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1

A tandem non-aldol aldol Mukaiyama aldol reaction.  

PubMed

[reaction: see text] A new one-pot tandem aldol process is described in which a secondary epoxy silyl ether is converted into the 1,5-bis-silyloxy-3-alkanone in good yield. Thus, treatment of the epoxy silyl ether 8 with TBSOTf and base affords the silyl enol ether 9 via non-aldol aldol rearrangement and addition of benzaldehyde and TBSOTf gives the ketone 10 with 4:1 syn selectivity. The diastereoselectivity changes to an anti preference for most aldehydes. This anti selectivity overwhelms the normal Felkin-Ahn preference; namely, the 1,5-anti isomer predominates even when it is anti-Felkin-Ahn. PMID:14627420

Jung, Michael E; van den Heuvel, Alexandra

2003-11-27

2

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

PubMed

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

Saadi, Jakub; Yamamoto, Hisashi

2013-02-19

3

Role of water in mukaiyama-aldol reaction catalyzed by lanthanide lewis Acid: a computational study.  

PubMed

Carbon-carbon bond formations, such as Kobayashi modification of the Mukaiyama-Aldol reaction, catalyzed by lanthanide (Ln) Lewis acid in aqueous solution comprise one of the most attractive types of reactions in terms of green chemistry. However, their detailed mechanisms and the role of water molecules remained unclear. In order to explore complex potential energy surfaces for the water and substrate coordination around Eu(3+) as well as the detailed mechanism of the Mukaiyama-Aldol reaction between trimethylsilyl (TMS) cylcohexenolate and benzaldehyde (BA) catalyzed by Eu(3+), the recently developed anharmonic downward distortion following (ADDF) and artificial force-induced reaction (AFIR) methods were used with the B3LYP-D3 theory. The most favorable water coordination structures are Eu(3+)(H2O)8 and Eu(3+)(H2O)9; they are comparable in free energy and are likely to coexist, with an effective coordination number of 8.3. Eu(3+)(H2O)8(BA) is the best aldehyde coordinated structure. Starting with this complex, the Mukaiyama-Aldol reaction proceeds via a stepwise mechanism, first C-C bond formation between the substrates, followed by proton transfer from water to BA and then TMS dissociation caused by nucleophilic attack by bulk water molecules. Why did the yield of the Mukaiyama-Aldol reaction catalyzed by Ln(3+) in organic solvent dramatically increase upon addition of water? Without water, the reverse reaction (C-C cleavage) takes place easily. Why did this reaction show syn-preference in water? The anti transition state for C-C formation in water is entropically less favored relative to the syn transition state because of the existence of a rigid hydrogen bond between the TMS part and coordination water around Eu(3+) in the former. PMID:24006879

Hatanaka, Miho; Morokuma, Keiji

2013-09-05

4

Catalysis of mukaiyama aldol reactions by a tricyclic aluminum alkoxide Lewis acid.  

PubMed

The Mukayiama aldol reaction of aldehydes is efficiently accomplished with a low concentration of the dimeric alumatrane catalyst 2 at mild or subambient temperatures. Our protocol tolerates a wide variety of electron-rich, neutral, and deficient aryl, alkyl, and heterocyclic aldehydes. A wide variety of enol silyl ethers are also tolerated. An intermediate that was isolated provides mechanistic information regarding the role of dimeric 2 in the Mukaiyama aldol reaction. Experimental evidence is presented for the stronger Lewis acidity of 5 compared with F3B. PMID:19545133

Raders, Steven M; Verkade, John G

2009-08-01

5

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

6

Facile uncatalyzed mukaiyama aldol reactions: an ab initio study of the effects of substituents.  

PubMed

High-level ab initio molecular orbital calculations at the G3(MP2) level of theory were carried out to investigate the effects of substituents on the energetics of the uncatalyzed Mukaiyama aldol reaction between trihydrosilyl enol ether and formaldehyde. The concerted pathway, via a twist-boat six-membered ring transition state, is strongly favored over the stepwise pathway which involves a four-membered ring oxetane intermediate. Six substituents (CH(3), NH(2), OH, F, SH, and CHO) on trihydrosilyl enol ether and eight substituents (CH(3), CF(3), NH(2), F, CHO, COOCH(3), CH=CH(2), and C(6)H(5)) on formaldehyde were considered. We find that the reaction exothermicity is the main factor that dominates reactivity. The calculated barriers vary considerably from 30 to 131 kJ mol(-1). With the exception of halogen substitution, the nucleophilicity of silyl enol ether and the electrophilicity of the aldehyde are important in promoting the reactivity of this class of aldol addition. The roles of frontier molecular orbital interactions and electrostatic interactions are also discussed. In addition, our study has revealed that employing substituents on both reactants can act in a cooperatively manner to reduce the activation barrier further. In particular, we predict that the reactions between NH(2)-substituted enol silane and CHO-, COOCH(3)-, and CF(3)-substituted aldehydes have remarkably low barriers (<12 kJ mol(-1)). Thus, these reactions may proceed readily without a catalyst below room temperature. Several substitutions on the silicon group, namely SiF(3), SiCl(3), SiMe(3), and silacyclobutyl, were considered. In agreement with experiment, the O-(silacyclobutyl) and O-(trichlorosilyl) derivatives are found to promote aldol reactivity. PMID:15624914

Wong, Chiong Teck; Wong, Ming Wah

2005-01-01

7

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

Microsoft Academic Search

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

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

2009-01-01

8

P(PhCH2NCH2CH2)3N catalysis of Mukaiyama aldol reactions of aliphatic, aromatic, and heterocyclic aldehydes and trifluoromethyl phenyl ketone.  

PubMed

Herein we find that proazaphosphatrane 1c is a very efficient catalyst for Mukaiyama aldol reactions of aldehydes with trimethylsilyl enolates in THF solvent. Only the activated ketone 2,2,2-trifluoroacetophenone underwent clean aldol product formation with a variety of trimethylsilyl enolates under similar conditions as the aldehydes. The reactions were carried out at room temperature using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane, whereas the temperature was -15 degrees C in the case of 1-phenyl-1-(trimethylsilyloxy)ethylene. The reaction conditions are mild and operationally simple, and a variety of aryl functional groups, such as nitro, amino, ester, chloro, trifluoromethyl, bromo, iodo, cyano, and fluoro groups, are tolerated. Product yields are generally better than or comparable to those in the literature. 1-Phenyl-1-(trimethylsilyloxy)ethylene, 1-(trimethylsilyloxy)cyclohexene, and 2-(trimethylsilyloxy)furan underwent clean conversion to beta-hydroxy carbonyl compounds under our reaction conditions. In the case of bulky (2,2-dimethyl-1-methylenepropoxy)trimethylsilane, only alpha,beta-unsaturated esters were isolated. Heterocyclic aldehydes, such as pyridine-2-carboxaldehyde, benzofuran-2-carboxaldehyde, benzothiophene-2-carboxaldehyde, and 1-methyl-2-imidazolecarboxaldehyde, gave good yields of Mukaiyama products. An optimized synthesis for the catalyst 1c is also reported herein. PMID:19795856

Chintareddy, Venkat Reddy; Wadhwa, Kuldeep; Verkade, John G

2009-11-01

9

Organolanthanide reagents and the Mukaiyama reaction  

SciTech Connect

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

Gong, L.

1989-01-01

10

Catalytic, enantioselective, vinylogous aldol reactions.  

PubMed

In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed. PMID:15940727

Denmark, Scott E; Heemstra, John R; Beutner, Gregory L

2005-07-25

11

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

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

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-07-04

12

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

13

syn-Selective Kobayashi aldol reaction using acetals.  

PubMed

The Kobayashi aldol reaction has been used to construct anti-aldol products by remote stereoinduction. Since the product of the Kobayashi aldol reaction has a typical polyketide structure, this reaction has been applied to the total synthesis of natural products. By varying this reaction, it was found that the reaction with acetals in the presence of Lewis acid proceeded to give syn adducts in high stereoselectivity. This is the first example of the stereoselective reaction of the chiral dienol ether and acetals. PMID:23331025

Tsukada, Hiroyuki; Mukaeda, Yuki; Hosokawa, Seijiro

2013-01-18

14

Investigation of the rh-catalyzed asymmetric reductive aldol reaction. Expanded scope based on reaction analysis.  

PubMed

[reaction: see text] A series of experiments are described that suggest that the Rh-catalyzed reductive aldol reaction proceeds by addition of a Rh(I) hydride, generated in situ, to the reacting acrylate followed by a stereochemistry-controlling aldol addition reaction. On the basis of this hypothesis, reaction conditions are engineered that allow for increased substrate scope. PMID:15228266

Russell, Albert E; Fuller, Nathan O; Taylor, Steven J; Aurriset, Pauline; Morken, James P

2004-07-01

15

An unprecedented, tandem Aldol-Grob reaction sequence  

Microsoft Academic Search

The authors report an unprecedented, tandem Aldol-Grob sequence involving the reaction of ketones with aromatic aldehydes in nonnucleophilic solvents in the presence of boron trifluoride. Although a detailed study of the reaction mechanism has not yet been completed, the consistent formation of (E)-alkene products, as well as the fact that aromatic aldehydes appear to be required, would point toward the

George W. Kabalka; David Tejedor; Nan-Sheng Li; Rama R. Malladi; Sarah Trotman

1998-01-01

16

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

17

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

18

Acetylphosphonate as a Surrogate of Acetate or Acetamide in Organocatalyzed Enantioselective Aldol Reactions  

PubMed Central

Highly enantioselective aldol reactions of acetylphosphonates and activated carbonyl compounds was realized with cinchona alkaloid derived catalysts, in which the acetylphosphonate was directly used as an enolate precursor for the first time. The aldol product obtained was converted in situ to its corresponding ester or amide through methanolysis or aminolysis. The overall process may be viewed as formal highly enantioselective acetate or acetamide aldol reactions, which are very difficult to achieve directly with organocatalytic methods.

Guang, Jie; Guo, Qunsheng

2012-01-01

19

A tandem Aldol-Grob reaction of ketones with aromatic aldehydes  

Microsoft Academic Search

Aromatic aldehydes react with ketones to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence. The reaction, initiated by boron trifluoride, also produces a carboxylic acid fragment.Aromatic aldehydes react with ketones in the presence of boron trifluoride to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence.

George W. Kabalka; David Tejedor; Nan-Sheng Li; Rama R. Malladi; Sarah Trotman

1998-01-01

20

An unprecedented, tandem Aldol-Grob reaction sequence  

SciTech Connect

The authors report an unprecedented, tandem Aldol-Grob sequence involving the reaction of ketones with aromatic aldehydes in nonnucleophilic solvents in the presence of boron trifluoride. Although a detailed study of the reaction mechanism has not yet been completed, the consistent formation of (E)-alkene products, as well as the fact that aromatic aldehydes appear to be required, would point toward the intermediacy of a carbocation derivative. A reasonable mechanism would involve the formation of the mixed aldol followed by the formation and subsequent nonsynchronous ring opening of a lactol. The proposed fragmentation is reminiscent of two-step Grob fragmentations that have been reported for N-halo-{alpha}-amino acids and cyclobutane hemiacetals as well as the acid-catalyzed fragmentation of {beta}-hydroxy acetals. The authors examined the effect of various acids on the reaction sequence in order to ascertain which would be most efficient. They conclude that boron trifluoride is the most effective of the acids studied in achieving the new tandem condensation-cleavage sequence.

Kabalka, G.W.; Tejedor, D.; Li, N.S.; Malladi, R.R.; Trotman, S. [Univ. of Tennessee, Knoxville, TN (United States)

1998-09-18

21

The Synthesis of Carboxylic Acids via an Aldol-Grob Reaction Sequence  

Microsoft Academic Search

Ketones react with aromatic aldehydes via a tandem Aldol-Grob reaction sequence. The reaction, initiated by boron trifluoride, produces a carboxylic acid fragment and can serve as an alternative to the Baeyer-Villiger reaction.

G. W. Kabalka; N.-S. Li; D. Tejedor; R. R. Malladi; X. Gao; S. Trotman

1999-01-01

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

Application of high pressure, induced by water freezing, to the direct asymmetric aldol reaction  

Microsoft Academic Search

High pressure, induced by water freezing, has been successfully applied to the direct catalytic asymmetric aldol reaction, in which higher yield and better enantioselectivity can be realized than in the reaction at room temperature under 0.1MPa.

Yujiro Hayashi; Wataru Tsuboi; Mitsuru Shoji; Noriyuki Suzuki

2004-01-01

26

A simple and scalable procedure for TiCl 4-promoted aldol reaction  

Microsoft Academic Search

TiCl4-promoted aldol reaction was carried out by adding TiCl4 to a solution of the aldol reaction substrates and (i-Pr)2NEt (DIPEA) in CH2Cl2. Compared to the conventional order of addition (sequentially adding TiCl4, DIPEA, and piperonal to the lactone 2 in CH2Cl2), this simplified procedure, gave a much cleaner reaction that could be executed on large scale and without cryogenic cooling.

Qiaogong Su; Jeffery L. Wood

2010-01-01

27

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

PubMed Central

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

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

2009-01-01

28

Synthesis of a Potential Intermediate for TMC-95A via an Organocatalyzed Aldol Reaction.  

PubMed

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

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

2013-09-24

29

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

ERIC Educational Resources Information Center

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

Coutlangus, Marilyn L.; And Others

1989-01-01

30

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

PubMed

A series of tripeptide organocatalysts containing a secondary amine group and two amino acids with polar side chain units were developed and evaluated in the direct asymmetric intermolecular aldol reaction of 4-nitrobenzaldehyde and cyclohexanone. The effectiveness of short polar peptides as asymmetric catalysts in aldol reactions to attain high yields of enantio- and diastereoselective isomers were investigated. In a comparison, glutamic acid and histidine produced higher % ee and yields when they were applied as the second amino acid in short trimeric peptides. These short polar peptides were found to be efficient organocatalysts for the asymmetric aldol addition reaction in aqueous media. Chirality 25:726-734, 2013. © 2013 Wiley Periodicals, Inc. PMID:23966316

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

2013-08-22

31

Direct aldol and tandem Mannich reactions in room temperature ammonia solutions  

Microsoft Academic Search

An economical, simple, and efficient direct aldol reaction via the double activation of both aldehydes and ketones by ammonia has been developed. An unprecedented tandem Mannich reaction was observed when hydroxybenzaldehydes, pyrrole-2-carboxyaldehyde, and indole-3-carboxyaldehyde were employed to afford 2,2-dimethyl-6-aryl-4-pyrilidinones in moderate to good yields.

Lichun Feng; Lijin Xu; Kimhung Lam; Zhongyuan Zhou; C. W. Yip; Albert S. C. Chan

2005-01-01

32

Hydrophobic Substituent Effects on Proline Catalysis of Aldol Reactions in Water  

PubMed Central

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

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

2013-01-01

33

Aldol reaction catalyzed by a hydrophilic catalyst in aqueous micelle as an enzyme mimic system.  

PubMed

Chitosan-supported L-proline complex was synthesized and applied as a catalyst for the direct asymmetric aldol reaction in various organic solvents and water as well. It was found that the novel synthesized catalyst was able to efficiently catalyze the aldol reaction in various media. The catalytic capacity and stereoselectivity of the catalyst were obviously improved with the introduction of aqueous micelle, possibly because the micelle functioned as a hydrophobic pocket, like the hydrophobic portion in enzymes. Moreover, the present synthetic catalyst showed performance similar to that of enzymes and could be used as a model of enzyme catalysis to help better understand the mystic mechanism of enzymes. PMID:18655166

Zhang, Hefeng; Zhao, Wenshan; Zou, Jun; Liu, Yi; Li, Runtao; Cui, Yuanchen

2009-05-01

34

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

PubMed

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

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

2011-12-19

35

Aggregation and cooperative effects in the aldol reactions of lithium enolates.  

PubMed

Density functional theory and Car-Parrinello molecular dynamics simulations have been carried out for model aldol reactions involving aggregates of lithium enolates derived from acetaldehyde and acetone. Formaldehyde and acetone have been used as electrophiles. It is found that the geometries of the enolate aggregates are in general determined by the most favorable arrangements of the point charges within the respective Lin On clusters. The reactivity of the enolates follows the sequence monomer?dimer>tetramer. In lithium aggregates, the initially formed aldol adducts must rearrange to form more stable structures in which the enolate and alkoxide oxygen atoms are within the respective Lin On clusters. Positive cooperative effects, similar to allosteric effects found in several proteins, are found for the successive aldol reactions in aggregates. The corresponding transition structures show in general sofa geometries. PMID:23964002

Larrañaga, Olatz; de Cózar, Abel; Bickelhaupt, F Matthias; Zangi, Ronen; Cossío, Fernando P

2013-08-21

36

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

EPA Science Inventory

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

37

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

2013-04-10

38

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

39

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

PubMed

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. PMID:23335856

Liao, Yuan-Xi; Hu, Qiao-Sheng

2012-09-01

40

Diastereoselective synthesis of glycosylated prolines as ?-glucosidase inhibitors and organocatalyst in asymmetric aldol reaction  

Microsoft Academic Search

1,3-Dipolar cycloaddition of azomethine ylides and glycosyl E-olefins in presence of LDA led to diastereoselective formation of C-glycosylated proline esters. The selected esters on regioselective hydrolysis with LiOH gave C-glycosyl prolines. Few of the proline esters exhibited very good ?-glucosidase inhibitory activity. The organocatalytic activity of the proline derivatives in a prototype Aldol reaction has also been investigated.

Jyoti Pandey; Namrata Dwivedi; Nimisha Singh; A. K. Srivastava; A. Tamarkar; R. P. Tripathi

2007-01-01

41

Synthesis of Substituted Chromanones: An Organocatalytic Aldol/oxa-Michael Reaction  

PubMed Central

A diastereoselective organocatalytic aldol/oxa-Michael reaction has been developed to efficiently deliver medicinally relevant 2,3-ring substituted chromanones. Development of this synthetic strategy revealed an unexpected kinetic anti-Saytzeff elimination; an origin for the observed selectivity is suggested based on the results of quantum chemical calculations. This unusual kinetic selectivity necessitated an isomerization protocol that in turn led to the discovery of an intriguing Pd-mediated isomerization/intramolecular Friedel-Crafts-type alkylation.

Butler, Jeffrey D.; Conrad, Wayne E.; Lodewyk, Michael W.; Fettinger, James C.; Tantillo, Dean J.; Kurth, Mark J.

2011-01-01

42

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

PubMed

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

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

2012-12-21

43

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

44

Direct and Diastereoselective Alkylation and Aldol Reactions of ?-Bromo-?-fluoro-?-lactams.  

PubMed

Herein, we describe the development of a method for the direct alkylation and aldol reaction of ?-bromo-?-fluoro-?-lactams. This method provides facile access to a wide range of 3-alkyl- and 3-hydroxyalkyl-fluoro-?-lactams in good yields under mild conditions. The products were obtained with complete diastereoselectivity with regard to the relative configuration of the ?-lactam ring at C3 and C4 positions. The reaction conditions were tolerant of a broad range of electrophiles, which highlights the overall scope and utility of this procedure. PMID:23865894

Tarui, Atsushi; Kawashima, Naoto; Kawakita, Tetsuya; Sato, Kazuyuki; Omote, Masaaki; Ando, Akira

2013-08-02

45

Unraveling the role of water in the stereoselective step of aqueous proline-catalyzed aldol reactions.  

PubMed

A multiscale computational study was performed with the aim of tracing the source of stereoselectivity and disclosing the role of water in the stereoselective step of propionaldehyde aldol self-condensation catalyzed by proline amide in water, a reaction that serves as a model for aqueous organocatalytic aldol condensations. Solvent mixing and hydration behavior were assessed by classical molecular dynamics simulations, which show that the reaction between propanal and the corresponding enamine takes place in a fully hydrated environment. First-principles molecular dynamics simulations were used to study the free-energy profile of four possible reaction paths, each of which yields a different stereoisomer, and high-level static first-principles calculations were employed to characterize the transition states for microsolvated species. The first solvation shell of the oxygen atom of the electrophilic aldehyde at the transition states contains two water molecules, each of which donates one hydrogen bond to the nascent alkoxide and thereby largely stabilizes its excess electron density. The stereoselectivity originates in an extra hydrogen bond donated by the amido group of proline amide in two reaction paths. PMID:23074080

Ribas-Arino, Jordi; Carvajal, Maria Angels; Chaumont, Alain; Masia, Marco

2012-10-16

46

Kinetics of acid-catalyzed aldol condensation reactions of aliphatic aldehydes  

NASA Astrophysics Data System (ADS)

Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet-visible (UV-vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C 2-C 8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols.

Casale, Mia T.; Richman, Aviva R.; Elrod, Matthew J.; Garland, Rebecca M.; Beaver, Melinda R.; Tolbert, Margaret A.

47

A Fluorogenic Aldehyde Bearing a 1,2,3-Triazole Moiety for Monitoring the Progress of Aldol Reactions  

PubMed Central

We have developed a new type of fluorogenic aldehyde bearing a 1,2,3-triazole moiety that is useful for monitoring the progress of aldol reactions through an increase in fluorescence. Whereas 6-methoxy-2-naphthaldehyde was highly fluorescent, the fluorogenic aldehyde, 4-formylbenzene connected to 6-methoxy-2-naphthyl group through 1,2,3-triazole moiety, was essentially non-fluorescent in aqueous solutions. We suggest that the 4-formylphenyl group acts as a quencher to suppress the fluorescence of the 6-methoxy-2-naphthyltriazole moiety. The product of the aldol reaction of this aldehyde does not have a quenching moiety and showed more than 800-fold higher fluorescence than the aldehyde. Assay systems using the fluorogenic aldehyde were validated by screening of aldol catalysts, ranking of the activities of the catalysts, and evaluation of reaction conditions.

Guo, Hai-Ming; Tanaka, Fujie

2009-01-01

48

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

Microsoft Academic Search

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

Shue Kobayashi; Iwao Hachiya

1994-01-01

49

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

PubMed Central

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

Bhanushali, Mayur

2011-01-01

50

Kinetics of Acid-Catalyzed Aldol Condensation Reactions of Aliphatic Aldehydes  

NASA Astrophysics Data System (ADS)

While it is well established that organic compounds compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, ultraviolet-visible (UV-Vis) spectroscopy was used to monitor the kinetics of formation of the products of the aldol condensation reaction of a range of aliphatic aldehydes (C2-C8) The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature.

Elrod, M. J.; Casale, M. T.; Richman, A. R.; Beaver, M. R.; Garland, R. M.; Tolbert, M. A.

2006-12-01

51

Construction of successive chiral centers adjacent to a chiral tetraalkylated quaternary center using an asymmetric aldol reaction.  

PubMed

The aldol reaction of 2? with a variety of different aldehydes gave the corresponding ?-lactones 4 bearing successive asymmetric centers adjacent to a chiral tetraalkylated quaternary center or the (E)-alkenes 8. The use of electronically neutral or electron-deficient aldehydes led to 4 in excellent yields with high diastereoselectivities, whereas electron-rich aldehydes performed poorly and underwent decarboxylation to afford 8. PMID:23577874

Esumi, Tomoyuki; Yamamoto, Chihiro; Tsugawa, Yuri; Toyota, Masao; Asakawa, Yoshinori; Fukuyama, Yoshiyasu

2013-04-11

52

Lewis base-catalyzed conjugate reduction and reductive aldol reaction of alpha,beta-unsaturated ketones using trichlorosilane.  

PubMed

Lewis bases such as Ph3P=O and HMPA catalyze the 1,4-reduction of alpha,beta-unsaturated ketones with trichlorosilane, and because the 1,2-reduction of aldehydes scarcely proceeded under the conditions, one-pot reductive aldol reactions with aldehydes were successfully achieved; preliminary studies using a chiral Lewis base revealed a high potential for enantioselective catalysis. PMID:18802553

Sugiura, Masaharu; Sato, Norimasa; Kotani, Shunsuke; Nakajima, Makoto

2008-07-17

53

Chiral dendritic bis(oxazoline) copper(II) complexes as Lewis acid catalysts for enantioselective aldol reactions in aqueous media  

Microsoft Academic Search

A series of copper(II) complexes, with chiral bis(oxazoline) ligands disubstituted at the carbon atom linking the two oxazolines by Fréchet-type polyether dendrimers, have been designed and synthesized. These complexes were used as Lewis acid catalysts in enantioselective aldol reactions in aqueous media. Good yields and moderate enantioselectivities were achieved, which are comparable with those resulting from the corresponding smaller catalysts.

Bai-Yuan Yang; Xiao-Min Chen; Guo-Jun Deng; Yi-Li Zhang; Qing-Hua Fan

2003-01-01

54

Activation of Mg–Al Hydrotalcite Catalysts for Aldol Condensation Reactions  

Microsoft Academic Search

The condensation of benzaldehyde and acetone to aldol has been investigated in the liquid phase at 273 K on hydrotalcites transformed into basic solids by activation following different procedures. No activity was observed on the pure hydrotalcite (carbonated) or on the solid just decarbonated at 723 K. The activity went through a maximum after calcination at 723 K, followed by

Kottapalli Koteswara Rao; Monique Gravelle; Jaime Sanchez Valente; François Figueras

1998-01-01

55

Unusual synthesis of new glycine antagonists via sequential aldol condensation-lactonization-elimination reaction  

Microsoft Academic Search

Compounds 2 and 3 were designed in order to probe the North-East region of the strichnine-insensitive glycine binding site of the NMDA receptor. The two products were obtained readily by a tandem aldol condensation-lactonization-elimination step which affords the desired E isomer with complete regioselection.

Simone A. Giacobbe; Davide Baraldi; Romano Di Fabio

1998-01-01

56

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

PubMed

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

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

2013-09-19

57

Synthesis of Dibenzoxepine Lactams via a Cu-Catalyzed One-Pot Etherification/Aldol Condensation Cascade Reaction: Application toward the Total Synthesis of Aristoyagonine.  

PubMed

A general synthesis of dibenzoxepine lactams has been developed using a one-pot Cu-catalyzed etherification/aldol condensation cascade reaction. The reaction of 4-hydroxyisoindolin-1-one with a wide range of 2-bromobenzaldehydes in the presence of a copper catalyst provided various aristoyagonine derivatives in good yields. PMID:24000941

Lim, Hye Sun; Choi, Young Lok; Heo, Jung-Nyoung

2013-09-03

58

The Vinylogous Aldol Reaction of Unsaturated Esters and Enolizable Aldehydes Using the Novel Lewis Acid Aluminum Tris(2,6-di-2-naphthylphenoxide)  

PubMed Central

The synthesis of the novel Lewis acid, aluminum tris(2,6-di-2-naphthylphenoxide) (ATNP), and its use in the vinylogous aldol reaction between methyl crotonate and enolizable aldehydes are described. ATNP is related to Yamamoto’s Lewis acid, aluminum tris(2,6-diphenylphenoxide) (ATPH), but the 2-naphthyl groups more effectively block the ?-position of aldehydes, enabling the selective enolization of crotonate esters in the presence of enolizable aldehydes. Vinylogous aldol reactions then proceed smoothly and in high yields with a variety of substrates.

Gazaille, Jeffrey A.

2012-01-01

59

Equilibrium between a vinylogous ylide and a phosphonium dienolate zwitterion: vinylogous Wittig olefination versus vinylogous aldol-type reaction  

PubMed Central

This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF3·Et2O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration.

Khong, San N.; Tran, Yang S.; Kwon, Ohyun

2010-01-01

60

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

PubMed

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

Sello, Guido; Di Gennaro, Patrizia

2013-05-31

61

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

EPA Science Inventory

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

62

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

PubMed

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

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

2012-04-18

63

Organocatalyzed Aldol Reaction between Pyridine-2-carbaldehydes and ?-Ketoacids: A Straightforward Route towards Indolizidines and Isotetronic Acids.  

PubMed

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

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

2013-09-13

64

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

PubMed Central

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

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

2012-01-01

65

Enantioselective Organocatalytic Domino Michael/Aldol Reactions: An Efficient Procedure for the Stereocontrolled Construction of 2H-Thiopyrano[2,3-b]quinoline Scaffolds.  

PubMed

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

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

2013-05-31

66

Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction.  

PubMed

A new three-dimensional alkaline-earth metal-organic framework (MOF) compound, [Mg(Pdc)(H(2)O)](n) (1) (H(2)Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg(2)-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m(2) g(-1). Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m(2) g(-1) due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N(2) sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H(2)O)](n) (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity. PMID:22584602

Saha, Debraj; Sen, Rupam; Maity, Tanmoy; Koner, Subratanath

2012-05-14

67

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

ERIC Educational Resources Information Center

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

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

2007-01-01

68

Catalytic asymmetric synthesis of 3-(alpha-hydroxy-beta-carbonyl) oxindoles by a Sc(III)-catalyzed direct aldol-type reaction.  

PubMed

A direct catalytic asymmetric aldol-type reaction of 3-substituted-2-oxindoles with glyoxal derivatives and ethyl trifluoropyruvate, catalyzed by a chiral N,N'-dioxide-Sc(OTf)(3) (Tf = trifluoromethanesulfonyl) complex, has been developed that tolerates a wide range of substrates. The reaction proceeds in good yields and excellent enantioselectivities (up to 93% yield, 99:1 diastereomeric ratio (dr), and >99% enantiomeric excess (ee)) under mild conditions, to deliver 3-(alpha-hydroxy-beta-carbonyl) oxindoles with vicinal quaternary-tertiary or quaternary-quaternary stereocenters. Even with 1 mol % catalyst loading or on scaleup (10 mmol of starting material), maintenance of ee was observed, which showed the potential value of the catalyst system. In studies probing the reaction mechanism, a positive nonlinear effect was observed and Sc(III)-based enolate intermediates were detected by using ESIMS. On the basis of the experimental results and previous reports, a possible catalytic cycle was assumed. PMID:20175165

Shen, Ke; Liu, Xiaohua; Zheng, Ke; Li, Wei; Hu, Xiaolei; Lin, Lili; Feng, Xiaoming

2010-03-22

69

Organolanthanide Reagents and the Mukaiyama Reaction.  

National Technical Information Service (NTIS)

The bis(pentamethylcyclopentadienyl) lutetium halide complex ((C5 Me5 )2 LuCl/center dot/THF) was synthesized and characterized. The crystal structure of this complex shows that the Lu is at the center of a distorted tetrahedron consisting of the centroid...

L. Gong

1989-01-01

70

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

2013-09-17

71

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

72

Tandem semipinacol-type 1,2-carbon migration/aldol reaction toward the construction of [5-6-7] all-carbon tricyclic core of Calyciphylline A-type alkaloids.  

PubMed

A Lewis acid promoted tandem semipinacol-type 1,2-carbon migration/aldol reaction of trimethylsilane-protected vinylogous ?-ketols with aldehyde or dimethyl acetals is reported. This reaction provides a direct and rapid way for the construction of 6-substituted spiro[4.5]decanes which extensively exist in Daphniphyllum alkaloids. By the use of this method, further construction of a [5-6-7] all-carbon tricyclic core of Calyciphylline A-type alkaloids was also completed. PMID:22992007

Yang, Ming; Wang, Lin; He, Zheng-He; Wang, Shao-Hua; Zhang, Shu-Yu; Tu, Yong-Qiang; Zhang, Fu-Min

2012-09-19

73

Combining Meyer-Schuster rearrangement with aldol and Mannich reactions: theoretical study of the intermediate interception strategy.  

PubMed

Interception of the transient allenyl enolate intermediate of the vanadium-catalyzed Meyer-Schuster rearrangement with aldehydes and imines has been studied computationally using density functional theory. Mechanistic details of the catalytic cycles for each of the reaction variants are established. In particular, it is shown that the active form of the catalyst contains two triphenylsiloxy ligands, the transesterification of vanadate occurs via ?-bond metathesis, and vanadium enolate is directly involved in the key C-C bond formation. The calculations also provide support for the dissociative course of the key 1,3-shift step. The stereochemistry of the reaction is thoroughly investigated, and the obtained energy barriers reproduce and rationalize the experimentally observed (Z)-, (E)-selectivity. The calculated free energy profiles are analyzed in terms of efficiency of the intermediate enolate interception. It is shown that the investigated reactions represent borderline cases, in which the intermediate trapping is only slightly favored over the undesired isomerization pathway. PMID:23106444

Kalek, Marcin; Himo, Fahmi

2012-11-08

74

A Multistep Organocatalysis Experiment for the Undergraduate Organic Laboratory: An Enantioselective Aldol Reaction Catalyzed by Methyl Prolinamide  

ERIC Educational Resources Information Center

|In recent years, there has been an explosion of research concerning the area of organocatalysis. A multistep capstone laboratory project that combines traditional reactions frequently found in organic laboratory curriculums with this new field of research is described. In this experiment, the students synthesize a prolinamide-based organocatalyst…

Wade, Edmir O.; Walsh, Kenneth E.

2011-01-01

75

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

PubMed Central

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

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

2010-01-01

76

Mechanism of the lanthanum bromide assisted electrochemical aldolization of. alpha. -bromo ketones  

SciTech Connect

Linear sweep voltammetry, preparative electrolyses under a variety of experimental conditions, and trapping experiments have been used to explore the mechanism of the formation of the aldol 2-benzoyl-1-phenylpropanol by electrochemical reduction of {alpha}-bromopropiophenone in the presence of benzaldehyde and lanthanum bromide. The aldol condensation occurs by reaction of the free (lithio) enolate with a lanthanum bromide-benzaldehyde-tetrahydrofuran complex. Electrochemical reduction of the bromo ketone forms the Z enolate highly stereospecifically. The erythro aldol is formed stereoselectively initially, but the condensation is reversible, and the equilibrium mixture of aldols, containing mostly the threo isomer, is isolated from the electrolysis.

Fry, A.J.; Susla, M. (Wesleyan Univ., Middletown, CT (USA))

1989-04-26

77

Solvent-Free, Cross-Aldol Condensation Reaction Using Silica-Supported, Phosphorus-Containing Reagents Leading to ?,??Bis(arylidene)cycloalkanones  

Microsoft Academic Search

This article describes an efficient, simple, and clean method for the synthesis of ?,??-bis(arylidene, furylidene and cinnamylidene)cycloalkanones under solvent-free conditions. The cross-aldol condensation of cycloalkanones with aldehydes in the presence of silica-supported phosphorus pentoxide (P2O5\\/SiO2) or silicaphosphinoxide (silphox, [POCl3-n(SiO2)n]) as heterogeneous reagents produces the title compounds in good to excellent yields.

Alireza Hasaninejad; Abdolkarim Zare; Laleh Balooty; Hadis Mehregan; Mohsen Shekouhy

2010-01-01

78

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

PubMed

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

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

2012-08-27

79

Contribution to the study of the aldol condensation process  

Microsoft Academic Search

The reaction course of aldol condensation has been studied. Diacetone alcohol is produced from acetone, using a basic ion exchanger as a catalyst. Experiments are carried out in a laboratory set-up (batch process). The analysis of reactants and products is made by the method of refractometry and gas chromatography, respectively. The reaction is performed at 293, 303, 313 and 323

N. Sišul; N. Cikovi?; J. Jelen?i?; N. Wolf

1989-01-01

80

Gas-Phase Aldol Condensation Over Tin on Silica Catalysts.  

National Technical Information Service (NTIS)

Contents: Aldol condensation; Catalyst preparation and composition; Catalyst performance; Kinetics; On the nature of the active site for the aldol condensation over tin on silica catalysts; Gas-phase aldol condensation of n-butanal over tin on silica cata...

J. Venselaar

1980-01-01

81

Convenient synthetic route to a dehydrorotenoid via selective intramolecular aldol condensation of 1,2-diaryl diketone  

Microsoft Academic Search

Synthesis of dehydrorotenoid (1) was successfully achieved via an intramolecular aldol reaction of the corresponding 1,2-diaryl diketone intermediate. The 1,2-diaryl diketone was prepared using a ruthenium-catalyzed oxidation of the corresponding substituted diaryl acetylene. Treatment of this 1,2-diketone with l-proline induced a selective intramolecular aldol condensation reaction, forming the desired benzopyranone over the alternative benzofuran. Deprotection, cyclization, and dehydration gave the

Jumreang Tummatorn; Prapas Khorphueng; Amorn Petsom; Nongnuch Muangsin; Narongsak Chaichit; Sophon Roengsumran

2007-01-01

82

Complexity from simplicity: the Ugi-Aldol sequence as an expeditious entry into several families of densely substituted N-heterocylces  

PubMed Central

All it takes is the Aldol Nitrogen containing heterocycles have been assembled by means of unprecedented domino processes, designed to take advantage of diversity assembly via strategically decorated Ugi products. The aldol reaction is the second common denominator which enables sequences of up to 5 steps in one pot producing unique molecular architecture in rapid fashion.

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

2012-01-01

83

RuCl 3 catalyses aldol condensations of aldehydes and ketones  

Microsoft Academic Search

Anhydrous RuCl3 catalyses the efficient cross aldol condensations of different ketones with various aromatic aldehydes in sealed tube under solvent free conditions without the occurrence of any self condensations. Regioselective self condensation reaction of some ketones and aldehydes are also described. The catalytic effect of Ru(III) is shown by performing similar reactions under thermal conditions without catalyst.

Nasser Iranpoor; Foad Kazemi

1998-01-01

84

Microwave Induced Rate Enhancement in Aldol Condensation  

Microsoft Academic Search

The rate of formation of aldol condensed products using microwave of various aromatic aldehydes and ketones in aqueous medium dramatically enhanced with respect to conventional methods in high yield (50-95.2%).

G. L. Kad; Kanwal Preet Kaur; Vasundhara Singh; Jasvinder Singh

1999-01-01

85

Discovery-Oriented Approach To Organic Synthesis: Tandem Aldol Condensation-Michael Addition Reactions. Identifying Diastereotopic Hydrogens in an Achiral Molecule by NMR Spectroscopy  

NASA Astrophysics Data System (ADS)

We have found a beautiful example of anisochrony of diastereotopic acyclic methylene hydrogens in a symmetric diketone, synthesized by techniques traditionally performed in an introductory organic laboratory course. Synthesis of the diketone is high-yielding and easy to carry out, and the products can be directly isolated with a good degree of purity with no need of further manipulation. The reaction can be accomplished in a single laboratory session.

Wachter-Jurcsak, Nanette; Reddin, Kendra

2001-09-01

86

Mechanism of the aldol condensation of aldehydes, catalyzed by the salts of metals and higher organic acids  

SciTech Connect

The salts of transition metals are the most active catalysts for the aldol condensation of aliphatic aldehydes. By IR spectroscopy it was found that an intermediate complex between the aldehyde and the catalyst is formed at the initial stage of the reaction. A chelate mechanism of catalysis is proposed for the aldol condensation and satisfactorily explains the order of formation of the intermediate and final products.

Katsnel'son, M.G.; Kagna, S.Sh.; Nikitina, L.I.; Oranskaya, O.M.; Semenskaya, I.V.

1987-01-10

87

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

88

A kinetic study of the aldol condensation of acetone using an anion exchange resin catalyst  

Microsoft Academic Search

The rate of the reversible aldol condensation of acetone (Ac) to diacetone alcohol (DAA) catalysed by Amberlite IRA-900 anion exchange resin in the hydroxide form is measured in the liquid phase, without solvent, using batch and continuous reactors. The desired reaction product is DAA, but its dehydration leads to the formation of mesityl oxide (MO) as a byproduct. Although the

G. G. Podrebarac; F. T. T. Ng; G. L. Rempel

1997-01-01

89

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

90

Aldol Condensation of Volatile Carbonyl Compounds in Acidic Aerosols  

NASA Astrophysics Data System (ADS)

Reactions of volatile organic compounds in acidic aerosols have been shown recently to be potentially important for organic aerosol formation and growth. Aldol condensation, the acid-catalyzed polymerization of carbonyl compounds, is a likely candidate to enhance the flux of organic matter from the gas phase to the condensed phase in the atmosphere. Until now these reactions have only been characterized for conditions relevant to synthesis (high acidities and liquid phase systems) and remote from atmospheric ones. In this work, the uptake of gas-phase acetone and 2,4\\-pentanedione by sulfuric acid solutions has been measured at room temperature using a Rotated Wetted Wall Reactor coupled to a Mass Spectrometer. The aldol condensation rate constants for 2,4\\-pentanedione measured so far for sulfuric acid solutions between 96 and 70 % wt. display a variation with acidity in agreement with what predicted in the organic chemical literature. The values of these constants, however, are much lower than expected for this compound, and comparable to the ones of acetone. Experiments are underway to complete this study to lower acidities and understand the discrepancies with the predicted reactivity.

Noziere, B.; Esteve, W.

2003-12-01

91

Stereoselective aldol condensations via boron enolates  

Microsoft Academic Search

A detailed investigation of the enolization of a variety of ketones and carboxylic acid derivatives with dialkylboryl triflates in the presence of a tertiary amine and the subsequent aldol condensations of these boron enolates was conducted. The stereochemistry of the enolates formed from acyclic ketones was found to be dependent on the structure of the ketone, the dialkylboryl triflate, and

D. A. Evans; J. V. Nelson; E. Vogel

1979-01-01

92

Discovery of a novel class of aldol-derived 1,2,3-triazoles: Potent and selective inhibitors of human cytochrome P450 19A1 (aromatase)  

Microsoft Academic Search

The discovery of a novel five-component 1,2,3-triazole-containing pharmacophore that exhibits potent and selective inhibition of aromatase (CYP 450 19A1) is described. All compounds are derived from an initial aldol reaction of a phenylacetate derivative with an aromatic aldehyde. Structure–activity data generated from both syn- and anti-aldol adducts provides initial insights into the requirements for both potency and selectivity.

James McNulty; Jerald J. Nair; Nesrin Vurgun; Benjamin R. DiFrancesco; Carla E. Brown; Bernice Tsoi; Denis J. Crankshaw; Alison C. Holloway

93

Aldol condensation of acetone over layered double hydroxides of the meixnerite type  

Microsoft Academic Search

Aldol condensation of acetone is performed at 273 K in liquid phase using as catalysts Mg–Al layered double hydroxides (LDH) with Cl? and\\/or CO32? as compensating anions. The products of the reaction are mainly diacetone alcohol and mesityl oxide. The catalytic activities increase with the Al content of the LDH and a conversion around 20% is reached when the carbonated

D Tichit; M Naciri Bennani; F Figueras; R Tessier; J Kervennal

1998-01-01

94

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

95

Aldol condensation of acetone in the two-phase system solid base-benzene in the presence of benzyltriethylammonium chloride  

Microsoft Academic Search

Conclusions 1.We propose a mechanism for the aldol condensation of acetone in the presence of solid base, explaining the optimum way of forming diacetone alcohol by filling the surface of the base with the diacetone alcohol and acetone anions.2.Disappearance of the diacetone alcohol from the reaction products after filling the principal centers of the free base was caused by its

S. S. Yufit; I. A. Esikova

1984-01-01

96

Stereoselective cross aldol condensation of bicyclo[3.2.0]alkanones.  

PubMed

A cross aldol reaction between [(S)-(-)] or [(R)-(+)]-benzyloxypropanal and silyl enol ethers derived from bicyclo[3.2.0]alkanones was carried out in the presence of TiCl4, leading with total stereoselectivity to a 1 : 1 mixture of enantiomerically pure diastereomers isolated in 81% overall yield. Thus, 5 stereogenic centers could be created starting from one. Furthermore, an efficient access to an enantiomerically pure tricyclo[5.3.0.0(2,6)]decane scaffold was possible via a 4 step reaction sequence. PMID:23657214

Miesch, Laurence; Welsch, Tania; Miesch, Michel

2013-06-28

97

Stereoselective total synthesis of furofuran lignans through dianion aldol condensation  

Microsoft Academic Search

Highly stereoselective total synthesis of (+)-eudesmin, (+)-yangambin, (?)-eudesmin, and (?)-yangambin is described. This method is useful to generate the core skeleton of furofuran rings utilizing modification of Evans asymmetric aldol condensation.

Jae-Chul Jung; Ju-Cheun Kim; Hyung-In Moon; Oee-Sook Park

2006-01-01

98

Spontaneous aldol and Michael additions of simple enoxytrimethylsilanes in DMSO  

Microsoft Academic Search

Activation of simple trimethylsilyl ketene acetals by dipolar aprotic solvents has been evidenced, allowing efficient solvent assisted aldol and Michael additions under extremely simple, mild and metal free conditions.

Yves Génisson; Liliane Gorrichon

2000-01-01

99

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

NASA Astrophysics Data System (ADS)

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

Nozière, Barbara; Esteve, William

100

A Rapid, One-Pot Synthesis of ?-Siloxy-?-Haloaldehydes  

PubMed Central

The Mukaiyama cross aldol reaction of ?-fluoro-, ?-chloro-, and ?-bromoacetaldehyde-derived (Z)-tris(trimethylsilyl)- silyl enol ethers furnishing anti-?-siloxy-?-haloaldehydes is described. A highly diastereoselective, one-pot, sequential double aldol process, affording novel ?,?-bissiloxy-?,?-bishaloaldehydes is developed. Reactions are catalyzed by C6F5CHTf2 and C6F5CTf2AlMe2 (0.5–1.5 mol%) and provide access to halogenated polyketide fragments.

Saadi, Jakub; Akakura, Matsujiro

2011-01-01

101

An overview of dehydration, aldol-condensation and hydrogenation processes for production of liquid alkanes from biomass-derived carbohydrates  

Microsoft Academic Search

We present results for the conversion of carbohydrate feedstocks to liquid alkanes by the combination of dehydration, aldol-condensation\\/hydrogenation, and dehydration\\/hydrogenation processing. With respect to the first dehydration step, we demonstrate that HMF can be produced in good selectivity from abundantly available polysaccharides (such as inulin, sucrose) containing fructose monomer units using a biphasic batch reactor system. The reaction system can

Juben N. Chheda; James A. Dumesic

2007-01-01

102

Hydrogen Transfer Reduction of 4- tert-Butylcyclohexanone and Aldol Condensation of Benzaldehyde with Acetophenone on Basic Solids  

Microsoft Academic Search

The liquid-phase reduction of 4-tert-butylcyclohexanone into 4-tert-butylcyclohexanol by reaction with isopropanol at 355 K has been studied on solid bases: mixed oxides obtained by calcination of hydrotalcites, NaBEA zeolites, KF\\/alumina, and La2O3 characterized by calorimetric FTIR adsorption of CO2 and FTIR pyridine adsorption. The aldol condensation of benzaldehyde and acetophenone at 423 K was investigated in parallel to clarify the

J. Lopez; J. Sanchez Valente; J.-M. Clacens; F. Figueras

2002-01-01

103

A novel approach for introduction of C-1 oxygenated group on decalin skeleton: first asymmetric total synthesis of 1?,6?-dihydroxy-eudesm-3-ene  

Microsoft Academic Search

This paper describes a novel approach for introduction of C-1 hydroxy on decalin ring system starting from (?)-carvone. Utilizing the substrate controlled Mukaiyama aldol reaction and alkaline cyclization as key steps, the C-1 oxygenated decalin eudesmane skeleton 2? and its four isomers were synthesized efficiently. What's more, X-ray structural analysis confirmed sufficiently that something was wrong about the structure of

Guojun Zheng; Jinchun Chen; Lijing Fang; Zhiyong Tang; Yulin Li

2004-01-01

104

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…

Bennett, George D.

2006-01-01

105

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

106

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

107

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

108

Direct synthesis of pterocarpans via aldol condensation of phenylacetates with benzaldehydes  

Microsoft Academic Search

Aldol condensation between phenylacetates and benzaldehydes affords 2,3-diaryl-3-hydroxypropanoates which are converted into pterocarpans via stepwise deprotection and cyclization in moderate to high yields.

Theunis G. van Aardt; Hendrik van Rensburg; Daneel Ferreira

1999-01-01

109

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

SciTech Connect

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

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

2012-05-23

110

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

PubMed

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

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

2012-04-13

111

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

PubMed

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

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

2011-12-16

112

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

113

Identification of an Unexpected 2-Oxonia[3,3]sigmatropic Rearrangement/Aldol Pathway in the Formation of Oxacyclic Rings. Total Synthesis of (+)-Aspergillin PZ  

PubMed Central

This paper reports the first unambiguous evidence that the cascade synthesis of tetrahydrofuran-containing oxacyclic molecules depicted in Scheme 12 can take place by a 2-oxonia[3,3]sigmatropic/aldol mechanism rather than by a Prins cyclization/pinacol rearrangement sequence. The 8-oxabicyclo[3.2.1]octyl aldehyde products of this reaction, 20 and 29, were employed to complete the first total synthesis of the structurally remarkable isoindolone alkaloid (+)-aspergillin PZ (1). The lack of activity seen in two tumor cell lines for synthetic (+)-aspergillin PZ calls into question the suggestion that aspergillin PZ, like many aspochalasin diterpenes, might exhibit useful antitumor properties.

Canham, Stephen M.; Tanis, Paul S.

2011-01-01

114

Concise total synthesis of spirocurcasone.  

PubMed

A concise total synthesis of spirocurcasone was accomplished. Key features of the synthesis involved a vinylogous Mukaiyama aldol reaction, a Carroll rearrangement of ?-keto allyl ester derivative, an intramolecular aldol condensation, and a spiro ring formation by ring-closing metathesis of the pentaene compound. This synthetic work was complete in nine steps from (S)- or (R)-perillaldehyde without the use of protecting groups. Interestingly, the optical rotation of the synthetic spirocurcasone was different from the reported value of the natural product. PMID:23448402

Abe, Hideki; Sato, Akimi; Kobayashi, Toyoharu; Ito, Hisanaka

2013-02-28

115

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

SciTech Connect

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

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

2011-02-15

116

Knoevenagel and aldol condensations catalysed by a new diamino-functionalised mesoporous material  

Microsoft Academic Search

Knoevenagel and aldol condensations have been reported by a new diamino-functionalised MCM-41 catalyst synthesised by condensation of the trimethoxysilylpropylethylenediamine on MCM-41. This solid base catalyst is found to be very efficient with reusability for a number of times with consistent activity.

B. M. Choudary; M. Lakshmi Kantam; P. Sreekanth; T. Bandopadhyay; F. Figueras; A. Tuel

1999-01-01

117

Catalytic effect of barium ferrite magnetic particles on aldol condensation of acetone  

Microsoft Academic Search

The catalytic effect of barium ferrite magnetic particles on aldol condensation was studied from the viewpoint of the reduction of this effect. The poisoning caused by different kinds of oxoacid ions was examined, and tungstate and molybdate ions were found to show high effectiveness for the deactivation of the above catalysis. These ions were adsorbed selectively on the side-planes (1100)

Haruo Watanabe; Jun'etsu Seto

1996-01-01

118

Aldol addition of dihydroxyacetone to N-Cbz-3-aminopropanal catalyzed by two aldolases variants in microreactors.  

PubMed

Aldol addition of dihydroxyacetone to N-Cbz-3-aminopropanal catalyzed by two d-fructose-6-phosphate aldolase variants, FSA A129S and FSA A129S/A165G, overexpressed in Escherichia coli was studied in microreactors. The presence of organic solvent was necessary due to poor solubility of N-Cbz-3-aminopropanal in water. Hence, three co-solvents were evaluated: ethyl acetate, acetonitrile and dimethylformamide (DMF). The influence of these solvents and their concentration on the enzyme activity was independently tested and it was found that all solvents significantly reduce the activity of FSA depending on their concentration. The reaction was carried out in three different microreactors; two without and one with micromixers. By increasing enzyme concentration, it was possible to achieve higher substrate conversion at lower residence time. Enzyme activity measured at the outlet flow of the microreactor at different residence time revealed that enzymes are more stable at lower residence times due to shorter time of exposure to organic solvent. The reaction in the batch reactor was compared with the results in microreactor with micromixers. Volume productivity was more than three fold higher in microreactor with micromixers than in the batch reactor for both aldolases. It was found to be 0.88Md(-1) and 0.80Md(-1) for FSA A129S and FSA A129S/A165G, respectively. PMID:23683703

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

2013-03-22

119

Convenient and facile cross-Aldol condensation catalyzed by molecular iodine: An efficient synthesis of ?,??-bis(substituted-benzylidene) cycloalkanones  

Microsoft Academic Search

Cross-Aldol condensation of aromatic aldehydes with cyclic ketones in the presence of catalytic amount of iodine at room temperature afforded ?,??-bis(substituted-benzylidene) cycloalkanones in high yields.

Biswanath Das; Ponnaboina Thirupathi; Ibram Mahender; Kongara Ravinder Reddy

2006-01-01

120

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

Microsoft Academic Search

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

Ryan K. Zeidan; Mark E. Davis

2007-01-01

121

Preparation and characterization of niobium oxide for the catalytic aldol condensation of acetone  

Microsoft Academic Search

Niobium oxide (Nb2O5) has been prepared from a precursor solution of NbCl5 in ethanol. The effect of pH, water content for hydrolysis and calcination temperature on microstructural, spectroscopic and acidic properties has been studied using N2 adsorption, X-ray diffraction (XRD), FTIR spectroscopy, temperature programmed desorption (TPD) of ammonia and DRIFTS of adsorbed ammonia. The activity for the aldol condensation of

M Paulis; M Mart??n; D. B Soria; A D??az; J. A Odriozola; M Montes

1999-01-01

122

Domino knoevenagel condensation/intramolecular aldol cyclization route to diverse indolizines with densely functionalized pyridine units.  

PubMed

A highly efficient [4 + 2] annulation route to polysubstituted indolizines is described employing a domino Knoevenagel condensation/intramolecular aldol cyclization process as a key step. Construction of pyridine rings in indolizine skeleton was rapidly achieved from several pyrrole-2-carboxaldehydes in good to excellent yields, leading to indolizines with various substituents at the 5, 6, and 7 positions depending on the reacting active methylene partners. PMID:24067193

Kim, Myungock; Jung, Youngeun; Kim, Ikyon

2013-10-08

123

Construction of perhydro indol-2-ones by a methoxide catalyzed deacetylation-Michael-aldol cascade.  

PubMed

An efficient, stereoselective Michael-aldol cascade for the one-pot construction of the perhydro indol-2-one bicyclic ring system using an acetate protected doubly-activated pyrrole-2-one pro-nucleophile and alpha,beta-unsaturated carbonyl compounds has been developed. Initiated by a methoxide deacetylation in methanol at room temperature, the cascade is easy to perform, stereoselective, efficient and broad in scope to this synthetically relevant structure. PMID:20177618

Ward, John W; Dodd, Karen; Rigby, Caroline L; De Savi, Chris; Dixon, Darren J

2010-01-13

124

Chiral phosphoramide-catalyzed aldol additions of ketone trichlorosilyl enolates. Mechanistic aspects.  

PubMed

The mechanism of the catalytic, enantioselective addition of trichlorosilyl enolates to aldehydes has been investigated. Kinetic studies using ReactIR and rapid injection NMR (RINMR) spectroscopy have confirmed the simultaneous operation of dual mechanistic pathways involving either one or two phosphoramides bound to a siliconium ion organizational center. This mechanistic dichotomy was initially postulated on the basis of catalyst loading studies and nonlinear effects studies. This duality explains the difference in reactivity and stereoselectivity of various classes of phosphoramides. Determination of Arrhenius activation parameters revealed that aldol addition occurs through the reversible albeit unfavorable formation of an activated complex, and natural-abundance 13C NMR kinetic isotope effect (KIE) studies have determined that the turnover limiting step is the aldol addition. A thorough examination of a range of phosphoramides has established empirical structure-activity selectivity relationships. In addition, the effects of catalyst loading, rate of addition, solvents, and additives have been studied and together allow the formulation of a unified mechanistic picture for the aldol addition. PMID:16674067

Denmark, Scott E; Pham, Son M; Stavenger, Robert A; Su, Xiping; Wong, Ken-Tsung; Nishigaichi, Yutaka

2006-05-12

125

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

NASA Astrophysics Data System (ADS)

Acid-base bifunctional heterogeneous catalysts containing carboxylic and amine groups, which were immobilized at defined distance from one another on the mesoporous solid were synthesized by immobilizing lysine onto carboxyl-SBA-15. The obtained materials were characterized by X-ray diffraction (XRD), N2 adsorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron micrographs (SEM), transmission electron micrographs (TEM), elemental analysis, and back titration. Proximal-C-A-SBA-15 with a proximal acid-base distance was more active than maximum-C-A-SBA-15 with a maximum acid-base distance in aldol condensation reaction between acetone and various aldehydes. It appears that the distance between acidic site and basic site immobilized on mesoporous solid should be an essential factor for catalysis optimization.

Yu, Xiaofang; Yu, Xiaobo; Wu, Shujie; Liu, Bo; Liu, Heng; Guan, Jingqi; Kan, Qiubin

2011-02-01

126

Diastereo- and Enantioselective Hydrogenative Aldol Coupling of Vinyl Ketones: Design of an Effective Monodentate TADDOL-Based Phosphonite Ligand  

PubMed Central

We report the first enantioselective reductive aldol couplings of vinyl ketones, which required the design of a novel monodentate TADDOL-based phosphonite ligand. Specifically, hydrogenation of commercially available methyl vinyl ketone (MVK) or ethyl vinyl ketone (EVK) in the presence of aldehydes using chirally modified cationic rhodium catalysts produces aldol adducts 1b-7b and 1c-7c with excellent levels of diastereo- and enantiocontrol. Through the use of (R,R)-ligand or (S,S)-ligand good levels of catalyst-directed diastereofacial selectivity are achieved in hydrogenative aldol couplings of MVK and EVK to glyceraldehyde acetonide, as demonstrated by the formation of aldol adducts 6b, 6c, 7b, and 7c. The absolute stereochemical assignment of adducts 1b-5b and 1c-5c was made in analogy to that determined for the 5-bromophthalimido derivative of aldol adduct 2b, which was established by single crystal x-ray diffraction analysis using the anomalous dispersion method. A structure of the catalyst ligand complex [Rh(COD)(Ligand-Q)2]OTf has been established by single crystal x-ray crystal, as reported in the supporting information.

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

2010-01-01

127

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

PubMed

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

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

2013-02-22

128

A new fatty aldol ester from the aerial part of Mimosa invisa (Mimosaceae).  

PubMed

A new aldol ester named 17-O-triacontanoylheptadecanal (1) was isolated from the aerial part of Mimosa invisa (Mimosaceae) together with eight known compounds identified as ?-sitosterol (2), ?-amyrine (3), lupeol (4), 4'-O-methylepinumisoflavone (5), alpinumisoflavone (6), betulinic acid (7), 3-O-?-D-glucopyranoside of sitosterol (8) and epirobinetinidol (9). The structures of compounds were determined on the basis of NMR and mass spectrometry data as well as by comparing the data reported in the literatures. The antimicrobial activities of the crude extract and compounds 1 and 9 were investigated against seven microbial species. The natural products showed moderate activities compared to that of the crude extract. PMID:22117104

Nana, Frederic; Sandjo, Louis Pergaud; Keumedjio, Felix; Kuete, Victor; Ngadjui, Bonaventure Tchaleu

2011-11-25

129

Single-reactor process for sequential aldol-condensation and hydrogenation of biomass-derived compounds in water  

Microsoft Academic Search

A bifunctional Pd\\/MgO-ZrO2 catalyst was developed for the single-reactor, aqueous phase aldol-condensation and hydrogenation of carbohydrate-derived compounds, furfural and 5-hydroxymethylfurfural (HMF), leading to large water-soluble intermediates that can be converted to liquid alkanes. The cross aldol-condensation of these compounds with acetone results in formation of water-insoluble monomer (C8–C9) and dimer (C13–C15) product species, which are subsequently hydrogenated in the same

C. J. Barrett; J. N. Chheda; G. W. Huber; J. A. Dumesic

2006-01-01

130

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...

131

Naturally occurring limonene to cinnamyl-type gamma-butyrolactone substituted aldol condensation derivatives as antioxidant compounds.  

PubMed

A method has been developed for the synthesis of gamma-butyrolactone substituted cinnamyl type Aldol condensation products under milder proline and triethylamine basic conditions. The antioxidant activity of all the synthesized compounds was assessed using three different assays. The cinnamyl type derivatives of gamma-butyrolactone bearing an -OH group in the benzene ring exhibited excellent antioxidant activity. PMID:23074886

Kaur, Pushpinder; Das, Pralay; Chaudhary, Abha; Singh, Bikram

2012-09-01

132

One-pot synthesis of substituted tetrahydrocyclobuta[a]naphthalenes by domino aldol condensation/olefin migration/electrocyclization.  

PubMed

A facile one-pot synthetic route for preparing the novel benzofused tricyclic skeleton of 1,2,2a,8b-tetrahydrocyclobuta[a]naphthalenes 5 is developed. The route was realized by a NaH-mediated tandem aldol condensation/olefin migration/electrocyclization of o-allylbenzaldehydes 1 with cinnamyl sulfones 3 in good yields. PMID:23697830

Chang, Meng-Yang; Wu, Ming-Hao; Chen, Yeh-Long

2013-05-22

133

Analysis of UDP-D-Apiose/UDP-D-Xylose Synthase-Catalyzed Conversion of UDP-D-Apiose Phosphonate to UDP-D-Xylose Phosphonate: Implications for a Retroaldol-Aldol Mechanism  

PubMed Central

UDP-D-apiose/UDP-D-xylose synthase (AXS) catalyzes the conversion of UDP-D-glucuronic acid to UDP-D-apiose and UDP-D-xylose. An acetyl-protected phosphonate analogue of UDP-D-apiose was synthesized and used in an in situ HPLC assay to demonstrate, for the first time, the ability of AXS to interconvert the two reaction products. Density functional theory calculations provided insight into the energetics of this process and the apparent inability of AXS to catalyze the conversion of UDP-D-xylose to UDP-D-apiose. The data suggest that this observation is unlikely to be due to an unfavorable equilibrium, but rather substrate inhibition by the most stable chair conformation of UDP-D-xylose. The detection of xylose cyclic phosphonate as the turnover product uncovers significant new detail about the AXS-catalyzed reaction and supports the proposed retroaldol-aldol mechanism of catalysis.

Choi, Sei-hyun; Mansoorabadi, Steven O.; Liu, Yung-nan; Liu, Hung-wen

2012-01-01

134

Stereoselective synthesis of novel antiproliferative steroidal (E, E) dienamides through a cascade aldol/cyclization process.  

PubMed

The stereoselective and metal-free protocol involving a cascade aldol/cyclization process for the synthesis of steroidal (E, E) dienamides from steroidal ?, ?-dicyanoalkene was reported. This protocol efficiently achieved the construction of CC bond and selective conversion of cyano group into carboxamide in one-pot procedure under mild condition. Further biological evaluation showed that some of these compounds had moderate to excellent cytotoxic activities against all the tested cancer cell lines and were more potent than well-known drug 5-fluorouracil. Particularly, compound 3c represented excellent inhibitory effect against MCF-7 (IC50=0.76?M), which was about 10-fold more potent than 5-fluorouracil. PMID:23954522

Yu, Bin; Sun, Xiao-Nan; Shi, Xiao-Jing; Qi, Ping-Ping; Fang, Yuan; Zhang, En; Yu, De-Quan; Liu, Hong-Min

2013-08-14

135

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

PubMed

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

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

2012-01-31

136

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

PubMed

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

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

2009-06-24

137

Tandem ring-closing metathesis/isomerization reactions for the total synthesis of violacein.  

PubMed

A series of 5-substituted 2-pyrrolidinones was synthesized through a one-pot ruthenium alkylidene-catalyzed tandem RCM/isomerization/nucleophilic addition sequence. The intermediates resulting from RCM/isomerization showed reactivity toward electrophiles in aldol condensation reactions which provided a new entry for the total synthesis of the antileukemic natural product violacein. PMID:23550830

Petersen, Mette T; Nielsen, Thomas E

2013-04-03

138

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

PubMed

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

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

2012-07-31

139

Tandem synthesis of pyrroloacridones via [3 + 2] alkyne annulation/ring-opening with concomitant intramolecular aldol condensation.  

PubMed

An efficient cascade strategy for the direct synthesis of pyrrolo[3,2,1-de]acridones 4a-v, 5a-h from iodo-pyranoquinolines 2a-i by the palladium-catalyzed regioselective [3 + 2] alkyne annulation/ring-opening followed by intramolecular aldol condensation under microwave irradiation is described. The chemistry involves the in situ formation of pyrroloquinolines Y, via palladium-catalyzed selective [3 + 2] annulation of iodopyranoquinolines and internal akynes with ring-opening and successive intramolecular cross-aldol condensation. Both the symmetrical and unsymmetrical internal alkynes were reacted smoothly to provide the desired pyrroloacridones in good yields. This methodology provides the facile conversion of easily accessble iodopyranoquinoline into highly functionalized biologically important pyrroloacridones in a single process. PMID:23642218

Verma, Akhilesh K; Kotla, Siva K Reddy; Aggarwal, Trapti; Kumar, Sonu; Nimesh, Hemlata; Tiwari, Rakesh K

2013-05-14

140

Base catalysis for the synthesis of ?,?-unsaturated ketones from the vapor-phase aldol condensation of acetone  

Microsoft Academic Search

The vapor-phase aldol condensation of acetone was studied over MgO promoted with 0.7–1.0 wt.-% of alkali (Li, Na, K and Cs) or alkaline earth (Ca, Sr and Ba) metal ions. The basic properties of the samples were characterized by chemisorption of carbon dioxide. The basicity of MgO increased on addition of the promoter following the basicity order of the promoter

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

1996-01-01

141

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

Microsoft Academic Search

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

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

2006-01-01

142

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

143

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

PubMed

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

Bielitza, Max; Pietruszka, Jörg

2013-04-19

144

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

2013-01-29

145

A Simple Organic Microscale Experiment Illustrating the Equilibrium Aspect of the Aldol Condensation  

NASA Astrophysics Data System (ADS)

A simple microscale experiment has been developed that illustrates the equilibrium aspect of the aldol condensation by using two versions of the standard preparation of tetraphenylcyclopentadienone (5) from benzil (1) and 1,3-diphenyl-2-propanone (2). In version (high base concentration) a mixture of 5 and the diastereomeric 4-hydroxy-2,3,4,5-tetraphenyl-2-cyclopenten-1-ones 3 and 4 are produced, while in the other (low base concentration) a mixture of 1, 2, 3, and 4 results. The experiment is typically carried out in conjunction with the previously reported preparation/dehydration of 3, thus the students provide themselves with authentic samples of 3 and 5. Using these, plus authentic samples of 1 and 2 which are made available, students are able to identify all of the components in the equilibrium mixtures, except 4, by TLC analysis. In the case of 4, students are expected to propose a reasonable structure for this compound based on the observed chemistry and the spectroscopic evidence which is provided (i.e., NMR, IR and mass spectra). The experiment lends itself nicely to either the traditional or problem-solving approach, and it also opens up opportunities for collaborative learning.

Harrison, Ernest A., Jr.

1998-05-01

146

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

NASA Astrophysics Data System (ADS)

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

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

147

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

148

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

149

Total synthesis of actinobolin from d-glucose by way of the stereoselective three-component coupling reaction  

Microsoft Academic Search

The total synthesis of (?)-actinobolin 3, an antipode of the natural product, starting from d-glucose is described. A three-component coupling reaction of functionalized cyclohexenone (+)-6 derived from d-glucose by way of Ferrier's carbocyclization reaction, with vinyl cuprate and 2-alkoxypropanal 7 effectively constructed the carbon framework of 3 in a highly stereoselective manner. In an aldol process of the three-component coupling

Satoshi Imuta; Hiroki Tanimoto; Miho K. Momose; Noritaka Chida

2006-01-01

150

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

151

Stereoselective aldol addition to rhenium(I) complexes and reversible dimerization with epimerization of the metal center.  

PubMed

Herein, we report several examples of stereoselective aldol additions of aldehydes or ketones to ReI tricarbonyl complexes to form monomeric derivatives in good yields. The metal-centered chirality defines the final stereochemistry of the carbon atom of the monomeric ReI complex after the addition. However, it cannot control the resulting stereochemistry of the enolate part, and thus, if the ?-carbon atom of the reagent is prochiral, a mixture of diastereoisomers is obtained. On the other hand, all of the monomeric complexes can be reversibly dimerized in basic media to form cis dimers, for which an epimerization of the metal-centered chirality is required in order to avoid steric congestion. All of these results are supported by exhaustive crystallographic analysis. PMID:23609984

Álvarez, Celedonio M; Carrillo, Romen; García-Rodríguez, Raúl; Miguel, Daniel

2013-04-22

152

Molecular Mechanism by which One Enzyme Catalyzes Two Reactions  

NASA Astrophysics Data System (ADS)

Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.

Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

153

Controlling reaction specificity in pyridoxal phosphate enzymes  

PubMed Central

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

Toney, Michael D.

2012-01-01

154

Synthesis of branched iminosugars through a hypervalent iodine(III)-mediated radical-polar crossover reaction.  

PubMed

The synthesis of a novel type of branched iminosugars is described. This synthetic strategy is based on two key reactions: first, an aldol reaction with formaldehyde in order to introduce selectively the hydroxymethyl branch, and second, a tandem ?-fragmentation-intramolecular cyclization reaction. The combination of both reactions afforded a battery of compounds exhibiting a great structural complexity, with the concomitant formation of a quaternary center, starting from readily available aldoses. With this approach we have demonstrated the usefulness of the fragmentation of anomeric alkoxyl radicals (ARF) promoted by the PhIO/I2 system for the preparation of new compounds with potential interest for both medicinal and synthetic chemists. PMID:23834195

Santana, Andrés G; Paz, Nieves R; Francisco, Cosme G; Suárez, Ernesto; González, Concepción C

2013-07-25

155

Production of methacrylic acid by vapor-phase aldol condensation of propionic acid with formaldehyde over silica-supported metal phosphate catalysts  

Microsoft Academic Search

The vapor-phase aldol condensation of propionic acid (PA) with formaldehyde (HCHO) to form methacrylic acid (MAA) was performed with a PA\\/HCHO molar ratio of 2 using various silica-supported metal phosphate catalysts. In the absence of water, a silica-supported tin phosphate with Sn\\/Si\\/P atomic ratio of 1\\/8\\/2.3 showed the same level of performance as a silica-supported vanadium phosphate with V\\/Si\\/P atomic

Mamoru Ai; Hideyuki Fujihashi; Sanae Hosoi; Akiyo Yoshida

2003-01-01

156

Photoaddition reactions of acetylpyridines with silyl ketene acetals: SET vs [2 + 2]-cycloaddition pathways.  

PubMed

Photoaddition reactions of silyl ketene acetals with 2-, 3- and 4-acetylpyridine have been explored. The results show that the acetylpyridines react with an electron rich, dimethyl-substituted silyl ketene acetal via a pathway in which excited state single electron transfer (SET) takes place to produce ?-hydroxyesters in high yields. In contrast, photochemical reactions of the acetylpyridines with an electron deficient, nonmethyl-substituted silyl ketene acetal generate oxetanes as major products, which arise via a route involving excited state [2 + 2]-cycloaddition. In addition, an increase in solvent polarity significantly enhances the relative efficiencies of the SET processes versus [2 + 2]-cycloaddition reactions. Importantly, the carbonyl groups rather than the pyridine moieties in the acetylpyridine substrates participate in both types of addition reactions. Finally, the results demonstrate that photoinduced electron transfer (PET)-promoted chemical reactions between acetylpyridines and electron rich silyl ketene acetals in polar solvent serve as useful methods to promote ?-hydroxyester forming, Claisen or Mukaiyama condensation reactions under mild conditions. PMID:23092504

Park, Hea Jung; Yoon, Ung Chan; Lee, Hyang-Yeol; Cho, Dae Won; Cho, Dae Won; Mariano, Patrick S

2012-10-31

157

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

2012-05-01

158

'Super Silyl' Group for Diastereoselective Sequential Reactions: Access to Complex Chiral Architecture in One Pot  

SciTech Connect

We have shown that the tris(trimethylsilyl)silyl (TTMSS) silyl enol ether of acetaldehyde undergoes aldehyde cross-aldol reactions with high selectivity and the extremely low catalyst loading (0.05 mol % of HNTf{sub 2}) allows for one-pot sequential reactions where acidic or basic nucleophiles can be subsequently added. Various ketone-derived silyl enol ethers, Grignard reagents, and dienes succeeded, generating relatively complex molecular architectures in a single step. This represents the first case where, in a single pot, highly acidic conditions followed by very basic conditions were tolerated to give products with high diastereoselectivities and good yields.

Boxer, Matthew B.; Yamamoto, Hisashi (UC)

2008-04-02

159

On the adsorption/reaction of acetone on pure and sulfate-modified zirconias.  

PubMed

In situ FTIR spectroscopy was employed to investigate some aspects of the ambient temperature (actually, IR-beam temperature) adsorption of acetone on various pure and sulfate-doped zirconia specimens. Acetone uptake yields, on all examined systems and to a variable extent, different types of specific molecular adsorption, depending on the kind/population of available surface sites: relatively weak H-bonding interaction(s) with surface hydroxyls, medium-strong coordinative interaction with Lewis acidic sites, and strong H-bonding interaction with Brønsted acidic centres. Moreover acetone, readily and abundantly adsorbed in molecular form, is able to undergo the aldol condensation reaction (yielding, as the main reaction product, adsorbed mesityl oxide) only if the adsorbing material possesses some specific surface features. The occurrence/non-occurrence of the acetone self-condensation reaction is discussed, and leads to conclusions concerning the sites that catalyze the condensation reaction that do not agree with either of two conflicting interpretations present in the literature of acetone uptake/reaction on, mainly, zeolitic systems. In particular, what turns out to be actually necessary for the acetone aldol condensation reaction to occur on the examined zirconia systems is the presence of coordinatively unsaturated O(2-) surface sites of basicity sufficient to lead to the extraction of a proton from one of the CH3 groups of adsorbed acetone. PMID:23873248

Crocellà, Valentina; Cerrato, Giuseppina; Morterra, Claudio

2013-08-28

160

Temperature-programmed reaction of C sub 4 oxygenates on unpromoted and K-promoted ZnCr oxide in relation to the mechanism of the higher alcohol synthesis  

SciTech Connect

The reaction mechanisms operating in the chain growth to C{sub 3+}primary alcohols and in the formation of ketones, secondary alcohols, methyl esters, ethers, and hydrocarbons during higher alcohol synthesis (HAS) over high-temperature modified methanol catalysts have been investigated by the temperature-programmed surface reaction (TPSR) technique. Experiments with linear and branched C{sub 4} alcohols, aldehydes, and acids over an unpromoted ZnCr oxide sample have indicated a series of major catalyst functions, namely aldol-like condensation (also with oxygen retention reversal), decarboxylation and decarboxylative condensations, hydrogenation-dehydrogenation, dehydration and hydrolysis, along with isomerization and cracking. TPSR experiments with linear C{sub 4} molecules over K-promoted ZnCr oxide have demonstrated the effects of alkali addition on the catalyst functions. The results are supportive of a mechanism of chain growth to C{sub 3+} primary alcohols based on a sequence of aldolic condensations of aldehydes, which do not operate over 2-methyl species. Formation of ketones under TPSR conditions is explained by decarboxylative condensation reactions of aldehydic and carboxylate species, as well as by aldol-like condensation reactions with oxygen retention reversal. Secondary alcohols detected in the products of the synthesis are formed by hydrogenation of ketones. Methyl esters and ethers are produced in the synthesis by alcoholysis of carboxylate and alkoxide species, respectively. Decarboxylation of carboxylate species, along with dehydration, may also play a role in the formation hydrocarbons during HAS.

Lietti, L.; Forzatti, P.; Tronconi, E.; Pasquon, I. (Dipartimento di Chimica Industriale ed Ingegneria Chimica G. Natta del Politecnico, Milano (Italy))

1990-12-01

161

Linked strategy for the production of fuels via formose reaction.  

PubMed

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

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

2013-02-07

162

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

163

Crystal structure of reaction intermediates in pyruvate class II aldolase: substrate cleavage, enolate stabilization, and substrate specificity.  

PubMed

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. Arg(70) 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 Arg(70) stabilize the negatively charged C4 oxygen following proton abstraction, the aldehyde alignment in aldol condensation, and the pyruvate enolate upon aldol cleavage as well as support proton exchange at C3. This role is corroborated by loss of aldol cleavage ability and pyruvate C3 proton exchange activity and by a 730-fold increase in the dissociation constant toward the pyruvate enolate analog oxalate in the R70A mutant. Based on the crystal structures, a mechanism is proposed involving the two enzyme-bound water molecules, W2 and W4, in acid/base catalysis that facilitates reversible aldol cleavage. The same reaction mechanism promotes decarboxylation of oxaloacetate. PMID:22908224

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

2012-08-20

164

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

NASA Astrophysics Data System (ADS)

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

Barsanti, Kelley C.; Pankow, James F.

165

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

166

Toward a computational tool predicting the stereochemical outcome of asymmetric reactions: development of the molecular mechanics-based program ACE and application to asymmetric epoxidation reactions.  

PubMed

The development and application of ACE, a program that predicts the stereochemical outcome of asymmetric reactions is presented. As major implementations, ACE includes a genetic algorithm to carry out an efficient global conformational search combined with a conjugate gradient minimization routine for local optimization and a corner flap algorithm to search ring conformations. Further improvements have been made that enable ACE to generate Boltzmann populations of conformations, to investigate highly asynchronous reactions, to compute fluctuating partial atomic charges and solvation energy and to automatically construct reactants and products from libraries of catalysts and substrates. Validation on previously investigated reactions (asymmetric Diels Alder cycloadditions and organocatalyzed aldol reactions) followed by application to a number of alkene epoxidation reactions and a comparative study of DFT-derived and ACE-derived predictions demonstrate the accuracy and usefulness of ACE in the context of asymmetric catalyst design. PMID:21735450

Weill, Nathanael; Corbeil, Christopher R; De Schutter, Joris W; Moitessier, Nicolas

2011-07-06

167

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

2013-09-25

168

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

PubMed

A series of 2,5-dimethyl-3-furyl chalcones [2E-1-(2,5-dimethyl-3-furyl)-3-(substituted phenyl)-2-propen-1-ones] have been synthesized by Hydrotalcite catalyzed aldol condensation between 3-acetyl-2,5-dimethylfuron and substituted benzaldehydes. Yields of chalcones are more than 80%. These chalcones were characterized by their physical constants and spectral data. The group frequencies of infrared ?(cm(-1)) of CO s-cis and s-trans, CH in-plane and out of plane, CH=CH out of plane, C=C out of plane modes, NMR chemical shifts ?(ppm) of H?, H?, CO, C? and C? of these chalcones were correlated with Hammett substituent constants, F and R parameters using single and multi-regression analyses. From the results of statistical analyses, the effects of substituents on the group frequencies are explained. Antibacterial, antifungal and insect antifeedant activities of these chalcones have been studied. PMID:23562741

Subramanian, M; Vanangamudi, G; Thirunarayanan, G

2013-03-14

169

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

170

Reaction of propionaldehyde over Rh-Y zeolite  

SciTech Connect

During the desorption of propionaldehyde from the Rh-Y zeolite into a He-CO(10%) stream, the concentration of propionaldehyde decreased with desorption time. n-Propanol formation was enhanced in the desorption of propionaldehyde into a He-H/sub 2/(10%) stream, while no appreciable enhancement was observed in the desorption into a He-H/sub 2/(10%)-CO(10%) stream. A faster decrease in the concentration of propionaldehyde was observed during the desorption into a helium stream than the desorption into the He-CO stream. In the desorption into the helium stream, formation of pentene was observed. However, no formation of pentene was observed in the desorption into a He-C/sub 2/H/sub 4/(10%) stream. In the desorption into a He-C/sub 3/H/sub 6/(10%) stream, the rate of pentene formation was lower than that in the desorption into the helium stream. These results suggest that the pentene is not formed by ethylene-propylene codimerization. The reduced RhCl/sub 3//SiO/sub 2/ catalyst which was physically mixed with the Na-Y zeolite showed comparable activity for pentene formation to that of Rh-Y zeolite in the reaction of propionaldehyde. However, neither the RhCl/sub 3//SiO/sub 2/ catalyst nor the Na-Y zeolite was effective by itself for pentene formation. The reduced RhCl/sub 3//SiO/sub 2/ and Rh-Y zeolite catalysts also showed activity for pentene formation in the reaction of 2-methyl-2-pentenal which is the product of aldol condensation of propionaldehyde. On the basis of the results, two sequential reactions, aldol condensation of propionaldehyde by the zeolite support followed by decarbonylation of 2-methyl-2-pentenal by rhodium metal particles, are proposed as a reaction path for the formation of pentene over the Rh-Y zeolite.

Takahashi, N.; Takizawa, M.; Sato, Y.

1986-03-01

171

Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—2. Dialdehydes, methylglyoxal, and diketones  

NASA Astrophysics Data System (ADS)

Predicting the formation of organic particulate matter (OPM) in the atmosphere by absorptive gas/particle partitioning requires a knowledge of the identities, atmospheric levels, and physical properties of all condensable species. Data from field and chamber experiments have shown that a portion of atmospheric OPM samples are comprised of products generated during oxidation of volatile organic compounds. It has been suggested that some of these initially formed oxidation products also contribute to the formation of atmospheric OPM via molecular-weight (MW) building "accretion reactions". The role of such reactions as well as a general theoretical approach for evaluating their thermodynamic relevance in regard to atmospheric OPM formation, have been discussed in prior work. This work utilizes that approach in considerations of accretion reactions of glyoxal, two other dialdehydes, methylglyoxal, and two diketones. The methods used to predict free energy of formation ( ?G°) values (and hence equilibrium constant ( K) values) indicate that: (1) for 1,4-butanedial, 2,3-butanedione, and 2,5-hexanedione, the accretion reactions considered are not favorable; (2) for C 6 and higher dialdehydes, reaction by aldol condensation may contribute to atmospheric OPM formation under certain circumstances, if kinetically favorable; and (3) for glyoxal, diol and subsequent oligomer formation, and for methylglyoxal, aldol condensation, are thermodynamically favorable, and may contribute significantly to OPM in the atmosphere, if kinetically favorable.

Barsanti, Kelley C.; Pankow, James F.

172

Vapor-phase reaction of acetophenone with methanol or dimethyl carbonate on magnesium oxide and magnesium phosphates  

SciTech Connect

The vapor-phase reaction of acetophenone with methanol on magnesium oxide, various magnesium phosphates, and combinations of the two types of catalysts was studied. The process was found to involve the Meerwein-Ponndorf-Verley reaction, aldol condensations, dehydrations, and hydrogenations. The presence of basic sites is indispensable for the reaction to develop; however, acid sites also play an active role. The selectivity for each reaction product depends on the particular catalyst used. The total conversion is maximal with the catalysts containing the largest populations of acid and basic sites. Also, catalysts with large numbers of acid sites exhibit an increased selectivity towards the corresponding alkenes. The use of dimethyl carbonate instead of methanol alters the reaction selectivity to an extent dependent on the particular catalyst and operating conditions. However, this also results in markedly decreased total conversion in some instances.

Aramendia, M.A.; Borau, V.; Jimenez, C.; Marinas, J.M.; Romero, F.J. [Univ. of Cordoba (Spain). Dept. of Organic Chemistry

1999-04-01

173

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

PubMed

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

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

2013-07-28

174

Organic reactions increasing the absorption index of atmospheric sulfuric acid aerosols  

NASA Astrophysics Data System (ADS)

Unlike most environments present at Earth's surface atmospheric aerosols can be favorable to organic reactions. Among them, the acid-catalyzed aldol condensation of aldehydes and ketones produces light-absorbing compounds. In this work the increase of the absorption index of sulfuric acid solutions 50-96 wt. % resulting from the uptake of gas-phase acetaldehyde, acetone, and 2-butanone (methyl ethyl ketone), has been measured in the near UV and visible range. Our results indicate that the absorption index between 200 and 500 nm for stratospheric sulfuric aerosols exposed to 100 pptV of acetaldehyde (1 pptV = 10-12 v/v) would increase by four orders of magnitude over a two-year lifetime. Rough estimates based on previous radiative calculations suggest that this reaction could result in an increase of the radiative forcing of sulfate aerosols of the order of 0.01 W m-2, and that these processes are worth further investigation.

Nozière, B.; Esteve, W.

2005-02-01

175

Hydrolysis/dehydration/aldol-condensation/hydrogenation of lignocellulosic biomass and biomass-derived carbohydrates in the presence of Pd/WO3-ZrO2 in a single reactor.  

PubMed

Hydrolysis/dehydration/aldol-condensation/hydrogenation of lignocellulosic-biomass (corncobs) and biomass-derived carbohydrates (tapioca flour) to produce water-soluble C5-C15 compounds was developed in a single reactor system. WO3-ZrO2 efficiently catalyzed the hydrolysis/dehydration of these feedstocks to 5-hydroxymethylfurfural and furfural, while the impregnation of WO3-ZrO2 with Pd allowed sequential aldolcondensation/hydrogenation of these furans to C5-C15 compounds. The highest C5-C15 yields of 14.8-20.3% were observed at a hydrolysis/dehydration temperature of 573 K for 5 min, an aldol-condensation temperature of 353 K for 30 h, and a hydrogenation temperature of 393 K for 6 h. The C5-C15 yield from tapioca flour was higher than that from corncobs (20.3% compared to 14.8%). Tapioca flour produced more C6/C9/C15, whereas corncobs generated more C5/C8/C13 compounds due to the presence of hemicellulose in the corncobs. These water-soluble organic compounds can be further converted to liquid alkanes with high cetane numbers for replacing diesel fuel in transportation applications. PMID:20934873

Dedsuksophon, W; Faungnawakij, K; Champreda, V; Laosiripojana, N

2010-09-22

176

Concerted reactions and mechanism of glucose pyrolysis and implications for cellulose kinetics.  

PubMed

Concerted reactions are proposed to be keys to understanding thermal decomposition of glucose in the absence of ionic chemistry, including molecular catalysis by ROH molecules such as H(2)O, other glucose molecules, and most of the intermediates and products. Concerted transition states, elementary-reaction pathways, and rate coefficients are computed for pyrolysis of ?-D-glucose (?-D-glucopyranose), the monomer of cellulose, and for related molecules, giving an improved and elementary-reaction interpretation of the reaction network proposed by Sanders et al. (J. Anal. Appl. Pyrolysis, 2003, 66, 29-50). Reactions for ring-opening and formation, ring contraction, retro-aldol condensation, keto-enol tautomerization, and dehydration are included. The dehydration reactions are focused on bicyclic ring formations that lead to levoglucosan and 1,6-?-D-anhydrousglucofuranose. The bimolecular ROH-assisted reactions are found to have lower activation energy compared to the unimolecular reactions. The same dehydration reaction to levoglucosan should occur for cellulose going to cellosan (e.g., cellotriosan) plus a shortened cellulose chain, a hypothesis supported by the very similar activation energies computed when alternate groups were substituted at the C1 glycosidic oxygen. The principles of Sanders et al. that distinguish D-glucose, D-fructose, sucrose, and cellulose pyrolysis prove useful in providing qualitative insights into cellulose pyrolysis. PMID:23082925

Seshadri, Vikram; Westmoreland, Phillip R

2012-11-09

177

Reactions & Rates  

NSDL National Science Digital Library

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

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

2006-12-01

178

Drug Reactions  

MedlinePLUS

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

179

Markers of heterogeneous reaction products in ?-pinene ozone secondary organic aerosol  

NASA Astrophysics Data System (ADS)

A gas chromatograph iontrap mass spectrometer (GC-ITMS) was used to analyze the gas-and particle-phase products of ?-pinene ozone oxidation in the presence of three different inorganic seed aerosols: sodium chloride, ammonium sulfate only, and ammonium sulfate with sulfuric acid. Products of ?-pinene ozone oxidation common to the literature showed little difference in gas or particle-phase concentrations between seed types within the precision of the measurements even though significantly different aerosol yields were found between seed types. Small amounts of ring-opening products of four-membered cyclic oxygenates and markers of aldol condensation products were tentatively identified in the particle-phase for all seed types. These tentatively identified products are thought to be the result of acid-catalyzed heterogeneous reactions in the particle-phase or during sampling processes or analysis. The mechanisms for their formation are also proposed in this study.

Czoschke, Nadine M.; Jang, Myoseon

180

Size-selective Lewis acid catalysis in a microporous metal-organic framework with exposed Mn2+ coordination sites.  

PubMed

Treatment of selected aldehydes and ketones with cyanotrimethylsilane in the presence of the microporous metal-organic framework Mn3[(Mn4Cl)3BTT8(CH3OH)10]2 (1, H3BTT = 1,3,5-benzenetristetrazol-5-yl) leads to rapid conversion to the corresponding cyanosilylated products. The transformation is catalyzed by coordinatively unsaturated Mn2+ ions that serve as Lewis acids and lead to conversion yields of 98 and 90% for benzaldehyde and 1-naphthaldehyde, the highest thus far for a metal-organic framework. Larger carbonyl substrates cannot diffuse through the pores of 1, and conversion yields are much lower for these, attesting to the heterogeneity of the reaction and its dependence on guest size. The Mukaiyama-aldol reaction, known to require much more active Lewis catalysts, is also catalyzed in the presence of 1, representing the first such example for a metal-organic framework. Conversion yields obtained for the reaction of selected aldehydes with silyl enolates reach 63%, on par with those obtained with zeolites. Size selectivity is demonstrated for the first time with this reaction through the use of larger silyl enolate substrates. PMID:18399629

Horike, Satoshi; Dinca, Mircea; Tamaki, Kentaro; Long, Jeffrey R

2008-04-10

181

[Synthesis of carbohydrate related compounds by using aldolase catalyzed reaction].  

PubMed

Enzymes proceed the reaction with high regio- and stereoselectivity under mild conditions, i.e. in an aqueous medium at room temperature. However, enzymatic reactions that catalyze carbon-carbon bond formation have not been utilized in organic synthesis until recently. We had an interest in an aldolase-catalyzed reaction which proceed carbon-carbon bond formation referred to aldol condensation, by which many bioactive compounds have been rationally synthesized. On the other hand, recent biological studies on cell recognition (cell adhesion) have disclosed the important roles of oligosaccharides on cell surfaces, especially which include glucuronic acid, 3-deoxy-D-manno-oct-2-ulosonic acid (KDO), and sialic acid in the structures e.g., sialyl Lewis X and endotoxins, in differentiation, induction, viral and bacterial infections, and immune response. As well as acidic oligosaccharides, basic ones have been utilized as practical medicines in the clinical level, like acarbose that acts as an amylase inhibitor. Based on these background, we embarked the synthesis of carbohydrate related compounds which can control the interaction between carbohydrates and carbohydrate recognition protein by the use of several aldolases. Azasugars, potent inhibitors toward glycosidases, were synthesized using fructose-1,6-diphosphate (FDP)-aldolase and other dihdroxyacetonephosphate (DHAP)-dependent aldolases in the key step. Sialyl Lewis X mimetic, peptidic mimetic of RNA having anti-Vero toxin activity, mycestericin D, and aza-idulonic acid were prepared by taking advantage of L-threonine aldolase catalyzed reaction, which afford beta-hydroxy-alpha-L-amino acids. A precursor of KDO, featured acidic sugar of endotoxins was provided by the reaction catalyzed with kynureninase, which generates beta-anion of L-alanine in its active site during the metabolic reaction from kynurenine to anthranilic acid. PMID:10655781

Kajimoto, T

2000-01-01

182

Adsorption and Reaction of Acetaldehyde on Stoichiometric and Defective SrTiO?(100) Surfaces  

SciTech Connect

The adsorption and reaction of acetaldehyde (CH{sub 3}CHO), on stoichiometric (TiO{sub 2}-terminated) and reduced SrTiO{sub 3}(100) surfaces, have been investigated using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Acetaldehyde adsorbs molecularly on the stoichiometric SrTiO{sub 3}(100) surface that contains predominantly Ti{sup 4+} cations. The Ti{sup 4+} sites on the stoichiometric SrTiO{sub 3}(100) surface are not sufficiently active for surface reactions such as aldol condensation, as opposed to the Ti{sup 4+} ions on the TiO{sub 2}(001) surface. However, decomposition and redox reactions of acetaldehyde occur in the presence of surface defects created by Ar{sup +} sputtering. The decomposition products following reactions of acetaldehyde on the defective surface include H{sub 2}, C{sub 2}H{sub 4}, CO, C{sub 4}H{sub 6}, and C{sub 4}H{sub 8}. Reductive coupling, to produce C{sub 2}H{sub 4} and C{sub 4}H{sub 8} is the main reaction pathway for decomposition of acetaldehyde on the sputter reduced SrTiO{sub 3}(100) surface.

Wang, Li Q.; Ferris, Kim F.; Azad, Samina; Engelhard, Mark H.; Peden, Charles HF.

2004-02-05

183

Isosynthesis reactions of CO/H/sub 2/ over zirconium dioxide  

SciTech Connect

The isosynthesis reactions of an equimolar mixture of carbon monoxide and hydrogen were studied over zirconium dioxide catalysts. The main objectives of this work were: (1) to investigate the reaction pathway, (2) identify the surface intermediates leading to the formation of i-butene, and (3) determine the mechanisms of carbon chain propagation. The reactions were conducted at 250-450/sup 0/C, 35 atm (500 psig) total pressure, and 100-200 cc/min total flow rate in a differential reactor. Oxygenated intermediates are proposed to exist on the zirconia surface. This is supported by the observations that oxygenated products were favored at lower reaction temperatures or at shorter residence times. Propylene, propionaldehyde, acetone, i-propanol, and n-propanol were used as probe molecules to examine the chain growth and branching mechanisms, leading to the formation of i-butene. Reaction schemes are proposed. Carbon-13 labeled acetone and methanol were utilized to examine quantitatively the above two schemes. The labeled acetone studies revealed that both the branched and linear olefins were formed from the acetone added. The presence of carbon-13 carbons in linear olefins indicated that methylation at the acetone methyl occurred. The labeled methanol studies revealed that aldol-type condensation did proceed over zirconia, leading to the formation of branching olefins.

Tseng, S.C.

1987-01-01

184

Chemical Reactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2009-05-01

185

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

186

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

2010-08-26

187

Named Reactions  

NSDL National Science Digital Library

This Web site lists 95 of the most important named reactions in organic chemistry. Each is linked to a Web page that gives the primary reference and equations for one or more recent literature examples that illustrate the use of the reaction.

188

Synthetic studies toward galbulimima alkaloid (-)-GB 13 and (+)-GB 16 and (-)-himgaline.  

PubMed

Condensation of (S)-3-aminobutan-1-ol with 1,3-cyclohexane-dione followed by an intramolecular alkylation afforded bicyclic enamine 32, which was converted into enone 35 through a diastereoselective hydrogenation. Mukaiyama-Michael addition of a bicyclic silyl enol ether to 35 and subsequent stereochemistry inversion by means of an oxidation/reduction strategy provided lactone 41. After reduction of lactone 41 with LAH, Swern oxidation was carried out to give enone 46 upon a spontaneous intramolecular aldol reaction and cleavage of the ketal protecting group. SmI(2) -mediated carbonyl-alkene reductive coupling of 46 proceeded smoothly in refluxing tetrahydrofuran to deliver pentacyclic intermediate 49, which was oxidized with 2-iodoxybenzoic acid and then treated with trifluoroacetic acid to furnish (-)-GB 13. The overall yield was 6.1% over 19 linear steps. By following the known procedure, our synthetic (-)-GB 13 was converted into himgaline. In addition, by starting from lactone 41, the first total synthesis of (+)-GB 16, a newly isolated member of the gabulimima alkaloid family, was achieved. This synthesis features an intramolecular condensation between an amine and a 1,3-diketone moiety. PMID:21254431

Zi, Weiwei; Yu, Shouyun; Ma, Dawei

2010-12-14

189

The combined C-H functionalization/Cope rearrangement: discovery and applications in organic synthesis.  

PubMed

The development of methods for the stereoselective functionalization of sp(3) C-H bonds is a challenging undertaking. This Account describes the scope of the combined C-H functionalization/Cope rearrangement (CHCR), a reaction that occurs between rhodium-stabilized vinylcarbenoids and substrates containing allylic C-H bonds. Computational studies have shown that the CHCR reaction is initiated by a hydride transfer to the carbenoid from an allyl site on the substrate, which is then rapidly followed by C-C bond formation between the developing rhodium-bound allyl anion and the allyl cation. In principle, the reaction can proceed through four distinct orientations of the vinylcarbenoid and the approaching substrate. The early examples of the CHCR reaction were all highly diastereoselective, consistent with a reaction proceeding via a chair transition state with the vinylcarbenoid adopting an s-cis conformation. Recent computational studies have revealed that other transition state orientations are energetically accessible, and these results have guided the development of highly stereoselective CHCR reactions that proceed through a boat transition state with the vinylcarbenoid in an s-cis configuration. The CHCR reaction has broad applications in organic synthesis. In some new protocols, the CHCR reaction acts as a surrogate to some of the classic synthetic strategies in organic chemistry. The CHCR reaction has served as a synthetic equivalent of the Michael reaction, the vinylogous Mukaiyama aldol reaction, the tandem Claisen rearrangement/Cope rearrangement, and the tandem aldol reaction/siloxy-Cope rearrangement. In all of these cases, the products are generated with very high diastereocontrol. With a chiral dirhodium tetracarboxylate catalyst such as Rh(2)(S-DOSP)(4) or Rh(2)(S-PTAD)(4), researchers can achieve very high levels of asymmetric induction. Applications of the CHCR reaction include the effective enantiodifferentiation of racemic dihydronaphthalenes and the total synthesis of several natural products: (-)-colombiasin A, (-)-elisapterosin B, and (+)-erogorgiaene. By combining the CHCR reaction into a further cascade sequence, we and other researchers have achieved the asymmetric synthesis of 4-substituted indoles, a new class of monoamine reuptake inhibitors. PMID:22577963

Davies, Huw M L; Lian, Yajing

2012-05-11

190

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

SciTech Connect

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

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

2007-01-01

191

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

SciTech Connect

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

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

1999-08-01

192

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

193

Adsorption and Reaction of Acetaldehyde on Stoichiometric and Defective SrTiO{sub 3}(100) Surfaces  

SciTech Connect

The adsorption and reaction of acetaldehyde (CH{sub 3}CHO), on stoichiometric (TiO{sub 2}-terminated) and reduced SrTiO{sub 3}(100) surfaces, have been investigated using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Acetaldehyde adsorbs molecularly on the stoichiometric SrTiO{sub 3}(100) surface that contains predominantly Ti{sup 4+} cations. The Ti{sup 4+} sites on the stoichiometric SrTiO{sub 3}(100) surface are not sufficiently active for surface reactions such as aldol condensation, as opposed to the Ti{sup 4+} ions on the TiO{sub 2}(001) surface. However, decomposition and redox reactions of acetaldehyde occur in the presence of surface defects created by Ar{sup +} sputtering. The decomposition products following reactions of acetaldehyde on the defective surface include H{sub 2}, C{sub 2}H{sub 4}, CO, C{sub 4}H{sub 6} and C{sub 4}H{sub 8}. Reductive coupling, to produce C{sub 2}H{sub 4} and C{sub 4}H{sub 8}, is the main reaction pathway for decomposition of acetaldehyde on the sputter reduced SrTiO{sub 3}(100) surface.

Wang, Li Q.; Ferris, Kim F.; Azad, Samina; Engelhard, Mark H.; Peden, Charles HF.

2004-02-05

194

Cooperative acid-base effects with functionalized mesoporous silica nanoparticles: applications in carbon-carbon bond-formation reactions.  

PubMed

Acid-base bifunctional mesoporous silica nanoparticles (MSN) were prepared by a one-step synthesis by co-condensation of tetraethoxysilane (TEOS) and silanes possessing amino and/or sulfonic acid groups. Both the functionality and morphology of the particles can be controlled. The grafted functional groups were characterized by using solid-state (29)Si and (13)C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy, thermal analysis, and elemental analysis, whereas the structural and the morphological features of the materials were evaluated by using XRD and N(2) adsorption-desorption analyses, and SEM imaging. The catalytic activities of the mono- and bifunctional mesoporous hybrid materials were evaluated in carbon-carbon coupling reactions like the nitroaldol reaction and the one-pot deacetalization-nitroaldol and deacetalization-aldol reactions. Among all the catalysts evaluated, the bifunctional sample containing amine and sulfonic acid groups (MSN-NNH(2)-SO(3)H) showed excellent catalytic activity, whereas the homogeneous catalysts were unable to initiate the reaction due to their mutual neutralization in solution. Therefore a cooperative acid-base activation is envisaged for the carbon-carbon coupling reactions. PMID:19569138

Shylesh, Sankaranarayanapillai; Wagner, Alex; Seifert, Andreas; Ernst, Stefan; Thiel, Werner R

2009-07-20

195

Drug Reactions  

MedlinePLUS

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

196

Enzyme Reactions  

NSDL National Science Digital Library

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

School, Maryland V.

197

Enantioselective synthesis of anti- and syn-homopropargyl alcohols via chiral Brønsted acid catalyzed asymmetric allenylboration reactions.  

PubMed

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 highly diastereoselective syntheses of a variety of anti, anti-stereotriads, the direct synthesis of which has constituted a significant challenge using previous generations of aldol and crotylmetal reagents. PMID:22731887

Chen, Ming; Roush, William R

2012-06-25

198

Reaction Time  

NSDL National Science Digital Library

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

Horton, Michael

2009-05-30

199

Formation of Lactic Acid from Cellulosic Biomass by Alkaline Hydrothermal Reaction  

NASA Astrophysics Data System (ADS)

Glucose, as a model compound of cellulosic biomass, was used as a test material. Ca(OH)2 and NaOH were selected as alkali. Results showed that both NaOH and Ca(OH)2, can promote the formation of lactic acid in a hydrothermal reaction of glucose. In the case of the addition of NaOH, lactic acid was obtained with a good yield of 27% based on a carbon base at 300 °C for 60 s with a NaOH concentration of 2.5 M. In the case of the addition of Ca(OH)2, the highest yield of lactic acid is 20%, which occurred at 300 °C for 60 s with a Ca(OH)2 concentration of 0.32 M. The formation mechanisms of lactic acid from glucose were also discussed according to intermediate products identified. Lactic acid may be generated via formaldehyde, glycolaldehyde besides via the aldose having three carbon atoms in hydrothermal reaction which all formed by the reverse aldol condensation of hexoses.

Yan, X.; Jini, F.; Kishita, A.; Enomoto, H.; Tohji, K.

2008-02-01

200

Total syntheses of Yingzhaosu A and of its C(14)-epimer including the first evaluation of their antimalarial and cytotoxic activities.  

PubMed

[reaction: see text] The molecular structure of the naturally occurring antimalarial agent yingzhaosu A (1) is characterized by a 2,3-dioxabicyclo[3.3.1]nonane system (3a), an allylic alcohol, a homoallylic alcohol, and five stereogenic centers. Herein we report on the total synthesis of yingzhaosu A (1) in eight steps and 7.3% overall yield starting from (S)-limonene (12). To maximize efficacy, the bridged bicyclic endoperoxide molecular core was constructed by a multicomponent free-radical domino reaction in which five bonds are formed in a single operation. In addition, reaction protocols that are compatible with the sensitivity of the peroxide function to strong basic and nucleophilic reagents as well as to reducing agents were employed. An intriguing step involved the selective hydrogenation of a carbon-carbon double bond in the presence of a peroxide and an aldehyde function to give aldehyde peroxide 7. The two major synthons (aldehydoperoxide 7 and its complementary five-carbon atom unit 35) were linked through a Mukaiyama aldol reaction followed by in situ dehydration under mild buffered basic conditions. The carbonyl group in the resulting peroxidic enone 39 was stereoselectively reduced with either R-CBS catalyst (42b) to give, after in situ desilylation, yingzhaosu A (1) or with S-CBS catalyst (42a) its C(14)-epimer 40. The first quantitative in vitro and in vivo data for the antimalarial activity of yingzhaosu A (1) and its C(14)-epimer 40 are reported. The C(14)-epiyingzhaosu A (40) exhibits potent cytotoxic activity against the KB nasal-pharyngeal cancer cell line in vitro. PMID:15844999

Szpilman, Alex M; Korshin, Edward E; Rozenberg, Haim; Bachi, Mario D

2005-04-29

201

Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate  

NASA Astrophysics Data System (ADS)

Reactions of glyoxal (Glx) and methylglyoxal (MG) with primary amines and ammonium salts may produce brown carbon and N-containing oligomers in aqueous aerosol. 1H NMR monitoring of reactant losses and product appearance in bulk aqueous reactions were used to derive rate constants and quantify competing reaction pathways as a function of pH and temperature. Glx + ammonium sulfate (AS) and amine reactions generate products containing C–N bonds, with rates depending directly on pH: rate = (70 ± 60) M?1 s?1fAld [Glx]totfAm [Am]tot, where fAld is the fraction of aldehyde with a dehydrated aldehyde functional group, and fAm is the fraction of amine or ammonia that is deprotonated at a given pH. MG + amine reactions generate mostly aldol condensation products and exhibit less pH dependence: rate = 10[(0.36 ± 0.06) × pH ? (3.6 ± 0.3)] M?1 s?1fAld [MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (Ea = 18 ± 8 kJ mol?1) than corresponding amine reactions (Ea = 50 ± 11 kJ mol?1). Using aerosol concentrations of [OH] = 10?12 M, [amine]tot = [AS] = 0.1 M, fGlx = 0.046 and fMG = 0.09, we estimate that OH radical reactions are normally the major aerosol-phase sink for both dicarbonyl compounds. However, reactions with AS and amines together can account for up to 12 and 45% of daytime aerosol-phase glyoxal and methylglyoxal reactivity, respectively, in marine aerosol at pH 5.5. Reactions with AS and amines become less important in acidic or non-marine aerosol, but may still be significant atmospheric sources of brown carbon, imidazoles, and nitrogen-containing oligomers.

Sedehi, Nahzaneen; Takano, Hiromi; Blasic, Vanessa A.; Sullivan, Kristin A.; De Haan, David O.

2013-10-01

202

Role of oxidized lipids in nonenzymic browning reactions  

Microsoft Academic Search

Different lipid oxidation products, such as free radicals, hydroperoxides and aldehydes, react with free amine groups of proteins and with free amino acids, forming yellow intermediary products which polymerize into dark brown macromolecules. The intermediary products are imines, pyridine derivatives and even aldolization products with low nitrogen content. The nutritional value of brown products is very low.

Jan Pokorný; Hidetoshi Sakurai

2002-01-01

203

Catalytic conversion of bio-oil to oxygen-containing fuels by simultaneous reactions with 1-butanol and 1-octene over solid acids: Model compound studies and reaction pathways.  

PubMed

Upgrading bio-oil by addition reactions across olefins represents a route to refine bio-oil to combustible and stable oxygen-containing fuels. Development and application of highly active strong solid acid catalysts with good hydrothermal stability has become a key determinant for success, because bio-oil's complexity includes large amounts of water. Temperatures of 120°C or more are needed for satisfactory kinetics. Batch upgrading of a model bio-oil (phenol/water/acetic acid/acetaldehyde/hydroxyacetone/d-glucose/2-hydroxymethylfuran) over five water-tolerant solid acid catalysts (Dowex50WX2, Amberlyst15, Amberlyst36, silica sulfuric acid (SSA) and Cs(2.5)H(0.5)PW(12)O(40) supported on K-10 clay (Cs(2.5)/K-10, 30wt.%)) with 1-octene/1-butanol were studied at 120°C/3h. SSA, , exhibited the highest water tolerance and activity. Upgrading using olefin/1-butanol is complex, involving many simultaneous competing esterification, etherification, olefin hydration, phenol alkylation, aldol condensation, sugar dehydration etc. reactions. PMID:23357587

Zhang, Zhi-Jun; Sui, Shu-Juan; Tan, Shun; Wang, Qing-Wen; Pittman, Charles U

2012-11-24

204

Synthesis of alcohols from carbon oxides and hydrogen. VIII. A temperature-programmed reaction study of n-butanal on a Zn-Cr-O catalyst  

SciTech Connect

The interaction of n-butanal with a Zn-Cr-O catalyst has been studied by temperature-programmed reaction. Using combined GC, GC-FTIR, and GC-MS techniques, a large number of desorption products have been identified, including 1-butanol, C/sub 8/ and C/sub 12/ aldehydes, C/sub 7/ and C/sub 8/ ketones, and C/sub 3/, C/sub 4/, and C/sub 7/ olefins, as well as CO/sub 2/, dienes, trienes, aromatics, and light hydrocarbons. The formation of most products is explained by assuming surface reactions of two classes of intermediate species originating from the adsorption of n-butanal and from the surface aldol-like condensation of two molecules of n-butanal. Results indicate that the Zn-Cr oxide catalyst is active in performing aldehyde condensation, hydrogenation, hydrolysis, dehydrogenation, decarboxylation, and dehydration, along with isomerization and cracking reactions. Different functionalities are associated with different temperature ranges. The detected chemical functionalities are discussed with respect to their relevance to the direct synthesis of methanol and higher alcohols from CO and H/sub 2/.

Lietti, L.; Botta, D.; Forzatti, P.; Mantica, E.; Tronconi, E.; Pasquon, I.

1988-06-01

205

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

206

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

207

Biochemical Reactions as Computations  

Microsoft Academic Search

Two main mechanisms behind the functioning of biochemical reactions are facilitation and inhibition; these mechanisms are\\u000a also central for the interaction between biochemical reactions. This observation underlies the theory of reaction systems\\u000a which is a formal framework for the investigation of biochemical reactions, and especially interactions between them.

Andrzej Ehrenfeucht; Grzegorz Rozenberg

2007-01-01

208

Catalytic asymmetric Henry reaction  

Microsoft Academic Search

The classical Henry reaction, the coupling of a nitroalkane with a carbonyl compound in the presence of a base, is an important C–C bond forming reaction in organic chemistry giving ?-nitroalcohols, which are useful synthons in organic synthesis. However, an asymmetric version of the reaction, that has been developed recently, gives a new dimension to the classical Henry reaction whereby

Joshodeep Boruwa; Naminita Gogoi; Partha Pratim Saikia; Nabin C. Barua

2006-01-01

209

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

210

[Adverse reactions to insulin].  

PubMed

The prevalence of allergic reactions to insuline has decreased during the last few years. Probably this is due to the use of the newly-developed recombinant human insuline. At present, adverse reactions to insuline occur in 5-10% of patients on therapy with insuline. Adverse reactions may be local (more frequent) or systemic (rare). Insuline resistance consists in a different type of immunological reaction. Diagnosis of allergy to insuline is based on clinical history and cutaneous and serological tests. Treatment depends upon the severity of the reaction. When insuline is indispensable despite a previous allergic reaction, a desensitization protocol may be implemented. PMID:9410127

Liñana, J J; Montoro, F J; Hernández, M D; Basomba, A

1997-07-01

211

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

212

Aromaticity and Pericyclic Reactions.  

National Technical Information Service (NTIS)

Pericyclic reactions formally resemble the conversion of one Kekule structure into another; the transition state may be 'aromatic', 'nonaromatic', or 'antiaromatic'. Thermally induced pericyclic reactions proceed preferentially via aromatic transition sta...

M. J. S. Dewar

1971-01-01

213

Pulmonary Transfusion Reactions  

PubMed Central

Summary Background In recent years, pulmonary transfusion reactions have gained increasing importance as serious adverse transfusion events. Methods Review of the literature. Results Pulmonary transfusion reactions are not extremely rare and, according to hemovigilance data, important causes of transfusion-induced major morbidity and death. They can be classified as primary with predominant pulmonary injury and secondary as part of another transfusion reaction. Primary reactions include transfusion-related acute lung injury (TRALI), transfusion-associated circulatory overload (TACO) and transfusion-associated dyspnea (TAD). Secondary pulmonary reactions are often observed in the wake of hemolytic transfusion reactions, hypotensive/anaphylactic reactions, and transfusion-transmitted bacterial infections. Conclusion Knowledge and careful management of cases of pulmonary transfusion reactions are essential for correct reporting to blood services and hemovigilance systems. Careful differentiation between TRALI and TACO is important for taking adequate preventive measures.

Bux, Jurgen; Sachs, Ulrich J. H.

2008-01-01

214

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

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

215

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

216

Microfluidic chemical reaction circuits  

DOEpatents

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

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

2012-06-26

217

Noneczematous Contact Reactions  

Microsoft Academic Search

\\u000a Not all skin contact reactions present as eczema or dermatitis. There are several distinct noneczematous contact reactions\\u000a which are more commonly seen. The mechanisms of these reactions are not clearly elucidated yet. It is very useful to clinicians\\u000a to be able to identify these dermatoses as contact reactions so that they may be confirmed with patch testing and other unnecessary

Anthony Goon; Chee-Leok Goh

218

Insights into the mechanisms on chemical reactions: reaction paths for chemical reactions. [Li + HF; OH + Hâ  

Microsoft Academic Search

We report reaction paths for two prototypical chemical reactions: Li + HF, an electron transfer reaction, and OH + Hâ, an abstraction reaction. In the first reaction we consider the connection between the energetic terms in the reaction path Hamiltonian and the electronic changes which occur upon reaction. In the second reaction we consider the treatment of vibrational effects in

T. H. Jr. Dunning; E. Rosen; R. A. Eades

1987-01-01

219

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.

220

Reaction coordinates for electron transfer reactions  

SciTech Connect

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

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

2008-12-07

221

The Dibenzalacetone Reaction Revisited  

Microsoft Academic Search

A modification of a classic experiment is described that incorporates a discovery approach to organic synthesis. Groups of students are assigned target molecules of the dibenzalketone type and are given a sample procedure for the parent dibenzalacetone reaction. They are asked to design a synthesis of their target based on the model reaction and to modify the model reaction so

Leslie A. Hull

2001-01-01

222

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

223

One-Pot Synthesis of 3-Triazolyl-2-iminochromenes via a Catalytic Three Component Cascade Reaction.  

PubMed

A variety of 3-triazolyl-2-iminochromenes were synthesized in a one-pot, catalytic, three component condensation. In this event, a Cu(I)-catalyzed cycloaddition between 2-azidoacetonitrile and an acetylene formed a triazole and activated the neighboring methylene group, inducing an aldol-cyclization-dehydration sequence in the presence of a salicylaldehyde. Further elaboration led to more complex polyheterocycles. PMID:23751086

Qian, Wenyuan; Amegadzie, Albert; Winternheimer, David; Allen, Jennifer

2013-06-10

224

Preparation of ?-haloacylsilane and its use for triethylborane-induced reformatsky type reaction  

Microsoft Academic Search

Treatment of 2-halo-2-trimethylsilyloxirane with metal salts such as ZnCl2, ZnBr2, NaI, and AgBF4 gave the corresponding ?-haloacylsilanes in good yields. An addition of triethylborane to haloacylsilane provided boron enolate which reacted with aldehydes to give aldol type adducts with high stereoselectivity.

Yoshihiro Horiuchi; Masahiko Taniguchi; Koichiro Oshima; Kiitiro Utimoto

1995-01-01

225

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

226

The Dibenzalacetone Reaction Revisited  

NASA Astrophysics Data System (ADS)

A modification of a classic experiment is described that incorporates a discovery approach to organic synthesis. Groups of students are assigned target molecules of the dibenzalketone type and are given a sample procedure for the parent dibenzalacetone reaction. They are asked to design a synthesis of their target based on the model reaction and to modify the model reaction so it will work for their synthesis. They show they have synthesized the target with 1H NMR.

Hull, Leslie A.

2001-02-01

227

Reaction-diffusion textures  

Microsoft Academic Search

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

Andrew P. Witkin; Michael Kass

1991-01-01

228

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

229

Metal-mullite reactions  

SciTech Connect

Mullite was reacted with pure Al and with Ti or Zr dissolved in Ag-Cu eutectic alloys at 1100 C in Ar. Analysis of the Ti and Zr-containing specimens showed reaction zones with compositions of Ti{sub 50}Cu{sub 3O}O{sub 20} and ZrO{sub 2}, respectively. The Al-mullite specimen showed much more extensive penetration into the ceramic and a more diffuse reaction zone than the other two systems. Al{sub 2}O{sub 3} and Si were the main reaction products for Al-mullite reaction.

Loehman, R.E. [Sandia National Labs., Albuquerque, NM (United States); Tomsia, A.P. [Pask Research and Engineering, Berkeley, CA (United States)

1993-11-01

230

Breakup Reactions of Halo Nuclei  

SciTech Connect

Different reaction mechanisms of breakup reactions are discussed and the microscopic reaction model for two-neutron halo dissociation is presented. Some examples of halo breakup in reactions with electrons, nucleons, and nuclei are given.

Ershov, S.N. [Bogolyubov Laboratory of Theoretical Physics, Joint Institute of Nuclear Research, Dubna, Moscow oblast, 141980 (Russian Federation)

2004-10-01

231

Chemical Reaction Problem Solving.  

ERIC Educational Resources Information Center

|Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

Veal, William

1999-01-01

232

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…

Cunningham, Kevin

2007-01-01

233

Clock Reaction: Outreach Attraction  

ERIC Educational Resources Information Center

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

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

2010-01-01

234

Emotional reactions to infidelity  

Microsoft Academic Search

We sought to identify emotional reactions to a partner's sexual infidelity and emotional infidelity. In a preliminary study, 53 participants nominated emotional reactions to a partner's sexual and emotional infidelity. In a second study, 655 participants rated each emotion for how likely it was to occur following sexual and emotional infidelity. Principal components analysis revealed 15 emotion components, including Hostile\\/Vengeful,

Todd K. Shackelford; Gregory J. LeBlanc; Elizabeth Drass

2000-01-01

235

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

236

Nonadiabatic chemical reactions  

Microsoft Academic Search

A mixed quantum-classical approach where the environment is treated classically and the reactive degrees of freedom are considered to be quantum mechanical can be used to describe many chemical reactions, such as proton and electron transfer processes. We present reactive flux correlation function expressions for the rate constants of nonadiabatic chemical reactions occurring in quantum-classical systems. By means of a

Alessandro Sergi; Raymond Kapral

2005-01-01

237

Hypersensitivity Reactions to Corticosteroids.  

PubMed

Hypersensitivity reactions to corticosteroids (CS) are rare in the general population, but they are not uncommon in high-risk groups such as patients who receive repeated doses of CS. Hypersensitivity reactions to steroids are broadly divided into two categories: immediate reactions, typically occurring within 1 h of drug administration, and non-immediate reactions, which manifest more than an hour after drug administration. The latter group is more common. We reviewed the literature using the search terms "hypersensitivity to steroids, adverse effects of steroids, steroid allergy, allergic contact dermatitis, corticosteroid side effects, and type I hypersensitivity" to identify studies or clinical reports of steroid hypersensitivity. We discuss the prevalence, mechanism, presentation, evaluation, and therapeutic options in corticosteroid hypersensitivity reactions. There is a paucity of literature on corticosteroid allergy, with most reports being case reports. Most reports involve non-systemic application of corticosteroids. Steroid hypersensitivity has been associated with type I IgE-mediated allergy including anaphylaxis. The overall prevalence of type I steroid hypersensitivity is estimated to be 0.3-0.5 %. Allergic contact dermatitis (ACD) is the most commonly reported non-immediate hypersensitivity reaction and usually follows topical CS application. Atopic dermatitis and stasis dermatitis of the lower extremities are risk factors for the development of ACD from topical CS. Patients can also develop hypersensitivity reactions to nasal, inhaled, oral, and parenteral CS. A close and detailed evaluation is required for the clinician to confirm the presence of a true hypersensitivity reaction to the suspected drug and choose the safest alternative. Choosing an alternative CS is not only paramount to the patient's safety but also ameliorates the worry of developing an allergic, and potentially fatal, steroid hypersensitivity reaction. This evaluation becomes especially important in high-risk groups where steroids are a life-saving treatment. The assessment should be done when the patient's underlying condition is in a quiescent state. PMID:23567983

Vatti, Rani R; Ali, Fatima; Teuber, Suzanne; Chang, Christopher; Gershwin, M Eric

2013-04-01

238

Modeling of surface reactions  

SciTech Connect

Mathematical models are used to elucidate properties of the monomer-monomer and monomer-dimer type chemical reactions on a two-dimensional surface. The authors use mean-field and lattice gas models, detailing similarities and differences due to correlations in the lattice gas model. The monomer-monomer, or AB surface reaction model, with no diffusion, is investigated for various reaction rates k. Study of the exact rate equations reveals that poisoning always occurs if the adsorption rates of the reactants are unequal. If the adsorption rates of the reactants are equal, simulations show slow poisoning, associated with clustering of reactants. This behavior is also shown for the two-dimensional voter model. The authors analyze precisely the slow poisoning kinetics by an analytic treatment for the AB reaction with infinitesimal reaction rate, and by direct comparison with the voter model. They extend the results to incorporate the effects of place-exchange diffusion, and they compare the AB reaction with infinitesimal reaction rate and no diffusion to the voter model with diffusion at rate 1/2. They also consider the relationship of the voter model to the monomer-dimer model, and investigate the latter model for small reaction rates. The monomer-dimer, or AB[sub 2] surface reaction model is also investigated. Specifically, they consider the ZGB-model for CO-oxidation, and in generalizations of this model which include adspecies diffusion. A theory of nucleation to describe properties of non-equilibrium first-order transitions, specifically the evolution between [open quote]reactive[close quote] steady states and trivial adsorbing states, is derived. The behavior of the [open quote]epidemic[close quote] survival probability, P[sub s], for a non-poisoned patch surrounded by a poisoned background is determined below the poisoning transition.

Ray, T.R.

1993-01-01

239

NEUTRONIC REACTION SYSTEM  

DOEpatents

A nuclear reactor system is described for breeding fissionable material, including a heat-exchange tank, a high- and a low-pressure chamber therein, heat- exchange tubes connecting these chambers, a solution of U/sup 233/ in heavy water in a reaction container within the tank, a slurry of thorium dioxide in heavy water in a second container surrounding the first container, an inlet conduit including a pump connecting the low pressure chamber to the reaction container, an outlet conduit connecting the high pressure chamber to the reaction container, and means of removing gaseous fission products released in both chambers. (AEC)

Wigner, E.P.

1963-09-01

240

[Abnormal pupils' reactions].  

PubMed

Examination of the pupils' light reaction and estimation of the pupils' diameter are the components of the routine physical examination of a patient. Disturbances in pupils' light reaction, unequal size of the pupils indicate damage of the nervous system and require careful diagnosis, both neurological and ophthalmological. Different aspects of anatomy, physiology and the most common pathological syndromes associated with disturbed pupils' light reaction and unequal diameters of the pupils were presented in the article. Early diagnosis and proper treatment can allow to improve prognosis in the analyzed patient group. PMID:20825073

Kowal, Joanna; Strza?ka, Anna; Kubicka-Trzaska, Agnieszka; Romanowska-Dixon, Bozena

2010-01-01

241

An Illuminating Reaction.  

ERIC Educational Resources Information Center

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

Matthews, Catherine E.

1996-01-01

242

TALYS: Nuclear Reaction Simulator  

NASA Astrophysics Data System (ADS)

TALYS is a nuclear reaction code that estimates the Maxwellian-averaged reaction rates that are of astrophysical relevance. This enables reaction rates to be calculated with increased accuracy and reliability and the approximations of previous codes to be investigated. The TALYS predictions for the thermonuclear rates of relevance to astrophysics are detailed and compared with those derived by widely-used codes for the same nuclear ingredients. TALYS predictions may differ significantly from those of previous codes, in particular for nuclei for which no or little nuclear data is available. The pre-equilibrium process is shown to influence the astrophysics rates of exotic neutron-rich nuclei significantly. The TALYS code provides a tool to estimate all nuclear reaction rates of relevance to astrophysics with improved accuracy and reliability.

Koning, Arjan; Hilaire, Stephane; Duijvestijn, Marieke

2012-02-01

243

Chemical reaction on polysaccharides  

Microsoft Academic Search

The article discusses the synthesis of pullulan derivatives containing chloroalkyl groups by the reaction of crosslinked pullulan microparticles with different chloroalkyl chlorides in organic basic solvents. These new products may allow the attachment of various bioactive compounds by covalent bonding.

G Mocanu; D Vizitiu; D Mihai; A Carpov

1999-01-01

244

Response reactions: equilibrium coupling.  

PubMed

It is pointed out and illustrated in the present paper that if a homogeneous multiple equilibrium system containing k components and q species is composed of the reactants actually taken and their reactions contain only k + 1 species, then we have a unique representation with (q - k) stoichiometrically independent reactions (SIRs). We define these as coupling reactions. All the other possible combinations with k + 1 species are the coupled reactions that are in equilibrium when the (q - k) SIRs are in equilibrium. The response of the equilibrium state for perturbation is determined by the coupling and coupled equilibria. Depending on the circumstances and the actual thermodynamic data, the effect of coupled equilibria may overtake the effect of the coupling ones, leading to phenomena that are in apparent contradiction with Le Chatelier's principle. PMID:16722770

Hoffmann, Eufrozina A; Nagypal, Istvan

2006-06-01

245

Adverse reactions to sulfites  

PubMed Central

Sulfites are widely used as preservatives in the food and pharmaceutical industries. In the United States more than 250 cases of sulfite-related adverse reactions, including anaphylactic shock, asthmatic attacks, urticaria and angioedema, nausea, abdominal pain and diarrhea, seizures and death, have been reported, including 6 deaths allegedly associated with restaurant food containing sulfites. In Canada 10 sulfite-related adverse reactions have been documented, and 1 death suspected to be sulfite-related has occurred. The exact mechanism of sulfite-induced reactions is unknown. Practising physicians should be aware of the clinical manifestations of sulfite-related adverse reactions as well as which foods and pharmaceuticals contain sulfites. Cases should be reported to health officials and proper advice given to the victims to prevent further exposure to sulfites. The food industry, including beer and wine manufacturers, and the pharmaceutical industry should consider using alternative preservatives. In the interim, they should list any sulfites in their products.

Yang, William H.; Purchase, Emerson C.R.

1985-01-01

246

Common Reactions After Trauma  

MedlinePLUS

... trauma? All kinds of trauma survivors commonly experience stress reactions. This is true for veterans, children, and disaster rescue or relief workers. If you understand what is happening when ...

247

Untoward penicillin reactions  

PubMed Central

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

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

1958-01-01

248

Skin Reactions to Cold  

PubMed Central

Although skin reactions to cold are seen surprisingly infrequently in Canada, it is important to manage them correctly when they do occur. Frostbite, cold urticarias, Raynaud's disease and phenomenon, and several miscellaneous changes are discussed.

Talpash, Orest

1976-01-01

249

Bad Reaction to Cosmetics?  

MedlinePLUS

... Tobacco Products Vaccines, Blood & Biologics Bad Reaction to Cosmetics? Tell FDA Search the Consumer Updates Section Lash ... M.D., director of the agency’s Office of Cosmetics and Colors. “So, consumers are one of FDA’s ...

250

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

251

Reactor for 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.degree. to 300.degree. 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, Jr., Lawrence A. (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

1993-01-01

252

Polyatomic Reaction Dynamics.  

National Technical Information Service (NTIS)

It is difficult to study the reaction dynamics of polyatomic systems. One of the principal problems is the calculation of the Born-Oppenheimer potential energy surface. In this thesis several useful approximations to the full potential energy surface are ...

T. Carrington

1985-01-01

253

An Illuminating Reaction.  

ERIC Educational Resources Information Center

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

Matthews, Catherine E.

1996-01-01

254

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

255

Suspected adverse reactions, 2008  

Microsoft Academic Search

Reports to the UK Suspected Adverse Reaction Surveillance Scheme (SARSS) in 2008 increase by around 11 per cent compared with 2007Low incidence of suspected adverse reactions following bluetongue virus vaccinationIncrease in reports of suspected lack of efficacy to canine parvovirus vaccinationRabbit deaths reported after off-label use of dexmedetomidineThese are some of the results from the SARSS in 2008, as discussed

F. Dyer; E. Brown; S. Cooles; A. Tait

2009-01-01

256

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

257

Adverse reaction to tetrazepam.  

PubMed

Adverse reactions caused by benzodiazepines rarely occur. We present a case of a 70-year-old man who developed a maculopapular exanthema after the ingestion of tetrazepam. For his diagnosis, skin tests were performed, including prick and patch tests, not only with the benzodiazepine implicated in the reaction, but also with benzodiazepines of other groups. Single-blind oral challenge tests were also performed in the patient, in order to assess his tolerance to other benzodiazepines. PMID:11642573

Palacios Benito, R; Domínguez Ortega, J; Alonso Llamazares, A; Rodríguez Morales, A; Plaza Díaz, A; Chamorro Gómez, M; Martínez-Cócera, C

2001-01-01

258

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

259

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

260

Water Nanodroplets as a Reaction Medium: FT-ICR Studies of the Stability, Structure and Reactivity of Hydrated Ions and Ionic Water Clusters  

NASA Astrophysics Data System (ADS)

With the help of a versatile ion source coupling laser vaporization with supersonic expansion, ionic clusters of the type X^±(H_2O)n are easily generated, and if desired, they can be mass selected in a Fourier Transform Ion Cyclotron (FT-ICR) mass spectrometer. The central ion, X^± can be for instance H^+ or OH^-, a free electron, or an ionized metal such as Na^+, Ag^+, Mg^+, or Al^+. Such "nanodroplets" solvated with up to 200 molecules of water or other ligands slowly fragment in the collision-free environment of the FT-ICR trap. They lose in a controlled way the solvent molecules, one by one on a millisecond timescale. The products of reactions which occur in the nanodroplet as a result of the loss of the stabilizing ligand can in the high-resolution mass spectrometer be unambiguously identified. In this way, a variety of solution processes such as ionic dissolution, fragmentation, neutralization, precipitation, reduction-oxidation reactions, or acid-base catalyzed reactions can be investigated in molecular, microscopic detail. Small droplets and particles are important for a variety of atmospheric processes and reactions occurring both in the troposphere and the stratosphere. This suggests the possibility of preparing such nano-droplets of suitable composition, and using them as a model system for investigating a large variety of reactions important for atmospheric chemistry. In the present talk, we will describe our apparatus and external source, and discuss a variety of results obtained recently with it in our laboratory. The aldol condensation of acetaldehyde as an example of an acid-base catalyzed reaction and the precipitation of AgCl show that a number of well-known reactions in solution have their counterpart on a single molecule level in the cluster. The competition between electron detachment and water loss of hydrated electrons e^-(H_2O)_n, n=13-36, provides interesting and unexpected insights into the coupling dynamics of the electron to its water environment.

Bondybey, Vladimir E.

2001-03-01

261

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

262

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.

263

Atomic force microscopy imaging of TiO{sub 2} surfaces active for C-C bond formation reactions in ultrahigh vacuum  

SciTech Connect

TiO{sub 2}(001) single crystal surfaces active for a variety of different chemistries were examined using atomic force microscopy (AFM). C-C bond forming reactions previously identified on these surfaces include carboxylic acid ketonization, aldol condensation, reductive carbonyl coupling, and alkyne cyclotrimerization. The surfaces were prepared in ultrahigh vacuum (UHV) and examined by AFM in air. Surfaces examined included the (011)-faceted surface, (114)-faceted surface, and argon-ion-bombarded surfaces, as well as the mechanically polished single-crystal surface prior to treatment in UHV. The one unifying feature of all the images was their extreme flatness. Root-mean-square roughnesses were routinely less than 10 {Angstrom} in 500 x 500 nm scans. These same scans showed the surfaces to have surface areas exceeding that of an ideal flat surface by no more than 1.2%. Images of the polished surface revealed a variety of surface features, including polishing scratches and particle-like features. The argon-ion-bombarded surface and the faceted surfaces were composed of large flat plateaus ranging in size from 21 to 75 nm. The size of the plateaus was essentially the same for the ion bombarded surface and the (011)-faceted surface. The (114)-faceted surfaced exhibited slightly smaller plateau regions than the other surfaces. The images indicate that argon-ion bombardment, while disordering the surface and causing significant composition changes, does not lead to observable morphological changes on this scale. The relative uniformity of the surfaces examined is consistent with the selectivity of carbon-carbon bond-forming reactions that have been shown to take place on these surfaces. The images also reveal how the surface topography on the scale of the plateau structures observed is only slightly changed during the transformation of the surface unit cell structure from the (011)- to the (114)-faceted surface. 29 refs., 6 figs., 1 tab.

Watson, B.A.; Barteau, M.A. [Univ. of Delaware, Newark, DE (United States)

1994-06-01

264

Positron Reaction Microscope  

NASA Astrophysics Data System (ADS)

We are developing a positron reaction microscope to measure kinematically complete ionization reactions of atoms and dissociative ionization of simple molecules by positron impact. The experiment is designed to use the slow positron beamline at the ARC Centre for Antimatter Matter Studies (CAMS) node at the Australian National University (ANU). This project is a collaboration among the University of North Texas, CAMS, and the Max Planck Insitute for Kern Phyzik in Heidelberg. Initial measurements and apparatus calibration will be performed using electrons. For positron measurements, the apparatus will be rolled into position on the slow positron beamline at the CAMS site at ANU.

Mueller, Dennis; Armitage, Simon; Vermet, Corbin; Lee, Chistopher; Dorn, Alexander; Buckman, Stephen; Sullivan, James

2012-10-01

265

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

266

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

267

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

268

Surface aligned reaction  

NASA Astrophysics Data System (ADS)

This paper reflects on three decades during which the study of surface aligned reaction (SAR) has advanced. The objective in SAR, which in considerable part still lies ahead, is the simultaneous control of atomic and molecular ``collision energies, collision angles, and impact parameter.'' Following a discussion of the benefits of such an approach we review the progress made, and, as a stimulus to experiment, present new calculations of SAR dynamics for bimolecular reaction at a metal surface. It seems reasonable to suppose that we are now entering a decade in which a combination of scanning tunneling microscopy and femtosecond laser spectroscopy will bring the full realisation of SAR.

Ning, Zhanyu; Polanyi, John C.

2012-09-01

269

Three Reaction Papers.  

ERIC Educational Resources Information Center

In reaction to presentations at the Airlie House Conference on the Implications of Research on Teaching for Practice, two papers (by O. Smith and N. L. Gage, respectively) discuss how far research on teaching has come as a field, while a third (by G. D. Fenstermacher) explains how implications of research on teaching can be used. (MP)

Smith, B. Othanel; And Others

1983-01-01

270

Azoxy rearrangement reactions  

NASA Astrophysics Data System (ADS)

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

Basch, Harold; Hoz, Tova

271

Oscillations in Catalytic Reactions  

Microsoft Academic Search

This paper deals with the status of knowledge concerning open catalytic reaction systems which, though exposed to constant conditions, exhibit sustained oscillatory states. Such behavior arouses interest because, aside from the practical aspects and matters of fundamental importance, it has a battling quality – it usually defles physical explantion offered in the total absence of a mathematical analysis, and hence

M. Sheintuch; H. A. Schmitz

1977-01-01

272

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

273

Geotropic Reaction of Plants.  

National Technical Information Service (NTIS)

Data on the physiology (auxins, amino acids, and other metabolites) of the geotropic reaction of plants is presented. Systems of perception and fixation of the geotropic stimulus are examined, as in the response phase of geotropic bending. The text is a m...

A. I. Merkis

1976-01-01

274

A Principal's Reaction  

ERIC Educational Resources Information Center

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

Zaretsky, Lindy

2004-01-01

275

Chain Reaction Polymerization.  

ERIC Educational Resources Information Center

The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

McGrath, James E.

1981-01-01

276

Introducing the Wittig Reaction.  

ERIC Educational Resources Information Center

An experiment is described which provides a simple example of the application of the Wittig reaction to the synthesis of unsaturated compounds. The experiment was designed with British HNC chemistry students in mind, but it is also suitable as a project-type exercise for final year GCE A-level students. (Author/BB)

Armstead, D. E. F.

1979-01-01

277

Modelling Reaction Times  

Microsoft Academic Search

We discuss the simulation of reaction times in connectionist systems. The obvious way to do this involves thinking in terms of neural activations building up towards some threshold in cascaded systems, but it has also been suggested that the output activation error scores in standard back-propagation networks should also be correlated with response times. The idea is that in the

John A. Bullinaria

278

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.

279

A World of Reactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2009-07-10

280

Rates of Chemical Reactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

1900-01-01

281

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.

282

Theory of resonance reactions  

Microsoft Academic Search

A general formal theory of resonance reactions and scattering is ; developed without the use of channel radii. The approach employed allows a ; simple physical interpretation of the two energies, one of which must be kept ; fixed while the other one is varied in order for a Breit-Wigner denominator to ; vanish. A new result, obtained without a

Luciano Fonda; Roger G. Newton

1960-01-01

283

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

284

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.

2013-05-15

285

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.…

Cooke, D. O.

1976-01-01

286

Biomass gasification reaction velocities  

SciTech Connect

The propagation of gaseous flames is determined by the flame velocity, V/sub f/ (the rate at which the flame propagates into the unburned fuel/oxidant). In the same way, gasification of solid fuels depends on the gasification reaction velocity (V/sub r), the rate at which the reaction interface can move into the unreacted solid fuel. We have developed a simple laboratory transparent downdraft gasifier for measuring this velocity for a variety of fuels and conditions. Air or oxygen is drawn down through a 5-cm-diameter quartz tube. If the reaction zone remains stationary in the tube, V/sub r/ is simply the volumetric feed rate. For some input conditions, the position of the incandescent reaction zone is quite stable in the quartz tube. This position depends on the relative rates of production of charcoal by pyrolysis of the biomass and gasification of the charcoal by the pyrolysis combustion gases and can move up or down, depending on conditions. In an uninsulated tube the zone may move down indicating that the char gasification rate exceeds the pyrolysis rate. Adding insulation to the tube increases the tendency for the zone to move up, indicating that the pyrolysis rate is faster than the gasification rate. In practical gasifiers it is necessary to stabilize the reaction front such that the propagation rate equals the feed rate. A number of methods of stabilizing this front have been found. We believe the data and observations presented here help form the basis for a model of downdraft biomass gasification which is significantly different from previous models, and we are continuing to gather data for this model.

Reed, T.B.; Markson, M.

1983-09-01

287

Reactions to dietary tartrazine.  

PubMed Central

Double blind challenges with tartrazine and benzoic acid were performed in hospital in 24 children whose parents gave a definite history of a purely behavioural immediate adverse reaction to one of these substances. The patients, whose ages ranged from 1.6 to 12.4 years, were on a diet that avoided these items, and in all there was a clear history that any lapse of the diet caused an obvious adverse behavioural reaction within two hours. In no patient was any change in behaviour noted either by the parents or the nursing staff after the administration of placebo or active substances. Twenty two patients returned to a normal diet without problems, but the parents of two children insisted on continuing the diet. While popular belief has it that additives may have harmful behavioural effects, objective verification is required to prevent overdiagnosis.

David, T J

1987-01-01

288

Electron transfer reactions  

NASA Astrophysics Data System (ADS)

During the tenure of this contract research was performed on a number of aspects of electron transfer reactions (solvent dynamics including vibrational effects, non-Debye solvent dynamics, early steps in bacterial photosynthesis) and of the use of artificial intelligence searching methods, the latter, in part, as a prelude to our current study of electron transfer reactions in structurally complicated systems such as proteins. Seven Technical Reports were issued during this period, and research on several topics was initiated: the study of the relation between charge transfer absorption and fluorescence spectra and the inverted region, a nonadiabatic/adiabatic coherent mechanism for electron transfers, and electron transfers between two immiscible-liquid phases and between a semiconductor and an electrolyte.

Marcus, R. A.

1989-07-01

289

Formation of aromatic compounds from carbohydrates. Reaction of xylose, glucose, and glucuronic acid in acidic solution at 300/sup 0/C  

SciTech Connect

For several years respective groups have investigated the formation of aromatic compounds from carbohydrates in aqueous solution at various pH values under reflux or hydrothermolytic conditions. Previous hydrothermolytic studies of cellulose indicated that certain aromatic products could be obtained when the pH was maintained in the range of 4-11. This suggested that aldol condensation, a prime route for the production of aromatics from saccharides, could function under moderately acidic conditions. The current research was initiated to study the competition between the formation of phenolic compounds (aldol involvement) and that of furans (dehydration and cyclization).

Theander, O.; Nelson, D.A.; Hallen, R.T.

1987-04-01

290

[Pulmonary allergic reactions].  

PubMed

Allergic diseases of the lungs may affect the airways, the pulmonary parenchyma and the pulmonary vessels. The most relevant representatives are allergic asthma, hypersensitivity pneumonitis, bronchopulmonary aspergillosis and the Churg-Strauss syndrome. The type of allergic reaction and the pathophysiological consequences vary considerably between these entities. New drugs target specific mechanisms based on new insights into the pathogenetic processes of the underlying disease. PMID:22806148

Koczulla, A R; Beutel, B; Greulich, T; Jerrentrup, A; Vogelmeier, C

2012-08-01

291

The reaction wheel pendulum  

Microsoft Academic Search

\\u000a The reaction wheel pendulum is one of the simplest non-linear underactuated systems. It is a pendulum with a rotating wheel\\u000a at the end, which is free to spin about an axis parallel to the axis of rotation of the pendulum (see Figure 7.1). The wheel is actuated by a DC-motor, while the pendulum is unactuated. The coupling torque generated by

Isabelle Fantoni; Rogelio Lozano

292

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

293

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

294

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

295

Addition reactions of fluoroalkenes  

Microsoft Academic Search

Summary 1.Perfluoropropene, in presence of alkalis, readily unites with alcohols and thiols, and the hydrogen atom of the hydroxyl group of the alcohol or of the mercapto group of the thiol, in contrast to its behavior, in the case of propene, adds to the middle carbon atom of perfluoropropene.2.The alkyl 2H-hexafluoropropyl ethers formed as a result of reaction of perfluoropropene

I. L. Knunyants; A. I. Shchekotikhin; A. V. Fokin

1953-01-01

296

Chemical Reactions in DSMC  

SciTech Connect

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

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

2011-05-20

297

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

SciTech Connect

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

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

1992-09-01

298

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

SciTech Connect

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

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

1992-01-01

299

Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory  

SciTech Connect

The relevant energy ranges for stellar nuclear reactions are introduced. Low-energy compound direct reactions are discussed. Stellar modifications of the cross sections are presented. Implications for experiments are outlined.

Rauscher, T. [Department of Physics, University of Basel, CH-4056 Basel (Switzerland)

2010-08-12

300

Microbial aldolases as C–C bonding enzymes—unknown treasures and new developments  

Microsoft Academic Search

Aldolases are a specific group of lyases that catalyze the reversible stereoselective addition of a donor compound (nucleophile) onto an acceptor compound (electrophile). Whereas most aldolases are specific for their donor compound in the aldolization reaction, they often tolerate a wide range of aldehydes as acceptor compounds. C–C bonding by aldolases creates stereocenters in the resulting aldol products. This makes

Anne K. Samland; Georg A. Sprenger

2006-01-01

301

A Study in Association Reaction and Reaction Time  

Microsoft Academic Search

This article discusses a study in association reaction and reaction time. In the spring of 1909 the writer became interested in the possibility of making an application of the association reaction as a test for guilty knowledge of crime. The problem was to determine which one of the four subjects tested had gone through this experience. The test proved successful

Harry. W. Crane

1915-01-01

302

ChemTeacher: Decomposition Reactions  

NSDL National Science Digital Library

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

2011-01-01

303

Bistable and oscillating chemical reactions  

NASA Astrophysics Data System (ADS)

In the last decade the number and the diversity of isothermal oscillating reactions in homogeneous aqueous solution have tremendously increased. We present an updated classified review of these chemical reactions.

Pacault, A.; Ouyang, Q.; de Kepper, P.

1987-09-01

304

Kinetics of actinide complexation reactions.  

National Technical Information Service (NTIS)

Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In li...

K. L. Nash J. C. Sullivan

1997-01-01

305

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

306

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

307

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

308

Fundamental Processess in Gaseous Reactions.  

National Technical Information Service (NTIS)

Fundamental processes in gas phase reactions (primarily decomposition and recombination reactions of simple diatomic and triatomic molecules) were studied using shock wave techniques. The investigation of energy transfer processes covered more areas: lase...

D. F. Hornig G. E. Leroi

1969-01-01

309

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

310

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

311

TALYS: Comprehensive nuclear reaction modeling  

Microsoft Academic Search

TALYS is a nuclear reaction program which simulates nuclear reactions that involve neutrons, gamma-rays, protons, deuterons, tritons, helions and alpha-particles, in the 1 keV - 200 MeV energy range. A suite of nuclear reaction models has been implemented into a single code system, enabling us to evaluate basically all nuclear reactions beyond the resonance range. An overview is given of

A. J. Koning; S. Hilaire; M. C. Duijvestijn

312

''Subthreshold'' reactions involving nuclear fission  

SciTech Connect

We analyze reactions of several types that are naively below threshold but can proceed because of the release of binding energy from nuclear fission and occasionally the formation of Coulombic bound states. These reactions include (i) photofission with pion production and (ii) charged current neutrino-nucleus reactions that lead to fission and/or formation of a Coulomb bound state of a {mu}{sup -} with the nucleus of a fission fragment. We comment on the possible experimental observation of these reactions.

Goldhaber, M.; Shrock, R.

2001-02-01

313

The Vitamin C Clock Reaction  

NASA Astrophysics Data System (ADS)

An iodine clock reaction that gives a colorless to black result similar to that of the familiar Landolt iodate-bisulfite clock reaction is described. The vitamin C clock reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, 3% hydrogen peroxide, and laundry starch. Orange juice may be used as the vitamin C source to give an orange to black reaction.

Wright, Stephen W.

2002-01-01

314

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

315

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.

2013-05-15

316

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

317

Magnetic Effects in Chemical Reactions  

Microsoft Academic Search

The Review discusses in what elementary chemical reactions the intrinsic angular momentum of electrons and nuclei is conserved and in what reactions it is not conserved, how weak electron-nuclear magnetic interaction and an external magnetic field influence the conservation of angular momentum and what are the consequences of this effect, and what magnetic effects occur in chemical reactions, as well

Anatolii L Buchachenko

1976-01-01

318

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

319

Peripherality of breakup reactions  

SciTech Connect

The sensitivity of elastic breakup to the interior of the projectile wave function is analyzed. Breakup calculations of loosely bound nuclei ({sup 8}B and {sup 11}Be) are performed with two different descriptions of the projectile. The descriptions differ strongly in the interior of the wave function, but exhibit identical asymptotic properties, namely the same asymptotic normalisation coefficient, and phase shifts. Breakup calculations are performed at intermediate energies (40-70 MeV/nucleon) on lead and carbon targets as well as at low energy (26 MeV) on a nickel target. No dependence on the projectile description is observed. This result confirms that breakup reactions are peripheral in the sense that they probe only the external part of the wave function. These measurements are thus not directly sensitive to the total normalization of the wave function, i.e., spectroscopic factor.

Capel, P. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T2A3 (Canada); Nunes, F. M. [National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)

2007-05-15

320

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

321

Microwave initiated reactions: Pechmann coumarin synthesis, Biginelli reaction, and acylation  

Microsoft Academic Search

An energy-efficient protocol has been developed for solvent-free reactions that are mildly exothermic but not spontaneous. The exothermic reaction mixture—on several g-scale—is exposed for about 30s to low power (about 200W) microwaves and then the microwave oven is switched off. After this short burst of energy, the exothermic reaction gets initiated and proceeds on its own to completion. A number

Maghar S. Manhas; Subhendu N. Ganguly; Somdatta Mukherjee; Amit K. Jain; Ajay K. Bose

2006-01-01

322

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

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

Hratchian, Hrant P.

2011-06-01

323

EXPERIMENTAL BONE MARROW REACTIONS  

PubMed Central

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

Muller, Gulli Lindh

1927-01-01

324

Reactions inside nanoscale protein cages  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

325

Enzymatic reactions on immobilised substrates.  

PubMed

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

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

2013-08-01

326

Microstructured reactors for catalytic reactions  

Microsoft Academic Search

This review addresses the catalytic reactions performed in microstructured reactors, which are more and more recognized in recent years as a novel approach for chemistry and chemical process industry. They are particularly suited for highly exothermic and fast reactions allowing temperature control and isothermal operation. A brief evaluation of the advantages for gas-phase, liquid-phase, and gas–liquid–solid reactions carried out in

Lioubov Kiwi-Minsker; Albert Renken

2005-01-01

327

Change in Temperature: Exothermic Reaction  

NSDL National Science Digital Library

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

Kessler, James H.; Galvan, Patricia M.

2007-01-01

328

Recent highlights on fragmentation reactions  

NASA Astrophysics Data System (ADS)

Fragmentation reactions constitute an optimum tool for exploring the nuclear landscape by producing nuclei far from stability at in-flight radioactive nuclear beam facilities. Moreover, they are routinely used in modern cancer therapy treatments. Nevertheless, the large dynamical and isospin range covered by this reaction mechanism are unique features for many fundamental studies. In this work we review some of the most salient recent results in fundamental nuclear physics studies based on fragmentation reactions.

Benlliure, José

2011-09-01

329

Charge Transfer Reactions  

NASA Astrophysics Data System (ADS)

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

Dennerl, Konrad

2010-12-01

330

Reactions at Oxygen Atoms  

NASA Astrophysics Data System (ADS)

Synthetic protocols based on carbohydrates require the differentiation of their abundant hydroxyl groups, by and large, in order to expose just one single hydroxyl group to the selected reagent. This differentiation is usually carried out with the assistance of protecting groups that block the rest of the hydroxyl groups while being compatible with the given reaction conditions. By corollary, the knowledge and apt choice of the appropriate protecting groups is a key factor in successful synthetic endeavors. In this chapter, an overview of the most commonly employed protecting groups in carbohydrate chemistry is given. Alkyl ethers, being robust protecting groups, have a long history in synthetic carbohydrate chemistry and in related structural studies of polysaccharides. Acetals and ketals, which are of fundamental importance in carbohydrate chemistry, are then discussed. Acyl and silyl protecting groups, which also play an important role in modern monosaccharide transformations, are also presented. Finally, recent blocking strategies are described, including orthogonal strategies, by which the protecting groups are harmoniously combined in modern carbohydrate chemistry.

Gómez, Ana M.

331

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

332

Continuous chemical reaction chromatography  

SciTech Connect

The past three years have been devoted to investigating simulated countercurrent chomatographic moving bed separators (SCMCS) and simulated countercurrent moving bed reactors (SCMCR). These are novel separators and reactors used for separation, or for carrying out a chemical reaction and separation continuously and simultaneously in fixed bed. In the SCMCR and the SCMCS the process aspects of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past stationary reactant inlet, is simulated by successively switching feed and product take-off streams through a series of inlets located at fixed intervals along a fixed bed or between a series of packed columns. The flow of solids past a fixed feed point, characteristic of countercurrent moving beds, is replaced by motion of the feed past a fixed packed bed. Feed enters a particular column for a fixed length of time, and then is switched to the next column. Product streams are also advanced simultaneously. When the feed point has progressed to the end it is returned to the starting position and the process repeated. The shifting of the feed and the product positions in the direction of fluid flow thus simulates the movement of solids in the opposite direction. The requisite motion between the feed and the bed, which is continuous for true countercurrency, is replaced by periodic, discrete steps in simulated countercurrency. The continuous, steady state operation characteristic of true countercurrency is replaced by periodic transients at each switch of the feed.

Aris, R.; Carr, R.W.

1992-01-01

333

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

334

Intrinsic fluctuations in explosive reactions  

SciTech Connect

A reaction is called explosive when the amount of a reactant becomes infinite in a finite time. When the intrinsic stochastic character of the reaction is taken into account, the explosion time is a random quantity. The authors compute its probability distribution, or at least its average and variance, for various kinds of reactions. If a reaction is unstable, so that a reactant can either explode or disappear, one first has to compute the probability for an explosion to occur at all, and then the average explosion time. Finally, the same ideas are applied to more general Markov processes.

van Kampen, N.G.

1987-03-01

335

Complement-Dependent Anaphylactic Reactions  

PubMed Central

The concept of elicitation of reactions of anaphylactic type by non-tissue-fixing antibody, through activation of complement and release of anaphylatoxins by antigen-antibody complexes in vivo, is not clearly defined by published evidence. Experimental data are presented to demonstrate that guinea pig immunoglobulin G2 (noncytotropic) complexed with antigen in vitro elicits dermal reactions in guinea pigs, and that pretreatment of animals with complement-inactivating cobra venom factor diminishes such reactions. The various pathways through which immediate hypersensitive reactions may occur are discussed.

Tom, B. H.; Raffel, S.

1975-01-01

336

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

337

Domino Heck-Pericyclic Reactions  

Microsoft Academic Search

Palladium-catalyzed cross-coupling reactions and cycloadditions as well as electrocyclic transformations\\u000a can efficiently be combined in one-pot sequences to build up complex molecular skeletons from simple\\u000a precursors. The intermolecular Heck reaction of alkenyl halides with alkenes leads to 1,3-butadienes\\u000a prone to undergo subsequent Diels–Alder reactions. Frequently, special precautions have to\\u000a be taken in order to avoid a domino reaction in which the

Paultheo von Zezschwitz; Armin de Meijere

338

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

339

Topologically invariant reaction coordinates for simulating multistate chemical reactions.  

PubMed

Evaluating free energy profiles of chemical reactions in complex environments such as solvents and enzymes requires extensive sampling, which is usually performed by potential of mean force (PMF) techniques. The reliability of the sampling depends not only on the applied PMF method but also the reaction coordinate space within the dynamics is biased. In contrast to simple geometrical collective variables that depend only on the positions of the atomic coordinates of the reactants, the E(gap) reaction coordinate (the energy difference obtained by evaluating a suitable force field using reactant and product state topologies) has the unique property that it is able to take environmental effects into account leading to better convergence, a more faithful description of the transition state ensemble and therefore more accurate free energy profiles. However, E(gap) requires predefined topologies and is therefore inapplicable for multistate reactions, in which the barrier between the chemically equivalent topologies is comparable to the reaction activation barrier, because undesired "side reactions" occur. In this article, we introduce a new energy-based collective variable by generalizing the E(gap) reaction coordinate such that it becomes invariant to equivalent topologies and show that it yields more well behaved free energy profiles than simpler geometrical reaction coordinates. PMID:23214508

Mones, Letif; Csányi, Gábor

2012-12-17

340

Liquid membranes: advancing reaction zone model for finite reactions  

SciTech Connect

An advancing reaction zone model has been proposed for a multiple emulsion liquid membrane for the case of simple permeation with finite reaction at the inner interphase. The model has been numerically solved and the effect of different system parameters on the rate of extraction and on the concentration profiles in the emulsion globule has been discussed. 18 references, 6 figures, 3 tables.

Janakiraman, B.

1985-01-01

341

Carbon insertion into arachno-6,9-C2B8H14 via acyl chlorides. skeletal alkylcarbonation (SAC) reactions: a new route for tricarbollides.  

PubMed

Reactions between arachno-6,9-C2B8H14 (1) and selected acyl chlorides, RCOCl, in the presence of PS (PS = "proton sponge", 1,8-dimethylamino naphthalene) in CH2Cl2 for 24 h at reflux, followed by in situ acidification with concentrated H2SO4 at 0 °C, generate a series of neutral alkyl and aryl tricarbollides 8-R-nido-7,8,9-C3B8H11 (2) (where R = CH3, 2a; C2H5, 2b; n-C4H9, 2c; C6H5, 2d; 4-Cl-C6H4, 2e; 4-Br-C6H4, 2f; 4-I-C6H4, 2g; 1-C10H7, 2h; and 2-C10H7, 2i). The best yields were achieved for aryl derivatives (80-95%) while the yields of the corresponding alkyl substituted compounds are lower (60-70%). These skeletal alkylcarbonation (SAC) reactions are consistent with an aldol-type condensation between the RCO group and open-face hydrogen atoms on the dicarbaborane 1, which is associated with the insertion of the carbonyl carbon atom into the structure of arachno-6,9-C2B8H14 (1) under elimination of three extra hydrogen atoms as H2O and HCl. The reactions thus result in an effective R-tricarbaborane cross-coupling. Individual compounds of structure 2 have been purified by chromatography on a silica gel support, using hexane as the mobile phase (R(F) = ?0.3). Deprotonation agents, such as NEt3, NaOH, NaH, etc., convert tricarbaboranes 2 into the corresponding conjugated anions [8-R-nido-7,8,9-C3B8H10](-) (2(-)) which were isolated as salts with suitable countercations (for example, Et3NH(+), Tl(+), NEt4(+), etc.). The compounds have been characterized by multinuclear ((11)B, (1)H, and (13)C) NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of anions [8-R-nido-7,8,9-C3B8H10]¯ (where R = C6H5, 4-I-C6H4 and 1-C10H7; 2a(-), 2g(-), and 2h(-)) and that of the neutral 8-(1-C10H7)-nido-7,8,9-C3B8H11 (2h) have been established by X-ray diffraction analyses. PMID:23885975

Bakardjiev, Mario; Štíbr, Bohumil; Holub, Josef; Pad?lková, Zde?ka; R?ži?ka, Aleš

2013-07-25

342

Nuclear Reactions in Solids  

NASA Astrophysics Data System (ADS)

Earlier work by the author disclosed evidence for nuclear transmutations in multi-layer thin-film Ni/Pd electrodes loaded to a high ratio of hydrogen/film metal using an electrolytic technique [1]. Nonnatural isotopes abundances were found for select products. A distinctive characteristic of this and similar experiments by others is a product yield curve vs. mass with four high yield peaks distributed between low and high masses. Attempts to explain this observation have evolved around the original swimming electron layer (SEL) theory [2]. Most recently Mitsubishi Corp. researchers have reported a real-time transmutation measurement using built-in XPS diagnostics where a surface layer of Sr-88 was transmuted into Mo-96 over a 200 hour run period during the diffusion of deuterium through a multi-layer thin-film Pd/CaO substrate [3]. Likewise in a companion experiment, Cs-133 was transmuted into Pr-141. These products exhibit a large deviation from natural isotopic abundance, and the characteristic signature is a mass change of 8 and charge change of 4. Takahashi has attempted to explain these results in terms of transient condensation of deuterons at lattice focal points [4]. An alternate explanation in terms of SEL theory will be presented. The objective is to provide a uniform understanding of both types of experiments presented in both Refs. 1,3. Acknowledgement: Partially supported by Lattice Energy, LLC [1] G. H. Miley and J. A. Patterson, J. New Energy 1, 3, 5-30 (1996). [2] H. Hora, et al., Physics Ltrs. A, 175, 138-143, (1993). [3] Y. Iwamura, T. Itoh, et al., "Low energy nuclear reaction induced by D gas permeation through multilayer film," Proc. ICCF 9, Beijing, China, April (2002), to be published Japanese J. Physics. [4] A. Takahashi, Condensation at lattice focal points," Proc. ICCF 9, Beijing, China, April (2002).

Miley, George H.; Hora, Heinrich

2002-10-01

343

Modeling and Simulating Chemical Reactions  

Microsoft Academic Search

Abstract Many students are familiar with the idea of modeling chemical reactions in terms of ordinary dieren tial equations. However, these deterministic reaction rate equations are really a certain large-scale limit of a sequence of ner-scale probabilistic models. In studying this hierarchy of models, students can be exposed to a range of modern ideas in applied and compu- tational mathematics.

Desmond J. Higham

2008-01-01

344

Semiclassical aspects of transfer reactions  

SciTech Connect

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

Bond, P.D.

1985-01-01

345

"Greening up" the Suzuki Reaction  

ERIC Educational Resources Information Center

This article describes the rapid, green synthesis of a biaryl compound (4-phenylphenol) via a Pd(0)-catalyzed Suzuki cross-coupling reaction in water. Mild reaction conditions and operational simplicity makes this experiment especially amenable to both mid- and upper-level undergraduates. The methodology exposes students to purely aqueous…

Aktoudianakis, Evangelos; Chan, Elton; Edward, Amanda R.; Jarosz, Isabel; Lee, Vicki; Mui, Leo; Thatipamala, Sonya S.; Dicks, Andrew P.

2008-01-01

346

Quantum Dynamics of Insertion Reactions  

Microsoft Academic Search

We describe quantum-dynamical calculations of insertion reactions involving metastable C, N and O atoms with hydrogen molecules. We use a time independent hyperspherical body-frame formalism. Reaction probabilities, rovibrational distributions, integral and differential cross sections and product translational energy distributions have been computed and compared with recent experimental data.

Pascal Honvault; Jean-Michel Launay

347

On Inventing Reactions for Atom  

Microsoft Academic Search

An important first step in making organic reactions more environ- mentally benign by design requires processes that are, to a first approximation, simple additions with anything else needed only catalytically. Since so few of the existing reactions are additions, synthesis of complex molecules requires the development of new atom-economic methodology. The prospect for such developments is probed in the context

BARRY M. TROST

348

Reaction dynamics: Surrounded by complications  

NASA Astrophysics Data System (ADS)

There is a long history of gas-phase studies of bimolecular reactions, but the presence of surrounding molecules complicates analogous studies in solution. Now, advances in ultrafast laser technology have enabled the detailed study of vibrational energy release in a reaction in solution.

Crim, F. Fleming

2011-05-01

349

Entropy Effects in Chelation Reactions.  

ERIC Educational Resources Information Center

The entropy change for a reaction in aqueous solution can be evaluated as a combination of entropy factors. Valuable insight or understanding can be obtained from a detailed examination of these factors. Several entropy effects of inorganic chemical reactions are discussed as examples. (Author/JN)

Chung, Chung-Sun

1984-01-01

350

Pharmacogenomics of adverse drug reactions.  

PubMed

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

Daly, Ann K

2013-01-29

351

Foreign body reaction to biomaterials  

Microsoft Academic Search

The foreign body reaction composed of macrophages and foreign body giant cells is the end-stage response of the inflammatory and wound healing responses following implantation of a medical device, prosthesis, or biomaterial. A brief, focused overview of events leading to the foreign body reaction is presented. The major focus of this review is on factors that modulate the interaction of

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

2008-01-01

352

Dynamics in Tangible Chemical Reactions  

Microsoft Academic Search

Spatial understanding and the understanding of dynamic change in the spatial structure of molecules during a reaction is essen- tial for designing new molecules. Knowing the physical processes in the reactions helps to speed up the designing process. To support the designer with the correct representation of the designed molecule as well as showing the dynamic behavior of the whole

Patrick Maier; Marcus T; Gudrun Klinker

353

Trends in catalytic reaction engineering  

Microsoft Academic Search

Catalytic reactions in multiphase systems are prevalent in production of fuels, bulk and specialty chemicals, pharmaceuticals, materials, food and feed, etc. Making useful products, at economical yields and selectivities, from the diverse chemistries in such a broad range of applications requires the ability to quantify the interplay of transport phenomena and kinetics. This is the domain of catalytic reaction engineering.

M. P. Dudukovic

1999-01-01

354

Knowledge discovery in reaction databases  

Microsoft Academic Search

Chemistry has long presented an interesting problem domain in which basic AI research has been conducted. Work on knowledge-based systems in this domain began in the early 1970’s. Two particularly active areas in the early years were reaction prediction and synthesis design. Because there were no really large reaction databases at this time, the amount of knowledge required for high

J. Royce Rose; Herbert L. Gelernter

1993-01-01

355

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

356

Adverse drug reactions in horses  

Microsoft Academic Search

Adverse drug reactions (ADRs) in horses are rare but cause serious anxiety to patients, owners, and veterinarians when they occur and are frequently the reason for legal action against veterinarians. Although not every ADR can be prevented or predicted, equine practitioners should be aware of some of the most common or most serious reactions to frequently used drugs. The most

Patricia M. Dowling

2002-01-01

357

"Greening up" the Suzuki Reaction  

ERIC Educational Resources Information Center

|This article describes the rapid, green synthesis of a biaryl compound (4-phenylphenol) via a Pd(0)-catalyzed Suzuki cross-coupling reaction in water. Mild reaction conditions and operational simplicity makes this experiment especially amenable to both mid- and upper-level undergraduates. The methodology exposes students to purely aqueous…

Aktoudianakis, Evangelos; Chan, Elton; Edward, Amanda R.; Jarosz, Isabel; Lee, Vicki; Mui, Leo; Thatipamala, Sonya S.; Dicks, Andrew P.

2008-01-01

358

Chemistry of heavy ion reactions  

SciTech Connect

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

Hoffman, D.C.

1988-10-01

359

Nitration reaction modification of asphalt  

SciTech Connect

An experimental design was prepared to study the nitration reaction of asphalts at various concentrations by Fourier Transform Infrared Spectroscopy (FT-IR) and physical methods. After selection of a usable treatment level (1% by weight), the nitration reaction was performed on eight asphalts. These asphalts were evaluated by physical methods and for elastic recovery and by FT-IR.

Boucher, J.L.; Ihsiung Wang; Romine, R.A. (Southwestern Labs., Inc., Houston, TX (United States))

1990-07-01

360

Foreperiod and simple reaction time  

Microsoft Academic Search

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

Pekka Niemi; Risto Näätänen

1981-01-01

361

TALYS: Comprehensive Nuclear Reaction Modeling  

NASA Astrophysics Data System (ADS)

TALYS is a nuclear-reaction program which simulates nuclear reactions that involve neutrons, gamma-rays, protons, deuterons, tritons, helions, and alpha-particles, in the 1 keV - 200 MeV energy range. A suite of nuclear-reaction models has been implemented into a single code system, enabling us to evaluate basically all nuclear reactions beyond the resonance range. An overview is given of the main nuclear models used, such as newly developed optical models, various compound nucleus, fission, gamma-ray strength, level density, and pre-equilibrium models, all driven by a comprehensive database of nuclear-structure parameters. The predictive power of the code is demonstrated by comparing calculated results with a very diverse set of experimental observables. Our aim is to show that TALYS represents a robust computational approach that covers the whole path from fundamental nuclear-reaction models to the creation of complete data libraries for nuclear applications.

Koning, A. J.; Hilaire, S.; Duijvestijn, M. C.

2005-05-01

362

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

363

Sodium concrete reaction: structural considerations  

SciTech Connect

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

Freskakis, G.N.

1984-09-01

364

Fundamental reaction pathways during coprocessing  

SciTech Connect

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

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

1992-12-01

365

TALYS: Comprehensive Nuclear Reaction Modeling  

SciTech Connect

TALYS is a nuclear-reaction program which simulates nuclear reactions that involve neutrons, gamma-rays, protons, deuterons, tritons, helions, and alpha-particles, in the 1 keV - 200 MeV energy range. A suite of nuclear-reaction models has been implemented into a single code system, enabling us to evaluate basically all nuclear reactions beyond the resonance range. An overview is given of the main nuclear models used, such as newly developed optical models, various compound nucleus, fission, gamma-ray strength, level density, and pre-equilibrium models, all driven by a comprehensive database of nuclear-structure parameters. The predictive power of the code is demonstrated by comparing calculated results with a very diverse set of experimental observables. Our aim is to show that TALYS represents a robust computational approach that covers the whole path from fundamental nuclear-reaction models to the creation of complete data libraries for nuclear applications.

Koning, A.J.; Duijvestijn, M.C. [Nuclear Research and Consultancy Group NRG, P.O. Box 25, NL-1755 ZG Petten (Netherlands); Hilaire, S. [Commissariat a l'Energie Atomique, DAM/DIF/DPTA, Boite Postale 12, 91680 Bruyeres-le-Chatel (France)

2005-05-24

366

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

367

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

368

Gray Scott Reaction Diffusion Model  

NSDL National Science Digital Library

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

Christian, Wolfgang

2012-05-26

369

Bioluminescent Reaction by Immobilized Luciferase  

NASA Astrophysics Data System (ADS)

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

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

370

Kumada cross-coupling reaction  

Microsoft Academic Search

\\u000a The Kumada cross-coupling reaction (also occasionally known as the Kharasch cross-coupling reaction) was originally reported\\u000a as the nickel-catalyzed crosscoupling of Grignard reagents with aryl-or alkenyl halides. It has subsequently been developed\\u000a to encompass the coupling of organolithium or organomagnesium compounds with aryl-, alkenyl or alkyl halides, catalyzed by\\u000a nickel or palladium. The Kumada cross-coupling reaction, as well as the Negishi,

Jie Jack Li

371

[Arthropod bite reactions and pyodermias].  

PubMed

Tourists in the tropics often develop reactions to bites or stings of mosquitoes, fleas, mites, ants, bedbugs, beetles, larva, millipedes, spiders and scorpions. In addition, they may have fresh or salt water exposure to sponges, corals, jellyfish and sea urchins with resultant injury and inflammation. Bacterial skin infections (pyodermias) can follow bites or stings as well as mechanical trauma. The most common bacteria involved in skin infections are staphylococci and streptococci. For tourists, bacterial infections are often complicating a pruritic bite reaction and scratching. It is important to know the cause of the bite reaction and pyoderma in order to take appropriate therapeutic measures. PMID:18626616

Hengge, U R

2008-08-01

372

Dimethylzinc-initiated radical reactions.  

PubMed

Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions. This Account describes our investigations of radical reactions initiated by dimethylzinc. In 2001, we unexpectedly observed this reaction while investigating the amidophosphane-copper-catalyzed asymmetric addition of dimethylzinc to N-sulfonyl imines with tetrahydrofuran (THF) as reaction solvent. However, instead of adding the desired methyl group to the N-sulfonyl imine, we produced the THF adduct in excellent yield. This result laid the foundation for our discovery of novel modes of reactivity. Further investigations of the unexpected addition reaction revealed that a trace amount of air was needed for reaction progress, indicating that radical intermediates were involved. Indeed, controlled injection of air into the reaction flask by a syringe pump through a sodium hydroxide tube afforded the products in good to excellent yield. In addition, the reaction proved to be chemoselective for a C=N bond over a C=O bond, as well as for 1,4-addition over 1,2-addition. We developed asymmetric variants of the radical addition reaction of ethers to imines using chiral N-sulfinyl imines to produce the adducts in reasonably high stereoselectivity (up to 11:1). A 93:7 diastereomeric ratio of the adduct was obtained when bis(8-phenylmenthyl) benzylidenemalonate was used in the radical addition of ethers to C=C bonds. Interestingly, in the presence of dimethylzinc and air, arylamines, alkoxyamines, and dialkylhydrazines react with THF to give amino alcohols, oximes, and hydrazones, respectively, in moderate to high yields. We performed a tin-free intermolecular addition of functionalized primary alkyl groups, generated from their corresponding iodides, to N-sulfonyl imines using dimethylzinc, air, boron trifluoride diethyl etherate, and a catalytic amount of copper(II) triflate. Direct C-H bond cleavage from cycloalkanes was also feasible in the presence of dimethylzinc, air, and boron trifluoride diethyl etherate to give the corresponding cycloalkyl radicals, which were suitable nucleophiles for N-sulfonyl imines. In all of the above reactions, dimethylzinc was a superior radical initiator than other conventional initiators such as dibenzoyl peroxide, diethylzinc, and triethylborane. We hope the coming decades will witness the report of other novel radical initiators that would complement the reactivity modes of existing ones. PMID:19113862

Akindele, Tito; Yamada, Ken-ichi; Tomioka, Kiyoshi

2009-02-17

373

Reciprocity Theory of Homogeneous Reactions.  

National Technical Information Service (NTIS)

The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to variou...

A. A. Agbormbai

1990-01-01

374

Thermodynamic Constraints in Catalytic Reactions.  

National Technical Information Service (NTIS)

The paper investigates in detail the implications of thermodynamic constraints on chemical reactions. A rigorous methodology and framework for such an analysis is developed. It is shown that thermodynamic analysis can be very useful in providing a structu...

R. Shinnar C. A. Feng

1982-01-01

375

Giant resonances: reaction theory approach.  

National Technical Information Service (NTIS)

The study of giant resonances through the use of reaction theory approach is presented and discussed. Measurements of cross-sections to the many available decay channels following excitation of giant multipole resonances (GMR) led one to view these phenom...

A. F. R. Toledo Piza G. A. Foglia

1989-01-01

376

Study of Manganese Phosphating Reactions.  

National Technical Information Service (NTIS)

Work was conducted to determine the composition of and the reactions associated with the formation of manganese-phosphate coatings. An improved phosphate coating was studied as produced from a stock manganese phosphating bath to which an addition of manga...

J. Menke

1971-01-01

377

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

378

Reactions of Mustard on Concrete.  

National Technical Information Service (NTIS)

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

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

2004-01-01

379

Nuclear Excitations and Reaction Mechanisms.  

National Technical Information Service (NTIS)

This is an interim report describing completed, continuing and proposed research activities for the period 1 August 1983-31 January 1985. These activities include studies of few-body systems, nuclear reaction models, atomic and molecular structure, nuclea...

S. Fallieros F. S. Levin

1983-01-01

380

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

381

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.degree. to 300.degree. 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, Jr., Lawrence (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

1993-01-01

382

Conversion Reactions in Student Aviators.  

National Technical Information Service (NTIS)

A study was made of student naval aviators who developed conversion reactions during training. Clinical information and results obtained from a questionnaire, Minnesota Multiphasic Personality Inventory, and psychiatric interview are described. (Author)

T. F. Mucha R. F. Reinhardt

1970-01-01

383

Fragmentation Processes in Nuclear Reactions.  

National Technical Information Service (NTIS)

Projectile and nuclear fragmentation are defined and processes referred to are recalled. The two different aspects of fragmentation are considered but the emphasis is also put on heavy ion induced reactions. The preliminary results of an experiment perfor...

R. Legrain

1984-01-01

384

Nitrosation Reactions of Ethyl Centralite.  

National Technical Information Service (NTIS)

Preliminary experiments are described in which ethyl centralite, a stabilizer frequently used in double-base propellants, was reacted with nitrous acid in various concentrations. The chemical reactions taking place led to the formation of numerous derivat...

B. T. Newbold K. Taymaz R. MacDonald

1977-01-01

385

Reactions at supercritical conditions: Applications and fundamentals  

Microsoft Academic Search

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

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

1995-01-01

386

Nuclear reactions for astrophysics and other applications  

NASA Astrophysics Data System (ADS)

Cross sections for compound-nuclear reactions are required for many applications. The surrogate nuclear reactions method provides an indirect approach for determining cross sections for reactions on unstable isotopes, which are difficult or impossible to measure otherwise. Current implementations of the method provide useful cross sections for (n,f) reactions, but need to be improved upon for applications to capture reactions.

Escher, J. E.; Burke, J. T.; Dietrich, F. S.; Scielzo, N. D.; Ressler, J. J.

2011-10-01

387

Reciprocity theory of homogeneous reactions  

NASA Astrophysics Data System (ADS)

The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to various classes of dissociation, recombination, rearrangement, ionizing, and photochemical reactions. It is shown that for the principle of reciprocity to be satisfied it is necessary that all chemical reactions exist in complementary pairs which consist of the forward and backward reactions. The backward reaction may be described by either the reverse or inverse process. The forward and backward processes must satisfy the same reciprocity equation. Because the number of dynamical variables is usually unbalanced on both sides of a chemical equation, it is necessary that this balance be established by including as many of the dynamical variables as needed before the reciprocity equation can be formulated. Statistical transformation models of the reactions are formulated. The models are classified under the titles free exchange, restricted exchange and simplified restricted exchange. The special equations for the forward and backward processes are obtained. The models are consistent with the H theorem and Le Chatelier's principle. The models are also formulated in the context of the direct simulation Monte Carlo method.

Agbormbai, Adolf A.

1990-03-01

388

Substrate selective catalytic molecular hydrogels: the role of the hydrophobic effect.  

PubMed

A catalytic hydrogel is reported for the substrate selective direct aldol reaction of aliphatic ketones based on their hydrophobicity and on the emergence of catalytic activity only after self-assembly of the catalyst. PMID:24098889

Berdugo, Cristina; Miravet, Juan F; Escuder, Beatriu

2013-10-17

389

Organocatalytic Enantioselective Synthesis of ?-Hydroxy Phosphonates  

PubMed Central

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

Samanta, Sampak; Zhao, Cong-Gui

2008-01-01

390

Reactions to injected influenza vaccine.  

PubMed

Almost 6,000 healthy adults inoculated with influenza vaccine were asked to record daily for 5 days the presence or absence of defined local and general symptoms; 70 percent completed and returned the record. The overall incidence of subjective reactions derived in this way was high; approximately 50 percent complained of local pain and 40 percent of general symptoms. Only about one-third of vaccinees recorded no symptoms. The incidence of subjective local reactions was about 8 percent higher in women than men. Among 5,600 vaccinees a total of 63 days sickness absence was attributed to reaction in the week of immunization (1.1 days per 100 employees). Almost all the absences were of less than 3 days duration, unsupported by a doctor's certificate. In the week of vaccination sickness absence among vaccinees was not higher than that of non-vaccinees. Although the incidence of subjective reaction was found to be high and vaccination might itself cause some sickness absence, most of the reactions appear to be trivial. Among 700 employees who were interviewed 1 or 2 days after vaccination in 1973, the incidence of what was judged to be significant local pain and erythema was about 5 percent. Nevertheless,the reactions appear to have an important effect on acceptance of influenza vaccination. From the answers given to a questionnaire 30 percent of employees who refused vaccination did so either because they previously had symptoms after vaccination, or because others had told them of their occurrence. In approximately 16,500 injections, only 2 patients had an acute reaction resembling anaphylaxis. PMID:1126581

Smith, J W; Fletcher, W B; Wherry, P J

1975-01-01

391

Electrogenic reactions of cytochrome bd.  

PubMed

Cytochrome bd is one of the two terminal quinol oxidases in the respiratory chain of Escherichia coli. The enzyme catalyzes charge separation across the bacterial membrane during the oxidation of quinols by dioxygen but does not pump protons. In this work, the reaction of cytochrome bd with O(2) and related reactions has been studied by time-resolved spectrophotometric and electrometric methods. Oxidation of the fully reduced enzyme by oxygen is accompanied by rapid generation of membrane potential (delta psi, negative inside the vesicles) that can be described by a two-step sequence of (i) an initial oxygen concentration-dependent, electrically silent, process (lag phase) corresponding to the formation of a ferrous oxy compound of heme d and (ii) a subsequent monoexponential electrogenic phase with a time constant <60 mus that matches the formation of ferryl-oxo heme d, the product of the reaction of O(2) with the 3-electron reduced enzyme. No evidence for generation of an intermediate analogous to the "peroxy" species of heme-copper oxidases could be obtained in either electrometric or spectrophotometric measurements of cytochrome bd oxidation or in a spectrophotometric study of the reaction of H(2)O(2) with the oxidized enzyme. Backflow of electrons upon flash photolysis of the singly reduced CO complex of cytochrome bd leads to transient generation of a delta psi of the opposite polarity (positive inside the vesicles) concurrent with electron flow from heme d to heme b(558) and backward. The amplitude of the delta psi produced by the backflow process, when normalized to the reaction yield, is close to that observed in the direct reaction during the reaction of fully reduced cytochrome bd with O(2) and is apparently associated with full transmembrane translocation of approximately one charge. PMID:11076519

Jasaitis, A; Borisov, V B; Belevich, N P; Morgan, J E; Konstantinov, A A; Verkhovsky, M I

2000-11-14

392

Ozone Reactions in Aqueous Solutions: A Bibliography.  

National Technical Information Service (NTIS)

A reaction oriented list of references is provided for published papers and reports containing rate data or information on mechanism for reactions of ozone with various substrates in aqueous solutions. Catalyzed, as well as uncatalyzed, reactions are incl...

F. Westley

1983-01-01

393

Reaction rates and reaction sequences in the rp-process  

NASA Astrophysics Data System (ADS)

Hot hydrogen burning has been analyzed for temperatures and densities typical for explosive burning on compact objects and in supernovae. Reaction flow impedances due to cyclic reaction sequences, the role of waiting point nuclei, and the transition from the rp-process to the alpha p-process are discussed as a function of increasing temperature and nuclear properties. The analysis gives a clear indication of which nuclei play a crucial role in the burning process. It is here where experimental verifications of the presented reaction rate estimates are highly desirable. The same nuclei can also be utilized to devise minimum-size energy generation networks to be employed in hydrodynamic explosion calculations. Examples for specific conditions during supernova explosions, nova outbursts, or the evolution of Thorne-Zytkow objects are given, with typical abundance patterns expected in such events.

van Wormer, L.; Goerres, J.; Iliadis, C.; Wiescher, M.; Thielemann, F.-K.

1994-09-01

394

Enzymatic Reactions in Microfluidic Devices  

NASA Astrophysics Data System (ADS)

We establish simple scaling laws for enzymatic reactions in microfluidic devices, and we demonstrate that kinetic parameters obtained conventionally using multiple stop-flow experiments may instead be extracted from a single microfluidic experiment. Introduction of an enzyme and substrate species in different arms of a Y-shaped channel allows the two species to diffuse across the parallel streamlines and to begin reacting. Measurements of the product concentration versus distance down the channel provide information about the kinetics of the reaction. In the limit where the enzyme is much larger (and thus less diffusive) than the substrate, we show that near the entrance the total amount of product (P) formed varies as a power law in the distance x down the channel. For reactions that follow standard Michaelis-Menten kinetics, the power law takes the form P˜(Vmax/Km) x^5/2, where Vmax and Km are the maximum reaction rate and Michaelis constant respectively. If a large excess of substrate is used, then Km is identified by measuring Vmax far downstream where the different species are completely mixed by diffusion. Numerical simulations and experiments using the bioluminescent reaction between luciferase and ATP as a model system are both shown to accord with the model. We discuss the implications for significant savings in the amount of time and enzyme required for determination of kinetic parameters.

Ristenpart, W. D.; Wan, J.; Stone, H. A.

2008-11-01

395

Quantifying mixing using equilibrium reactions  

SciTech Connect

A method of quantifying equilibrium reactions in a microchannel using a fluorometric reaction of Fluo-4 and Ca{sup 2+} ions is presented. Under the proper conditions, equilibrium reactions can be used to quantify fluid mixing without the challenges associated with constituent mixing measures such as limited imaging spatial resolution and viewing angle coupled with three-dimensional structure. Quantitative measurements of CaCl and calcium-indicating fluorescent dye Fluo-4 mixing are measured in Y-shaped microchannels. Reactant and product concentration distributions are modeled using Green's function solutions and a numerical solution to the advection-diffusion equation. Equilibrium reactions provide for an unambiguous, quantitative measure of mixing when the reactant concentrations are greater than 100 times their dissociation constant and the diffusivities are equal. At lower concentrations and for dissimilar diffusivities, the area averaged fluorescence signal reaches a maximum before the species have interdiffused, suggesting that reactant concentrations and diffusivities must be carefully selected to provide unambiguous, quantitative mixing measures. Fluorometric equilibrium reactions work over a wide range of pH and background concentrations such that they can be used for a wide variety of fluid mixing measures including industrial or microscale flows.

Wheat, Philip M. [Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States); Posner, Jonathan D. [Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States); Department of Chemical Engineering, Arizona State University, Tempe, Arizona 85287-6106 (United States)

2009-03-15

396

Dynamical model of surrogate reactions  

SciTech Connect

A new dynamical model is developed to describe the whole process of surrogate reactions: Transfer of several nucleons at an initial stage, thermal equilibration of residues leading to washing out of shell effects, and decay of populated compound nuclei are treated in a unified framework. Multidimensional Langevin equations are employed to describe time evolution of collective coordinates with a time-dependent potential energy surface corresponding to different stages of surrogate reactions. The new model is capable of calculating spin distributions of the compound nuclei, one of the most important quantities in the surrogate technique. Furthermore, various observables of surrogate reactions can be calculated, for example, energy and angular distribution of ejectile and mass distributions of fission fragments. These features are important to assess validity of the proposed model itself, to understand mechanisms of the surrogate reactions, and to determine unknown parameters of the model. It is found that spin distributions of compound nuclei produced in {sup 18}O+{sup 238}U{yields}{sup 16}O+{sup 240}*U and {sup 18}O+{sup 236}U{yields}{sup 16}O+{sup 238}*U reactions are equivalent and much less than 10({h_bar}/2{pi}) and therefore satisfy conditions proposed by Chiba and Iwamoto [Phys. Rev. C 81, 044604 (2010)] if they are used as a pair in the surrogate ratio method.

Aritomo, Y.; Chiba, S.; Nishio, K. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)

2011-08-15

397

Potential reactions among indoor pollutants  

NASA Astrophysics Data System (ADS)

Reactions among indoor pollutants can produce products that, otherwise, might not be present in an indoor environment. To be relevant in an indoor setting, a chemical reaction must occur within a time interval shorter than or comparable to the residence time for a packet of indoor air. At typical air exchange rates, the reactions that meet this criterion include those of ozone with nitric oxide, nitrogen dioxide, and selected unsaturated hydrocarbons; thermal decomposition of peroxyacyl nitrates; numerous free radical reactions; and selected heterogeneous processes. Stable products include aldehydes, ketones, carboxylic acids and various organic nitrates. These reactions also generate free radicals, starting with the nitrate radical, Criegree biradicals, and peroxyacyl radicals, and leading to the hydroxyl, alkyl, alkylperoxy, hydroperoxy, and alkoxy radicals. Such radicals can react with other indoor species yielding additional aldehydes, ketones, carboxylic acids, dinitrates and peroxyacyl nitrates. Some of the potential products are known or suspected to be irritating (e.g. methacrolein, nonanoic acid, 1,2-propanediol dinitrate, peroxybenzoyl nitrate, and radical anions of the type [Cl… NO 2] -) However, some of these same products are difficult to detect using the sampling and analysis techniques currently applied to indoor air.

Weschler, Charles J.; Shields, Helen C.

398

Inorganic Reaction Mechanisms Part II: Homogeneous Catalysis  

ERIC Educational Resources Information Center

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

Cooke, D. O.

1976-01-01

399

Enzyme catalysts in organic synthesis Cloning, expression, and characterisation of 2Deoxyribose5- phosphate Aldolase  

Microsoft Academic Search

The use of enzymes in organic synthesis is widely exploited due to their high regio-, chemo- and stereo-specificity. The aldol condensation is a classic carbon-carbon bond forming reaction in organic chemistry. Aldolases are enzymes that catalyze the aldol reaction and are of particular interest in carbohydrate chemistry, but have seen limited use as they show low activity towards non-natural substrates.

Mikael Gudmundsson

400

The Maillard reaction in foods.  

PubMed

The nonenzymatic browning (NEB) reaction in food systems has been studied extensively since its first discovery in 1912. The reaction contributes both to positive and negative effects on food quality and safety. Of interest to the food industry is the control of the browning reaction. Classic control methods include elimination of reactable substrate, lowering of pH, chelation of trace minerals, limiting the water content, maintaining low temperatures and the use of inhibitors like sulfite. Since 1986, when the FDA banned the use of sulfite in certain instances, there has been renewed interest in browning inhibition studies. This paper will review the classical methods used to inhibit browning and then focus on the recent work on acyclic formation rate of sugars and cysteine inhibition. PMID:2675033

Kaanane, A; Labuza, T P

1989-01-01

401

Spatial model of autocatalytic reactions  

NASA Astrophysics Data System (ADS)

Biological cells with all of their surface structure and complex interior stripped away are essentially vesicles—membranes composed of lipid bilayers which form closed sacs. Vesicles are thought to be relevant as models of primitive protocells, and they could have provided the ideal environment for prebiotic reactions to occur. In this paper, we investigate the stochastic dynamics of a set of autocatalytic reactions, within a spatially bounded domain, so as to mimic a primordial cell. The discreteness of the constituents of the autocatalytic reactions gives rise to large sustained oscillations even when the number of constituents is quite large. These oscillations are spatiotemporal in nature, unlike those found in previous studies, which consisted only of temporal oscillations. We speculate that these oscillations may have a role in seeding membrane instabilities which lead to vesicle division. In this way synchronization could be achieved between protocell growth and the reproduction rate of the constituents (the protogenetic material) in simple protocells.

de Anna, Pietro; di Patti, Francesca; Fanelli, Duccio; McKane, Alan J.; Dauxois, Thierry

2010-05-01

402

Polymerase Chain Reaction and Reverse Transcription-Polymerase Chain Reaction  

Microsoft Academic Search

\\u000a Polymerase chain reaction (PCR) enables one to determine if a specific needle is present in a haystack, and it can be used\\u000a as a step toward the characterization of the needle. It is a quick, powerful, inexpensive DNA amplification technique that\\u000a has become a fundamental tool in molecular pathology.

Dwight Oliver

403

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

404

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

405

Reaction of organylthiochloroacetylenes with organylselenols  

Microsoft Academic Search

The reaction of organylthiochloroacetylenes RSCa=CßCl with selenols in a DMSO solution containing KOH leads to organylthio(organylseleno)acetylenes RSC=CSeR'. When the reaction of organylthiochloroacetylenes with selenols was carried out in diethyl ether, the previously unknown 1-organylthio-2-organylseleno-2-chloroethenes RSCH=CClSeR' were obtained in the form of Z- and E-isomers. The hydrochlorination of organylthio(organylseleno)acetylenes results in Z- and E-1-organylthio-2-organylseleno-1-chloroethenes RSCCl=CHSeR'.

A. V. Martynov; S. G. Seredkina; A. N. Mirskova

1990-01-01

406

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

407

Nuclear excitations and reaction mechanisms  

NASA Astrophysics Data System (ADS)

Research concerning nuclear excitations and reaction mechanisms is described. Among the various subjects discussed are: photon scattering, consistency condition between seagull quadrapole terms and the absorption sum rule, Raman scattering to negative-parity states, non-local terms due to exchange and retardation effects in charge-transfer equations, consistency and meaning of various approximate channel coupling array equations, derivation of equations used in empirical nuclear reaction analyses, multi-cluster n-particle scattering theory, converged molecular bound state calculations, and WKB-type approximation in angular momenta for central potentials.

Fallieros, S.; Levin, S. F.; Li, C. T.

1980-10-01

408

Direct Reactions of Borromean Nuclei  

SciTech Connect

There are so-called Borromean nuclei on the drip-line in the nuclear chart, where any two-body subsystem has no bound state. The exotic structure and responses of Borromean nuclei have been studied by measurements of three-body (final-state) channels produced via direct reactions. Measurement of the three-body decay of the isospin partner of light drip-line nuclei populated by the charge exchange reaction is discussed as a means for studying the neutron halo structure. Experimental efforts to study nuclei beyond the drip-line, where many-body resonances may appear, are also presented.

Shimoura, S. [Center for Nuclear Study (CNS), University of Tokyo, Wako branch at RIKEN, Wako, Saitama 351-0198 (Japan)

2008-04-29

409

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

2011-09-02

410

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

411

Quantum tunneling and back reaction  

Microsoft Academic Search

We give a correction to the tunneling probability by taking into account the back reaction effect to the metric of the black hole spacetime. We then show how this gives rise to the modifications in the semiclassical black hole entropy and Hawking temperature. Finally, we reproduce the familiar logarithmic correction to the Bekenstein–Hawking area law.

Rabin Banerjee; Bibhas Ranjan Majhi

2008-01-01

412

Photosynthesis-The Light Reactions  

Microsoft Academic Search

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

K. Sauer

1979-01-01

413

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

414

Perceptual Anticipation and Reaction Time  

Microsoft Academic Search

To determine the effect of perceptual anticipation upon reaction time, two different types of experiment were carried out. In the first a skilled response had occasionally to be altered at a given point after a variable warning period. In the second the subject had to react to two auditory signals separated by a short time interval which was systematically varied,

E. C. Poulton

1950-01-01

415

Reaction: Student Press Law Center.  

ERIC Educational Resources Information Center

Provides a reaction from the Student Press Law Center to the Hazelwood School District versus Kuhlmeier decision. Urges student journalists and advisors to continue to do their best to produce quality, intelligent publications and to educate school administration and community about the importance of a free student press. (MG)

Goodman, Mark

1988-01-01

416

Infrared Laser Catalyzed Chemical Reactions  

Microsoft Academic Search

The development of the laser some twelve years ago has resulted in the creation and\\/or the resuscitation of a number of experimental disciplines involving measurements of energy transfer, chemical reaction rates, high resolution spectroscopy as well as nonlinear effects. In the last three years more and more work involving the use of lasers has been reported on in the literature

A. M. Ronn

1975-01-01

417

Transsilylation Reactions of Phosphazene Precursors,  

National Technical Information Service (NTIS)

Me3SiN-P(OCH2CF3)Me2 (1) are useful precursors to poly-(alkyl/arylphosphazenes) via a thermally induced condensation polymerization process. Aside from this important thermolysis reaction, however, the chemistry of these phosphazene precursors has not bee...

U. G. Wettermark R. H. Neilson

1987-01-01

418

Reactions to threatening health messages  

PubMed Central

Background Threatening health messages that focus on severity are popular, but frequently have no effect or even a counterproductive effect on behavior change. This paradox (i.e. wide application despite low effectiveness) may be partly explained by the intuitive appeal of threatening communication: it may be hard to predict the defensive reactions occurring in response to fear appeals. We examine this hypothesis by using two studies by Brown and colleagues, which provide evidence that threatening health messages in the form of distressing imagery in anti-smoking and anti-alcohol campaigns cause defensive reactions. Methods We simulated both Brown et al. experiments, asking participants to estimate the reactions of the original study subjects to the threatening health information (n = 93). Afterwards, we presented the actual original study outcomes. One week later, we assessed whether this knowledge of the actual study outcomes helped participants to more successfully estimate the effectiveness of the threatening health information (n = 72). Results Results showed that participants were initially convinced of the effectiveness of threatening health messages and were unable to anticipate the defensive reactions that in fact occurred. Furthermore, these estimates did not improve after participants had been explained the dynamics of threatening communication as well as what the effects of the threatening communication had been in reality. Conclusions These findings are consistent with the hypothesis that the effectiveness of threatening health messages is intuitively appealing. What is more, providing empirical evidence against the use of threatening health messages has very little effect on this intuitive appeal.

2012-01-01

419

Ocular reaction to timolol maleate.  

PubMed

A patient prescribed timolol maleate for the control of hypertension developed dryness of the eyes. The symptoms improved on withdrawal of the drug. Vigilance for such adverse reactions must be observed in the use of any beta-adrenoreceptor blocking agent. PMID:548951

Frais, M A; Bayley, T J

1979-12-01

420

Emergent computation by catalytic reactions  

Microsoft Academic Search

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

Wolfgang Banzhaf; Peter Dittrich

1996-01-01

421

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

422

Knoevenagel Reaction of Unprotected Sugars  

NASA Astrophysics Data System (ADS)

The Knoevenagel reaction of unprotected sugars was investigated in the 1950s using zinc chloride as promoter. The so-called Garcia Gonzalez reaction had been almost forgotten for 50 years, until the emergence of new water tolerant catalysts having Lewis acid behavior. The reaction was thus reinvestigated and optimal conditions have been found to prepare trihydroxylated furan derivatives from pentose or ?-tetrahydrofuranylfuran from hexoses with non-cyclic ?-keto ester or ?-diketones. Other valuable compounds such as ?-linked tetrahydrobenzofuranyl glycosides or hydroxyalkyl-3,3,6,6,-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione can be obtained using cyclic ?-dicarbonylic derivatives. Apart from one report in the 1950s, the Knoevenagel reaction of unprotected carbohydrate in basic condition has been studied only in the mid-1980s to prepare C-glycosyl barbiturates from barbituric acids and, later on, from non-cyclic ?-diketones, ?-C-glycosidic ketones. The efficient method exploited to prepare such compounds has found an industrial development in cosmetics.

Scherrmann, Marie-Christine

423

Wall Displays--Children's Reactions.  

ERIC Educational Resources Information Center

|A study reports that, while elementary students dislike bare classroom walls, they have little interest in other children's work, but like and remember having their own work displayed. Children do not absorb the content of wall displays, but they have strong emotional reactions to decorations. (Author/SJL)|

Collingford, Cedric

1978-01-01

424

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

425

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

426

Surface Science of Heterogeneous Reactions  

Microsoft Academic Search

Some of the present and future directions for surface science as a growing and naturally interdisciplinary subject are reviewed. Particular attention is given to surface reaction chemistry as it is related to heterogeneous catalysis, a subject area where there are abundant opportunities for detailed measurements of structure and dynamics at the molecular level.

John M. White

1982-01-01

427

Reaction synthesis of titanium aluminides  

Microsoft Academic Search

The formation of titanium aluminides from the elemental powders has been investigated. A traditional powder metallurgy route of compaction (by cold isostatic pressing, hot pressing or hot extrusion) followed by heat treatment was compared with the novel technique of hot extrusion reaction synthesis (HERS). The products from these different production methods were characterised by x-ray diffraction and microscopy (light and

E. K. Y. Fu; R. D. Rawlings; H. B. McShane

2001-01-01

428

Anaphylactic reactions to tolperisone (Mydocalm).  

PubMed

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

Ribi, Camillo; Vermeulen, Christophe; Hauser, Conrad

2003-06-28

429

Millisecond chemical reactions and reactors  

Microsoft Academic Search

Short contact time chemical reactors have many features which are very different from conventional packed bed reactors in that temperatures are determined by inlet parameters only, performance is nearly unchanged over wide variations in flow rate, and highly nonequilibrium products can be obtained at high conversions. Chemical reactions occur in regions of large gradients in composition and temperature, so the

Lanny D. Schmidt

2000-01-01

430

Matter and Energy in Reactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

1900-01-01

431

Ureteral reaction to suture material.  

PubMed

Dog ureters were anastomosed end to end using either chromic catgut, polyglycolic acid (PGA), polyglactin-910, or polypropylene sutures. Analysis of luminal diameters, fibrosis, scar vascularity, and inflammatory reaction four and seven months later indicated that in ureters of the uninfected dog the best results were obtained with polyglycolic acid. Ureters anastomosed with catgut gave results that were slightly less acceptable. PMID:6301130

Smith, M W; Bartone, F F; Tan, E C; Gardner, P J

1983-03-01

432

FOREIGN BODY REACTION TO BIOMATERIALS  

PubMed Central

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

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

2008-01-01

433

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

434

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

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

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

435

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

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

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

436

Novelty as a stimulus of special reactions  

Microsoft Academic Search

The stimulus which is of nutritional significance employed in the usual environment of feeding causes simultaneously a general reaction (orientation reflex) and the corresponding food reaction. A new stimulus, especially employed in unusual conditions, causes a general (orientation) reaction and the reflex of biological caution. Novelty, as a stimulus, causes special reactions reflecting congenital or acquired experience of the animals.

E. F. Polezhaev; V. V. Parin

1959-01-01

437

Reactions of arsine with hemoglobin  

SciTech Connect

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

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

1996-02-09

438

Ruthenium nanocatalysis on redox reactions.  

PubMed

Nanoparticles have generated intense interest over the past 20 years due to their high potential applications in different areas such as catalysis, sensors, nanoscale electronics, fuel and solar cells and optoelectronics. As the large fractions of metal atoms are exposed to the surface, the use of metal nanoparticles as nanocatalysts allows mild reaction conditions and high catalytic efficiency in a large number of chemical transformations. They have emerged as sustainable heterogeneous catalysts and catalyst supports alternative to conventional materials. This review focuses on the synthesis, characterization and catalytic role of ruthenium nanoparticles (RuNPs) on the redox reactions of heteroatom containing organic compounds with the green reagent H2O2, a field that has attracted immense interest among the chemical, materials and industrial communities. We intend to present a broad overview of Ru nanocatalysts for redox reactions with an emphasis on their performance, stability and reusability. The growth in the chemistry of organic sulfoxides and N-oxides during last decade was due to their importance as synthetic intermediates for the production of a wide range of chemically and biologically active molecules. Thus design of efficient methods for the synthesis of sulfoxides and N-oxides becomes important. This review concentrates on the catalysis of RuNPs on the H2O2 oxidation of organic sulfides to sulfoxides and amines to N-oxides. The deoxygenation reactions of sulfoxides to sulfides and reduction of nitro compounds to amines are fundamental reactions in both chemistry and biology. Here, we also highlight the catalysis of metal nanoparticles on the deoxygenation of sulfoxides and sulfones and reduction of nitro compounds with particular emphasis on the mechanistic aspects. PMID:23901501

Veerakumar, Pitchaimani; Ramdass, Arumugam; Rajagopal, Seenivasan

2013-07-01

439

Reactions of arsine with hemoglobin.  

PubMed

The mechanism of arsine (AsH3) induced hemolysis was studied in vitro using isolated red blood cells (RBCs) from the rat or dog. AsH3-induced hemolysis of dog red blood cells was completely blocked by carbon monoxide (CO) preincubation and was reduced by pure oxygen (O2) compared to incubations in air. Since CO and O2 bind to heme and also reduce hemolysis, these results suggested a reaction between AsH3 and hemoglobin in the heme-ligand binding pocket or with the heme iron. Further, sodium nitrite induction of methemoglobin (metHb) to 85% and 34% of total Hb in otherwise intact RBCs resulted in 56% and 16% decreases in hemolysis, respectively, after incubation for 4 h. This provided additional evidence for the involvement of hemoglobin in the AsH3-induced hemolysis mechanism. Reactions between AsH3 and hemoglobin were studied in solutions of purified dog hemoglobin. Spectrophotometric studies of the reaction of AsH3 with various purified hemoglobin species revealed that AsH3 reacted with HbO2 to produce metHb and, eventually, degraded Hb characterized by gross precipitation of the protein. AsH3 did not alter the spectrum of deoxyHb and did not cause degradation of metHb in oxygen, but bound to and reduced metHb in the absence of oxygen. These data indicate that a reaction of AsH3 with oxygenated hemoglobin HbO2, may lead to hemolysis, but there are reactions between AsH3 and metHb that may not be directly involved in the hemolytic process. PMID:8598571

Hatlelid, K M; Brailsford, C; Carter, D E

1996-02-01

440

Low temperature reaction path for coal liquefaction  

Microsoft Academic Search

Onset of a solvent-coal reaction occurs in the 200 to 300°C temperature range. The temperature and extent of this reaction are dependent on the coal and solvent. In this initial reaction, THF soluble products increase but solvent is lost indicating formation of a THF soluble, coal-solvent reaction product. This reaction product, defined in the preasphaltene or asphaltal compounds, results in

M. G. Thomas; R. K. Traeger

1979-01-01

441

Quantum reaction boundary to mediate reactions in laser fields  

NASA Astrophysics Data System (ADS)

Dynamics of passage over a saddle is investigated for a quantum system under the effect of time-dependent external field (laser pulse). We utilize the recently developed theories of nonlinear dynamics in the saddle region, and extend them to incorporate both time-dependence of the external field and quantum mechanical effects of the system. Anharmonic couplings and laser fields with any functional form of time dependence are explicitly taken into account. As the theory is based on the Weyl expression of quantum mechanics, interpretation is facilitated by the classical phase space picture, while no ``classical approximation'' is involved. We introduce a quantum reactivity operator to extract the reactive part of the system. In a model system with an optimally controlled laser field for the reaction, it is found that the boundary of the reaction in the phase space, extracted by the reactivity operator, is modulated with time by the effect of the laser field, to ``catch'' the system excited in the reactant region, and then to ``release'' it into the product region. This method provides new insights in understanding the origin of optimal control of chemical reactions by laser fields.

Kawai, Shinnosuke; Komatsuzaki, Tamiki

2011-01-01

442

MEANS FOR TERMINATING NUCLEAR REACTIONS  

DOEpatents

An apparatus is presented for use in a reactor of the heterogeneous, fluid cooled type for the purpose of quickly terminating the reaction, the coolant being circulated through coolant tubes extending through the reactor core. Several of the tubes in the critical region are connected through valves to a tank containing a poisoning fluid having a high neutron capture crosssection and to a reservoir. When it is desired to quickly terminate the reaction, the valves are operated to permit the flow of the poisoning fluid through these particular tubes and into the reservoir while normal coolant is being circulated through the remaining tubes. The apparatus is designed to prevent contamination of the primary coolant by the poisoning fluid.

Cooper, C.M.

1959-02-17

443

Hypersensitivity reactions to vaccine components.  

PubMed

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

Heidary, Noushin; Cohen, David E

2005-09-01

444

THE SPECIFICITY OF ALLERGIC REACTIONS  

PubMed Central

Intradermal injection of a simple hapten (e.g., 1-fluoro-2,4-dinitrobenzene) in water-in-oil emulsion results in contact hypersensitivity to surface application of the homologous hapten and, after appearance of circulating antibody, in Arthus type hypersensitivity to a conjugate of homologous hapten with guinea pig serum. Intradermal administration of this conjugate induces delayed and subsequently Arthus hypersensitivity to the conjugate, but no evidence of a contact reaction to the hapten alone. When a conjugate of hapten plus solubilized guinea pig skin is used as the sensitizing antigen, both contact hypersensitivity to the hapten and delayed and/or Arthus reactions to the conjugate develop. These observations are consistent with the hypothesis that the specificity of contact sensitivity is directed toward some particular protein of the skin which has been modified by combination with hapten.

Salvin, S. B.; Smith, R. F.

1961-01-01

445

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.

446

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

447

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

448

Low-Energy Nuclear Reactions  

Microsoft Academic Search

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

Norman D. Cook

449

Inclusive neutrino reactions in nuclei  

SciTech Connect

The charged current inclusive neutrino reaction cross section on a {sup 12}C target is obtained for electron neutrino energies from threshold to 100 MeV. An averaged cross section over the Michel spectrum is also obtained. The method here makes use of a tensor which describes the hadronic part of the interaction and which is obtained from total muon capture data and from electron scattering data in and around the giant dipole resonance. Applications to other nuclei are discussed.

Mintz, S.L.; Pourkaviani, M.

1993-04-01

450

Management of cutaneous drug reactions  

Microsoft Academic Search

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

K. S. Babu; Geeta Belgi

2002-01-01

451

Chemical Reactions Among Indoor Pollutants  

Microsoft Academic Search

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

Glenn Morrison

452

Redox Reactions in Polymeric Systems  

NASA Astrophysics Data System (ADS)

Reduction-Oxidization (redox) reactions performed in polymeric environments resulted in the reversible formation of stable silver nanoparticle and two reductive radicals. The reversible formation of stable silver nanoparticles in polyvinyl alcohol (PVA) and polyacrylic acid (PAA) crosslinked polymer films containing silver ions was achieved by electrochemical methods for potential applications in electrochromic devices. Cyclic voltammetry and galvanostatic methods were used to reversibly generate silver particles while the particle formation and decay optical absorption spectra were used to evaluate reversibility, relative particle size and minimum cycle speeds. Mechanisms for the formation and decay of particles are discussed with electron microscopy data determining actual size of generated silver particles. Light activated polymeric radicals produced from sulfonated polyether ether ketone (SPEEK) with PVA or SPEEK with sodium formate solutions were generated using 350 nm photons. The mechanism of radical generation is discussed for potential application for dehalogenating a well known environmental hazard carbon tetrachloride (CCl4). The reaction of the generated radicals with CCl4 was followed by ion selective electrode specific for chlorine allowing for the attainment of kinetic data and reaction mechanisms. The degradation of CCl4 was observed in both SPEEK/PVA and SPEEK/formate solutions but the kinetic data revealed SPEEK/formate to be more efficient. The success of SPEEK radicals in dechlorinating CCl4 lead to the investigation of polymeric blends, films and solution of SPEEK and polyamines for the generation of SPEEK radicals with a higher redox potential. SPEEK/polyamine radicals were generated by exposing polymer blends to 350 nm photons. Optical and electron spin resonance (ESR) spectra confirmed the generation of the anionic radical with a higher reducing potential. Kinetic data was obtained for selected system by following the formation and decay of the optical and ESR signatures. The reactions leading to the generation of highly reductive radicals is discussed.

Black, James R., II

453

Transport and Reactions of Pollutants  

Microsoft Academic Search

The aim of this chapter is to provide the food scientist and engineer with tools for understanding the principles of transport\\u000a and reaction of pollutants and their fate after being released or deposited into the environment. Furthermore, on the grounds\\u000a of this understanding of basic principles, the food scientist and engineer will possess the ability to model these processes.\\u000a Mathematical

Vassilis Gekas; Ioanna Paraskaki

2009-01-01

454

Milestoning without a Reaction Coordinate  

PubMed Central

Milestoning is a method for calculating kinetics and thermodynamics of long time processes typically not accessible for straightforward Molecular Dynamics (MD) simulation. In the Milestoning approach, the system of interest is partitioned into cells by dividing hypersurfaces (Milestones) and transitions are computed between nearby hypersurfaces. Kinetics and thermodynamics are derived from the statistics of these transitions. The original Milestoning work concentrated on systems in which a one-dimensional reaction coordinate or an order parameter could be identified. In many biomolecular processes the reaction proceeds via multiple channels or following more than a single order parameter. A description based on a one-dimensional reaction coordinate may be insufficient. In the present paper we introduce a variation that overcomes this limitation. Following the ideas of Vanden-Eijnden and Venturoli on Voronoi cells that avoid the use of an order parameter (J. Chem. Phys. 2009, 130, 194101), we describe another way to “Milestone” systems without a reaction coordinate. We examine the assumptions of the Milestoning calculations of mean first passage times (MFPT) and describe strategies to weaken these assumptions. The method described in this paper, Directional Milestoning, arranges hypersurfaces in higher dimensions that “tag” trajectories such that efficient calculations can be done and at the same time the assumptions required for exact calculations of MFPTs are satisfied approximately. In the original Milestoning papers trajectories are initiated from an equilibrium set of conformations. Here a more accurate distribution, that mimics the first hitting point distribution, is used. We demonstrate the usage of Directional Milestoning in conformational transitions of alanine dipeptide (in vacuum and in aqueous solution) and compare the correctness, efficiency, and statistical stability of the method with exact MD and with a related method.

Majek, Peter; Elber, Ron

2010-01-01

455

Milestoning without a Reaction Coordinate.  

PubMed

Milestoning is a method for calculating kinetics and thermodynamics of long time processes typically not accessible for straightforward Molecular Dynamics (MD) simulation. In the Milestoning approach, the system of interest is partitioned into cells by dividing hypersurfaces (Milestones) and transitions are computed between nearby hypersurfaces. Kinetics and thermodynamics are derived from the statistics of these transitions. The original Milestoning work concentrated on systems in which a one-dimensional reaction coordinate or an order parameter could be identified. In many biomolecular processes the reaction proceeds via multiple channels or following more than a single order parameter. A description based on a one-dimensional reaction coordinate may be insufficient. In the present paper we introduce a variation that overcomes this limitation.Following the ideas of Vanden-Eijnden and Venturoli on Voronoi cells that avoid the use of an order parameter (J. Chem. Phys. 2009, 130, 194101), we describe another way to "Milestone" systems without a reaction coordinate. We examine the assumptions of the Milestoning calculations of mean first passage times (MFPT) and describe strategies to weaken these assumptions. The method described in this paper, Directional Milestoning, arranges hypersurfaces in higher dimensions that "tag" trajectories such that efficient calculations can be done and at the same time the assumptions required for exact calculations of MFPTs are satisfied approximately.In the original Milestoning papers trajectories are initiated from an equilibrium set of conformations. Here a more accurate distribution, that mimics the first hitting point distribution, is used. We demonstrate the usage of Directional Milestoning in conformational transitions of alanine dipeptide (in vacuum and in aqueous solution) and compare the correctness, efficiency, and statistical stability of the method with exact MD and with a related method. PMID:20596240

Májek, Peter; Elber, Ron

2010-01-01

456

Chemical reaction and reactor engineering  

SciTech Connect

This book discusses research and design problems, simplifying reactor design considerations such as choice of reactor configuration, optimization, and scaleup, and modern surface analysis techniques for interpreting catalytic phenomena, and deciding on the most advantageous method for the selection, testing, development, and application of catalysts. It also covers how to develop models and formulate design strategies for gas-solid catalytic and noncatalytic reactions, overcoming such obstacles as complex hydrodynamics and inaccurate chemical kinetics in the modeling of fixed-bed catalytic processes.

Carberry, J.J.; Varma, A.

1987-01-01

457

Nuclear reaction studies: Progress report  

SciTech Connect

A principal focus of recent research has been the three-body problem. A great deal of effort has been devoted to the creation of a computer program to calculate physical observables in the three body problem below 1 GeV. Successful results have been obtained for the triton. Additional work concerns scattering of K/sup +/ mesons from nuclei, antinucleon physics, relativistic nuclear physics and inclusive reactions. (DWL)

Thaler, R.M.

1986-11-19

458

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

459

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

460

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

461

Transfer reactions with heavy elements  

SciTech Connect

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

Hoffman, D.C.

1986-04-01

462

Classical and Quantum Radiation Reaction  

NASA Astrophysics Data System (ADS)

This thesis reports on work undertaken in comparing the effects of the phenomenon of radiation reaction in classical and quantum theories of electrodynamics. Specifically, it is concerned with the prediction of the change in position of a particle due to the inclusion of the self-force in the theory. We calculate this position shift for the classical theory, treating radiation reaction as a perturbation in line with the reduction of order procedure. We calculate the contributions to the position shift in the hbar-> 0 limit of quantum field theory to order e(2) in the coupling, the order of the classical self-force. These calculations contain the emission and forward scattering one loop processes of quantum electrodynamics. The quantum calculations are completed for the case of a particle represented by a scalar field wave packet and then for a particle represented by the Dirac spinor field. We additionally give an alternative derivation of the scalar results using the interpretation of radiation reaction via a Green's function decomposition, in order to explain and contrast the results achieved.

Martin, Giles D. R.

2008-05-01

463

Substituted stilbenes and their reactions  

US Patent & Trademark Office Database

The present invention relates to stilbene and quinone compounds related to combretastatin A-4 and their use as anticancer compounds and prodrugs. The compounds include those with an alkyl group on the double bond of cis or trans-stilbenes, compounds with one or more (and preferably 2 or 3) alkyl group substituents on the stilbene A ring, compounds with an alkoxy group other than methoxy at position 3, 4, and/or 5 of the stilbene A ring, compounds (or prodrugs) in which BOC amino acid esters are formed with the phenolic hydroxyl at the 3-position of the B ring and compounds (or prodrugs) based on a benzoquinone B ring. The present invention further relates to the photochemical reactions of stilbene compounds, either the above compounds disclosed for the first time herein or compounds based on prior art stilbenes. These reactions include the photochemical release of an active form of the compound from a prodrug conjugate and the photochemical isomerisation of the compounds, especially from a trans to cis form of compounds. The reactions can be used alone or in combination to convert inactive or comparatively less active forms of the compounds to more active forms, thereby allowing the compounds to be selectively targeted, e.g. activating them at the site of a tumour.

2007-05-22

464

Hydrogen Tunneling in Enzyme Reactions  

NASA Astrophysics Data System (ADS)

Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that kH/kT = (kD/kT)3.26, where kH, kD, and kT are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.

Cha, Yuan; Murray, Christopher J.; Klinman, Judith P.

1989-03-01

465

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

466

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

467

Neutrino Reactions on the deuteron  

NASA Astrophysics Data System (ADS)

Recently the neutrino-deuterium (?-d) reactions have been studied extensively, which are strongly motivated by the experiment at the Sudbury Neutrino Observatory (SNO). The first exciting results of the SNO was announced recently. (Q. R. Ahmad et al.), nucl-ex/0106015 Here the uncertainty due to the theoretical ?-d cross section is comparable to the experimental errors. Further theoretical efforts to refine the cross section is definitely necessary. In this work we report our study of ?-d and bar?-d reactions with the use of the phenomenological Lagrangian approach(NSGK) (S. Nakamura et al.), Phys. Rev. C 63, 034617 (2001) and further development from our original NSGK work. As our further study, we have estimated the possible model dependences on (1) the exchange axial vector current and (2) nucleon-nucleon potential. The improvements are (1) the use of the updated value of axial vector coupling constant gA and (2) the inclusion of the radiative corrections. It was pointed out that the radiative corrections could be a few percent effects, which was the similar magnitude as our estimation of the theoretical errors. With these improvements, we discuss the updated values and the estimation on the theoretical errors of the important cross sections of the ?-d reactions.

Nakamura, S.; Sato, T.; Gudkov, V.; Kubodera, K.

2001-10-01

468

Molecular beam studies of reaction dynamics  

SciTech Connect

Thrust was to elucidate simple elementary reactions and to unravel mechanism of complex/photochemical reactions. Molecular beams are used to study reactions between molecules or to monitor photodissociation events in a collision-free environment. Recent activities centered on reactions involving oxygen atoms with unsaturated hydrocarbons, endothermic substitution reactions, dependence of reactivity of excited atoms on alignment of excited orbitals, photochemical reactions of polyatomic, energy transfer, free radicals in combustion processes, infrared absorption spectra of carbonium ions and hydrated hydronium ions, and bond-selective photodissociation.

Lee, Yuan T.

1993-03-01

469

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

470

Quantum Normal Form Approach to Reactive Scattering: The Cumulative Reaction Probability for Collinear Exchange Reactions.  

National Technical Information Service (NTIS)

The quantum normal form approach to quantum transition state theory is used to compute the cumulative reaction probability for collinear exchange reactions. It is shown that for heavy atom systems like the nitrogen exchange reaction the quantum normal for...

A. Goussev H. Waalkens R. Schubert S. Wiggins

2009-01-01

471

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

Microsoft Academic Search

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

James W. Duff; Donald G. Truhlar

1975-01-01

472

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

473

Suppression of reactions to certain cosmetics.  

PubMed

Reactions to hair dyes and bleaches may be "suppressed" with corticosteroids and antihistamines. Reactions to nail polish may be prevented by a "drying" or "polymerizing" technique. Sensitization to certain perfume ingredients may be inhibited by a "quenching" phenomenon. PMID:19206

Fisher, A A

1977-08-01

474

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

475

Theoretical Studies of Chemical Reactions: Dynamics.  

National Technical Information Service (NTIS)

Theoretical studies have been performed on the dynamics of interesting chemical reactions. The systems studied included the recombination reaction of methyl radicals to form ethylene, the addition of hydrogen atoms to carbon monoxide and the thermal disso...

A. F. Wagner M. J. Davis G. C. Schatz R. J. Duchovic R. Steckler

1988-01-01

476

Characterizing polymeric methylene diphenyl diisocyanate reactions ...  

Treesearch

Title: Characterizing polymeric methylene diphenyl diisocyanate reactions with wood. ... adhesion, plant cell walls, loblolly pine, chemical reactions, nanotechnology, ... This article was written and prepared by U.S. Government employees on ...

477

Effective radii of deuteron-induced reactions  

SciTech Connect

The continuum-discretized coupled-channels method (CDCC) for exclusive reactions and the eikonal reaction theory (ERT) as an extension of CDCC to inclusive reactions are applied to deuteron-induced reactions. The CDCC result reproduces experimental data on the reaction cross section for d+{sup 58}Ni scattering at 200 MeV/nucleon, and ERT provides data on the neutron-stripping cross section for inclusive {sup 7}Li(d,n) reaction at 40 MeV. For deuteron-induced reactions at 200 MeV/nucleon, target-dependence of the reaction, elastic-breakup, nucleon-stripping, nucleon-removal, and complete- and incomplete-fusion cross sections is clearly explained by simple formulas. Accuracy of the Glauber model is also investigated.

Hashimoto, Shintaro; Chiba, Satoshi [Advanced Science Research Center, Japan Atomic Energy Agency, Ibaraki 319-1195 (Japan); Yahiro, Masanobu; Ogata, Kazuyuki; Minomo, Kosho [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan)

2011-05-15

478

Kinetics of reactions occurring during polyurethane synthesis  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

479