

401

Highly enantioselective organocatalytic Biginelli reaction.  

PubMed

A series of binol- and H8-binol-based phosphoric acids have for the first time been evaluated for their ability to catalyze Biginelli reactions of aldehydes, thiourea or urea, and beta-keto esters. A new chiral phosphoric acid, derived from 3,3'-diphenyl-H8-binol, exhibited superior catalytic activity and enantioselectivity compared to its structural analogues, affording high enantioselectivities ranging from 85 to 97% ee with a wide scope of substrates. A metal-free preparation of optically active monastrol was achieved on the basis of the current process. PMID:17105279

Chen, Xiao-Hua; Xu, Xiao-Ying; Liu, Hua; Cun, Lin-Feng; Gong, Liu-Zhu

2006-11-22

402

Reaction Kinetics of C60 Fullerene Ozonation  

Microsoft Academic Search

It has been verified that the reaction between O3 and C60 follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C?C][O3]. The reaction rate constant k has been measured ?(1.5 ± 0.3) × 10 L mol s. The value of this rate constant has the same order of magnitude of the rate constant measured for instance

Metodi P. Anachkov; Franco Cataldo; Slavtcho K. Rakovsky

2003-01-01

403

Side-Chain Reactions of Benzene Derivatives  

Microsoft Academic Search

WE have recently examined a number of side-chain reactions in the light of the postulate that the differences in the rates of reaction of a series of similarly constituted compounds under identical conditions are to be ascribed solely to different energies of activation, substituents contributing additively to the total energy1. Our results2 for the reaction of hydrogen ion with various

W. S. Nathan; H. B. Watson

1934-01-01

404

Hypersensitivity Reactions to Drugs: Evaluation and Management  

Microsoft Academic Search

Most hypersensitivity reactions to drugs occur within several weeks of administration; signs and symptoms are often consistent with known immune-mediated reactions, including anaphylaxis, rashes, fever, cytopenias and vasculitis. The culprit immune mechanisms range from immunoglobulin E antibody to T cells inducing apoptosis of keratinocytes, in the case of bullous exfolia- tive rashes. Many drugs induce reactions via altered hepatic metabolism,

GILLIAN M. SHEPHERD

405

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

406

Infant Defensive Reactions to Visual Occlusion.  

ERIC Educational Resources Information Center

This paper describes the initial organization of the infant's reaction to having his vision occluded by an opaque cloth; traces the development of this reaction over the first six months; and probes the role the occlusion of vision plays in provoking the reaction. Fifty videotaped sessions of infants during two conditions - eyes covered with an…

Adamson, Lauren; Tronick, Edward

407

Reaction Order Ambiguity in Integrated Rate Plots  

ERIC Educational Resources Information Center

Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical…

Lee, Joe

2008-01-01

408

Severe photosensitivity reaction induced by topical diclofenac  

PubMed Central

Albeit uncommon, photosensitivity reaction induced by diclofenac can be an unfortunate adverse reaction complicating its use as a topical analgesic. We here present a case of a patient who suffered such a reaction as a result of exposure to diclofenac, employed as a topical analgesic for low backache. The lesions healed with conservative management without extensive scarring or other complications.

Akat, Pramod B.

2013-01-01

409

Ester synthesis in lipase-catalyzed reactions  

Microsoft Academic Search

This review discusses the myriad of reaction systems employed in ester production catalyzed by lipases. Enzyme behavior in reaction systems is a consequence of certain structural patterns typical of lipases. Water has a profound effect on the lipase behavior either directly by affecting the hydration of the enzyme or indirectly by changing the nature of the reaction media and\\/or enzyme

Ahmad R. M Yahya; William A Anderson; Murray Moo-Young

1998-01-01

410

The Guerbet reaction applied to diodone  

Microsoft Academic Search

Summary The Guerbet reaction is a test for the presence of an aromatic nucleus. Diodone acid is found to give a positive test. The reaction has been followed step by step, the reaction products being separated by thin-layer chromatography and identified by mass spectrometry. The loss of the acetic acid group during the nitration step is remarkable.

H. A. Dingjan; H. A. Crezée

1978-01-01

411

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

412

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?

413

A Generalized Selection Rule for Pericyclic Reactions.  

ERIC Educational Resources Information Center

Describes a convenient procedure, the Odd-Even Rule, for predicting the allowedness of forbiddenness of ground-state, pericyclic reactions. The rule is applied to a number of specific reactions. In contrast to the Woodward-Hoffman approach, the application to each reaction is always the same. (JN)

He, Fu-Cheng; Pfeiffer, Gary V.

1984-01-01

414

The Spinning World of Spacecraft Reaction Wheels  

NSDL National Science Digital Library

This is a activity about how reaction wheels affect spacecraft orientation (attitude). Learners will observe Newton's Third Law (action-reaction) in the changes caused by a reaction wheel acting upon a spacecraft suspended from a support wire and in the ensuing interfering forces from the wire support. The experiment includes an option for demonstration and for learner investigation. Notes about gyroscopes are included.

415

Parental Reactions to Cleft Palate Children.  

ERIC Educational Resources Information Center

This literature review examines parental reactions following the birth of a cleft lip/palate child, focusing primarily on the mother's reactions. The research studies cited have explored such influences on maternal reactions as her feelings of lack of control over external forces and her feelings of guilt that the deformity was her fault. Delays…

Vanpoelvoorde, Leah

416

Severe photosensitivity reaction induced by topical diclofenac.  

PubMed

Albeit uncommon, photosensitivity reaction induced by diclofenac can be an unfortunate adverse reaction complicating its use as a topical analgesic. We here present a case of a patient who suffered such a reaction as a result of exposure to diclofenac, employed as a topical analgesic for low backache. The lesions healed with conservative management without extensive scarring or other complications. PMID:24014923

Akat, Pramod B

2013-01-01

417

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

418

ACUTE CATATONIC REACTION OF ADOLESCENCE  

PubMed Central

In a study of 21 cases of catatonic schizophrenic reaction of adolescence, sexual conflict situations and stern religious orientation of the family were noted in most cases. Incest was a factor in four of the female patients and masturbatory guilt was a prominent reaction in the remainder. Sex education was mostly misinformation and threats of dire consequences for sexual activity. Fourteen of the cases involved broken homes for significant periods of childhood or adolescence. It was hypothesized that sexual conflict situations grew out of incompatible socio-cultural attitudes and normal adolescent psychological and physiological drives. We formulated the “defined body contact” technique as a means of facilitating the reversal of the catatonic behavior, which we saw as the primary device whereby the patient limited physical contacts. The contacts we used in this technique were defined explicitly and implicitly as non-sexual. The catatonic symptoms remitted in days to several weeks in 13 of the cases. Seven patients required electroshock therapy. Twenty of the 21 patients returned to their homes or to non-institutional residences. The length of hospitalization was materially influenced by the degree of readiness of the outside environment to accept the returnee.

Kurland, Leonard; Teicher, Joseph D.

1963-01-01

419

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

420

Mechanisms of direct reactions with halo nuclei  

NASA Astrophysics Data System (ADS)

Halo nuclei are exotic nuclei which exhibit a strongly clusterised structure: they can be seen as one or two valence nucleons loosely bound to a core. Being observed at the shoulder of the valley of stability, halo nuclei are studied mostly through reactions. In this contribution the reaction models most commonly used to analyse experimental data are reviewed and compared to one another. A reaction observable built on the ratio of two angular distributions is then presented. This ratio enables removing most of the sensitivity to the reaction mechanism, which emphasises the effects of nuclear structure on the reaction.

Capel, P.; Nunes, F. M.; Esbensen, H.; Johnson, R. C.

2013-04-01

421

Stereoselectivity of the Honda-Reformatsky Reaction in Reactions with Ethyl Bromodifluoroacetate with ?-Oxygenated Sulfinylimines.  

PubMed

The Reformatsky reaction of ethyl bromodifluoroacetate to ?-oxygenated sulfinylimines is described. Using Honda-Reformatsky conditions, the reaction proceeds with double diastereodifferentiation, with the configuration of the sulfinyl group determining the stereochemical course of the reaction. Excellent diastereoselectivities (>94:6) are obtained for the matched cases. In contrast, reaction with sulfinylimines derived from unsubstituted alkanals proceeded with virtually no diastereoselectivity. PMID:24746314

Fontenelle, Clément Q; Conroy, Matthew; Light, Mark; Poisson, Thomas; Pannecoucke, Xavier; Linclau, Bruno

2014-05-01

422

Determination of (n,?) reaction rates at s-process branching points via their inverse reactions  

Microsoft Academic Search

We present our method to determine the (n,?) reaction rates of s-process branching point nuclei using data of the inverse (?,n) reaction. As an example, we selected 95Zr. The analysis of the data of the reaction 96Zr(?,n)95Zr is still in progress. Therefore, we describe the characteristics of this reaction and first preliminary results.

K. Sonnabend; A. Mengoni; P. Mohr; T. Rauscher; K. Vogt; A. Zilges

2003-01-01

423

Catalytic asymmetric Petasis reactions of vinylboronates.  

PubMed

Binaphthol-catalyzed asymmetric Petasis reactions of salicylaldehydes with dibutyl vinylboronates and secondary amines in the presence of 4 Å molecular sieves (MS) afforded products with up to 99% ee in isolated yields of 39-94%. The 99% ee of the product indicated that the reaction by the binaphthol-catalyzed pathway was roughly 500 times faster than the uncatalyzed pathway. NMR experiments ((1)H and (11)B) showed that the amine component played a role in triggering the reaction between the binaphthol catalyst and the vinylboronate in the catalytic reaction sequence. The 4 Å MS enhanced both the rate and enantioselectivity by effective removal of water from the reaction system. A novel rearrangement reaction of the unconjugated allylic amine Petasis reaction product to a conjugated allylic amine was also observed. PMID:23971730

Shi, Xianglin; Kiesman, William F; Levina, Anna; Xin, Zhili

2013-09-20

424

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

Walch, Stephen P.

1990-01-01

425

Phototoxic and photoallergic cutaneous drug reactions.  

PubMed

A variety of topical and systemic drugs can induce cutaneous photosensitive reactions. These drugs and their metabolites accumulate in the skin and increase photosensitivity of the skin typically in the UVA spectrum of light. Concerning the underlying biochemical mechanisms and the phenotype of reactions, photosensitivity can be divided into phototoxic and photoallergic reactions. In phototoxic reactions, often highly reactive oxygen molecules are formed that induce tissue damage. Skin changes resemble sunburn and develop within hours after incubation with the drug together with sunlight. In contrast, photoallergic reactions are type IV hypersensitivity reactions, and therefore resemble eczema. They usually develop within days and are less common than phototoxic reactions. Diagnosis is based on a synopsis of complete history, clinical examination, phototesting for minimal phototoxicity dose, patch testing including photopatch tests, and histopathology. Mainstays of treatment are the withdrawal of the culprit drug, and avoidance of sunlight by wearing protective clothing and broadband sunscreens with UVA filters. PMID:22613861

Glatz, Martin; Hofbauer, Günther F L

2012-01-01

426

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

427

Catalyst systems for polycondensation reactions  

US Patent & Trademark Office Database

The invention pertains to new catalyst systems for polycondensation reactions, for example for producing polyethylene terephthalate. In accordance with the invention, complex compounds with hydrotalcite-analogous structures of general formula [M(II).sub.1-x M(III).sub.x (OH).sub.2 ].sup.x+ (A.sup.n-.sub.x/n).mH.sub.2 O are used, wherein M(II) represents divalent metals, preferably Mg or Zn or NI or Cu or Fe(II) or Co, and M(III) represents trivalent metals, for example Al or Fe(III), and A represents anions, preferably carbonates or borates. These catalysts can be calcinated and can be used in combination with phosphorus compounds that contain at least one hydrolyzable phosphorus-oxygen bond.

2004-12-07

428

The OH + HBr reaction revisited  

NASA Technical Reports Server (NTRS)

Variable-temperature measurements of the rate coefficient /k(1)/ for the reaction OH + HBr yield Br + H2O are presented. The measurements are verified by two techniques: one involved a 266-nm pulsed-laser photolysis of O3/H2O/HBr/He mixtures in conjunction with time-resolved resonance fluorescence detection of OH, the second comprised pulsed laser-induced fluorescence detection of OH following 248-nm pulsed-laser photolysis of H2O2/HBr/Ar mixtures. It is reported that k(1) = (11.9 + or -1.4 x 10 to the -12th (cu cm)/(molecule)(s) independent of temperature. The measurements are compared with other available results.

Ravishankara, A. R.; Wine, P. H.; Wells, J. R.

1985-01-01

429

Radiation reaction of multipole moments  

SciTech Connect

A Poincare-invariant description is proposed for the effective dynamics of a localized system of charged particles in classical electrodynamics in terms of the intrinsic multipole moments of the system. A relativistic-invariant definition for the intrinsic multipole moments of a system of charged particles is given. A new generally covariant action functional for a relativistic perfect fluid is proposed. In the case of relativistic charged dust, it is proven that the description of the problem of radiation reaction of multipole moments by the model of particles is equivalent to the description of this problem by a hydrodynamic model. An effective model is obtained for a pointlike neutral system of charged particles that possesses an intrinsic dipole moment, and the free dynamics of this system is described. The bound momentum of a point dipole is found.

Kazinski, P. O. [Tomsk State University (Russian Federation)], E-mail: kpo@phys.tsu.ru

2007-08-15

430

Granulomatous reactions in mycosis fungoides.  

PubMed

Granulomatous reaction characterized by the formation of noncaseating accumulations of epithelioid histiocytes and multinucleated giant cells of the foreign-body type is a rare, poorly understood, and generally ignored phenomenon seen in various types of lymphoma. Its presence in cutaneous infiltrates of mycosis fungoides is equally unusual, but some favorable prognostic significance has been ascribed to it previously. In this paper, four patients with typical mycosis fungoides and granulomas demonstrated histologically in their cutaneous infiltrates are presented. All four died of disseminated disease with evidence of central nervous system involvement in three of them. These clinical histories lend no support to the notion that granulomatous mycosis fungoides is a benign variant of this lymphoma. Relevant literature is reviewed and discussed. PMID:3560956

Dabski, K; Stoll, H L

1987-04-01

431

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

432

Palladium-catalyzed oxidative carbonylation reactions.  

PubMed

Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions. PMID:23307763

Wu, Xiao-Feng; Neumann, Helfried; Beller, Matthias

2013-02-01

433

Charge exchange reactions and applications to astrophysics  

SciTech Connect

Neutrino-induced reactions have been known to play important roles as the neutrino process on the nucleosynthesis in core collapsing supernovae (SNe) explosions because expected neutrino flux and energy are sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. However, we do not have enough data for the neutrino reaction to be exploited in the network calculation. Only a sparse data in the relevant energy range is known, in specific, for {sup 12}C. Therefore we have to rely on theoretical estimation of the reaction, which has two different modes, charge current (CC) and neutral current (NC). In particular, CC reactions are closely related to charge exchange reactions (CEXRs) which are feasible in the experiment, such as, (p,n) or (n,p) reactions. These CEXRs are usually dominated by the Gamow-Teller (GT) transition in the lower energy region. In this respect, any theoretical approaches for the neutrino reaction should be investigated for the CEXR because we have and expect more useful experimental data. After confirming our models to the GT strength deduced from the CEXR, we calculated neutrino-induced reactions in the energy range below the quasielastic region for nuclei of astrophysical importance. Our calculations are carried out with the Quasi-particle Random Phase Approximation (QRPA), which successfully described the nuclear beta decays of relevant nuclei. To describe neutrino-nucleus reactions, general multipole transitions by the weak interaction are considered for CC and NC reactions. Both reactions are described in a theoretical framework. Our results are shown to well reproduce the data from CEXRs and the sparse experimental data related to the neutrino-induced reaction, and further extended for neutrino reactions on various nuclear targets. Parts of the results are reported in this talk.

Cheoun, Myung-Ki; Ha, Eunja; Kajino, T. [Department of Physics, Soongsil University, Seoul, 156-743 (Korea, Republic of); National Astronomical Observatory, Mitaka, Tokyo 181-8589 (Japan) and Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan)

2012-11-12

434

Charge exchange reactions and applications to astrophysics  

NASA Astrophysics Data System (ADS)

Neutrino-induced reactions have been known to play important roles as the neutrino process on the nucleosynthesis in core collapsing supernovae (SNe) explosions because expected neutrino flux and energy are sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. However, we do not have enough data for the neutrino reaction to be exploited in the network calculation. Only a sparse data in the relevant energy range is known, in specific, for 12C. Therefore we have to rely on theoretical estimation of the reaction, which has two different modes, charge current (CC) and neutral current (NC). In particular, CC reactions are closely related to charge exchange reactions (CEXRs) which are feasible in the experiment, such as, (p,n) or (n,p) reactions. These CEXRs are usually dominated by the Gamow-Teller (GT) transition in the lower energy region. In this respect, any theoretical approaches for the neutrino reaction should be investigated for the CEXR because we have and expect more useful experimental data. After confirming our models to the GT strength deduced from the CEXR, we calculated neutrino-induced reactions in the energy range below the quasielastic region for nuclei of astrophysical importance. Our calculations are carried out with the Quasi-particle Random Phase Approximation (QRPA), which successfully described the nuclear beta decays of relevant nuclei. To describe neutrino-nucleus reactions, general multipole transitions by the weak interaction are considered for CC and NC reactions. Both reactions are described in a theoretical framework. Our results are shown to well reproduce the data from CEXRs and the sparse experimental data related to the neutrino-induced reaction, and further extended for neutrino reactions on various nuclear targets. Parts of the results are reported in this talk.

Cheoun, Myung-Ki; Ha, Eunja; Kajino, T.

2012-11-01

435

Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft  

NASA Technical Reports Server (NTRS)

A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

Rizvi, Farheen

2013-01-01

436

Reaction class transition state theory: Hydrogen abstraction reactions by hydrogen atoms as test cases  

SciTech Connect

We present a new method called Reaction Class Transition State Theory (RC-TST) for estimating thermal rate constants of a large number of reactions in a class. This method is based on the transition state theory framework within the reaction class approach. Thermal rate constants of a given reaction in a class relative to those of its principal reaction can be efficiently predicted from only its differential barrier height and reaction energy. Such requirements are much less than what is needed by the conventional TST method. Furthermore, we have shown that the differential energetic information can be calculated at a relatively low level of theory. No frequency calculation beyond those of the principal reaction is required for this theory. The new theory was applied to a number of hydrogen abstraction reactions. Excellent agreement with experimental data shows that the RC-TST method can be very useful in design of fundamental kinetic models of complex reactions. (c) 2000 American Institute of Physics.

Truong, Thanh N. [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, 315 South 1400 E, room 2020, Salt Lake City, Utah 84112 (United States)] [Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, University of Utah, 315 South 1400 E, room 2020, Salt Lake City, Utah 84112 (United States)

2000-09-22

437

Optimization of reaction conditions for REM resin-bound quaternization reactions.  

PubMed

A study into the effect of reaction variables on the quaternization of REM resin-bound tertiary amines was undertaken. The influence of resin matrix, solvent, reaction time, temperature, and amount of quaternization agent on the outcome of reaction was evaluated by reaction monitoring using (19)F NMR. The highest yields of tertiary amine products were seen when DMSO was used as reaction solvent in conjunction with a reaction time of 18 h at room temperature. The use of heating for extended reaction times tended to depress yields, indicating product cleavage during quaternization. Quaternization on PS-DVB resin was found to be more robust than reaction on PS-PEG matrices where yields were generally considerably lower than the observed conversions. DMSO was the most efficient reaction solvent for both resins despite poor swelling of the quaternization starting material. PMID:12005478

Cameron, Kenneth S; Morphy, J Richard; Rankovic, Zoran; York, Mark

2002-01-01

438

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

439

Reaction zone structure in supracompressed detonating explosives  

SciTech Connect

Nanosecond time resolved particle velocity histories of supracompressed detonation waves in TNT-, TATB-, and HMX-based explosives are measured using a VISAR laser velocimeter and calculated using the ignition and growth reactive flow hydrodynamic computer code model. The Zeldovich-von Neumann-Doering (ZND) detonation wave structure is observed at pressures more than twice the self-sustaining detonation wave pressure. TNT and TATB exhibited a fast reaction which liberates approximately 80% of the total available exothermicity within 50 ns, followed by a slower reaction which lasts another 100--200 ns. These reaction rates are not strongly dependent on the initial shock pressure. The slower reaction is attributed to diffusion controlled solid carbon coagulation. The ignition and growth model using a ZND type model with a fast reaction preceding a slower reaction to the fully reacted product state accurately calculates the VISAR experimental data for TNT, LX-17, PBX 9404 and RX-26-AF. 21 refs., 15 figs., 3 tabs.

Green, L.G.; Tarver, C.M.; Erskine, D.J.

1989-08-18

440

Explosive Alpha Capturing Reactions at High Temperature  

NASA Astrophysics Data System (ADS)

It has been recognised that some alpha capturing reactions may proceed explosively at some stellar situations more particularly at presupernova stage of stellar evolution.The effect of temperature on the mass of nuclear involved in these reactions are studied. Corrections for volume and surface energy are considered. There is a considerable change in the mass along with the temperature.With these new masses Q values for the reactions are calculated. With the new values reaction rates are modified. These reactions rates are then used to calculate the abundance of elements. It is expected that a new picture will emerge in the stellar abundence scenario. We have also calculated the energy generation rate using the new Q values and new reaction rates.Now comparing the nutrino dessipation rate with the enegry generation rate it is tried to obtain the evolutionary properties of a star in its later stages

Bezbaruah, Aditi; Duorah, Kalpana

441

Disulfiram-like reaction with ornidazole.  

PubMed

Many drugs are implicated in causation of disulfiram-like reaction. The disulfiram-like reaction can vary in severity and can occasionally be fatal. The reaction is believed to result from inhibition of metabolism of acetaldehyde to acetate by inhibition of aldehyde dehydrogenase. The increase in serum acetaldehyde results in unpleasant clinical manifestations. Metronidazole is known to cause disulfiram-like reaction. Although no previous report has implicated ornidazole in causation of disulfiram-like reaction, caution has been advised with the use of all imidazoles. We report the case of a 48-year-old male, who was taking ornidazole and developed features of disulfiram-like reaction after taking alcohol. The patient was managed with supportive measures and improved. The report highlights the need for clinicians to advise patients to restrict intake of alcohol if they are being prescribed imidazole derivatives. PMID:20083883

Sharma, V; Sharma, A; Kumar, V; Aggarwal, S

2009-01-01

442

Neutrino-nuclear response and photonuclear reactions  

NASA Astrophysics Data System (ADS)

Photonuclear reactions are shown to be used for studying neutrino (weak) nuclear responses involved in astroneutrino nuclear interactions and double beta decays. Charged current weak responses for ground and excited states are studied by using photonuclear reactions through isobaric analog states of those states, while neutral current weak responses for excited states are studied by using photonuclear reactions through the excited states. The weak interaction strengths are studied by measuring the cross sections of the photonuclear reactions, and the spin and parity of the states are studied by measuring angular correlations of particles emitted from the photonuclear reactions. Medium-energy polarized photons obtained from laser photons scattered off GeV electrons are very useful. Nuclear responses studied by photonuclear reactions are used to evaluate neutrino (weak) nuclear responses, i.e., nuclear beta and double beta matrix elements and neutrino-nuclear interactions, and to verify theoretical calculations for them.

Ejiri, H.; Titov, A. I.; Boswell, M.; Young, A.

2013-11-01

443

[Adverse reaction to fillers. Diagnosis and management].  

PubMed

Injectable fillers are an established component of aesthetic medicine. In general they are safe to use. However, adverse reactions are possible for the whole spectrum of products. These reactions can occur immediately, subacute or delayed, e.g. after years. Erythema, edema, abscesses, nodule formation or even ulcerations can be observed. A correct diagnoses of these reactions is important to allow an appropriate treatment, taking into consideration the clinic, the injected material and if applicable other diseases/treatments that might contribute to these reactions. All of these reactions should be reported either to specialized registries and/or to the appropriate national agencies. Only then will we be able to learn more about these reactions and the best possible treatment. PMID:23443639

Rzany, B; Bachmann, F; Nast, A

2013-03-01

444

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

445

Proton transfer reactions for ionized water clusters  

Microsoft Academic Search

Calculations of formation energies of the ionized water clusters and energies of reactions between small (including less than\\u000a eight water molecules) neutral and positively ionized water chisters are presented. Moreover, we discuss some reaction paths\\u000a between neutral and positively charged dimers, trimers and tetramers and proton transfer reactions (PTR) between cyclic clusters\\u000a and H3O+ ions which can appear in beam,

T. Wròblewski; L. Ziemczonek; G. P. Karwasz

2004-01-01

446

Ultrafast Photochromic Reactions of Fulgide Photoswitches  

Microsoft Academic Search

The dynamics of fulgide photoswitches has been investigated applying femtosecond transient absorption spectroscopy. The switching performance of differently substituted fulgides is equally improved in polymer (PMMA) environment as compared to liquid solution (toluene). In the polymer a single pathway for the ring-closure reaction, i.e., without the intermediate observed in toluene, allows for sub-picosecond reaction times. The ring-opening (on-switching) reaction in

H. Port; P. Gärtner; M. Hennrich; I. Ramsteiner; T. Schöck

2005-01-01

447

Allergic reactions to foods by inhalation  

Microsoft Academic Search

Although allergic reactions to foods occur most commonly after ingestion, inhalation of foods can also be an underlying cause\\u000a of these reactions. For example, published reports have highlighted the inhalation of allergens from fish, shellfish, seeds,\\u000a soybeans, cereal grains, hen’s egg, cow’s milk, and many other foods in allergic reactions. Symptoms have typically included\\u000a respiratory manifestations such as rhinoconjunctivitis, coughing,

John M. James; Jesús Fernández Crespo

2007-01-01

448

Diamine Ligands in Copper-Catalyzed Reactions  

PubMed Central

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

Surry, David S.

2012-01-01

449

Novel Reagents for Multi-Component Reactions  

NASA Astrophysics Data System (ADS)

Ketenimines are a class of versatile and highly reactive intermediates that can participate in a variety of organic reactions, such as nucleophilic additions, radical additions, [2 + 2] and [2 + 4] cycloadditions, and sigmatropic rearrangements. In this presentation, we report on a series of multi-component reactions that involve a ketenimine intermediate. These reactions could furnish diverse heterocyclic compounds, including functionalized iminocoumarin, iminodihydroqunolines, iminothiochromens, pyrrolines, isoquinolines, pyridines, ?-lactams, imino-1,2-dihydrocoumarins, and benzimidazoles.

Wang, Yanguang; Basso, Andrea; Nenajdenko, Valentine G.; Gulevich, Anton V.; Krasavin, Mikhail; Bushkova, Ekaterina; Parchinsky, Vladislav; Banfi, Luca; Basso, Andrea; Cerulli, Valentina; Guanti, Giuseppe; Riva, Renata; Rozentsveig, Igor B.; Rozentsveig, Gulnur N.; Popov, Aleksandr V.; Serykh, Valeriy J.; Levkovskaya, Galina G.; Cao, Song; Shen, Li; Liu, Nianjin; Wu, Jingjing; Li, Lina; Qian, Xuhong; Chen, Xiaopeng; Wang, Hongbo; Feng, Jinwu; Wang, Yanguang; Lu, Ping; Heravi, Majid M.; Sadjadi, Samaheh; Kazemizadeh, Ali Reza; Ramazani, Ali; Kudyakova, Yulia S.; Goryaeva, Marina V.; Burgart, Yanina V.; Saloutin, Victor I.; Mossetti, Riccardo; Pirali, Tracey; Tron, Gian Cesare; Rozhkova, Yulia S.; Mayorova, Olga A.; Shklyaev, Yuriy V.; Zhdanko, Alexander G.; Nenajdenko, Valentine G.; Stryapunina, Olga G.; Plekhanova, Irina V.; Glushkov, Vladimir A.; Shklyaev, Yurii V.

450

Efficiently gap-filling reaction networks  

PubMed Central

Background Flux Balance Analysis (FBA) is a genome-scale computational technique for modeling the steady-state fluxes of an organism’s reaction network. When the organism’s reaction network needs to be completed to obtain growth using FBA, without relying on the genome, the completion process is called reaction gap-filling. Currently, computational techniques used to gap-fill a reaction network compute the minimum set of reactions using Mixed-Integer Linear Programming (MILP). Depending on the number of candidate reactions used to complete the model, MILP can be computationally demanding. Results We present a computational technique, called FastGapFilling, that efficiently completes a reaction network by using only Linear Programming, not MILP. FastGapFilling creates a linear program with all candidate reactions, an objective function based on their weighted fluxes, and a variable weight on the biomass reaction: no integer variable is used. A binary search is performed by modifying the weight applied to the flux of the biomass reaction, and solving each corresponding linear program, to try reducing the number of candidate reactions to add to the network to generate a working model. We show that this method has proved effective on a series of incomplete E. coli and yeast models with, in some cases, a three orders of magnitude execution speedup compared with MILP. We have implemented FastGapFilling in MetaFlux as part of Pathway Tools (version 17.5), which is freely available to academic users, and for a fee to commercial users. Download from: biocyc.org/download.shtml. Conclusions The computational technique presented is very efficient allowing interactive completion of reaction networks of FBA models. Computational techniques based on MILP cannot offer such fast and interactive completion.

2014-01-01

451

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

452

Mechanisms of Phototoxic and Photoallergic Reactions  

Microsoft Academic Search

\\u000a Solar radiation represents an important environmental stress for human skin. The biological reactions resulting from this\\u000a interaction leads to physiological and pathological reactions such as an increased photosensitivity. The present chapter focuses\\u000a on the mechanisms underlying photosensitivity, especially phototoxic and photoallergic reactions caused by exogenous and endogenous\\u000a chemicals, especially drugs.

Renz Mang; Helger Stege; Jean Krutmann

453

Demisable Reaction-Wheel Assembly  

NASA Technical Reports Server (NTRS)

A document discusses the concept of a demisable motor-drive-and-flywheel assembly [reaction-wheel assembly (RWA)] used in controlling the attitude of a spacecraft. Demisable as used here does not have its traditional legal meaning; instead, it signifies susceptible to melting, vaporizing, and/or otherwise disintegrating during re-entry of the spacecraft into the atmosphere of the Earth so as not to pose a hazard to anyone or anything on the ground. Prior RWAs include parts made of metals (e.g., iron, steel, and titanium) that melt at high temperatures and include structures of generally closed character that shield some parts (e.g., magnets) against re-entry heating. In a demisable RWA, the flywheel would be made of aluminum, which melts at a lower temperature. The flywheel web would not be a solid disk but would have a more open, nearly-spoke-like structure so that it would disintegrate more rapidly; hence, the flywheel rim would separate more rapidly so that parts shielded by the rim would be exposed sooner to re-entry heating. In addition, clearances between the flywheel and other components would be made greater, imparting a more open character and thus increasing the exposure of those components.

Roder, Russell; Ahronovich, Eliezer; Davis, Milton C., III

2008-01-01

454

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

455

Vertical two chamber reaction furnace  

DOEpatents

A vertical two chamber reaction furnace. 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.degree. and 800.degree. C.) on TBCCO or BCCO tape or wire (the second reactant) at its simultaneous annealing temperature in the upper chamber of about 800.degree. to 950.degree. 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.

Blaugher, Richard D. (Evergreen, CO)

1999-03-16

456

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

457

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

458

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.

Stevens, A A

1982-01-01

459

Pyrotechnic reaction residue particle analysis.  

PubMed

Pyrotechnic reaction residue particle (PRRP) production, sampling and analysis are all very similar to that for primer gunshot residue. In both cases, the preferred method of analysis uses scanning electron microscopy to locate suspect particles and then uses energy dispersive x-ray spectroscopy to characterize the particle's constituent chemical elements. There are relatively few times when standard micro-analytical chemistry performed on pyrotechnic residues may not provide sufficient information for forensic investigators. However, on those occasions, PRRP analysis provides a greatly improved ability to discriminate between materials of pyrotechnic origin and other unrelated substances also present. The greater specificity of PRRP analysis is the result of its analyzing a large number of individual micron-sized particles, rather than producing only a single integrated result such as produced using standard micro-analytical chemistry. For example, PRRP analyses are used to demonstrate its ability to successfully (1) discriminate between pyrotechnic residues and unrelated background contamination, (2) identify that two different pyrotechnic compositions had previously been exploded within the same device, and (3) establish the chronology of an incident involving two separate and closely occurring explosions. PMID:16566762

Kosanke, Kenneth L; Dujay, Richard C; Kosanke, Bonnie J

2006-03-01

460

[Dental materials can cause oral allergic reactions].  

PubMed

A large number of materials used in the diagnosis, treatment and prevention of dental, periodontal and oral mucosal diseases may induce acute or chronic reactions in the oral cavity including allergic reactions. Clinically, it may be difficult to discriminate oral mucosal changes caused by dental materials from changes related to oral mucosal diseases. Diagnosis and management of allergic reactions in the oral mucosa may therefore be a major challenge. The purpose of this paper is to draw attention to commonly used dental materials, which can trigger typical, but also atypical, symptoms and clinical signs of an allergic reaction. PMID:23773217

Røn Larsen, Kristine; Johansen, Jeanne Duus; Arenholt-Bindslev, Dorthe; Reibel, Jesper; Pedersen, Anne Marie Lynge

2013-06-17

461

Categorization of some oscillatory enzymatic reactions  

SciTech Connect

We investigate the categorization of two or more proposed reaction mechanisms for each of the following oscillatory enzymatic reactions: (1) the peroxidase-oxidase reaction; (2) glycolytic oscillations; (3) oscillations of cyclic AMP in smile mold cells; (4) enzymatic pH oscillations; (5) calcium spiking in cytosol. We use prior work in stoichiometric network analysis and categorization of oscillatory reactions to identify in each proposed reaction mechanism essential and nonessential species, the specific role of each essential species, the connectivity of the essential species, including the identification of the reactions leading to oscillatory instabilities, and the category. For each model, we predict the result of several experiments including relative amplitudes, quench amplitudes, phase shifts, and sign symbolic concentration shifts and compare them with those from available experiments. These and several other experiments such as bifurcation analysis, phase response curves, entrainment experiments, qualitative and quantitative pulsed species response, delay experiments, and external periodic perturbation provide stringent tests of proposed reaction mechanisms, and appropriate ones are suggested to discriminate among competing mechanisms for a given reaction. We find the necessity for introducing a new subcategory in our categorization of oscillatory reactions. 45 refs., 6 figs., 6 tabs.

Schreiber, I. [Prague Inst. of Chemical Technology (Czechoslovakia)] [Prague Inst. of Chemical Technology (Czechoslovakia); Hung, Y.F.; Ross, J. [Stanford Univ., CA (United States)] [Stanford Univ., CA (United States)

1996-05-16

462

Method of integral transforms to calculate reactions  

NASA Astrophysics Data System (ADS)

A method to calculate reactions in quantum mechanics is outlined. It is advantageous, in particular, in problems with many open channels of various nature, i.e., when energy is not low. In the difference with more conventional approaches the dynamics calculations to be performed are bound-state type-calculations. Continuum spectrum states never enter the game. In the course of calculations there is no need to consider reaction channels, as well as reaction thresholds. Reaction channels and thresholds come into play at merely the kinematics level and only after a dynamics calculation is done.

Efros, V. D.

2014-03-01

463

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.

Pfaff, Dominik; Nemecek, Gregor

2013-01-01

464

Acute anaphylactoid reactions during hemodialysis in France.  

PubMed

A retrospective survey of anaphylactoid reactions during dialysis in France was conducted. In 52 of 112 hemodialysis units surveyed 111 patients who had suffered one or more anaphylactoid reactions during dialysis were identified. According to the Hamilton/Adkinson classification, in 31 patients reactions were minor, in 54 patients moderate, and in 26 patients severe. Four patients died of their reactions. A preponderance of reactions (75 and 11%) occurred with cuprammonium cellulose hollow-fiber and plate dialyzers, respectively. Severe dialyzer reactions were found to occur more frequently after the long (weekend) interdialytic interval. In an in vitro study, six brands of cuprammonium cellulose hollow-fiber dialyzers were rinsed with water and the eluates analyzed by size exclusion chromatography for contaminant particles. Substantial variation in the amount of extractable material was found between dialyzers of different brands, despite the fact that all dialyzers used membranes from the same manufacturer. Previous data by others has suggested that this extractable material is a derivative of cellulose. Results of our epidemiologic survey in France are similar to those previously reported in the United States and suggest an increased incidence of dialyzer reactions with ethylene oxide-sterilized cuprammonium cellulose dialyzers. The presence of cellulose-derived particles in the rinsing fluid of such dialyzers and the possible increased incidence of reactions after the long (weekend) interdialytic interval suggest that allergy to cellulose-derived particles eluted from cellulosic dialyzers may contribute to dialyzer hypersensitivity reactions. PMID:3593044

Forêt, M; Kuentz, F; Meftahi, H; Milongo, R; Hachache, T; Elsener, M; Dechelette, E; Cordonnier, D

1987-04-01

465

Multicomponent reactions - opportunities for the pharmaceutical industry.  

PubMed

Multicomponent reactionsreactions that combine three or more starting materials in one pot to give a single product that contains essentially all of the atoms of the reactants – offer many exciting opportunities for medicinal chemistry. Their most obvious application is in the drug discovery phase, where they can provide efficient access to large numbers of analogs for lead discovery or optimization. By contrast, the inherent 'greenness' of multicomponent reactions makes them of increasing importance in the sustainable production of pharmaceuticals. We will discuss recent advances in both fields as well as general drivers and barriers for the application of multicomponent reactions in a medicinal chemistry context. PMID:24050225

Ruijter, Eelco; Orru, Romano V A

2013-01-01

466

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

467

Precautions and Adverse Reactions during Blood Transfusion  

MedlinePLUS

... leukocyte reduction), allergic reactions are less common. Fluid overload: Transfusion recipients can receive more fluid than their ... Special Blood Donation Procedures Next: Overview of Iron Overload

468

EXFOR Library of Experimental Nuclear Reaction Data  

DOE Data Explorer

The EXFOR library contains an extensive compilation of experimental nuclear reaction data up to 1 GeV. Neutron reactions have been compiled systematically since the discovery of the neutron, while charged particle(up to carbon) and photon reactions have been covered less extensively. Files contain nuclear reaction data such as cross sections, spectra, angular distributions, polarizations, etc, along with information on experimental technique, error analysis, and applied standards. Numerous search parameters include: target, beam, product, experimental method, and even author and publication names. The library contains data from more than 20,000 experiments. (Specialized Interface)

469

Energy distribution among reaction products. V.  

NASA Technical Reports Server (NTRS)

Discussion of three reactions, one point of theoretical interest being the predicted correlation between barrier height and barrier location. The H + Br 2 reaction having a lower activation barrier than H + Cl 2, should have an earlier barrier, and hence a greater percentage attractive energy release and higher efficiency of vibrational excitation. Information is developed concerning the effect of isotopic substitution in the pair of reactions H + Cl 2 and D + Cl 2. The 'arrested relaxation' method was used. Essentially, the method involves reacting two diffuse reagent beams in a reaction vessel with background pressure less than 0.001 torr, and with walls cooled by liquid nitrogen or liquid helium.

Anlauf, K. G.; Horne, D. S.; Macdonald, R. G.; Polanyi, J. C.; Woodall, K. B.

1972-01-01

470

Organic syntheses employing supercritical carbon dioxide as a reaction solvent  

NASA Technical Reports Server (NTRS)

Chemical reactions are readily carried out using supercritical carbon dioxide as the reaction medium. Supercritical carbon dioxide is of special value as a reaction medium in reactions for synthesizing polypeptides, for sequencing polypeptides, or for amino acid analysis.

Barstow, Leon E. (Inventor); Ward, Glen D. (Inventor); Bier, Milan (Inventor)

1993-01-01

471

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

472

Reaction energetics on long-range corrected density functional theory: Diels-Alder reactions.  

PubMed

The possibility of quantitative reaction analysis on the orbital energies of long-range corrected density functional theory (LC-DFT) is presented. First, we calculated the Diels-Alder reaction enthalpies that have been poorly given by conventional functionals including B3LYP functional. As a result, it is found that the long-range correction drastically improves the reaction enthalpies. The barrier height energies were also computed for these reactions. Consequently, we found that dispersion correlation correction is also crucial to give accurate barrier height energies. It is, therefore, concluded that both long-range exchange interactions and dispersion correlations are essentially required in conventional functionals to investigate Diels-Alder reactions quantitatively. After confirming that LC-DFT accurately reproduces the orbital energies of the reactant and product molecules of the Diels-Alder reactions, the global hardness responses, the halves of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, along the intrinsic reaction coordinates of two Diels-Alder reactions were computed. We noticed that LC-DFT results satisfy the maximum hardness rule for overall reaction paths while conventional functionals violate this rule on the reaction pathways. Furthermore, our results also show that the HOMO-LUMO gap variations are close to the reaction enthalpies for these Diels-Alder reactions. Based on these results, we foresee quantitative reaction analysis on the orbital energies. PMID:23037888

Singh, Raman K; Tsuneda, Takao

2013-02-15

473

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

474

Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions  

EPA Science Inventory

Magnetite-sulfonic acid (NanocatFe-OSO3H), prepared by wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter reaction which can be used in several reaction cycles without any loss of activity....

475

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.

476

Surrogate Nuclear Reactions - An Indirect Method for Determining Reaction Cross Sections  

SciTech Connect

An indirect method for determining cross sections of reactions proceeding through a compound nucleus is presented. Some applications of the Surrogate nuclear reaction approach are considered and challenges that need to be addressed are outlined.

Escher, J; Ahle, L; Bernstein, L; Burke, J; Church, J A; Dietrich, F; Forssen, C; Hoffman, R; Gueorguiev, V

2005-03-23

477

Reaction of Metal Sulfates with Molybdenum Oxide, a High Temperature Reaction Step for Thermochemical Cycles.  

National Technical Information Service (NTIS)

The reaction of sulfates with molybdenum oxide at high temperature was studied to determine the feasibility of using these reactions in a thermochemical process for making hydrogen. The experiments were performed by heating the blended powders to temperat...

C. M. Hollabaugh T. C. Wallace M. G. Bowman W. M. Jones

1980-01-01

478

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

479

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.

2011-01-01

480

pH & Rate of Enzymatic Reactions.  

ERIC Educational Resources Information Center

A quantitative and inexpensive way to measure the rate of enzymatic reaction is provided. The effects of different pH levels on the reaction rate of an enzyme from yeast are investigated and the results graphed. Background information, a list of needed materials, directions for preparing solutions, procedure, and results and discussion are…

Clariana, Roy B.

1991-01-01

481

Infrared Emission from Gas-Aerosol Reactions.  

National Technical Information Service (NTIS)

The present investigation has been designed to produce infrared emission by means of an exothermic reaction between a liquid aerosol and a gas. A number of gas-aerosol systems employing acid-base reactions have been examined and significant levels of radi...

R. A. Mackay E. W. Stuebing

1982-01-01

482

Cutaneous reactions to transdermal therapeutic systems.  

PubMed

Transdermal therapeutic systems (TTSs) are commonly used to treat many diverse medical conditions. There are several advantages to this form of drug delivery; however, adverse cutaneous reactions are common. This review article provides an update on skin reactions due to TTSs containing medications newly available in TTS form, including buprenorphine, diclofenac, lidocaine, oxybutynin, rotigotine, methylphenidate, rivastigmine, teriparatide, and nicardipine. PMID:21781635

Bershow, Andrea; Warshaw, Erin

2011-01-01

483