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Primary Products (primary + products)
Selected AbstractsAb initio chemical kinetics for the NH2 + HNOx reactions, part II: Kinetics and mechanism for NH2 + HONOINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2009Shucheng Xu The kinetics and mechanism for the reaction of NH2 with HONO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The reaction producing the primary products, NH3 + NO2, takes place via precomplexes, H2N,,,c -HONO or H2N,,,t -HONO with binding energies, 5.0 or 5.9 kcal/mol, respectively. The rate constants for the major reaction channels in the temperature range of 300,3000 K are predicted by variational transition state theory or Rice,Ramsperger,Kassel,Marcus theory depending on the mechanism involved. The total rate constant can be represented by ktotal = 1.69 × 10,20 × T2.34 exp(1612/T) cm3 molecule,1 s,1 at T = 300,650 K and 8.04 × 10,22 × T3.36 exp(2303/T) cm3 molecule,1 s,1 at T = 650,3000 K. The branching ratios of the major channels are predicted: k1 + k3 producing NH3 + NO2 accounts for 1.00,0.98 in the temperature range 300,3000 K and k2 producing OH + H2NNO accounts for 0.02 at T > 2500 K. The predicted rate constant for the reverse reaction, NH3 + NO2 , NH2 + HONO represented by 8.00 × 10,26 × T4.25 exp(,11,560/T) cm3 molecule,1 s,1, is in good agreement with the experimental data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 678,688, 2009 [source] Oxidation of small alkenes at high temperatureINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2002Barbara Heyberger If the mechanism of formation of alkenes, the main primary products of the combustion of alkanes above 1000 K, is now well understood, their ways of degradation have been much less studied. Following a previous modeling of the oxidation of propene in a static and a jet-stirred reactors by using an automatically generated mechanism, the present paper shows new validations of the same mechanism for ignition delays in a shock tube. It also describes the extension of the rules used for the automatic generation to the case of 1-butene. The predictions of the mechanism produced for the oxidation of 1-butene are compared successfully with two sets of experimental results: the first obtained in a jet-stirred reactor between 900 and 1200 K; the second being new measurements of ignitions delays behind reflected shock waves for temperatures from 1200 up to 1670 K, pressures from 6.6 to 8.9 atm, equivalence ratios from 0.5 to 2, and with argon as bath gas. Flux and sensitivity analyses show that the role of termination reactions involving the very abundant allylic radicals is less important for 1-butene than for propene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 666,677, 2002 [source] Catalytic cracking, dehydrogenation, and aromatization of isobutane over Ga/HZSM-5 and Zn/HZSM-5 at low pressuresINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2002Yanping Sun Isobutane cracking, dehydrogenation, and aromatization over Ga/HZSM-5 and Zn/HZSM-5 has been investigated in a Knudsen cell reactor and the kinetics of the primary reaction steps for isobutene and propene formation have been accurately determined. Although cracking is the dominant reaction channel, with propene and methane being primary products, methane formation is significantly less than propene formation. This indicates that a proportion of the cracking proceeds via Lewis acid attack at CC bonds, and not just via alkanium ion formation at Bronsted acid sites. This is particularly apparent over Zn/HZSM-5. Intrinsic rate constants for cracking, calculated from the rate of propene formation, are and for dehydrogenation, calculated from the rate of isobutene formation, are Large preexponential factors for cracking and dehydrogenation over Ga/HZSM-5 indicate that either the coverage of active sites is significantly less than the coverage of exposed sites or the intrinsic reaction step involves a large entropy change between reactant and transition state. For Zn/HZSM-5 the small preexponential factors suggest either small entropy changes during activation, perhaps initiated by Lewis acid sites, or a steady-state distribution of active and exposed sites is rapidly reached. Differences in intrinsic activation energies may reflect the ratio of Lewis and Bronsted acid sites on the respective catalyst surfaces. Aromatization is more prolific over Ga/HZSM-5 than over Zn/HZSM-5 under the low-pressure conditions. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 467,480, 2002 [source] In vivo 13C magnetic resonance spectroscopy of human brain on a clinical 3 T scanner using [2- 13C]glucose infusion and low-power stochastic decouplingMAGNETIC RESONANCE IN MEDICINE, Issue 3 2009Shizhe Li Abstract This study presents the detection of [2- 13C]glucose metabolism in the carboxylic/amide region in the human brain, and demonstrates that the cerebral metabolism of [2- 13C]glucose can be studied in human subjects in the presence of severe hardware constraints of widely available 3 T clinical scanners and with low-power stochastic decoupling. In the carboxylic/amide region of human brain, the primary products of 13C label incorporation from [2- 13C]glucose into glutamate, glutamine, aspartate, ,-aminobutyric acid, and N-acetylaspartate were detected. Unlike the commonly used alkanyl region where lipid signals spread over a broad frequency range, the carboxylic carbon signal of lipids was found to be confined to a narrow range centered at 172.5 ppm and present no spectral interference in the absence of lipid suppression. Comparison using phantoms shows that stochastic decoupling is far superior to the commonly used WALTZ sequence at very low decoupling power at 3 T. It was found that glutamine C1 and C5 can be decoupled using stochastic decoupling at 2.2 W, although glutamine protons span a frequency range of ,700 Hz. Detailed specific absorption rate analysis was also performed using finite difference time domain numerical simulation. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Treatment methods for the determination of ,2H and ,18O of hair keratin by continuous-flow isotope-ratio mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2005Gabriel J. Bowen The structural proteins that comprise ,90% of animal hair have the potential to record environmentally and physiologically determined variation in ,2H and ,18O values of body water. Broad, systematic, geospatial variation in stable hydrogen and oxygen isotopes of environmental water and the capacity for rapid, precise measurement via methods such as high-temperature conversion elemental analyzer/isotope ratio mass spectrometry (TC/EA-IRMS) make these isotope systems particularly well suited for applications requiring the geolocation of hair samples. In order for such applications to be successful, however, methods must exist for the accurate determination of hair ,2H and ,18O values reflecting the primary products of biosynthesis. Here, we present the results of experiments designed to examine two potential inaccuracies affecting ,2H and ,18O measurements of hair: the contribution of non-biologic hydrogen and oxygen to samples in the form of sorbed molecular water, and the exchange of hydroxyl-bound hydrogen between hair keratin and ambient water vapor. We show that rapid sorption of molecular water from the atmosphere can have a substantial effect on measured ,2H and ,18O values of hair (comprising ,7.7% of the measured isotopic signal for H and up to ,10.6% for O), but that this contribution can be effectively removed through vacuum-drying of samples for 6 days. Hydrogen exchange between hair keratin and ambient vapor is also rapid (reaching equilibrium within 3,4 days), with 9,16% of the total hydrogen available for exchange at room temperature. Based on the results of these experiments, we outline a recommended sample treatment procedure for routine measurement of ,2H and ,18O in mammal hair. Copyright © 2005 John Wiley & Sons, Ltd. [source] Mechanistic Study of Partial Oxidation of Methane to Syngas Using In Situ Time-Resolved FTIR and Microprobe Raman SpectroscopiesTHE CHEMICAL RECORD, Issue 2 2002Mechanism of Methane Partial Oxidation Abstract In situ time-resolved Fourier transform infrared (FTIR) and microprobe Raman spectroscopies were used to characterize the reaction mechanisms of the partial oxidation of methane to syngas over SiO2 - and ,-Al2O3 -supported rhodium and ruthenium catalysts. The interaction of both pure methane and a methane/oxygen mixture at a stoichiometric feed ratio with an oxygen-rich catalyst surface led to the formation of CO2 and H2O as the primary products. For the H2 -pretreated samples, the reaction mechanisms with the catalysts differ. Only Rh/SiO2 is capable of catalyzing the direct oxidation of methane to syngas, while syngas formation over Rh/g-Al2O3, Ru/SiO2, and Ru/g-Al2O3 can be achieved mainly via a combustion-reforming scheme. The significant difference in the mechanisms for partial oxidation of methane to syngas over the catalysts can be correlated to the differences in the concentration of oxygen species (O2,) on the catalyst surface during the reaction, mainly due to the difference in the nature of the metals and supports. © 2002 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 2:102,112, 2002: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.10016 [source] Sources of Growth and Structural Change in the Vietnamese Economy, 1996,2003: A Computable General Equilibrium Analysis,ASIAN ECONOMIC JOURNAL, Issue 2 2009James A. Giesecke C68; D58; F14; O12 We use the MONASH-VN model, a dynamic computable general equilibrium model of the Vietnamese economy, to investigate Vietnam's rapid growth and structural change over the period 1996 to 2003. We do this in two steps. First, we estimate changes in variables representing production technologies, consumer preferences, government policy and other structural features of the economy. Movements in these structural and policy variables are then used to explain the recent history of Vietnam's rapid growth and structural change. We find the most important sources of growth and change to be technical improvements, favorable shifts in foreign demand for Vietnamese goods and employment growth. Other important factors include movement in household preferences away from primary products and towards manufactures and services, expansion in agricultural land supply, and tax reform. [source] Interest of industrial actors in biorefinery concepts in EuropeBIOFUELS, BIOPRODUCTS AND BIOREFINING, Issue 3 2009Klaus Menrad Abstract To satisfy the rising demand for agricultural and forestry products it is becoming more and more important to use biomass as efficiently as possible. One way of achieving that goal is to implement biorefinery systems in which biomass can be utilized entirely by conversion through multiple processes into a number of valuable products. To pursue the implementation of biorefinery systems, it is important to know to what extent the industry is interested in such concepts. This perspective deals with the results of a cross-European survey investigating the interests of potential industrial actors in biorefinery concepts. A high resonance was identified amongst companies belonging to the biofuels industry; companies active in this sector, therefore, could possibly provide access to further integrated concepts. On the whole, the results reflect a very positive attitude toward biorefinery concepts. But there are also problems with respect to the political and legal framework; policy and legislation may be required to establish stable framework conditions and provide planning security for investment decisions. Oilseed and lignocellulosic feedstock is primarily utilized within the surveyed companies; fuel, heat and power are the primary products produced from biomass. Additionally, the survey showed that biorefinery concepts are highly influenced by aspects concerning regional value chains. On the upstream side ,feedstock issues' appear to be especially important for biorefineries. In general, sustainability aspects are considered to be a benefit of biorefinery concepts. This suggests opportunities for the design of marketing and communication strategies based on ecological aspects of biorefinery implementation. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd [source] Promoting ,-secretase cleavage of beta-amyloid with engineered proteolytic antibody fragmentsBIOTECHNOLOGY PROGRESS, Issue 4 2009Srinath Kasturirangan Abstract Deposition of beta-amyloid (A,) is considered as an important early event in the pathogenesis of Alzheimer's Disease (AD), and reduction of A, levels by various therapeutic approaches is actively being pursued. A potentially non-inflammatory approach to facilitate clearance and reduce toxicity is to hydrolyze A, at its ,-secretase site. We have previously identified a light chain fragment, mk18, with ,-secretase-like catalytic activity, producing the 1,16 and 17,40 amino acid fragments of A,40 as primary products, although hydrolysis is also observed following other lysine and arginine residues. To improve the specific activity of the recombinant antibody by affinity maturation, we constructed a single chain variable fragment (scFv) library containing a randomized CDR3 heavy chain region. A biotinylated covalently reactive analog mimicking ,-secretase site cleavage was synthesized, immobilized on streptavidin beads, and used to select yeast surface expressed scFvs with increased specificity for A,. After two rounds of selection against the analog, yeast cells were individually screened for proteolytic activity towards an internally quenched fluorogenic substrate that contains the ,-secretase site of A,. From 750 clones screened, the two clones with the highest increase in proteolytic activity compared to the parent mk18 were selected for further study. Kinetic analyses using purified soluble scFvs showed a 3- and 6-fold increase in catalytic activity (kcat/KM) toward the synthetic A, substrate compared to the original scFv primarily due to an expected decrease in KM rather than an increase in kcat. This affinity maturation strategy can be used to select for scFvs with increased catalytic specificity for A,. These proteolytic scFvs have potential therapeutic applications for AD by decreasing soluble A, levels in vivo. © 2009 American Institute of Chemical Engineers. Biotechnol. Prog., 2009 [source] Prostanoid receptor antagonists: development strategies and therapeutic applicationsBRITISH JOURNAL OF PHARMACOLOGY, Issue 1 2009RL Jones Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP1, EP2 ,) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP1, TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP2). While some antagonists are structurally related to the natural agonist, most recent compounds are ,non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD2 (acting on DP1 and DP2 receptors) and PGE2 (on EP1 and EP4 receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage. [source] Alkane Activation over Acidic Zeolites: The First StepCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2010Benoit Louis Dr. Abstract The heterogeneous acid-catalyzed activation step of alkanes leading to the reaction intermediates (carbocationic or alkoxy species) was up to now the matter of a longstanding controversy. Gas chromatography and online mass spectroscopy measurements show that H2 and methane are formed over H-zeolites, whereas HD and CH3D are formed over D-zeolites as the primary products in the reaction with isobutane. These results indicate that ,-bond protolysis by strong acid sites is the first step for hydrocarbon activation on these catalysts at mild temperatures (473,K), in analogy to the activation path occurring in liquid superacid media. [source] | |||||||||||||