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1

Reactions of astronauts under weightless conditions  

NASA Technical Reports Server (NTRS)

Experimental data show that weightlessness conditions lasting 5 days or more (18-25) do not produce significant disturbances in physical reactions of astronauts, with the exception of some singularities in functioning of the cardiovascular system: A reduction in heart rate and somewhat large fluctuations in the physiological indicators of cutaneogalvanic reactions.

Kasyan, I. I.; Kopanev, V. I.; Yazdovskiy, V. I.

1975-01-01

2

Aluminum/water reactions under extreme conditions  

NASA Astrophysics Data System (ADS)

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

Hooper, Joseph

2013-03-01

3

Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.  

PubMed

A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b. PMID:20023883

John, Alex; Shaikh, Mobin M; Ghosh, Prasenjit

2009-12-21

4

Transketolase reaction under credible prebiotic conditions.  

PubMed

A transketolase reaction was catalyzed by cyanide ion under prebiotic conditions instead of its modern catalyst, thiamine pyrophosphate (TPP). Cyanide ion converted fructose plus glyceraldehyde to erythrose plus xylulose, the same products as are formed in modern biochemistry (but without the phosphate groups on the sugars). Cyanide was actually a better catalyst than was TPP in simple solution, where there is a negligible concentration of the C-2 anion of TPP, but of course not with an enzyme in modern biology. The cyanide ion was probably not toxic on prebiotic earth, but only when the oxygen atmosphere developed and iron porphyrin species were needed, which cyanide poisons. Thus, catalyses by TPP that are so important in modern biochemistry in the Calvin cycle for photosynthesis and the gluconic acid pathway for glucose oxidation, among other processes, were probably initially performed instead by cyanide ion until its toxicity with metalloproteins became a problem and primitive enzymes were present to work with TPP, or most likely its primitive precursors. PMID:23440198

Breslow, Ronald; Appayee, Chandrakumar

2013-03-12

5

Action of bimetallic nanocatalysts under reaction conditions and during catalysis: evolution of chemistry from high vacuum conditions to reaction conditions.  

PubMed

Bimetallic catalysts are one of the main categories of metal catalysts due to the tunability of electronic and geometric structures through alloying a second metal. The integration of a second metal creates a vast number of possibilities for varying the surface structure and composition of metal catalysts toward designing new catalysts. It is well acknowledged that the surface composition, atomic arrangement, and electronic state of bimetallic catalysts could be different from those before a chemical reaction or catalysis based on ex situ studies. Thanks to advances in electron-based surface analytical techniques, the surface chemistry and structure of bimetallic nanoparticles can be characterized under reaction conditions and during catalysis using ambient pressure analytical techniques including ambient pressure XPS, ambient pressure STM, X-ray absorption spectroscopy and others. These ambient pressure studies revealed various restructurings in the composition and arrangement of atoms in the surface region of catalysts under reaction conditions or during catalysis compared to that before reaction. These restructurings are driven by thermodynamic and kinetic factors. The surface energy of the constituent metals and adsorption energy of reactant molecules or dissociated species on a metal component are two main factors from the point of view of thermodynamics. Correlations between the authentic surface structure and chemistry of catalysts during catalysis and simultaneous catalytic performance were built for understanding catalytic mechanisms of bimetallic catalysts toward designing new catalysts with high activity, selectivity, and durability. PMID:23023152

Tao, Franklin Feng; Zhang, Shiran; Nguyen, Luan; Zhang, Xueqiang

2012-12-21

6

The Eschenmoser coupling reaction under continuous-flow conditions  

PubMed Central

Summary The Eschenmoser coupling is a useful carbon–carbon bond forming reaction which has been used in various different synthesis strategies. The reaction proceeds smoothly if S-alkylated ternary thioamides or thiolactames are used. In the case of S-alkylated secondary thioamides or thiolactames, the Eschenmoser coupling needs prolonged reaction times and elevated temperatures to deliver valuable yields. We have used a flow chemistry system to promote the Eschenmoser coupling under enhanced reaction conditions in order to convert the demanding precursors such as S-alkylated secondary thioamides and thiolactames in an efficient way. Under pressurized reaction conditions at about 220 °C, the desired Eschenmoser coupling products were obtained within 70 s residence time. The reaction kinetics was investigated and 15 examples of different building block combinations are given.

Singh, Sukhdeep; Kohler, J Michael; Schober, Andreas

2011-01-01

7

Boundary conditions for surface reactions in lattice Boltzmann simulations  

NASA Astrophysics Data System (ADS)

A surface reaction boundary condition in multicomponent lattice Boltzmann simulations is developed. The method is applied to a test case with nonlinear reaction rates and nonlinear density profiles. The results are compared to the corresponding analytical solution, which shows that the error of the method scales with the square of the lattice spacing.

Gillissen, J. J. J.; Looije, N.

2014-06-01

8

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

9

A domino annulation reaction under Willgerodt-Kindler conditions.  

PubMed

Butanone side chains at arenes and hetarenes, efficiently introduced by a Heck-type reaction, are transformed to annulated thieno[3,2-b]thiophenes in a domino redox process under Willgerodt-Kindler conditions. A nucleophilic aromatic substitution with an intermediary thioenolate is a reasonable key step of this process. PMID:18505288

Kadzimirsz, Daniel; Kramer, Daniel; Sripanom, Lertnarong; Oppel, Iris M; Rodziewicz, Pawel; Doltsinis, Nikos L; Dyker, Gerald

2008-06-20

10

Chemical reactions in viscous liquids under space conditions  

NASA Astrophysics Data System (ADS)

A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment. But the space conditions are very specific for chemical reactions. A high vacuum, high energy particles, X-rays, UV- and VUV-irradiations, atomic oxygen, microgravity have a significant influence on chemical reactions. Polymerisation reactions in liquid active mixture were studied in simulated space environment. The epoxy resins based on Bisphenol A and amine curing agents were investigated under vacuum, microwave plasma discharge and ion beam. An acceleration of polymerisation reaction with free radicals formation was observed. The polymerisation reaction can be carried out under space environment. The study was supported by Alexander von Humboldt Foundation (A. Kondyurin) and European Space Agency, ESTEC (contract 17083/03/NL/Sfe "Space Environmental Effects on the Polymerisation of Composite Structures").

Kondyurin, A.; Lauke, B.; Richter, E.

11

Fulleranes by Direct Reaction with Hydrogen Gas at Elevated Conditions  

NASA Astrophysics Data System (ADS)

Reaction of solid fullerenes with hydrogen gas occurs with or without catalysts at elevated conditions. Composition of hydrofullerene mixture obtained in this reaction depends strongly on temperature (350-450°C), hydrogen pressure (typically 10-120 bar) and duration of treatment. Saturation of hydrogenation occurs after tens of hours, depending on temperature of reaction. In case of extra strong hydrogenation prolonged reaction leads to formation of fulleranes with composition C60Hx approaching number of hydrogen atoms X = 60. These fulleranes are highly unstable and decompose first with formation of fragmented hydrofullerenes with progressively smaller number of carbon atoms C59, C58, C57 etc., followed by collapse of cage structure. Since the collapse occurs at the conditions of high temperature and high hydrogen pressure, all breaking C-C bonds are saturated immediately with hydrogen and new C-H bonds are formed. Therefore, large fragments of fullerane molecules are able to survive and large polycyclic aromatic hydrocarbons (PAH's) formed as a result of cage structure collapse.

Talyzin, Alexandr V.

12

Reactions of animals and people under conditions of brief weightlessness  

NASA Technical Reports Server (NTRS)

It has been shown that under brief weightlessness sensory reactions arise in a number of people, mainly those under these conditions for the first time, in the form of spatial and visual illusions, motor excitation, in which tonic and motor components can be distinguished, and vestibular-vegetative disturbances (nausea, vomiting, etc.). In repeated flights with creation of weightlessness, a decrease in the extent of expression and, then, disappearance of these reactions occurred in a significant majority of those studied. Experiments in weightlessness with the vision cut off and with the absence of vestibular functions in the subjects confirm the hypothesis that spatial conceptions of people in weightlessness depend on predominance of gravireceptor or visual afferent signals under these conditions.

Kitayev-Smik, L. A.

1975-01-01

13

Effects of Meteorological Conditions on Reactions to Noise Exposure  

NASA Technical Reports Server (NTRS)

More than 80,000 residents' responses to transportation noise at different times of year provide the best, but imprecise, statistical estimates of the effects of season and meteorological conditions on community response to noise. Annoyance with noise is found to be slightly statistically significantly higher in the summer than in the winter in a seven-year study in the Netherlands. Analyses of 41 other surveys drawn from diverse countries, climates, and times of year find noise annoyance is increased by temperature, and may be increased by more sunshine, less precipitation, and reduced wind speeds. Meteorological conditions on the day of the interview or the immediately preceding days do not appear to have any more effect on reactions than do the conditions over the immediately preceding weeks or months.

Shepherd, Kevin P. (Technical Monitor); Fields, James M.

2004-01-01

14

Reactions of aminomalononitrile with electrophiles. [simulating prebiotic conditions  

NASA Technical Reports Server (NTRS)

Aminomalononitrile (HCN trimer) reacts with electrophiles such as aldehydes and acrylonitrile under very mild conditions of temperature and pH to produce intermediates which, after acid hydrolysis, yield amino acids. The following amino acids have been identified and quantitated: glycine, D,L-erythro- and D,L-threo-beta-hydroxyaspartic acids, D,L glutamic acid, and D,L-threonine and allo-threonine. The mechanism of their formation and the possible significance of these reactions in prebiotic syntheses are discussed.

Thanassi, J. W.

1975-01-01

15

Creatine kinase in serum: 1. Determination of optimum reaction conditions.  

PubMed

To establish optimum conditions for creatine kinase (EC 2.7.3.2) activity measurement with the creatine phosphate in equilibrium creatine reaction, we re-examined all kinetics factors relevant to an optimal and standardized enzyme assay at 30 and 25 degrees C. We determined the pH optimum in vaious buffers, considering the effect of the type and concentration of the buffer, as well as the influence of various buffer anions on the activity. The relation between activity and substrate concentration was shown and the apparent Michaelis constants of creatine kinase for creatine phosphate and ADP were evaluated. We tested the effect on creatine kinase measurement of the concentration of substrates (glucose and NADP+) in the auxillary and indicator reactions, especially the influence of the added auxiliary (hexokinase) and indicator (glucose-6-phosphate dehydrogenase) enzymes on the lag phase, at different temperatures. The NADP+ concentration proved to be the factor limiting the duration of constant reaction rate. We studied the inhibition of creatine kinase and adenylate kinase by AMP and established a convenient AMP concentration. For reactivation of creatine kinase, N-acetyl cysteine as sulfhydryl compound was introduced. Finally, we examined the relationship between activity and temperature. PMID:4240

Szasz, G; Gruber, W; Bernt, E

1976-05-01

16

Reaction pathways of glucose oxidation by ozone under acidic conditions.  

PubMed

The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The origin of small molecules such as tartaric, erythronic, and oxalic acids is clarified. Finally, new reaction pathways and tentative mechanisms consistent with the formation of ketoaldonic acids and smaller acids are proposed. PMID:19524217

Marcq, Olivier; Barbe, Jean-Michel; Trichet, Alain; Guilard, Roger

2009-07-27

17

Synthesis of potato starch sulfate and optimization of the reaction conditions  

Microsoft Academic Search

Potato starch sulfate was obtained by the reaction between potato starch and chlorosulfonic acid in pyridine. It was characterized by FT-IR and SEM. The reaction conditions were studied systematically, which included the volume ratio of pyridine to chlorosulfonic acid, reaction temperature and time in preparing sulfating agent process, and the ratio of starch mass to chlorosulfonic acid volume, reaction temperature

Dapeng Cui; Mingzhu Liu; Lan Wu; Yinghui Bi

2009-01-01

18

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

PubMed

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

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

2002-01-01

19

Kinetics of diamond-silicon reaction under high pressure-high temperature conditions  

Microsoft Academic Search

In this dissertation work, the kinetics of the reaction between diamond and silicon at high pressure-high temperature conditions was investigated. This study was motivated by the extremely limited amount of information related to the kinetics of the reaction in diamond-silicon carbide composites formation. It was found that the reaction between diamond and melted silicon and the subsequent silicon carbide formation

Cristian Pantea

2004-01-01

20

Physiological reactions of a passenger to transportation conditions  

NASA Technical Reports Server (NTRS)

The effect of transportation conditions on the performance capacity of a passenger were studied, in order to establish the time for his most rapid inclusion in production activity after the trip. It was concluded that the transportation conditions impair the functional condition of the passenger's organism. The restoration of the functional state to the initial level occurs mainly in the space of one day. It is shown that it is necessary to take into consideration the adaptation of the organism during transfer to another climate zone.

Lakshin, A. M.; Novoselov, V. P.

1980-01-01

21

Effect of environmental conditions on expansion in concrete due to alkali–silica reaction (ASR)  

Microsoft Academic Search

The environmental conditions to which a concrete element incorporating alkali–silica reactive aggregates is exposed play a major role in dictating the progression and manifestation of the reaction. This paper reports and analyses the results of research programs investigating the comparative evaluation of the effect of environmental conditions on the development of alkali–silica reaction (ASR) in concrete specimens stored in outdoor

Benoit Fournier; Jason H. Ideker; Kevin J. Folliard; Michael D. A. Thomas; Pierre-Claver Nkinamubanzi; Ray Chevrier

2009-01-01

22

Room-temperature Cannizzaro reaction under mild conditions facilitated by magnesium bromide ethyl etherate and triethylamine.  

PubMed

[reaction: see text] A room-temperature convenient Cannizzaro reaction prompted by magnesium bromide ethyl etherate and triethylamine is described for smooth conversion of aromatic aldehydes into their respective alcohols and carboxylic acids. The methodology is applicable to both inter- and intramolecular reactions and could be directed to obtain the carboxylic moiety in the form of an acid, an amide, or an ester compound depending on the selected reaction conditions or workup procedure. PMID:16354093

Abaee, M Saeed; Sharifi, Roholah; Mojtahedi, Mohammad M

2005-12-22

23

Reactions to Ostracism in Adolescents with Autism Spectrum Conditions  

ERIC Educational Resources Information Center

Little is known about how adolescents with autism spectrum conditions (ASC) experience the initial impact of ostracism. This study investigated whether a mild, short-term episode of experimentally induced ostracism (Cyberball) would affect self-reported anxiety, mood, and the extent to which four social needs (self-esteem, belonging, control and…

Sebastian, Catherine; Blakemore, Sarah-Jayne; Charman, Tony

2009-01-01

24

Uranium plasma emission at gas-core reaction conditions  

NASA Technical Reports Server (NTRS)

The results of uranium plasma emission produced by two methods are reported. For the first method a ruby laser was focused on the surface of a pure U-238 sample to create a plasma plume with a peak plasma density of about 10 to the 20th power/cu cm and a temperature of about 38,600 K. The absolute intensity of the emitted radiation, covering the range from 300 to 7000 A was measured. For the second method, the uranium plasma was produced in a 20 kilovolt, 25 kilojoule plasma-focus device. The 2.5 MeV neutrons from the D-D reaction in the plasma focus are moderated by polyethylene and induce fissions in the U-235. Spectra of both uranium plasmas were obtained over the range from 30 to 9000 A. Because of the low fission yield the energy input due to fissions is very small compared to the total energy in the plasma.

Williams, M. D.; Jalufka, N. W.; Hohl, F.; Lee, J. H.

1976-01-01

25

Kinetics of OH + CO reaction under atmospheric conditions  

NASA Technical Reports Server (NTRS)

A pulsed laser photolysis-pulsed laser-induced fluorescence technique is used to directly measure the temperature, pressure, and H2O concentration dependence on k1 in air. K1 is found to increase linearly with increasing pressure at pressures of not greater than 1 atm, and the pressure dependence of k1 at 299 K is the same in N2 buffer gas as in O2 buffer gas. The rate constant in the low-pressure limit and the slope of the k1 versus pressure dependence are shown to be the same at 262 K as at 299 K. The present results significantly reduce the current atmospheric model uncertainties in the temperature dependence under atmospheric conditions, in the third body efficiency of O2, and in the effect of water vapor on k1.

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

1986-01-01

26

Formation of ?-dicarbonyl fragments from mono- and disaccharides under caramelization and Maillard reaction conditions  

Microsoft Academic Search

Glyoxal, methylglyoxal and diacetyl were identified as reaction products from non-enzymatic browning of D-glucose (Glc),\\u000a D-fructose (Fru), maltose and maltulose. The ?-dicarbonyl compounds were quantified throughout the reaction. Monosaccharides\\u000a formed more dicarbonyl fragments than disaccharides and Glc formed more than Fru. It is suggested that Fru tends to yield\\u000a cyclic products rather than fragmentation products under the reaction conditions used.

A. Hollnagel; L. W. Kroh

1998-01-01

27

A Microkinetic Analysis of the Water–Gas Shift Reaction under Industrial Conditions  

Microsoft Academic Search

To form the basis for a microkinetic understanding of the low-temperature water–gas shift reaction over Cu-based catalysts as operated industrially, the kinetics have been measured under a wide range of reaction conditions. To elucidate possible support effects the reaction was studied over catalysts of Cu supported on Al2O3, SiO2, or mixed ZnO\\/Al2O3. The proposed microkinetic model is based on a

C. V. Ovesen; B. S. Clausen; B. S. Hammershøi; G. Steffensen; T. Askgaard; I. Chorkendorff; J. K. Nørskov; P. B. Rasmussen; P. Stoltze; P. Taylor

1996-01-01

28

Influence of operating conditions on the observed reaction rate in the single channel monolith reactor  

Microsoft Academic Search

The catalytic hydrogenation of nitrobenzoic acid (NBA) to the aminobenzoic acid was used as a model reaction for a quantitative study of influences of the operating conditions on the observed reaction rate in a single channel monolith reactor operated in Taylor flow regime. A simple mathematical model was derived and used for the analysis of hydrogenation experiments carried out in

Gorazd Ber?i?

2001-01-01

29

Formation of phenol under conditions of the reaction of oxidative carbonylation of benzene to benzoic acid  

SciTech Connect

This paper describes conditions for the oxidation of benzene to phenol. It is shown that a reaction mixture of water, carbon monoxide, and oxygen are essential to the oxidation. The oxidation is a side reaction found to occur during the oxidative carbonylation of benzene to benzoic acid in a medium of trifluoroacetic acid.

Kalinovsky, I.O.; Leshcheva, A.N.; Pogorelov, V.V.; Gelbshtein, A.I.

1993-12-31

30

Operation conditions affecting the performance of airlift reactors for immobilized enzyme reactions  

Microsoft Academic Search

The applicability of concentric airlift reactors for immobilized enzyme reaction has been studied. Because of simple mechanical structure, good mixing, relatively low shear stress, and lower power consumption, the airlift reactor is apealing for immobilized enzyme reaction. The operation conditions can be optimized by manipulating aeration rate, top clearance space, and solid content.

Chun-Min Chang; Wen Jang Lu; Ku Song Own; Shyh-Jye Hwang

1993-01-01

31

Influence of Processing Conditions on the Microstructure and Mechanical Properties of Reaction Sintered Silicon Nitride.  

National Technical Information Service (NTIS)

The microstructure of reaction bonded silicon nitride (RBSN) was changed in a wide range by varying green density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of individual microstruc...

J. Heinrich

1980-01-01

32

Three-phase slug flow in microchips can provide beneficial reaction conditions for enzyme liquid-liquid reactions.  

PubMed

Here, we introduce a solution to low stability of a two-phase slug flow with a chemical reaction occurring at the phase interface in a microfluidic reactor where substantial merging of individual reacting slugs results in the loss of uniformity of the flow. We create a three-phase slug flow by introducing a third fluid phase into the originally two-phase liquid-liquid slug flow, which generates small two-phase liquid slugs separated by gas phase. Introduction of the third phase into our system efficiently prevents merging of slugs and provides beneficial reaction conditions, such as uniform flow pattern along the whole reaction capillary, interfacial area with good reproducibility, and intensive water-oil interface renewal. We tested the three-phase flow on an enzyme hydrolysis of soybean oil and compared the reaction conversion with those from unstable two-phase slug flows. We experimentally confirmed that the three-phase slug flow arrangement provides conversions and pressure drops comparable or even better with two-phase liquid-liquid arrangements. PMID:24404066

Cech, Ji?í; P?ibyl, Michal; Snita, Dalimil

2013-01-01

33

Tribological reactions of perfluoroalkyl polyether oils with stainless steel under ultrahigh vacuum conditions at room temperature  

NASA Technical Reports Server (NTRS)

The reaction between three types of commercial perfluoroalkyl polyether (PFPE) oils and stainless steel 440C was investigated experimentally during sliding under ultrahigh vacuum conditions at room temperature. It is found that the tribological reaction of PFPE is mainly affected by the activity of the mechanically formed fresh surfaces of metals rather than the heat generated at the sliding contacts. The fluorides formed on the wear track act as a boundary layer, reducing the friction coefficient.

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

34

Esterification reaction using solid heterogeneous acid catalysts under solvent-less condition  

Microsoft Academic Search

The preparation of di-2-ethylhexylphthalate (DOP) via esterification reaction of phthalic anhydride by 2-ethylhexanol in the presence of solid acidic catalysts has been investigated. The used catalysts were natural zeolite, synthetic zeolites (ZEOKAR-2, ASHNCH-3), heteropolyacid H4Si(W3O10)4 and sulfated ZrO2. The reactions were carried out under solvent-less conditions. It was observed that sulfated ZrO2 has higher reactivity and efficiency among the investigated

Firdovsi Tataroglu Sejidov; Yagoub Mansoori; Nadereh Goodarzi

2005-01-01

35

Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides  

NASA Technical Reports Server (NTRS)

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

Collins, J.; Rosner, D. E.; Castillo, J.

1992-01-01

36

Experimental Studies of Hydrogenation and Other Reactions on Surfaces Under Astrophysically Relevant Conditions  

NASA Technical Reports Server (NTRS)

The goal of our project is to study hydrogen recombination reactions on solid surfaces under conditions that are relevant in astrophysics. Laboratory experiments were conducted using low-flux, cold atomic H and D beams impinging on a sample kept under ultra high vacuum conditions. Realistic analogues of interstellar dust grains were used. Our results show that current models for hydrogen recombination reactions have to be modified to take into account the role of activated diffusion of H on surfaces even at low temperature.

Vidali, Gianfranco

1998-01-01

37

Carboxymethylation of Cassava Starch in Different Solvents and Solvent-Water Mixtures: Optimization of Reaction Conditions  

NASA Astrophysics Data System (ADS)

The influence of reaction medium on carboxymethylation process was investigated by treating cassava starch with sodium monochloroacetate in different solvents and solvent-water mixtures under alkaline conditions. The amount of carboxyl groups introduced into the starch moiety was determined titrimetrically and used to calculate the Degree of Substitution (DS) and Reaction Efficiency (RE). The results showed that carboxymethylation is significantly affected by the nature of reaction medium at p<0.05. Carboxymethylation in different solvent-water mixtures showed that aqueous 80% n-propanol offered the best medium for carboxymethylation. Optimization of reaction conditions in aqueous 80% n-propanol showed that the best condition for carboxymethylation was at starch-liquor ratio of 1:3, NaOH/reagent molar ratio of 4.0 and reagent-starch molar ratio of 0.35. An increase in temperature was required to effect the reaction at shorter time. At 55°C the highest values of DS and RE achieved in 0.5 h would require three hours to achieve the same values of DS and RE at 45°C.

Nwokocha, Louis M.; Ogunmola, Gabiel B.

38

Reaction progress pathways for glass and spent fuel under unsaturated conditions  

SciTech Connect

The source term for the release of radionuclides from a nuclear waste repository is the waste form. In order to assess the performance of the repository and the engineered barrier system (EBS) compared to regulations established by the Nuclear Regulatory Commission and the Environmental Protection Agency it is necessary (1) to use available data to place bounding limits on release rates from the EBS, and (2) to develop a mechanistic predictive model of the radionuclide release and validate the model against tests done under a variety of different potential reaction conditions. The problem with (1) is that there is little experience to use when evaluating waste form reaction under unsaturated conditions such that errors in applying expert judgment to the problem may be significant. The second approach, to test and model the waste form reaction, is a more defensible means of providing input to the prediction of radionuclide release. In this approach, information related to the source term has a technical basis and provides a starting point to make reasonable assumptions for long-term behavior. Key aspects of this approach are an understanding of the reaction progress mechanism and the ability to model the tests using a geochemical code such as EQ3/6. Current knowledge of glass, UO{sub 2}, and spent fuel reactions under different conditions are described below.

Bates, J.; Finn, P.; Bourcier, W.; Stout, R.

1994-10-01

39

Using Group-Inquiry to Study Differing Reaction Conditions in the E2 Elimination of Cyclohexyl Halides  

ERIC Educational Resources Information Center

In this experiment, students individually conduct one of several variations of an E2 dehydrohalogenation reaction on a cyclohexyl halide substrate for 30 min, which is sufficient only for a partial reaction to occur. The variations examine reaction conditions including different leaving groups, decreased reaction temperature, or reduced base…

Long, Robert D.

2012-01-01

40

Facilitative and suppressive effects of punishment on the reaction time in humans under various conditions  

Microsoft Academic Search

The effects of brief shock as the punishing stimulus during a simple or choice reaction time task (SRT or CRT) and the change in skin resistance during a key-pressing response were investigated under various conditions. A slowing of the SRT and CRT occurred similarly during the shock phase under both the response-contingent and response-independent shock conditions. After the elimination of

Mitsuro Kida

1983-01-01

41

Solid phase synthesis of hydantoins by thermal cyclization and screening of reaction conditions using APOS 1200.  

PubMed

A novel strategy for solid-phase synthesis of hydantoins with high optical purity is described using a thermal pH-neutral cyclization and simultaneous release from resin. Hereby even hydantoins bearing a pH-sensitive side chain (protection) are available. The reaction conditions are well screened applying the parallel organic synthesizer APOS 1200. PMID:10729901

Karnbrock, W; Deeg, M; Gerhardt, J; Rapp, W

1998-01-01

42

Passerini three-component reaction of alcohols under catalytic aerobic oxidative conditions.  

PubMed

Alcohols instead of aldehydes were used in the Passerini three-component reaction under catalytic aerobic conditions. Mixing alcohols, isocyanides, and carboxylic acids in toluene in the presence of a catalytic amount of cupric chloride, NaNO(2), and TEMPO afforded, under an oxygen atmosphere, the P-3CR adducts in good yields. PMID:20218637

Brioche, Julien; Masson, Géraldine; Zhu, Jieping

2010-04-01

43

Effect of moisture conditions and transfers on alkali silica reaction damaged structures  

Microsoft Academic Search

The aim of this paper is to point out the water driving effect on the alkali silica reaction (ASR) expansion and particularly when modifications of moisture conditions occur. After being submitted to a unidirectional moisture gradient during 14months, the upper faces of ASR reactive beams were covered by water for 9months. This late water supply on the upper face rapidly

Stéphane Multon; François Toutlemonde

2010-01-01

44

A General Access to 2-Silylthiazolidines and Their Reactions Under Fluoride Ion Conditions  

Microsoft Academic Search

Trimethylsilylthiazolidines were readily obtained through reaction of aminoethanethiol with (bromomethoxymethyl)trimethylsilane and efficiently N-functionalized with a variety of protecting groups. Such N-protected thiazolidines can then be satisfactorily reacted with several organic electrophiles under fluoride ion conditions, with a clean transfer of the thiazolidine moiety, to afford good yields of 2- functionalized heterocycles.

Antonella Capperucci; Alessandro Degl' Innocenti; Tiziano Nocentini; Alessandro Mordini; Simona Biondi; Francesca Dini

2004-01-01

45

The effect of reaction conditions on the stability of Au\\/CeZrO 4 catalysts in the low-temperature water–gas shift reaction  

Microsoft Academic Search

Au\\/CeZrO4 catalysts are highly active for the water–gas shift reaction but tend to be unstable and deactivate with time on stream. In this study, in situ DRIFTS-GC was used to investigate the nature of the Au under a range of reaction conditions as the deactivation rate is observed to vary with feed conditions (water concentration, presence of CO2) and reaction

H. Daly; A. Goguet; C. Hardacre; F. C. Meunier; R. Pilasombat; D. Thompsett

2010-01-01

46

Runaway reactions, their courses and the methods to establish safe process conditions  

NASA Astrophysics Data System (ADS)

Much of the literature on runaway reactions deals with the consequences such as mechanical damage toxic and flammable release. The DIERS literature provides effective methods for vent sizing where experimental information is requested. Thermal stability measurements provide information on the onset temperature and kinetic data for chemical reactions. There is less information on the way the runaway reactions occur whereas the runaway reactions may have different causes. The purpose of this paper is to describe the various process deviations which can cause a runaway reaction to occur and to discuss the experimental information necessary for risk assessment, the choice of a safe process and the mitigation of the consequences of the runaway reaction. Each possible hazardous process deviation is illustrated by examples from the process industry and/or relevant experimental information obtained from laboratory experiments. The typical hazardous situations to be considered are the following: 1) The homogeneous thermal runaway due to too high a temperature. 2) The homogeneous runaway reaction by unintended introduction of additional reactants or catalyst. 3) The heterogeneous runaway reaction due to too high a local temperature. 4) The heterogeneous runaway reaction caused by slow heat conduction to the outside. 5) The runaway reaction caused by excess residence time at the process temperature (autocatalytic reactions). 6) The runaway reaction caused by reactant accumulation. The controling reactant feed rate is higher than the consumption rate perhaps because the temperature is too low, or the catalyst is absent. 7) The runaway reaction due to the pressurization of the enclosure by gaseous oxidizing intermediates (typical of nitric oxidations). 8) The runaway reaction due to phase separation of unstable species (liquids, solids) by loss of mixing or on cooling. 9) The runaway reaction on mixing of fast reacting chemicals in separate phases. 10)The runaway reaction due to fire or external heating. Considering the various runaway situations, the effectiveness of the following approaches is discussed: - Theoretical and experimental information required for hazard assessment. - Choice of adequate process conditions. - Choice of adequate methods for process control. - Experimental information required for vent sizing. La plus grande partie de la littérature sur les emballements thermiques traite des conséquences de l'accident telles que les effets mécaniques, les émissions toxiques et inflammables. Les travaux publiés par le DIERS fournissent des méthodes permettant le dimensionnement d'évents, nécessitant des déterminations expérimentales. Il y a moins d'information sur la manière dont les emballements thermiques peuvent survenir alors que ceux-ci peuvent avoir différentes causes. Le propos de cet article est de décrire les différentes dérives de procédé qui peuvent entraîner un emballement thermique et de déterminer l'information expérimentale nécessaire pour l'analyse des risques du procédé, le choix de conditions opératoires sûres et la réduction des conséquences de l'emballement thermique. Chaque dérive de procédé dangereuse, est illustrée par des exemples connus dans l'industrie chimique et par des données expérimentales obtenues dans des essais de laboratoire. Les conditions de procédé dangereuses prises en compte sont les suivantes: 1)L'emballement thermique homogène dû à une température excessive; 2) L'emballement thermique homogène par introduction d'un catalyseur ou d'un réactif contrôlant; 3) L'emballement thermique hétérogène dû à une température locale excessive; 4)L'emballement thermique hétérogène dû à une faible conduction thermique vers l'extérieur; 5) L'emballement thermique dû à un temps de séjour excessif à la température du procédé (Réactions autocatalytiques); 6) L'emballement thermique par accumulation de réactifs. La vitesse d'introduction d'un réactif contrôlant est supérieure à la vitesse de consommation de ce réactif, parce que la temp

Gustin, J. L.

1991-08-01

47

Optimization of reaction conditions for enzymatic synthesis of palm fatty hydrazides using response surface methodology.  

PubMed

Optimization of the enzymatic synthesis of palm fatty hydrazide by the response surface methodology (RSM) was conducted using the Design-Expert 6 software. The palm fatty hydrazide was synthesized from refined, bleached and deodorized palm olein (RBDPOo) and neutralized hydrazine monohydrate in the presence of Rhizomucor miehei lipase, Lipozyme RMIM, an immobilized lipase in n-hexane. The reaction conditions such as the percentage of enzyme, reaction temperature, stirring speed and reaction time were selected as independent variables or studied factors, while the amount of crude palm fatty hydrazide obtained was selected as a dependent variable or response. The study was conducted using a central composite design (CCD) at five coded levels and the experimental data were analyzed using a quadratic model. The analysis of variance (ANOVA) indicates that the model was significant at 95% confidence level with Prob>F of 0.0033, where the regression coefficient value, R² was 0.8415 and lack-of-fit of 0.0984. A percentage of enzyme of 6%, a reaction temperature of 40°C, a stirring speed of 350 rpm and a reaction time of 18 h were found to be the optimum conditions for the conversion of RBDPOo into palm fatty hydrazide. PMID:22531058

Tuan Noor Maznee, T I; Hazimah, A H; Wan Zin, W Y

2012-01-01

48

Direct kinetic and mechanistic study of the OH/sup +/ dimethylsulfide reaction under atmospheric conditions  

SciTech Connect

The authors employed a pulsed laser photolysis - pulsed laser induced fluorescence technique to carry out direct, real time studies of OH reactions with DMS and DMS-d/sub 6/ in N/sub 2/, air and O/sub 2/ buffer gases. Both temperature and pressure dependencies have been investigated. They find that the observed rate constant (K/sub obs/ identical to d(OH)/(OH)(DMS)dt) depends on the O/sub 2/ concentration. The results are consistent with a mechanism which includes an abstraction route, a reversible addition route, and an adduct + O/sub 2/ reaction which competes with adduct decomposition under atmospheric conditions.

Hynes, A.J.; Wine, P.H.

1986-04-01

49

Method and apparatus for measuring coupled flow, transport, and reaction processes under liquid unsaturated flow conditions  

DOEpatents

The present invention is a method and apparatus for measuring coupled flow, transport and reaction processes under liquid unsaturated flow conditions. The method and apparatus of the present invention permit distinguishing individual precipitation events and their effect on dissolution behavior isolated to the specific event. The present invention is especially useful for dynamically measuring hydraulic parameters when a chemical reaction occurs between a particulate material and either liquid or gas (e.g. air) or both, causing precipitation that changes the pore structure of the test material.

McGrail, Bernard P. (Pasco, WA); Martin, Paul F. (Richland, WA); Lindenmeier, Clark W. (Richland, WA)

1999-01-01

50

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

PubMed

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

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

2014-06-01

51

A proposed abiotic reaction scheme for hydroxylamine and monochloramine under chloramination relevant drinking water conditions.  

PubMed

Drinking water monochloramine (NH2Cl) use may promote ammonia-oxidizing bacteria (AOB). AOB use (i) ammonia monooxygenase for biological ammonia (NH3) oxidation to hydroxylamine (NH2OH) and (ii) hydroxylamine oxidoreductase for NH2OH oxidation to nitrite. NH2Cl and NH2OH may react, providing AOB potential benefits and detriments. The NH2Cl/NH2OH reaction would benefit AOB by removing the disinfectant (NH2Cl) and releasing their growth substrate (NH3), but the NH2Cl/NH2OH reaction would also provide a possible additional inactivation mechanism besides direct NH2Cl reaction with cells. Because biological NH2OH oxidation supplies the electrons required for biological NH3 oxidation, the NH2Cl/NH2OH reaction provides a direct mechanism for NH2Cl to inhibit NH3 oxidation, starving the cell of reductant by preventing biological NH2OH oxidation. To investigate possible NH2Cl/NH2OH reaction implications on AOB, an understanding of the underlying abiotic reaction is first required. The present study conducted a detailed literature review and proposed an abiotic NH2Cl/NH2OH reaction scheme (RS) for chloramination relevant drinking water conditions (?M concentrations, air saturation, and pH 7-9). Next, RS literature based kinetics and end-products were evaluated experimentally between pHs 7.7 and 8.3, representing (i) the pH range for future experiments with AOB and (ii) mid-range pHs typically found in chloraminated drinking water. In addition, a (15)N stable isotope experiment was conducted to verify nitrous oxide and nitrogen gas production and their nitrogen source. Finally, the RS was slightly refined using the experimental data and an AQUASIM implemented kinetic model. A chloraminated drinking water relevant RS is proposed and provides the abiotic reaction foundation for future AOB biotic experiments. PMID:24862953

Wahman, David G; Speitel, Gerald E; Machavaram, Madhav V

2014-09-01

52

Methanol reactions on bimetallic Ru(0001)-based surfaces under UHV conditions.  

PubMed

This article focuses on thermally induced methanol reactions on bimetallic Ru(0001)-based catalyst surfaces performed under ultrahigh vacuum conditions. Specifically, reaction intermediates and pathways on various clean and oxygen covered surfaces (Ru(0001), Cu/Ru(0001), Pt/Ru(0001), and Pt(x)Ru(1-x)/Ru(0001) surface alloys) have been studied by means of Fourier transform infrared spectroscopy and temperature programmed desorption. On the basis of our results and results reported in the literature methanol reactions on metal surfaces can be subdivided into two major pathways: (i) total dehydrogenation of methanol leading to CO, and (ii) an oxidation pathway which produces gaseous CO(2). On the clean surfaces either the dehydrogenation pathway is observed or no reaction occurs at all. The CO(2) producing path opens up only upon adsorption of oxygen. In parallel, the CO formation diminishes. In this context, the influence of oxygen on the yields of possible reaction products is analyzed. Generally, it is found that methanol reactions are promoted by disordered and dilute oxygen layers; dense and ordered O-overlayers, on the other hand, passivate the surface effectively. Referring to the direct methanol fuel cell (DMFC), a significant drawback of adding oxygen is the reaction of the oxygen atoms with hydrogen from methanol dehydrogenation to gaseous water. As hydrogen is the energy provider in a DMFC the desorbing water represents an unwanted drain of H atoms. Interestingly, the surfaces which produce the highest amount of CO(2) are also most efficient with respect to water formation. As the drain of H atoms on oxygen covered Pt(x)Ru(1-x)/Ru(0001) surface alloys is limited and they nonetheless exhibit CO(2) as a final product they represent a compromise regarding the ideal catalyst material for a DMFC. In particular, alloys with a Pt content of 50-80% are found to display superior performance. PMID:23247830

Gazdzicki, Pawel; Jakob, Peter

2013-02-01

53

The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions  

NASA Astrophysics Data System (ADS)

During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, ?, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (? 2 -5 ?m grain size) form next to calcite and elongated palisade-shaped grains (1-6 ?m diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 ?m thick granular dolomite layer and a 7 ?m thick palisade-shaped layer evolve. At similar conditions and a differential stress of 30 MPa, the rim thickness remains similar; consequently the effect of non-isostatic stress on dolomite rim growth is negligible. Platinum markers show that the initial calcite-magnesite interface is located between granular and palisade-forming dolomite, indicating that rim growth occurs by counter diffusion of MgO and CaO. Diffusion of MgO across the dolomite reaction rim into calcite forms additionally magnesio-calcite grains with diameters of ? 13 - 46 ?m, depending on the experimental conditions and increasing with increasing distance to the dolomite boundary. At T = 750°C, t = 29 hours, the thickness of the magnesio-calcite layer is 32 ?m (isostatic) - 35 ?m (? = 30 MPa). The experiments indicate that solid-state reaction rim growth of dolomite between calcite and magnesite is primarily controlled by diffusion of MgO and CaO, forming layers with different microstructures during growth into the educt phases. The kinetics of the reaction in the carbonate system are not significantly changed by differential stresses up to 40 MPa. We suggest that volume diffusion is the dominant transport mechanism, which is presumably less affected by non-isostatic stresses than grain boundary diffusion.

Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

2013-12-01

54

Search for reaction conditions and catalyst for selective prebiotic formation of Aldopentoses from Glycolaldehyde and Formaldehyde  

NASA Astrophysics Data System (ADS)

Formation of organic compounds from simple precursors appears to have been one of the first steps from geochemistry towards modern biochemistry. The Earth lagoons, hydrothermal springs, cosmic dust, meteorites, protoplanetary disk, etc. has been considered as the possible ``reactors'' in which the prebiotic synthesis could have taken place. The finding of reactions and reaction conditions which allow to produce the high yields of the biologically relevant substances from simple compounds could help us to verify different hypothesis of plausible prebotic conditions. In this work we have studied the formation of vitally important sugars, namely aldopentoses (ribose, xylose, lyxose and arabinose), from glycolaldehyde and formaldehyde over catalysts. Aldopentoses nowadays play the important roles as the components of polysaccharides, glycosides, nucleic acids and ATP. Glycolaldehyde is the simplest monosaccharide, which was found in the interstellar space [1], where it could be generated as a result of several processes, for instance, condensation of formaldehyde under UV-radiation [2]. In this work the peculiarities of interaction between glycolaldehyde and formaldehyde in the presence of soluble (phosphate and borate buffers) and solid (minerals apatite and montmorillonites) catalysts were studied. The dependences of composition of the reaction products on the catalyst nature, molar ratio of substrates, pH value of reaction mixture were revealed. The yields of aldopentoses amount to ca. 60-65% in the presence of borate catalyst under optimized reaction conditions. Borate acts not only as a catalyst, but also as the stabilizer of active intermediates and aldopentoses from side reactions [3]. Borates are present in some mineral and clays (serpentine, montmorillonite etc.) and in water of Cityhot springs (Geyser valley, placeKamchatka) in rather high concentrations. Therefore catalysis by borates could be considered as plausible prebotic condition. Acknowledgements. We thank Dr. S. Yashnik for providing the montmorillonite clays. The financial support of Program RAS (program ``Origin of biosphere and evolution biogeology systems'') is gratefully acknowledged. Hollis, J., Jewell, P., Lovas, F., et al., The Astrophysical Journal. 613, L45--L48, 2004 Pestunova, O., Simonov, A., Snytnikov, V., et al., Adv. Space Res. 36/2, 214-219, 2005. Ricardo, A., Carrigan, M.A., Olcott, A.N., Benner, S.A. Science. 303, 5655, 196, 2004.

Delidovich, Irina; Taran, Oxana; Parmon, Valentin; Gromov, Nikolay

2012-07-01

55

Swellings due to alkali-silica reaction and delayed ettringite formation: Characterisation of expansion isotropy and effect of moisture conditions  

Microsoft Academic Search

This paper investigates the effect of different conditions on the development of concrete expansions due to alkali-silica reaction (ASR), delayed ettringite formation (DEF) and their combination. The presence of products of the two reactions has been observed during structure diagnosis. The aim of this research is to study the two reactions in concretes with close mix designs but with various

Hassina Bouzabata; Stéphane Multon; Alain Sellier; Hacène Houari

56

Influence of Catalyst Structure and Reaction Conditions on anti- versus syn-Aminopalladation Pathways in Pd-Catalyzed Alkene Carboamination Reactions of N-Allylsulfamides.  

PubMed

The Pd-catalyzed coupling of N-allylsulfamides with aryl and alkenyl triflates to afford cyclic sulfamide products is described. In contrast to other known Pd-catalyzed alkene carboamination reactions, these transformations may be selectively induced to occur by way of either anti- or syn-aminopalladation mechanistic pathways by modifying the catalyst structure and reaction conditions. PMID:24938206

Fornwald, Ryan M; Fritz, Jonathan A; Wolfe, John P

2014-07-01

57

Optimized extract preparation methods and reaction conditions for improved yeast cell-free protein synthesis.  

PubMed

Cell-free protein synthesis (CFPS) has emerged as a powerful platform technology to help satisfy the growing demand for simple, affordable, and efficient protein production. In this article, we describe a novel CFPS platform derived from the popular bio-manufacturing organism Saccharomyces cerevisiae. By developing a streamlined crude extract preparation protocol and optimizing the CFPS reaction conditions we were able to achieve active firefly luciferase synthesis yields of 7.7?±?0.5?µg?mL(-1) with batch reactions lasting up to 2?h. This duration of synthesis is the longest ever reported for a yeast CFPS batch reaction. Furthermore, by removing extraneous processing steps and eliminating expensive reagents from the cell-free reaction, we have increased relative product yield (µg protein synthesized per $ reagent cost) over an alternative commonly used method up to 2000-fold from ?2?×?10(-4) to ?4?×?10(-1) ?µg?$(-1) , which now puts the yeast CPFS platform on par with other eukaryotic CFPS platforms commercially available. Our results set the stage for developing a yeast CFPS platform that provides for high-yielding and cost-effective expression of a variety of protein therapeutics and protein libraries. PMID:23832321

Hodgman, C Eric; Jewett, Michael C

2013-10-01

58

Efficient and robust reforming catalyst in severe reaction conditions by nanoprecursor reduction in confined space.  

PubMed

The in situ autocombustion synthesis route is shown to be an easy and efficient way to produce nanoscaled nickel oxide containing lanthanum-doped mesoporous silica composite. Through this approach, ~3 nm NiO particles homogeneously dispersed in the pores of silica are obtained, while lanthanum is observed to cover the surface of the silica pore wall. Subsequent reduction of such composite precursors under hydrogen generates Ni(0) nanoparticles of a comparable size. Control over the size and size distribution of metallic nanoparticles clearly improved catalytic activity in the methane dry reforming reaction. In addition, these composite materials exhibit excellent stability under severe reaction conditions. This was achieved through the presence of LaOx species, which reduced active-site carbon poisoning, and the confinement effect of the mesoporous support, which reduced metallic particle sintering. PMID:24323543

Dacquin, Jean-Philippe; Sellam, Djamila; Batiot-Dupeyrat, Catherine; Tougerti, Asma; Duprez, Daniel; Royer, Sébastien

2014-02-01

59

Temperature-dependent reaction-rate expression for oxygen recombination at Shuttle entry conditions  

NASA Technical Reports Server (NTRS)

A temperature-dependent oxygen surface reaction-rate coefficient has been determined from experimental STS-2 heating and wall temperature data at altitudes of 77.91 km, 74.98 km, and 71.29 km. The coefficient is presented in an Arrhenius form and is shown to be less temperature dependent than previous results. Finite-rate viscous-shock-layer heating rates based on this present expression have been compared with predicted heating rates using the previous rate coefficients and with experimental heating data obtained over an extensive range of STS-2 and STS-3 entry conditions. A substantial improvement is obtained in comparison of experimental data and predicted heating rates using the present oxygen reaction-rate expression.

Zoby, E. V.; Simmonds, A. L.; Gupta, R. N.

1984-01-01

60

A Molecular Dynamics Study of Chemical Reactions of Solid Pentaerythritol Tetranitrate at Extreme Conditions  

SciTech Connect

We have carried out density functional based tight binding (DFTB) molecular dynamics (MD) simulation to study energetic reactions of solid Pentaerythritol Tetranitrate (PETN) at conditions approximating the Chapman-Jouguet (CJ) detonation state. We found that the initial decomposition of PETN molecular solid is characterized by uni-molecular dissociation of the NO{sub 2}groups. Interestingly, energy release from this powerful high explosive was found to proceed in several stages. The large portion of early stage energy release was found to be associated with the formation of H{sub 2}O molecules within a few picoseconds of reaction. It took nearly four times as long for majority of CO{sub 2} products to form, accompanied by a slow oscillatory conversion between CO and CO{sub 2}. The production of N{sub 2} starts after NO{sub 2} loses its oxygen atoms to hydrogen or carbon atoms to form H{sub 2}O or CO. We identified many intermediate species that emerge and contribute to reaction kinetics, and compared our simulation with a thermo-chemical equilibrium calculation. In addition, a detailed chemical kinetics of formation of H{sub 2}O, CO, and CO{sub 2} were developed. Rate constants of formations of H{sub 2}O, CO{sub 2} and N{sub 2} were reported.

Wu, C J; Manaa, M R; Fried, L E

2006-05-30

61

Electron transfer reaction dynamics of p-nitroaniline in water from liquid to supercritical conditions.  

PubMed

Photoexcitation dynamics of p-nitroaniline (pNA) have been investigated by femto-second transient absorption spectroscopy in water from liquid to supercritical conditions; along the isochoric line from the ambient condition to 664 K at 40.1 MPa and along the isothermal line from 40.1 to 36.1 MPa at 664 K. The rates of the back electron transfer reaction from the photoexcited charge transfer state to the electronic ground state was determined by the bleach recovery of the ground state absorption, and the successive vibrational relaxation in the electronic ground state was determined by the hot-band decay which was apparent at the red edge of the absorption. The variation of the back electron transfer rate was compared with the prediction based on the electron transfer theory including the Franck-Condon active vibrational modes. The results indicated that both the free energy change of the reaction and the change of the intramolecular vibrational reorganization energy cause the characteristic density (or temperature) dependence of the back electron transfer rate. The density dependence of the vibrational relaxation rate was compared with the collision frequency and the coordination number of the solvent molecule around the solute estimated by the molecular dynamics simulations. The density dependence of the coordination of a water oxygen atom to an amino hydrogen atom of pNA was found to be correlated with the density dependence of vibrational relaxation rate. PMID:22909090

Osawa, Koji; Terazima, Masahide; Kimura, Yoshifumi

2012-09-20

62

Reaction of perfluoroalkylpolyethers (PFPE) with 440C steel in vacuum under sliding conditions at room temperature  

NASA Technical Reports Server (NTRS)

Reactions of perfluoroalkylpolyethers (PFPE: Fomblin, Demnum and Krytox) were studied during the sliding contact of stainless steel specimens under ultrahigh vacuum conditions. All three fluids reacted with the steel specimens during sliding. Fomblin, which has acetal linkages, decomposed under the sliding conditions generating gaseous products, (COF2 and fluorinated carbons) which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the Demnum and Krytox fluids. The amount of gaseous products from Fomblin increased with increasing sliding speed. At the end of the sliding experiments, the wear scar and deposits on the specimens were examined by small spot size XPS. The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surface. The surface of the wear scar and deposits were covered with adsorbed PFPE. Based on these results, it was concluded that the decomposition reaction on Fomblin was initiated by contacting the fluid with a fresh metal surface which was formed during sliding.

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

63

Rapid and effective oxidative pretreatment of woody biomass at mild reaction conditions and low oxidant loadings  

PubMed Central

Background One route for producing cellulosic biofuels is by the fermentation of lignocellulose-derived sugars generated from a pretreatment that can be effectively coupled with an enzymatic hydrolysis of the plant cell wall. While woody biomass exhibits a number of positive agronomic and logistical attributes, these feedstocks are significantly more recalcitrant to chemical pretreatments than herbaceous feedstocks, requiring higher chemical and energy inputs to achieve high sugar yields from enzymatic hydrolysis. We previously discovered that alkaline hydrogen peroxide (AHP) pretreatment catalyzed by copper(II) 2,2?-bipyridine complexes significantly improves subsequent enzymatic glucose and xylose release from hybrid poplar heartwood and sapwood relative to uncatalyzed AHP pretreatment at modest reaction conditions (room temperature and atmospheric pressure). In the present work, the reaction conditions for this catalyzed AHP pretreatment were investigated in more detail with the aim of better characterizing the relationship between pretreatment conditions and subsequent enzymatic sugar release. Results We found that for a wide range of pretreatment conditions, the catalyzed pretreatment resulted in significantly higher glucose and xylose enzymatic hydrolysis yields (as high as 80% for both glucose and xylose) relative to uncatalyzed pretreatment (up to 40% for glucose and 50% for xylose). We identified that the extent of improvement in glucan and xylan yield using this catalyzed pretreatment approach was a function of pretreatment conditions that included H2O2 loading on biomass, catalyst concentration, solids concentration, and pretreatment duration. Based on these results, several important improvements in pretreatment and hydrolysis conditions were identified that may have a positive economic impact for a process employing a catalyzed oxidative pretreatment. These improvements include identifying that: (1) substantially lower H2O2 loadings can be used that may result in up to a 50-65% decrease in H2O2 application (from 100 mg H2O2/g biomass to 35–50 mg/g) with only minor losses in glucose and xylose yield, (2) a 60% decrease in the catalyst concentration from 5.0 mM to 2.0 mM (corresponding to a catalyst loading of 25 ?mol/g biomass to 10 ?mol/g biomass) can be achieved without a subsequent loss in glucose yield, (3) an order of magnitude improvement in the time required for pretreatment (minutes versus hours or days) can be realized using the catalyzed pretreatment approach, and (4) enzyme dosage can be reduced to less than 30 mg protein/g glucan and potentially further with only minor losses in glucose and xylose yields. In addition, we established that the reaction rate is improved in both catalyzed and uncatalyzed AHP pretreatment by increased solids concentrations. Conclusions This work explored the relationship between reaction conditions impacting a catalyzed oxidative pretreatment of woody biomass and identified that significant decreases in the H2O2, catalyst, and enzyme loading on the biomass as well as decreases in the pretreatment time could be realized with only minor losses in the subsequent sugar released enzymatically. Together these changes would have positive implications for the economics of a process based on this pretreatment approach.

2013-01-01

64

Measurements of enhanced electron screening in d+d reactions under UHV conditions  

NASA Astrophysics Data System (ADS)

Observation of the enhanced electron screening in metallic environments is of fundamental importance for the understanding of strongly coupled astrophysical plasmas. Experimental screening energies determined by different groups for many metals are much larger than the theoretical predictions. However, a comparison between experimental and theoretical data is rather ambiguous because of the contributions of systematic errors in the experiments. One of the most important problems is the uncertainty resulting from the oxidation of the target surface during the measurements. Here, we present results of the first ultra-high vacuum (UHV) experiments studying d+d nuclear reactions in a deuterized Zr target for which the experimental discrepancies are especially large. The total cross sections and angular distributions of the 2H(d,p)3H and 2H(d,n)3He reactions have been measured using a deuteron beam of energies between 8 and 30 keV provided by an electron cyclotron resonance ion source with excellent long-term stability. The cleanness of the target surface has been assured by combining Ar sputtering of the target and Auger spectroscopy. In an on-line analysis method, the homogeneity of the implanted deuteron densities could be monitored also. The resulting screening energy for Zr confirms the large value obtained in a previous experiment under poorer vacuum conditions.

Czerski, K.; Huke, A.; Martin, L.; Targosz, N.; Blauth, D.; Górska, A.; Heide, P.; Winter, H.

2008-01-01

65

Conditions of polymerase chain reaction amplification by magnetic enrichment and nanoscale detection sensitivity.  

PubMed

In this research, we reported a method of polymerase chain reaction (PCR) amplification by means of magnetic enrichment. First, after denaturation, the target sequence was combined with biotin-modified specific primer through hybridization and enriched at the surface of gamma-Fe2O3 by biotin-avidin special interaction. Then single target sequence was gained through denaturation, and general PCR amplification was performed. The experiment conditions such as the hybridization temperature between target sequence and biotin-modified specific primer, and the dosage of magnetic nanoparticles gamma-Fe2O3 were optimized. Finally, the sensitivity of the method was checked. The lowest concentration of target sequence was detected as low as 5 x 10(-7) ng/mL. This simple method could provide a quick and early diagnosis of malignant infectious diseases such as SARS, avian flu and swine flu etc., that occur occasionally nowadays. PMID:22852317

He, Nongyue; Mou, Xianbo; Deng, Yan; Liu, Hongna; Li, Song; Xu, Lijian; Li, Xiaolong

2012-05-01

66

[Effect of reaction conditions on the removal of pathogenic protozoan from secondary effluent in flocculation process].  

PubMed

Cryptosporidium and Giardia in reclaimed water are endangering the health of human beings by direct and indirect ways. Compared with traditional disinfection measures, flocculation, clarification and filtration can remove the pathogenic protozoan from wastewater more effectively. The factors affecting the removal of pathogenic protozoan from secondary effluent in flocculation process, including type and dosage of flocculant, pH, temperature and other reaction conditions were studied. The experimental results showed that the effectiveness of pathogenic protozoan removal appeared to be good at pH 6 - 8 and bad at low temperature. The effectiveness increased with the increase of ferric chloride dosage. Aluminium sulphate and poly aluminium chloride gave better performance in removal of pathogenic protozoan at the dosage of 70 mg/L and 20 mg/L respectively. PMID:17926405

Zhang, Tong; Hu, Hong-Ying; Wu, Qian-Yuan; Zong, Zu-Sheng

2007-08-01

67

Controlled release of volatiles under mild reaction conditions: from nature to everyday products.  

PubMed

Volatile organic compounds serve in nature as semiochemicals for communication between species, and are often used as flavors and fragrances in our everyday life. The quite limited longevity of olfactive perception has led to the development of pro-perfumes or pro-fragrances--ideally nonvolatile and odorless fragrance precursors which release the active volatiles by bond cleavage. Only a limited amount of reaction conditions, such as hydrolysis, temperature changes, as well as the action of light, oxygen, enzymes, or microorganisms, can be used to liberate the many different chemical functionalities. This Review describes the controlled chemical release of fragrances and discusses additional challenges such as precursor stability during product storage as well as some aspects concerning toxicity and biodegradability. As the same systems can be applied in different areas of research, the scope of this Review covers fragrance delivery as well as the controlled release of volatiles in general. PMID:17605134

Herrmann, Andreas

2007-01-01

68

REtools: A laboratory program for restriction enzyme work: enzyme selection and reaction condition assistance  

PubMed Central

Background Restriction enzymes are one of the everyday tools used in molecular biology. The continuously expanding panel of known restriction enzymes (several thousands) renders their optimal use virtually impossible without computerized assistance. Several manufacturers propose on-line sites that assist scientists in their restriction enzyme work, however, none of these sites meet all the actual needs of laboratory workers, and they do not take into account the enzymes actually present in one's own laboratory. Results Using FileMaker Pro, we developed a stand-alone application which can run on both PCs and Macintoshes. We called it REtools, for Restriction Enzyme tools. This program, which references all currently known enzymes (>3500), permits the creation and update of a personalized list of restriction enzymes actually available in one's own laboratory. Upon opening the program, scientists will be presented with a user friendly interface that will direct them to different menus, each one corresponding to different situations that restriction enzyme users commonly encounter. We particularly emphasized the ease of use to make REtools a solution that laboratory members would actually want to use. Conclusion REtools, a user friendly and easily customized program to organize any laboratory enzyme stock, brings a software solution that will make restriction enzyme use and reaction condition determination straightforward and efficient. The usually unexplored potential of isoschizomers also becomes accessible to all, since REtools proposes all possible enzymes similar to the one(s) chosen by the user. Finally, many of the commonly overlooked subtleties of restriction enzyme work, such as methylation requirement, unusual reaction conditions, or the number of flanking bases required for cleavage, are automatically provided by REtools.

Martin, Patrick; Boulukos, Kim E; Pognonec, Philippe

2006-01-01

69

Photoelectric currents across planar bilayer membranes containing bacterial reaction centers. Response under conditions of single electron turnover.  

PubMed Central

Light-induced electric current and potential responses have been measured across planar phospholipid membranes containing reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides. Under conditions in which the reaction centers are restricted to a single electron turnover, the responses can be correlated with the light-induced electron transfer reactions associated with the reaction center. The results indicate that electron transfer from the bacteriochlorophyll dimer to the primary ubiquinone molecule, and from ferrocytochrome c to the oxidized dimer occur in series across the planar membrane. Electron transfer from the primary to secondary ubiquinone molecule is not electrogenic.

Packham, N K; Dutton, P L; Mueller, P

1982-01-01

70

The influences of reaction conditions on magnetic porous pseudo-carbon paste electrode for schistosoma egg antigen detection.  

PubMed

A novel and sensitive electrochemical sensor based on magnetic porous pseudo-carbon paste electrode (MPPCPE) for schistosoma egg antigen (SEA) detection was described. The influences of immune reaction conditions such as time, pH and temperature on the detection current were investigated, and the influences of the blocking times of mercaptoethanol and ethanolamine on the background current were investigated. The experimental results shown that the high detection current and low background current could be obtained when the immune reaction temperature was 30 degrees C, the immune reaction time was 40 min, the immune reaction pH was 7.2, the blocking time of ethanolamine was 40 min, and the blocking time of mercaptoethanol was 60 min. At the optimum reaction conditions, a limit of detecting SEA as low as 0.01 microg/mL was obtained using MPPCPE. PMID:23755683

Xu, Lijian; Du, Jingjing; He, Nongyue

2013-03-01

71

A more robust model of the biodiesel reaction, allowing identification of process conditions for significantly enhanced rate and water tolerance.  

PubMed

A more robust kinetic model of base-catalysed transesterification than the conventional reaction scheme has been developed. All the relevant reactions in the base-catalysed transesterification of rapeseed oil (RSO) to fatty acid methyl ester (FAME) were investigated experimentally, and validated numerically in a model implemented using MATLAB. It was found that including the saponification of RSO and FAME side reactions and hydroxide-methoxide equilibrium data explained various effects that are not captured by simpler conventional models. Both the experiment and modelling showed that the "biodiesel reaction" can reach the desired level of conversion (>95%) in less than 2min. Given the right set of conditions, the transesterification can reach over 95% conversion, before the saponification losses become significant. This means that the reaction must be performed in a reactor exhibiting good mixing and good control of residence time, and the reaction mixture must be quenched rapidly as it leaves the reactor. PMID:24508659

Eze, Valentine C; Phan, Anh N; Harvey, Adam P

2014-03-01

72

Hyporheic transport and biogeochemical reactions in pool-riffle systems under varying ambient groundwater flow conditions  

NASA Astrophysics Data System (ADS)

the interface between stream water, groundwater, and the hyporheic zone (HZ), important biogeochemical processes that play a crucial role in fluvial ecology occur. Solutes that infiltrate into the HZ can react with each other and possibly also with upwelling solutes from the groundwater. In this study, we systematically evaluate how variations of gaining and losing conditions, stream discharge, and pool-riffle morphology affect aerobic respiration (AR) and denitrification (DN) in the HZ. For this purpose, a computational fluid dynamics model of stream water flow is coupled to a reactive transport model. Scenarios of variations of the solute concentration in the upwelling groundwater were conducted. Our results show that solute influx, residence time, and the size of reactive zones strongly depend on presence, magnitude, and direction of ambient groundwater flow. High magnitudes of ambient groundwater flow lower AR efficiency by up to 4 times and DN by up to 3 orders of magnitude, compared to neutral conditions. The influence of stream discharge and morphology on the efficiency of AR and DN are minor, in comparison to that of ambient groundwater flow. Different scenarios of O2 and NO3 concentrations in the upwelling groundwater reveal that DN efficiency of the HZ is highest under low upwelling magnitudes accompanied with low concentrations of O2 and NO3. Our results demonstrate how ambient groundwater flow influences solute transport, AR, and DN in the HZ. Neglecting groundwater flow in stream-groundwater interactions would lead to a significant overestimation of the efficiency of biogeochemical reactions in fluvial systems.

Trauth, Nico; Schmidt, Christian; Vieweg, Michael; Maier, Uli; Fleckenstein, Jan H.

2014-05-01

73

Reciprocal unconditional-conditional organization of the fundamental emotions and paraadaptive personality reactions.  

PubMed

Paraadaptive personality reactions (PPR) are modes of behavior and experience on the borderline of normal psychology and psychopathology. In them the thinking is overdetermined or obsessive. Overdetermined PPR are well illustrated in common proverbs. The people's wisdom has also knowledge of the obsessive (or "magic") paraadaptive rituals for prevention of possible misfortunes (such as touching wood, keeping away from a black cat, etc.). One part of the PPR is described in the psychoanalytical literature as defense mechanisms. The analysis of thought dissociation in schizophrenia shows that the reciprocal relations could be considered as a basic principle of functional organization on all levels of nervous and psychic activity. Proceeding from this assumption, the author proposes the conception of a reciprocal neuropsychological unconditional-conditional affect-behavioral system (ABS). It consists of ten subsystems corresponding to the basic emotions. Each subsystem stimulates the personality toward predetermined forms of thinking and behavior. In adequate conditions the reciprocal processes in the ABS are well counterweighted and integrated. In some persons and in situations of greater affective "loading" this reciprocal balance is disorganized, which leads to PPR. In this paper a neuropsychological analysis is made of the overdetermined PPR, reflected in such proverbs as "Not being able to beat the donkey, he beats the packsaddle" and "The thief cries catch the thief." PMID:2616226

Zaimov, K

1989-01-01

74

Establishment of broadly applicable reaction conditions for the palladium-catalyzed direct arylation of heteroatom-containing aromatic compounds.  

PubMed

Conditions for the palladium-catalyzed direct arylation of a wide range of heterocycles with aryl bromides are reported. Those conditions employ a stoichiometric ratio of both coupling partners, as well as a substoichiometric quantity of pivalic acid, which results in significantly faster reactions. An evaluation of the influence of the nature of the aryl halide has also been carried out. PMID:19206211

Liégault, Benoît; Lapointe, David; Caron, Laurence; Vlassova, Anna; Fagnou, Keith

2009-03-01

75

Study of photosensitization reaction progress in a 96 well plate with photosensitizer rich condition using Talaporfin sodium  

NASA Astrophysics Data System (ADS)

To quantitatively investigate photosensitization reaction in vitro against myocardial cells with photosensitizer rich condition in solution using Talaporfin sodium in the well of a 96 well plate, we studied photosensitization reaction progress in this well. We have proposed non-thermal conduction block of myocardium tissue using the photosensitization reaction with laser irradiation shortly after Talaporfin sodium injection. In above situation, the photosensitizer is located outside the myocardial cells in high concentration. To understand interaction of the photosensitization reaction in which the photosensitizer distributes outside cells, the photosensitization reaction progress in the well was studied. Talaporfin sodium (799.69 MW) solution and a 663 nm diode laser were used. The photosensitizer solution concentrations of 12.5-37.5 ?M were employed. The photosensitizer fluorescence with 0.29 W/cm2 in irradiance, which was optimized in previous cell death study, was measured during the laser irradiation until 40 J/cm2. The photosensitizer solution absorbance and dissolved oxygen pressure after the laser irradiation were also measured. We found that the photosensitization reaction progress had 2 distinctive phases of different reaction rate: rapid photosensitization reaction consuming dissolved oxygen and gentle photosensitization reaction with oxygen diffusion from the solution-air boundary. The dissolved oxygen pressure and photosensitizer solution absorbance were 30% and 80% of the initial values after the laser irradiation, respectively. Therefore, oxygen was rate-controlling factor of the photosensitization reaction in the well with the photosensitizer rich condition. In the oxygen diffusion phase, the oxygen pressure was maintained around 40 mmHg until the laser irradiation of 40 J/cm2 and it is similar to that of myocardium tissue in vivo. We think that our 96 well plate in vitro system may simulate PDT in myocardial tissue with photosensitization reaction parameters mentioned above.

Ogawa, Emiyu; Takahashi, Mei; Arai, Tsunenori

2013-02-01

76

A Knoevenagel Initiated Annulation Reaction Using Room Temperature or Microwave Conditions  

ERIC Educational Resources Information Center

An experiment is presented that has the student execute a Knoevenagel initiated annulation reaction. The reaction can be carried out either through use of a microwave reactor or by allowing the mixture to stand at room temperature for two days. The student is then challenged to identify the reaction product through a guided prelab exercise of the…

Cook, A. Gilbert

2007-01-01

77

Liquid metal reactions under postulated accident conditions for fission and fusion reactors  

SciTech Connect

Sodium and lithium reactions are considered in the context of a postulated breach of a coolant boundary. Specific topics addressed are coolant-atmosphere and coolant-material reactions which may contribute to the overall consequence of a postulated accident scenario, and coolant reaction extinguishment and effluent control which may be desirable for containment of the spilled coolant.

Muhlestein, L.D.

1980-04-01

78

1,4-Addition of TMSCCl3 to Nitroalkenes: Efficient Reaction Conditions and Mechanistic Understanding.  

PubMed

Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70?%) and excellent purity. Compounds of the type NBu4 X [X=Ph3 SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4-additions to a range of cyclic and acyclic nitroalkenes, in THF at 0-25?°C, typically in moderate to excellent yields (37-95?%). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies ((1) H, (19) F, (13) C and (29) Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13?M) at -20?°C, in the absence of nitroalkene, leads immediately to mixtures of Me3 SiF, Ph3 SiF and NBu4 CCl3 . The latter is stable to at least 0?°C and does not add nitroalkene from -20 to 0?°C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13?M at -20?°C), when treated with TBAT, leads to immediate formation of the 1,4-addition product, suggesting the reaction proceeds via a transient [Me3 Si(alkene)CCl3 ] species, in which (alkene) indicates an Si???O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3 (-) addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4 [CH2 ?NO2 ] is an efficient promoter. Use of H2 C?CH(CH2 )2 CH?CHNO2 in air affords radical-derived bicyclic products arising from aerobic oxidation. PMID:24849249

Wu, Na; Wahl, Benoit; Woodward, Simon; Lewis, William

2014-06-16

79

The reactions of nitroalkanes over Cu-MFI and Fe-MFI catalysts under hydrocarbon-selective catalytic reduction conditions  

Microsoft Academic Search

The reactions of 2-nitropropane (2NP) and 2-methyl-2-nitropropane (2M2NP), typical of secondary and tertiary nitroalkanes, respectively, have been investigated over Cu-MFI and Fe-MFI catalysts under conditions relevant to the selective catalytic reduction (SCR) of NO with the use of alkanes. With both catalysts the primary reaction is decomposition to form NO and the alkene, propene from 2NP, and isobutene from 2M2NP.

Irene O. Y. Liu; Noel W. Cant

2005-01-01

80

Subduction-related rodingites from East Othris, Greece: Mineral reactions and physicochemical conditions of formation  

NASA Astrophysics Data System (ADS)

The partly to pervasively metasomatized doleritic and gabbroic dykes or small to medium sized bodies found in East Othris, within Mid to Late Jurassic serpentinized peridotites of ophiolitic units and ophiolitic mélange formations are classified as rodingites and can be divided into two types. Type 1 rodingites are mainly characterized by the frequent occurrence of prehnite, while Type 2 rodingites include mostly garnets and vesuvianite. Isocon analysis showed that rodingitization essentially occurred with mass and volume preservation. Desilification, depletion of alkalies, as well as Ca enrichment was more intense for the Type 2 rodingites. Al, Fe and Mg remained rather immobile, while Ti, Y, Zr and REE were variably depleted. Rodingitization took place in an intraoceanic subduction system. It occurred in three successive stages during the exhumation of the mafic-ultramafic mantle wedge rocks in a fore-arc setting within a serpentinitic subduction channel, which developed close to the slab. The incorporation of the mafic rocks to the subduction channel probably resulted after entraining a directed mantle flow towards the slab. The first stage of rodingitization formed mainly grossular, hydrogrossular, Ti- and Cr-bearing hydrogarnets and calcite under relatively acidic and mildly oxidizing physicochemical conditions, with increased CO2/H2O ratio. During the second and more extensive rodingitization stage, alkaline and reducing conditions prevailed and CO2/H2O ratio was decreased. The modeling of the mineral reactions of this stage, using the software winTWQ v. 2.34 in the CFMASH system, reveals that in Type 1 rocks prehnite replaced most of the initial garnet, while Type 2 rocks continued to be rodingitized, mostly forming grossular and/or hydrogrossular and chlorite. Hydrogrossular, instead of grossular, was crystallized from hydrous fluids under high silica activity. Type 2 rodingites underwent further rodingitization during the third stage, due to infiltration of Ca-rich hydrothermal fluids of oceanic and/or subducted slab origin, at lower temperatures and depths. This stage is characterized by the appearance of hydroandradite and vesuvianite, under alkaline and oxidizing conditions, due to very low CO2/H2O ratio and relatively high fO2. All three rodingitization stages are estimated to have occurred under relatively moderate temperature and pressure (~ 300 to 400 °C; ~ 3-6 kbar respectively). Locally, Type 2 rodingites show derodingitization of variable extent, forming high-variance assemblages mostly consisting of chlorite ± pumpellyite. Some chlorite marginal zones in rodingite dykes may also have been developed by Mg-rich diffusional fluid flow, during this derodingitization process.

Koutsovitis, Petros; Magganas, Andreas; Pomonis, Panagiotis; Ntaflos, Theodoros

2013-07-01

81

Reaction of carboxylic acids with vinyl ethers under solvent-free conditions using molecular iodine as a catalyst.  

PubMed

The reaction of vinyl ethers with carboxylic acids using iodine as a catalyst under solvent-free conditions was investigated. The reaction of saturated carboxylic acids with vinyl ethers gave the corresponding esters. Mechanistic studies revealed the production of the adduct of the vinyl ether with the carboxylic acid, which then rearranged to form the ester. At low temperatures, the reaction of 2-(1-hydroxycyclohexyl)acetic acid (1) and butyl vinyl ether yielded a butyl ester. However, at a reaction temperature of 80°C, both the esterification and the elimination of a water molecule occurred, yielding the unsaturated butyl ester butyl 2-cyclohexenylacetate. The reaction of 2-((1S,2S,4R)-2-hydroxy-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl)acetic acid (12) with butyl vinyl ether at low temperatures resulted in a mixture of four compounds. However, similar to the high-temperature (>60°C) reaction of 1, the esterification was accompanied by the elimination of a water molecule to give the unsaturated butyl ester (E)-butyl 2-((1S,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)acetate. While a ?-hydrogen was abstracted to form the endo-type double bond in the reaction of 1, an ?-hydrogen was abstracted to form the exo-type double bond in the reaction of 12. PMID:23357815

Hanzawa, Yohko; Kasashima, Yoshio; Hashimoto, Kahoko; Sasaki, Tatsuhiro; Tomisaki, Keita; Mino, Takashi; Sakamoto, Masami; Fujita, Tsutomu

2013-01-01

82

Conditions for diffusion-limited and reaction-limited recombination in nanostructured solar cells.  

PubMed

The performance of Dye-sensitized solar cells (DSC) and related devices made of nanostructured semiconductors relies on a good charge separation, which in turn is achieved by favoring charge transport against recombination. Although both processes occur at very different time scales, hence ensuring good charge separation, in certain cases the kinetics of transport and recombination can be connected, either in a direct or an indirect way. In this work, the connection between electron transport and recombination in nanostructured solar cells is studied both theoretically and by Monte Carlo simulation. Calculations using the Multiple-Trapping model and a realistic trap distribution for nanostructured TiO2 show that for attempt-to-jump frequencies higher than 10(11)-10(13) Hz, the system adopts a reaction limited (RL) regime, with a lifetime which is effectively independent from the speed of the electrons in the transport level. For frequencies lower than those, and depending on the concentration of recombination centers in the material, the system enters a diffusion-limited regime (DL), where the lifetime increases if the speed of free electrons decreases. In general, the conditions for RL or DL recombination depend critically on the time scale difference between recombination kinetics and free-electron transport. Hence, if the former is too rapid with respect to the latter, the system is in the DL regime and total thermalization of carriers is not possible. In the opposite situation, a RL regime arises. Numerical data available in the literature, and the behavior of the lifetime with respect to (1) density of recombination centers and (2) probability of recombination at a given center, suggest that a typical DSC in operation stays in the RL regime with complete thermalization, although a transition to the DL regime may occur for electrolytes or hole conductors where recombination is especially rapid or where there is a larger dispersion of energies of electron acceptors. PMID:24712803

Ansari-Rad, Mehdi; Anta, Juan A; Arzi, Ezatollah

2014-04-01

83

Vitamin B(12) model complex catalyzed methyl transfer reaction to alkylthiol under electrochemical conditions with sacrificial electrode.  

PubMed

Catalytic methyl transfer reactions from methyl tosylate to 1-octanethiol catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C(1)ester]ClO(4), were investigated under electrochemical conditions. As a model study for the cobalamin-dependent methyl transfer reaction from methyltetrahydrofolate to homocysteine, controlled-potential electrolyses were carried out at -1.0 V vs. Ag/AgCl using a zinc plate as the sacrificial anode at 50 degrees C in the dark. A turnover behaviour for the methyl transfer reaction was observed for the first time under non-enzymatic reaction conditions. Co(I) species, which is generated from the continuous electrolysis of [Cob(II)7C(1)ester]ClO(4), and its methylated CH(3)-Co complex were found to be important intermediates. The mechanism for such a methyl transfer reaction was investigated by product analysis, electronic spectroscopy and ESR spin-trapping experiments. A simple vitamin B(12) model complex was also utilized as the catalyst for the methyl transfer reaction. PMID:19885539

Pan, Ling; Shimakoshi, Hisashi; Masuko, Takahiro; Hisaeda, Yoshio

2009-11-28

84

A COMPARATIVE STUDY BETWEEN CROSS AND DOWN-THE-LINE FOREHAND DRIVES UNDER CHOICE REACTION CONDITION IN SOFT-TENNIS  

Microsoft Academic Search

The purpose of this study was to clarify the mechanics involved in making two different shots, namely, cross (C) and down-the-line (D), under a two-choice reaction condition in soft-tennis. Using the images from two high-speed cameras, forehand drive motions under these conditions were analyzed with the direct linear transformation procedure. The authors considered that for the selected objects of analysis,

Seiji Kusubori; Hirofumi Ida; Motonobu Ishii

85

State-to-state quantum dynamics of O + O2 isotope exchange reactions reveals nonstatistical behavior at atmospheric conditions  

PubMed Central

The O + O2 exchange reaction is a prerequisite for the formation of ozone in Earth’s atmosphere. We report here state-to-state differential and integral cross sections for several O + O2 isotope-exchange reactions obtained by dynamically exact quantum scattering calculations at collision energies relevant to atmospheric conditions. These reactions are shown to be highly nonstatistical, evidenced by dominant forward scattering and deviation of the integral cross section from the statistical limit. Mechanistic analyses revealed that the nonstatistical channel is facilitated by short-lived osculating resonances. The theoretical results provided an in-depth interpretation of a recent molecular beam experiment of the exchange reaction and shed light on the initial step of ozone recombination.

Sun, Zhigang; Liu, Lan; Lin, Shi Ying; Schinke, Reinhard; Guo, Hua; Zhang, Dong H.

2010-01-01

86

Methods for quantifying the influences of pressure and temperature variation on metal hydride reaction rates measured under isochoric conditions  

NASA Astrophysics Data System (ADS)

Analysis techniques for determining gas-solid reaction rates from gas sorption measurements obtained under non-constant pressure and temperature conditions often neglect temporal variations in these quantities. Depending on the materials in question, this can lead to significant variations in the measured reaction rates. In this work, we present two new analysis techniques for comparison between various kinetic models and isochoric gas measurement data obtained under varying temperature and pressure conditions in a high pressure Sievert system. We introduce the integral pressure dependence method and the temperature dependence factor as means of correcting for experimental variations, improving model-measurement fidelity, and quantifying the effect that such variations can have on measured reaction rates. We use measurements of hydrogen absorption in LaNi5 and TiCrMn to demonstrate the effect of each of these methods and show that their use can provide quantitative improvements in interpretation of kinetics measurements.

Voskuilen, Tyler G.; Pourpoint, Timothée L.

2013-11-01

87

Kinetics of coal gasification reactions at process conditions. Final technical report  

SciTech Connect

An entire fixed bed coal gasification reactor is suspended from a large analytical balance for thermogravimetric measurement of the reaction rate. This thermobalance has advantages over the hanging basket types in that sample size can be larger, thermocouples can be embedded directly in the reacting bed, and there is more control over extraparticle mass transfer resistance. Steam gasification of a North Dakota lignitic coal was studied at pressures from 20 to 33 atmospheres and temperatures from 720 to 900/sup 0/C. The observed reaction order was close to one. The gasification rates were essentially independent of the measured temperature. The suggested explanation for this behavior was that the particles act collectively, giving a large resistance to mass and heat transport. The reaction took place under a strong diffusional control. Gas chromatographic analysis of the products indicated that the carbon-steam reaction is the principal gasification mechanism. Steam was in excess, and the products underwent the water-gas shift reaction. Hydrogasification studies were complicated by the observation of an ignition phenomena in the coal bed when the exothermic heat of reaction could not be removed fast enough. An expression for the temperature dependence of the reaction rate was determined. 6 references, 28 figures, 9 tables.

Gardner, N.C.; Zheng, C.; Pehmoeller, D.; Gorecka, B.

1984-01-01

88

Dynamics of morphological manifestations of reactions of the organism under conditions of hypergravitation  

NASA Technical Reports Server (NTRS)

The dynamics of the reaction of the hypothalamus-hypophysis-adrenal system to g-forces of 4 G's magnitude reveal a phasal nature of the adaptational system, dependent both on duration of force and position of the body.

Knyazeva, G. D.; Podymov, V. K.; Savina, Y. A.

1975-01-01

89

Gas phase reactions of alkyl nitrates with hydroxyl radicals under tropospheric conditions in comparison with photolysis  

Microsoft Academic Search

Rate constants for the reaction of OH radicals with some branched alkyl nitrates have been measured applying a competitive technique. Methyl nitrite photolysis in synthetic air was used as OH radical source at 295±2 K and 1000 mbar total pressure. Using a rate constant of 2.53×10-12 cm3 s-1 for the reaction of OH radicals with n-butane as reference, the following

K. H. Becker; K. Wirtz

1989-01-01

90

Formation of Flavor Components by the Reaction of Amino Acid and Carbonyl Compounds in Mild Conditions  

Microsoft Academic Search

This work describe products of reactions between four R-dicarbonyl compounds (diacetyl, pentan- 2,3-dione, glyoxal, and methylglyoxal) or two R-hydroxy ketones, (acetoine and acetol) and amino acids present in wines. The results shows the formation of odorous products or strong-smelling additives resulting from the Maillard and Strecker reaction in a primarily aqueous medium, at low temperature and low pH (pH 3.5)

Laura Pripis-Nicolau; Gilles de Revel; Alain Bertrand; Alain Maujean

2000-01-01

91

Description of the Equilibrium Conditions of Chemical Reactions in Various Solvents. Microcalorimetric and Radiochemical Studies into the Complexing of Monovalent Metal Salts by Macrocyclic Polyethers.  

National Technical Information Service (NTIS)

Empirical knowledge is taken as the basis for establishing a method to predict the equilibrium conditions of reactions of macrocyclic polyethers and monovalent metal cations in various solvents. The reactions in the solvents under review can be well descr...

H. Roehl

1983-01-01

92

Synthesis of trifluoromethyl alcohols from tert-butoxy-?-(trifluoromethyl)styrenes and trifluoromethylbenzyl ketones under the conditions of the Leuckart–Wallach reaction  

Microsoft Academic Search

A novel pathway towards trifluoromethylalcohols by an unexpected reaction of tert-butoxy-?-(trifluoromethyl)styrenes or corresponding trifluoromethylbenzyl ketones under the conditions of the Leuckart–Wallach reaction was elaborated.

Vasiliy M. Muzalevskiy; Valentine G. Nenajdenko; Aleksey V. Shastin; Elizabeth S. Balenkova; Günter Haufe

2008-01-01

93

Manganese triazacyclononane oxidation catalysts grafted under reaction conditions on solid cocatalytic supports.  

PubMed

Manganese complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) are highly active and selective alkene oxidation catalysts with aqueous H(2)O(2). Here, carboxylic acid-functionalized SiO(2) simultaneously immobilizes and activates these complexes under oxidation reaction conditions. H(2)O(2) and the functionalized support are both necessary to transform the inactive [(tmtacn)Mn(IV)(?-O)(3)Mn(IV)(tmtacn)](2+) into the active, dicarboxylate-bridged [(tmtacn)Mn(III)(?-O)(?-RCOO)(2)Mn(III)(tmtacn)](2+). This transformation is assigned on the basis of comparison of diffuse reflectance UV-visible spectra to known soluble models, assignment of oxidation state by Mn K-edge X-ray absorption near-edge spectroscopy, the dependence of rates on the acid/Mn ratios, and comparison of the surface structures derived from density functional theory with extended X-ray absorption fine structure. Productivity in cis-cyclooctene oxidation to epoxide and cis-diol with 2-10 equiv of solid cocatalytic supports is superior to that obtained with analogous soluble valeric acid cocatalysts, which require 1000-fold excess to reach similar levels at comparable times. Cyclooctene oxidation rates are near first order in H(2)O(2) and near zero order in all other species, including H(2)O. These observations are consistent with a mechanism of substrate oxidation following rate-limiting H(2)O(2) activation on the hydrated, supported complex. This general mechanism and the observed alkene oxidation activation energy of 38 ± 6 kJ/mol are comparable to H(2)O(2) activation by related soluble catalysts. Undesired decomposition of H(2)O(2) is not a limiting factor for these solid catalysts, and as such, productivity remains high up to 25 °C and initial H(2)O(2) concentration of 0.5 M, increasing reactor throughput. These results show that immobilized carboxylic acids can be utilized and understood like traditional carboxylic acids to activate non-heme oxidation catalysts while enabling higher throughput and providing the separation and handling benefits of a solid catalyst. PMID:21970696

Schoenfeldt, Nicholas J; Ni, Zhenjuan; Korinda, Andrew W; Meyer, Randall J; Notestein, Justin M

2011-11-23

94

Mizoroki-heck cross-coupling reactions catalyzed by dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium under mild reaction conditions.  

PubMed

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family of easy accessible, very cheap, and air stable, but highly active and universally applicable C-C cross-coupling catalysts with an excellent functional group tolerance. Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1), the least stable complex within this series towards protons; e.g. in the form of water, allows an eased nanoparticle formation and hence, proved to be the most active Heck catalyst within this series at 100 °C and is a very rare example of an effective and versatile catalyst system that efficiently operates under mild reaction conditions. Rapid and complete catalyst degradation under work-up conditions into phosphonates, piperidinium salts and other, palladium-containing decomposition products assure an easy separation of the coupling products from catalyst and ligands. The facile, cheap, and rapid synthesis of 1,1',1"-(phosphinetriyl)tripiperidine and 1 respectively, the simple and convenient use as well as its excellent catalytic performance in the Heck reaction at 100 °C make 1 to one of the most attractive and greenest Heck catalysts available. We provide here the visualized protocols for the ligand and catalyst syntheses as well as the reaction protocol for Heck reactions performed at 10 mmol scale at 100 °C and show that this catalyst is suitable for its use in organic syntheses. PMID:24686532

Oberholzer, Miriam; Frech, Christian M

2014-01-01

95

In situ generation of palladium nanoparticles: ligand-free palladium catalyzed pivalic acid assisted carbonylative Suzuki reactions at ambient conditions.  

PubMed

Highly selective carbonylative Suzuki reactions of aryl iodides with arylboronic acids using an in situ generated nanopalladium system furnished products in high yields. The reactions were performed under ambient conditions and in the absence of an added ligand. The key to success is the addition of pivalic acid, which can effectively suppress undesired Suzuki coupling. The synthesis can be easily scaled up, and the catalytic system can be reused up to nine times. The nature of the active catalytic species are discussed. PMID:24397578

Zhou, Qing; Wei, Shaohua; Han, Wei

2014-02-01

96

Hiyama cross-coupling of arenediazonium salts under mild reaction conditions.  

PubMed

Palladium acetate [Pd(OAc)(2)]-catalyzed Hiyama cross-coupling of arenediazonium salts with organosilanes was found to generate biaryl products in high yields in alcoholic solutions. The simple and efficient protocol does not require any bases, ligands, or air/moisture. The transformation can tolerate either electron-donating or electron-withdrawing functional groups. Theoretical studies show that the transmetalation is the rate-limiting step for the cross-coupling reaction and both acetate and tetrafluoroborate anions may be involved in the direct reaction with the silicon atom. PMID:21995729

Cheng, Kai; Wang, Chen; Ding, Yiyuan; Song, Qingbao; Qi, Chenze; Zhang, Xian-Man

2011-11-18

97

Reaction of spruce cells toward heavy metals and the influence of culture conditions  

Microsoft Academic Search

Plant cell cultures may serve as biosensors for the detection of heavy metals and other toxic substances. Standard culture media and protocols are frequently utilised, but in these media no care is usually taken to control the influence of hormones and nutrients on the reaction of the enzymes or m under consideration as parts of the sensor. The present paper

Peter Schröder; file DbackslashDocuments Claudia Fischer

2004-01-01

98

Convenient Synthesis of 2Aminothiophene Derivatives by Acceleration of Gewald Reaction Under Ultrasonic Aqueous Conditions  

Microsoft Academic Search

Under ultrasound irradiation and in the presence of H2O\\/Et2NH, ethyl cyanoacetate or malononitrile can combine with ?-methylene carbonyl compounds and elemental sulfur to efficiently yield 2-aminothiophene derivatives within a few minutes. Products are easily obtained by simple filtration because of their spontaneous precipitation in the reaction mixtures.

Mohammad M. Mojtahedi; M. Saeed Abaee; Peyman Mahmoodi; Mehdi Adib

2010-01-01

99

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

DOEpatents

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

Werpy, Todd (West Richland, WA) [West Richland, WA; Frye, Jr., John G. (Richland, WA); Wang, Yong (Richland, WA) [Richland, WA; Zacher, Alan H. (Kennewick, WA) [Kennewick, WA

2003-12-30

100

Experimental Studies in Insect Parasitism. XI. The Haemocytic Reaction of a Caterpillar under Varied Conditions  

Microsoft Academic Search

Eggs or young larvae of an ichneumonid parasite, Nemeritis, injected into caterpillars of the tomato moth, Diataraxia, evoked a rapid reaction of the haemocytes, which led to the encapsulation of the parasite within 4 h. The further development of the capsule is described, and evidence is adduced that the encapsulated parasites were killed by asphyxiation. Encapsulation was blocked by injection

G. Salt

1960-01-01

101

Reaction of polysulfide anions with ?,? unsaturated isoprenoid aldehydes in aquatic media: simulation of oceanic conditions  

Microsoft Academic Search

Polysulfide anions react with ?,? unsaturated aldehydes in aquatic media. Michael addition mechanisms control the first step, which follows the same pathway as in phase transfer catalysis (PTC) systems. The end products are polysulfide cross-linked oligo-polymers. The kinetic profiles, measured by 1H NMR and elemental analysis, changed dramatically with the length of the carbon skeleton. The reaction rates are controlled

Alon Amrani; Zeev Aizenshtat

2004-01-01

102

Kinetics and Mechanism of the Reaction of Hydoxyl Radicals with Acetonitrile under Atmospheric Conditions  

NASA Technical Reports Server (NTRS)

The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH3CN (1) and its isotopic variants, OH + CD3CN (2), OD + CH3CN (3), and OD + CD3CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N2, N2/O2, and He buffer gases. In the absence of O2 all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-first rate constants which were proportional to substrate concentration. Data obtained in N2 over the range 50-700 Torr at 298 K are consistent with k(sub 1), showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures in k(sub 1)(T) = (1.1(sup +0.5)/(sub -0.3)) x 10(exp -12) exp[(-1130 +/- 90)/T] cu cm /(molecule s). The kinetics of reaction 2 are found to be pressure dependent with k(sub 2) (298 K) increasing from (1.21 +/- 0.12) x 10(exp -14) to (2.16 +/- 0.11) x 10(exp -14) cm(exp 3)/ (molecule s) over the pressure range 50-700 Torr of N2 at 298 K. Data at pressures greater than 600 Torr give k(sub 2)(T) = (9.4((sup +13.4)(sub -5.0))) x 10(exp -13) exp[(-1180 +/- 250)/T] cu cm/(molecule s). The rates of reactions 3 and 4 are found to be independent of pressure over the range 50-700 Torr of N2 with 298 K rate coefficient given by k(sub 3) =(3.18 +/- 0.40) x 10(exp -14) cu cm/(molecule s) and k(sub 4) = (2.25 +/-0.28) x 10(exp -14) cu cm/(molecule s). In the presence of O2 each reaction shows complex (non-pseudo-first-order) kinetic behavior and/or an apparent decrease in the observed rate constant with increasing [O2], indicating the presence of significant OH or OD regeneration. Observation of regeneration of OH in (2) and OD in (3) is indicative of a reaction channel which proceeds via addition followed by reaction of the adduct, or one of its decomposition products, with O2. The observed OH and OD decay profiles have been modeled by using a simple mechanistic scheme to extract kinetic information about the adduct reations with O2 and branching ratios for OH regeneration. A plausible mechanism for OH regeneration in (2) involves OH addition to the nitrogen atom followed by O2 addition to the cyano carbon atom, isomeriazation and decomposition to D2CO + DOCN + OH. Our results suggest that the OH + CH3CN reaction occurs via a complex mechanism involving both bimolecular and termolecular pathways, analogous to the mechanisms for the the important atmospheric reactions of OH with CO and HNO3.

Hynes, A. J.; Wine, P. H.

1997-01-01

103

A learned flavor preference persists despite the extinction of conditioned hedonic reactions to the cue flavors  

Microsoft Academic Search

Learned flavor preferences can be strikingly persistent in the face of behavioral extinction. Harris, Shand, Carroll, and\\u000a Westbrook (2004) suggested that this persistence may be due to flavor preference conditioning’s producing a long-lasting change\\u000a in the hedonic response to the conditioned stimulus (CS+) flavor. In the present study, the CS+ flavor was presented in simultaneous\\u000a compound with 16% sucrose, whereas

Dominic M. Dwyer; Hannah L. Pincham; Thida Thein; Justin A. Harris

2009-01-01

104

Sharp Estimates for the Global Attractor of Scalar Reaction-Diffusion Equations with a Wentzell Boundary Condition  

NASA Astrophysics Data System (ADS)

In this paper, we derive optimal upper and lower bounds on the dimension of the attractor {A}W for scalar reaction-diffusion equations with a Wentzell (dynamic) boundary condition. We are also interested in obtaining explicit bounds on the constants involved in our asymptotic estimates, and to compare these bounds to previously known estimates for the dimension of the global attractor {A}K, K?{D,N,P}, of reaction-diffusion equations subject to Dirichlet, Neumann and periodic boundary conditions. The explicit estimates we obtain show that the dimension of the global attractor {A}W is of different order than the dimension of {A}K, for each K?{D,N,P}, in all space dimensions that are greater than or equal to three.

Gal, Ciprian G.

2012-02-01

105

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions  

Microsoft Academic Search

Substituted pyrrolidino- and 3-alkyl-2-pyrazolinofullerenes ionize under ESI and MALDI mass spectrometry conditions and negative\\u000a mode of detection undergoing mass spectral fragmentations, which can be easily correlated with the reported results for the\\u000a thermal and electrochemical retro-cycloaddition reactions of these compounds. 2-Pyrazolinofullerenes lead directly to a [60]fullerene\\u000a product ion formed through a retro-cycloaddition process regardless of the substituents attached at the

Juan Luis Delgado; Salvatore Filippone; Angel Martín-Domenech; Margarita Altable; Enrique Maroto; Fernando Langa; Nazario Martín; Roberto Martínez-Alvarez

2011-01-01

106

Main mineral melting behavior and mineral reaction mechanism at molecular level of blended coal ash under gasification condition  

Microsoft Academic Search

The main mineral melting behavior and mineral reaction mechanism at molecular level of Chinese blended coal ash under gasification condition (30% H2, 66% CO, 4% CO2) from 1073K to 1573K were studied through the ASTM test, X-ray diffraction (XRD), ternary phase diagram system and quantum chemistry calculation with ab-initio calculations. The results show that with increasing blending mass fraction of

Xiaojiang Wu; Zhongxiao Zhang; Yushuang Chen; Tuo Zhou; Junjie Fan; Guilin Piao; Nobusuke Kobayashi; Shigekatsu Mori

2010-01-01

107

Subcortical correlates of differential classical conditioning of aversive emotional reactions in social phobia  

Microsoft Academic Search

Background: Conditioning processes have been proposed to play a role in the development of anxiety disorders. As yet, the neurobiologic correlates of emotional learning have not been fully understood in these patients. Accordingly, brain activity was studied in subcortical and cortical regions involved in the processing of negative affect during differential aversive classical conditioning.Methods: Twelve patients with social phobia and

Frank Schneider; Ute Weiss; Christoph Kessler; Hans-Wilhelm Müller-Gärtner; Stefan Posse; Jasmin B. Salloum; Wolfgang Grodd; Frank Himmelmann; Wolfgang Gaebel; Niels Birbaumer

1999-01-01

108

Photosystem II Reaction Center Damage and Repair in Dunaliella salina (Green Alga) (Analysis under Physiological and Irradiance-Stress Conditions).  

PubMed Central

Mechanistic aspects of the photosystem II (PSII) damage and repair cycle in chloroplasts were investigated. The D1/32-kD reaction center protein of PSII (known as the psbA chloroplast gene product) undergoes a frequent light-dependent damage and turnover in the thylakoid membrane. In the model organism Dunaliella salina (green alga), growth under a limiting intensity of illumination (100 [mu]mol of photons m-2 s-1; low light) entails damage, degradation, and replacement of D1 every about 7 h. Growth under irradiance-stress conditions (2000 [mu]mol of photons m-2 s-1; high light) entails damage to and replacement of D1 about every 20 min. Thus, the rate of damage and repair of PSII appears to be proportional to the light intensity during plant growth. Low-light-grown cells do not possess the capacity for high rates of repair. Upon transfer of low-light-grown cells to high-light conditions, accelerated damage to reaction center proteins is followed by PSII disassembly and aggregation of neighboring reaction center complexes into an insoluble dimer form. The accumulation of inactive PSII centers that still contain the D1 protein suggests that the rate of D1 degradation is the rate-limiting step in the PSII repair cycle. Under irradiance-stress conditions, chloroplasts gradually acquire a greater capacity for repair. The induction of this phenomenon occurs with a half-time of about 24 h.

Kim, J. H.; Nemson, J. A.; Melis, A.

1993-01-01

109

Reactions of boron atoms and clusters with methane, methyl bromide and water under matrix isolation conditions  

SciTech Connect

Boron was evaporated with a pulsed XeCl excimer laser, and the vapor cocondensed on a cold window (near 10 K) with argon mixtures of CH{sub 4}, CH{sub 3}Br, and H{sub 2}O, and {sup 13}C and {sup 2}H labeled analogues. consumption of B and B{sub 2} was monitored by UV-vis spectroscopy, and reaction products were monitored with FT-IR. Atom insertion products H{sub 3}CBH, H{sub 3}CBBr, and HOBH were detected. Evidence was found for B{sub 2} reactions with CH{sub 4} and CH{sub 3}Br, suggesting the formation of dinuclear bridges hydrogen species. Larger boron clusters were detected by FT-IR, which were unreactive with CH{sub 4} and, in one cases, with water.

Jeong, G.H.; Boucher, R.; Klabunde, K.J. (Kansas State Univ., Manhattan (USA))

1990-04-25

110

Kinetics and mechanism of the reaction of hydroxyl radicals with acetonitrile under atmospheric conditions  

SciTech Connect

The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH{sub 3}CN (1) and its isotopic variants, OH + CD{sub 3}CN (2), OD + CH{sub 3}CN (3), and OD + CD{sub 3}CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N{sub 2}, N{sub 2}/O{sub 2}, and He buffer gases. In the absence of O{sub 2} all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-firt-order rate constants which were proportional to substrate concentration. Data obtained in N{sub 2} over the range 50-700 Torr at 298 K are consistent with k{sub 1} showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures is k{sub 1}(T) = (1.1{sub {minus}0.3}{sup +0.5}) {times} 10{sup {minus}12} exp(({minus}1,130 {plus minus} 90)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The kinetics of reaction 2 are found to be pressure dependent with k{sub 2} (298 K) increasing from (1.21 {plus minus} 0.12) {times} 10{sup {minus}14} to (2.16 {plus minus} 0.11) {times} 10{sup {minus}14} cm{sup 3} molecule{sup {minus}1}s{sup {minus}1} over the pressure range 50-700 Torr of N{sub 2} at 298 K. Data at pressures >600 Torr give k{sub 2}(T) = (9.4{sub {minus}5.0}{sup +13.4}) {times} 10{sup {minus}13} exp(({minus}1,180 {plus minus} 250)/T) cm{sup 3} molecule{sup {minus}1}s{sup {minus}1}.

Hynes, A.J.; Wine, P.H. (Georgia Inst. of Tech., Atlanta (USA))

1991-02-07

111

An effective rate equation approach to reaction kinetics in small volumes: Theory and application to biochemical reactions in nonequilibrium steady-state conditions  

NASA Astrophysics Data System (ADS)

Chemical master equations provide a mathematical description of stochastic reaction kinetics in well-mixed conditions. They are a valid description over length scales that are larger than the reactive mean free path and thus describe kinetics in compartments of mesoscopic and macroscopic dimensions. The trajectories of the stochastic chemical processes described by the master equation can be ensemble-averaged to obtain the average number density of chemical species, i.e., the true concentration, at any spatial scale of interest. For macroscopic volumes, the true concentration is very well approximated by the solution of the corresponding deterministic and macroscopic rate equations, i.e., the macroscopic concentration. However, this equivalence breaks down for mesoscopic volumes. These deviations are particularly significant for open systems and cannot be calculated via the Fokker-Planck or linear-noise approximations of the master equation. We utilize the system-size expansion including terms of the order of ?-1/2 to derive a set of differential equations whose solution approximates the true concentration as given by the master equation. These equations are valid in any open or closed chemical reaction network and at both the mesoscopic and macroscopic scales. In the limit of large volumes, the effective mesoscopic rate equations become precisely equal to the conventional macroscopic rate equations. We compare the three formalisms of effective mesoscopic rate equations, conventional rate equations, and chemical master equations by applying them to several biochemical reaction systems (homodimeric and heterodimeric protein-protein interactions, series of sequential enzyme reactions, and positive feedback loops) in nonequilibrium steady-state conditions. In all cases, we find that the effective mesoscopic rate equations can predict very well the true concentration of a chemical species. This provides a useful method by which one can quickly determine the regions of parameter space in which there are maximum differences between the solutions of the master equation and the corresponding rate equations. We show that these differences depend sensitively on the Fano factors and on the inherent structure and topology of the chemical network. The theory of effective mesoscopic rate equations generalizes the conventional rate equations of physical chemistry to describe kinetics in systems of mesoscopic size such as biological cells.

Grima, R.

2010-07-01

112

Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions  

NASA Astrophysics Data System (ADS)

Chamber studies of glyoxal uptake onto neutral ammonium sulphate aerosol were performed under dark and irradiated conditions to gain further insight into processes controlling glyoxal uptake onto ambient aerosol. Organic fragments from glyoxal dimers and trimers were observed within the aerosol under dark and irradiated conditions; glyoxal oligomer formation and overall organic growth were found to be reversible under dark conditions. Analysis of high-resolution time-of-flight aerosol mass spectra provides evidence for irreversible formation of carbon-nitrogen (C-N) compounds in the aerosol. These compounds are likely to be imidazoles formed by reaction of glyoxal with the ammonium sulphate seed. To the authors' knowledge, this is the first time C-N compounds resulting from condensed phase reactions with ammonium sulphate seed have been detected in aerosol. Organosulphates were not detected under dark conditions. However, active oxidative photochemistry, similar to that found in cloud processing, was found to occur within aerosol during irradiated experiments. Organosulphates, carboxylic acids, and organic esters were identified within the aerosol. Our study suggests that both C-N compound formation and photochemical processes should be considered in models of secondary organic aerosol formation via glyoxal.

Galloway, M. M.; Chhabra, P. S.; Chan, A. W. H.; Surratt, J. D.; Flagan, R. C.; Seinfeld, J. H.; Keutsch, F. N.

2008-12-01

113

Hot-Fire Testing of 100 LB(sub F) LOX/LCH4 Reaction Control Engine at Altitude Conditions  

NASA Technical Reports Server (NTRS)

Liquid oxygen/liquid methane (LO2/LCH4 ) has recently been viewed as a potential green propulsion system for both the Altair ascent main engine (AME) and reaction control system (RCS). The Propulsion and Cryogenic Advanced Development Project (PCAD) has been tasked by NASA to develop these green propellant systems to enable safe and cost effective exploration missions. However, experience with LO2/LCH4 as a propellant combination is limited, so testing of these systems is critical to demonstrating reliable ignition and performance. A test program of a 100 lb f reaction control engine (RCE) is underway at the Altitude Combustion Stand (ACS) of the NASA Glenn Research Center, with a focus on conducting tests at altitude conditions. These tests include a unique propellant conditioning feed system (PCFS) which allows for the inlet conditions of the propellant to be varied to test warm to subcooled liquid propellant temperatures. Engine performance, including thrust, c* and vacuum specific impulse (I(sub sp,vac)) will be presented as a function of propellant temperature conditions. In general, the engine performed as expected, with higher performance at warmer propellant temperatures but better efficiency at lower propellant temperatures. Mixture ratio effects were inconclusive within the uncertainty bands of data, but qualitatively showed higher performance at lower ratios.

Marshall, William M.; Kleinhenz, Julie E.

2010-01-01

114

Kinetics of elementary steps in the reactions of atomic bromine with isoprene and 1,3-butadiene under atmospheric conditions.  

PubMed

Laser flash photolysis of CF(2)Br(2) has been coupled with time-resolved detection of atomic bromine by resonance fluorescence spectroscopy to investigate the gas-phase kinetics of early elementary steps in the Br-initiated oxidations of isoprene (2-methyl-1,3-butadiene, Iso) and 1,3-butadiene (Bu) under atmospheric conditions. At T ? 526 K, measured rate coefficients for Br + isoprene are independent of pressure, suggesting that hydrogen transfer (1a) is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 526 K ? T ? 673 K: k(1a)(T) = (1.22 ± 0.57) × 10(-11) exp[(-2100 ± 280)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2? and represent precision of the Arrhenius parameters). At 271 K ? T ? 357 K, kinetic evidence for the reversible addition reactions Br + Iso ? Br-Iso (k(1b), k(-1b)) and Br + Bu ? Br-Bu (k(3b), k(-3b)) is observed. Analysis of the approach to equilibrium data allows the temperature- and pressure-dependent rate coefficients k(1b), k(-1b), k(3b), and k(-3b) to be evaluated. At atmospheric pressure, addition of Br to each conjugated diene occurs with a near-gas-kinetic rate coefficient. Equilibrium constants for the addition/dissociation reactions are obtained from k(1b)/k(-1b) and k(3b)/k(-3b), respectively. Combining the experimental equilibrium data with electronic structure calculations allows both second- and third-law analyses of thermochemistry to be carried out. The following thermochemical parameters for the addition reactions 1b and 3b at 0 and 298 K are obtained (units are kJ mol(-1) for ?(r)H and J mol(-1) K(-1) for ?(r)S; uncertainties are accuracy estimates at the 95% confidence level): ?(r)H(0)(1b) = -66.6 ± 7.1, ?(r)H(298)(1b) = -67.5 ± 6.6, and ?(r)S(298)(3b) = -93 ± 16; ?(r)H(0)(3b) = -62.4 ± 9.0, ?(r)H(298)(3b) = -64.5 ± 8.5, and ?(r)S(298)(3b) = -94 ± 20. Examination of the effect of added O(2) on Br kinetics under conditions where reversible adduct formation is observed allows the rate coefficients for the Br-Iso + O(2) (k(2)) and Br-Bu + O(2) (k(4)) reactions to be determined. At 298 K, we find that k(2) = (3.2 ± 1.0) × 10(-13) cm(3) molecule(-1) s(-1) independent of pressure (uncertainty is 2?, precision only; pressure range is 25-700 Torr) whereas k(4) increases from 3.2 to 4.7 × 10(-13) cm(3) molecule(-1) s(-1) as the pressure increases from 25 to 700 Torr. Our results suggest that under atmospheric conditions, Br-Iso and Br-Bu react with O(2) to produce peroxy radicals considerably more rapidly than they undergo unimolecular decomposition. Hence, the very fast addition reactions appear to control the rates of Br-initiated formation of Br-Iso-OO and Br-Bu-OO radicals under atmospheric conditions. The peroxy radicals are relatively weakly bound, so conjugated diene regeneration via unimolecular decomposition reactions, though unimportant on the time scale of the reported experiments (milliseconds), is likely to compete effectively with bimolecular reactions of peroxy radicals under relatively warm atmospheric conditions as well as in 298 K competitive kinetics experiments carried out in large chambers. PMID:22435953

Laine, Patrick L; Sohn, Yoon S; Nicovich, J Michael; McKee, Michael L; Wine, Paul H

2012-06-21

115

Kinetics of the OH + CH/sub 3/SH reaction under atmospheric conditions  

SciTech Connect

The pulsed laser photolysis-pulsed laser-induced fluorescence technique has been employed to study the kinetics of OH reactions with CH/sub 3/SH (k/sub 1/) and CD/sub 3/SH (k/sub 2/) in N/sub 2/, air, and O/sub 2/ buffer gases. They find that k/sub 1/ and k/sub 2/ are independent of O/sub 2/ concentration. Measured k/sub 1/ values are in excellent agreement with previous flash photolysis-resonance fluorescence studies, all of which employed reaction mixtures containing no O/sub 2/. However, the observation of no O/sub 2/ dependence is in marked disagreement with a number of relative rate studies where NO/sub x/-containing species were employed as photolytic precursors for OH and olefins were used as the reference compound. k/sub 2/ is found to be approx. 13% slower than k/sub 1/, suggesting the occurrence of a minor methyl hydrogen abstraction channel. In the course of investigating complications which result from photolysis of the mercaptan reactants, they found that 266-nm photolysis of either CH/sub 3/SH or CD/sub 3/SH in the presence of O/sub 2/ (but in the absence of other OH photolytic precursors) results in production of OH.

Hynes, A.J.; Wine, P.H.

1987-06-18

116

The reaction of cell-free oxyhemoglobin with nitrite under physiologically relevant conditions: Implications for nitrite-based therapies.  

PubMed

Nitric oxide (NO*) participates in the regulation of a wide array of biological processes and its deficit contributes to the severity of many diseases. Recently, a role of NO deficiency that occurs as a result of intravascular hemolysis and increases in levels of cell-free hemoglobin in the pathway of chronic anemic pathologies has been suggested. Experimental evidence for deoxyhemoglobin-catalyzed reduction of nitrite to NO* leads to the possibility of nitrite infusion-based therapies to correct NO* deficits. However, the presence of plasma hemoglobin also raises the possibility of deleterious free radical-mediated oxidative damage from the reaction between nitrite and oxyhemoglobin in the vasculature. We show that the conditions required for the reaction between nitrite and oxyhemoglobin to exhibit free radical-mediated autocatalytic kinetics are highly unlikely to occur in the plasma compartment, even during extensive hemolysis and with pharmacological nitrite doses. Although the presence of haptoglobin enhances the rate of the reaction between nitrite and oxyhemoglobin, common plasma antioxidants-ascorbate and urate, as well as catalase-prevent autocatalysis. Our findings suggest that pharmacological doses of nitrite are unlikely to cause free radical or ferrylhemoglobin formation in plasma originating from the reaction of nitrite with cell-free oxyhemoglobin in vivo. PMID:19010434

Piknova, Barbora; Keszler, Agnes; Hogg, Neil; Schechter, Alan N

2009-03-01

117

Identification of alterations in the Jacobian of biochemical reaction networks from steady state covariance data at two conditions.  

PubMed

Model building of biochemical reaction networks typically involves experiments in which changes in the behavior due to natural or experimental perturbations are observed. Computational models of reaction networks are also used in a systems biology approach to study how transitions from a healthy to a diseased state result from changes in genetic or environmental conditions. In this paper we consider the nonlinear inverse problem of inferring information about the Jacobian of a Langevin type network model from covariance data of steady state concentrations associated to two different experimental conditions. Under idealized assumptions on the Langevin fluctuation matrices we prove that relative alterations in the network Jacobian can be uniquely identified when comparing the two data sets. Based on this result and the premise that alteration is locally confined to separable parts due to network modularity we suggest a computational approach using hybrid stochastic-deterministic optimization for the detection of perturbations in the network Jacobian using the sparsity promoting effect of [Formula: see text]-penalization. Our approach is illustrated by means of published metabolomic and signaling reaction networks. PMID:23708492

Kügler, Philipp; Yang, Wei

2014-06-01

118

The effect of high pressure-high temperature processing conditions on acrylamide formation and other Maillard reaction compounds.  

PubMed

The effect of high pressure-high temperature (HPHT) processing on the formation of acrylamide and other Maillard-type reaction compounds was investigated in order to elucidate the impact of HPHT conditions on the different stages of the Maillard reaction. This study was performed in equimolar asparagine-glucose model systems that were treated at various HP/HT conditions (100-115 °C, 400-700 MPa, 0-60 min), and, for comparison, the model system was also heat-treated at ambient pressure. On the treated samples, the concentration of acrylamide, reactants, hydroxymethylfurfural, organic acids, and melanoidins was determined and the pH prior to and after treatment was measured. Based on the measured responses, the retarding effect of high pressure on the overall Maillard reaction was demonstrated; no or little differences were observed between 400 and 700 MPa. The study was conducted in two types of buffer, i.e. phosphate and MES buffer. In case of acrylamide, aspartic acid and browning, a higher concentration was generated in the MES buffer system, but these differences with the phosphate buffer system could be ascribed to pH changes resulting from the application of combined high pressure and high temperature. Based on the results, acrylamide formation is not expected to pose a major hazard to HPHT-treated products. PMID:20973553

De Vleeschouwer, Kristel; Van der Plancken, Iesel; Van Loey, Ann; Hendrickx, Marc E

2010-11-24

119

Boundary conditions for developing a safety concept for an exothermal reaction  

Microsoft Academic Search

Kinetic calculations for an example exothermal chemical process, the production of TCB, are carried out. They address both parameter uncertainties and random failures of the cooling system. In this way, they enable one to establish comprehensive boundary conditions for a safety system in terms of unavailability, the quantities of the undesired by-product (TCDD) produced and the times available before a

Ulrich Hauptmanns

2007-01-01

120

A new synthesis of TATB using inexpensive starting materials and mild reaction conditions  

SciTech Connect

TATB is currently manufactured in US by nitration of the expensive TCB to give 2,4,6-trichloro-1,3,5-trinitrobenzene which is then aminated to yield TATB. Elevated temperatures (150 C) are required for both reactions. There is a need for a more economical synthesis of TATB that also addresses current environmental issues. We have recently found that 1,1,1-trimethylhydrazinium iodide (TMHI) allows the amination of nitroarenes at ambient temperature via Vicarious Nucleophilic Substitution of hydrogen. TMHI reacts with picramide in presence of strong base (NaOMe or t-BuOK) to give TATB in over 95% yield. TMHI and picramide can be obtained from either inexpensive starting materials or surplus energetic materials from demilitarization activities, such as the 30,000 metric tons of UDMH (surplus rocket propellant) from the former Soviet Union.

Mitchell, A.R.; Pagoria, P.F.; Schmidt, R.D.

1996-04-01

121

Solubility and Reaction Rates of Aluminum Solid Phases Under Hydrothermal Conditions  

SciTech Connect

Experimental studies involving equilibrium solubility and dissolution/precipitation rates were initiated on boehmite (AIOOH) using a hydrogen-electrode concentration cell (HECC). This cell provides continuous, accurate in situ pH measurements of solid/solution mixtures to 295 C with provision for either removing solution samples for analysis of the metal content, or adding either of two titrants. This cell has been recently used to measure the solubility of minerals such as brucite; boehmite, zincite, arid magnetite. The ability to perturb pH, isothermally by addition of acidic or basic titrant opens the door for studies of the kinetics of dissolution/precipitation, even for relatively fast reactions. By monitoring the change in pH, with time, detailed kinetic information can be obtained without the need for sampling.

Benezeth, P.; Palmer, D.A.; Wesolowski, D.

1999-11-14

122

Bone tissue formation under ideal conditions in a scaffold generated by a reaction-diffusion system.  

PubMed

The design of porous scaffolds for tissue engineering requires methods to generate geometries in order to control the stiffness and the permeability of the implant among others characteristics. This article studied the potential of the reaction-diffusion systems to design porous scaffolds for bone regeneration. We simulate the degradation of the scaffold material and the formation of new bone tissue over canal-like, spherical and ellipsoid structures obtained by this approach. The simulations show that the degradation and growth rates are affected by the form of porous structures. The results have indicated that the proposed method has potential as a tool to generate scaffolds with internal porosities and is comparable with other methodologies to obtain this type of structures. PMID:24015480

Velasco, A Marco; Garzón-Alvarado, Diego A

2013-06-01

123

Mass Spectrometry Studies of the Retro-Cycloaddition Reaction of Pyrrolidino and 2-Pyrazolinofullerene Derivatives Under Negative ESI Conditions  

NASA Astrophysics Data System (ADS)

Substituted pyrrolidino- and 3-alkyl-2-pyrazolinofullerenes ionize under ESI and MALDI mass spectrometry conditions and negative mode of detection undergoing mass spectral fragmentations, which can be easily correlated with the reported results for the thermal and electrochemical retro-cycloaddition reactions of these compounds. 2-Pyrazolinofullerenes lead directly to a [60]fullerene product ion formed through a retro-cycloaddition process regardless of the substituents attached at the carbon and nitrogen atoms of the heterocyclic ring. These results are different from whose reported for the thermal and electrochemical processes. In contrast, pyrrolidinofullerenes undergo different fragmentative reactions depending upon the substituents (hydrogen, alkyl, or acyl) attached at the nitrogen atom of the heterocyclic ring leading eventually to the pristine C60 in the last step of the fragmentation pathway.

Delgado, Juan Luis; Filippone, Salvatore; Martín-Domenech, Angel; Altable, Margarita; Maroto, Enrique; Langa, Fernando; Martín, Nazario; Martínez-Alvarez, Roberto

2011-03-01

124

Mass spectrometry studies of the retro-cycloaddition reaction of pyrrolidino and 2-pyrazolinofullerene derivatives under negative ESI conditions.  

PubMed

Substituted pyrrolidino- and 3-alkyl-2-pyrazolinofullerenes ionize under ESI and MALDI mass spectrometry conditions and negative mode of detection undergoing mass spectral fragmentations, which can be easily correlated with the reported results for the thermal and electrochemical retro-cycloaddition reactions of these compounds. 2-Pyrazolinofullerenes lead directly to a [60]fullerene product ion formed through a retro-cycloaddition process regardless of the substituents attached at the carbon and nitrogen atoms of the heterocyclic ring. These results are different from whose reported for the thermal and electrochemical processes. In contrast, pyrrolidinofullerenes undergo different fragmentative reactions depending upon the substituents (hydrogen, alkyl, or acyl) attached at the nitrogen atom of the heterocyclic ring leading eventually to the pristine C(60) in the last step of the fragmentation pathway. PMID:21472574

Delgado, Juan Luis; Filippone, Salvatore; Martín-Domenech, Angel; Altable, Margarita; Maroto, Enrique; Langa, Fernando; Martín, Nazario; Martínez-Alvarez, Roberto

2011-03-01

125

Accurate Time-dependent Wave Packet Study of the H++LiH Reaction at Early Universe Conditions  

NASA Astrophysics Data System (ADS)

The dynamics and kinetics of the H+ + LiH reaction have been studied using a quantum reactive time-dependent wave packet (TDWP) coupled-channel quantum mechanical method on an ab initio potential energy surface at conditions of the early universe. The total reaction probabilities for the H+ + LiH(v = 0, j = 0) ? H+ 2 + Li process have been calculated from 5 × 10-3 eV up to 1 eV for total angular momenta J from 0 to 110. Using a Langevin model, integral cross sections have been calculated in that range of collision energies and extrapolated for energies below 5 × 10-3 eV. The calculated rate constants are found to be nearly independent of temperature in the 10-1000 K interval with a value of ?10-9 cm3 s-1, which is in good agreement with estimates used in evolutionary models of the early universe lithium chemistry.

Aslan, E.; Bulut, N.; Castillo, J. F.; Bañares, L.; Aoiz, F. J.; Roncero, O.

2012-11-01

126

Spectroscopy of unbound states under quasifree scattering conditions: One-neutron knockout reaction of {sup 14}Be  

SciTech Connect

Full Faddeev-type calculations are performed for one-neutron knockout reaction of {sup 14}Be on proton target at 69 MeV/nucleon incident energy. Inclusive transverse momentum distributions for the outgoing ({sup 12}Be+n) system and semi-inclusive cross sections are presented. A significant proton-core single scattering contribution emerges where the valence neutron has nonzero angular momentum relative to the core. This indicates that distorted-wave impulse approximation is inadequate and the complete multiple scattering series must be taken into account for the considered reaction. The magnitude of the semi-inclusive cross section at quasifree scattering conditions is a clear signature of the angular momentum of the valence nucleon.

Crespo, R. [Centro de Fisica Nuclear, Universidade de Lisboa, Av. Prof. Gama Pinto 2, P-1649-003 Lisboa (Portugal); Departamento de Fisica, Instituto Superior Tecnico, Taguspark, Av. Prof. Cavaco Silva, Taguspark P-2780-990 Porto Salvo, Oeiras (Portugal); Deltuva, A.; Rodriguez-Gallardo, M.; Cravo, E.; Fonseca, A. C. [Centro de Fisica Nuclear, Universidade de Lisboa, Av. Prof. Gama Pinto 2, P-1649-003 Lisboa (Portugal)

2009-01-15

127

The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride  

NASA Technical Reports Server (NTRS)

The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

Heinrich, J.

1980-01-01

128

A simple and efficient Suzuki reaction catalyzed by palladium-modified nanopore silica under solvent-free conditions  

Microsoft Academic Search

In this paper our recent results of the Suzuki reaction using [Pd(NH3)4]2+-modified nanopore silica under solvent-free conditions are described. [Pd(NH3)4]2+-modified nanopore silica was prepared by impregnation using an aqueous solution of [Pd(NH3)4]Cl2 in water or in acetonitrile. The BET surface area, BJH mean pore diameter and pore volume are 138.8m2\\/g, 8.7nm, and 0.34cm3\\/g, respectively, and the pore size distribution shows

Wonghil Chang; Jihye Shin; Yunghee Oh; Byoung Joon Ahn

2008-01-01

129

Do Geriatric Conditions Increase Risk of Adverse Drug Reactions in Ambulatory Elders? Results From the VA GEM Drug Study  

PubMed Central

Background. Many clinicians prescribe cautiously to older adults with common geriatric conditions for fear of causing adverse drug reactions (ADRs). However, little is known about the association between these conditions and risk of ADRs. Methods. Using data from the VA Geriatric Evaluation and Management Drug Study, we determined any, preventable, and serious ADRs in 808 elders for 12 months after hospital discharge using a validated process involving patient self-report and chart review adjudicated by two health care professionals. Eight common geriatric conditions (activities of daily living, dementia, incontinence, falls, difficulty ambulating, malnourishment, depression, and prolonged bed rest) were evaluated at study baseline through self-report and structured assessments. We used Poisson regression to model the relationship between these geriatric conditions and ADRs. Results. Participants had a mean of 2.9 ± 1.2 geriatric conditions. Over the 12-month follow-up period, 497 ADRs occurred in 269 participants, including 187 ADRs considered preventable and 127 considered severe. On multivariable analyses, participants with dependency in one or more activities of daily living were less likely to suffer ADRs than those who were fully independent (incidence rate ratio: 0.78, 95% confidence interval = 0.62–1.00). None of the other seven geriatric conditions assessed were associated with ADR risk. Results were similar for preventable and serious ADRs, although participants with a history of falls were more likely to develop serious ADRs (incidence rate ratio: 1.49, 95% confidence interval = 1.00–2.21). Conclusions. Many geriatric conditions were not associated with risk of ADRs. Although it is prudent to prescribe judiciously in patients with these conditions, excessive caution may not be warranted.

Hanlon, Joseph T.; Sloane, Richard J.; Boscardin, W. John; Schmader, Kenneth E.

2011-01-01

130

Ammonium tetrathiomolybdate: a versatile catalyst for hydrogen evolution reaction from water under ambient and hostile conditions.  

PubMed

The lack of catalysts that can selectively reduce protons to produce hydrogen from water in the presence of oxygen and other conventional inhibitors of hydrogen evolution reaction (HER) has been a fundamental problem stalling the development of a practical hydrogen economy. Ammonium tetrathiomolybdate (ATM), a common laboratory reagent, spontaneously assembles on Au electrodes. Atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy data indicate formation of multiple layers of ATM which are stable over a wide pH range for days. These assemblies can produce hydrogen with very low onset potentials. It shows a turnover rate of 1.4 s(-1) and turnover number >5 × 10(4) in pH 7 at 180 mV overpotential. The pH dependence of the peak potential suggests that the generation of H2 from water proceeds likely via a ligand based proton coupled electron transfer process which precludes inhibition by O2. The ATM functionalized Au electrodes are found to efficiently catalyze HER in saline rich, CO saturated, and sulfide rich water sources with minimal inhibition of catalytic activity. PMID:24261567

Chatterjee, Sudipta; Sengupta, Kushal; Dey, Subal; Dey, Abhishek

2013-12-16

131

Communications : Suppression of sintering of size-selected Pd clusters under realistic reaction conditions for catalysis.  

SciTech Connect

The stability of model catalysts based on size-selected Pd clusters supported on graphite surfaces has been explored under realistic conditions for catalytic oxidation of methane at mild temperatures. The experimental results show that aggregated films of nanoparticles are highly unstable, but clusters pinned to the surface in the submonolayer coverage regime are much more stable against sintering. The degree of sintering of the pinned clusters, which does occur, proceeds by the release of clusters from their pinning sites. The suppression of sintering depends on the cluster deposition energy with respect to the pinning threshold.

Yin, F.; Lee, S.; Abdela, A.; Vajda, S.; Palmer, R. E. (Center for Nanoscale Materials); ( MSD); ( XSD); (Univ. of Birmingham); (Yale Univ.)

2011-04-08

132

QuadraPure-Supported Palladium Nanocatalysts for Microwave-Promoted Suzuki Cross-Coupling Reaction under Aerobic Condition  

PubMed Central

Cross-linked resin-captured palladium (XL-QPPd) was readily prepared by simple physical adsorption onto the high loading QuadraPure macroporous resin and a subsequent reduction process. To enhance the mechanical stability, entrapped palladium nanocatalysts were cross-linked with succinyl chloride. Both transmission electron microscopy images and X-ray diffraction analysis revealed that the palladium nanoparticles were well dispersed with diameters ranging in 4–10?nm. The catalyst performed good catalytic activity in microwave-promoted Suzuki cross-coupling reactions in water under aerobic condition with mild condition by using various aryl halides and phenylboronic acid. In addition, the catalyst showed an excellent recyclability without significant loss of catalytic activity.

Loh, Poh Lee; Juan, Joon Ching; Yarmo, Mohd Ambar; Yusop, Rahimi M.

2014-01-01

133

F-18 labeling protocol of peptides based on chemically orthogonal strain-promoted cycloaddition under physiologically friendly reaction conditions.  

PubMed

We introduce the high-throughput synthesis of various (18)F-labeled peptide tracers by a straightforward (18)F-labeling protocol based on a chemo-orthogonal strain-promoted alkyne azide cycloaddition (SPAAC) using aza-dibenzocyclootyne-substituted peptides as precursors with (18)F-azide synthon to develop peptide based positron emission tomography (PET) molecular imaging probes. The SPAAC reaction and subsequent chemo-orthogonal purification reaction with azide resin proceeded quickly and selectively under physiologically friendly reaction conditions (i.e., toxic chemical reagents-free, aqueous medium, room temperature, and pH ?7), and provided four (18)F-labeled tumor targetable bioactive peptides such as cyclic Arg-Gly-Asp (cRGD) peptide, bombesin (BBN), c-Met binding peptide (cMBP), and apoptosis targeting peptide (ApoPep) in high radiochemical yields as direct injectable solutions without any HPLC purification and/or formulation processes. In vitro binding assay and in vivo PET molecular imaging study using the (18)F-labeled cRGD peptide also demonstrated a successful application of our (18)F-labeling protocol. PMID:22770524

Sachin, Kalme; Jadhav, Vinod H; Kim, Eun-Mi; Kim, Hye Lan; Lee, Sang Bong; Jeong, Hwan-Jeong; Lim, Seok Tae; Sohn, Myung-Hee; Kim, Dong Wook

2012-08-15

134

Design of reaction conditions for the enhancement of microbial degradation of dyes in sequential cycles.  

PubMed

The present study evaluated the potential of white-rot fungal strain Coriolus versicolor to decolorize five structurally different dyes in sequential batch reactors under optimized conditions. The experiments were run continuously for seven cycles of 8 d each. High decolorizing activity was observed even during the repeated reuse of the fungus, especially when the old medium was replaced with fresh medium after every cycle. Biodegradation was the dominating factor as the fungus was able to produce the enzyme laccase mainly, to mineralize synthetic dyes. The nutrients and composition of the medium played important roles in sustaining the decolorisation potential of the fungus. Corncob was found be an easy and cheap substitute for carbon source for the fungus. Glucose consumption by the fungus was in accordance to its decolorisation activity and chemical oxygen demand (COD) reduction. PMID:20131593

Sanghi, Rashmi; Dixit, Awantika; Verma, Preeti; Puri, Sadhna

2009-01-01

135

Reactions of 2-(pyrrol-1-yl)benzyl radicals and related species under flash vacuum pyrolysis conditions.  

PubMed

2-(Pyrrol-1-yl)phenoxyl, aminyl, thiophenoxyl and benzyl radicals 2a-2d, respectively, were generated in the gas-phase under flash vacuum pyrolysis conditions. In all cases except the phenoxyl, cyclisation took place providing acceptable synthetic routes to the fused heterocycles 11, 14 and 15, respectively. Only sigmatropic rearrangement products were isolated, in low yields, from the phenoxyl 2a. The pyrrolo[1,2-a]benzimidazole 11 adopts the 1H-tautomer exclusively in chloroform solution. Electrophilic substitution reactions of pyrrolo[2,1-b]benzothiophene 14 were studied, including protonation, deuterium exchange, Vilsmeier formylation and reaction with dimethyl acetylenedicarboxylate. 2-(2,5-Diarylpyrrol-1-yl)thiophenoxyl, phenoxyl and aminyl radicals 23a-f, were also generated in the gas-phase under similar conditions. The thiophenoxyls 23a/b gave extremely complex pyrolysate mixtures in which primary cyclisation products were formed by attack of the radical at the pyrrrole ring and attack at the ipso-, ortho- and meta- positions of the aryl ring. Secondary pyrolysis products were obtained by specific sigmatropic shifts of the N-aryl group. The 2,5-di(thien-2-yl)thiophenoxyl radical 23c gave the pyrrolobenzothiazole 31c as the only cyclisation product in low yield. FVP of the phenoxyl and aminyl radical generators 26d and 26f, respectively, gave 3-arylpyrrolo[1,2-f]phenanthridines 46d and 46f, respectively, by a hydrogen transfer-cyclisation mechanism. PMID:20024114

Cadogan, J I G; Clark, Bernard A J; Ford, Daniel; Macdonald, Ranald J; Macpherson, Andrew D; McNab, Hamish; Nicolson, Iain S; Reed, David; Sommerville, Craig C

2009-12-21

136

Adaptive locomotor training on an end-effector gait robot: evaluation of the ground reaction forces in different training conditions.  

PubMed

The main goal of robotic gait rehabilitation is the restoration of independent gait. To achieve this goal different and specific patterns have to be practiced intensively in order to stimulate the learning process of the central nervous system. The gait robot G-EO Systems was designed to allow the repetitive practice of floor walking, stair climbing and stair descending. A novel control strategy allows training in adaptive mode. The force interactions between the foot and the ground were analyzed on 8 healthy volunteers in three different conditions: real floor walking on a treadmill, floor walking on the gait robot in passive mode, floor walking on the gait robot in adaptive mode. The ground reaction forces were measured by a Computer Dyno Graphy (CDG) analysis system. The results show different intensities of the ground reaction force across all of the three conditions. The intensities of force interactions during the adaptive training mode are comparable to the real walking on the treadmill. Slight deviations still occur in regard to the timing pattern of the forces. The adaptive control strategy comes closer to the physiological swing phase than the passive mode and seems to be a promising option for the treatment of gait disorders. Clinical trials will validate the efficacy of this new option in locomotor therapy on the patients. PMID:22275689

Tomelleri, Christopher; Waldner, Andreas; Werner, Cordula; Hesse, Stefan

2011-01-01

137

Experimental determination of the yield of pyrolysis products of polyethene and polypropene. Influence of reaction conditions  

SciTech Connect

The influence of temperature, residence time, concentration level of reactants and products, polymer type, and composition of the polymer mixture on the product spectra obtained from pyrolysis of polyethene (PE) and polypropene (PP) was determined. In the study the temperature was varied between 650 and 850 C, whereas residence times between 0.1 and 1 s were used. Thermodynamic calculations revealed that aromatics and methane are formed as the main products under conditions pertaining to chemical equilibrium. The ratio between these compounds is governed by the C/H ratio in the original polymer. Experiments were performed using a tubular reactor. The main products of the pyrolysis of PE and PP at 750 C and a residence time of 1 s are ethene (respectively 45 and 19 wt%), propene (24 and 45 wt%), and butene (23 and 27 wt%). At higher reactor temperatures the yields of ethane and methane increase, while the yields of both propene and butene decrease. The influences of the residence time, product concentration, polymer type, and composition of the polymer mixture on the product distribution are negligible compared to the influence of temperature.

Westerhout, R.W.J.; Kuipers, J.A.M.; Swaaij, W.P.M. van [Univ. of Twente, Enschede (Netherlands). Faculty of Chemical Engineering] [Univ. of Twente, Enschede (Netherlands). Faculty of Chemical Engineering

1998-03-01

138

A quantitative method for assessing of the affective component of the pain: conditioned response associated with CO 2 laser-induced nocifensive reaction  

Microsoft Academic Search

Sensory and affective components are included in the overall behavioral manifestation in a nocifensive reaction. We have developed a behavioral model using classical conditioning to differentiate the affective component from the sensory responses following a thermal noxious stimulus. In laser-pain conditioning, free moving rats were trained to associate a tone (conditioned stimulus, CS) and short CO2 laser pulsation (unconditioned stimulus,

Bai-Chuang Shyu; Sin-Chee Chai; Jen-Chuang Kung; Ruey-Jane Fan

2003-01-01

139

Investigation of influence of hypomagnetic conditions closely similar to interplanetary magnetic filed on behavioral and vegetative reactions of higher mammals  

NASA Astrophysics Data System (ADS)

To study the influence of long being under reduced magnetic field on behavioral and vegetative reactions of higher mammals the white rat males were put into the 700-1000 times reduced geomagnetic field (50-70 nT) for 25 days. Such field was obtained by using automatic compensation of the horizontal and vertical components of the GMF at a frequencies up to 10 Hz by means of solenoids of the experimental magnetic system. Control animals were located in the same room under usual laboratory GMF conditions (52 uT). Two days before the experiment the behavioral reactions were studied in the "open field" by means of a set of tests, characterizing the level of emotionality, moving and orientational-investigative activities of the animals under conditions of unimpeded behavior. 60 white underbred rat males with the initial body mass of 200 g were divided into three clusters. Animals with average indices were selected for the experiment. We have judged behavioral reaction disturbances of the rats under hypomagnetic conditions using videotape recordings carried out in the entire course of the chronic experiment. According to the obtained results during the period of maximum activity (from 230 to 330 a.m.) the number of interrelations between the individuals increased appreciably for experimental rats including interrelations with aggressive character. This was real during all 25 days of observation. We observed a certain dynamics of this index differed from that of the control group. We have also analyzed the final period of observation from the 21th to the 25th days. In this period we studied the 24 hours' dynamics of interrelations which were noted during 5 minutes in every hour around the clock. In the control group the number of interrelation was at a constantly low level. For experimental animals the number of interrelations was higher in the night hours than in the day ones. Moreover it exceeded the similar indexes observed from the 1st to the 20th day. For example from 300 to 305 a.m. on the 23th day we recorded 27 contacts of aggressive character between the individuals. So, in hypomagnetic field conditions the irritability of the animals' central nervous system grows, that expresses itself in the increase of contacts of aggressive and non-aggressive character between the individuals. Also we have carried out the Spirman correlation analysis between studied indices of moving activity and chemiluminescence of blood plasma and urine, electrolytic composition of urine and muscles. For control animals the quantity of correlation connections between electrolyte concentrations in studied substrata was higher than for experimental animals. The physiological sense of these correlation connections is discussed.

Krivova, Natalie; Trukhanov, Kiril; Zamotshina, Tatyana; Zaeva, Olga; Khodanovich, Marina; Misina, Tatyana; Tukhvatulin, Ravil; Suhko, Valery

140

Evolution of fracture permeability through fluid rock reaction under hydrothermal conditions  

NASA Astrophysics Data System (ADS)

We report flow-through experiments on a natural fracture in novaculite under moderate effective stresses (˜ 1.4 MPa) and temperatures (20-120 °C) to examine the effect on flow and transport characteristics. The efflux of fluid and dissolved minerals were measured throughout the 3150-h experiment. After the experiment the fracture was imaged by X-ray CT, impregnated with Wood's metal, and a cast recovered of the Wood's metal-filled fracture. These measurements constrain the evolution of fracture structure, and the change in permeability that resulted from stress- and temperature-dependent dissolution at both propping asperities and fracture void surfaces. During the first 1500 h, the aperture of one fracture decreased from 18.5 to 7.5 ?m, when it was loaded with constant effective stress of 1.4 MPa, at room temperature, and a flow rate decreasing with time from 1 to 0.0625 mL/min. This reduction is attributed to the removal of mineral mass from bridging asperities. After 1500 h the fracture aperture increased, ultimately reaching 13 ?m. Apparently the dominant dissolution process switched from prop removal to etching of the void surfaces. We used X-ray CT images, digital radiographs, and fracture casts as independent methods to constrain the resulting architecture of the evolved fracture porosity, and developed a simple process-based model to examine the relative roles of asperity removal and free-face dissolution. The comparison of the model with the measurements identifies the relative importance of mass removal at fracture faces and at propping asperities. The experiments underscore the importance of dissolution in determining the sense, the rates and the magnitude of permeability-enhancement within rock fractures stimulated by chemical permeants in geothermal and petroleum reservoirs, and to a lesser degree under natural conditions pushed far-from-equilibrium.

Yasuhara, Hideaki; Polak, Amir; Mitani, Yasuhiro; Grader, Abraham S.; Halleck, Phillip M.; Elsworth, Derek

2006-04-01

141

Green chemistry: a facile synthesis of polyfunctionally substituted thieno[3,4-c]pyridinones and thieno[3,4-d]pyridazinones under neat reaction conditions.  

PubMed

A facile, solvent free, ecofriendly approach for the synthesis of pyridine-2,6-diones 4a-d, pyridazinone derivatives 8a-c and thienoazines 6 and 9 is herein described employing neat reaction conditions under both microwave and ultrasound irradiations. This solventless methodology is environmentally benign as it completely eliminates the use of solvent from the reaction procedure. PMID:20064736

Al-Zaydi, Khadijah M; Borik, Rita M; Mekheimer, Ramadan A; Elnagdi, Mohamed H

2010-06-01

142

Personnel Reactions to Incentives, Naval Conditions and Experiences (PRINCE): Demographic and Background Information, Expectations, Attitudes, Values and Motivations of New Recruits.  

National Technical Information Service (NTIS)

As part of a longitudinal study of the reactions of enlisted personnel incentives, Naval conditions and experiences, information on backgrounds, expectations, attitudes, values and motivations were obtained at entry into the Navy from 6,795 recruits in Ca...

A. Katz

1971-01-01

143

Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions  

NASA Astrophysics Data System (ADS)

Chamber studies of glyoxal uptake onto ammonium sulphate aerosol were performed under dark and irradiated conditions to gain further insight into processes controlling glyoxal uptake onto ambient aerosol. Organic fragments from glyoxal dimers and trimers were observed within the aerosol under dark and irradiated conditions. Glyoxal monomers and oligomers were the dominant organic compounds formed under the conditions of this study; glyoxal oligomer formation and overall organic growth were found to be reversible under dark conditions. Analysis of high-resolution time-of-flight aerosol mass spectra provides evidence for irreversible formation of carbon-nitrogen (C-N) compounds in the aerosol. We have identified 1H-imidazole-2-carboxaldehyde as one C-N product. To the authors' knowledge, this is the first time C-N compounds resulting from condensed phase reactions with ammonium sulphate seed have been detected in aerosol. Organosulphates were not detected under dark conditions. However, active photochemistry was found to occur within aerosol during irradiated experiments. Carboxylic acids and organic esters were identified within the aerosol. An organosulphate, which had been previously assigned as glyoxal sulphate in ambient samples and chamber studies of isoprene oxidation, was observed only in the irradiated experiments. Comparison with a laboratory synthesized standard and chemical considerations strongly suggest that this organosulphate is glycolic acid sulphate, an isomer of the previously proposed glyoxal sulphate. Our study shows that reversibility of glyoxal uptake should be taken into account in SOA models and also demonstrates the need for further investigation of C-N compound formation and photochemical processes, in particular organosulphate formation.

Galloway, M. M.; Chhabra, P. S.; Chan, A. W. H.; Surratt, J. D.; Flagan, R. C.; Seinfeld, J. H.; Keutsch, F. N.

2009-05-01

144

Stress response in Pectobacterium atrosepticum SCRI1043 under starvation conditions: adaptive reactions at a low population density.  

PubMed

The adaptive reactions of plant pathogenic bacterium Pectobacterium atrosepticum SCRI1043 under starvation conditions were studied. The main emphasis was given to the peculiarities of stress responses depending on the bacterial population densities. When bacteria were subjected to starvation at high population densities (10(7)-10(9) CFU ml(-1)), their adaptive reactions conformed to the conventional conception of bacterial adaptation related to autolysis of part of the population, specific modification of cell ultrastructure, activation of expression of stress responsive genes and acquiring cross protection against other stress factors. In contrast, at low initial population densities (10(3)-10(5) CFU ml(-1)), as described in our recent work, the cell density increased due to multiple cell division despite the absence of exogenous growth substrate. Here we present data that demonstrate that such unconventional behavior is part of a stress response, which provides increased stress tolerance while retaining virulence. Cell morphology and gene expression in high- and low-cell-density starving Pba cultures were compared. Our investigation demonstrates the existence of alternative adaptive strategies enabling pathogenic bacteria to cope with a variety of stress factors, including starvation, especially necessary when residing outside of their host. PMID:24300393

Petrova, Olga; Gorshkov, Vladimir; Daminova, Amina; Ageeva, Marina; Moleleki, Lucy N; Gogolev, Yuri

2014-01-01

145

ACCURATE TIME-DEPENDENT WAVE PACKET STUDY OF THE H{sup +}+LiH REACTION AT EARLY UNIVERSE CONDITIONS  

SciTech Connect

The dynamics and kinetics of the H{sup +} + LiH reaction have been studied using a quantum reactive time-dependent wave packet (TDWP) coupled-channel quantum mechanical method on an ab initio potential energy surface at conditions of the early universe. The total reaction probabilities for the H{sup +} + LiH(v = 0, j = 0) {yields} H{sup +} {sub 2} + Li process have been calculated from 5 Multiplication-Sign 10{sup -3} eV up to 1 eV for total angular momenta J from 0 to 110. Using a Langevin model, integral cross sections have been calculated in that range of collision energies and extrapolated for energies below 5 Multiplication-Sign 10{sup -3} eV. The calculated rate constants are found to be nearly independent of temperature in the 10-1000 K interval with a value of Almost-Equal-To 10{sup -9} cm{sup 3} s{sup -1}, which is in good agreement with estimates used in evolutionary models of the early universe lithium chemistry.

Aslan, E.; Bulut, N. [Department of Physics, Firat University, 23169 Elazig (Turkey); Castillo, J. F.; Banares, L.; Aoiz, F. J. [Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas (Unidad Asociada CSIC), Universidad Complutense de Madrid, 28040 Madrid (Spain); Roncero, O., E-mail: jfernand@quim.ucm.es [Instituto de Fisica Fundamental, CSIC, C/Serrano 123, E-28006 Madrid (Spain)

2012-11-01

146

A relevant coupled particle-tracking solution for network reaction and multirate mass transfer under heterogeneous conditions  

NASA Astrophysics Data System (ADS)

Considering complex physical and reactive processes is necessary to a trustable plume behavior prediction. However, complexity is often synonym of inefficiency and numerical problem for existing model. We present an efficient particle method to simulate plumes evolution moved by advection-dispersion and affected by network reactions and multirate-mass transfer processes under heterogeneous spatial conditions. The stochastic approach is based on the derivation of the probability that a particle being at a certain position, specie and mobility zone will move into another specie and/or zone. Transport processes are fully coupled with reactions. The particle method is free of numerical dispersion and overcomes the inherent numerical problems stemming from the incorporation of heterogeneities into reactive transport codes based on Eulerian approaches. Even if the method aims to be universal, we show that analytical solutions can be provided for the simpler cases, which may improve consequently the model efficiency. Illustratively, we apply our method to model the sequential degradation of chlorinated solvents (PCE ? TCE ? DCE ? VC ? 0) into a finely discretized field and show how spatially variable coefficients of hydraulic permeability, bio-decay and mass transfer affect the spatial and temporal behavior of the four reactive plumes.

Henri, Christopher; Fernàndez-Garcia, Daniel

2013-04-01

147

H2S-CO2 Reaction with Hydrated Class H Well Cement under Geologic Sequestration Conditions  

NASA Astrophysics Data System (ADS)

The technology to inject CO2 into geological formations is available and practiced at several locations in the world, e.g. Sleipner, Norway and the Weyburn project in Alberta, Canada. In addition to CO2, acid gas (a mixture of CO2 and H2S) injection is also currently employed and on the rise. For example, there are currently over 40 wells used for acid gas injection in Alberta, Canada. Few studies address the physical and chemical characteristics of well cement exposed to acid gas under geologic sequestration conditions. The objective of this study is to determine how oilwell cement is affected by the addition of H2S in a CO2 injection scenario. Laboratory experiments have been performed in order to determine the physical and chemical changes in cement exposed to acid gas vs. pure CO2 under simulated sequestration reservoir conditions, including both aqueous and supercritical CO2. Obvious differences were observed between the H2S-CO2 and CO2-only exposed cement. Differences were also observed between the submerged and headspace exposed portions of the samples. The H2S-CO2 exposed cement underwent a combination of carbonation and redox reactions that ultimately affected the physical properties. The outer rim of the cylindrical cement samples were characterized by a zone of carbonation and the sulfidation of tetracalcium aluminoferrites to pyrite. Beyond the carbonation rim is evidence of significant impact from the H2S in the form of ettringite and very small grains of pyrite. Ettringite is formed due to oxidation of H2S which produces sulfides which in turn reacts with Ca-compounds. The carbonation reaction lowers the pH in the cement matrix to allow dissolution of ettringite and the tetracalcium aluminoferrite for pyrite formation. Implications regarding geologic co-sequestration and wellbore integrity are significant.

Kutchko, B. G.; Hawthorne, S.; Strazisar, B. R.; Miller, D.

2009-12-01

148

Reaction and transport in wellbore interfaces under CO2 storage conditions: Experiments simulating debonded cement-casing interfaces  

NASA Astrophysics Data System (ADS)

Debonding-defects at the interfaces between wellbore casing and cement are widely recognized as providing potential pathways for CO2 escape from geological storage systems. This study addresses how chemical reaction between CO2, cement and steel may affect the transport properties of such defects under near-static conditions, representative for early stages in leakage pathway development, prior to the formation of a fully connected defect network. Debonded cement-steel interfaces were simulated by constructing composite samples, containing a spacer-imposed gap. These were reacted with CO2 and water, brine or a solution pre-saturated with cement. Each sample was subjected to 7 sequential batch reaction runs, namely 6 runs of 5 days duration, followed by a single extended run, of 42 days, to study long-term effects. The reaction runs were conducted at 80°C and 14 MPa applied CO2-pressure. Permeability was measured after each run and microstructural analyses were performed after completion of the experiment. We investigated two ranges in gap-width, namely 50-120 ?m (denoted SA samples) and 270-350 ?m (LA samples). Reaction-induced permeability changes were limited and less than 1 order in all samples, and occurred in the early stage of testing. Corrosion product or scale (mainly Fe-carbonates, with minor Fe-hydroxides) formed extensively within the open gap, on the surfaces of both the casing steel and cement. Lack of calcium carbonates in these areas suggests the corrosion scale which formed on the cement surface produced a significant reduction in cement carbonation rate, similar to the decrease in corrosion rate observed when these precipitates create a protective film on steel surfaces only. CaCO3 precipitation occurred extensively on the cement side at locations beneath the spacers used to create the gap between the cement and steel plates, where corrosion scale did not form. Our results imply that healing of debonding defects at casing-cement interfaces in wellbores will be slower and less effective than healing of fractures in cement under comparable, near-static conditions, due to the formation of thin corrosion scale films on the cement surfaces. These films inhibit release of calcium from the cement into the aperture and impede the precipitation of calcium carbonates that was previously found to promote sealing in fractured cement when only local transport is possible. If thin corrosion scale films of the type observed in our experiments form in real wellbore systems, local small debonding defects (gaps less than a few tens of micrometres) can be expected to heal due to clogging by corrosion scale film. In larger debonding defects, where scale film development is insufficient to produce sealing, their retarding effect on further reaction has the potential to maintain an open interfacial pathway, should long-range connectivity and transport ensue. It is, therefore, important to incorporate the effects of early corrosion scale film development in future analyses of long-range leakage pathways along cement-casing interfaces.

Wolterbeek, T. K.; Peach, C. J.; Spiers, C. J.

2013-12-01

149

Charge distribution analysis of catalysts under simulated reaction conditions. Final report, October 1, 1993--June 30, 1995  

SciTech Connect

A new technique has been developed to measure mobile charge carriers in dielectric materials, insulators and catalysts. The technique, Charge Distribution Analysis, is based on the measurement of the dielectric polarization in an electric field gradient, contact-free, at 0 Hertz under minimum perturbation conditions. The measured parameter is the force F{sup +-} experienced by the sample in a gradient of reversible polarity. CDA allows to determine the sign of the majority charge carriers and the density of surface charges which may be correlated to the chemical or catalytic activity. Throughout this work a microbalance has been used as a force-sensing device. CDA can be applied to any dielectric material, compact or porous, in inert or reactive and corrosive gas environments. To conduct CDA experiments under simulated reaction conditions that are relevant to coal liquefaction research, e.g. in reactive and in part chemically corrosive atmospheres, several modifications were introduced to the current design. In particular, the stainless steel sample chamber and furnace/electrode assembly were built, and the gas flow system was redesigned. The CDA instrument was equipped with new data acquisition capabilities. Tests were performed in inert gases and in reactive and corrosive atmosphere between ambient temperature and 500{degrees}C on iron oxide and partially sulfidized iron oxide catalysts as well as on pyrite (FeS{sub 2}) single crystals.

Freund, F.

1996-02-01

150

Highly Regio- and Stereoselective Diels-Alder Cycloadditions via Two-Step and Multicomponent Reactions Promoted by Infrared Irradiation under Solvent-Free Conditions  

PubMed Central

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1–3 with the Knoevenagel adducts 4–6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13–17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13–16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations.

Flores-Conde, Maria Ines; Reyes, Leonor; Herrera, Rafael; Rios, Hulme; Vazquez, Miguel A.; Miranda, Rene; Tamariz, Joaquin; Delgado, Francisco

2012-01-01

151

CO2 reaction with hydrated class H well cement under geologic sequestration conditions: effects of flyash admixtures.  

PubMed

The rate and mechanism of reaction of pozzolan-amended Class H cement exposed to both supercritical CO2 and CO2-saturated brine were determined under geologic sequestration conditions to assess the potential impact of cement degradation in existing, wells on CO2 storage integrity. The pozzolan additive chosen, Type F flyash, is the most common additive used in cements for well sealing in oil-gas field operations. The 35:65 and 65:35 (v/v) pozzolan-cement blends were exposed to supercritical CO2 and CO2-saturated brine and underwent cement carbonation. Extrapolation of the carbonation rate for the 35:65 case suggests a penetration depth of 170-180 mm for both the CO2-saturated brine and supercritical CO2 after 30 years. Despite alteration in both pozzolan systems, the reacted cement remained relatively impermeable to fluid flow after exposure to brine solution saturated with CO2, with values well below the American Petroleum Institute recommended maximum well cement permeability of 200 microD. Analyses of 50: 50 pozzolan-cement cores from a production well in a sandstone reservoir exhibited carbonation and low permeability to brine solution saturated with CO2, which are consistent with our laboratory findings. PMID:19544912

Kutchko, Barbara G; Strazisar, Brian R; Huerta, Nicolas; Lowry, Gregory V; Dzombak, David A; Thaulow, Niels

2009-05-15

152

Clean bio-oil production from fast pyrolysis of sewage sludge: effects of reaction conditions and metal oxide catalysts.  

PubMed

Fast pyrolysis of sewage sludge was carried out under different reaction conditions, and its effects on bio-oil characteristics were studied. The effect of metal oxide catalysts on the removal of chlorine in the bio-oil was also investigated for four types of catalysts. The optimal pyrolysis temperature for bio-oil production was found to be 450 degrees C, while much smaller and larger feed sizes adversely influenced production. Higher flow and feeding rates were more effective but did not greatly affect bio-oil yields. The use of the product gas as the fluidizing medium gave an increased bio-oil yield. Metal oxide catalysts (CaO and La2O3) contributed to a slight decrease in bio-oil yield and an increase in water content but were significantly effective in removal of chlorine from the bio-oil. The fixed catalyst bed system exhibited a higher removal rate than when metal oxide-supported alumina was used as the fluidized bed material. PMID:19635664

Park, Hyun Ju; Heo, Hyeon Su; Park, Young-Kwon; Yim, Jin-Heong; Jeon, Jong-Ki; Park, Junhong; Ryu, Changkook; Kim, Seung-Soo

2010-01-01

153

Gas-phase proton transfer reactions involving multiply charged cytochrome c ions and water under thermal conditions  

Microsoft Academic Search

Investigations of gas-phase proton transfer reactions have been performed on protein molecular ions generated by electrospray\\u000a ionization (ESI). Their reactions were studied in a heated capillary inlet\\/reactor prior to expansion into a quadrupole mass\\u000a spectrometer. Results from investigations involving protonated horse heart cytochrome c and H, O suggest that Coulombit effects\\u000a can lower reaction barriers as well as aid in

Brian E. Winger; Karen J. Light-Wahl; Richard D. Smith

1992-01-01

154

Effect of reaction conditions on the catalytic performance of H 3 PW 12 O 40 heteropolyacid catalyst in the direct preparation of dichloropropanol from glycerol in a liquid-phase batch reactor  

Microsoft Academic Search

Direct chlorination of glycerol to dichloropropanol (DCP) was conducted in a liquid-phase batch rector using homogeneous H3PW12O40 heteropolyacid (HPA) catalyst. The effect of reaction conditions (reaction time, reaction pressure, reaction temperature,\\u000a and catalyst amount) on the catalytic performance of H3PW12O40 in the direct preparation of DCP from glycerol was examined. The optimum reaction pressure and reaction temperature were\\u000a found to

Sang Hee Lee; Dong Ryul Park; Heesoo Kim; Joohyung Lee; Ji Chul Jung; Sung Yul Woo; Won Seob Song; Myong Suk Kwon; In Kyu Song

2008-01-01

155

Acetamide hydrolyzing activity of Bacillus megaterium F-8 with bioremediation potential: Optimization of production and reaction conditions.  

PubMed

Bacillus megaterium F-8 exhibited an intracellular acetamide hydrolyzing activity (AHA) when cultivated in modified nutrient broth with 3 % tryptone, 1.5 % yeast extract, and 0.5 % sodium chloride, at pH 7.2, 45 °C for 24 h. Maximum AHA was recorded in the culture containing 0.1 M of sodium phosphate buffer, (pH 7.5) at 45 °C for 20 min with 0.2 % of acetonitrile and resting cells of B. megaterium F-8 equivalent to 0.2 ml culture broth. This activity was stable up to 55 °C and was completely inactivated at or above 60 °C. Maximum acyl transferase activity (ATA) was recorded in the reaction medium containing 0.1 M of potassium phosphate buffer, (pH 8.0) at 55 °C for 5 min with 0.85 mM of acetamide as acyl donor and hydroxylamine hydrochloride as acyl acceptor and resting cells of B. megaterium F-8 equivalent to 0.94 mg cells (dry weight basis). This activity was stable up to 60 °C and a rapid decline in enzyme activity was recorded above it. Under the optimized conditions, this organism hydrolyzed various nitriles and amides such as propionitrile, propionamide, caprolactam, acetamide, and acrylamide to corresponding acids. Acyl group transfer capability of this organism was used for the production of acetohydroxamic acid. ATA of B. megaterium F-8 showed broad substrate specificity such as for acetamide followed by propionamide, acrylamide, and lactamide. This amide hydrolyzing and amidotransferase activity of B. megaterium F-8 has potential applications in enzymatic synthesis of hydroxamic acids and bioremediation of nitriles and amides contaminated soil and water system. PMID:24723348

Sogani, Monika; Bakre, Prakash P; Mathur, Nupur; Sharma, Pratibha; Bhatnagar, Pradeep

2014-07-01

156

Amberlyst-15: An efficient reusable heterogeneous catalyst for aza-Michael reactions under solvent-free conditions  

Microsoft Academic Search

The aza-Michael reactions of amines with ?,?-unsaturated carbonyl and nitrile compounds have efficiently been carried out at room temperature using Amberlyst-15 as a heterogeneous reusable catalyst. The products were formed in short reaction times and in high yields.

Biswanath Das; Nikhil Chowdhury

2007-01-01

157

The use of a microreactor for rapid screening of the reaction conditions and investigation of the photoluminescence mechanism of carbon dots.  

PubMed

A microreactor is applied and reported, for the first time, in the field of research of carbon dots (CDs), including rapid screening of the reaction conditions and investigation of the photoluminescence (PL) mechanism. Various carbonaceous precursors and solvents were selected and hundreds of reaction conditions were screened (ca. 15?min on average per condition). Through analyzing the screened conditions, tunable PL emission maxima, from about 330 to 550?nm with respectable PL quantum yields, were achieved. Moreover, the relationship between different developmental stages of the CDs and the PL properties was explored by using the microreactor. The PL emission was observed to be independent of the composition, carbonization extent, and morphology/size of the CDs. This study unambiguously presents that a microreactor could serve as a promising tool for the research of CDs. PMID:24623603

Lu, Yue; Zhang, Ling; Lin, Hengwei

2014-04-01

158

The zinc iodide-osmium tetroxide (ZIO) reaction on nerve endings in the median eminence of the rat under normal and experimental conditions  

Microsoft Academic Search

The reaction of nerve endings in the median eminence of the rat to zinc iodide-osmium tetroxide (ZIO) staining was examined electron microscopically under normal and experimental conditions. The experimental condition of catecholamine exhaustion in the nerve endings was induced by the administration of H44\\/68 and reserpine. Vesicles in the terminals of catecholaminergic nerves reacted similarly to ZIO staining in both

T. Matsuura; Y. Ibata; Y. Sano

1976-01-01

159

Efficient batch and continuous flow Suzuki cross-coupling reactions under mild conditions, catalysed by polyurea-encapsulated palladium (II) acetate and tetra-n-butylammonium salts.  

PubMed

Suzuki cross-coupling reactions are effected in both conventional organic solvents, under continuous flow conditions at 70 degree C, and in batch mode in supercritical carbon dioxide (scCO2), at temperatures as low as 40 degrees C in the presence of palladium(II) acetate microencapsulated in polyurea [PdEnCat] and tetra-n-butylammonium salts. PMID:15846438

Lee, Connie K Y; Holmes, Andrew B; Ley, Steven V; McConvey, Ian F; Al-Duri, Bushra; Leeke, Gary A; Santos, Regina C D; Seville, Jonathan P K

2005-04-28

160

Direct one-pot conversion of acylated carbohydrates into their alkylated derivatives under heterogeneous reaction conditions using solid NaOH and a phase transfer catalyst  

Microsoft Academic Search

A convenient one-pot protocol for the direct conversion of acyl-protected carbohydrates into their alkylated counterparts has been developed by using alkyl halides in the presence of solid sodium hydroxide and a phase transfer catalyst. These economically convenient, mild, two-phase reaction conditions allow the preparation of a variety of monosaccharide intermediates for use in the synthesis of complex oligosaccharides.

Soni Kamlesh Madhusudan; Geetanjali Agnihotri; Devendra S. Negi; Anup Kumar Misra

2005-01-01

161

HIGHLY DIASTEREOSELECTIVE MICHAEL REACTION UNDER SOLVENT-FREE CONDITIONS USING MICROWAVES: CONJUGATE ADDITION OF FLAVANONE TO ITS CHALCONE PRECURSOR  

EPA Science Inventory

Microwave-assisted reaction of 2'-hydroxychalcones in the presence of DBU resulted in the formation of hitherto unknown dimers by conjugate addition of the intermediate cyclic ketone to the starting enone....

162

Direct ethanol fuel cell (DEFC): Electrical performances and reaction products distribution under operating conditions with different platinum-based anodes  

Microsoft Academic Search

Ethanol electro-oxidation at different Pt-based electrodes was investigated in a single direct ethanol fuel cell (DEFC) in terms of reaction product distribution depending on the anode catalyst. In DEFC experiments, only three reaction products were detected using HPLC: acetaldehyde (AAL), acetic acid (AA) and CO2. The addition of tin to platinum increases the activity of the catalyst by several order

S. Rousseau; C. Coutanceau; C. Lamy; J.-M. Léger

2006-01-01

163

Enhancement of reaction conditions for the radiolabelling of DOTA-peptides with high activities of yttrium-90  

Microsoft Academic Search

Peptide receptor radionuclide therapy (PRRT) has recently expanded due to radiolabelling of DOTA-peptides, such as the somatostatin analogues [DOTA0, Tyr3]octreotate (DOTATATE).The achievement of high specific activities during procedures has been indicated as the critical factor to consent effective therapy. Several radiochemical factors may negatively impact reaction procedures such as pH, temperature and time of reaction. Our study was undertaken to

Anna Nardelli; Elena Castaldi; Giovanni Ortosecco; Antonio Speranza; Giovanni Storto; Leonardo Pace; Marco Salvatore

2011-01-01

164

An experimental investigation of the reaction of hydrogen chloride with lead oxide under simulated hazardous waste incineration conditions  

SciTech Connect

To simulate the behavior of lead during hazardous waste incineration, pellets of sintered lead oxide were treated with hydrogen chloride at concentrations of 2000 and 4000 ppm in air in a laboratory tube furnace. The chemical reaction kinetics and mass transfer properties of the solid-gas and solid-liquid reactions were examined at temperatures between 260 and 680{degrees}C. Lead dichloride was found to form and became more volatile at elevated temperatures. At temperatures above 300{degrees}C, chemical reaction kinetic limitations were absent and mass transfer resistance in the developing liquid lead oxide, lead dichloride eutectic phases were controlling. Above 590{degrees}C, a curious anomaly occurred: The observed global reaction rate appeared to increase slightly while the volatilization of lead dichloride dropped during the initial stages of the reaction. A thick film of a lead oxychloride compound was found which displayed low lead dichloride activity. Below 590{degrees}C, a different lead oxychloride compound was identified by x-ray diffraction in which lead dichloride activity was high, and this compound was much more volatile than the oxychloride formed above 5900{degrees}C.

Shor, J.T. [Oak Ridge National Lab., TN (United States); Frazier, G.C. [Univ. of Tennessee, Knoxville, TN (United States)

1996-04-01

165

How Pragmatic Interpretations Arise from Conditionals: Profiling the Affirmation of the Consequent Argument with Reaction Time and EEG Measures  

ERIC Educational Resources Information Center

Conditional reasoning consists in combining a conditional premise with a categorical premise and inferring a conclusion from them. Two well-known conditional arguments are Modus Ponens (MP: "If P then Q; P//"therefore Q), which is logically valid and Affirmation of the Consequent (AC: "If P then Q; Q//"therefore "P"), which is not. The latter is…

Bonnefond, Mathilde; Van der Henst, Jean-Baptiste; Gougain, Marion; Robic, Suzanne; Olsen, Matthew D.; Weiss, Oshri; Noveck, Ira

2012-01-01

166

A novel system for in-situ observations of early hydration reactions in wet conditions in conventional SEM  

SciTech Connect

A novel system enabling wet microscopy in conventional SEM is described and its performance for in-situ study of hydration reactions is demonstrated. The technology is based on a sealed specimen capsule, which is protected from the microscope vacuum by an electron-transparent partition membrane. Thus, the wet sample can be placed and observed in a 'conventional' SEM without the need for drying or employing environmental SEM. Early hydration reactions of gypsum and cement systems were followed during the first 24 h.

Katz, A. [National Building Research Institute, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology, Haifa (Israel); Bentur, A. [National Building Research Institute, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology, Haifa (Israel)]. E-mail: bentur@tx.technion.ac.il; Kovler, K. [National Building Research Institute, Faculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology, Haifa (Israel)

2007-01-15

167

A reaction cell with sample laser heating for in situ soft X-ray absorption spectroscopy studies under environmental conditions.  

PubMed

A miniature (1 ml volume) reaction cell with transparent X-ray windows and laser heating of the sample has been designed to conduct X-ray absorption spectroscopy studies of materials in the presence of gases at atmospheric pressures. Heating by laser solves the problems associated with the presence of reactive gases interacting with hot filaments used in resistive heating methods. It also facilitates collection of a small total electron yield signal by eliminating interference with heating current leakage and ground loops. The excellent operation of the cell is demonstrated with examples of CO and H2 Fischer-Tropsch reactions on Co nanoparticles. PMID:23592631

Escudero, Carlos; Jiang, Peng; Pach, Elzbieta; Borondics, Ferenc; West, Mark W; Tuxen, Anders; Chintapalli, Mahati; Carenco, Sophie; Guo, Jinghua; Salmeron, Miquel

2013-05-01

168

LENGTH-HETEROGENEITY POLYMERASE CHAIN REACTION (LH-PCR) AS AN INDICATOR OF STREAM SANITARY AND ECOLOGICAL CONDITION: OPTIMAL SAMPLE SIZE AND HOLDING CONDITIONS  

EPA Science Inventory

The use of coliform plate count data to assess stream sanitary and ecological condition is limited by the need to store samples at 4oC and analyze them within a 24-hour period. We are testing LH-PCR as an alternative tool to assess the bacterial load of streams, offering a cost ...

169

Indene formation under single-collision conditions from the reaction of phenyl radicals with allene and methylacetylene--a crossed molecular beam and ab initio study.  

PubMed

Polycyclic aromatic hydrocarbons (PAHs) are regarded as key intermediates in the molecular growth process that forms soot from incomplete fossil fuel combustion. Although heavily researched, the reaction mechanisms for PAH formation have only been investigated through bulk experiments; therefore, current models remain conjectural. We report the first observation of a directed synthesis of a PAH under single-collision conditions. By using a crossed-molecular-beam apparatus, phenyl radicals react with C(3)H(4) isomers, methylacetylene and allene, to form indene at collision energies of 45 kJ mol(-1). The reaction dynamics supported by theoretical calculations show that both isomers decay through the same collision complex, are indirect, have long lifetimes, and form indene in high yields. Through the use of deuterium-substituted reactants, we were able to identify the reaction pathway to indene. PMID:21956874

Parker, Dorian S N; Zhang, Fangtong; Kaiser, Ralf I; Kislov, Vadim V; Mebel, Alexander M

2011-11-01

170

Further evaluation of ELSTAR (Environmental Lagrangian Simulator of Transport and Atmospheric Reactions) in Los Angeles under different meteorological conditions  

Microsoft Academic Search

This report describes the further evaluation of the ELSTAR model (Environmental Lagrangian Simulator of Transportation and Atmospheric Reactions) in the Los Angeles basin. The model is applied to six days: three within the period of the Los Angeles Reactive Pollutant Program (LARPP), two ozone (Oâ) episode days, and one nitrogen dioxide (NOâ) episode day. Comparisons were focused on the observed

D. Godden; F. Lurmann; A. Lloyd; B. Nitta; C. Kwan

1980-01-01

171

Molecularly imprinted soluble nanogels as a peroxidase-like catalyst in the oxidation reaction of homovanillic acid under aqueous conditions  

Microsoft Academic Search

A novel type of soluble peroxidase-like imprinted nanogels incorporating hemin, acrylamide and 4-vinylpyridine as functional monomers was prepared by solution polymerization method. Such highly crosslinked nanogels could be conveniently separated from the reaction mixture through precipitation, ultracentrifugation or ultrafiltration, whereby they could be analyzed by gel permeation chromatography (GPC), transmission electron microscopy (TEM), dynamic light scattering (DLS) and environmental scanning

Zhiyong Chen; Zhendong Hua; Jun Wang; Yuan Guan; Meiping Zhao; Yuanzong Li

2007-01-01

172

Simulation Chamber Studies of the Atmospheric Oxidation of 2Methyl3-Buten-2-ol: Reaction with Hydroxyl Radicals and Ozone Under a Variety of Conditions  

Microsoft Academic Search

This article presents a complete study of the diurnal chemical reactivity of the biogenic volatile organic compound (BVOC),\\u000a 2-methyl-3-buten-2-ol (MBO) in the troposphere. Reactions of MBO with OH and with ozone were studied to analyse the respective\\u000a parts of both processes in the global budget of MBO atmospheric reactivity. They were investigated under controlled conditions\\u000a for pressure (atmospheric pressure) and

N. Carrasco; J. F. Doussin; M. O’Connor; J. C. Wenger; B. Picquet-Varrault; R. Durand-Jolibois; P. Carlier

2007-01-01

173

Determination of kinetic parameters for the water–gas shift reaction on copper catalysts under realistic conditions for fuel cell applications  

Microsoft Academic Search

The kinetic parameters for water–gas shift reaction on Cu-based catalysts were measured under fuel reformer conditions for fuel cell applications (7% CO, 8.5% CO2, 22% H2O, 37% H2, and 25% Ar) at 1 atm total pressure and temperature in the range of 200°C. The rate per unit of Cu surface area at the stated concentrations was 0.8×10?6 molm?2s?1 at 200°C.

N. A. Koryabkina; A. A. Phatak; W. F. Ruettinger; R. J. Farrauto; F. H. Ribeiro

2003-01-01

174

Reactions of Peroxynitrite with Uric Acid: Formation of Reactive Intermediates, Alkylated Products and Triuret, and In Vivo Production of Triuret Under Conditions of Oxidative Stress  

Microsoft Academic Search

Hyperuricemia is associated with hypertension, metabolic syndrome, preeclampsia, cardio-vascular disease and renal disease, all conditions associated with oxidative stress. We hypothesized that uric acid, a known antioxidant, might become prooxidative following its reaction with oxidants; and, thereby contribute to the pathogenesis of these diseases. Uric acid and 1,3-N2-uric acid were reacted with peroxynitrite in different buffers and in the presence

Christine Gersch; Sergiu P. Palii; Witcha Imaram; Kyung Mee Kim; S. Ananth Karumanchi; Alexander Angerhofer; Richard J. Johnson; George N. Henderson

2009-01-01

175

The effect of annealing conditions on the crystallization of Er–Si–O formed by solid phase reaction  

Microsoft Academic Search

Er–Si–O crystal is one of the promising materials for Si-based opto-electronic devices. Crystallization of Er–Si–O is obtained by solid phase reaction of an amorphous preform which contains Er–O and Si–O bonds. However detailed crystallization mechanism is not clear. This study reports that the control of oxygen content of the sample in the annealing process for crystallization affects the fine arrangements

K. Masaki; H. Isshiki; T. Kawaguchi; T. Kimura

2006-01-01

176

Selectivity of competitive-consecutive reactions depending on the turbulent mixing conditions in a co-axial jet mixer  

NASA Astrophysics Data System (ADS)

This paper considers the numerical results on the interaction between a turbulent co-axial jet and a co-flow of incompressible fluid (Schmidt number Sc?1000) when competitive-consecutive reactions occur in a co-axial jet mixer. Firstly, RANS modeling was performed to predict flow phenomena. Two different mixing regimes were analyzed with and without a recirculation zone near a mixer wall. To describe the problem mathematically, the two-parameter turbulence k-? model and various models for the computation of the averaged mixture fraction \\skew3\\bar f and its variance ?2 were used and verified by comparing them with the experimental and large eddy simulation (LES) data. The results revealed that the decay of \\skew5\\bar f and ?2 obtained by the developed RANS mixing model with the low-Reynolds-number effects (mechanical-to-scalar time ratio and turbulent Schmidt number in the transfer equation for ?2 as a function of Ret) was similar to the one found by LES and experiment. Second, the behavior of the competitive-consecutive reactions (A+B?P, B+R?S) in the co-axial mixer was considered. To calculate averaged chemical reaction rates, the transfer equations for concentrations adopted two approaches: a model with no regard to concentration fluctuations and the Li-Toor model with the Gaussian PDF of the mixture fraction. The yield of a desired product R was found to depend strongly on the mixing regime. The regime without recirculation zone appeared to be preferable as the reaction selectivity was smaller within the whole range of Reynolds number and initial reactant concentration ratio. This means that the amount of an undesired by-product S to be formed is minimal.

Chorny, A.; Kornev, N.; Hassel, E.

2010-12-01

177

A quantitative method for assessing of the affective component of the pain: conditioned response associated with CO2 laser-induced nocifensive reaction.  

PubMed

Sensory and affective components are included in the overall behavioral manifestation in a nocifensive reaction. We have developed a behavioral model using classical conditioning to differentiate the affective component from the sensory responses following a thermal noxious stimulus. In laser-pain conditioning, free moving rats were trained to associate a tone (conditioned stimulus, CS) and short CO2 laser pulsation (unconditioned stimulus, US). A monotonous tone (800 Hz, 0.6 s) was delivered through a loudspeaker as the CS. CO(2) laser pulses (5 W at 100 ms in duration) applied to the hind paw were adopted as the US. The CS-US interval was 0.5 s. The conditioned responses as quantitatively measured by their body movement were developed over a period of 40 CS-US pairings. These conditioned responses were found retained when the rats were tested by presenting CS alone, immediate to and 24 h subsequent to training. The conditioned responses however diminished significantly following both morphine and buspirone treatment. This method demonstrated that neutral auditory stimuli could form association with unlearned nocifensive responses evoked by noxious CO2 laser pulses stimuli. Thus, the assessment of conditioned response may be a valuable tool for the measurement of the affective component of nociception. PMID:12928039

Shyu, Bai-Chuang; Chai, Sin-Chee; Kung, Jen-Chuang; Fan, Ruey-Jane

2003-08-01

178

Encouraging conceptual change: the use of bridging analogies in the teaching of action reaction forces and the `at rest' condition in physics  

NASA Astrophysics Data System (ADS)

The qualitative study described in this paper examined the effectiveness of bridging analogies intended to bring about conceptual change as part of a constructivist approach to teaching about action reaction forces in the ‘at rest’ condition in physics. Twenty-one 15-year-old students were involved in the investigation with subgroups previously exposed to different information regarding forces, weight and the accepted cause of the reaction force, in simple physical arrangements, including objects on tables. In-depth ‘think aloud’ interviews were used to track each student’s conceptual status as they worked with bridging analogies and transcript coding was carried out using open and axial coding (as in a grounded theory methodology). The findings showed that the bridging analogies were effective in engaging students with the idea of action reaction forces; students were adept in mapping each of the analogies to the target concept and using them to generate and refine their causal theories for the reaction force. There was evidence to suggest that, for some students, bridging analogies were more effective in bringing about conceptual change than didactic teaching. Their use extends beyond illustrative purposes and supports the development of meta-cognitive skills.

Bryce, Tom; MacMillan, Kenneth

2005-06-01

179

Nature of Ptn/TiO2(110) Interface under Water-Gas Shift Reaction Conditions: A Constrained ab Initio Thermodynamics Study  

SciTech Connect

The electronic structure of small Ptn (n = 1-8) clusters supported on the stoichiometric and partially reduced rutile TiO2(110) surface have been investigated using density functional theory. Pt atoms prefer to form a close-packed structure with (111) facet near an oxygen vacancy of the TiO2 support and a less dense structure with (100) facet away from oxygen vacant sites. Themain focus of this study is on identifying a realistic catalyst model for the Pt/TiO2 interface under watergas shift (WGS) reaction conditions. Constrained ab initio thermodynamic simulations on the stability of oxygen vacancies and formation of adsorbed gas phase molecules such as oxygen, CO, and hydrogen at the metal/oxide interface reveal that under WGS reaction conditions the formation of surface oxygen vacancies are thermodynamically favorable, platinum oxide species (PtOx) can easily be reduced and should not be present, CO adsorbs only weakly on interfacial Pt atoms, and CO poisoning of these sites should be less important. While hydrogen generally interacts weakly with interfacial Pt atoms, it forms very stable hydride species on Pt atoms neighboring an oxygen vacancy of the TiO2(110) support, possibly negatively affecting the WGS reaction rate.

Ammal, Salai Cheettu; Heyden, Andreas

2011-10-06

180

Externally controlled pressure and temperature microreactor for in situ x-ray diffraction, visual and spectroscopic reaction investigations under supercritical and subcritial conditions  

SciTech Connect

A microreactor has been developed for in situ, spectroscopic investigations of materials and reaction processes with full external pressure and temperature control from ambient conditions to 400 C and 310 bar. The sample chamber is in direct contact with an external manifold, whereby gases, liquids or fluids can be injected and their activities controlled prior to and under investigation conditions. The microreactor employs high strength, single crystal moissanite windows which allow direct probe beam interaction with a sample to investigate in situ reaction processes and other materials properties. The relatively large volume of the cell, along with full optical accessibility and external temperature and pressure control, make this reaction cell well suited for experimental investigations involving any combination of gas, fluid, and solid interactions. The microreactor's capabilities are demonstrated through an in situ x-ray diffraction study of the conversion of a meta-serpentine sample to magnesite under high pressure and temperature. Serpentine is one of the mineral candidates for the implementation of mineral carbonation, an intriguing carbon sequestration candidate technology.

Diefenbacher, J.; McKelvy, M.; Chizemeshya, A.V.; Wolf, G.H. (ASU)

2010-07-13

181

Externally controlled pressure and temperature microreactor for in situ x-ray diffraction, visual and spectroscopic reaction investigations under supercritical and subcritical conditions  

SciTech Connect

A microreactor has been developed for in situ, spectroscopic investigations of materials and reaction processes with full external pressure and temperature control from ambient conditions to 400 deg. C and 310 bar. The sample chamber is in direct contact with an external manifold, whereby gases, liquids or fluids can be injected and their activities controlled prior to and under investigation conditions. The microreactor employs high strength, single crystal moissanite windows which allow direct probe beam interaction with a sample to investigate in situ reaction processes and other materials properties. The relatively large volume of the cell, along with full optical accessibility and external temperature and pressure control, make this reaction cell well suited for experimental investigations involving any combination of gas, fluid, and solid interactions. The microreactor's capabilities are demonstrated through an in situ x-ray diffraction study of the conversion of a meta-serpentine sample to magnesite under high pressure and temperature. Serpentine is one of the mineral candidates for the implementation of mineral carbonation, an intriguing carbon sequestration candidate technology.

Diefenbacher, Jason; McKelvy, Michael; Chizmeshya, Andrew V.G.; Wolf, George H. [Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 (United States); Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1504 (United States)

2005-01-01

182

The influence of reaction conditions in the oxidation of organic compounds of nuclear laundry water by ozone.  

PubMed

This paper presents a summary of degrading organic compounds of nuclear laundry water by ozonation in different conditions of pH, hydrogen peroxide and ultraviolet radiation. The degradation of organic compounds was analysed by chemical oxygen demand (COD), total organic carbon (TOC) and biochemical oxygen demand (BOD). The optimal degradation conditions were at pH 7 with ozone, UV radiation and hydrogen peroxide addition. The transfer of ozone increased significantly, thus resulting in decreased treatment time compared to ozone treatment alone. The reductions of COD, TOC and BOD were 46%, 32% and 70%, respectively. PMID:20453328

Vilve, M K; Sillanpää, M E T

2010-01-01

183

Optimal conditions to use Pfu exo– DNA polymerase for highly efficient ligation-mediated polymerase chain reaction protocols  

PubMed Central

Ligation-Mediated Polymerase Chain Reaction (LMPCR) is the most sensitive sequencing technique available to map single-stranded DNA breaks at the nucleotide level of resolution using genomic DNA. LMPCR has been adapted to map DNA damage and reveal DNA–protein interactions inside living cells. However, the sequence context (GC content), the global break frequency and the current combination of DNA polymerases used in LMPCR affect the quality of the results. In this study, we developed and optimized an LMPCR protocol adapted for Pyrococcus furiosus exo– DNA polymerase (Pfu exo–). The relative efficiency of Pfu exo– was compared to T7-modified DNA polymerase (Sequenase 2.0) at the primer extension step and to Thermus aquaticus DNA polymerase (Taq) at the PCR amplification step of LMPCR. At all break frequencies tested, Pfu exo– proved to be more efficient than Sequenase 2.0. During both primer extension and PCR amplification steps, the ratio of DNA molecules per unit of DNA polymerase was the main determinant of the efficiency of Pfu exo–, while the efficiency of Taq was less affected by this ratio. Substitution of NaCl for KCl in the PCR reaction buffer of Taq strikingly improved the efficiency of the DNA polymerase. Pfu exo– was clearly more efficient than Taq to specifically amplify extremely GC-rich genomic DNA sequences. Our results show that a combination of Pfu exo– at the primer extension step and Taq at the PCR amplification step is ideal for in vivo DNA analysis and DNA damage mapping using LMPCR.

Angers, Martin; Cloutier, Jean-Francois; Castonguay, Andre; Drouin, Regen

2001-01-01

184

Influence of varying hydraulic conditions on hyporheic exchange and reactions in an in-stream gravel bar  

NASA Astrophysics Data System (ADS)

In the hyporheic zone (HZ) important biogeochemical transformations occur with crucial impact on nutrient cycling in fluvial systems. Here we investigate the interplay between stream flow and HZ exchange of a natural in-stream gravel bar (ISGB), by using three-dimensional steady state simulations of a coupled surface and subsurface numerical model. Stream flow is simulated by the open source computational fluid dynamics (CFD) software OpenFOAM. It is sequentially coupled by the hydraulic head distribution to the top boundary of the groundwater model code MIN3P, simulating flow, solute transport, aerobic respiration (AR) and denitrification (DN) in the HZ. The modelling approach is validated to the stream rating curve and the subsurface travel times in the ISGB based on field measurements. Hydraulic conditions are varied by stream discharge, ranging from low discharge, sufficient to allow stream water flow through both stream channels surrounding the ISGB (0.1 m³/s), to conditions where the ISGB is completely submerged (5.0 m³/s). Ambient groundwater flow is assigned by constant head boundaries upstream and downstream of the ISGB. By varying stream discharge or ambient groundwater heads the general flow field of the ISGB can be adjusted from losing via neutral to gaining conditions. Reactive transport scenarios consider stream water as the primary source of dissolved oxygen and dissolved organic carbon. Furthermore, two nitrate sources originated from the stream water and ambient groundwater are included in the model. Results show that highest hyporheic exchange and longest residence times occur under neutral conditions, where the extent of the hyporheic flow cell is at a maximum. Hence, the stronger the system is gaining and losing, the smaller is the hyporheic exchange flux and the shorter are the residence times in the HZ of the ISGB. AR and DN efficiencies of the ISGB are lowest under gaining conditions because infiltrating solutes are restriced to the hyporheic flow cells and hence to small reactive areas. In contrast, under losing conditions stream solutes infiltrate deep into the HZ and overreach the extent of the hyporheic flow cells, resulting in large reactive areas with highest AR and DN efficiencies.

Trauth, Nico; Schmidt, Christian; Maier, Uli; Fleckenstein, Jan H.

2014-05-01

185

Formation characteristics of calcium phosphate deposits on a metal surface by H 2O 2-electrolysis reaction under various conditions  

Microsoft Academic Search

The cathodic electrolysis of H2O2 (H2O2+e??OH?+OH) on a metal surface in the presence of calcium and phosphate ions results in the formation of calcium phosphate deposits on the metal surface. In this study, the deposits formed under various treatment conditions (pHs, concentrations and ratios of calcium\\/phosphate ions, and so on) were characterized by scanning electron spectroscopy (SEM), and X-ray diffractometry.

Kazuaki Kanamoto; Koreyoshi Imamura; Nobuhide Kataoka; Jun Oshitani; Hiroyuki Imanaka; Kazuhiro Nakanishi

2009-01-01

186

The reduction of (ImH)[trans-RuIIICl4(dmso)(Im)] under physiological conditions: preferential reaction of the reduced complex with human serum albumin.  

PubMed

A systematic study of the reduction of (ImH)[trans-RuCl(4)(dmso)(Im)] (NAMI-A; dmso is dimethyl sulfoxide, Im is imidazole), a promising antimetastasing agent, by L-ascorbic acid under physiological conditions is reported. Under blood plasma conditions (pH 7.4, 0.1-0.15 M NaCl , 37 degrees C) the rapid reduction of trans-[Ru(III)Cl(4)(dmso)(Im)](-) results in the formation of trans-[Ru(II)Cl(4)(dmso)(Im)](2-) within seconds, and is followed by successive dissociation of the chloride ligands, whereas neither dmso nor imidazole ligands are released during the reaction. Under our experimental conditions, the formation of the ascorbate dianion is the rate-determining step, and once it has formed it reacts rapidly with NAMI-A. Moreover, the NAMI-A complex is very unstable at physiological pH (7.4); therefore, the hydrolysis of NAMI-A cannot be excluded as a competing reaction. During hydrolysis, aquated derivatives via stepwise dissociation of chloride and dmso ligands are formed, and most of these species have a higher redox potential and are expected to be even more easily reduced by ascorbic acid. Thus, it is very likely that the reduced form of NAMI-A or the reduction products of its hydrolytic derivatives react with albumin. The reaction of reduced NAMI-A with human serum albumin leads to the formation of stable adducts, with a binding efficiency very similar to that of the parent complex, viz., 3.2+/-0.3 and 4.0+/-0.4 mol of Ru(II) and Ru(III) per mole of albumin, respectively, however with a significantly higher reactivity. PMID:18438690

Brindell, Malgorzata; Stawoska, Iwona; Supel, Justyna; Skoczowski, Andrzej; Stochel, Grazyna; van Eldik, Rudi

2008-08-01

187

Hydroformylation of 1Hexene Catalyzed by [Rh(COD)(2Picoline) 2 ]PF 6 Immobilized on Poly(4-Vinylpyridine) Under Water Gas Shift Reaction Conditions  

Microsoft Academic Search

Reported here is the influence of the reaction conditions variation (1-hexene\\/rhodium content (S\\/C) = 16 - 105, temperature (T) = 70 - 110 C and carbon monoxide pressure (P(CO)) = 0.6 - 1.8 atm) on the catalytic hydroformylation of 1-hexene to aldehydes (heptanal and 2-methyl-hexanal) by the rhodium(I)\\u000a complex, [Rh(COD)(2-picoline)2]PF6 (COD = 1,5-cyclooctadiene)immobilized on poly(4-vinylpyridine) in contact with 10 mL

Alvaro J. Pardey; José Brito; María Fernández; Angel B. Rivas; Marisol C. Ortega; Clementina Longo; Pablo J. Baricelli; Eduardo Lujano; Sergio A. Moya

2001-01-01

188

Model predictions of realgar precipitation by reaction of As(III) with synthetic mackinawite under anoxic conditions  

USGS Publications Warehouse

This study investigates the removal of As(III) from solution using mackinawite, a nanoparticulate reduced iron sulfide. Mackinawite suspensions (0.1-40 g/L) effectively lower initial concentrations of 1.3 ?? 10 -5 M As(III) from pH 5-10, with maximum removal occurring under acidic conditions. Based on Eh measurements, it was found that the redox state of the system depended on the mackinawite solids concentration and pH. Higher initial mackinawite concentrations and alkaline pH resulted in a more reducing redox condition. Given this, the pH edge data were modeled thermodynamically using pe (-log[e-]) as a fitting parameter and linear pe-pH relationships within the range of measured Eh values as a function of pH and mackinawite concentration. The model predicts removal of As(III) from solution by precipitation of realgar with the formation of secondary oxidation products, greigite or a mixed-valence iron oxide phase, depending on pH. This study demonstrates that mackinawite is an effective sequestration agent for As(III) and highlights the importance of incorporating redox into models describing the As-Fe-S-H2O system. ?? 2008 American Chemical Society.

Gallegos, T. J.; Han, Y. -S.; Hayes, K. F.

2008-01-01

189

Wavelength dependence of the fluorescence emission under conditions of open and closed Photosystem II reaction centres in the green alga Chlorella sorokiniana.  

PubMed

The fluorescence emission characteristics of the photosynthetic apparatus under conditions of open (F0) and closed (FM) Photosystem II reaction centres have been investigated under steady state conditions and by monitoring the decay lifetimes of the excited state, in vivo, in the green alga Chlorella sorokiniana. The results indicate a marked wavelength dependence of the ratio of the variable fluorescence, FV=FM-F0, over FM, a parameter that is often employed to estimate the maximal quantum efficiency of Photosystem II. The maximal value of the FV/FM ratio is observed between 660 and 680nm and the minimal in the 690-730nm region. It is possible to attribute the spectral variation of FV/FM principally to the contribution of Photosystem I fluorescence emission at room temperature. Moreover, the analysis of the excited state lifetime at F0 and FM indicates only a small wavelength dependence of Photosystem II trapping efficiency in vivo. PMID:24561096

Rizzo, Federico; Zucchelli, Giuseppe; Jennings, Robert; Santabarbara, Stefano

2014-06-01

190

A carborane-derivative "click" reaction under heterogeneous conditions for the synthesis of a promising lipophilic MRI/GdBNCT agent.  

PubMed

In this study, the Huisgen reaction has been used to functionalise a carborane cage with a lipophilic moiety and a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) ligand to obtain a new Gd boron neutron-capture therapy (BNCT)/magnetic resonance imaging (MRI) agent. The introduction of the triazole units has been accomplished under both heterogeneous conditions, by the use of a Cu-supported ionic-liquid catalyst, and homogeneous conditions. The ability of the Gd complex of the synthesised ligand to form stable adducts with low-density lipoproteins (LDLs) has been evaluated and then MRI has been performed on tumour melanoma cells incubated in the presence of a Gd-complex/LDL imaging probe. It has been concluded that the high amount of intracellular boron necessary to perform BNCT can be reached even in the presence of a relatively low-boron-containing LDL concentration. PMID:23154917

Toppino, Antonio; Bova, Maria Elena; Geninatti Crich, Simonetta; Alberti, Diego; Diana, Eliano; Barge, Alessandro; Aime, Silvio; Venturello, Paolo; Deagostino, Annamaria

2013-01-01

191

Reaction and transport in debonded wellbore casing-cement interfaces under CO2 storage conditions: From batch reaction tests to flow-through experiments on the 2m length scale  

NASA Astrophysics Data System (ADS)

Debonding at interfaces between wellbore casing and cement is widely recognized as providing potential pathways for leakage from CO2 storage systems. This study addresses how the transport properties of such debonding-defects are affected by chemical reaction between cement, steel and CO2-bearing fluids. Our first set of experiments investigates near-static conditions, representative for stages prior to the formation of a fully connected defect network. Debonded cement-steel interfaces were simulated by constructing composite samples containing a spacer-imposed gap. Each sample was reacted with CO2 and an aqueous fluid, at 80°C and 14 MPa applied CO2 pressure, in seven sequential batch reaction runs (cumulative duration: 72 days). Permeability was measured after each run and microstructural analyses were performed after completion of the experiment. Reaction-induced permeability changes were limited, being less than one order of magnitude for all samples. Corrosion scale (Fe-carbonate, minor Fe-hydroxide) formed within the gap, on the surfaces of both the steel and cement. Here, the observed lack of Ca-carbonates suggests this corrosion scale produced a significant reduction in cement carbonation, similar to the decrease in corrosion rate observed when corrosion scale forms a protective film on steel. In contrast, Ca-carbonate did precipitate on the cement at locations beneath the spacers used to create the gap between the cement and steel plates, where corrosion scale did not form. Overall, the thin corrosion scale films on the cement surfaces seem to inhibit release of Ca from the cement into the gap and impede the precipitation of Ca- carbonates, which in other studies was found to promote sealing in fractured cement. Our batch reaction results imply that in local debonding-defects where corrosion scale development is insufficient to produce sealing, the scale's retarding effect on further reaction has the potential to maintain an open interfacial pathway. Ongoing changes in the temperature and stress state could lead these defects to propagate and connect, possibly resulting in a long-range pathway. Our second set of experiments is currently ongoing and addresses how such interconnected debonding-defects are affected by long-range chemical reaction and transport under flow-through conditions. Cement slurry was poured into a coil made of steel tube and was subsequently cured at 80°C. After curing, debonding was promoted by causing the steel tube to lift off the cement, providing us with a sample that contains a 2 m long section of (partially) debonded cement-steel interface. A flow-through permeameter, maintained at 80°C, will be used to one-sidedly flood the coil with CO2-bearing fluid, while continuously measuring sample permeability and pump/fluid volume (indicative for extent of reaction). Post-experiment microstructural analysis will be performed on the coil. To our knowledge, this will be the first experimental investigation of the cement-steel interface that includes reactive transport phenomena that occur on the metre length scale.

Wolterbeek, Tim; Peach, Colin; Spiers, Chris

2014-05-01

192

The photostat-1 device for studying the reaction of organisms to physical conditions on the planet Mars  

NASA Technical Reports Server (NTRS)

A description of the photostat device which reproduces the basic parameters of the physical environment of the planet Mars is presented. Any given temperature may be maintained in its working chamber from -35 to +30 C with a maintenance accuracy of + or - 0.5 deg; it can produce a change in temperature with varying rates of cooling or heating and maintain any given pressure in a range from 5 to 95 mm Hg. The system of ultraviolet filters in the device permits irradiation with the following individual lines of the ultraviolet spectrum: 1-253.7, 280 and 356 nm, and 220-320 nm. All operational conditions of the device are maintained automatically for given programs and are recorded by automatic recording devices.

Zaar, E. I.; Zelikson, V. G.; Kitaygorodskiy, M. G.; Koshelev, I. V.; Lozina-Lozinskiy, L. K.; Rybin, M. A.

1973-01-01

193

Bridging the Pressure Gap: in Situ Atomic-Level Investigations of Model Platinum Catalyst Surfaces Under Reaction Conditions by Scanning Tunneling Microscopy.  

NASA Astrophysics Data System (ADS)

The dream of surface scientists to elucidate the atomic structure of catalyst surfaces in the course of a chemical reaction in real conditions, has become possible by the recent development of a Scanning Tunneling Microscope (STM) (which was built during the course of research that led to this Ph.D. thesis) that operates inside an atmospheric pressure chemical reactor cell. With this microscope, atomic-scale structures of platinum under atmospheric pressures of hydrogen, oxygen, and carbon monoxide have been observed in situ, for the first time, as have a wide variety of adsorbate structures under catalytic hydrogenation reaction conditions. This unique High Pressure STM (HPSTM) allows in situ operation in pressures ranging from ultrahigh vacuum (<10^{-9} Torr) up to hundreds of atmospheres and temperatures ranging from 300 up to 450 Kelvin. The stability of hydrocarbons on catalyst surfaces while under reaction conditions and the subsequent process of coking of catalysts upon hydrocarbon decomposition are subjects of major interest to the catalysis industry. With this microscope, the stability of propylene on Pt(111) and the morphology of decomposition products as a function of atmospheric environment (hydrogen, H^2 /propylene, and CO) and sample temperature (300K -900K) has been investigated. Clusters of carbonaceous material were formed as a result of various decomposition pathways. The clusters and cluster aggregates were observed to form regular patterns whose size and shape depended on decomposition environment and temperature. In the course of experiments with the HPSTM system, it was also discovered that carbonaceous clusters could be catalytically rehydrogenated by the STM tip. This novel method of nanoscale modification opens the way for a wide range of possible applications --from gaining insights to fundamental questions of catalysis and surface reactions to creating chemical templates with atomic precision. The dynamics of coadsorbate interactions (coadsorbate-induced compression) for sulfur and carbon monoxide on Pt(111) were also observed in situ in UHV and high vacuum conditions. These results demonstrate the importance of lateral interactions between adsorbates and may provide a mechanism for carrying out catalytic reactions on metal surfaces that are covered with strongly chemisorbed layers. Combined theoretical and experimental observations of the atomic contrast of the sulfur overlayer was also carried out demonstrating the significance of the specific atom termination of the tunneling tip on the observed STM image contrast and corrugation for atomic-resolution imaging. Finally, in the course of coadsorption experiments with CO and sulfur on Pt(111) it was observed that in 10^{ -6} Torr of CO the sulfur covered Pt(111) surface may undergo a coadsorbate-induced reconstruction. In conclusion, these results demonstrating the usefulness of the HPSTM as a tool for catalyst characterization open the way for very exciting experiments that will allow the in situ study of the chemical and catalytic activity of surfaces with atomic resolution.

McIntyre, Brian James

194

Catalytic reduction of NO by CO over rhodium catalysts. 2. Effect of oxygen on the nature, population, and reactivity of surface species formed under reaction conditions  

SciTech Connect

The effect of oxygen on the nature, population, and reactivity of surface species formed during reduction of NO by CO over Rh/TiO{sub 2} catalysts has been examined employing FTIR and transient MS techniques. It has been found that the activity of Rh is hindered by accumulation of surface oxygen originating from NO decomposition and gas-phase oxygen in the feed. Adsorbed CO and reduced TiO{sub 2{minus}x} species in the vicinity of Rh particles act as oxygen atom scavengers and, under fuel-rich conditions, remove atomic oxygen from the surface and restore the catalytic properties. Results of the present study provide additional evidence that production of N{sub 2} is related to dissociation of adsorbed Rh-NO{sup {minus}} while production of N{sub 2}O is related to the presence of Rh(NO){sub 2}. The presence of reduced RH{sup 0} sites is necessary for the formation of both reduction products. In the absence of oxygen in the feed, surface isocyanate species are also observed under reaction conditions. Their formation requires the presence of adjacent Rh{sup 0}-CO and reduced Rh{sup 0} sites. Although these species are favored under conditions in which NO conversion to reduction products is observed, there is no evidence that they are catalytically active species.

Kondarides, D.I.; Chafik, T.; Verykios, X.E.

2000-04-01

195

Simulation of blast-furnace raceway conditions in a wire-mesh reactor: interference by the reactions of molybdenum mesh and initial results  

SciTech Connect

A novel trapped air injection system has been built for a wire-mesh reactor to enable tests with short exposure times to air that are intended to simulate typical residence times in blast-furnace raceways. Initial tests have shown that the molybdenum wire-mesh sample-holder reacts with O{sub 2} under conditions intended for this work. By varying the proportions of solid MoO{sub 2} (weight gain), vapor phase oxides (weight loss) may form, depending on reaction conditions. Oxide formation pathways thus become relevant to coal weight loss determinations during experiments. If, in addition to solid MoO{sub 2} formation, significant formation of vapor phase oxides occurs, then the weight change is more complicated to understand and the impact on the O{sub 2} concentration cannot be unravelled. Furthermore, it turns out that O{sub 2}-scavenging by the mesh affects the amount of O{sub 2} that is available to react with the coal sample. It was concluded that it is only possible to conduct reliable tests under conditions which the favor the formation of solid MoO{sub 2} only, as this leads to a quantifiable weight gain. Its impact can then be accounted for in the evaluation of the experimental weight change. In the case of MoO{sub 2} formation, the impact of the mesh oxidation on the amount of O{sub 2} available to react with the sample can also be estimated. It has been found that the wire-mesh reactor, equipped with the trapped air injection system, can be used to obtain valid data at up to 1600{sup o} C and 0.5 MPa. This pressure is similar to that of the blast-furnace raceway, but the temperature is several hundred degrees lower. However, preliminary tests have shown that useful kinetic data on the extents of reaction can be obtained with the equipment, provided it is operated under conditions that minimize the formation of vapor phase Mo oxides. 18 refs., 13 figs., 3 tabs.

Long Wu; N. Paterson; D.R. Dugwell; R. Kandiyoti [Imperial College London, London (United Kingdom). Department of Chemical Engineering

2006-12-15

196

Co-formation of hydroperoxides and ultra-fine particles during the reactions of ozone with a complex VOC mixture under simulated indoor conditions  

NASA Astrophysics Data System (ADS)

In this study we examined the co-formation of hydrogen peroxide and other hydroperoxides (collectively presented as H 2O 2*) as well as submicron particles, including ultra-fine particles (UFP), resulting from the reactions of ozone (O 3) with a complex mixture of volatile organic compounds (VOCs) under simulated indoor conditions. The VOC mixture contained 23 compounds, including two terpenes ( d-limonene and ?-pinene), two unsaturated alkenes (1-decene and 1-octene), and 19 other saturated organic compounds. These compounds are commonly found in indoor air but their concentrations were higher than typical indoor levels. When O 3 was added to a 25-m 3 controlled environmental facility (CEF) containing the 23 VOC mixture, both H 2O 2* and submicron particles were formed. The 2-h average concentration of H 2O 2* was 1.89±0.30 ppb, and the average total particle number concentration was 46,000±12,000 particles cm -3. A small increase of UFP (0.02-0.1 ?m) occurred 5 min after the O 3 addition (17 min after the VOC addition) and a sharp increase of UFP occurred 13 min after the O 3 addition, suggesting homogeneous nucleation. The delayed onset of this event might reflect the time required to achieve saturated concentrations of the condensable organics. When the 2 terpenes were removed from the O 3/23 VOCs mixture, no H 2O 2* or particles were formed, indicating that the reactions of O 3 with the two terpenes were the key processes contributing to the formation of H 2O 2* and submicron particles in the O 3/23 VOCs system. The present study confirmed the findings of a previous study carried out in a real-world office and generated new findings regarding co-formation of UFP. Through a comparative analysis of H 2O 2* yields under different reaction conditions, this study demonstrates that VOCs co-present with the terpenes and O 3 may play a role in producing H 2O 2*.

Fan, Zhihua; Weschler, Charles J.; Han, In-Kyu; Zhang, Junfeng (Jim)

197

Si-rich layer formation on olivine surfaces during reaction with water and supercritical carbon dioxide under conditions relevant for geologic carbon storage  

NASA Astrophysics Data System (ADS)

The reaction of Mg-silicate minerals (i.e. olivine) with carbon dioxide (CO2) is a promising method for secure, long-term, geologic carbon storage. Several technical challenges must be overcome before implementing mineral carbonation technology on a large scale, one of which is slow reaction kinetics. This study probes surface reaction limitations of olivine carbonation, specifically the formation of a passivating, Si-rich layer on olivine surfaces upon exposure to water and CO2 under sequestration conditions (elevated temperature and pressure). A series of batch reactions were performed at 60°C and 100 bar CO2 pressure in Dickson-style rocker bombs, varying the length of reaction and the amount of mixing (rocking). The initial aqueous phase was spiked with 29Si. Fluid samples were taken periodically and analyzed for cation content, alkalinity, and dissolved inorganic carbon. At the end of each experiment, the solid products were analyzed with a Sensitive High Resolution Ion Microprobe Reverse Geometry (SHRIMP-RG) in order to measure the amount of 29Si incorporated into the Si-rich layer on reacted olivine grains. We also cut cross sections of reacted grains from each experiment using a Focused Ion Beam (FIB) which were thinned to <100nm and imaged using Transmission Electron Microscopy (TEM). SHRIMP-RG results show incorporation of 29Si on olivine grain surfaces reacted for 19 days with no mixing, and TEM images of olivine grains from the same experiment show an amorphous, Si-rich layer that is 30nm thick. Similarly, SHRIMP-RG results for olivine grains reacted for 19 days with mixing indicate 29SiO2 precipitation and TEM images reveal a Si-rich layer 60nm thick. In both experiments, EDS (energy dispersive spectroscopy) data show a step change in composition from the bulk rock to the surface layer in addition to the sharp crystalline/amorphous interface visible in the TEM images. Olivine from the unmixed experiment also has a slow decrease in Mg relative to Si before the step change, suggesting that, at least in this experiment, a Si-rich layer precipitated on top of a Mg-depleted layer that formed via a leaching process. SHRIMP-RG data also imply the presence of a precipitated Si-rich layer on top of a leached Si-rich layer, as the 29Si penetration depth is only 25-65% of the total Si-rich layer thickness. The combination of SHRIMP-RG and FIB/TEM analysis leads us to hypothesize that a Si-rich layer forms quickly on olivine surfaces due to preferential Mg removal from the surface (the traditional 'leached' layer), and as the reaction proceeds, amorphous silica reaches saturation in the fluid and precipitates on surfaces inside the reactor (including olivine grains).

Johnson, N. C.; Jackson, A.; Maher, K.; Bird, D. K.; Brown, G. E.

2013-12-01

198

Coordination modes of multidentate ligands in fac-[Re(CO)(3)(polyaminocarboxylate)] analogues of (99m)Tc radiopharmaceuticals. dependence on aqueous solution reaction conditions.  

PubMed

We study Re analogues of (99m)Tc renal agents to interpret previous results at the (99m)Tc tracer level. The relative propensities of amine donors versus carboxylate oxygen donors of four L = polyaminocarboxylate ligands to coordinate in fac-[Re(I)(CO)(3)L](n) complexes were assessed by examining the reaction of fac-[Re(I)(CO)(3)(H(2)O)(3)](+) under conditions differing in acidity and temperature. All four L [N,N-bis-(2-aminoethyl)glycine (DTGH), N,N-ethylenediaminediacetic acid, diethylenetriamine-N-malonic acid, and diethylenetriamine-N-acetic acid] can coordinate as tridentate ligands while creating a dangling chain terminated in a carboxyl group. Dangling carboxyl groups facilitate renal clearance in fac-[(99m)Tc(I)(CO)(3)L](n) agents. Under neutral conditions, the four ligands each gave two fac-[Re(I)(CO)(3)L](n) products with HPLC traces correlating well with known traces of the fac-[(99m)Tc(I)(CO)(3)L](n) mixtures. Such mixtures are common in renal agents because the needed dangling carboxyl group can compete for a coordination site. However, the HPLC separations needed to assess the biodistribution of a single tracer are impractical in a clinical setting. One goal in investigating this Re chemistry is to identify conditions for avoiding this problem of mixtures in preparations of fac-[(99m)Tc(I)(CO)(3)L](n) renal tracers. After separation and isolation of the fac-[Re(I)(CO)(3)L](n) products, NMR analysis of all products and single crystal X-ray crystallographic analysis of both DTGH products, as well as one product each from the other L, allowed us to establish coordination mode unambiguously. The product favored in acidic conditions has a dangling amine chain and more bound oxygen. The product favored in basic conditions has a dangling carboxyl chain and more bound nitrogen. At the elevated temperatures used for simulating tracer preparation, equilibration was facile (ca. 1 h or less), allowing selective formation of one product by utilizing acidic or basic conditions. The results of this fundamental study offer protocols and guidance useful for the design and preparation of fac-[(99m)Tc(I)(CO)(3)L](n) agents consisting of a single tracer. PMID:20201565

Lipowska, Malgorzata; He, Haiyang; Xu, Xiaolong; Taylor, Andrew T; Marzilli, Patricia A; Marzilli, Luigi G

2010-04-01

199

Coordination Modes of Multidentate Ligands in fac-[Re(CO)3(polyaminocarboxylate)] Analogues of 99mTc Radiopharmaceuticals. Dependence on Aqueous Solution Reaction Conditions  

PubMed Central

We study Re analogues of 99mTc renal agents to interpret previous results at the 99mTc tracer level. The relative propensities of amine donors vs. carboxylate oxygen donors of four L = polyaminocarboxylate ligands to coordinate in fac-[ReI(CO)3L]n complexes were assessed by examining the reaction of fac-[ReI(CO)3(H2O)3]+ under conditions differing in acidity and temperature. All four L [N,N-bis-(2-aminoethyl)glycine (DTGH), N,N-ethylenediaminediacetic acid, diethylenetriamine-N-malonic acid, and diethylenetriamine-N-acetic acid] can coordinate as tridentate ligands while creating a dangling chain terminated in a carboxyl group. Dangling carboxyl groups facilitate renal clearance in fac-[99mTcI(CO)3L]n agents. Under neutral conditions, the four ligands each gave two fac-[ReI(CO)3L]n products with HPLC traces correlating well with known traces of the fac-[99mTcI(CO)3L]n mixtures. Such mixtures are common in renal agents because the needed dangling carboxyl group can compete for a coordination site. However, the HPLC separations needed to assess the biodistribution of a single tracer are impractical in a clinical setting. One goal in investigating this Re chemistry is to identify conditions for avoiding this problem of mixtures in preparations of fac-[99mTcI(CO)3L]n renal tracers. After separation and isolation of the fac-[ReI(CO)3L]n products, NMR analysis of all products and single crystal X-ray crystallographic analysis of both DTGH products as well as one product each from the other L allowed us to establish coordination mode unambiguously. The product favored in acidic conditions has a dangling amine chain and more bound oxygen. The product favored in basic conditions has a dangling carboxyl chain and more bound nitrogen. At the elevated temperatures used for simulating tracer preparation, equilibration was facile (ca. one hour or less), allowing selective formation of one product by utilizing acidic or basic conditions. The results of this fundamental study offer protocols and guidance useful for the design and preparation of fac-[99mTcI(CO)3L]n agents consisting of a single tracer.

Lipowska, Malgorzata; He, Haiyang; Xu, Xiaolong; Taylor, Andrew T.; Marzilli, Patricia A.; Marzilli, Luigi G.

2010-01-01

200

Reaction mechanism for the aqueous-phase mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions.  

PubMed

Mineral carbonation is known as one of the safest ways to sequester CO2. Nevertheless, the slow kinetics and low carbonation rates constitute a major barrier for any possible industrial application. To date, no studies have focused on reacting serpentinite with a relatively low partial pressure of CO2 (pCO2) close to flue gas conditions. In this work, finely ground and heat-treated serpentinite [Mg3Si2O5(OH)4] extracted from mining residues was reacted with a 18.2 vol % CO2 gas stream at moderate global pressures to investigate the effect on CO2 solubility and Mg leaching. Serpentinite dissolution rates were also measured to define the rate-limiting step. Successive batches of gas were contacted with the same serpentinite to identify surface-limiting factors using scanning electron microscopy (SEM) analysis. Investigation of the serpentinite carbonation reaction mechanisms under conditions close to a direct flue gas treatment showed that increased dissolution rates could be achieved relative to prior work, with an average Mg dissolution rate of 3.55 × 10(-11) mol cm(-2) s(-1). This study provides another perspective of the feasibility of applying a mineral carbonation process to reduce industrial greenhouse gas (GHG) emissions from large emission sources. PMID:24669999

Pasquier, Louis-César; Mercier, Guy; Blais, Jean-François; Cecchi, Emmanuelle; Kentish, Sandra

2014-05-01

201

Influence of deformation mechanisms and metamorphic reactions during strain localization in the continental crust under lower amphibolite facies conditions: an example from the Gotthard massif  

NASA Astrophysics Data System (ADS)

Ductile shear zones are the result of the process of strain localization in the continental crust. Depending on the metamorphic conditions during deformation, strain localization is coeval with dramatic changes in microstructures, mineralogy and mass transfers, due to the interactions with externally-derived fluid. Therefore, to accurately model the mechanisms of strain localization, it is critical to identify deformation mechanisms related to the recrystallization of the quartzo-feldspathic assemblages, and to better constrain the role of metamorphic reactions during deformation. The aim of this contribution is to characterize the mineralogical, geochemical, textural and microstructural evolution of a high strain zone from the Fibbia granite, which is located in the Gotthard Massif (External Crystalline Massif, Central Alps). This variscan massif has been affected by Alpine Tertiary metamorphism and deformation under lower amphibolite facies conditions. The strain gradient is approximately a meter width. The rock texture evolves from a weakly deformed granite, toward an orthogneiss, a mylonite and a ~10 cm-wide ultramylonite. The mineralogical assemblage changes from a metastable magmatic assemblage consisting of Qtz + Kspar + Pla + Bio ± Pheng ± Grt ± Ep to a fine banded texture consisting of a quartzo-feldspathic matrix, with metamorphic phyllosilicates (biotite and phengite) and garnet in the ultramylonite. Cathodoluminescence (CL) imaging has been used to quantify the modal proportions of phases in the quartzo-feldspathic matrix in this strain gradient. More specifically, in the orthogneiss and the mylonite, CL imaging reveals a subtle layering consisting of alternating bands of quartz-rich ribbons, K-feldspars and coupled quartz- and plagioclase-rich ribbons. The texture in the ultramylonite is more homogeneous with isolated single quartz and K-feldspar grains. CL imaging has also revealed chemical zoning, as "core and mantle" texture in plagioclases. With increasing strain, modal abundance of K-feldspars decreases from 28% to 16%, whereas both micas increase from 5% to 21%. Similarly, albite evolves from 25% to 8%, whereas oligoclase evolves from 5% to 25%. Deformation mechanisms responsible for these microstructures have been studied by combining a quantitative textural analysis (CSD, SPO, grain boundary frequency and orientation - PolyLX MatlabTM toolbox; Lexa, 2005) and a crystallographic study by EBSD. Deformation mechanisms of quartz, K-feldspar and plagioclase are a combination of SGR and GBM in the orthogneiss and in the mylonite, whereas GBS is active in the ultramylonite. CPO characteristic features are still a matter of debate. Because mass transfers occurred in this shear zone (gains of MnO, CaO, Fe2O3, P2O5 and TiO2) without volume change, thermodynamic modeling of phase relations in such open system must consider the variations of effective bulk rock composition during deformation. In this example, phase relations have been mapped using Perple_X'07 (Connolly, 2005) as a function of P, T, M(H2O) and X(bulk composition), in order to highlight the influence of subtle mass transfers on the syn-deformation stability of mineral assemblages at 500°C and 7.2 kbars. A particular attention has been paid to the role of water content on the stable assemblage and on compositions of metamorphic phyllosilicates. Water under-saturated conditions induce the stability of aluminosilicates, and should increase the Xmg in biotite and decrease the amount of tschermak substitution in phengite. P- and T-M(H20) diagram suggest that the Alpine ductile shear zones occurred under water-saturated conditions. This study reveals that strain localization is related to the metamorphic reactions (breakdowns of K-feldspars to phengites and magmatic plagioclase to albite and oligoclase), which induce a strong decrease in grain size reduction and a switch in deformation mechanism from SGR and GBM to GBS in the ultramylonite. The good agreement between phase diagram section predictions and the observations suggest that high

Oliot, E.; Goncalves, P.; Schulmann, K.; Marquer, D.

2009-04-01

202

Effects of the catalyst and reaction conditions on the integrated process of coal pyrolysis with CO{sub 2} reforming of methane  

SciTech Connect

Our previous works showed that the tar yield of coal pyrolysis can obviously be improved by integrated CO{sub 2} reforming of methane to coal pyrolysis in a fixed-bed reactor consisting of an upper catalyst layer and a lower coal layer. In this work, the effects of catalyst supports (MgO, Al{sub 2}O{sub 3}, SiO{sub 2}, and NaY) and reaction conditions on tar and water yields, CH{sub 4} conversion in pyrolysis of Chinese Pingshuo coal, and the carbon deposition on different catalysts were investigated. The results indicated that the catalyst support has an important effect on the integrated process and MgO is the best among the studied supports. A higher tar yield, lower water yield, and lower carbon deposition can be obtained with Ni/MgO as the catalyst. The tar yield increases with the increase of the pyrolysis temperature, holding time, CO{sub 2}/CH{sub 4} ratio, and CH{sub 4} flow rate, respectively, while the char yield decreases with an increasing pyrolysis temperature. 22 refs., 7 figs., 1 tab.

Jiahe Liu; Haoquan Hu; Lijun Jin; Pengfei Wang [Dalian University of Technology, Dalian (China). State Key Laboratory of Fine Chemicals

2009-09-15

203

Research on active particle distribution in the crop stalk plasma reaction under the condition of streaming and discharging micro electric current  

NASA Astrophysics Data System (ADS)

In order to further study sugar-production mechanism in the crop stalk plasma reaction under the condition of streaming and discharging micro electric current with N2 and H2O as the electro-discharging gases, the active particles distribution is researched and analyzed. Through the study of methods and theories of statistical mechanics and statistica thermodynamics, the ionization process of the mixed discharging gas and the distribution features of the active particles changing with temperature in the plasma reactor are discussed. The constant pressure form of Saha equation that applies to this experiment is deduced. And the active particles generated in the dense ionization discharging process and the crop stalk conversion processes are also analyzed. The experimental results show that N2 and H2 can ionize synchronously. And it is found that during the crop stalk conversion process, while one gas is ionised, the other gas will not take the energy away, which will not affect the conversion. Among the discharging gases consisting of water vapour and nitrogen, the main components are ions of H2O+, H+, N2+ and molecules of N2, H2O, which are all beneficial to a high sugar yield.

Song, C. L.; Pi, S. G.; Liu, X. Y.; Xu, H. B.

2013-03-01

204

Liraglutide protects Rin-m5f ? cells by reducing procoagulant tissue factor activity and apoptosis prompted by microparticles under conditions mimicking Instant Blood-Mediated Inflammatory Reaction.  

PubMed

Instant Blood-Mediated Inflammatory Reaction (IBMIR) occurs at the vicinity of transplanted islets immediately after intraportal infusion and is characterized by cytokine secretion, tissue factor (TF) expression, and ß cell loss. Microparticles (MPs) are cellular effectors shed from the plasma membrane of apoptotic cells. Modulation of the properties of ß cell-derived MPs by liraglutide was assessed in a cellular model designed to mimic IBMIR oxidative and inflammatory conditions. Rin-m5f rat ? cells were stimulated by H2 O2 or a combination of IL-1? and TNF-?. Cell-derived MPs were applied to naive Rin-m5f for 24 h. Apoptosis, MP release, TF activity, P-I?B expression, and MP-mediated apoptosis were measured in target cells. Direct protection by liraglutide was shown by a significant decrease in the oxidative stress-induced apoptosis (18.7% vs. 7.6%, P < 0.0001 at 1 ?m liraglutide) and cellular TF activity (-40% at 100 nm liraglutide). Indirect cytoprotection led to 20% reduction in MP generation, thereby lowering MP-mediated apoptosis (6.3% vs. 3.7%, P = 0.022) and NF-?B activation (-50%) in target cells. New cytoprotective effects of liraglutide were evidenced, limiting the expression of TF activity by ß cells and the generation of noxious MPs. Altogether, these data suggest that liraglutide could target pro-apoptotic and pro-inflammatory MPs in transplanted islets. PMID:24612163

Gleizes, Céline; Constantinescu, Andrei; Abbas, Malak; Bouhadja, Houda; Zobairi, Fatiha; Kessler, Laurence; Toti, Florence

2014-07-01

205

Influence of experimental conditions on the formation of PCDD/Fs during the thermal reactions of 2,4,6-trichlorophenol.  

PubMed

In order to obtain information on thermochemical reactions of chlorophenols, which are well known as dioxin precursors, occurring during the combustion of municipal solid wastes, the combustion of 2,4,6-trichlorophenol (2,4,6-T(3)CP) in an air stream was investigated over a temperature range of 500-800 degrees C for a residence time of 1-20s using a quartz flow reactor. Gas chromatographic/mass spectrometric (GC/MS) analysis of the gaseous products and residues showed that 2,4,6-T(3)CP began to decompose at 500 degrees C and produced several compounds, with 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo-p-dioxins (T(4)CDD) as the major products. In addition, more than fifty organic products were observed in our experimental conditions. The yields of polychlorinated benzenes, phenols, dibenzofurans, and dibenzo-p-dioxins formed during the combustion of 2,4,6-T(3)CP were plotted as a function of temperature and residence time. Furthermore, it was found that the yields and the compositions of these gaseous products were strongly dependent on the residence time in the flow reactor. PMID:19398119

Kishi, Tomohiro; Suzuki, Shota; Takagi, Mai; Kawakami, Tsuyoshi; Onodera, Sukeo

2009-06-01

206

Comparison of human serum and bovine serum albumins on oxidation dynamics induced by talaporfin sodium photosensitization reaction with albumin rich conditions: solution experiments  

NASA Astrophysics Data System (ADS)

In order to understand extracellular-photosensitization reaction (PR) using talaporfin sodium, we studied comparison of oxidation dynamics of albumin and talaporfin sodium in solution system by visible and ultraviolet absorption spectrum measurements. Almost all talaporfin sodium particles may be bound to albumin in interstitial fluid, and this binding would affect the oxidation dynamics during this PR. Bovine serum albumin (BSA) is commonly used in vitro study but its binding characteristics with talaporfin sodium are different from human serum albumin (HSA). PR was operated in a solution composed of 20 ?g/ml talaporfin sodium and 1.3 mg/ml HSA or BSA to simulate myocardial extracellular PR condition. Laser radiation of 662 nm was irradiated to this solution with irradiance of 0.29 W/cm2. Absorption spectra of these solutions were measured during the PR. We estimated oxidized ratio by absorption difference around 240 nm before and after the PR. Talaporfin sodium was oxidized 100% with HSA and BSA by the PR of 100 J/cm2 in radiant exposure. On the other hand, HSA and BSA were oxidized 60% and 94%, respectively in this radiant exposure. Q-band absorption peak of talaporfin sodium with HSA was shifted to 1 nm longer wavelength increasing radiant exposure up to 100 J/cm2. This longer wavelength shift would mean binding ratio of non-oxidized talaporfin sodium to non-oxidized HSA was increased with increasing radiant exposure. Therefore it would be possible that PR with talaporfin sodium bound to HSA might present efficient PDT than PR bound to BSA.

Kurotsu, Mariko; Nakamura, Tetsuya; Takahashi, Mei; Ogawa, Emiyu; Arai, Tsunenori

2014-02-01

207

Remarkably Facile Heck Reactions in Aqueous Two-Phase System Catalyzed by Reusable Pd\\/C Under Ligand-Free Condition  

Microsoft Academic Search

A fast and convenient Heck reaction was achieved catalyzed by Pd\\/C in aqueous two-phase system. The aqueous two-phase system has been shown to be a highly active solvent for Heck reactions of aryl halides even in the absence of organic ligands.

Yan-Qin Yuan; Sheng-Rong Guo

2011-01-01

208

Remarkably Facile Heck Reactions in Aqueous Two-Phase System Catalyzed by Reusable Pd\\/C Under Ligand-Free Conditions  

Microsoft Academic Search

A fast and convenient Heck reaction was achieved catalyzed by Pd\\/C in aqueous two-phase system. The aqueous two-phase system has been shown to be a highly active solvent for Heck reactions of aryl halides even in the absence of organic ligands.

Yan-Qin Yuan; Sheng-Rong Guo

2012-01-01

209

Reaction between triphenylphosphine and aromatic amines in the presence of diethyl azodicarboxylate: an efficient synthesis of aryliminophosphoranes under neutral and mild conditions  

Microsoft Academic Search

An efficient synthesis of aryliminophosphoranes is described. A mixture of an aromatic amine, diethyl azodicarboxylate and triphenylphosphine undergo a Mitsonobu type reaction at ambient temperature in dry dichloromethane to afford aryliminophosphoranes in excellent yields.

Mehdi Adib; Ehsan Sheikhi; Azadeh Deljoush

2011-01-01

210

Bench- and Pilot-Scale Studies of Reaction and Regeneration of Ni-Mg-K/Al2O3 for Catalytic Conditioning of Biomass-Derived Syngas  

SciTech Connect

The National Renewable Energy Laboratory (NREL) is collaborating with both industrial and academic partners to develop technologies to help enable commercialization of biofuels produced from lignocellulosic biomass feedstocks. The focus of this paper is to report how various operating processes, utilized in-house and by collaborators, influence the catalytic activity during conditioning of biomass-derived syngas. Efficient cleaning and conditioning of biomass-derived syngas for use in fuel synthesis continues to be a significant technical barrier to commercialization. Multifunctional, fluidizable catalysts are being developed to reform undesired tars and light hydrocarbons, especially methane, to additional syngas, which can improve utilization of biomass carbon. This approach also eliminates both the need for downstream methane reforming and the production of an aqueous waste stream from tar scrubbing. This work was conducted with NiMgK/Al{sub 2}O{sub 3} catalysts. These catalysts were assessed for methane reforming performance in (i) fixed-bed, bench-scale tests with model syngas simulating that produced by oak gasification, and in pilot-scale, (ii) fluidized tests with actual oak-derived syngas, and (iii) recirculating/regenerating tests using model syngas. Bench-scale tests showed that the catalyst could be completely regenerated over several reforming reaction cycles. Pilot-scale tests using raw syngas showed that the catalyst lost activity from cycle to cycle when it was regenerated, though it was shown that bench-scale regeneration by steam oxidation and H{sub 2} reduction did not cause this deactivation. Characterization by TPR indicates that the loss of a low temperature nickel oxide reduction feature is related to the catalyst deactivation, which is ascribed to nickel being incorporated into a spinel nickel aluminate that is not reduced with the given activation protocol. Results for 100 h time-on-stream using a recirculating/regenerating reactor suggest that this type of process could be employed to keep a high level of steady-state reforming activity, without permanent deactivation of the catalyst. Additionally, the differences in catalyst performance using a simulated and real, biomass-derived syngas stream indicate that there are components present in the real stream that are not adequately modeled in the syngas stream. Heavy tars and polycyclic aromatics are known to be present in real syngas, and the use of benzene and naphthalene as surrogates may be insufficient. In addition, some inorganics found in biomass, which become concentrated in the ash following biomass gasification, may be transported to the reforming reactor where they can interact with catalysts. Therefore, in order to gain more representative results for how a catalyst would perform on an industrially-relevant scale, with real contaminants, appropriate small-scale biomass solids feeders or slip-streams of real process gas should be employed.

Magrini-Bair, K. A.; Jablonski, W. S.; Parent, Y. O.; Yung, M. M.

2012-05-01

211

Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions.  

PubMed

We present a detailed description of the construction of an in situ electrochemical ATR-FTIR setup combined with a wall-jet electrode to investigate the electrocatalytic properties of nanoparticulate catalysts in situ under controlled mass transport conditions. The presented setup allows the electrochemical interface to be probed in combination with the simultaneous determination of reaction rates. At the same time, the high level of automation allows it to be used as a standard tool in electrocatalysis research. The performance of the setup was demonstrated by probing the oxygen reduction reaction on a platinum black catalyst in sulfuric electrolyte. PMID:23902087

Nesselberger, Markus; Ashton, Sean J; Wiberg, Gustav K H; Arenz, Matthias

2013-07-01

212

Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions  

NASA Astrophysics Data System (ADS)

We present a detailed description of the construction of an in situ electrochemical ATR-FTIR setup combined with a wall-jet electrode to investigate the electrocatalytic properties of nanoparticulate catalysts in situ under controlled mass transport conditions. The presented setup allows the electrochemical interface to be probed in combination with the simultaneous determination of reaction rates. At the same time, the high level of automation allows it to be used as a standard tool in electrocatalysis research. The performance of the setup was demonstrated by probing the oxygen reduction reaction on a platinum black catalyst in sulfuric electrolyte.

Nesselberger, Markus; Ashton, Sean J.; Wiberg, Gustav K. H.; Arenz, Matthias

2013-07-01

213

Quantum chemical study of the mechanism of reaction between NH (X 3sigma-) and H2, H2O, and CO2 under combustion conditions.  

PubMed

Reactions of ground-state NH (3sigma-) radicals with H2, H2O, and CO2 have been investigated quantum chemically, whereby the stationary points of the appropriate reaction potential energy surfaces, that is, reactants, products, intermediates, and transition states, have been identified at the G3//B3LYP level of theory. Reaction between NH and H2 takes place via a simple abstraction transition state, and the rate coefficient for this reaction as derived from the quantum chemical calculations, k(NH + H2) = (1.1 x 10(14)) exp(-20.9 kcal mol(-1)/RT) cm3 mol(-1) s(-1) between 1000 and 2000 K, is found to be in good agreement with experiment. For reaction between triplet NH and H2O, no stable intermediates were located on the triplet reaction surface although several stable species were found on the singlet surface. No intersystem crossing seam between triplet NH + H2O and singlet HNO + H2 (the products of lowest energy) was found; hence there is no evidence to support the existence of a low-energy pathway to these products. A rate coefficient of k(NH + H2O) = (6.1 x 10(13)) exp(-32.8 kcal mol(-1)/RT) cm3 mol(-1) s(-1) between 1000 and 2000 K for the reaction NH (3sigma-) + H2O --> NH2 (2B) + OH (2pi) was derived from the quantum chemical results. The reverse rate coefficient, calculated via the equilibrium constant, is in agreement with values used in modeling the thermal de-NO(x) process. For the reaction between triplet NH and CO2, several stable intermediates on both triplet and singlet reaction surfaces were located. Although a pathway from triplet NH + CO2 to singlet HNO + CO involving intersystem crossing in an HN-CO2 adduct was discovered, no pathway of sufficiently low activation energy was discovered to compare with that found in an earlier experiment [Rohrig, M.; Wagner, H. G. Proc. Combust. Inst. 1994, 25, 993.]. PMID:16366650

Mackie, John C; Bacskay, George B

2005-12-29

214

Direct capture in the 130Sn(n,?)131Sn and 132Sn(n,?)133Sn reactions under r-process conditions  

NASA Astrophysics Data System (ADS)

The cross sections of the 130Sn(n,?)131Sn and 132Sn(n,?)133Sn reactions are calculated in the direct capture model at low energies below 1.5 MeV. Using recent data from (d,p) transfer experiments on 130Sn and 132Sn, it is possible to avoid global input parameters with their inherent uncertainties and to determine all inputs to the direct capture model by local adjustments. The calculated direct capture cross sections of 130Sn and 132Sn are almost identical and have uncertainties of less than a factor of 2. The stellar reaction rates NA?v show a slight increase with temperature. Finally, an estimate for the influence of low-lying resonances to the stellar reaction rates is given.

Mohr, Peter

2012-12-01

215

Suitable conditions for advanced oxidation process by the amount of ozone reaction and the amount of dioxin degradation in landfill leachate  

NASA Astrophysics Data System (ADS)

One of the processes to degrade dioxin in landfill leachate is the AOP(advanced oxidation process) method that uses ultraviolet rays or hydrogen peroxide together with ozone. In this research, we used the experimental result of the AOP method and applied to various kinds of experimental systems to determine the relationship between the amount of ozone reaction and the amount of dioxin degradation. The main results were as follows: The TOC(Total Organic Carbon) in the raw leachate consumed the supplied ozone by approximately 3.1(mgO3/mgTOC). It could be expressed in a linear equation between the ozone reaction amount revised by the TOC and the amount of dioxin degradation, and the slope was about 11.5(pgDXN/mgO3). A function of AOP can be expressed by comparing the quantity of suitable ozone reaction to the dioxin degradation. From the degradation ratio of each homologs, the degradation is mainly caused by the hydroxyl radical. To follow the dioxin discharge standard value, it is sufficient to guarantee the revised ozone reaction amount is more than 200mg/l.

Yoshikawa, Katsuhiko; Kanjo, Yoshinori; Matsufuji, Yasushi; Fukunaga, Isao; Urabe, Shinro; Yagi, Yoshio

216

Thermophoresis and chemical reaction effects on non-Darcy MHD mixed convective heat and mass transfer past a porous wedge in the presence of variable stream condition  

Microsoft Academic Search

An analysis is presented to investigate the effect of thermophoresis particle deposition and variable viscosity on non-Darcy MHD mixed convective heat and mass transfer of a viscous, incompressible and electrically conducting fluid past a porous wedge in the presence of chemical reaction. The wall of the wedge is embedded in a uniform non-Darcian porous medium in order to allow for

Ismoen Muhaimin; Ramasamy Kandasamy; I. Hashim

2009-01-01

217

Competing reactions in three-way catalytic converters: modelling of the NO x conversion maximum in the light-off curves under net oxidising conditions  

Microsoft Academic Search

Automobile exhaust gas conversion was simulated with a reactor model based on first principles. The monolithic reactor was modelled as adiabatically operating with a uniform flow distribution over the channels and with constant heat and mass transfer coefficients. The kinetic rate equations in the model were constructed from elementary step kinetics of the individual global reactions. The model predictions for

J. H. B. J. Hoebink; R. A. van Gemert; J. A. A. van den Tillaart; GBMM Marin

2000-01-01

218

Suitable conditions for advanced oxidation process by the amount of ozone reaction and the amount of dioxin degradation in landfill leachate  

Microsoft Academic Search

One of the processes to degrade dioxin in landfill leachate is the AOP(advanced oxidation process) method that uses ultraviolet rays or hydrogen peroxide together with ozone. In this research, we used the experimental result of the AOP method and applied to various kinds of experimental systems to determine the relationship between the amount of ozone reaction and the amount of

Katsuhiko Yoshikawa; Yoshinori Kanjo; Yasushi Matsufuji; Isao Fukunaga; Shinro Urabe; Yoshio Yagi

2008-01-01

219

Studies in Reaction to Disability. XII: Structure of Attitudes toward the Physically Disabled; Disability Factor Scales--Amputation, Blindness, Cosmetic Conditions.  

ERIC Educational Resources Information Center

To describe and to develop instruments to measure attitudes toward amputees, the blind, and those with cosmetic conditions, three groups of subjects responded to one of three large pools of items tapping attitudes toward the three disability conditions. Three new groups of about 500 subjects of diverse demographic characteristics were given one of…

Siller, Jerome; And Others

220

Synthesis and Characterization of a New Semi-Aliphatic Poly(amide-imide) and Evaluation of the Effect of Reaction Conditions  

Microsoft Academic Search

Synthesis and characterization of a new aliphatic–aromatic poly(amide-imide) (PAI) with regular microstructure obtained via a two-step polymerization method was investigated. Firstly a fully imidized diimide-diacid (DIDA) intermediate was synthesized from trimellitic anhydride acid (TMA) and an aliphatic diamine with the ratio of 2:1; then, the corresponding PAI was prepared via a polycondensation reaction of the DIDA and an aromatic diisocyanate.

H. Afsharian-Moghadam; V. Haddadi-Asl

2008-01-01

221

Preferential CO oxidation in hydrogen (PROX) on ceria-supported catalysts, part I: Oxidation state and surface species on Pt\\/CeO 2 under reaction conditions  

Microsoft Academic Search

The CO content of hydrogen feed to proton-exchange membrane fuel cells (PEMFCs) must be kept under 1–100 ppm for their proper operation. This can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen (PROX). The present study reports on the mechanism of the PROX reaction on Pt\\/CeO2 catalyst, using catalytic tests, in situ

O. Pozdnyakova; D. Teschner; A. Wootsch; J. Kröhnert; B. Steinhauer; H. Sauer; L. Toth; F. C. Jentoft; A. Knop-Gericke; Z. Paál; R. Schlögl

2006-01-01

222

Drug Reactions  

MedlinePLUS

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

223

Development of a detailed high-pressure reaction model for methane\\/methanol mixtures under pyrolytic and oxidative conditions and comparison with experimental data  

Microsoft Academic Search

Experimental data of methanol in a flow reactor are obtained under pyrolysis, fuel lean condition (?=0.75), and stoichiometric condition (?=1.0), and as mixtures with methane; both temperature and pressure are varied. Methanol pyrolysis is studied at 1073 K over a pressure range of 1–10 atm. Methanol oxidation experiments are conducted over a temperature range of 873–1073 K and a pressure

Wen-Chiun Ing; Chad Y. Sheng; Joseph W. Bozzelli

2003-01-01

224

Optimization of reaction conditions towards multiple types of framework isomers and periodic-increased porosity: luminescence properties and selective CO2 adsorption over N2.  

PubMed

Three new metal-organic frameworks (MOFs) were prepared by solvo(hydro)thermolysis and further characterized as framework isomers. The structural transformation from non-porous to porous MOFs and the purity of these products can be modulated by controlling the reaction temperature. The periodic-increased porosity observed was further confirmed by CO2 adsorption isotherms. Owing to the presence of acylamide groups in the pore walls and the flexible nature of the skeleton of these MOFs, highly selective CO2 adsorption over N2 was observed, as well as structure-dependent periodic varieties in luminescence properties. PMID:24038959

Wu, Xiao-Liu; Luo, Feng; Sun, Gong-Ming; Zheng, An-Min; Zhang, Jian; Luo, Ming-Biao; Xu, Wen-Yuan; Zhu, Yan; Zhang, Xiao-Min; Huang, Shu-Yun

2013-10-21

225

Hydride as a leaving group in the reaction of pinacolborane with halides under ambient Grignard and Barbier conditions. One-pot synthesis of alkyl, aryl, heteroaryl, vinyl, and allyl pinacolboronic esters.  

PubMed

Grignard reagents (aliphatic, aromatic, heteroaromatic, vinyl, or allylic) react with 1 equiv of 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane, PinBH) at ambient temperature in tetrahydrofuran (THF) to afford the corresponding pinacolboronates. The initially formed dialkoxy alkylborohydride intermediate quickly eliminates hydridomagnesium bromide (HMgBr) and affords the product boronic ester in very good yield. Hydridomagnesium bromide (HMgBr) in turn disproportionates to a 1:1 mixture of magnesium hydride (MgH(2)) and magnesium bromide (MgBr(2)) on addition of pentane to the reaction mixture. DFT calculations (Gaussian09) at the B3LYP/6-31G(d) level of theory show that disproportionation of HMgBr to MgH(2) and MgBr(2) is viable in the coordinating ethereal solvents. This reaction also can be carried out under Barbier conditions, where the neat PinBH is added to the flask prior to the in situ formation of Grignard reagent from the corresponding organic halide and magnesium metal. Pinacolboronic ester synthesis under Barbier conditions does not give Wurtz coupling side products from reactive halides, such as benzylic and allylic halides. The reaction between PinBH and various Grignard reagents is an efficient, mild, and general method for the synthesis of pinacolboronates. PMID:22040316

Clary, Jacob W; Rettenmaier, Terry J; Snelling, Rachel; Bryks, Whitney; Banwell, Jesse; Wipke, W Todd; Singaram, Bakthan

2011-12-01

226

The reaction rates of O2 with closed-shell and open-shell Al(x)? and Ga(x)? clusters under single-collision conditions: experimental and theoretical investigations toward a generally valid model for the hindered reactions of O2 with metal atom clusters.  

PubMed

In order to characterize the oxidation of metallic surfaces, the reactions of O2 with a number of Al(x)(-) and, for the first time, Ga(x)(-) clusters as molecular models have been investigated, and the results are presented here for x = 9-14. The rate coefficients were determined with FT-ICR mass spectrometry under single-collision conditions at O2 pressures of ~10(-8) mbar. In this way, the qualitatively known differences in the reactivities of the even- and odd-numbered clusters toward O2 could be quantified experimentally. To obtain information about the elementary steps, we additionally performed density functional theory calculations. The results show that for both even- and odd-numbered clusters the formation of the most stable dioxide species, [M(x)O2](-), proceeds via the less stable peroxo species, [M(x)(+)···O2(2-)](-), which contains M-O-O-M moieties. We conclude that the formation of these peroxo intermediates may be a reason for the decreased reactivity of the metal clusters toward O2. This could be one of the main reasons why O2 reactions with metal surfaces proceed more slowly than Cl2 reactions with such surfaces, even though O2 reactions with both Al metal and Al clusters are more exothermic than are reactions of Cl2 with them. Furthermore, our results indicate that the spin-forbidden reactions of (3)O2 with closed-shell clusters and the spin-allowed reactions with open-shell clusters to give singlet [M(x)(+)···O2(2-)](-) are the root cause for the observed even/odd differences in reactivity. PMID:24564371

Neumaier, Marco; Olzmann, Matthias; Kiran, Boggavarapu; Bowen, Kit H; Eichhorn, Bryan; Stokes, Sarah T; Buonaugurio, Angela; Burgert, Ralf; Schnöckel, Hansgeorg

2014-03-01

227

Low-Temperature Liquid-Phase Radiation-Induced Oxidation of Hexafluoropropylene with Molecular Oxygen: Effect of Reaction Conditions on the Structure of Perfluoropolyether Polyperoxide  

Microsoft Academic Search

The formation and development of innovative technologies required the production of liquid polymers that possess a set of unique properties for operation under severe physicochemical conditions. The main requirements imposed on these polymers, which are designed for use as heat-transfer agents, dielectric materials, pressure fluids, oils, lubricants, etc., are high chemical and thermal stability, insolubility in commonly used organic solvents,

V. V. Shapovalov

2000-01-01

228

1-( p -Fluorophenyl)-2-(2?-pyridyl)ethanol and 1-( p -fluorophenyl)-2-(2?-pyridyl)ethene obtained from the condensation reaction of 2-picoline and p -fluorophenylaldehyde under catalyst-and solvent-free conditions  

Microsoft Academic Search

The novel intermediate 1-(p-fluorophenyl)-2-(2?-pyridyl)ethanol or 2-[2?-(1-hydroxy-1-(p-fluorophenyl)ethyl]pyridine and the corresponding novel dehydration compound 1-(p-fluorophenyl)-2-(2?-pyridyl)ethene or 2-[p-fluorophenylvinyl]pyridine were obtained from the condensation reaction of p-fluorophenylaldehyde and 2-picoline under catalyst-and solvent-free conditions. The intermediate 1-(p-fluorophenyl)-2-(2?-pyridyl)ethanol was obtained at 42 h reaction time and temperature of 120?C, respectively. 1H-NMR, IR spectroscopic data of the 1-(p-fluorophenyl)-2-(2-pyridyl)ethanol clearly showed the presence of the-CH2-CHOH-group. The compound was

M. Judith Percino; Víctor M. Chapela; Omar Urzúa; Ling-Fa Montiel; Cecilia Rodríguez-Barbarín

2007-01-01

229

The role of Fe and redox conditions in olivine carbonation rates: An experimental study of the rate limiting reactions at 90 and 150 °C in open and closed systems  

NASA Astrophysics Data System (ADS)

The mechanisms and rates of olivine carbonation reactions have been the object of a number of studies, but the thermodynamic limitations and the kinetics of the elementary processes that control the overall reaction are still poorly understood and characterized. The main objective of this study is to probe the effect of Fe on the measured rates of olivine carbonation and its role in the formation of Si-rich surface layers, which can significantly inhibit olivine dissolution and limit the extent of the carbonation reaction. A series of batch and flow-through reactor experiments was conducted in pure water at 90 and 150 °C and under a CO2 partial pressure of 100 and 200 bar, using both a natural sample of Fe-bearing olivine (Fo88) and a synthetic sample of pure forsterite (Fo100). Experimental results show that Fe plays an ambivalent role in the carbonation rates of olivine. On one hand, the presence of Fe favors the formation of Fe-Si-rich protective layers at the interface between olivine and aqueous solution, slowing down the dissolution reaction and limiting the extent of carbonation, whereas pure silica coatings have little to no inhibiting effect on measured carbonation rates. On the other hand, Fe enhances olivine to carbonate conversion rates at low degrees of supersaturation, by promoting the formation of fast precipitating Mg-Fe carbonate solid solutions. The passivating properties of Fe-Si-rich layers originate from the strong Fe(III)-Si interaction and are linked to the permanence of oxidizing conditions in the aqueous fluid. As a consequence, under reducing conditions, olivine carbonation rates can be significantly increased by higher extents of dissolution and by the formation of ferroan magnesites (Mg,Fe)CO3, which nucleate faster than the pure Mg end-member. Forsterite and olivine carbonation reactions can be hindered by the formation of secondary Mg sheet-silicates but, at the conditions studied, the formation of such silicate phases was observed to be transitional and not affecting significantly the rates of carbonation at the end of one-month long experimental runs. This work presents new measurements of olivine carbonation rates and delivers relevant information that suggest new reference criteria for the assessment of the sequestration potential of CO2 repositories and the optimization of the mineral carbonation process in mafic and ultramafic rocks.

Saldi, Giuseppe D.; Daval, Damien; Morvan, Gilles; Knauss, Kevin G.

230

Cognitive factors in differential conditioning of the GSR: Use of a reaction time task as the UCS with normals and schizophrenics  

Microsoft Academic Search

22 normals and 22 schizophrenics underwent differential conditioning of the GSR, using 8-sec tones of differing frequencies as the CSs, an 8-sec CS-UCS interval, and a UCS comprised of an RT task signaled by a low-intensity light. Both intertrial reports and postconditioning interviews were obtained. 12 Ss in the normal group verbalized the CS relations accurately, compared to 3 Ss

Paul E. Baer; Marcus J. Fuhrer

1969-01-01

231

Preparation and reaction mechanistic characterization of sol–gel indium\\/alumina catalysts developed for NO x reduction by propene in lean conditions  

Microsoft Academic Search

The impregnation and sol–gel preparation methods were investigated to develop high activity catalysts and understand the significance of the indium–aluminium interaction on alumina-supported indium catalysts in NOx reduction with propene. Active In\\/alumina catalysts with a very high surface area (270 m2\\/g) and thermal stability were prepared in controlled conditions by sol–gel processing. When Al isopropoxide and In nitrate in ethyl

T. Maunula; Y. Kintaichi; M. Haneda; H. Hamada

1999-01-01

232

A new cascade-less engine operated from subsonic to hypersonic conditions: designed by computational fluid dynamics of compressible turbulence with chemical reactions  

NASA Astrophysics Data System (ADS)

By using our computational fluid dynamic models, a new type of single engine capable of operating over a wide range of Mach numbers from subsonic to hypersonic regimes is proposed for airplanes, whereas traditional piston engines, turbojet engines, and scram engines work only under a narrower range of operating conditions. The new engine has no compressors or turbines such as those used in conventional turbojet engines. An important point is its system of super multijets that collide to compress gas for the transonic regime. Computational fluid dynamics is applied to clarify the potential of this engine. The peak pressure at the combustion center is over 2.5 MPa, while that just before ignition is over 1.0 MPa. The maximum power of this engine will be sufficient for actual use. Under the conditions of higher Mach numbers, the main intake passage located in front of the super multijet nozzles, takes in air more. That results in a ram or scramjet engine for supersonic and hypersonic conditions.

Naitoh, Ken; Nakamura, Kazushi; Emoto, Takehiro

2010-12-01

233

Two-way avoidance acquisition is negatively related to conditioned freezing and positively associated with startle reactions: a dissection of anxiety and fear in genetically heterogeneous rats.  

PubMed

The double, fear-driven "passive avoidance/active avoidance" conflict appearing during acquisition of two-way active avoidance, involves high levels of anxiety and a dominant tendency for freezing responses, which in turn run against the appearance of active escape/avoidance behavior. In the present study, by using a large sample genetically heterogeneous (N/Nih-HS) rats, we have tested the hypothesis that rats showing relatively higher levels of context-conditioned freezing (during the initial trials of that task) should show lower efficiency to acquire two-way avoidance behavior, i.e. the prediction that the initial context-conditioned freezing in the shuttle box would be negatively related to avoidance acquisition efficiency. In agreement with such a hypothesis, the results from the three rat subsamples used show that context-conditioned freezing (during the first 5 inter-trial intervals of the 40-trial two-way avoidance session) is negatively correlated (r=-0.34 to r=-0.64, p<0.001) with two-way avoidance acquisition, in a way that subgroups of rats with extremely high or low levels of freezing markedly differ in their avoidance performance: "high freezer" rats show much worse avoidance acquisition than "low freezers". Moreover, the relationships of conditioned freezing and avoidance acquisition with baseline and fear-potentiated startle, as well as with unconditioned anxiety (in the elevated zero-maze test), have also been studied. Taken collectively, the results indicate that: (i) context conditioned freezing is a reliable (and negative) predictor of two-way avoidance acquisition; (ii) baseline and fear-potentiated startle responses show positive associations with avoidance responding, and (iii) unconditioned anxiety in the elevated zero-maze is also negatively associated with two-way avoidance acquisition. Such patterns of associations are considered to be very informative in regard to the search for (common or differential) neural and genetic mechanisms of different forms of (unlearned or learned) anxious or fear responses. PMID:21163279

Vicens-Costa, Elia; Martínez-Membrives, Esther; López-Aumatell, Regina; Guitart-Masip, Marc; Cañete, Toni; Blázquez, Gloria; Tobeña, Adolf; Fernández-Teruel, Alberto

2011-05-01

234

CO2 Reaction Induced Wettability Alteration and its Impacts on CO2 Storage: Pore to Core Scale Reservoir Condition Experimental Studies  

NASA Astrophysics Data System (ADS)

Wettability of the mineral surfaces plays an important role in subsurface multiphase flow and transport. Wettability affects the capillary pressure-saturation (Pc- S) relations, relative permeability (kr) of each fluid phase, and relative phase occupancy in reservoir pores. Although wettability issues have been studied extensively in other fields, significant knowledge gaps remain when applying the existing understanding to geological carbon sequestration; due largely to the unique physical-chemical properties of supercritical (sc) CO2 relative to other common non-wetting fluids such as air and oil. Here, we report our recent progress on wettability alteration upon reaction with CO2 and the resulting differences in capillary trapping of CO2 versus air. (1) Pore Scale Studies. There are conflict predictions in the literature concerning the effect of wettability on capillary trapping; some find that larger contact angles lead to lower capillary trapping while others have found opposite behavior. We hypothesized that spontaneous imbibition becomes energetically unfavorable with decreased wettability, so that increased residual trapping of scCO2 should occur during the post-injection inbibition stage. We developed a laboratory high-pressure and elevated temperature microscopic-micromodel system that is capable of controlling fine scale capillary pressure of scCO2-brine, and enabled us to conduct imbibition under controlled capillary pressures at the pore scale. We found that the de-wetting enhanced scCO2 capillary trapping is significant. These results suggest that scCO2 reaction induced dewetting can result in higher degrees of CO2 residual trapping in the post-injection stage than previously predicted. (2) Core Scale Studies. Capillary scaling is used routinely to predict Pc(S) relations for scCO2-brine systems at field scale, based on relations measured with air-water or mercury porosimetry. However, scaling-based predictions for CO2-brine systems have not been fully tested. Current limitations include the fact that imbibition curves are seldom measured due to experimental difficulties in controlling capillary pressure, and wettability (contact angles) is usually unknown and applied as adjustable parameters. Applying a new laboratory system to accurately control Pc at high total P, and we measured Pc(S) of a homogeneous quartz sand (selected because its 'normal' hydraulic properties are very well constrained). Drainage and imbibition experiments were conducted to directly measure Pc(S) with air-brine, then with scCO2-brine. With scCO2, intermediate levels of S shifted to Pc values 30% to 90% lower than predicted based on scaling with interfacial tension. Capillary trapping of CO2 were measured at Pc = 0 during brine imbibition, with trapped volumes for scCO2 significantly greater than for trapped air. We conclude that the observed deviations from scaling predictions make predicting the hydraulic behavior of scCO2 in reservoirs more challenging, and that an understanding of scCO2-induced wettability change is needed.

Wan, J.; Tokunaga, T. K.; Kim, Y.; Jung, J.; Kim, T.; Dong, W.

2013-12-01

235

Surface reaction of LiCoO2/Li system under high-voltage conditions by X-ray spectroscopy and two-dimensional correlation spectroscopy (2D-COS).  

PubMed

We studied the surface reactions of a LiCoO(2)/Li cell under high-voltage conditions using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and two-dimensional correlation spectroscopy (2D-COS). 2D XPS correlation spectra show that Li(2)CO(3) is formed first by decomposition of the organic solvents, and then polycarbonate, which is formed by polymerization of the electrolytes, is produced on the cathode surface of the LiCoO(2)/Li system under high-voltage conditions. XAS measurements also confirm that the solid electrolyte interface (SEI) layer is formed on the LiCoO(2) electrode by decomposition of the organic solvents. The thickness of the SEI layer is less than 100 Å. PMID:21352653

Park, Yeonju; Kim, Nam Hoon; Kim, Jong Myong; Kim, Young Chul; Jeong, Yeon Uk; Lee, Sung Man; Choi, Hyun Chul; Jung, Young Mee

2011-03-01

236

Diels-Alder reactions of 3-substituted coumarins in water and under high-pressure condition. An uncatalyzed route to tetrahydro-6H-benzo[c]chromen-6-ones.  

PubMed

[reaction: see text] Diels-Alder reactions of 3-substituted coumarins 1a-g with methyl-1,3-butadienes 2a-c carried out in water alone and in CH2Cl2 under 9 kbar pressure are reported. In aqueous medium satisfactory results were obtained by operating at 150 degrees C, whereas under high pressure the cycloadditions were complete at 60-70 degrees C with excellent yields (85-95%). The reactions with isoprene (2b) always resulted in the exclusive formation of para cycloadducts, whereas with (E)-piperylene (2c) only ortho products were detected. The cycloaddition of 3-phenylsulfonylcoumarin (1a) with (E)-piperylene (2c) allowed the endo adduct to be obtained exclusively, whereas 3-carboxycoumarin (1b) reacted with 2c to give a mixture of the corresponding endo/exo adducts in a 58:42 ratio in water and in a 45:55 ratio under high-pressure condition. PMID:16388619

Girotti, Rugiada; Marrocchi, Assunta; Minuti, Lucio; Piermatti, Oriana; Pizzo, Ferdinando; Vaccaro, Luigi

2006-01-01

237

Effect of Immersion Reaction Condition on the Morphology and Optical Properties of ZnO Nanorods Grown on Porous Silicon Substrates  

NASA Astrophysics Data System (ADS)

We report the structural and optical properties of ZnO nanorods grown on porous silicon substrate using sol-gel immersion method under different conditions. A simple method to prepare the ZnO nanorods from aqueous solution that contain zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and hexamethylenetetramine (C6H12N4) is presented. All the samples were characterized using scanning electron microscope (SEM) and photoluminescence (PL) spectroscope. The results demonstrate that the morphology and the optical properties of ZnO nanorods on porous silicon are determined by the concentration of precursors and growth time. The growth of ZnO nanorods is most sensitive to temperatures and the size of the rods can be controlled by adjusting the precursor concentration and by the growth time.

Amizam, S.; Mamat, M. H.; Khusaimi, Z.; Rafaie, H. A.; Sahdan, M. Z.; Abdullah, S.; Rusop, M.

2009-06-01

238

Reactions of (+)-catechin with salivary nitrite and thiocyanate under conditions simulating the gastric lumen: Production of dinitrosocatechin and its thiocyanate conjugate.  

PubMed

Abstract Catechins are ingested as food components and supplements. It is known that catechins are transformed to dinitrosocatechins by nitrite under acidic conditions, suggesting the possibility of their formation in the stomach because saliva contains nitrite. This paper deals with nitrite-induced transformation of (+)-catechin in methanol extracts of adzuki bean into 6,8-dinitrosocatechin in acidified saliva (pH ? 1.9). As the mechanism of its formation, addition of nitric oxide (NO) to (+)-catechin semiquinone radical, both of which were produced in nitrous acid/(+)-catechin systems, was proposed. The dinitrosocatechin was oxidized to the quinone by nitrous acid, and the quinone reacted with a salivary component thiocyanate producing 6'-thiocyanato-6,8-dinitrosocatechin. Since quinones are toxic, we propose a function of thiocyanate as a scavenger of the o-quinone formed from dinitrosocatechins in the stomach. PMID:24886172

Takahama, U; Yamauchi, R; Hirota, S

2014-08-01

239

In situ infrared emission spectroscopy for quantitative gas-phase measurement under high temperature reaction conditions: an analytical method for methane by means of an innovative small-volume flowing cell.  

PubMed

We have used infrared emission spectroscopy (IRES) in order to perform in situ studies under flowing gas-phase conditions. When the small-volume cell developed herein is used, we can (1) observe emission spectra from a hot gas-phase sample having an effective volume much less than one milliliter, (2) observe spectra of typical molecular species present, and (3) observe spectra of the more important molecular species down to below 10% and in some cases even as low as 1%. In addition, an analytical method has been derived in order to conduct quantitative studies under typical reaction conditions. We show that simplifications can be made in the data acquisition and handling for a direct linear correlation between band intensity and concentration with only simple background correction. The practical lower limit for methane in the present setup is approximately 0.5-1% v/v depending on the selected temperature. Our data were collected at 500, 600, and 700 degrees C, respectively. The major features of the present cell design are fairly simple and basically formed by a quartz tube (outer diameter=6 mm, inner diameter=4 mm) inside a metal pipe and two tubular ceramic heaters. This simple setup has advantages and attractive features that have extended the application of IRES to new fields and, in particular, for in situ studies of hydrocarbon reactions at different residence times at high temperature. PMID:20149274

Usseglio, Sandro; Thorshaug, Knut; Karlsson, Arne; Dahl, Ivar M; Nielsen, Claus J; Jens, Klaus-J; Tangstad, Elisabeth

2010-02-01

240

Epoxide Reactions  

NASA Astrophysics Data System (ADS)

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

Bertolini, Thomas

2002-07-01

241

Oxidative dimerization of (E)- and (Z)-2-propenylsesamol with O2 in the presence and absence of laccases and other catalysts: selective formation of carpanones and benzopyrans under different reaction conditions.  

PubMed

The oxidative dimerization of 2-propenylsesamol to carpanone with O(2) as the oxidant, which probably proceeds as a domino phenol oxidation/anti-?,?-radical coupling/intramolecular hetero Diels-Alder reaction, can be efficiently catalyzed by laccases. Experiments with laccases and other catalysts like a Co(salen) type catalyst and PdCl(2) clearly demonstrate that the diastereoselectivity of the carpanone formation does not depend on the catalyst but on the double-bond geometry of the substrate. With (E)-2-propenylsesamol as the substrate, carpanone and a so far unknown carpanone diastereoisomer are formed in a 9:1 ratio. When (Z)-2-propenylsesamol is used as starting material, carpanone is accompanied by two carpanone diastereoisomers unknown so far in a 5:1:4 ratio. All three carpanone diastereoisomers have been separated by HPLC, and their structures have been elucidated unambiguously by NMR spectroscopy, DFT calculations, and spin work analysis. When the oxidation of 2-propenylsesamol with O(2) is performed in the absence of any catalyst two diastereoisomeric benzopyrans are formed, probably as the result of a domino oxidation/intermolecular hetero Diels-Alder reaction. Under these conditions, carpanone is formed in trace amounts only. PMID:22458664

Constantin, Mihaela-Anca; Conrad, Jürgen; Meri?or, Elena; Koschorreck, Katja; Urlacher, Vlada B; Beifuss, Uwe

2012-05-18

242

Reaction time  

Microsoft Academic Search

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

V. A. C. Henmon

1918-01-01

243

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

244

Enzyme Reactions  

NSDL National Science Digital Library

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

School, Minerva D.

2011-10-03

245

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

246

The redox-Mannich reaction.  

PubMed

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

Chen, Weijie; Seidel, Daniel

2014-06-01

247

Green chemistry approaches to the synthesis of 5-alkoxycarbonyl-4-aryl-3,4- dihydropyrimidin-2(1H)-ones by a three-component coupling of one-pot condensation reaction: comparison of ethanol, water, and solvent-free conditions.  

PubMed

A general and practical green chemistry route to the Biginelli cyclocondensation reaction using cerium(III) chloride as the catalyst (25% mol) is described under three different sets of reaction conditions. This method provides an efficient and much improved modification of original Biginelli reaction reported in 1893, in terms of high yields, short reaction times, and simple work-up procedure, and it has the ability to tolerate a wide variety of substitutions in all three components, which is lacking in existing procedures. PMID:12530887

Bose, D Subhas; Fatima, Liyakat; Mereyala, Hari Babu

2003-01-24

248

FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

249

Biogeochemical Reactions Under Simulated Europa Ocean Conditions  

Microsoft Academic Search

Galileo data have demonstrated the probable presence of a liquid water ocean on Europa, and existence of salts and carbon dioxide in the satellite's surface ice (e.g., Carr et al., 1998; McCord et al., 1999, Pappalardo et al., 1999; Kivelson et al., 2000). Subsequently, the discovery of chemical signatures of extinct or extant life in Europa's ocean and on its

X. Amashukeli; S. A. Connon; D. F. Gleeson; R. S. Kowalczyk; R. T. Pappalardo

2007-01-01

250

Laboratory study on new particle formation from the reaction OH + SO2: influence of experimental conditions, H2O vapour, NH3 and the amine tert-butylamine on the overall process  

NASA Astrophysics Data System (ADS)

Nucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13-61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4-300)·105 molecule cm-3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7-2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing a first estimate. Addition of 1.2·1011 molecule cm-3 or 1.2·1012 molecule cm-3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions. NH3 showed a contribution to particle growth. Adding the amine tert-butylamine instead of NH3, the enhancing impact for nucleation and particle growth appears to be stronger.

Berndt, T.; Stratmann, F.; Sipilä, M.; Vanhanen, J.; Petäjä, T.; Mikkilä, J.; Grüner, A.; Spindler, G.; Mauldin, R. Lee, III; Curtius, J.; Kulmala, M.; Heintzenberg, J.

2010-03-01

251

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

252

Title: Elucidation of Environmental Fate of Artificial Sweeteners (Aspartame, Acesulfame K and Saccharin) by Determining Bimolecular Rate Constants with Hydroxyl Radical at Various pH and Temperature Conditions and Possible Reaction By-Products  

NASA Astrophysics Data System (ADS)

Use of artificial sweeteners in beverages and food has been rapidly increasing because of their non-calorie nature. In Japan, aspartame, acesulfame K and sucralose are among the most widely used artificial sweeteners. Because the artificial sweeteners are not metabolized in human bodies, they are directly excreted into the environment without chemical transformations. We initiated a study to better understand the fate of artificial sweeteners in the marine environment. The hydroxyl radical (OH), the most potent reactive oxygen species, reacts with various compounds and determines the environmental oxidation capacity and the life-time of many compounds. The steady-state OH concentration and the reaction rate constants between the compound and OH are used to estimate the life-time of the compound. In this study, we determine the bimolecular rate constants between aspartame, acefulfame K and saccharin and OH at various pH and temperature conditions using a competition kinetics technique. We use hydrogen peroxide as a photochemical source of OH. Bimolecular rate constant we obtained so far for aspartame was (2.6±1.2)×109 M-1 s-1 at pH = 3.0 and (4.9±2.3)×109 M-1 s-1 at pH = 5.5. Little effect was seen by changing the temperatures between 15 and 40 oC. Activation energy (Ea) was calculated to be -1.0 kJ mol-1 at pH = 3.0, +8.5 kJ mol-1 at pH = 5.5, which could be regarded as zero. We will report bimolecular rate constants at different pHs and temperatures for acesulfame K and saccharin, as well. Possible reaction by-products for aspartame will be also reported. We will further discuss the fate of aspartame in the coastal environment.

Teraji, T.; Arakaki, T.; Suzuka, T.

2012-12-01

253

QD-antibody conjugates via carbodiimide-mediated coupling: a detailed study of the variables involved and a possible new mechanism for the coupling reaction under basic aqueous conditions.  

PubMed

A detailed study into the optimization of carbodiimide-mediated coupling of antibodies (Ab) and quantum dots (QD) for use in cellular imaging has been undertaken. This involved the grafting of commercially available carboxyl-modified QDs (Evident Technologies "Lake Placid Blue" Evitag and eBioscience's eflour nanocrystals) with anti-Cdc8 Abs to produce conjugates with specific affinity for fission yeast tropomyosin Cdc8 protein. The water-soluble carbodiimide 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was used to activate the QDs prior to their incubation with antibody, and a range of QD-carboxyl/EDC/Ab mole ratios were used in the experiments in attempts to optimize fluorescence and bioaffinity of the conjugate products (EDC to QD-carboxyl-600 nmol/15 pmol to 0.12 nmol/15 pmol and QD to Ab 120 pmol/24 pmol to 120 pmol/1.2 pmol). It was observed that a specific "optimum" ratio of the three reactants was required to produce the most fluorescent and biologically active product and that it was generated at alkaline pH 10.8. Increasing the ratio of Ab to QD produced conjugate which was less fluorescent while reducing the ratio of EDC to QD in the activation step led to increased fluorescence of product. Conjugates were tested for their possession of antibody by measurement of their absorption at OD(280 nm) and for their fluorescence by assay ?(max(em)) at 495 nm. A quantitative assay of the bioactivity of the conjugates was developed whereby a standardized amount of Cdc8 antigen was spotted onto nylon membranes and reacted with products from conjugation reactions in a sandwich-type colormetric assay The "best" conjugate was used in intracellular imaging of yeast Cdc8 protein and produced brighter, higher definition images of fixed yeast cell actin structure than a fluorescein-Ab conjugate routinely produced in our laboratory. The QD-Ab conjugate was also significantly more resistant to photobleaching than the fluorescein-Ab conjugate. Results from other experiments involving EDC, the water-soluble carbodiimide 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulphonate (CMC), and EDC.HCl have suggested a new reaction mechanism for EDC coupling under basic aqueous conditions. In summary, a robust understanding of commercial QD-COOH surface chemistry and the variables involved in the materials' efficient conjugation with a bioligand using carbidiimide has been obtained along with an optimized approach for Ab-QD conjugate production. A novel assay has been developed for bioassay of QD-Ab conjugates and a new mechanism for EDC coupling under basic aqueous conditions is proposed. PMID:21970592

East, Daniel A; Mulvihill, Daniel P; Todd, Michael; Bruce, Ian J

2011-11-15

254

Reaction Time  

NSDL National Science Digital Library

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

Science, New Y.

1999-01-01

255

Reaction Kinetics  

NASA Astrophysics Data System (ADS)

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

Peiris, Suhithi M.

256

Laboratory study on new particle formation from the reaction OH + SO2: influence of experimental conditions, H2O vapour, NH3 and the amine tert-butylamine on the overall process  

NASA Astrophysics Data System (ADS)

Nucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13-61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4-300) ×105 molecule cm-3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7-2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing an upper limit. Addition of 1.2×1011 molecule cm-3 or 1.2×1012 molecule cm-3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions, i.e. a rise of the particle number by 1-2 orders of magnitude at RH = 13% and only by a factor of 2-5 at RH = 47% (NH3 addition: 1.2×1012 molecule cm-3). Using the amine tert-butylamine instead of NH3, the enhancing impact of the base for nucleation and particle growth appears to be stronger. Tert-butylamine addition of about 1010 molecule cm-3 at RH = 13% enhances particle formation by about two orders of magnitude, while for NH3 only a small or negligible effect on nucleation in this range of concentration appeared. This suggests that amines can strongly influence atmospheric H2SO4-H2O nucleation and are probably promising candidates for explaining existing discrepancies between theory and observations.

Berndt, T.; Stratmann, F.; Sipilä, M.; Vanhanen, J.; Petäjä, T.; Mikkilä, J.; Grüner, A.; Spindler, G.; Mauldin, R. Lee, III; Curtius, J.; Kulmala, M.; Heintzenberg, J.

2010-08-01

257

Lithium Cell Reactions.  

National Technical Information Service (NTIS)

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

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

1985-01-01

258

Lithium Cell Reactions.  

National Technical Information Service (NTIS)

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

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

1983-01-01

259

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.

260

[Periosteal reaction].  

PubMed

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

Fukuda, K

1999-06-01

261

Drug Reactions  

MedlinePLUS

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

262

Section i: Thermodynamic Properties of Hydrocarbon Radicals, Peroxy Hydrocarbon and Peroxy Chlorohydrocarbon Molecules and Radicals. Section II. Kinetics and Reaction Mechanisms For: (1) Chloroform Pyrolysis and Oxidation; (2) Benzene and Toluene Oxidation Under Atmospheric Conditions.  

NASA Astrophysics Data System (ADS)

Alkyl radicals are important active intermediates in gas phase photochemistry and combustion reaction systems. With the exception of a limited number of the most elementary radicals, accurate thermodynamic properties of alkyl radicals are either not available or only rough estimations exist. An H atom Bond Increment approach is developed and a data base is derived, for accurately estimating thermodynamic properties (Delta H_{f }^circ298, S ^circ298 and Cp(T)) for generic classes of hydrocarbon radical species. Reactions of alkyl radicals with molecular oxygen are one of the major reaction paths for these radicals in atmospheric photochemistry, oxidation of hydrocarbon liquids and combustion process. Alkyl hydroperoxides are subsequently formed through the alkyl peroxy radicals reactions with varied chemical species present in the reaction system. Thermodynamic properties of the alkyl hydroperoxides and related radicals are therefore frequently required in gas phase modeling and kinetic studies on these systems. The thermodynamic properties of alkyl hydroperoxides, alkyl peroxy radicals and hydroperoxyl-1-ethyl radicals including the species with fluorine and chlorine substituents on the alpha-carbon are evaluated using molecular orbital calculations. Chloroform is used as a model chlorocarbon system with high Cl/H ratio to investigate thermal decomposition processes of chlorocarbons in oxidative and pyrolytic reaction environments. A detailed reaction mechanism is developed to describe the important features of products and reagent loss and is shown to predict the experimental data well. Reaction pathways and rate constants are developed for CCl _3, CCl_2 and rm C_2Cl_3 radical addition to O_2 and combination with O, OH HO_2 and ClO. The reversible addition reaction of OH radical with benzene to form the hydroxyl-2,4-cyclohexadienyl (benzene -OH) adduct and the subsequent reactions of this benzene -OH adduct with O_2 are important initial steps for the photooxidation of benzene and other aromatic species in the atmosphere. OH addition to the benzene ring, the subsequent reaction of O_2 with the hydroxyl-2,4-cyclohexadienyl to form hydroxyl -2-peroxy-4-cyclohexenyl (benzene-OH-O_2 adduct), are chemical activation reactions and are a function of both pressure and temperature. The kinetics of these two reaction systems at various pressure & temperatures using a quantum version of Rice-Ramsperger-Kassel theory (QRRK) and a modified strong collision approach are analyzed and calculated. The analogue reaction system of toluene photooxidation is also analyzed. Reaction mechanisms are developed for initial steps of atmospheric oxidation of benzene and toluene, which include reverse reaction rates determined from thermodynamic parameters and microscopic reversibility. The model results show good agreement with the limited available experimental data.

Lay, Tsan-Horng

1995-01-01

263

A 3D-RISM-SCF method with dual solvent boxes for a highly polarized system: application to 1,6-anhydrosugar formation reaction of phenyl ?- and ?-D-glucosides under basic conditions.  

PubMed

One of the difficulties in application of the usual reference interaction site model self-consistent field (RISM-SCF) method to a highly polarized and bulky system arises from the approximate evaluation of electrostatic potential (ESP) with pure point charges. To improve this ESP evaluation, the ESP near a solute is directly calculated with a solute electronic wavefunction, that distant from a solute is approximately calculated with solute point charges, and they are connected with a switching function. To evaluate the fine solvation structure near the solute by incorporating the long-range solute-solvent Coulombic interaction with low computational cost, we introduced the dual solvent box protocol; one small box with the fine spacing is employed for the first and the second solvation shells and the other large box with the normal spacing is employed for long-range solute-solvent interaction. The levoglucosan formation from phenyl ?- and ?-d-glucosides under basic conditions is successfully inspected by this 3D-RISM-SCF method at the MP2 and SCS-MP2 levels, though the 1D-RISM-SCF could not be applied to this reaction due to the presence of highly polarized and bulky species. This 3D-RISM-SCF calculation reproduces the experimentally reported higher reactivity of the ?-anomer. The 3D-RISM-SCF-calculated activation free energy for the ?-anomer is closer to the experimental value than the PCM-calculated one. Interestingly, the solvation effect increases the difference in reactivity between these two anomers. The reason is successfully elucidated with 3D-RISM-SCF-calculated microscopic solvation structure and decomposition analysis of solute-solvent interaction. PMID:23525092

Aono, Shinji; Hosoya, Takashi; Sakaki, Shigeyoshi

2013-05-01

264

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

PubMed

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

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

2006-01-01

265

Reaction Time  

NSDL National Science Digital Library

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

Boston, Wgbh

2003-01-01

266

Reaction time  

Microsoft Academic Search

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

V. A. C. Henmon

1916-01-01

267

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.

268

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

269

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

PubMed

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

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

2014-05-01

270

Metal Reactions  

NSDL National Science Digital Library

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

Industry, Oregon M.

1997-01-01

271

Side-Chain Reactions of Benzene Derivatives  

Microsoft Academic Search

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

W. S. Nathan; H. B. Watson

1934-01-01

272

Infant Defensive Reactions to Visual Occlusion.  

ERIC Educational Resources Information Center

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

Adamson, Lauren; Tronick, Edward

273

Delta9-tetrahydrocannabinol and cannabidiol, but not ondansetron, interfere with conditioned retching reactions elicited by a lithium-paired context in Suncus murinus: An animal model of anticipatory nausea and vomiting  

Microsoft Academic Search

Chemotherapy patients report not only acute nausea and vomiting during the treatment itself, but also report anticipatory nausea and vomiting upon re-exposure to the cues associated with the treatment. We present a model of anticipatory nausea based on the emetic reactions of the Suncus murinus (musk shrew). Following three pairings of a novel distinctive contextual cue with the emetic effects

Linda A. Parker; Magdalena Kwiatkowska; Raphael Mechoulam

2006-01-01

274

Section i: Thermodynamic Properties of Hydrocarbon Radicals, Peroxy Hydrocarbon and Peroxy Chlorohydrocarbon Molecules and Radicals. Section II. Kinetics and Reaction Mechanisms For: (1) Chloroform Pyrolysis and Oxidation; (2) Benzene and Toluene Oxidation Under Atmospheric Conditions  

Microsoft Academic Search

Alkyl radicals are important active intermediates in gas phase photochemistry and combustion reaction systems. With the exception of a limited number of the most elementary radicals, accurate thermodynamic properties of alkyl radicals are either not available or only rough estimations exist. An H atom Bond Increment approach is developed and a data base is derived, for accurately estimating thermodynamic properties

Tsan-Horng Lay

1995-01-01

275

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

NASA Technical Reports Server (NTRS)

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2010-01-01

276

Related Conditions  

MedlinePLUS

... increased symptoms. Celiac Disease An adverse reaction to gluten is known as celiac disease or “celiac sprue.” ... chronic digestive disease requires a lifelong restriction of gluten, which is found in wheat, rye, barley, and ...

277

Diamine Ligands in Copper-Catalyzed Reactions  

PubMed Central

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

Surry, David S.

2012-01-01

278

Decomposition of Methane over Iron Catalysts at the Range of Moderate Temperatures: The Influence of Structure of the Catalytic Systems and the Reaction Conditions on the Yield of Carbon and Morphology of Carbon Filaments  

Microsoft Academic Search

Decomposition of high-purity methane in the presence of ?-Fe-based catalysts to produce filamentous carbon was investigated. The reaction was studied in the temperature range of 650 to 800°C. Filamentous carbon was demonstrated to form at temperatures not lower than 680°C in the presence of both bare ?-Fe and catalysts based thereon with admixtures of various hard-to-reduce oxides (SiO2, Al2O3, ZrO2,

Marina A Ermakova; Dmitry Yu Ermakov; Andrey L Chuvilin; Gennady G Kuvshinov

2001-01-01

279

Catalytic Organometallic Reactions of Ammonia  

PubMed Central

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

Klinkenberg, Jessica L.

2012-01-01

280

Mechanisms of reactions of open-shell, heavier group 14 derivatives with small molecules: n-?* back-bonding in isocyanide complexes, C-H activation under ambient conditions, CO coupling, and ancillary molecular interactions.  

PubMed

The main themes of this review are the mechanisms of the reactions of germanium and tin analogues of carbenes with isocyanides, CO, ammonia, and related molecules. The treatment of Ge(Ar(Me6))2 (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2) with MeNC or Bu(t)NC afforded 1:1 complexes, but the increase in the electron density at germanium leads to C-H activation at the isocyanide methyl or tert-butyl substituents. For MeNC, the initial adduct formation is followed by a migratory insertion of the MeNC carbon into a Ge-C(ipso) bond of an aryl substituent. The addition of excess MeNC led to sequential insertions of two further MeNC molecules. The third insertion led to methylisocyanide methyl group C-H activation, to afford an azagermacyclopentadienyl species. The Bu(t)NC complex (Ar(Me6))2GeCNBu(t) spontanously transforms into (Ar(Me6))2Ge(H)CN and isobutene with C-H activation of the Bu(t) substituent. The germylene Ge(Ar(Me6))(Ar(Pr(i)4)) [Ar(Pr(i)4) = C6H3-2,6(C6H3-2,6-Pr(i)2)2] reacted with CO to afford ?-germyloxyketones. The initial step is the formation of a 1:1 complex, followed by migratory insertion into the Ge-C bond of the Ar(Pr(i)4) ligand to give Ar(Me6)GeC(O)Ar(Pr(i)4). Insertion of a second CO gave Ar(Me6)GeC(O)C(O)Ar(Pr(i)4), which rearranges to afford ?-germyloxyketone. No reaction was observed for Sn(Ar(Me6))2 with RNC (R = Me, Bu(t)) or CO. Spectroscopic (IR) results and density functional theory (DFT) calculations showed that the reactivity can be rationalized on the basis of Ge-C (isocyanide or CO) Ge(n) ? ?* (ligand) back-bonding. The reaction of Ge(Ar(Me6))2 and Sn(Ar(Me6))2 with ammonia or hydrazines initially gave 1:1 adducts. However, DFT calculations show that there are ancillary N-H---N interactions with a second ammonia or hydrazine, which stabilizes the transition state to form germanium(IV) hydride (amido or hydrazido) products. For tin, arene elimination is favored by a buildup of electron density at the tin, as well as the greater polarity of the Sn-C(ipso) bond. Germanium(IV) products were observed upon reaction of Ge(Ar(Me6))2 with acids, whereas reactions of Sn(Ar(Me6))2 with acids did not give tin(II) products. In contrast to reactions with NH3, there is no buildup of negative charge at tin upon protonation, and its subsequent reaction with conjugate bases readily affords the tin(IV) products. PMID:23683137

Brown, Zachary D; Power, Philip P

2013-06-01

281

Multisite reversible geminate reaction.  

PubMed

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

Park, Soohyung; Agmon, Noam

2009-02-21

282

Magnetized target fusion ignition conditions  

Microsoft Academic Search

Magnetized Target Fusion (MTF) consists of the hydrodynamic compression of a wall, hot, magnetized DT plasma to ignition conditions. MTF takes advantage of two benefits of a magnetic field in a plasma: reduction of the thermal conductivity and enhancement of the charged particle reaction product energy deposition. To study the ignition conditions, we evaluate the gains brought by compression and

R. de Peretti; M. Sabatier

1995-01-01

283

Skin Conditions  

MedlinePLUS

... redness, swelling, burning, and itching. Allergies, irritants, your genetic makeup, and certain diseases and immune system problems can cause rashes, hives, and other skin conditions. Many skin problems, ...

284

Chemical reaction dynamics  

PubMed Central

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

Crim, F. Fleming

2008-01-01

285

Platinum-cobalt catalysts for the oxygen reduction reaction in high temperature proton exchange membrane fuel cells - Long term behavior under ex-situ and in-situ conditions  

NASA Astrophysics Data System (ADS)

Platinum cobalt catalysts (Pt-Co) have attracted much interest as cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high activity toward oxygen reduction reaction (ORR). Many of the reported catalysts show outstanding performance in ex-situ experiments. However, the laborious synthesis protocols of these Pt-Co catalysts disable an efficient and economic production of membrane electrode assemblies (MEAs). We present an economic, flexible and continuous Pt-M/C catalyst preparation method as part of a large scale membrane electrode assembly manufacturing. In comparison, the as-prepared Pt-Co/C based high temperature (HT)-PEM MEA showed an equal performance to a commercially available HT-PEM MEA during 600 h of operation under constant load, although the commercial one had a significantly higher Pt loading at the cathode.

Schenk, Alexander; Grimmer, Christoph; Perchthaler, Markus; Weinberger, Stephan; Pichler, Birgit; Heinzl, Christoph; Scheu, Christina; Mautner, Franz-Andreas; Bitschnau, Brigitte; Hacker, Viktor

2014-11-01

286

On the formation of ethynylbiphenyl (C14D5H5; C6D5C6H4CCH) isomers in the reaction of D5-phenyl radicals (C6D5; X2A1) with phenylacetylene (C6H5C2H; X1A1) under single collision conditions  

NASA Astrophysics Data System (ADS)

Reaction dynamics of the D5-phenyl radical with phenylacetylene were investigated in crossed molecular beams at a collision energy of 120.7 kJ mol?1 supported by ab initio calculations. The reaction displays indirect, complex forming scattering dynamics, and adduct formation, with D5-phenyl attacking the phenyl ring of phenylacetylene at the ortho, meta and para positions over small entrance barriers. The adduct (C6D5C8H6) undergoes hydrogen emission through tight exit transition states of 34–47 kJ mol?1 above the separated products. The phenyl addition–hydrogen elimination mechanism produces various ethynylbiphenyls exoergically by 25–38 kJ mol?1. No phenanthrene was formed under our experimental conditions.

Parker, Dorian S. N.; Yang, Tao; Kaiser, Ralf I.; Landera, Alexander; Mebel, Alexander M.

2014-03-01

287

Experimental Study of Serpentinization Reactions  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

288

Microwave Irradiation and Multicomponent Reactions  

Microsoft Academic Search

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

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

2010-01-01

289

Reactions of nitrate salts with ammonia in supercritical water  

Microsoft Academic Search

Reactions involving nitrate salts and ammonia were investigated in supercritical water at temperatures from 450 to 530 C and pressures near 300 bar. Reaction products included nitrite, nitrogen gas, and nitrous oxide. Observed reaction rates and product distributions provided evidence for a free-radical reaction mechanism with NOâ, NO, and NHâ· as the primary reactive species at supercritical conditions. In the

Philip C. Dell'Orco; Earnest F. Gloyna; Steven J. Buelow

1997-01-01

290

Shock tube measurements of rate coefficients of elementary gas reactions  

Microsoft Academic Search

The primary objective of this paper is to review the current status of rate coefficient determinations of elementary gas reactions using modern shock tube measurement technques. The major inaccuracies in these determinations arise from uncertainties in reaction conditions due to gas dynamic effects, uncertainties introduced by interfering rate processes such as vibrational relaxation, competing reactions, or reactions involving impurities, and

Craig T. Bowman; Ronald K. Hanson

1979-01-01

291

Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ  

Microsoft Academic Search

Summary  Final reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibres at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation. Reaction rates recorded in different

Dirk Pette; Universitfit Konstanz

1981-01-01

292

Sequential evolution of different phases in metastable Gd(2-x)Ce(x)Zr(2-x)Al(x)O7 (0.0 ? x ? 2.0) system: crucial role of reaction conditions.  

PubMed

The Gd(2-x)Ce(x)Zr(2-x)Al(x)O7 (0.0 ? x ? 2.0) series was synthesized by the gel combustion method. This system exhibited the presence of a fluorite-type phase, along with a narrow biphasic region, depending upon the Ce/Gd content in the sample. Thermal stability of these new compounds under oxidizing and reducing conditions has been investigated. The products obtained on decomposition of Gd(2-x)Ce(x)Zr(2-x)Al(x)O7 in oxidizing and reducing conditions were found to be entirely different. It was observed that in air the fluorite-type solid solutions of Gd(2-x)Ce(x)Zr(2-x)Al(x)O7 composition undergo phase separation into perovskite GdAlO3 and fluorite-type solid solutions of Gd-Ce-Zr-O or Ce-Zr-Al-O depending upon the extent of Ce and Al substitution. On the other hand, Gd(2-x)Ce(x)Zr(2-x)Al(x)O7 samples on heating under reducing conditions show a phase separation to CeAlO3 perovskite and a defect-fluorite of Gd2Zr2O7. The extent of metastability for a typical composition of Gd(1.2)Ce(0.8)Zr(1.2)Al(0.8)O7 (nano), Gd(1.2)Ce(0.8)Zr(1.2)Al(0.8)O(6.6) (heated under reduced conditions), Gd(1.2)Ce(0.8)Zr(1.2)Al(0.8)O7 (heated in air at 1200 °C) has been experimentally determined employing a high temperature Calvet calorimeter. On the basis of thermodynamic stability data, it could be inferred that the formation of a more stable compound in the presence of two competing cations (i.e., Gd(3+) and Ce(3+)) is guided by the crystallographic stability. PMID:23790240

Shukla, Rakesh; Sayed, Farheen N; Phapale, Suhas; Mishra, Ratikant; Tyagi, Avesh K

2013-07-15

293

Nuclear Chain Reaction  

NSDL National Science Digital Library

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

Bauer, W. (Wolfgang), 1959-

2011-11-29

294

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

295

Developmental changes in cognitive reaction time of children aged 6–12 years  

Microsoft Academic Search

Using a visual Go\\/Nogo paradigm and subtraction methods, we examined detailed developmental changes in the cognitive reaction times of 153 healthy children aged 6–12 years. Three conditions were studied: simple reaction, even rate reaction (50% Go), and high rate reaction (80% Go). The subtraction of simple reaction time from even rate reaction time was considered to reflect discrimination time, while

Yukako Iida; Makoto Miyazaki; Sunao Uchida

2010-01-01

296

Dopamine D1-Like and D2-Like Receptors in the Dorsal Striatum Control Different Aspects of Attentional Performance in the Five-Choice Serial Reaction Time Task Under a Condition of Increased Activity of Corticostriatal Inputs  

PubMed Central

We investigated the interaction between the corticostriatal glutamatergic afferents and dopamine D1-like and D2-like receptors in the dorsomedial striatum (dm-STR) in attention and executive response control in the five-choice serial reaction time (5-CSRT) task. The competitive NMDA receptor antagonist 3-(R)-2-carboxypiperazin-4-propyl-1-phosphonic acid (CPP) injected in the mPFC impaired accuracy and increased premature and perseverative responding, raising GLU, DA, and GABA release in the dm-STR. The D1-like antagonist SCH23390 injected in the dm-STR reversed the CPP-induced accuracy deficit but did not affect the increase in perseverative responding. In contrast, the D2-like antagonist haloperidol injected in the dm-STR reduced the CPP-induced increase in perseverative responding but not the accuracy deficit. The different roles of dorsal striatal D1-like and D2-like receptor were further supported by the finding that activation of D1-like receptor in the dm-STR by SKF38393 impaired accuracy but not perseverative responding while the D2-like agonist quinpirole injected in the dm-STR increased perseverative responding but did not affect accuracy. These findings suggest that integration of cortical information by D1-like receptors in the dm-STR is a key mechanism of the input selection process of attention while the integration of corticostriatal signals by D2-like receptors preserves the ability to switch from one act/response to the next in a complex motor sequence, thus providing for behavioral flexibility.

Agnoli, Laura; Mainolfi, Pierangela; Invernizzi, Roberto W; Carli, Mirjana

2013-01-01

297

Cutaneous reactions to transdermal therapeutic systems.  

PubMed

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

Bershow, Andrea; Warshaw, Erin

2011-01-01

298

Partial Oxidation Reactions of Methane and Oxygen  

Microsoft Academic Search

In considering the typical experimental conditions used for studies of methane oxidation to oxygenates or hydrocarbons in the presence of catalysts, it is clear that a significant potential exists for the appearance of non-catalyzed, thermally activated gas-phase reactions of methane and oxygen. In order to identify and describe the contribution of the gas phase processes during catalyzed reactions, a chemical

M. W. Droege; L. M. Hair; W. J. Pitz; C. K. Westbrook

1989-01-01

299

The Mechanism of the Formaldehyde Clock Reaction.  

ERIC Educational Resources Information Center

Provides background information and problems with the formaldehyde clock reaction, including comparisons of experimental clock times reported in the literature and conditions for the reliable use of the formaldehyde clock based on a method discussed. (JN)

Burnett, M. G.

1982-01-01

300

Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.  

SciTech Connect

A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

2010-06-01

301

Acceleration of Petasis reactions of salicylaldehyde derivatives with molecular sieves.  

PubMed

Mild reaction conditions for Petasis reactions of substituted salicylaldehydes with various amines and arylboronic acids in the presence of molecular sieves were developed. Molecular sieves (MS) significantly accelerated the reaction rates and drove the reactions to high conversions. The conditions were applied to the synthesis of the core structure of BIIB042, a ?-secretase modulator, without stereochemical erosion of a stereogenic center in the salicylaldehyde intermediate. PMID:22171661

Shi, Xianglin; Hebrault, Dominique; Humora, Michael; Kiesman, William F; Peng, Hairuo; Talreja, Tina; Wang, Zezhou; Xin, Zhili

2012-01-20

302

Syngas Conditioning  

SciTech Connect

A brief review of water gas shift (WGS) catalysis is provided. An overview of the four general classes of WGS catalysts is presented, which include: 1) high temperature shift (HTS), 2) low temperature shift (LTS), 3) sulfur-tolerant shift catalysts, and 4) precious metal-based shift catalysts. A review of WGS utilizing monoliths or other reactor technologies that pertain to fuel cell applications, an area of increasing interest over the past several years, is also presented. Ratnasamy and Wagner have recently provided an outstanding and comprehensive review of WGS catalysis. A particular emphasis of that work is “catalyst surface structures, active sites, reaction intermediates, and mechanisms”, particularly for noble metal-based catalysts1. The summary provided here is a succinct review of water gas shift catalysis and reactors, with an emphasis on fuel processing applications for fuel cells, and is not intended to provide a comprehensive review of WGS technology.

Dagle, Robert A.; Karim, Ayman M.; Li, Guosheng; Su, Yu; King, David L.

2011-04-29

303

Mathematical model to predict drivers' reaction speeds.  

PubMed

Mental distractions and physical impairments can increase the risk of accidents by affecting a driver's ability to control the vehicle. In this article, we developed a linear mathematical model that can be used to quantitatively predict drivers' performance over a variety of possible driving conditions. Predictions were not limited only to conditions tested, but also included linear combinations of these tests conditions. Two groups of 12 participants were evaluated using a custom drivers' reaction speed testing device to evaluate the effect of cell phone talking, texting, and a fixed knee brace on the components of drivers' reaction speed. Cognitive reaction time was found to increase by 24% for cell phone talking and 74% for texting. The fixed knee brace increased musculoskeletal reaction time by 24%. These experimental data were used to develop a mathematical model to predict reaction speed for an untested condition, talking on a cell phone with a fixed knee brace. The model was verified by comparing the predicted reaction speed to measured experimental values from an independent test. The model predicted full braking time within 3% of the measured value. Although only a few influential conditions were evaluated, we present a general approach that can be expanded to include other types of distractions, impairments, and environmental conditions. PMID:22431214

Long, Benjamin L; Gillespie, A Isabella; Tanaka, Martin L

2012-02-01

304

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

305

A Lewis acid-promoted Pinner reaction  

PubMed Central

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

Pfaff, Dominik; Nemecek, Gregor

2013-01-01

306

Sequential Injection Analysis for Optimization of Molecular Biology Reactions  

PubMed Central

In order to automate the optimization of complex biochemical and molecular biology reactions, we developed a Sequential Injection Analysis (SIA) device and combined this with a Design of Experiment (DOE) algorithm. This combination of hardware and software automatically explores the parameter space of the reaction and provides continuous feedback for optimizing reaction conditions. As an example, we optimized the endonuclease digest of a fluorogenic substrate, and showed that the optimized reaction conditions also applied to the digest of the substrate outside of the device, and to the digest of a plasmid. The sequential technique quickly arrived at optimized reaction conditions with less reagent use than a batch process (such as a fluid handling robot exploring multiple reaction conditions in parallel) would have. The device and method should now be amenable to much more complex molecular biology reactions whose variable spaces are correspondingly larger.

Allen, Peter B.; Ellington, Andrew D.

2011-01-01

307

Microwave Irradiation and Multicomponent Reactions  

Microsoft Academic Search

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

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

308

Enhanced sludge dewatering by dual polyelectrolytes conditioning  

Microsoft Academic Search

Sludge dewatering by dual polyelectrolytes conditioning was investigated in this study. Single polyelectrolyte is utilized in sludge conditioning conventionally, in which charge neutralization and bridging are involved in the reactions. In the current study, both cationic and non-ionic polyelectrolytes were utilized simultaneously in the conditioning. Waste activated sludge was sampled from a synthetic fiber plant, and used in the experiment.

C. H Lee; J. C Liu

2000-01-01

309

Learning to Predict Chemical Reactions  

PubMed Central

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

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

2011-01-01

310

Learning to predict chemical reactions.  

PubMed

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

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

2011-09-26

311

Glycosylation reaction of unprotected sugars with hydroxyalkylthymine.  

PubMed

Under mild conditions (Lewis acid/solvent/room temperature), the reaction of unprotected glucose, deoxyribose or xylose with hydroxylalkylthymine gives selectively nucleoside analogs with a spacer arm between sugar and base moiety. Experimental conditions (Lewis acid, solvent) for this new strategy leading to nucleoside analogs synthesis are discussed. PMID:15281363

Zerrouki, Rachida; Billard, Luc; Granet, Robert; Krausz, Pierre

2004-05-01

312

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

313

Oral Hypersensitivity Reactions  

MedlinePLUS

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

314

Prediction of global reaction kinetics by solution of the Arrhenius parameterised component elementary reactions: microkinetic analysis  

Microsoft Academic Search

Microkinetic analysis of heterogeneous catalytic reactions originated in the early 1970s from a program (KINPAK) that was written to predict the performance of an industrial naphta cracker. This program accepted as input a statement of elementary gas phase cracking and radical-induced hydrogen abstraction reactions, together with their Arrhenius parameters. The reactor conditions of temperature, pressure, flow rate, reactor dimensions, composition

Kenneth C Waugh

1999-01-01

315

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.

316

Self-inhibited rate in gas-solid noncatalytic reactions. The shrinking core model  

Microsoft Academic Search

The shrinking core model is examined for gas-solid noncatalytic reactions with a self-inhibited rate form and it is shown that multiple reaction pathways are possible for solid particles reacted under identical conditions. The observed reaction rate can have up to two discontinuities (jumps) during reaction for particles of spherical and cylindrical shape. The geometric instability analysis reveals that the reaction

Henry F. Erk; Milorad P. Dudukovic

1984-01-01

317

Alkali-hydrogen reactions  

Microsoft Academic Search

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

King-Chuen Lin; Raymond Vetter

2002-01-01

318

Distribution function, reaction rates and spectral line profile  

Microsoft Academic Search

Quantum mechanics predicts the existence of power law “tails” in the distribution function over momentum in dense media even at the condition of thermodynamics equilibrium. Generalized expressions for the threshold process reaction rates show that reaction rates with released energy (e.g. vibrational-translational relaxation, chemical reaction, fusion rates) may be substantially increased due to quantum corrections. Spectral line profile also may

A. N Starostin; A. G Leonov; Yu. V Petrushevich; Vl. K Roerich

2004-01-01

319

Distribution function, reaction rates and spectral line profile  

Microsoft Academic Search

Quantum mechanics predicts the existence of power law ``tails'' in the distribution function over momentum in dense media even at the condition of thermodynamics equilibrium. Generalized expressions for the threshold process reaction rates show that reaction rates with released energy (e.g. vibrational-translational relaxation, chemical reaction, fusion rates) may be substantially increased due to quantum corrections. Spectral line profile also may

A. N. Starostin; A. G. Leonov; Yu. V. Petrushevich; Vl. K. Roerich

2004-01-01

320

REACTIONS OF FUEL NITROGEN COMPOUNDS UNDER CONDITIONS OF INERT PYROLYSIS  

EPA Science Inventory

The paper describes the pyrolysis of fossil fuels and model nitrogen compounds in helium in a small quartz plow reactor, as part of a study of the chemical mechanisms involved in the conversion of fuel-nitrogen compounds to nitric oxide (NO) during combustion. Hydrogen cyanide (H...

321

ENVIRONMENTALLY FRIENDLIER SYNTHESES USING MICROWAVES AND ALTERNATIVE REACTION CONDITIONS  

EPA Science Inventory

A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports such as alumina, silica, clay, or doped surfaces is presented which is applicable to a wide range of cleavage, c...

322

CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

323

Diels-Alder reaction of maldoxin with an isopropenylallene  

PubMed Central

The Diels–Alder reaction of maldoxin with an isopropenylallene at 60-75 °C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0-11%) that underwent an ene reaction to generate the chloropupukeanolide D (11-22%) skeleton. The Diels–Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions whereas the analogous Diels–Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction.

Yu, Min; Snider, Barry. B.

2011-01-01

324

The smallest chemical reaction system with bistability  

PubMed Central

Background Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity. Results Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i) reactants, (ii) reactions, and (iii) terms in the corresponding ordinary differential equations (decreasing importance from i-iii). The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular). We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature. Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc.), we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.). This helps modelling multistable systems and it is important for corresponding synthetic biology projects. Conclusion The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with simple systems and for synthetically designing new bistable systems. Our simple model system is also well suited for corresponding teaching purposes.

Wilhelm, Thomas

2009-01-01

325

Reactions in microemulsions: Effect of thermal fluctuations on reaction kinetics  

NASA Astrophysics Data System (ADS)

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

Ganesan, Venkat; Fredrickson, Glenn H.

2000-08-01

326

Reaction modeling in geothermal systems  

NASA Astrophysics Data System (ADS)

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

Stefansson, A.

2012-12-01

327

Carbon-carbon bond-forming reactions using alkyl fluorides  

Microsoft Academic Search

This account summarizes our recent results on C-C bond formation reactions using alkyl fluorides mostly focusing on the transition-metal-catalyzed reactions. These reactions proceed efficiently under mild conditions by the combined use of Grignard reagents and tran- sition-metal catalysts, such as Ni, Cu, and Zr. It is proposed that ate complex intermediates formed by the reaction of these transition metals with

Jun Terao; Hirohisa Todo; Hiroyasu Watabe; Aki Ikumi; Yoshiaki Shinohara; Nobuaki Kambe

2008-01-01

328

[Adverse reactions to vaccines].  

PubMed

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

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

2003-01-01

329

Mukaiyama Aldol Reactions in Aqueous Media  

PubMed Central

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

Kitanosono, Taku; Kobayashi, Shu

2013-01-01

330

Induced reaction within the peroxy-compounds  

Microsoft Academic Search

The induced reaction occurring in the H2O2-H2S2O8- KMnO4 [and Ce(SO4)2, resp.,] system was studied in detail and established that it strongly depends on the experimental conditions such as rate of stirring, speed of titration, dilution of the solution, temperature, concentrations of partners of the reaction, acid concentration etc. It was found further that the induced disappearence of peroxydisulphate as well

L. J. Csányi; J. Bátyai; F. Solymosi

1963-01-01

331

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.

332

Prebiotic condensation reactions using cyanamide  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

333

The reaction between spodumene and tachyhydrite  

NASA Astrophysics Data System (ADS)

The reaction between spodumene (Li2O • A12O2 • 4SiO2) and tachyhydrite (CaCl2 2MgCl2 • 12H2O) at temperatures above 1270 K, when the spodumene has transformed from the unreactive ?-form to the ?-form, was studied varying the reaction temperature and the relative proportions of the two minerals in the reaction mixtures. Mass balances as well as X-ray diffraction to identify the reaction products indicate that the reactions that occur are 1. a decomposition of the tachyhydrite, losing at first some of its water of crystallization, followed by MgCl2 hydrolyzing to MgO; 2. a transformation of the ?-spodumene into ?-spodumene; and 3. a reaction between the ?-spodumene, MgO produced from tachyhydrite, and CaCl2 of the tachyhydrite according to the equation: Li2O • A12O3 • 4SiO2 + CaCl2 + 8MgO = 2LiCl + CaO • MgO • SiO2 + 3SiO2 • 2MgO + A12O3 • MgO. X-ray diffraction confirmed the presence of all the phases in the products except the phase containing alumina. Considerations of the quaternary phase diagram Al203-SiO2-MgO-CaO show that the phases indicated as reaction products are the ones expected under equilibrium conditions at the reaction temperature. Calculated standard free energy change (?G°) of the suggested reaction is -211926 Joules at 1423 K, indicating that under standard conditions the reaction is possible.

El-Naggar, M. M. A.; Medina, L. F.; Espinola, A.

1988-08-01

334

Weathering Reactions and Soil-Groundwater Reactions  

NSDL National Science Digital Library

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

Sherman, David M.; Bristol, University O.

335

Reactions of C1 Building Blocks  

NASA Astrophysics Data System (ADS)

The chapter “Reactions of C1 Building Blocks” covers the direct conversion of methane to aromatics, the methanol-to-hydrocarbons (MTHC) conversion with respect to gasoline (methanol to gasoline) and olefins (methanol to olefins, methanol-to-propene) as well as some combinations like the TIGAS and Mobil's olefin-to-gasoline and distillate processes. The main focus within this chapter will be on the industrial processes, especially concerning the MTHC reactions - including catalytic systems, reaction conditions, process - and to a minor extent related to the mechanistic aspects and kinetic considerations.

Stöcker, Michael

336

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

337

Immediate Contact Reactions  

Microsoft Academic Search

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

David Basketter; Arto Lahti

338

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

339

New Serological Reactions in Syphilis.  

National Technical Information Service (NTIS)

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

M. E. Hadida M. Allinne J. Orfila

1966-01-01

340

Marketing Mix Reactions to Entry  

Microsoft Academic Search

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

William T. Robinson

1988-01-01

341

Organocatalytic asymmetric epoxidation and tandem epoxidation/Passerini reaction under eco-friendly reaction conditions.  

PubMed

An eco-friendly synthesis of highly functionalized epoxides and their incorporation into an organocatalytic multicomponent approach are reported. For this, a modified class of diarylprolinol silyl ethers was designed to enable high catalytic activity in an environmentally benign solvent system. The one-pot procedure showed great efficiency in promoting stereoselective multicomponent transformations in a tandem, 'green' fashion. Because of its non-residual, efficient and selective character, this synthetic design shows promise for large-scale applications in both diversity and target-oriented syntheses. PMID:22918441

Deobald, Anna Maria; Corrêa, Arlene G; Rivera, Daniel G; Paixão, Márcio Weber

2012-10-14

342

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

343

Smell the Maillard Reaction  

NSDL National Science Digital Library

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

Exploratorium

2012-10-03

344

Surface catalyzed mercury transformation reactions  

NASA Astrophysics Data System (ADS)

Mercury is a known pollutant that has detrimental effect on human health and environment. The anthropogenic emissions of mercury account for 10 to 30% of worldwide mercury emissions. There is a need to control/reduce anthropogenic mercury emissions. Many mercury control technologies are available but their effectiveness is dependent on the chemical form of mercury, because different chemical forms of mercury have different physical and chemical properties. Mercury leaves the boiler in its elemental form but goes through various transformations in the post-combustion zone. There is a need to understand how fly ash and flue gas composition affect speciation, partitioning, and reactions of mercury under the full range of post-combustion zone conditions. This knowledge can then be used to predict the chemical transformation of mercury (elemental, oxidized or particulate) in the post combustion zone and thus help with the control of mercury emissions from coal-burning power plants. To accomplish this goal present study was conducted using five coal fly ashes. These ashes were characterized and their catalytic activity was compared under selected reaction conditions in a fixed bed reactor. Based on the results from these fly ash experiments, three key components (carbon, iron oxide and calcium oxide) were chosen. These three components were then used to prepare model fly ashes. Silica/alumina was used as a base for these model fly ashes. One, two or three component model fly ashes were then prepared to investigate mercury transformation reactions. The third set of experiments was performed with five different oxidation catalysts to further understand the mercury oxidation process. Based on the results of these three studies the key components were predicted for different fly ash compositions under variety of flue gas conditions. A fixed bed reactor system was used to conduct this study. In all the experiments, the inlet concentration of Hg0(g) was maintained at 35 mug/m 3 using a diffusion tube as the source of Hg0(g). All experiments were conducted using 4% O2 in nitrogen mix as a reaction gas, and other reactants (HCl, H2O and SO2, NO 2, Br2) were added as required. The fixed bed reactor was operated over a temperature range of 200 to 400°C. In each experiment, the reactor effluent was analyzed using the modified Ontario-Hydro method. After each experiment, fly ash particles were also analyzed for mercury. The results show that the ability of fly ash to adsorb and/or oxidize mercury is primarily dependent on its carbon, iron and calcium content. There can be either one or more than one key component at a particular temperature and flue gas condition. Surface area played a secondary role in effecting the mercury transformations when compared to the concentration of the key component in the fly ash. Amount carbon and surface area played a key important role in the adsorption of mercury. Increased concentration of gases in the flue gas other than oxygen and nitrogen caused decreased the amount of mercury adsorbed on carbon surface. Mercury adsorption by iron oxide primarily depended on the crystalline structure of iron oxide. alpha-iron oxide had no effect on mercury adsorption or oxidation under most of the flue gas conditions, but gamma-iron oxide adsorbed mercury under most of the flue gas conditions. Bromine is a very good oxidizing agent for mercury. But in the presence of calcium oxide containing fly ashes, all the oxidized mercury would be reduced to elemental form. Among the catalysts, it was observed that presence of free lattice chlorine in the catalyst was very important for the oxidation of mercury. But instead of using the catalyst alone, using it along with carbon may better serve the purpose by providing the adsorption surface for mercury and also some extra surface area for the reaction to occur (especially for fly ashes with low surface area).

Varanasi, Patanjali

345

Dynamical properties of Discrete Reaction Networks.  

PubMed

Reaction networks are commonly used to model the dynamics of populations subject to transformations that follow an imposed stoichiometry. This paper focuses on the efficient characterisation of dynamical properties of Discrete Reaction Networks (DRNs). DRNs can be seen as modeling the underlying discrete nondeterministic transitions of stochastic models of reaction networks. In that sense, a proof of non-reachability in a given DRN has immediate implications for any concrete stochastic model based on that DRN, independent of the choice of kinetic laws and constants. Moreover, if we assume that stochastic kinetic rates are given by the mass-action law (or any other kinetic law that gives non-vanishing probability to each reaction if the required number of interacting substrates is present), then reachability properties are equivalent in the two settings. The analysis of two types of global dynamical properties of DRNs is addressed: irreducibility, i.e., the ability to reach any discrete state from any other state; and recurrence, i.e., the ability to return to any initial state. Our results consider both the verification of such properties when species are present in a large copy number, and in the general case. The necessary and sufficient conditions obtained involve algebraic conditions on the network reactions which in most cases can be verified using linear programming. Finally, the relationship of DRN irreducibility and recurrence with dynamical properties of stochastic and continuous models of reaction networks is discussed. PMID:23722628

Paulevé, Loïc; Craciun, Gheorghe; Koeppl, Heinz

2014-07-01

346

Study of chemical reactions under the influence of ultrasound  

NASA Astrophysics Data System (ADS)

At Los Alamos, the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin

347

[Allergic reactions to vaccines].  

PubMed

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

Turkalj, Mirjana; Erceg, Damir

2012-01-01

348

Role of microbes in the smectite-to-illite reaction  

NASA Technical Reports Server (NTRS)

Temperature, pressure, and time have been thought to control the smectite-to-illite (S-I) reaction, an important diagenetic process used for petroleum exploration. We demonstrated that microorganisms can promote the S-I reaction by dissolving smectite through reduction of structural Fe(III) at room temperature and 1 atmosphere within 14 days. This reaction typically requires conditions of 300 degrees to 350 degrees C, 100 megapascals, and 4 to 5 months in the absence of microbial activity. These results challenge the conventional concept of the S-I reaction and of reaction kinetic models.

Kim, Jinwook; Dong, Hailiang; Seabaugh, Jennifer; Newell, Steven W.; Eberl, Dennis D.

2004-01-01

349

Chemical reactions with aerosols  

NASA Astrophysics Data System (ADS)

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

Matijevi?, Egon

350

Reaction interface in reduction  

SciTech Connect

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

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

1980-07-01

351

Heck reactions of steroidal alkenyl iodides.  

PubMed

Heck reactions of some steroid derivatives possessing iodo-alkenyl moiety (17-iodo-androst-16-ene, 1, 17-iodo-4-aza-4-methyl-androst-16-en-3-one, 2, 17-iodo-4-aza-androst-16-en-3-one, 3) were carried out in the presence of palladium catalysts using various olefins (methyl acrylate, ethyl methacrylate, allyl alcohol and allyl acetate) as coupling partners. With methyl acrylate, a side reaction was observed: the coupling product underwent a Diels-Alder reaction with the excess of methyl acrylate resulting in a six-membered carbocyclic E-ring. Reaction conditions of the synthesis of the Heck-product were optimized. Although the coupling with allyl alcohol led to the formation of 21-formyl-16-pregnene derivatives, the synthesis of the corresponding steroidal unsaturated alcohol could be achieved only via hydrolysis of the coupling product of the alkenyl iodide with allyl acetate. PMID:9516719

Skoda-Földes, R; Bodnár, M; Kollár, L; Horváth, J; Tuba, Z

1998-02-01

352

Reaction Rate Calculations in Dense Stellar Matter  

NASA Astrophysics Data System (ADS)

Pycnonuclear fusion processes take place in the extreme density conditions anticipated to exist in the cores of white dwarfs and the crusts of neutron stars. Accurate modelling of pycnonuclear reactions is essential for understanding energy generation and transport in neutron stars. Calculation of pycnonuclear fusion rates strongly relies on knowledge of reaction cross sections. In most cases relevant cross section data is not availble and as such, cross section models must be used that are validated when ever possible by experimental measurements. Recently a formalism for calculating pycnonuclear reactions was developed for isotopes between boron and silicon. The pycnonuclear reaction rates will be presented and the results of the nucleosynthesis simulations will be discussed. This work was supported by the Joint Institute for Nuclear Astrophysics (NSF-PHY-0822648).

Beard, Mary; Brown, E.; Gasques, L.; Lau, R.; Schatz, H.; Wiescher, M.; Yakovlev, D.

2012-05-01

353

A comparison of bimolecular reaction models for stochastic reaction-diffusion systems.  

PubMed

Stochastic reaction-diffusion models have become an important tool in studying how both noise in the chemical reaction process and the spatial movement of molecules influences the behavior of biological systems. There are two primary spatially-continuous models that have been used in recent studies: the diffusion limited reaction model of Smoluchowski, and a second approach popularized by Doi. Both models treat molecules as points undergoing Brownian motion. The former represents chemical reactions between two reactants through the use of reactive boundary conditions, with two molecules reacting instantly upon reaching a fixed separation (called the reaction-radius). The Doi model uses reaction potentials, whereby two molecules react with a fixed probability per unit time, ?, when separated by less than the reaction radius. In this work, we study the rigorous relationship between the two models. For the special case of a protein diffusing to a fixed DNA binding site, we prove that the solution to the Doi model converges to the solution of the Smoluchowski model as ???, with a rigorous [Formula: see text] error bound (for any fixed ?>0). We investigate by numerical simulation, for biologically relevant parameter values, the difference between the solutions and associated reaction time statistics of the two models. As the reaction-radius is decreased, for sufficiently large but fixed values of ?, these differences are found to increase like the inverse of the binding radius. PMID:23579988

Agbanusi, I C; Isaacson, S A

2014-04-01

354

Integrating reaction and analysis: investigation of higher-order reactions by cryogenic trapping  

PubMed Central

Summary A new approach for the investigation of a higher-order reaction by on-column reaction gas chromatography is presented. The reaction and the analytical separation are combined in a single experiment to investigate the Diels–Alder reaction of benzenediazonium-2-carboxylate as a benzyne precursor with various anthracene derivatives, i.e. anthracene, 9-bromoanthracene, 9-anthracenecarboxaldehyde and 9-anthracenemethanol. To overcome limitations of short reaction contact times at elevated temperatures a novel experimental setup was developed involving a cooling trap to achieve focusing and mixing of the reactants at a defined spot in a fused-silica capillary. This trap functions as a reactor within the separation column in the oven of a gas chromatograph. The reactants are sequentially injected to avoid undefined mixing in the injection port. An experimental protocol was developed with optimized injection intervals and cooling times to achieve sufficient conversions at short reaction times. Reaction products were rapidly identified by mass spectrometric detection. This new approach represents a practical procedure to investigate higher-order reactions at an analytical level and it simultaneously provides valuable information for the optimization of the reaction conditions.

Stockinger, Skrollan

2013-01-01

355

Integrating reaction and analysis: investigation of higher-order reactions by cryogenic trapping.  

PubMed

A new approach for the investigation of a higher-order reaction by on-column reaction gas chromatography is presented. The reaction and the analytical separation are combined in a single experiment to investigate the Diels-Alder reaction of benzenediazonium-2-carboxylate as a benzyne precursor with various anthracene derivatives, i.e. anthracene, 9-bromoanthracene, 9-anthracenecarboxaldehyde and 9-anthracenemethanol. To overcome limitations of short reaction contact times at elevated temperatures a novel experimental setup was developed involving a cooling trap to achieve focusing and mixing of the reactants at a defined spot in a fused-silica capillary. This trap functions as a reactor within the separation column in the oven of a gas chromatograph. The reactants are sequentially injected to avoid undefined mixing in the injection port. An experimental protocol was developed with optimized injection intervals and cooling times to achieve sufficient conversions at short reaction times. Reaction products were rapidly identified by mass spectrometric detection. This new approach represents a practical procedure to investigate higher-order reactions at an analytical level and it simultaneously provides valuable information for the optimization of the reaction conditions. PMID:24062850

Stockinger, Skrollan; Trapp, Oliver

2013-01-01

356

TRIMOLECULAR REACTIONS OF URANIUM HEXAFLUORIDE WITH WATER  

SciTech Connect

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

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

2010-02-25

357

Alkali-Silica Reaction in Concrete Structures.  

National Technical Information Service (NTIS)

A recent survey of high-strength concrete bridges has revealed several structures with significant distress due to alkali-silica reaction (ASR) and a larger number with minor distress due to ASR. Since 1982, a study has been undertaken on conditions which...

A. Carse P. F. Dux

1988-01-01

358

Charge exchange reactions in astrophysical plasmas  

Microsoft Academic Search

A review is presented of charge exchange reactions of multiply charged ions with atomic hydrogen and helium at thermal-eV energies, typical of the physical conditions encountered in planetary nebulae. The basic features of the processes are analyzed in the framework of the molecular model of atomic collisions. A discussion is given of the different theoretical approaches to the calculation of

R. McCarroll; P. Valiron; L. Opradolce

1983-01-01

359

Modeling of uncertainties in biochemical reactions.  

PubMed

Mathematical modeling is an indispensable tool for research and development in biotechnology and bioengineering. The formulation of kinetic models of biochemical networks depends on knowledge of the kinetic properties of the enzymes of the individual reactions. However, kinetic data acquired from experimental observations bring along uncertainties due to various experimental conditions and measurement methods. In this contribution, we propose a novel way to model the uncertainty in the enzyme kinetics and to predict quantitatively the responses of metabolic reactions to the changes in enzyme activities under uncertainty. The proposed methodology accounts explicitly for mechanistic properties of enzymes and physico-chemical and thermodynamic constraints, and is based on formalism from systems theory and metabolic control analysis. We achieve this by observing that kinetic responses of metabolic reactions depend: (i) on the distribution of the enzymes among their free form and all reactive states; (ii) on the equilibrium displacements of the overall reaction and that of the individual enzymatic steps; and (iii) on the net fluxes through the enzyme. Relying on this observation, we develop a novel, efficient Monte Carlo sampling procedure to generate all states within a metabolic reaction that satisfy imposed constrains. Thus, we derive the statistics of the expected responses of the metabolic reactions to changes in enzyme levels and activities, in the levels of metabolites, and in the values of the kinetic parameters. We present aspects of the proposed framework through an example of the fundamental three-step reversible enzymatic reaction mechanism. We demonstrate that the equilibrium displacements of the individual enzymatic steps have an important influence on kinetic responses of the enzyme. Furthermore, we derive the conditions that must be satisfied by a reversible three-step enzymatic reaction operating far away from the equilibrium in order to respond to changes in metabolite levels according to the irreversible Michelis-Menten kinetics. The efficient sampling procedure allows easy, scalable, implementation of this methodology to modeling of large-scale biochemical networks. PMID:20830674

Miškovi?, Ljubiša; Hatzimanikatis, Vassily

2011-02-01

360

Anaphylaxis-Like Reactions  

MedlinePLUS

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

361

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

362

Chemisorption And Precipitation Reactions  

EPA Science Inventory

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

363

Translated chemical reaction networks.  

PubMed

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

Johnston, Matthew D

2014-05-01

364

[Paranoid reactions and culture].  

PubMed

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

Sizaret, P; Degiovanni, A; Faure, M

1987-09-01

365

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

366

Chemical Reactions and Pancakes  

NSDL National Science Digital Library

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

367

Polymerase Chain Reaction  

NSDL National Science Digital Library

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

Foundation, Wgbh E.

2009-12-07

368

Gold-based catalysts for the water–gas shift reaction: Active sites and reaction mechanism  

Microsoft Academic Search

The water–gas shift (WGS, CO+H2O?H2+CO2) reaction was studied on a series of gold\\/oxide catalysts. The results of in situ measurements with X-ray absorption spectroscopy indicate that the active phase of Au-ceria and Au-titania catalysts under the reaction conditions of the water–gas shift consists of metallic nanoparticles of gold on a partially reduced oxide support. In spite of the lack of

José A. Rodriguez

2011-01-01

369

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

370

Predicting Idiosyncratic Drug Reactions  

Microsoft Academic Search

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

Alastair Cribb

371

Safety of chlorination reactions  

Microsoft Academic Search

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

Jean-Louis Gustin; Alexandre Fines

1996-01-01

372

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

373

Phototoxic and Photoallergic Reactions  

Microsoft Academic Search

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

Margarida Gonçalo

374

Optimization of the derivatization reaction and the solid-phase microextraction conditions using a D-optimal design and three-way calibration in the determination of non-steroidal anti-inflammatory drugs in bovine milk by gas chromatography-mass spectrometry.  

PubMed

An experimental design optimization is reported of an analytical procedure used in the simultaneous determination of seven non-steroidal anti-inflammatory drugs (NSAIDs) in bovine milk by gas chromatography with mass spectrometry detection (GC-MS). This analytical procedure involves a solid-phase microextraction (SPME) step and an aqueous derivatization procedure of the NSAIDs to ethyl esters in bovine milk. The following NSAIDs are studied: ibuprofen (IBP), naproxen (NPX), ketoprofen (KPF), diclofenac (DCF), flufenamic acid (FLF), tolfenamic acid (TLF) and meclofenamic acid (MCL). Three kinds of SPME fibers - polyacrylate (PA), polydimethylsiloxane/divinylbenzene (PDMS/DVB) and polydimethylsiloxane (PDMS) - are compared to identify the most suitable one for the extraction process, on the basis of two steps: to determine the equilibrium time of each fiber and to select the fiber that provides the best figures-of-merit values calculated with three-way PARAFAC-based calibration models at the equilibrium time. The best results were obtained with the PDMS fiber. Subsequently, 8 experimental factors (related to the derivatization reaction and the SPME) were optimized by means of a D-optimal design that involves only 14 rather than 512 experiments in the complete factorial design. The responses used in the design are the sample mode loadings of the PARAFAC decomposition which are related to the quantity of each NSAID that is extracted in the experiment. Owing to the fact that each analyte is unequivocally identified in the PARAFAC decomposition, a calibration model is not needed for each experimental condition. The procedure fulfils the performance requirements for a confirmatory method established in European Commission Decision 2002/657/EC. PMID:21636091

Arroyo, David; Ortiz, M Cruz; Sarabia, Luis A

2011-07-15

375

Reactions of cresol in hot aqueous borate solutions  

SciTech Connect

Phenol and methylphenol (cresol) are constituents of certain waste streams being considered for underground injection. We studied reactions of these compounds in solutions with other constituents of the waste streams and suspended clay at concentrations and temperatures higher than expected in natural situations, i.e. at 200{degrees}C and 250{degrees}C. Under these conditions, the predominant reaction was the demethylation of cresol to form phenol. This reaction was catalyzed strongly by clay. We were able to quantify phenol production. Other important reactions were a variety of condensation reactions in which two cresol molecules fuse. We found evidence of the intermolecular migration of methyl groups from the molecular weights of some of these condensation reactions. By digesting a sample of reacted clay with hydrofluoric acid we determined that under these conditions phenol and cresol did not bind appreciably to clay but that the condensation products did.

Tsao, L. [Lawrence Berkeley Lab., CA (United States); Weres, O. [Sonoma Research Co., Vineburg, CA (United States)

1992-04-01

376

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

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

Vecitis, Chad David

377

The Condition of Education  

NSDL National Science Digital Library

The very title of this website would perhaps draw only hushed whispers from those commentators in the world of education policy, and thatâÂÂs probably not a bad reaction. The site makes good on the promise of its title, as it offers the casual and seasoned visitor a wide variety of indicators in the forms of tables and charts, including total enrollments in grades K-12, trends in half-day kindergarten, and past and projected undergraduate enrollment figures. Culled from annual reports created by the National Center for Education Statistics, these helpful pieces of information and data are complemented nicely by a series of special analyses, including âÂÂMobility in the Teacher Workforceâ and âÂÂPrivate Schools: A Brief PortraitâÂÂ. If visitors encounter any problems finding the information they desire, they should consult the âÂÂUserâÂÂs GuideâÂÂ, which contains directions on how to best navigate the site. Finally, the site is rounded out by a brief summary that highlights some of the findings of the 2005 Condition of Education report.

Statistics, National C.

378

Kinetic and mechanistic studies of blue tetrazolium reaction with phenylhydrazines.  

PubMed

The reaction kinetics of blue tetrazolium with selected arylhydrazines were investigated under pseudo-first-order conditions. The reaction rate constants were obtained at various temperatures, and the enthalpy (8.4-11.2 kcal/mole) and entropy (-38--45 eu) of activations were calculated. A Hammett plot yielded a straight line with a slope of 0.52. The reaction was inhibited by atmospheric oxygen and iodine. A free radical mechanism is presented. PMID:660510

Biehl, E R; Wooten, R; Kenner, C T; Graham, R E

1978-07-01

379

Effect of mineral admixtures on alkali-silica reaction  

Microsoft Academic Search

The influence of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70 °C is studied. The results\\u000a show that silica, slag and fly ash may inhibit alkali-silica reaction only under suitable content. When the content is less\\u000a than 10%, silica fume does not markedly influence the expansion of alkalisilica reaction. When the content is 15%–20%,

Chengzhi Zhang; Aiqin Wang

2008-01-01

380

Applications of Nigella sativa seed lipase in oleochemical reactions  

Microsoft Academic Search

The possible applications of the native lipase of Nigella sativa seed in oleochemical reactions were investigated in relation to the process parameters. The investigated enzyme-catalyzed reactions were the hydrolysis of used frying oil and esterification of oleic acid with glycerol and methanol. All reactions were carried out under solvent-free conditions and catalyzed by pressed seed as the lipase source.The hydrolysis

L. Dandik; H. A. Aksoy

1996-01-01

381

Immediate reaction to clarithromycin.  

PubMed

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

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

2001-01-01

382

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

383

An interrupted Ugi reaction enables the preparation of substituted indoxyls and aminoindoles  

PubMed Central

In a variation of the classical Ugi reaction, an acid promoted reaction between imines and isocyanides forms both 3-aminoindoles and substituted indoxyls. A recently reported triflyl phosphoramide is shown to be critical to obtain high yields under mild conditions.

Schneekloth, John S.; Kim, Jimin; Sorensen, Erik J.

2011-01-01

384

Stereochemical lability of azatitanacyclopropanes: dynamic kinetic resolution in reductive cross-coupling reactions with allylic alcohols.  

PubMed

Azatitanacyclopropanes (titanaziridines) are shown to be stereochemically labile under reaction conditions for reductive cross-coupling. This fundamental property has been employed to realize highly selective asymmetric coupling reactions with allylic alcohols that proceed by dynamic kinetic resolution. PMID:23963189

Yang, Dexi; Micalizio, Glenn C

2013-10-01

385

The hydrothermal reaction kinetics of aspartic acid  

NASA Astrophysics Data System (ADS)

Experimental data on the hydrothermal reaction kinetics of aspartic acid were acquired using a custom-built spectrophotometric reaction cell which permits in situ observation under hydrothermal conditions. The results of this study indicate that the reaction kinetics of dilute aspartic acid solutions are significantly different depending on the presence or absence of catalytic surfaces such as standard metal alloys. The spectroscopic data presented here represent the first direct observations, in situ and in real time, of an amino acid reacting in a hydrothermal solution. Quantitative kinetic information, including rate constants, concentration versus time profiles, and calculations of the individual component spectra, was obtained from the data using a chemometric approach based on factor analysis/principle component analysis which treats the rate expressions simultaneously as a system of differential algebraic equations (DAE) of index 1. Identification of the products was confirmed where possible by high pressure anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The reaction kinetics of aspartic acid under hydrothermal conditions was observed to be highly complex, in contrast to previous studies which indicated almost exclusively deamination. At lower temperatures (120-170 °C), several different reaction pathways were observed, including decarboxylation and polymerization, and the catalytic effects of reactor surfaces on the aspartic acid system were clearly demonstrated. At higher temperatures (above 170 °C), aspartic acid exhibited highly complex behaviour, with evidence indicating that it can simultaneously dimerize and cyclize, deaminate (by up to two pathways), and decarboxylate (by up to two pathways). These higher temperature kinetics were not fully resolvable in a quantitative manner due to the complexity of the system and the constraints of UV spectroscopy. The results of this study provide strong evidence that the reaction kinetics of aspartic acid are very sensitive to parameters such as temperature, reactor materials (i.e., reactive surfaces), and additives, and that previous observations on aspartic acid were specific to the choice of experimental conditions.

Cox, Jenny S.; Seward, Terry M.

2007-02-01

386

Effect of inclusion complex on nitrous acid reaction with flavonoids  

NASA Astrophysics Data System (ADS)

The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively stable products were detected by spectrophotometric techniques. pH dependence of the reactions has been examined and the rate constants of reactions were obtained by non-linear fitting of kinetic profiles. The effect of ?-cyclodextrin on the oxidation pathway was another object of this study. It is shown that ?-cyclodextrin has an inhibitory effect on the oxidation reaction. The rate constants of oxidation reactions for complexed forms and their stability constants were obtained based on changes in the reaction rates as a function of ?-cyclodextrin concentration.

Khalafi, Lida; Rafiee, Mohammad; Sedaghat, Sajjad

2011-10-01

387

Chemical reactions on metal oxide surfaces investigated by vibrational spectroscopy  

Microsoft Academic Search

The most successful method to unravel the microscopic mechanisms governing reactions in heterogeneous catalysis is the “surface science” approach which is based on well-controlled studies on model catalysts (usually single crystal surfaces) under ultrahigh vacuum (UHV) conditions [G. Ertl, Angew. Chem. 47 (2008) 3524]. In this review our recent vibrational spectroscopic studies on selected model reactions at various single-crystalline metal

Yuemin Wang; Christof Wöll

2009-01-01

388

The refractory period and serial choice-reactions  

Microsoft Academic Search

An experiment is described in which subjects had to make consecutive 2-choice reactions to light and sound stimuli, the interval between signals being fixed for anyone series of presentations. When under these conditions, reaction times to the second signal are compared to those obtained when the first signal is used only as a warning, delays are found for short intervals.

Robert Borger

1963-01-01

389

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

390

Effects of discriminatory interview questions and gender on applicant reactions  

Microsoft Academic Search

Justice and signalling theory were used to explain the effects of discriminatory interview questions on applicant reactions. Participants were randomly assigned to a hypothetical interview condition with four, two or no discriminatory questions. Discriminatory questions had a significant negative effect on participant’s reactions to the interview and interviewer; perceptions of employee treatment; and intentions to pursue employment, accept a job

Alan M. Saks; Julie M. McCarthy

2006-01-01

391

Reaction Time as an Index of Traffic Sign Perception  

Microsoft Academic Search

Verbal reaction times to identify and to classify 20 traffic sign messages were measured under three conditions-sign alone, sign plus visual loading task, and sign plus visual loading task plus visual distraction. Similar trends were found in the three experiments: reaction times were smaller for the classification task than for the identification task, smaller for warning than for regulatory signs,

Robert E. Dewar; Jerry G. Ells; Glen Mundy

1976-01-01

392

Reaction/Momentum Wheel  

NASA Technical Reports Server (NTRS)

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

1997-01-01

393

Stellar evolution and the triple-? reactions  

NASA Astrophysics Data System (ADS)

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

Suda, Takuma

2014-05-01

394

Reversal of the superoxide dismutase reaction revisited.  

PubMed

Reversal of the superoxide dismutase (SOD) reaction was measured in terms of the reduction of tetranitromethane (TNM) by O2-. Cu,ZnSOD caused a biphasic reduction of TNM by H2O2. The rapid initial phase was stoichiometric with the enzyme and was followed by a slower catalytic phase that was oxygen dependent and was augmented by HCO3-. The reaction scheme explaining this behavior is presented and a rate constant for the reduction of O2 by the cuprous enzyme is estimated. This rate constant is so low that it precludes significant O2- production by the reduced enzyme under the conditions explored. PMID:12654479

Liochev, Stefan I; Fridovich, Irwin

2003-04-01

395

Turing instability in reaction-subdiffusion systems  

NASA Astrophysics Data System (ADS)

We determine the conditions for the occurrence of Turing instabilities in activator-inhibitor systems, where one component undergoes subdiffusion and the other normal diffusion. If the subdiffusing species has a nonlinear death rate, then coupling between the nonlinear kinetics and the memory effects of the non-Markovian transport process advances the Turing instability if the inhibitor subdiffuses and delays the Turing instability if the activator subdiffuses. We apply the results of our analysis to the Schnakenberg model, the Gray-Scott model, the Oregonator model of the Belousov-Zhabotinsky reaction, and the Lengyel-Epstein model of the chlorine dioxide-iodine-malonic acid reaction.

Yadav, A.; Milu, Shane M.; Horsthemke, Werner

2008-08-01

396

Hypersensitivity reaction to desipramine.  

PubMed

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

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

1987-07-01

397

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

398

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

399

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

400

Electrographic correlates of “internal states” evoked by positive conditioned stimuli during operant training in dogs  

Microsoft Academic Search

Experiments were performed to address the energy characteristics (power spectra) of short-term (less than 1 sec) EEG reactions arising in different areas of the neocortex in response to positive conditioned stimuli presented in conditions of selective attention. These EEG reactions directly preceded the motor reactions, which consisted of a strong blow with the paw on a feeder pedal to obtain

V. N. Dumenko; M. K. Kozlov

2005-01-01

401

The role of calorimetry in chemical plant safety: a chlorination reaction  

Microsoft Academic Search

The use of isoperibolic (near-isothermal) and adiabatic reaction calorimetry is discussed with particular reference to a chlorination reaction. The reaction, involving the semi-batch addition of a liquid substrate to a chlorine-saturated solution of dichloromethane containing a catalytic quantity of pyridine, was simulated under isoperibolic conditions (to assess the heat of reaction and extent of reagent accumulation at the proposed reaction

Stephen M. Rowe

1996-01-01

402

Reaction Time and Intelligence.  

ERIC Educational Resources Information Center

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

Jensen, Arthur R.

403

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.

404

Types of Allergic Reactions  

MedlinePLUS

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

405

Quinoprotein-catalysed reactions.  

PubMed Central

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

Anthony, C

1996-01-01

406

High Temperature Reaction Calorimetry.  

National Technical Information Service (NTIS)

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

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

1970-01-01

407

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

408

The aromatic ene reaction  

NASA Astrophysics Data System (ADS)

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

Niu, Dawen; Hoye, Thomas R.

2014-01-01

409

Reaction Formulation: A Bibliography.  

ERIC Educational Resources Information Center

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

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

410

Chemical Reactions at Surfaces  

SciTech Connect

Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

Michael Henderson and Nancy Ryan Gray

2010-04-14

411

Organic Reactions and Biofuels  

NSDL National Science Digital Library

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

2011-02-16

412

Online Access: User Reaction.  

ERIC Educational Resources Information Center

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

Pawley, Carolyn

1982-01-01

413

Gas Producing Micro-Reaction  

NSDL National Science Digital Library

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

House, The S.

2014-01-28

414

What Is a Reaction Rate?  

ERIC Educational Resources Information Center

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

Schmitz, Guy

2005-01-01

415

Inorganic Reaction Mechanisms. Part I  

ERIC Educational Resources Information Center

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

Cooke, D. O.

1976-01-01

416

A taxonomy of integral reaction path analysis  

SciTech Connect

W. C. Gardiner observed that achieving understanding through combustion modeling is limited by the ability to recognize the implications of what has been computed and to draw conclusions about the elementary steps underlying the reaction mechanism. This difficulty can be overcome in part by making better use of reaction path analysis in the context of multidimensional flame simulations. Following a survey of current practice, an integral reaction flux is formulated in terms of conserved scalars that can be calculated in a fully automated way. Conditional analyses are then introduced, and a taxonomy for bidirectional path analysis is explored. Many examples illustrate the resulting path analysis and uncover some new results about nonpremixed methane-air laminar jets.

Grcar, Joseph F.; Day, Marcus S.; Bell, John B.

2004-12-23

417

Intensified reaction of dilute thiophenes in nanoreactor.  

PubMed

A discovery that catalytic reactivity is intensified on reducing the size of reactor toward several nanometers scale was applied for the separation of dilute species, for example, the thiophenic compounds in transportation fuels, in the present study. A characteristic reaction of the dilute species was selected as the separation mechanism, and a nanoreactor was formed with preloading reactant/catalyst in volumes of mesopore dimension. Probability for the dilute species to contact the nanoreactor radically enlarged due to the integration of such volumes in a porous material. Because all reagents and the reaction product stayed inside the nanoreactor, separation of fuel from sulfuric compounds and the surplus chemicals used in reaction becomes simple. It was experimentally shown that the nanoreaction exhibited first-order kinetics, and all thiophenes and benzothiophenes contained in different types of model fuels were completely removed at moderate conditions. PMID:18251529

Zhou, Li; Wang, Shengqiang; Dai, Wei; Zhou, Yaping

2008-03-01

418

Efficiency of the Polymerase Chain Reaction  

PubMed Central

The polymerase chain reaction (PCR) has found wide application in biochemistry and molecular biology such as gene expression studies, mutation detection, forensic analysis and pathogen detection. Increasingly quantitative real time PCR is used to assess copy numbers from overall yield. In this study the yield is analyzed as a function of several processes: (1) thermal damage of the template and polymerase occurs during the denaturing step, (2) competition exists between primers and templates to either anneal or form dsDNA, (3) polymerase binding to annealed products (primer/ssDNA) to form ternary complexes and (4) extension of ternary complexes. Explicit expressions are provided for the efficiency of each process, therefore reaction conditions can be directly linked to the overall yield. Examples are provided where different processes play the yield-limiting role. The analysis will give researchers a unique understanding of the factors that control the reaction and will aid in the interpretation of experimental results.

Booth, Christine S.; Pienaar, Elsje; Termaat, Joel R.; Whitney, Scott E.; Louw, Tobias M.; Viljoen, Hendrik J.

2011-01-01

419

Efficiency of the Polymerase Chain Reaction.  

PubMed

The polymerase chain reaction (PCR) has found wide application in biochemistry and molecular biology such as gene expression studies, mutation detection, forensic analysis and pathogen detection. Increasingly quantitative real time PCR is used to assess copy numbers from overall yield. In this study the yield is analyzed as a function of several processes: (1) thermal damage of the template and polymerase occurs during the denaturing step, (2) competition exists between primers and templates to either anneal or form dsDNA, (3) polymerase binding to annealed products (primer/ssDNA) to form ternary complexes and (4) extension of ternary complexes. Explicit expressions are provided for the efficiency of each process, therefore reaction conditions can be directly linked to the overall yield. Examples are provided where different processes play the yield-limiting role. The analysis will give researchers a unique understanding of the factors that control the reaction and will aid in the interpretation of experimental results. PMID:21799540

Booth, Christine S; Pienaar, Elsje; Termaat, Joel R; Whitney, Scott E; Louw, Tobias M; Viljoen, Hendrik J

2010-09-01

420

Moist air reaction with excess UF{sub 6}  

SciTech Connect

The moist air reaction with uranium hexafluoride (UF{sub 6}) has been studied at conditions simulating UF{sub 6} hydrolysis during air inleakage in the cascade. In excess UF{sub 6}, the reaction mechanism is more complicated than predicted by the simple gas-phase reaction of one UF{sub 6} molecule with two water molecules to form uranyl fluoride and hydrogen fluoride. The initial UF{sub 6} consumption is significantly greater than predicted, suggesting that a metastable uranium compound is formed during the hydrolysis reaction. This intermediate uranium compound may facilitate uranyl fluoride transport in the cascade.

Reiner, R.H.

1989-08-01

421

Preparation of functionalized heteroaromatics using an intramolecular Wittig reaction.  

PubMed

The development of efficient methods for the synthesis of heteroaromatic compounds is always of great importance for chemists. In this 'Perspective', we describe a general approach for the synthesis of functionalized heteroaromatics via intramolecular Wittig reactions. In all cases, the reaction proceeds via in situ generated phosphorus ylides. We especially emphasize the importance of chemoselective intramolecular Wittig reactions using designed Michael acceptors and suitable acyl chloride as trapping reagents, which allows formation of two different classes of heteroaromatics from the same substrates. This metal-free approach is quite general and works in a number of examples, furnishing the corresponding products in moderate to good yields under relatively mild reaction conditions. PMID:24802304

Das, Utpal; Tsai, Yi-Ling; Lin, Wenwei

2014-05-28

422

Reaction rate and products for the reaction O/3P/ + H2CO  

NASA Technical Reports Server (NTRS)

A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

Chang, J. S.; Barker, J. R.

1979-01-01

423

Computational analysis of methyl transfer reactions in dengue virus methyltransferase.  

PubMed

S-Adenosyl-l-methionine (SAM) dependent methyltransferases (MTases) play crucial roles in many biological processes. The MTase of the dengue virus is of particular interest for the development of antiviral drugs against flaviviruses. It catalyzes two distinct methylation reactions at the N7 and the 2'O position of the viral RNA cap structure. Based on density functional theory (DFT) electronic structure calculations, the molecular basis of the underlying chemical reactions involved in the N7 and the 2'O methyl transfer reactions of this enzyme were investigated using model systems. Calculations in the condensed phase show that both reactions are exergonic with significant activation barriers of 13.7 and 17.6 kcal/mol and stable product states, stabilized by 23.5 and 16.9 kcal/mol compared to the reactant states for the N7 and the 2'O reaction, respectively. We find that the reaction rate for the 2'O reaction is significantly enhanced in the presence of the native proton acceptor group, which lowers the activation barrier in the catalyzed reaction by 3.8 kcal/mol compared to the uncatalyzed reaction in aqueous solution. Furthermore, the 2'O reaction involves a methyl and a proton transfer reaction. Our results suggest that these two reactions occur in a concerted fashion in which the methyl group and the proton are transferred simultaneously. From a therapeutic viewpoint, SAM analogues stable under physiological conditions are particularly relevant. One such compound in MeAzaSAM, an isostructural mimic of SAM, for which the present calculations suggest that the methyl transfer reaction is unlikely to occur under biologically relevant conditions. PMID:24809209

Schmidt, Tobias; Schwede, Torsten; Meuwly, Markus

2014-06-01

424

Intact implicit learning in autism spectrum conditions  

Microsoft Academic Search

Individuals with autism spectrum condition (ASC) have diagnostic impairments in skills that are associated with an implicit acquisition; however, it is not clear whether ASC individuals show specific implicit learning deficits. We compared ASC and typically developing (TD) individuals matched for IQ on five learning tasks: four implicit learning tasks—contextual cueing, serial reaction time, artificial grammar learning, and probabilistic classification

Jamie Brown; Balazs Aczel; Luis Jiménez; Scott Barry Kaufman; Kate Plaisted Grant

2010-01-01

425

Different reaction mechanisms for cis- and trans-prenyltransferases  

SciTech Connect

Octaprenyl diphosphate synthase (OPPs) and undecaprenyl diphosphate synthases (UPPs) catalyze consecutive condensation reactions of farnesyl diphosphate (FPP) with 5 and 8 isopentenyl diphosphate (IPP) to generate C{sub 40} and C{sub 55} products with trans- and cis-double bonds, respectively. In this study, we used IPP analogue, 3-bromo-3-butenyl diphosphate (Br-IPP), in conjunction with radiolabeled FPP, to probe the reaction mechanisms of the two prenyltransferases. Using this alternative substrate with electron-withdrawing bromo group at the C3 position to slow down the condensation step, trapping of farnesol in the OPPs reaction from radiolabeled FPP under basic condition was observed, consistent with a sequential mechanism. In contrast, UPPs reaction yielded no farnesyl carbocation intermediate under the same condition with radiolabeled FPP and Br-IPP, indicating a concerted mechanism. Our data demonstrate the different reaction mechanisms for cis- and tran-prenyltransferases although they share the same substrates.

Lu Yenpin [Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Liu Hunge [Institute of Biological Chemistry, 128 Academia Rd. sec. 2, Academia Sinica, Taipei 115, Taiwan (China); Liang, P-H. [Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Institute of Biological Chemistry, 128 Academia Rd. sec. 2, Academia Sinica, Taipei 115, Taiwan (China)], E-mail: phliang@gate.sinica.edu.tw

2009-02-06

426

Reaction synthesis of intermetallics  

SciTech Connect

Exothermicity associated with the synthesis of aluminides was utilized to obtain nickel, iron, and cobalt aluminides. Combustion synthesis, extrusion, and hot pressing were utilized to obtain intermetallics and their composites. Extrusion conditions, reduction ratios, and hot-pressing conditions of the intermetallics and their composites are discussed.

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

1994-12-31

427

Magnetically suspended reaction wheels  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

428

Heat Speeds Up Reactions  

NSDL National Science Digital Library

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

Shaw, Maisie; Gomez, Maria

2009-01-01

429

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

430

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

431

Diastereoselective reactions of enolates  

Microsoft Academic Search

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

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

1996-01-01

432

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

433

Allergic reactions to fish  

Microsoft Academic Search

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

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