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Different Reaction Mechanisms (different + reaction_mechanism)

Distribution by Scientific Domains
Life Sciences40%
Chemistry40%

Selected Abstracts

Reactions of platinum cluster ions with benzene

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2006
Hongtao Liu
In this work, the cation and anion products of the reactions between platinum clusters produced by laser ablation and the benzene molecules seeded in argon have been studied using a high-resolution reflectron time-of-flight mass spectrometer (RTOFMS). The dominant cation products are [C6nH6n,,,k]+ and [Ptm(C6H6)n]+ complexes, while the dominant anion products are dehydrogenated species, [C6H5PtH],, [PtC12Hk], and [PtmC6H4,·,·,·,(C6H6)n],, etc. Some important intermediate structures ([PtC6H6]+, [Pt(C6H6)2]+, [Pt2(C6H6)3]+, [C6H5PtH],, [Pt2C6H4],, [Pt3C6H4], and [Pt4C6H4],) have been analyzed using density functional theory (DFT) calculations. Different reaction mechanisms are proposed for platinum cluster cations and anions with benzene, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Kinetics and mechanism of the reaction between maleic anhydride and fatty acid esters and the structure of the products

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2008
Florina Stefanoiu
Abstract Alkenyl succinic anhydrides (ASA) were obtained by reaction between maleic anhydride and high-oleic sunflower oil (HOSO) esters. A kinetics study of the maleinization of alkyl esters indicated that the maleinization reaction was second order overall and first order with respect to the individual reactants, and the activation energy was 77.2,±,3.3,kJ/mol in the investigated temperature range (185,225,°C). These results showed that the cis configuration and the central position of the double bond in HOSO esters facilitate the maleinization of the latter. On the contrary, the length of the linear ester moiety had no influence on the course of the maleinization reaction. Moreover, new evidence demonstrates that there are two different reaction mechanisms: ene-reaction and addition in allylic position with a 2,:,1 ratio, respectively. This ratio was constant throughout the reaction, thus indicating that these mechanisms are independent. [source]

Influence of reaction mechanisms, grid spacing, and inflow conditions on the numerical simulation of lifted supersonic flames

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2010
P. Gerlinger
Abstract The simulation of supersonic combustion requires finite-rate chemistry because chemical and fluid mechanical time scales may be of the same order of magnitude. The size of the chosen reaction mechanism (number of species and reactions involved) has a strong influence on the computational time and thus should be chosen carefully. This paper investigates several hydrogen/air reaction mechanisms frequently used in supersonic combustion. It is shown that at low flight Mach numbers of a supersonic combustion ramjet (scramjet), some kinetic schemes can cause highly erroneous results. Moreover, extremely fine computational grids are required in the lift-off region of supersonic flames to obtain grid-independent solutions. The fully turbulent Mach 2 combustion experiment of Cheng et al. (Comb. Flame 1994; 99: 157,173) is chosen to investigate the influences of different reaction mechanisms, grid spacing, and inflow conditions (contaminations caused by precombustion). A detailed analysis of the experiment will be given and errors of previous simulations are identified. Thus, the paper provides important information for an accurate simulation of the Cheng et al. experiment. The importance of this experiment results from the fact that it is the only supersonic combustion test case where temperature and species fluctuations have been measured simultaneously. Such data are needed for the validation of probability density function methods. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Evaluation of solution oxygenation requirements for azonitrile-based oxidative forced degradation studies of pharmaceutical compounds

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2006
Eric D. Nelson
Abstract AIBN and ACVA oxidative forced degradation models are examined for two drug molecules whose predominant oxidation chemistries arise from different reaction mechanisms (i.e., free radical vs. nucleophilic). Stress was conducted under a variety of initiator concentrations, and under ambient and pressurized oxygen atmospheres. In each case examined, the azonitrile initiator solutions served as a good predictive model of the major oxidative degradation products observed in pharmaceutical formulations. At low to moderate inititator concentrations, the degradation product distributions and degree of reactivity were similar for samples stored in ambient and pressurized oxygen environments. These results are rationalized with reference to the oxygen consumption kinetics of AIBN and ACVA solutions as a function of initiator concentration. The data suggests that ambient air provides sufficient oxygen to enable chain propagation of peroxy radicals in azonitrile solutions of concentrations appropriate to the forced degradation of pharmaceutical compounds. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95: 1527,1539, 2006 [source]

Elucidation of the mechanism and end products of glutaraldehyde crosslinking reaction by X-ray structure analysis

BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007
Yariv Wine
Abstract Glutaraldehyde has been used for several decades as an effective crosslinking agent for many applications including sample fixation for microscopy, enzyme and cell immobilization, and stabilization of protein crystals. Despite of its common use as a crosslinking agent, the mechanism and chemistry involved in glutaraldehyde crosslinking reaction is not yet fully understood. Here we describe feasibility study and results obtained from a new approach to investigate the process of protein crystals stabilization by glutaraldehyde crosslinking. It involves exposure of a model protein crystal (Lysozyme) to glutaraldehyde in alkaline or acidic pH for different incubation periods and reaction arrest by medium exchange with crystallization medium to remove unbound glutaraldehyde. The crystals were subsequently incubated in diluted buffer affecting dissolution of un-crosslinked crystals. Samples from the resulting solution were subjected to protein composition analysis by gel electrophoresis and mass spectroscopy while crosslinked, dissolution resistant crystals were subjected to high resolution X-ray structural analysis. Data from gel electrophoresis indicated that the crosslinking process starts at specific preferable crosslinking site by lysozyme dimer formation, for both acidic and alkaline pH values. These dimer formations were followed by trimer and tetramer formations leading eventually to dissolution resistant crystals. The crosslinking initiation site and the end products obtained from glutaraldehyde crosslinking in both pH ranges resulted from reactions between lysine residues of neighboring protein molecules and the polymeric form of glutaraldehyde. Reaction rate was much faster at alkaline pH. Different reaction end products, indicating different reaction mechanisms, were identified for crosslinking taking place under alkaline or acidic conditions. Biotechnol. Bioeng. 2007;98:711,718. © 2007 Wiley Periodicals, Inc. [source]