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Molar Fraction (molar + fraction)
Selected AbstractsMolecular dynamics of phase transitions in clusters of alkali halidesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2001Pedro C. R. Rodrigues Abstract Molecular dynamics simulations of unconstrained alkali halide clusters with 8, 64, 216, 512, 1000, 1728, 2744, 4096, 5832, and 8000 ions have been carried out using the Born,Mayer,Huggins potential. All the clusters exhibit first-order melting and freezing transitions. The melting temperature increases with the number of ions and approaches the melting temperature of the bulk. Clusters with a number of ions less than approximately 1000 present hysteresis cycles and practically do not have phase coexistence. Clusters with a number of ions over 1000 present phase coexistence during a significant part of the transition region and hysteresis is progressively eliminated as the clusters size increases. It is suggested that hysteresis is an intrinsic characteristic of small clusters. In the transition regions the calculations have been performed by fixing the total energy of the clusters. It is shown that such a technique provides a better way of analyzing the transition mechanism than the usual procedure of fixing the temperature by ad hoc rescaling the velocities or by using canonical molecular dynamics or Monte Carlo. A detailed analysis of the melting transition is presented. The effects of interfaces and impurities are discussed. A method based on the velocity autocorrelation functions is proposed, in order to determine the molar fraction of the ions present in the solid and liquid phases as well as to produce colored snapshots of the phases in coexistence. The overall agreement of the estimated melting points and enthalpies of melting with the experiment is fairly good. The estimated melting point and enthalpy of melting for KCl in particular are in excellent agreement with the experimental values. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem 84: 169,180, 2001 [source] Synthesis and properties of homopolyamide and copolyamides fibers based on 2,6-bis(p -aminophenyl)benzo[1,2-d;5,4- d,]bisoxazoleJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Xiangqun Chen Abstract A novel aromatic homopolyamide with benzobisoxazole units in the main chain was synthesized with 2,6-bis(p -aminophenyl)benzo[1,2- d;5,4- d,]bisoxazole and terephthaloyl chloride by low temperature solution polycondensation, the inherent viscosity of which was 1.98 dL/g. The diamine and p -phenylendiamine with terephthaloyl chloride were used to synthesize the copolyamides. The structures of homopolyamide and copolyamides were characterized by IR spectra, elemental analysis, and wide-angle X-ray diffraction. Wide-angle X-ray diffraction measurements showed that homopolyamide and copolyamides were predominantly crystallinity. The results of thermal analysis indicated that the thermal stabilities of the copolymer increased with an increase of the molar fraction of benzobisoxazole in the copolymers. The thermal stability of the copolyamides with decomposition temperatures (at 10% weight loss) above 570°C was better than that of poly(p -phenylene terephthalamide) (PPTA). Fibers of homopolyamide and copolyterephthalamides were spun from lyotropic liquid crystal dope in 100% H2SO4. When compared with PPTA fibers prepared under the same conditions, the tensile strengths of copolyamides fibers improved by 20,33% with tensile strengths of 1.81 GPa, tensile moduli of 76 GPa, and elongations at break of 3.8,4.1%, which indicated that copolyamides fibers had outstanding mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Behavior of an organic solvent drop during the supercritical extraction of emulsionsAICHE JOURNAL, Issue 5 2010Facundo Mattea Abstract The behavior of a drop of dichloromethane in water in contact with CO2 at high pressure has been investigated with the purpose of analyzing the phenomena that takes place during the supercritical fluid extraction of emulsions process. Experiments have been performed with and without a solute (,-carotene) and a surfactant (n -octenylsuccinic anhydride-modified starch) dissolved in the drop, and the evolution of the drop volume as well as of the interfacial tension between the drop and the aqueous phase has been measured. Additionally, a mathematical model has been developed that allows describing the mass transfer. Results show that the drop undergoes swelling and shrinking processes due to diffusion of CO2 into the drop and dichloromethane out of the drop. CO2 concentration in the drop can be as high as 0.9 (molar fraction). Emulsion drops behave as miniature gas antisolvent precipitators and many particles are formed inside the drop. The interfacial tension between the drop and the aqueous phase increases during the process, therefore destabilizing the emulsion. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Styrene/1,3-butadiene copolymerization by C2 -symmetric group 4 metallocenes based catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2008Mariagrazia Napoli Abstract C2 -symmetric group 4 metallocenes based catalysts (rac -[CH2(3- tert -butyl-1-indenyl)2]ZrCl2(1), rac -[CH2(1-indenyl)2]ZrCl2(2) and rac -[CH2(3- tert -butyl-1-indenyl)2]TiCl2(3)) are able to copolymerize styrene and 1,3-butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by 13C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain-end happens prevailingly with 1,4- trans configuration. In the butadiene homosequences, using zirconocene-based catalysts, the 1,4- trans arrangement is favored over 1,4- cis, but the latter is prevailing in the presence of titanocene (3). Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r1 × r2 = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene,butadiene copolymers (r1 × r2 = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (ns = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476,1487, 2008 [source] Polymerization of 1,2:5,6-diepithio-3,4-di- O -methyl- D -mannitol, 1,2:5,6-diepithio-3,4-di- O -methyl- L -iditol, and 1,2:5,6-diepithio-3,4-di- O -methyl-allitol using zinc complexes: The regio- and stereoselectivities and asymmetric synthesis of thiosugar polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2005Toshifumi Satoh Abstract The polymerizations of the diepisulfides 1,2:5,6-diepithio-3,4-di- O -methyl- D -mannitol (1a), 1,2:5,6-diepithio-3,4-di- O -methyl- L -iditol (1b), and 1,2:5,6-diepithio-3,4-di- O -methyl-allitol (1c) were carried out with ZnEt2/H2O, ZnEt2/alcohol, and ZnEt2/(S or R)-1,1,-bi-2-naphthol (BN) as the initiator systems. All the polymerizations proceeded without any gel formation and gave white, powdery products. The number-average molecular weights of the obtained polymers were changed in the range of 5300,33,600. The polymerization of 1a using the ZnEt2/H2O (1/1) catalyst in tetrahydrofuran proceeded through a regio- and stereoselective cyclopolymerization mechanism to produce thiosugar polymers mainly consisting of 2,5-anhydro-1,5-dithio- D -glucitol as the five-membered ring units. The polymers obtained from 1b and 1c with ZnEt2/H2O exhibited lower stereoregularities than that from 1a. For the polymers obtained from 1a with the ZnEt2/alcohol systems, the molar fraction of the five-membered ring units depended on the alcohol used as a ligand. On the other hand, the polymerization of 1c using ZnEt2/(R or S)-BN asymmetrically proceeded, and optically active polymers consisting of desulfurized acyclic units were obtained. When ZnEt2/(R)-BN (1/1) was used in toluene, the polymer with [,]D23 = +56.9° was obtained in an 88.6% yield. The resulting polymer had an isotactic-rich structure consisting of about 90% (R)-configurational units and about 10% (S)-units. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4118,4125, 2005 [source] Preparation of amphiphilic statistical copolymers of 2-hydroxyethyl methacrylate with 2-diethylaminoethyl methacrylate, precursors of water-soluble copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2002Gerardo Martinez Abstract Statistical copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2-diethylaminoethyl methacrylate (DEA) were synthesized at 50 °C by free-radical copolymerization in bulk and in a 3 mol L,1N,N,-dimethylformamide solution with 2,2,-azobisisobutyronitrile as an initiator. The solvent effect on the apparent monomer reactivity ratios was attributed to the different aggregation states of HEMA monomer in the different solvents. The copolymers obtained were water-insoluble at a neutral pH but soluble in an acidic medium when the molar fraction of the DEA content was higher than 0.5. The quaternization of DEA residues increased the hydrophilic character of the copolymers, and they became water-soluble at a neutral pH when the HEMA content was lower than 0.25. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2427,2434, 2002 [source] Analysis of segregation process of n -alkanes in binary mixtures by FTIR and Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2005Andrzej Hacura Abstract In the FTIR and Raman spectroscopic studies, the phenomena of normal n -alkanes segregation in the binary mixtures of solid-state paraffin at room temperature were examined. Samples, in which one of the ingredients had been deuterated were prepared in different molar concentrations. Components of the mixture separated in time, creating separate domains, were observed in the changing of shape of infrared and Raman bands. The process of segregation depended on the difference of the chains' length of the mixture's ingredients and the molar fraction, in which the mixtures were prepared. The size of the created microdomains has been estimated based on the model describing shape and the splitting of the IR bands developed by Hiebert and Hornig. By applying the micro-Raman imaging technique, a number of surface maps have been obtained indicating the separating process of ingredients of the mixtures. This allowed comparing and verifying time dependent results of the IR study. Copyright © 2005 John Wiley & Sons, Ltd. [source] Activation energy of Mg in a -plane Ga1,xInx N (0 < x < 0.17)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009Daisuke Iida Abstract We investigated the electrical properties of Mg-doped Ga1,xInx N grown on an a -plane template. High-hole-concentration p-type Mg-doped Ga1,xInx N films with an InN molar fraction of 0.17 were fabricated on sidewall-epitaxial-lateral overgrown a -plane GaN grown on an r -plane sapphire substrate by MOVPE. Variable-temperature Hall effect measurement showed that a maximum hole concentration of 1.4 × 1019 cm,3 for x = 0.17 was reproducibly achieved at room temperature. The activation energy of Mg acceptors in Mg-doped a -plane Ga0.83In0.17N was found to be as low as 48 meV. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comparison of wild-type and class I integrase mutant-FIV vectors in retina demonstrates sustained expression of integrated transgenes in retinal pigment epitheliumTHE JOURNAL OF GENE MEDICINE, Issue 12 2003Nils Loewen Abstract Background In neonatal and adult rodent retina, substantial lentiviral vector expression has been detected primarily in retinal pigment epithelium (RPE), except in very young animals (2,5 days post-natal). In non-retinal tissues, studies of lentiviral vectors have utilized various controls. Among the most stringent are class I integrase mutants, which selectively block the integration reaction while leaving all other gag/pol -encoded functions intact. For HIV-1 vectors injected into brain, these have been used to simultaneously control for pseudotransduction and verify that long-term expression requires integration. Such experiments compare particles that differ only in a single amino acid within a single enzyme that forms a very small molar fraction of the virion. Class I integrase mutants have not been described for feline immunodeficiency virus (FIV) integrase, or tested in the eye for any lentiviral vector. Methods We compared subretinally and intravitreally injected FIV vectors and followed animals for up to 7 months, a duration that exceeds prior studies. We also compared the wild-type (WT) vector with one incorporating a single class I amino acid mutation in FIV integrase (D66V). A mock vector (packaging construct absent) was an alternative control. All vectors were vesicular stomatitis virus glycoprotein G (VSV-G)-pseudotyped and were injected on day 7 of life. One group of animals received either subretinal or intravitreal injections of WT vector in the right eyes. Control left eyes were injected with mock vector. These animals were sacrificed at 2 or 7 days post-injection. A second group received subretinal injections of either WT vector or equivalent D66V vector (reverse transcriptase-normalized to WT), and were analyzed after 2, 3 and 7 months. All eyes were scored for marker gene (,-galactosidase) expression by an observer blinded to vector assignments. Results Subretinal FIV vector injections were much more effective than intravitreal injections. The RPE was the principal retinal layer transduced by the WT vector, and at least 50% of the area of the retina expressed the marker gene at 3 and 7 months. Occasional cells in inner retinal layers also expressed ,-galactosidase at these time points. The sustained retinal expression produced by subretinally injected vector was blocked by the D66V mutation. Conclusions These results show that class I integrase mutant FIV vectors are useful control vectors, and that VSV-G-pseudotyped FIV vectors produce extensive retinal expression for at least 215 days, the longest duration yet reported for lentiviral vectors in retina. Transgene expression is mostly restricted to RPE after post-natal day 7 in rats, suggesting that FIV vectors could be used to target RPE for gene therapy. Copyright © 2003 John Wiley & Sons, Ltd. [source] Kinetics and Film Properties of Boron Nitride Derived from Trimethoxyborane/Ammonia by Chemical Vapor Deposition,CHEMICAL VAPOR DEPOSITION, Issue 6 2004H. Strakov Abstract The kinetics of the CVD of boron nitride from trimethoxyborane (TMOB) and ammonia (NH3) under atmospheric pressure was investigated by varying the following process parameters: temperature, residence time of the reactants, molar fraction of TMOB, and the NH3/TMOB ratio, ,. A kinetic power law equation was derived, that describes the experimental results with good accuracy. The reaction order with respect to TMOB is found to be 0.9 and ,,0.2 with respect to NH3. Between 800,°C and 950,°C, the deposition rate is controlled by the surface reaction kinetics with apparent activation energy of 115.1,kJ,mol,1. The deposited BN films were characterized by IR spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The microstructure of the deposits depends on the nature of the substrates used. Turbostratic boron nitride (t-BN) was deposited on graphite, and hexagonal boron nitride (h-BN) on alumina substrates. X-ray photoelectron spectroscopy (XPS) analyses show nearly stoichiometric BN films for deposition temperatures in the range 850,950,°C for high amounts of ammonia (100,<,,,<,150) in the feed gas. [source] Acoustical Properties of Binary Mixtures of Heptane with Ethyl Acetate or Butyl AcetateCHINESE JOURNAL OF CHEMISTRY, Issue 3 2010Divya Shukla Abstract Mixed solvents rather than single pure liquids are of utmost practical importance in chemical and industrial processes as they provide an ample opportunity for the continuous adjustment of desired properties of the medium. Therefore, ultrasonic velocity (u) and density (,) were measured for the binary mixtures formed by heptane with ethyl acetate or butyl acetate at temperatures 293, 298 and 303 K over the entire composition range. Deviation in ultrasonic velocity (,u), deviation in isentropic compressibility (,,s), and excess intermolecular free length (LEf) have been evaluated using the ultrasonic velocity data and the computed results were fitted to the Redlich-Kister polynomial equation. The values of ,u, ,,s and LEf were plotted against the molar fraction of heptane. The observed positive and negative values of excess parameters were discussed in terms of molecular interaction between the components of the mixtures. Experimental values of ultrasonic velocity and density were compared with the results obtained by theoretical estimation procedures. The results were discussed in terms of average absolute deviation (AAD). [source] Competitive Enzymatic Fluorescence Immunoassay for Human IgG by Using a Temperature-Sensitive Phase Separating Polymer with Regulated Phase Transition TemperatureCHINESE JOURNAL OF CHEMISTRY, Issue 4 2008Peng LIN Abstract A new enzymatic fluorescence immunoassay for human IgG was developed using a temperature-sensitive polymer, poly(N -isopropylacrylamide-co-acrylamide) [P(NIP-AA)], as a carrier. The lower critical solution temperature of the P(NIP-AA) containing molar fraction of 8% for AA was 37 °C. In a competitive immunoassay, immobilized IgG and the standard IgG (or sample) competed for binding to a horseradish peroxidase labeled antibody at 33 °C in homogeneous format. After changing the temperature to separate the polymer-immune complex, the complex precipitate was re-dissolved and determined by coupling with the fluorescence reaction of hydrogen peroxide and p -hydroxyphenylacetic acid. The calibration graph for human IgG was linear over the range of 100,1000 ng/mL with a detection limit of 2.0 ng/mL. The method is rapid, sensitive and simple. The immune reaction efficiency was improved. In addition, the sensitivity of this method was close to that using traditional microtitration plates as carriers. However, the assay was much faster (the assay time decreased from 100,120 to 30 min). The method has been applied to the determination of the human IgG levels in human sera with satisfactory results. [source] Properties of 2,2,2-Trifluoroethanol/Water Mixtures: Acidity, Basicity, and DipolarityHELVETICA CHIMICA ACTA, Issue 2 2005Paz Sevilla, Sierra In this report, we focus our attention on the characterization of 2,2,2-trifluoroethanol(TFE)/H2O mixtures and describe their intrinsic parameters; i.e., solvent acidity (SA), solvent basicity (SB), and solvent dipolarity/polarizability (SPP), by the probe/homomorph-couple method for a range of mixtures from 0,100% (v/v) TFE. Variation of these parameters is not linear and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based on these parameters, we describe the TFE-induced changes in some physical properties; i.e., viscosity (,), partial molar volume (V,), density (,), dielectric constant (,), vapor pressure (pv), and spectroscopic properties; i.e., NMR chemical shifts (,(1H)) of TFE Me group for all molar fractions studied. In addition, by means of CD studies, we report that formation of the secondary structure, as percentage of helical content, ,, of a polypeptide, poly(L -lysine), in several TFE/H2O mixtures is adequately described by these mixture parameters. SA, SB, and SPP of TFE/H2O mixtures provide an excellent tool for the interpretation of formation and stability of intramolecular H-bonds, and, thus, of secondary structures in polypeptides. [source] Kinetic modeling study of carbon nanotubes synthesis by fluidized bed chemical vapor depositionAICHE JOURNAL, Issue 2 2009R. Philippe Abstract The kinetic and physical laws developed in the first part of the study have been implemented in a modified version of the bubbling bed Kato and Wen model to represent multiwalled carbon nanotubes (MWCNTs) synthesis by catalytic chemical vapor deposition from ethylene as carbon source and using an Fe/Al2O3 catalyst. The absolute deviation for MWCNT productivity between experimental results of Part 1 and simulations is of 17.3% when only considering experiments for which the bed is mainly in bubbling regime. The influence of the main operating parameters on the evolutions with time of the species molar fractions, the weight of MWCNTs formed, and the bed characteristics has been numerically studied. Such capabilities can help designing new reactors. Finally, the model has been used for scale up purposes, by increasing the reactor diameter and catalyst weight. Simulations have shown that the process productivity could reach 74 tons/year of MWCNTs in a reactor 45 cm in diameter. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Nonstationary model of the semicontinuous depolymerization of polycarbonateAICHE JOURNAL, Issue 12 2006Raúl Piñero-Hernanz Abstract The experimental work for the depolymerization process of Bisphenol A polycarbonate pellets and CD/DVD wastes in a semicontinuous reactor and a novel nonstationary model to describe the process is presented. The different steps of the process to develop the model are analyzed thoroughly. The kinetics of the alkali-catalyzed methanolysis of polycarbonate was determined. The reactor and kinetic models were validated by a series of 21 experiments performed in a laboratory semicontinuous tubular reactor at isothermal conditions from 90 to 180°C and pressures from 1.0 to 20.0 MPa in liquid phase, with and without NaOH concentrations of 1 × 10,3 to 5 × 10,3 kg/L, flow rates from 2.3 × 10,3 to 10.2 × 10,3 L/min, and CO2 molar fractions from zero to 0.374. The effects of temperature, pressure, catalyst amount, mass transfer (solvent flow rate), and CO2 addition in kinetics were investigated. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Novel, biodegradable, functional poly(ester-carbonate)s by copolymerization of trans -4-hydroxy- L -proline with cyclic carbonate bearing a pendent carboxylic groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Ren-Shen Lee Abstract Water-soluble poly(ester-carbonate) having pendent amino and carboxylic groups on the main-chain carbon is reported for the first time. This article describes the melt ring-opening/condensation reaction of trans -4-hydroxy- N -benzyloxycarbonyl- L -proline (N -CBz-Hpr) with 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the copolymers was investigated. The polymerizations were carried out in bulk at 110 °C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester-carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, 1H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (Mn = 6000,14,700 g mol,1) with reasonable molecular weight distributions (Mw/Mn = 1.11,2.23). The values of the glass-transition temperature (Tg) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the Tg increased from 16 to 48 °C. The relationship between the poly(N -CBz-Hpr- co -MBC) Tg and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N -CBz-Hpr- co -MBC)s was evaluated from weight-loss measurements and the change of Mn and Mw/Mn. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester-carbonate), 4, with pendent amino and carboxylic groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2303,2312, 2004 [source] Effective biosynthesis of poly(3-hydoxy- butyrate- co -4-hydroxybutyrate) with high 4-hydroxybutyrate fractions by Wautersia eutropha in the presence of ,-amino acidsPOLYMER INTERNATIONAL, Issue 1 2008Hiroshi Kimura Abstract BACKGROUND: Biopolymers produced by microbes are in demand as their biodegradable and biocompatible properties make them suitable for disposable products and for potential use as biomaterials for medical applications. The effective microbial production of copolyesters of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate(4HB) with high molar fractions of 4HB unit by a wild-type Wautersia eutropha H16 was investigated in culture media containing 4-hydroxybutyric acid (4HBA) and different carbon substrates in the presence of various ,-amino acids. RESULTS: The addition of carbon sources such as glucose, fructose and acetic acid to the culture medium containing 4HBA in the presence of ,-amino acids resulted in the production of random poly(3HB- co -4HB) with compositions of up to 77 mol% 4HB unit, but the yields of copolyesters with 60,77 mol% 4HB units were less than 15 wt% of dried cell weights. In contrast, when carbon sources such as propionic acid and butyric acid were used as the co-substrates of 4HBA in the presence of ,-amino acids, poly(3HB- co -4HB) copolyesters with compositions of 72,86 mol% 4HB were produced at maximally 47.2 wt% of dried cell weight (11.3 g L,1) and the molar conversion yield of 4HBA to 4HB fraction in copolyesters was as high as 31.4 mol%. Further, poly(3HB- co -4HB) copolyesters with compositions of 93,96 mol% 4HB were isolated at up to 35.2 wt% of dried cell weights by fractionation of the above copolymers with chloroform/n-hexane. CONCLUSION: The productivity of copolyesters with over 80 mol% 4HB fractions was as high as 0.146 g L,1 h,1 (3.51 g L,1 for 24 h) by flask batch cultivation. Copyright © 2007 Society of Chemical Industry [source] Synthesis and monomer reactivity ratios of ethyl ,-acetoxyacrylate and acrylic acid copolymersPOLYMER INTERNATIONAL, Issue 11 2005Cédric Loubat Abstract The synthesis of ethyl ,-acetoxyacrylate (EAA) and the study of its radical polymerization is described. We report the monomer reactivity ratios for copolymers of EAA and acrylic acid (AA) using three different methods: the Jaacks, the Macret and the Fineman,Ross methods. Copolymers were obtained by free radical polymerization initiated by 2,2,-azobisisobutyronitrile in acetonitrile solutions and were analyzed by NMR and HPLC. The HPLC analysis was used to determine the molar fractions of EAA and AA in the copolymers. The reactivity ratios were estimated to be close to 1 for each monomer. Thus, copolymers of poly(acrylic acid) bearing some biodegradable units of EAA in the chain were subsequently prepared. The study of the hydrolysis of these units shows that only basic conditions were efficient to lead to hydrolyzed monomer units. Copyright © 2005 Society of Chemical Industry [source] Gas-phase tautomerism in 1-phenylazonaphthalene-4-ol: verification of the responses of individual tautomersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2009Daniela Nedeltcheva Gas-phase tautomerism in 1-phenylazonaphthalene-4-ol (1) was studied by using electron ionization (EI) mass spectrometry on the basis of the fragmentations of the model enol and keto tautomers, where the movable proton is replaced by a methyl group. These fixed tautomers were obtained as an easy separable mixture by simple methylation of the cheap and easily accessible diazene (1). It was found that their EI mass spectral fragmentations are in full congruence with the already published theoretical predictions. The relative energies required for bond cleavage in 1 and its fixed tautomers were estimated by stepwise increasing of the electron energy of the ion source of the mass spectrometer. A simple equation for the approximate estimation of the molar fractions of the individual tautomers was suggested. It was shown that the enol form is dominant in the temperature range of 200,300°C. Copyright © 2009 John Wiley & Sons, Ltd. [source] A metal-chelate affinity reverse micellar system for protein extractionBIOTECHNOLOGY PROGRESS, Issue 1 2010Xiao-Yan Dong Abstract A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W0) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1,2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W0, hydrodynamic radius (Rh), and aggregation number (Nag). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), Rh of the Cu-RM is also linearly related to W0. However, Nag is determined to be 30,90 at W0 of 5,30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||