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Reaction Scheme (reaction + scheme)
Selected AbstractsAn Investigation of the Al,Pd,Fe Phase Diagram Between 50 and 100 at.% Al: Reaction Scheme.CHEMINFORM, Issue 32 2005S. Balanetskyy No abstract is available for this article. [source] Access to Any Site-Directed Isotopomer of Methionine, Selenomethionine, Cysteine, and Selenocysteine , Use of Simple, Efficient Modular Synthetic Reaction Schemes for Isotope IncorporationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2004Arjan H. G. Siebum Abstract Simple modular reaction schemes that allow access to any isotopomer of protected serine and homoserine have been worked out. These systems could be simply converted into cysteine, selenocysteine, homocysteine, homoselenocysteine, the essential amino acid methionine, and selenomethionine by Mitsunobu chemistry. These sulfur- and selenium-containing amino acids fulfil many essential roles in the living organism. In addition, homoserine could be converted in a few steps into optically active L -vinylglycine. As well as the stable isotopes 13C, 15N, 17O, and 18O, the radioactive isotopes of sulfur, selenium and carbon can also be easily introduced in a site-directed fashion. In view of the wide scope of the Mitsunobu reaction, we feel that many more important systems with the carbon skeleton of serine and homoserine should be preparable through this basic chemistry in any site-directed isotopically labeled form. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Study of the Complexation, Adsorption and Electrode Reaction Mechanisms of Chromium(VI) and (III) with DTPA Under Adsorptive Stripping Voltammetric ConditionsELECTROANALYSIS, Issue 19 2003Sylvia Sander Abstract The complexation of Cr(III) and Cr(VI) with diethylenetriaminepentaacetic acid (DTPA), the redox behavior of these complexes and their adsorption on the mercury electrode surface were investigated by a combination of electrochemical techniques and UV/vis spectroscopy. A homogenous two-step reaction was observed when mixing Cr(III), present as hexaquo complex, with DTPA. The first reaction product, the electroactive 1,:,1 complex, turns into an electroinactive form in the second step. The results indicate that the second reaction product is presumably a 1,:,2 Cr(III)/DTPA complex. The electroreduction of the DTPA-Cr(III) complex to Cr(II) was found to be diffusion rather than adsorption controlled. The Cr(III) ion, generated in-situ from Cr(VI) at the mercury electrode at about ,50,mV (vs. Ag|AgCl) (3,mol,L,1 KCl), was found to form instantly an electroactive and adsorbable complex with DTPA. By means of electrocapillary measurements its surface activity was shown to be 30 times higher than that of the complex built by homogenous reaction of DTPA with the hydrated Cr(III). Both components, DTPA and the in-situ built complex Cr(III) ion were found to adsorb on the mercury electrode. The effect of nitrate, used as catalytic oxidant in the voltammetric determination method, on the complexation reaction and on the adsorption processes was found to be negligible. The proposed complex structures and an overall reaction scheme are shown. [source] Flame structure and NO emissions in gas combustion of low calorific heating valueINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2003Jeong Park Abstract Numerical study on addition effects of CO and CO2 in fuel side (H2/Ar) on flame structure and NO emission behaviour in counterflow diffusion flame has been conducted with detailed chemistry to fundamentally understand gas combustion of low calorific heating value. A modified Miller,Bowman reaction scheme including a complementary C2 -reaction subset is adopted. The radiative heat loss term, which is based on an optically thin model and it especially important at low strain rates, is included to cover the importance of the temperature dependence on NO emission. Special interest is taken to estimate the roles of added CO and CO2 in fuel side on flame structure and NO emission characteristics. Increasing CO concentration in fuel side contributes to the enhancement of combustion due to the increase effect of the concentration of reactive species. The increase of added CO2 concentration in fuel side suppresses overall reaction rate due to the high heat capacity. It is seen that chemical effects due to the breakdown of added CO2 in fuel side make C2 -branch chemical species be remarkably formed and the prevailing contribution of prompt NO is a direct outcome of these effects. It is found that in the combined forms of H2/CO/CO2/Ar fuels the effects of added CO and CO2 concentrations in fuel side compete contrarily to each other in NO emission behaviour. Particularly the role of added CO is stressed in the side of restraining prompt NO. Copyright © 2003 John Wiley & Sons, Ltd. [source] Formation of new thermosets by the reaction of cyanates with thiophenolsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Monika Bauer Abstract Sulfur-containing aromatic thermosets, mainly consisting of aryloxy- and arylthio-substituted 1,3,5-triazines, have been prepared through the reaction of difunctional cyanates with mono- and difunctional aromatic thiols. A straightforward three-step reaction scheme is proposed and verified by the identification of key substances: (1) the addition of thiol and cyanate groups, (2) the stepwise addition of (thio)imino carbonic esters with one another, and (3) the ring closure of chain-extended (thio)imino carbonic esters to form 1,3,5-triazines. Reactions of types 2 and 3 are associated with an abstraction of phenol or thiophenol, which can enter into reaction 1 again. Characterization of the curing behavior of dicyanate of bisphenol A with thiophenol as well as dimercaptodiphenyl sulfide by differential scanning calorimetry shows that the reaction rates are significantly enhanced by the admixture of thiols to the cyanate. Dynamic mechanical analysis of resulting thermosets showed that large amounts of comonomers can be incorporated into the network resulting in a decrease of glass temperature but increase of fracture toughness. Finally, the fully cured thermosets resulting from the reaction of dicyanate of bisphenol A with different admixtures of dimercaptodiphenyl sulfide were characterized by cone calorimetry to get information about flame retardancy. The flame retardancy is influenced by incorporation of dimercaptodiphenyl sulfide into the triazine network only slightly. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Selectivity effects on series reactions by reactant storage and PSA operationAICHE JOURNAL, Issue 11 2000Adriaan J. Kodde This work evaluates adsorptive reactors used to improve the operation of a sequential reaction scheme, , for the total removal of A from a stream with an excess of B. In the adsorptive-reactor concept, the reactor is filled with a physical mixture of catalyst and an adsorbent, the latter being thermodynamically selective toward primary reactant A. In this case, the sorbent is periodically regenerated using the principles of pressure swing adsorption and purged with secondary reactant D. This concept is restricted to low temperatures to have sufficient adsorption capacity. Improved reaction selectivity arises from the accumulation of A in the unit. The reaction of A maximizes the driving force for regeneration and thus accelerates the regeneration half-cycle. The adsorptive reactor is compared to a conventional plug-flow reactor (PFR) and to PSA and PFR units in series. Reaction selectivity improved and pure B recovered over these alternative reactors under realistic conditions. The volume-based productivity is lower than that of PFR, but higher than that of PSA. The purge-gas flow rate can be manipulated to balance the sorption flux and reaction rate, thereby maximizing the conversion of A. The influence of differences in sorption kinetics is discussed and the required sorbent characteristics are identified. [source] Synthesis, characterization, and antimicrobial activity of some novel poly(ether ketone)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2003Samir A. Patel Abstract Low molecular weight poly(ether ketone)s were synthesized from phenol, 1,4-phenylenedioxy diacetylchloride, chloroacetylchloride, and dichloroalkanes [1,2-dichloroethane and dichloromethane] by a Friedel,Crafts reaction with anhydrous aluminum chloride as a catalyst and carbon disulfide as a solvent. The conditions for the preparation of the poly(ether ketone)s and the chlorine contents obtained with the Carius method were examined, and a reaction scheme for each resin was established. The molecular weights and polydispersities of the resins were obtained by gel permeation chromatography. The polyketones were characterized by IR spectroscopy. The characteristic frequencies due to different functional groups were assigned. The thermal properties of the resins were studied with thermogravimetry and differential scanning calorimetry. The characteristic temperatures of thermal degradation for the poly(ether ketone)s were evaluated with thermogravimetric analysis. The kinetic parameters for the decomposition reactions of the resins were obtained with Broido and Doyle's method, and the heats of fusion were obtained from differential scanning calorimetry thermograms. The polyketones were thermally stable up to 200 °C. All the polyketones were tested for their microbial properties against bacteria, fungi, and yeast. The effect of poly(ether ketone)s on the growth of these microorganisms was investigated, and the polyketones were found to inhibit the growth of the microorganisms to a considerable extent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2335,2344, 2003 [source] A Simplified Model for Prediction of Molecular Weight Distributions in Ethylene-Hexene Copolymerization Using Ziegler-Natta CatalystsMACROMOLECULAR REACTION ENGINEERING, Issue 5 2007Duncan E. Thompson Abstract A simplified steady-state model has been developed to predict molecular weight distributions and average compositions of ethylene-hexene copolymers produced using heterogeneous Ziegler-Natta catalysts in gas-phase reactors. The model uses a simplified reaction scheme to limit the number of parameters that must be estimated. The number of parameters is further reduced by assuming that different types of active sites share common rate constants for some reactions. Estimates of kinetic parameters are obtained using deconvolution analysis of industrial copolymer samples produced using a variety of isothermal steady-state operating conditions. The parameter estimates should prove useful as initial guesses for future parameter estimation in a non-isothermal model. [source] Model Development in Thermal Styrene PolymerizationMACROMOLECULAR SYMPOSIA, Issue 1 2007Bryan Matthews Abstract Summary: The thermal polymerization of styrene is usually modeled by relying on a reaction scheme and a set of equations that were developed more than three decades ago by Hui and Hamielec. Many detailed models of styrene polymerization are available in the open literature and they are mostly based on the work of Hui and Hamielec, which nearly makes this the standard to follow in explaining the behavior of polystyrene reactors. The model of Hui and Hamielec does a very nice job of describing monomer conversion data but discrepancies are seen between observed and predicted values of number and weight average molecular weights, Mn and Mw. Discrepancies in number average molecular weight seem to be the result of random noise. Discrepancies in weight average molecular weight grow as the polymerization temperature decreases and some of the trends observed in the residuals over the entire temperature range cannot be attributed to random noise. Hui and Hamielec attributed the observed deficiencies to a standard deviation of ±10% in their GPC measurements. A new data set with an experimental error of 2% for average molecular weights is presented. The set contains measured values of Mn, Mw and Mz, so the polymerization scheme has been extended to include third order moments. The data set also includes the effect of ethylbenzene as a chain transfer agent. We present the results of comparing model predictions to our measurements and the adjustments made in the original set of kinetic parameters published by Hui and Hamielec. [source] A Study of L-Lactide Ring-Opening Polymerization KineticsMACROMOLECULAR SYMPOSIA, Issue 1 2007Jean-Pierre Puaux Abstract Summary: The paper presents an experimental study of L-lactide polymerization in molten state using as initiator the Stannous Octoate. The experiments were performed in a Haake mixer. The operating temperatures were between 170 and 195°C, the reaction time up to 60 min and monomer to initiator initial molecular ratio between 102 and 5,·,103. The conversion was determined by using 1H NMR and the molecular weights distributions by SEC. A preliminary mathematical modeling study was also performed, based on experimental data and a previously published reaction scheme. [source] Kinetic Analysis and Optimization for the Catalytic Esterification Step of PPT PolymerizationMACROMOLECULAR THEORY AND SIMULATIONS, Issue 1 2005Saptarshi Majumdar Abstract Summary: A well-validated kinetic scheme has been studied for PPT, poly(propylene terephthalate) polymerization process in batch and semi-batch mode with tetrabutoxytitanium (TBOT), a proven catalyst. Optimization study and analysis for PPT are rare, as the industrial relevance of PPT just became vibrant due to the commercial availability of one of its monomers in industrial scale in the recent past. Correctness of the analysis is checked by a new approach and parameters for the model are estimated from available experimental data. Solubility of terephthalic acid (TPA) is less in reaction medium and this effect is also considered along with the reaction scheme. Several simulations have been performed to see various process dynamics and this ultimately helps in formulating optimization problems. Using recently developed and well tested real-coded non-dominated sorting genetic algorithm-II, a state-of-the art evolutionary optimization algorithm, a couple of three objective optimization problems have been solved and corresponding Pareto sets are presented. Results show remarkably promising aspects of productivity enhancement with an improvement in product quality. Sensitivity analysis for relatively uncertain solubility parameter is also performed to estimate its effect over the proposed optimal solutions. Multiobjective Pareto front for 3 objectives: degree of polymerization, time and (bTPA,+,bPG). [source] Redox Photochemistry of Thiouredopyrenetrisulfonate,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2004Alexander B. Kottyar ABSTRACT 1-Thiouredopyrene-3,6,8-trisulfonate (TUPS) has recently been used as a photoinduced covalent redox label capable of reducing various cofactors of proteins. A new reaction of this dye, whereby its excited triplet state oxidizes suitable electron donors, is now reported. The characteristic difference spectrum of the reduced radical of TUPS is determined. We also observe the self-exchange electron transfer between two TUPS molecules in their triplet excited states and determine the reaction scheme and the rate constants of the various pathways in the process of triplet depletion. The ability of photoexcited TUPS to withdraw an electron from reduced cytochrome-c is also observed. It is thus demonstrated that TUPS is an appropriate photoinduced covalent redox label for initiating both the oxidative and reductive phases of electron transfer processes in biological macromolecules. [source] Dual curing of carbon fiber reinforced photoresins for rapid prototypingPOLYMER COMPOSITES, Issue 6 2002A. Gupta Photo-thermal dual-curing of a carbon fiber reinforced photoresin is reported in this study. The primary limitation of carbon fibers is that they are opaque to ultra-violet (UV) light, and the resin present inside the carbon fiber tow remains uncured if only a photolytic mechanism is used. Therefore, a dual-curing resin formulation was developed that consisted of acrylate ester of bisphenol A-epoxy (primary resin), 1-hydroxycyclohexyl phenyl ketone (a photoinitiator), and lauroyl peroxide (thermal initiator). The fibers were dispersed in the resin and photocured by UV radiation. Subsequently, the composites were thermally cured to solidify the resin present inside the fiber tow. Differential scanning calorimetry indicates that the thermal initiator activates at approximately 70°C. The dual-cured composites, processed by a dip-coating technique and also in a desktop photolithography unit, were tack-free and fully solidified in the interior. Thus, it was established that by using a dualcuring resin formulation, the resin present outside and inside the carbon fiber tow could be cured to produce a carbon fiber reinforced photoresin. Such a reaction scheme has application in composite photolithography where incorporation of carbon fibers into photopolymers can enhance electrical and thermal conductivities of rapid tooling materials. [source] Influence of ionic strength on the time course of force development and phosphate release by dogfish muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Timothy G. West We measured the effects of ionic strength (IS), 200 (standard) and 400 mmol l,1 (high), on force and ATP hydrolysis during isometric contractions of permeabilized white fibres from dogfish myotomal muscle at their physiological temperature, 12°C. One goal was to test the validity of our kinetic scheme that accounts for energy release, work production and ATP hydrolysis. Fibres were activated by flash photolysis of the P3 -1-(2 nitrophenyl) ethyl ester of ATP (NPE-caged ATP), and time-resolved phosphate (Pi) release was detected with the fluorescent protein MDCC-PBP, N -(2[1-maleimidyl]ethyl)-7-diethylamino-coumarin-3-carboxamide phosphate binding protein. High IS slowed the transition from rest to contraction, but as the fibres approached the isometric force plateau they showed little IS sensitivity. By 0.5 s of contraction, the force and the rate of Pi release at standard and high IS values were not significantly different. A five-step reaction mechanism was used to account for the observed time courses of force and Pi release in all conditions explored here. Only the rate constants for reactions of ATP, ADP and Pi with the contractile proteins varied with IS, thus suggesting that the actin,myosin interactions are largely non-ionic. Our reaction scheme also fits previous results for intact fibres. [source] Structure of Hordeum vulgare NADPH-dependent thioredoxin reductase 2.ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Unwinding the reaction mechanism Thioredoxins (Trxs) are protein disulfide reductases that regulate the intracellular redox environment and are important for seed germination in plants. Trxs are in turn regulated by NADPH-dependent thioredoxin reductases (NTRs), which provide reducing equivalents to Trx using NADPH to recycle Trxs to the active form. Here, the first crystal structure of a cereal NTR, HvNTR2 from Hordeum vulgare (barley), is presented, which is also the first structure of a monocot plant NTR. The structure was determined at 2.6,Å resolution and refined to an Rcryst of 19.0% and an Rfree of 23.8%. The dimeric protein is structurally similar to the structures of AtNTR-B from Arabidopsis thaliana and other known low-molecular-weight NTRs. However, the relative position of the two NTR cofactor-binding domains, the FAD and the NADPH domains, is not the same. The NADPH domain is rotated by 25° and bent by a 38% closure relative to the FAD domain in comparison with AtNTR-B. The structure may represent an intermediate between the two conformations described previously: the flavin-oxidizing (FO) and the flavin-reducing (FR) conformations. Here, analysis of interdomain contacts as well as phylogenetic studies lead to the proposal of a new reaction scheme in which NTR,Trx interactions mediate the FO to FR transformation. [source] Optimal operation of tubular reactors for naphtha cracking by numerical simulationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009G.-Y. Gao Abstract Process gas temperature profile and steam-to-hydrocarbon ratio in the feed have important impact on product yields and coking rate in tubular reactors for naphtha cracking. This study is to evaluate these effects quantitatively based on numerical simulation. Steady-state operation of the tubular reactor in an industrial thermal cracking furnace was first simulated in HYSYS with a molecular reaction scheme. Various case studies then investigate the influence of process gas temperature profile and inlet steam-to-hydrocarbon ratio so that the ethylene/propylene product yields and coking rate can be evaluated. Finally, steady-state optimization was applied to the operation of this industrial furnace. The optimal process temperature profile and the optimal inlet steam-to-naphtha ratio were found to maximize the operation profit. This study will provide significant guidance to process engineers in the ethylene industry. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] A fundamental analysis of continuous flow bioreactor and membrane reactor models with noncompetitive product inhibitionASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Mark Ian Nelson Abstract We analyze the steady-state production of a product produced through the growth of microorganisms in both a continuous flow bioreactor and in an idealized continuous flow membrane reactor. The reaction is assumed to be governed by Monod growth kinetics subject to noncompetitive product inhibition. Although this reaction scheme is often mentioned in textbooks, a stability analysis does not appear in the literature. The steady-state solutions of the model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained. Knowledge of the steady-state solutions and their asymptotic limits may be useful to estimate parameter values from experimental data. The key dimensionless parameter that controls the degree of noncompetitive product inhibition is identified and we quantify the effect that this has on the reactor performance in the limit when product inhibition is 'small' and 'large'. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Structure of spinach acetohydroxyacid isomeroreductase complexed with its reaction product dihydroxymethylvalerate, manganese and (phospho)-ADP-riboseACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2000Karine Thomazeau Acetohydroxyacid isomeroreductase catalyses a two-step reaction composed of an alkyl migration followed by an NADPH-dependent reduction. Both steps require a divalent cation and the first step has a strong preference for magnesium. Manganese ions are highly unfavourable to the reaction: only 3% residual activity is observed in the presence of this cation. Acetohydroxyacid isomeroreductase has been crystallized with its substrate, 2-aceto-2-hydroxybutyrate (AHB), Mn2+ and NADPH. The 1.6,Å resolution electron-density map showed the reaction product (2,3-dihydroxy-3-methylvalerate, DHMV) and a density corresponding to (phospho)-ADP-ribose instead of the whole NADP+. This is one of the few structures of an enzyme complexed with its reaction product. The structure of this complex was refined to an R factor of 19.3% and an Rfree of 22.5%. The overall structure of the enzyme is very similar to that of the complex with the reaction-intermediate analogue IpOHA [N -hydroxy- N -isopropyloxamate; Biou et al. (1997), EMBO J.16, 3405,3415]. However, the active site shows some differences: the nicotinamide is cleaved and the surrounding amino acids have rearranged accordingly. Comparison between the structures corresponding to the reaction intermediate and to the end of the reaction allowed the proposal of a reaction scheme. Taking this result into account, the enzyme was crystallized with Ni2+ and Zn2+, for which only 0.02% residual activity were measured; however, the crystals of AHB/Zn/NADPH and of AHB/Ni/NADPH also contain the reaction product. Moreover, mass-spectrometry measurements confirmed the cleavage of nicotinamide. [source] Identification of flurbiprofen and its photoproducts in methanol by gas chromatography,mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 5 2007Su-Hui Chao Abstract A sample of 10 mm flurbiprofen in methanol (or ethanol) was photoirradiated with sixteen 8 W low-pressure quartz mercury lamps irradiated at 306 nm in a Panchum PR-2000 photochemical reactor. In total, four major photoproducts derived from each sample were observed from the HPLC chromatogram. The photoproducts were separated and their structures elucidated by various spectroscopic methods. Alternatively, using GC-MS, 11 major photoproducts were observed. A reaction scheme of flurbiprofen in methanol is proposed: the photochemical reaction routes occur mainly via esterification and decarboxylation, followed by oxidation with singlet oxygen to produce a ketone, alcohols and other derivatives. Copyright © 2007 John Wiley & Sons, Ltd. [source] Glycerol Etherification over Highly Active CaO-Based Materials: New Mechanistic Aspects and Related Colloidal Particle FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2008Agnieszka Abstract Glycerol is an attractive renewable building block for the synthesis of di- and triglycerols, which have numerous applications in the cosmetic and pharmaceutical industries. In this work, the selective etherification of glycerol to di- and triglycerol was studied in the presence of alkaline earth metal oxides and the data are compared with those obtained with Na2CO3 as a homogeneous catalyst. It was found that glycerol conversion increased with increasing catalyst basicity; that is, the conversion increases in the order: MgO Photochemical Z,E Isomerization of a Hemithioindigo/Hemistilbene ,-Amino AcidCHEMPHYSCHEM, Issue 11 2007Thorben Cordes Abstract The molecule HTI, which combines hemithioindigo and hemistilbene molecular parts, allows reversible switching between two isomeric states. Photochromic behaviour of the HTI molecule is observed by irradiation with UV/Vis light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI molecule, namely, an ,-amino acid, the Z,E isomerization process occurs on a timescale of 30 ps. In the course of the reaction fast processes on the 1,10 ps timescale are observed which point to motions of the molecule on the potential-energy surface of the excited state. The combination of transient absorption experiments in the visible spectral range with time-resolved fluorescence and infrared measurements reveal a photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications of the nature of the involved intermediates. [source] Access to Any Site-Directed Isotopomer of Methionine, Selenomethionine, Cysteine, and Selenocysteine , Use of Simple, Efficient Modular Synthetic Reaction Schemes for Isotope IncorporationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2004Arjan H. G. Siebum Abstract Simple modular reaction schemes that allow access to any isotopomer of protected serine and homoserine have been worked out. These systems could be simply converted into cysteine, selenocysteine, homocysteine, homoselenocysteine, the essential amino acid methionine, and selenomethionine by Mitsunobu chemistry. These sulfur- and selenium-containing amino acids fulfil many essential roles in the living organism. In addition, homoserine could be converted in a few steps into optically active L -vinylglycine. As well as the stable isotopes 13C, 15N, 17O, and 18O, the radioactive isotopes of sulfur, selenium and carbon can also be easily introduced in a site-directed fashion. In view of the wide scope of the Mitsunobu reaction, we feel that many more important systems with the carbon skeleton of serine and homoserine should be preparable through this basic chemistry in any site-directed isotopically labeled form. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of thiophene/phenylene co-oligomers.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2003We report the synthesis of various thiophene/phenylene co-oligomers with a total number of thiophene and benzene (phenylene) rings of 6 to 8. These compounds include a phenyl-capped sexithiophene, a thienyl-capped quaterphenylene, as well as block and alternating co-oligomers. The synthesis is based on either the Suzuki coupling reaction or the direct dimerization coupling. The latter method produces symmetric molecules with an even total ring number. These reaction schemes enabled us to obtain the target compounds in high quality. Although the resulting materials are difficult to dissolve in organic solvents and therefore difficult to identify by usual 1H nmr spectroscopy, they have successfully been identified through Fourier-transform ir spectroscopy. The specific group frequencies of ring-stretching and out-of-plane deformation modes are characteristic of the substitution pattern of the individual thiophene and benzene rings. [source] NETmix®, a new type of static mixer: Modeling, simulation, macromixing, and micromixing characterizationAICHE JOURNAL, Issue 9 2009Paulo E. Laranjeira Abstract NETmix® is a new technology for static mixing based on a network of chambers connected by channels. The NETmix® model is the basis of a flow simulator coupled with chemical reaction used to characterize macro and micromixing in structured porous media. The chambers are modeled as perfectly mixing zones and the channels as plug flow perfect segregation zones. A segregation parameter is introduced as the ratio between the channels volume and the whole network volume. Different kinetics and reactants injection schemes can be implemented. Results show that the number of rows in the flow direction and the segregation parameter control both macro and micromixing, but the degree of micromixing is also controlled by the reactants injection scheme. The NETmix® model enables the systematic study of micromixing and macromixing for different network structures and reaction schemes, enabling the design of network structures to ensure the desired yield and selectivity. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Thermodynamic analysis of reaction schemes with empty routesAICHE JOURNAL, Issue 12 2006Alexander K. Avetisov No abstract is available for this article. [source] SmiLib v2.0: A Java-Based Tool for Rapid Combinatorial Library EnumerationMOLECULAR INFORMATICS, Issue 3 2007Andreas Schüller Abstract An updated version of the SMILIB software tool for rapid combinatorial library enumeration was developed. SmiLib v2.0 offers the possibility to construct very large combinatorial libraries using the flexible and portable SMILES format. Libraries were created at rates of approximately 8,700,000 molecules per minute. Combinatorial building blocks are attached to scaffolds by means of linkers rather than to concatenate them directly. This allows for creation of customized libraries using linkers of different sizes and chemical nature. New features are: platform independence, correct handling of stereo chemistry, flexible reaction schemes, improved usability, a unique identifier for each molecule, the option to create libraries in SD format, a conformity check for SmiLib v2.0 SMILES notation restrictions, and decreased library enumeration times. SmiLib v2.0 is available as interactive graphical user interface application and command line tool. [source] 3-Fluoro-2,4-dioxa-3-phosphadecalins as Inhibitors of Acetylcholinesterase.CHEMISTRY & BIODIVERSITY, Issue 3 2009A Reappraisal of Kinetic Mechanisms, Diagnostic Methods Abstract A systematic survey of the acetylcholine-mimetic 2,4-dioxa-3-phosphadecalins as irreversible inhibitors of acetylcholinesterase revealed hitherto overlooked properties as far as the kinetic mechanisms of interaction are concerned. As a support to past and future work in this field, we describe the kinetics of eight reaction schemes that may be found in irreversible enzyme modification and compare them with two mechanism of reversible, slow-binding inhibition. The relevant kinetic equations and their associated graphical representations are given for all mechanisms, and concrete examples illustrate their practical use. Since irreversible inhibition is a time-dependent phenomenon, kinetic analysis is greatly facilitated by fitting the appropriate integrated rate equations to reaction-progress curves by nonlinear regression. This primary scrutiny provides kinetic parameters that are indispensable tools for diagnosing the kinetic mechanism and for calculating inhibition constants. Numerical integration of sets of differential equations is an additional useful investigation tool in critical situations, e.g., when inhibitors are unstable and/or act as irreversible modifiers only temporarily. [source]
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