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Reaction Process (reaction + process)
Kinds of Reaction Process Selected AbstractsEfficient Entry to Polysubstituted Pyrrolizidines, Indolizidines and Quinolizidines via a Sequential Reaction Process.CHEMINFORM, Issue 38 2006Dawei Ma Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] An Efficient Sequential Reaction Process to Polysubstituted Indolizidines and Quinolizidines and Its Application to the Total Synthesis of Indolizidine 223A.CHEMINFORM, Issue 27 2005Wei Zhu Abstract For Abstract see ChemInform Abstract in Full Text. [source] A New Amperometric Hydrazine Sensor Based on Prussian Blue/Single-walled Carbon Nanotube NanocompositesELECTROANALYSIS, Issue 16 2010Cong Wang Abstract A slow reaction process has been successfully used to synthesize Prussian blue/single-walled carbon nanotubes (PB/SWNTs) nanocomposites. Electrochemical and surface characterization by cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) confirmed the presence of PB nanocrystallites on SWNTs. PB/SWNTs modified glassy carbon electrode (GCE) exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. The fabricated hydrazine sensor showed a wide linear range of 2.0×10,6,6.0×10,3,M with a response time less than 4,s and a detection limit of 0.5,,M. PB/SWNTs modified electrochemical sensors are promising candidates for cost-effective in the hydrazine assays. [source] Electrochemically Initiated Catalytic Oxidation of 5-Thio-2-Nitrobenzoic Acid (TNBA) in the Presence of Thiols at a Boron Doped Diamond Electrode: Implications for Total Thiol DetectionELECTROANALYSIS, Issue 21 2003Olga Nekrassova Abstract The electrochemical response of 5,5-dithiobis(2-nitrobenzoic acid) (DTNB) to increasing additions of thiol species has been examined at a boron doped diamond electrode. A reaction has been shown to occur with a range of biologically relevant thiols and proceeds via a CECC' process. A total thiol detection methodology has been developed showing that the sensitivities of the standard addition plots are independent of the individual thiol species added to the solution. The analytical utility of the reaction process has been assessed using chronoamperometry with the corresponding data producing detection limits of 5.7,,M, 4.4,,M and 5.8,,M for the detection of cysteine, homocysteine and glutathione respectively. [source] The Electrochemical Oxidation of 5-Thio-2-nitrobenzoic acid (TNBA) at a Boron Doped Diamond Electrode: Demonstration of a CEC ReactionELECTROANALYSIS, Issue 19 2003Olga Nekrassova Abstract The oxidation of 5-thio-2-nitrobenzoic acid (TNBA) over a wide pH range has been investigated using cyclic voltammetry at a boron doped diamond electrode. The reaction has been shown to proceed via a CEC reaction process in which at lower pH the thiol moiety of the TNBA species has to undergo deprotonation before oxidation. DIGISIM modelling of the voltammetric profiles deduced a value of 5.2 for the pKa of the thiol moiety which is in good agreement with that obtained from spectrophotometric data. Also reported are the rate constants for all the heterogeneous and homogeneous processes. [source] Electrochemical Reduction of Oxygen on Carbon Supported Pt and Pt/Ru Fuel Cell Electrodes in Alkaline SolutionsFUEL CELLS, Issue 4 2003E.H. Yu Abstract A study of O2 reduction in 1 M NaOH solution at gas diffusion electrodes made from carbon supported Pt and Pt/Ru catalysts is reported. Two Tafel regions were observed for both the Pt and Pt/Ru electrodes. Although the same mechanism was suggested for oxygen reduction on both Pt and Pt/Ru catalysts, the O2 reduction activity was lower on Ru. Electrochemical Impedance Spectroscopy (EIS) analysis was carried out at different potentials and showed the significant contribution of diffusion on the reaction process and kinetics. The effect of methanol on O2 reduction was investigated in solutions containing various concentrations of methanol. The electrode performance deteriorated with increasing methanol concentration because of a mixed cathode potential. The methanol tolerance, i. e., the methanol concentration which polarises the O2 reduction reaction for O2 reduction, at the Pt/C electrode with a Pt loading of 1.2 mg cm,2 is 0.2 M methanol in 1 M NaOH. [source] Chemical modification of pyroclastic rock by hot water: an experimental investigation of mass transport at the fluid,solid interfaceGEOFLUIDS (ELECTRONIC), Issue 1 2009J. HARA Abstract Hydrothermal water,(pyroclastic) rock interactions were examined using flow-through experiments to deduce the effect of mass transport phenomena on the reaction process. A series of experiments were conducted over the temperature range 75,250°C, with a constant temperature for each experiment, and at saturated vapour pressure, to estimate the apparent rate constants as a function of temperature. Based on the chemistry of analysed solutions, the water,rock interaction in the experiments was controlled by diffusion from the reaction surface and by the existence of a surface layer at the rock,fluid interface, which regulated the chemical reaction rate. The reaction progress depended to a high degree on flow velocity and temperature conditions, with element abundances in the fluid significantly affected by these factors. Mass transport coefficients for diffusion from the rock surface to the bulk solution have been estimated. Ca is selectively depleted under lower temperature conditions (T < 150°C), whereas Na is greatly depleted under higher temperature conditions (T > 150°C), and K reaction rates are increased when flow velocity increases. Using these conditions, specific alkali and alkali earth cations were selectively leached from mineral surfaces. The ,surface layer' comprised a 0.5,1.8 mm boundary film on the solution side (the thickness of this layer has no dependence on chemical character) and a reaction layer. The reaction layer was composed of a Si, Al-rich cation-leached layer, whose thickness was dependent on temperature, flow velocity and reaction length. The reaction layer varied in thickness from about 10,4 to 10,7 mm under high temperature/low fluid velocity and low temperature/high fluid velocity conditions, respectively. [source] Selective Patterned Growth of Single-Crystal Ag,TCNQ Nanowires for Devices by Vapor,Solid Chemical Reaction,ADVANCED FUNCTIONAL MATERIALS, Issue 19 2008Kai Xiao Abstract We report the deterministic growth of individual single-crystal organic semiconductor nanowires of silver,tetracyanoquinodimethane (Ag,TCNQ) with high yield (>90%) by a vapor,solid chemical reaction process. Ag,metal films or patterned dots deposited onto substrates serve as chemical reaction centers and are completely consumed during the growth of the individual or multiple nanowires. Selective-area electron diffraction (SAED) revealed that the Ag,TCNQ nanowires grow preferentially along the strong ,,, stacking direction of Ag,TCNQ molecules. The vapor,solid chemical reaction process described here permits the growth of organic nanowires at lower temperatures than chemical vapor deposition (CVD) of inorganic nanowires. The single-crystal Ag,TCNQ nanowires are shown to act as memory switches with high on/off ratios, making them potentially useful in optical storage, ultrahigh-density nanoscale memory, and logic devices. [source] Numerical simulation of model scramjet combustor flowfieldHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2007Yuan-Guang Wang Abstract A new concept has been raised and adopted in this paper to enlarge the scope of the two-dimensional model particularly for the purpose of dealing with three-dimensional normal injection cases. Meanwhile, the method has a very good performance for its short cyclic period. The new idea was realized through special resolution with continuity equations; i.e., mass flow was directly added in the source term of the continuity equation. To prove the robustness of this illuminating method, comparisons using calculations were carried out, and the results are satisfactory. A model scramjet combustor tested on the free-jet scramjet test facility was illustrated and underwent numerical calculations with the two-dimensional program, adopting the above simplified injecting method. To simulate the chemical reaction process in the scramjet tunnel, a five-species, single-step reaction model was introduced in the calculation process. This research presents the major aerodynamic parameters and components of mass fraction distribution within the model combustor channel, which made it easy to observe and analyze the flowfield. Finally, wall pressure comparisons between the numerical and experimental results were carried out to verify the accuracy of the calculation model. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(5): 295, 302, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20159 [source] Evaluating the transport and removal of chromate using pyrite and biotite columnsHYDROLOGICAL PROCESSES, Issue 14 2007Chul-Min Chon Abstract To remove chromate from a wastewater, a porous permeable reactive barrier system (PRBS), using pyrite and biotite, was adapted. This study included bench-scale column experiments to evaluate the efficiency of the PRBS and investigate the reaction process. The total chromium concentration of the effluent from the biotite and pyrite columns reached the influent concentration of 0·10 mM after passing through more than 150 pore volumes (PVs) and 27 PVs respectively, and remained constant thereafter. The CrVI concentration in the effluent from the biotite column became constant at about 0·08 mM, accounting for approximately 80% of the influent concentration, after passing through 200 PVs. Moreover, in the pyrite column, the CrVI concentration remained at about 0·01 mM, 10% of the input level, after passing through 116 PVs. This shows that both columns maintained their levels of chromate reduction once the CrVI breakthrough curves (BTCs) had reached the steady state, though the steady-state output concentration of total chromium had reached the influent level. The variances of the iron concentration closely followed those of the chromium. The observed data for both columns were fitted to the predicted BTCs calculated by CXTFIT, a program for estimating the solute transport parameters from experimental data. The degradation coefficient µ of the total chromium BTCs for both columns was zero, suggesting the mechanisms for the removal of chromate limit the µ of the CrVI BTCs. The CrVI degradation of the pyrite column (6·60) was much greater than that of the biotite column (0·27). In addition, the CrVI retardation coefficient R of the pyrite column (253) was also larger than that of the biotite column (125). The R values for the total chromium BTCs from both columns were smaller than those of the CrVI BTC. Whereas the total chromium BTC for the pyrite column showed little retardation (1·5), the biotite column showed considerable retardation (80). The results for the 900 °C heat-treated biotite column were analogous to those of the control column (quartz sand). This suggests that the heat-treated biotite played no role in the retardation and removal of hexavalent chromium. The parameters of the heat-treated biotite were calculated to an R of 1·2 and µ of 0·01, and these values confirmed quantitatively that the heated biotite had little effect on the transport of CrVI. These solute transport parameters, calculated by CXTFIT from the data obtained from the column tests, can provide quantitative information for the evaluation of bench- or field-scale columns as a removal technology for CrVI in wastewater or contaminated groundwater. Copyright © 2006 John Wiley & Sons, Ltd. [source] Gold(I)-Catalyzed Cascade for Synthesis of Pyrrolo[1,2- a:2,,1,- c]-/Pyrido[2,1- c]pyrrolo[1,2- a]quinoxalinonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Yu Zhou Abstract An efficient and convenient method was developed for the one-pot construction of the complex polycyclic heterocycles pyrrolo[1,2- a:2,,1,- c]-/pyrido[2,1- c]pyrrolo[1,2- a]quinoxalinones from two simple starting materials via a gold(I)-catalyzed domino reaction. This strategy presents an atom economical and environmentally friendly transformation, in which two new CN bonds and one new CC bond are formed in a one-pot reaction process. [source] Formation pathways of DMSO from DMS-OH in the presence of O2 and NOx: A theoretical studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2009Juan M. Ramírez-Anguita Abstract The relative importance of the reaction pathways and thus the product yields in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been said to be influenced by the content of nitrogen oxides (NOx) in chamber experiments. In this study, ab initio and density functional electronic structure calculations of all the possible reaction pathways corresponding to the reaction process initiated by DMS-OH + oxygen (O2), leading to the formation of the dimethyl sulfoxide (DMSO) product in the presence of NOx (NO and NO2), are carried out for the first time. The results for the different pathways are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO formation yields. Our theoretical results clearly show the existence of NOx -dependent pathways leading to the formation of DMSO in addition to O2 -dependent channels. So then, NOx -containing conditions would have to modify the relative importance of the addition channel in the DMS oxidation process. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Dynamic optimization of the methylmethacrylate cell-cast process for plastic sheet productionAICHE JOURNAL, Issue 6 2009Martín Rivera-Toledo Abstract Traditionally, the methylmethacrylate (MMA) polymerization reaction process for plastic sheet production has been carried out using warming baths. However, it has been observed that the manufactured polymer tends to feature poor homogeneity characteristics measured in terms of properties like molecular weight distribution. Nonhomogeneous polymer properties should be avoided because they give rise to a product with undesired wide quality characteristics. To improve homogeneity properties force-circulated warm air reactors have been proposed, such reactors are normally operated under isothermal air temperature conditions. However, we demonstrate that dynamic optimal warming temperature profiles lead to a polymer sheet with better homogeneity characteristics, especially when compared against simple isothermal operating policies. In this work, the dynamic optimization of a heating and polymerization reaction process for plastic sheet production in a force-circulated warm air reactor is addressed. The optimization formulation is based on the dynamic representation of the two-directional heating and reaction process taking place within the system, and includes kinetic equations for the bulk free radical polymerization reactions of MMA. The mathematical model is cast as a time dependent partial differential equation (PDE) system, the optimal heating profile calculation turns out to be a dynamic optimization problem embedded in a distributed parameter system. A simultaneous optimization approach is selected to solve the dynamic optimization problem. Trough full discretization of all decision variables, a nonlinear programming (NLP) model is obtained and solved by using the IPOPT optimization solver. The results are presented about the dynamic optimization for two plastic sheets of different thickness and compared them against simple operating policies. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(,-olefin)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Yingying Lu Abstract This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s-PS), and elastomers, such as poly(ethylene- co -1-octene) and poly(ethylene- co -styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ,270 °C to low glass-transition temperature ,,60 °C. The chemistry involves two reaction steps, including the preparation of a borane group-terminated polyolefin by the combination of a metallocene catalyst and a borane chain-transfer agent as well as the interconversion of a borane terminal group to an anionic (O,K+) terminal group for the subsequent ring-opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of ,-olefins to the ring-opening polymerization of ethylene oxide. The well-defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (Mw/Mn < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416,3425, 2002 [source] Room-Temperature Solid-State Reaction Behavior, Hydrothermal Crystallization and Physical Characterization of NaRE(MoO4)2, and Na5Lu(MoO4)4 CompoundsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Jianhua Wu In the context, a novel composite synthesis technology is engaged in the preparation of NaRE(MoO4)2 (RE=Y, La, Nd, Eu, Gd, Tb, Er, and Yb) and Na5Lu(MoO4)4 compounds, which involves a room-temperature solid-state reaction and hydrothermal crystallization process. The synthesis mechanism is predicted, indicating that higher temperature and moisture can speed up the reaction process and especially the existence of crystalline water molecules in the precursor is necessary for the solid-state reaction at room temperature. It is found that different rare-earth nitrate precursors present different reactivity to sodium molybdate at room temperature. The crystallization degree of the products after the room-temperature solid-state reaction depends on the melting point of rare-earth nitrate precursors. The hydrothermal treatment is beneficial for the good crystallization of NaRE(MoO4)2 (RE=Y, La, Nd, Eu, Gd, Tb, Er, and Yb) and Na5Lu(MoO4)4. Finally, the photoluminescent spectra for these NaRE(MoO4)2:Eu3+ (La, Gd, and Y) are studied, which depend on the species of rare-earth ions. [source] Electrical Properties of Gadolinium,Europium Zirconate CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Xiao-Liang Xia (Gd1,xEux)2Zr2O7 (0,x,1.0) ceramics are prepared via a solid-state reaction process at 1973 K for 10 h in air. (Gd1,xEux)2Zr2O7 (0.2,x,1.0) ceramics exhibit an ordered pyrochlore-type structure; however, Gd2Zr2O7 has a disordered defect fluorite-type structure. Raman spectroscopy analysis indicates that the degree of structural ordering increases with the increase of Eu content. The electrical properties of (Gd1,xEux)2Zr2O7 ceramics are investigated using complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz from 623 to 923 K. Electrical conductivity obeys the Arrhenius equation. Both the activation energy and the preexponential factor for grain conductivity decrease with increasing europium content from Gd2Zr2O7 (x=0) to Eu2Zr2O7 (x=1.0). The measured electrical conductivity of (Gd1,xEux)2Zr2O7 ceramics increases with increasing Eu content and temperature. Electrical conductivity of the pyrochlore-type materials is higher than that of the defect fluorite-type material in (Gd1,xEux)2Zr2O7 solid solution systems. The electrical conductivity of (Gd0.4Eu0.6)2Zr2O7 is almost independent of oxygen partial pressure from 1.0 × 10,4 to 1.0 atm. The high ionic transference number of (Gd0.4Eu0.6)2Zr2O7 ceramic at different temperatures proves that conduction is purely ionic with negligible electronic contribution. [source] Electric Field-Dependent Dielectric Properties and High Tunability of Porous Ba0.5Sr0.5TiO3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007Yuanyuan Zhang Porous Ba0.5Sr0.5TiO3 (BST) ceramics were fabricated by the traditional solid-state reaction process, and their structural, microstructural, dielectric, and tunability properties were systemically investigated. Compared with the fully dense BST samples, porous samples exhibit smaller grain sizes, a more uniform microstructure, and much lower dielectric constants, while at the same time, exhibiting little increase in tunability, which is beneficial to the development of microwave-tunable applications. At a frequency of 10 kHz and a temperature of 18°C, as porosity increased from 0% to 28.8%, the dielectric constant of the BST ceramics (under zero bias field) decreased from ,r(0),1690 to ,r(0),990, while the dielectric losses were still less than 0.2%, and the tunability increased from 17.6% to 19.6% (2.6 kV/mm). [source] Neutron Thermodiffractometry Study of Calcium Zirconate/Magnesium Oxide Formation in the ZrO2,CaO,MgO SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Sara Serena The reaction process to obtain CaZrO3/MgO specimens in the ZrO2,CaO,MgO system from two mixtures of natural and synthetic raw materials were analyzed by neutron thermodiffractometry; differential thermal analysis,thermogravimetry (DTA-TG) also was used. The results from the different techniques provided a complete description of the decomposition and reaction process in the samples and proved that high-temperature neutron diffraction is a powerful tool for analyzing in situ reactions up to 1250°C in both mixtures. In the present work, the evolution of the crystalline phases, the mechanism and temperature of formation of CaZrO3, and the activation energy were properly established in terms of the neutron thermodiffraction study. [source] Characterization of Methyl Methacrylate Grafting onto Preirradiated Biodegradable Lignocellulose Fiber by , -RadiationMACROMOLECULAR BIOSCIENCE, Issue 1 2005Ferdous Khan Abstract Summary: Gamma-radiation-induced graft copolymerization of methyl methacrylate onto natural lignocellulose (jute) fiber was carried out by the preirradiation method in an aqueous medium by using octylphenoxy-polyethoxyethanol as an emulsifier. The different factors that influenced the graft copolymer reaction process were investigated. In the case of radiation-dose-dependent grafting, samples irradiated in the presence of air produced up to 73% graft weight compared to 53% obtained in the case of irradiation in a nitrogen environment. By assuming Arrhenius reaction kinetics, the activation energy (Ea) of the grafting reaction process was evaluated for different reaction temperatures. Moreover, the graft copolymer reaction was controlled by incorporating a homopolymer-inhibiting agent and three different chain-transfer agents in the reaction medium. The mechanical and thermal properties of jute fiber ,as received' and jute- graft -poly(methyl methacrylate) were also investigated. The results showed that the percentage of grafting with jute fiber has a significant effect on the properties. The kinetic parameters were evaluated from TGA thermograms by using Broido's method in the temperature range 240,350,°C. Scanning electron micrographs show that the structural changes on the surface of jute fibers were induced by graft copolymerization of methyl methacrylate monomer. Fiber-fiber surface friction was measured in terms of the average maximum load and the kinetic friction. SEM of jute- graft -poly(methyl methacrylate). [source] Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007Chao Zhang Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,·,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,°C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source] Real-time reaction monitoring by probe electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Zhan Yu Probe electrospray ionization (PESI) is a modified version of the electrospray ionization (ESI), where the capillary for sampling and spraying is replaced by a solid needle. High tolerance to salts and direct ambient sampling are major advantages of PESI compared with conventional ESI. In this study, PESI-MS was used to monitor some biological and chemical reactions in real-time, such as acid-induced protein denaturation, hydrogen/deuterium exchange (HDX) of peptides, and Schiff base formation. By using PESI-MS, time-resolved mass spectra and ion chromatograms can be obtained reproducibly. Real-time PESI-MS monitoring can give direct and detailed information on each chemical species taking part in reactions, and this is valuable for a better understanding of the whole reaction process and for the optimization of reaction parameters. PESI-MS can be considered as a potential tool for real-time reaction monitoring due to its simplicity in instrumental setup, direct sampling with minimum sample preparation and low sample consumption. Copyright © 2010 John Wiley & Sons, Ltd. [source] Molecular-scale investigation of polymerization, nucleation, and growth of polystyrene particle by atomic force microscopyASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Tetsuya Yamamoto Abstract To clarify the mechanism of the nucleation and growth processes in the soap-free polymerization of polystyrene latex particles in water, the polymerization process was investigated on a molecular scale, by using an atomic force microscope (AFM), as well as a scanning electron microscope (SEM) and a dynamic light scattering apparatus (DLS). A ,cationic' initiator was employed to make all the polymeric materials produced, such as oligomers, embryos, nuclei, and grown particles, adsorb electrostatically on the negatively charged mica plate of molecular-scale smoothness. This in situ transfer of polymeric materials in the bulk onto the mica surface enables us to observe the images of polymeric materials during the reaction process and to estimate what is happening in the nucleation and growth processes of particles, at least qualitatively. The most important findings of the present study are that1 these molecular-scale polymeric materials, to which much attention has not been paid probably because of the difficulty of detection, are continuously born in the bulk throughout the reaction process of particle formation, and2 they play an important role in the growth of particles. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Osmolyte controlled fibrillation kinetics of insulin: New insight into fibrillation using the preferential exclusion principleBIOTECHNOLOGY PROGRESS, Issue 5 2009Arpan Nayak Abstract Amyloid proteins are converted from their native-fold to long ,-sheet-rich fibrils in a typical sigmoidal time-dependent protein aggregation curve. This reaction process from monomer or dimer to oligomer to nuclei and then to fibrils is the subject of intense study. The main results of this work are based on the use of a well-studied model amyloid protein, insulin, which has been used in vitro by others. Nine osmolyte molecules, added during the protein aggregation process for the production of amyloid fibrils, slow-down or speed up the process depending on the molecular structure of each osmolyte. Of these, all stabilizing osmolytes (sugars) slow down the aggregation process in the following order: tri > di > monosaccharides, whereas destabilizing osmolytes (urea, guanidium hydrochloride) speed up the aggregation process in a predictable way that fits the trend of all osmolytes. With respect to kinetics, we illustrate, by adapting our earlier reaction model to the insulin system, that the intermediates (trimers, tetramers, pentamers, etc.) are at very low concentrations and that nucleation is orders of magnitude slower than fibril growth. The results are then collated into a cogent explanation using the preferential exclusion and accumulation of osmolytes away from and at the protein surface during nucleation, respectively. Both the heat of solution and the neutral molecular surface area of the osmolytes correlate linearly with two fitting parameters of the kinetic rate model, that is, the lag time and the nucleation rate prior to fibril formation. These kinetic and thermodynamic results support the preferential exclusion model and the existence of oligomers including nuclei and larger structures that could induce toxicity. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Production of ,-Galactosyl Epitopes via Combined Use of Two Recombinant Whole Cells Harboring UDP-Galactose 4-Epimerase and ,-1,3-GalactosyltransferaseBIOTECHNOLOGY PROGRESS, Issue 4 2000Xi Chen ,-Galactosyl epitopes (or ,-Gal, oligosaccharides with a terminal Gal,1,3Gal sequence) are a class of biologically important oligosaccharides in great demand in bulk quantities for basic and clinical studies on preventing hyperacute rejection in pig-to-primate organ xenotransplantaion. A truncated bovine ,-1,3-galactosyltransferase, the key enzyme responsible for the biosynthesis of the terminal structure of ,-Gal, was cloned and overexpressed previously. The acceptor specificity was further studied in the present paper, and lactose and galactose derivatives were found to be good acceptors. To develop a more proficient reaction process, we report herein an example of an efficient enzymatic synthesis of ,-Gal oligosaccharides catalyzed by the combination of two recombinant Escherichia coli whole cells harboring the genes of a UDP-galactose 4-epimerase and the ,-1,3-galactosyltransferase, respectively. Using lactosyl azide (LacN3) as the acceptor for the glycosyltransferase, the combined use of the two recombinant cells efficiently produced ,-Gal epitope Gal,1,3LacN3 in 60,68% yield. [source] Experimental and Numerical Studies of Fe2O3 Particle Formation Processes in a Flat Flame BurnerCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 6 2007M. Beck Abstract Particle formation processes are of interest for many industrial applications. This work focuses on investigating Fe2O3 particle formation. The particles form during thermal decomposition of an iron chloride solution in so-called spray roasting reactors. To analyze the reaction process, a laboratory reactor was designed which reproduces the conditions required for a systematic study of the particle formation process. Furthermore, a simplified particle conversion model was developed to simulate the realistic geometries and particle numbers on an industrial scale by CFD codes. [source] Variation of Cell Voltage with Reaction Time in Electrochemical Synthesis Process of Sodium DichromateCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2006C. W. Li Abstract To address the problems existing in the traditional production technique of sodium dichromate, a new green technology of producing sodium dichromate with an electrochemical synthesis method was studied. Using a self-made electrosynthesis reactor of pure titanium and stainless steel, with a multiple-unit metal oxides combination anode, a cathode of stainless steel, and a reinforcing combination cation exchange membrane with perfluorosulfonic and perfluorocarboxylic polymers, experiments were carried out on the direct electrochemical synthesis of sodium dichromate from sodium chromate. From the experimental results and electrochemical reaction principles, it was shown that the electrochemical synthesis reaction process of sodium dichromate may be quantitatively determined from the variation of the cell voltage measured macroscopically with reaction time. Cell voltages were experimentally measured at different initial sodium chromate concentrations in the anolyte, and the dependence of the cell voltage on reaction time was discussed. The mathematical model of the variation of cell voltage with reaction time and the change rate equation of cell voltage were established, and satisfactorily formulated the change law of cell voltage in the electrochemical synthesis process of sodium dichromate. [source] A Three-Component Reaction Based on a Remote-Group-Directed Dynamic Kinetic Aza-Michael Addition: Stereoselective Synthesis of Imidazolidin-4-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Zhenghu Xu Dr. In control: An ,-amino amide reacted with an aldehyde and a Michael acceptor to form stable imidazolidin-4-ones with high stereoselectivity. A dynamic kinetic aza-Michael addition was discovered and applied to the three-component reaction to enforce high stereoselectivity. A remote group was incorporated to invert the reaction process and direct the reaction towards the desired product (see scheme). [source] Controlled Synthesis, Growth Mechanism, and Properties of Monodisperse CdS Colloidal SpheresCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Xin-Hao Li Abstract Highly monodisperse submicrometer CdS colloidal spheres (CSCS) with a controllable and tunable size (between 80 and 500,nm) have been synthesized through a facile solvothermal technique. Owing to the controllability of the reaction process, the growth mechanism of the colloidal spheres has been elucidated in detail. The whole growth process can be summarized as homogenous and slow nucleation of nanocrystals, formation of "cores" through 3D-oriented attachment of nanocrystals, and further surface-induced growth to monodisperse colloidal spheres through in situ formation and random attachment of additional nanocrystals. It has been demonstrated that the obtained CSCS colloidal particles are able to be assembled into films which show characteristic stop band gaps of photonic crystals. By using the CSCS as a template, Ag2S, Bi2S3, Cu2S, HgS, and Sb2S3 colloidal spheres, which are difficult to obtain directly, have also been prepared successfully through ion exchange. [source] The Electrochemical Behavior of ,-Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological SamplesELECTROANALYSIS, Issue 12 2004Li Yang Abstract The voltammetric behavior of ,-ketoglutarate (,-KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH,4.5, 0.2,M NaAc-HAc buffer solution), a sensitive reductive wave of ,-KG was obtained by linear scan voltammetry (LSV) and the peak potential was ,1.18,V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were ,=0.3 and ks=0.72,1/s. There was a linear relationship between peak current ip, ,-KG and ,-KG concentration in the range of 2×10,6,8×10,4,M ,-KG. The detection limit was 8×10,7,M and the relative standard deviation was 2.0% (C,-KG=8×10,4,M, n=10). Applications of the reductive wave of ,-KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of ,-KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between ,-KG and aluminum, a linear relationship holds between the decrease of peak current of ,-KG ,ip and the added Al concentration C in the range of 5.0×10,6,2.5×10,4,M. The detection limit was 2.2×10,6,M and the relative standard deviation was 3.1% (C=4×10,5,M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP-AES. (3) It was also applied to study the effect of AlIII on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of ,-KG+NH+NADH,L -glutamate+NAD++H2O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD+ and ,-KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes. [source] Theoretical study on the mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile catalyzed by magnesium ethoxideINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2009Lin-Sen Heng The mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile for the synthesis of 2-dicyanomethylene-4,5,5-trimethyl-2,5-dihydrofuran-3-carbonitrile catalyzed by magnesium ethoxide was investigated by density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states, and products were calculated at the B3LYP/6,31G(d) level. The vibration analysis and the IRC analysis demonstrated the authenticity of transition states, and the reaction processes were confirmed by the changes of charge density at bond-forming critical point. The results indicated that magnesium ethoxide is an effective catalyst in the synthesis of 2-dicyanomethylene-4,5,5-trimethyl-2,5-dihydrofuran-3-carbonitrile from malononitrile and 3-hydroxy-3-methyl-2-butanone. The activation energy of reaction with magnesium ethoxide decreased by 102.37 kJ mol,1 compared with that of the reaction without it. The mechanism of reaction with catalyst magnesium ethoxide differs from that of reaction without it. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 227,235, 2009 [source] | ||||||||||||||||||||||||||||||||||