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Reaction Solution (reaction + solution)
Selected AbstractsIntegrated Enzymatic Synthesis and Adsorption of Isomaltose in a Multiphase Fluidized Bed ReactorENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 5 2006M. Ergezinger Abstract Dextransucrase catalyzes the formation of dextran, but also of numerous oligosaccharides from sucrose and different acceptors, if appropriate conditions are chosen. A process on a technical scale with immobilized enzyme was established to produce isomaltose, a disaccharide of industrial interest. Isomaltose is also a reactant for dextransucrase and has to be quickly taken out of the reaction solution. This was realized by integrated adsorption of isomaltose on zeolites. In the case of biotransformation the reactor works with a fluidized bed of immobilized enzyme and the in situ separation is realized with a suspension flow of adsorbent. This process was investigated experimentally and theoretically. With a design model consisting of hydrodynamics, kinetics of enzymatic synthesis, and thermodynamics of adsorption, a comparison was made between experimental and calculated data. [source] Size- and Shape-Controlled Synthesis and Assembly of a Silver Nanocomplex in UV-Irradiated TSA SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006Liangbao Yang Abstract In this paper we describe the size-controlled synthesis ofa silver nanocomplex based on the reduction of silvernitrate (AgNO3) by UV-irradiated tungstosilicate acid [H4(SiW12O40), TSA] solution. This method allows the synthesis of ellipsoidal particles with an average size that is tunable between 2.4 and 84 nm by varying the molar ratio of silver nitrate to TSA, the pH of the reaction solution, and the reaction temperature. Silver nanorods can be formed from the ellipsoidal nanoparticles by controlling the aging time. The formation mechanism of these nanorods is also discussed. The nanoparticles are characterized by UV/Vis spectroscopy, FTIR spectroscopy, XRD analysis, XPS, electron diffraction (ED), TEM, and with a Zetasizer instrument. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] First (Peroxo)vanadium(V) Complex with Heteroligand Formed in Reaction System , Synthesis, Structure and Reactivity of K[VO(O2)(omeida)]·H2O {omeida = N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetato(2,)}EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003Michal Sivák Abstract The crystalline peroxo complex of vanadium(V), K[VO(O2)(omeida)]·H2O, where omeida is a ,-lactone derivative, N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetate(2,), has been obtained by reaction of vanadate with H2O2 and N -(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) in acidic aqueous solution at pH = 3 and 278 K. X-ray analysis revealed a distorted pentagonal-bipyramidal coordination around the vanadium atom, with a typical cis arrangement of oxo and peroxo ligands in apical and equatorial positions, respectively. Two amino nitrogen atoms of the tetradentate omeida(2,)-N1,N2,O1,O2 ligand occupy the neighbouring equatorial positions of the pentagonal plane, and two oxygen atoms of carboxymethyl groups bound to the same N1 nitrogen atom are in equatorial and apical positions. The six-membered lactone ring in omeida was formed in the reaction solution from carboxy and hydroxy groups not involved in coordination with the vanadium atom. The 51V NMR spectra of K[VO(O2)(omeida)]·H2O, and of peroxovanadate/HEDTA/H2O and vanadate/HEDTA/H2O solutions, as well as the 1H NMR spectrum of HEDTA, proved that lactone ring closure proceeds only in peroxovanadate but not vanadate solutions. Spectroscopic investigation of the oxygen transfer reaction from the peroxo ligand in [VO(O2)(omeida)], to the thiolato sulfur atom in [Co(en)2{S(CH2)2NH2}]2+ or [Co(en)2(cyst)]+, and of the oxidation of N -acetyl- L -cysteine by K[VO(O2)(omeida)]·H2O, revealed much more complicated reaction mechanisms than those of other (amino-polycarboxylato)monoperoxo complexes of vanadium(V). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Illuminating Dark Plasmons of Silver Nanoantenna Rings to Enhance Exciton,Plasmon InteractionsADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Hong-Mei Gong Abstract The chemical growth of silver nanorings that possess singly twinned crystals and a circular cross section via a reductive reaction solution is reported. The wire and ring diameters of the synthesized nanorings are in the ranges 80,200,nm and 4.5,18.0,,m, respectively. By lighting up the multipolar dark plasmons with slanted illumination, the silver nanoring exhibits unique focused scattering and large local-field enhancement. We also demonstrate strong exciton,plasmon interactions between a monolayer of CdSe/ZnS semiconductor quantum dots and a single silver antenna-like nanoring (nanoantenna) at the "hot spots" located at the cross points of the incident plane and nanoring; the position of these spots are tunable by adjusting the incidence angle of illumination. The tunable plasmonic behavior of the silver nanorings could find applications as optical nanoantennae or plasmonic nanocavities. [source] Hierarchical Shelled ZnO Structures Made of Bunched Nanowire Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 8 2007P. Jiang Abstract The size- and morphology-controlled growth of ZnO nanowire (NW) arrays is potentially of interest for the design of advanced catalysts and nanodevices. By adjusting the reaction temperature, shelled structures of ZnO made of bunched ZnO NW arrays are prepared, grown out of metallic Zn microspheres through a wet-chemical route in a closed Teflon reactor. In this process, ZnO NWs are nucleated and subsequently grown into NWs on the surfaces of the microspheres as well as in strong alkali solution under the condition of the pre-existence of zincate (ZnO22,) ions. At a higher temperature (200,°C), three different types of bunched ZnO NW or sub-micrometer rodlike (SMR) aggregates are observed. At room temperature, however, the bunched ZnO NW arrays are found only to occur on the Zn microsphere surface, while double-pyramid-shaped or rhombus-shaped ZnO particles are formed in solution. The ZnO NWs exhibit an ultrathin structure with a length of ca.,,500,nm and a diameter of ca.,10,nm. The phenomenon may be well understood by the temperature-dependent growth process involved in different nucleation sources. A growth mechanism has been proposed in which the degree of ZnO22,saturation in the reaction solution plays a key role in controlling the nucleation and growth of the ZnO NWs or SMRs as well as in oxidizing the metallic Zn microspheres. Based on this consideration, ultrathin ZnO NW cluster arrays on the Zn microspheres are successfully obtained. Raman spectroscopy and photoluminescence measurements of the ultrathin ZnO NW cluster arrays have also been performed. [source] Syzygium cumini leaf and seed extract mediated biosynthesis of silver nanoparticles and their characterizationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2010Vineet Kumar Abstract BACKGROUND: Plant mediated synthesis of metallic nanoparticles has been studied and reported, however, to date, the biomolecules involved in the synthesis of metallic nanoparticles have not been characterized. This study was therefore undertaken to characterize the biomolecules of Syzygium cumini involved in the synthesis of silver nanoparticles. RESULTS: Synthesis kinetics and morphological characterization of silver nanoparticles (SNP) synthesized using leaf extract (LE) and seed extract (SE) as well as their polar (water) fractions from Syzygium cumini were compared. The polyphenols content and high performance liquid chromatography (HPLC) profile of different fractions revealed good correlation between size and synthesis rate of SNP. SE contains more polyphenols and biochemical constituents than LE and therefore, showed higher synthesis rate and bigger sized SNP. To analyse the nature of biomolecules involved in the synthesis of SNP, LE and SE were fractionated on a polarity basis by solvent,solvent partitioning. Only the water fractions of LE and SE showed potential for SNP synthesis. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis of SNP indicated that all fractions catalyze the synthesis of spherical nanoparticles. The average size of SNP synthesized by LE, leaf water fraction, SE and seed water fraction were 30, 29, 92, and 73 nm respectively. CONCLUSION: Results suggest that only highly polar soluble constituents are responsible for SNP synthesis. The size of SNP was found to be directly correlated with the amount of polyphenols as well as surfactants present in the reaction solution. Thus, the amount of polyphenols could be one of the crucial parameters determining the size and distribution of SNP. Copyright © 2010 Society of Chemical Industry [source] Preparation of Mg-Al hydrotalcite by urea method and its catalytic activity for transesterificationAICHE JOURNAL, Issue 5 2009Hong-Yan Zeng Abstract Layered double hydroxides based on the structure (Mg6Al2(OH)16CO3·4H2O) were synthesized by urea hydrolysis method and characterized by XRD, FTIR, SEM, and EDS. The results revealed that pH played a crucial role in the Mg-Al hydrotalcite precipitation by controlling [urea]/[NO] molar ratio in reaction solution at 378 K and the optimized [urea]/[NO] molar ratio was 4.0. The sample calcined at 773 K was used as a solid catalyst for biodiesel synthesis. The catalyst was found to have a high catalytic activity in transesterification of rape oil to methanol with about 94% oil conversion at 338 K for 3 h. The water content of the oil could be kept below 2.0 wt % and free fatty acid content of the oil could be kept below 3.0 mg KOH·g[oil],1 in order to get the best conversion. So, the solid catalyst was more tolerant to free fatty acid and water in rape oil than homogeneous basic-catalysts. Moreover, the catalyst could be reused, but catalytic activity decreased on reuse of the catalyst although it remained highly active for the five uses. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Determination of the 2,3-pentadienedioic acid enantiomer interconversion energy barrier 1.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15 2006Classical kinetic approach Abstract A classical kinetic method was used to determine the energy barrier for the interconversion of 2,3-pentadienedioic acid enantiomers. Each individual enantiomer was isolated by collecting the appropriate peaks from the HPLC enantiomeric separation, of racemic 2,3-pentadienedioic acid. The isolated enantiomers were racemized at 22°C using various interconversion times. The ratio of enantiomers in each reaction solution was determined by HPLC at 22°C. The corresponding peak areas of the enantiomers and the interconversion times obtained from the HPLC chromatograms were used to calculate both the interconversion rate constants describing (+) , (,) and (,) , (+) interconversions as well as the energy barriers. It was confirmed that the interconversion of 2,3-pentadienedioic acid enantiomers is a first-order kinetic reaction. Both semiempirical and ab initio methods were used to explore the mechanism of the interconversion of 2,3-pentadienedioic acid enantiomers, and to calculate the interconversion energy barrier. Comparison of the interconversion energy barriers found by the ab initio method (,G# = 110.7 kJ/mol) and by classical kinetics in the mobile phase solution at 22°C (,Gapp = 93.9 ± 0.2 kJ/mol) shows a difference which may be attributed to the different conditions assumed in the theoretical calculation (i. e., a gaseous state) and the actual experimental conditions (i. e., liquid solution) and a possible catalytic effect of the solution composition. [source] Synthesis of ZnO whiskers with different aspect ratios by a facile solution routePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008Juan Xie Abstract Monodispersed zinc oxide (ZnO) whiskers with different aspect ratios were successfully prepared via a simple solution route at low temperature. It is found that the diameter and aspect ratio of ZnO whiskers depend critically on the structure and type of ionic surfactant added in the reaction solution. To further understand the effect of the surfactants on the formation process of ZnO whiskers, concentration measurements of Zn(II) remaining in the solution as well as scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analyses of the solid product have been made at regular intervals throughout the reaction with and without the surfactants. A possible formation process has been reasonably suggested based on these systematic experimental results. It is believed that anion surfactants are capable of slowing down the nucleation and growth rate of ZnO crystallite, which is favorable for the anisotropic growth habit of ZnO crystal to form needle-like whiskers. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Helical opposition in poly(2-methoxyaniline) by tuning the concentration of salts in reaction solutionPOLYMER INTERNATIONAL, Issue 9 2010Guo-Li Yuan Abstract The synthesis and application of helical polyaniline derivatives (PANIs) have attracted much interest. However, most of these syntheses have been carried out in organic solutions. In our previous reports, helical PANIs were successfully realized in aqueous solution. Because helical architecture in the backbones of PANIs is an induced rather than the natural arrangement, it is significant to study the change in helicity in aqueous solution, especially opposition or reversion. One excess-handed helicity was induced in poly(2-methoxyaniline) (PMOA) by electrochemical polymerization of 2-methoxyaniline at pH = 2.5 in the presence of protonated ,-cyclodextrin sulfate (CDS, H+). When 0.04 mol L,1 NaCl was added to the reaction solution, the PMOA backbone took on an opposite excess of one-handed helicity, which was confirmed by induced circular dichroism. Such a result originates from the dynamic switch between electrostatic and hydrogen-bonding interactions. The helix-inducing process in PMOA depends on the interaction between PMOA and chiral CDS. Due to the competition of Na+ Cl, with PMOA+ CDS,, the electrostatic interaction between PMOA and CDS is limited or weakened. Thus, the slightly preferred interaction between them switches from electrostatic to hydrogen bonding. Simultaneously, the interaction positions and distance are changed. The changed steric hindrance induces PMOA into adopting an opposite excess-handed helicity. Copyright © 2010 Society of Chemical Industry [source] Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2006Hubert W. Vesper The general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA-Hb) and its primary metabolite glycidamide (GA-Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA-Hb and GA-Hb between pH 3,10 and at 35,55°C at different time intervals, and the applicability of liquid-liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6,7, heating the reaction solution at 55°C for 2,h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129,pmol/g globin (range: 27,453,pmol/g globin) and 97,pmol/g globin (range: 27,240,pmol/g globin) for AA-Hb and GA-Hb, respectively. The GA-Hb/AA-Hb ratio decreases significantly with increasing AA-Hb values indicating that measurement of AA-Hb as well as GA-Hb are needed to appropriately assess human exposure to acrylamide. Published in 2006 by John Wiley & Sons, Ltd. [source] Effects of citraconylation on enzymatic modification of human proinsulin using trypsin and carboxypeptidase BBIOTECHNOLOGY PROGRESS, Issue 4 2009Young-Jin Son Abstract Insulin is a polypeptide hormone which is produced by the ,-cell of pancreas and controls the blood glucose level in the human body. Enzymatic modification of human proinsulin using trypsin and carboxypeptidase B generally causes high accumulation of insulin derivatives, leading to more complicated purification processes. A simple method including citraconylation and decitraconylation in the enzymatic modification process was developed for the reduction of a major derivative, des-threonine human insulin. Addition of 3.0 g citraconic anhydride per g protein into the reaction solution led to the citraconylation of lysine residues in human proinsulin and reduction of relative des-threonine insulin content from 13.5 to 1.0%. After the enzymatic hydrolysis of the citraconylated proinsulin, 100% of lysine residues can be decitraconylated and restored by adjusting pH to 2,3 at 25 °C. Combination of hydrogen peroxide addition and citraconylation of proinsulin expressed in recombinant Escherichia coli remarkably improved the conversion yield of insulin from 52.7 to 77.7%. Consequently, citraconylation of lysine residues blocked the unexpected cleavage of human proinsulin by trypsin, minimized the formation of des-threonine insulin and hence increased the production yield of active insulin. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Homo-coupling of Aryl Iodide and Bromide Catalyzed by Immobilized Palladium with a Bidentate Nitrogen LigandCHINESE JOURNAL OF CHEMISTRY, Issue 10 2009Xiaofang Chen Abstract The immobilized palladium onto organic-inorganic hybrid material, which contains bidentate nitrogen ligands, was a very effective catalyst for homo-coupling of aryl iodide and bromide. The protocol involved the use of N,N -dimethylacetamide as a solvent, and n -tributylamine as a base. The reaction generated the corresponding homo-coupling products in good to excellent yields at low catalyst loading (0.20 mol%). Furthermore, the silica-supported palladium catalyst could be recovered and recycled by a simple filtration of the reaction solution and used for five consecutive trials without loss of its activity. [source] Synthesis, structures and magnetic properties of a series of polynuclear copper(II)-lanthanide( III) complexes assembled with carboxylate and hydroxide ligandsCHINESE JOURNAL OF CHEMISTRY, Issue 5 2000Xiao-Ming Chen Abstract Heterometallic copper(II)-lanthanide(III) complexes have been made with a variety of exclusively O -donor ligands including betaines (zwitterionic carboxylates) and chloroacetate, which are dinuclear CuLn, tetranuclear Cu2Ln2, pentanuclear Cu3Ln2, and octadecanuclear Cu12 complexes. The results show that subtle changes in both the carboxylates and acidity of the reaction solution can cause drastic changes in the structures of the products. Magnetic studies exhibit that shielding of the Ln3+ 4f electrons by the outer shell electrons is very effective to preclude significant coupling interaction between the Ln3+ 4f electrons and Cu2+ 3d electrons in either a mono-atomic hydroxide-bridged, or a carboxylate-bridged system. [source] Asymmetric aldol reactions catalyzed by efficient and recyclable silica-supported proline-based peptidesCHIRALITY, Issue 4 2009Jincan Yan Abstract A series of silica-supported proline-based peptides were synthesized and applied as catalysts for direct asymmetric intermolecular aldol reactions. Among these, a peptide with two L -proline units was found to be the most efficient one for the asymmetric aldol reactions between acetone and aromatic aldehydes. The reactions generated the corresponding products with satisfactory isolated yields (up to 97%) and enantiomeric excesses (up to 96%) in the presence of this catalyst (5 mol %). Furthermore, the silica-supported organocatalyst could be recovered and recycled by a simple filtration of the reaction solution and used for five consecutive trials without loss of its reactivity. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] Synthesis, Mechanism, and Gas-Sensing Application of Surfactant Tailored Tungsten Oxide NanostructuresADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Suman Pokhrel Abstract Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, 1H, and 13C NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a,=,0.7297,nm, b,=,0.7539,nm, c,=,0.7688,nm, and ,-i;,=,90.91,°. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15,nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40,60,nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials. [source] Grafting of Molecularly Ordered Mesoporous Phenylene-Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Abstract Arenetricarbonyl complexes, or the general formula C6H4Mo(CO)3, were incorporated into crystal-like mesoporous phenylene-silica by liquid-phase deposition of molybdenum hexacarbonyl [Mo(CO)6]. By adjusting the reaction conditions, different molybdenum loadings of 1.5 and 5.9,wt% were obtained, which correspond to 3% and 14% of the phenylene contents. The texture properties of the materials as well as the nature of the surface-fixed complexes were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, FT-IR, UV-vis and MAS (13C, 29Si) NMR spectroscopy. The derivatized organosilicas were examined as catalyst precursors for the liquid-phase epoxidation of cis -cyclooctene, 1-octene, trans -2-octene and (R)-(+)-limonene at 55,°C, using tert -butyl hydroperoxide as the oxidant. For each olefin the corresponding epoxide was the only product detected. In the case of cyclooctene, the intrinsic reaction rates per surface molybdenum atom were similar for both Mo loadings (TOF,1150 mol,molMo,1,h,1), suggesting that the resultant materials act as single site epoxidation catalysts. Leaching tests and metal analyses of reaction solutions showed that the catalytic activity stemmed from the immobilized species and not from the leaching of active species into solution. The oxidation of limonene gave limonene oxide as the only product in 95% yield at 3,h, which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond. [source] Fullerene-functionalized polycarbonate: Synthesis under microwave irradiation and nonlinear optical propertyPOLYMER ENGINEERING & SCIENCE, Issue 4 2006Huixia Wu Fullerenation of polycarbonate (PC), a commercially important optical polymer, was achieved by direct reaction of C60 and PC in the presence of azo-bis-isobutyronitrile (AIBN), using 1,1,2,2-tetrachloroethane as the solvent under microwave irradiation (MI). Compared with conventional heating process, MI could significantly enhance the rate of the fullerenation under identical reaction conditions. The C60 content of the fullerene-functionalized polycarbonate (C60 -PC) could be controlled via varying the C60/PC feed ratio and the reaction time. The C60 -PCs are soluble in common organic solvents such as THF and chloroform. The products were characterized by gel permeation chromatography, UV,vis, FTIR, TGA, DSC, 1H NMR, and 13C NMR. The reaction of C60 with PC under MI was monitored by electron spin resonance spectra, the fullerene radicals were detected in reaction solutions and also in the solid product polymers, indicating the radical mechanism of the reaction. The nonlinear optical property of C60 -PCs in THF was investigated by the open-aperture z -scan technique at 527 nm, and its nonlinear absorption coefficient was found to be in the same order as that of C60. POLYM. ENG. SCI., 46:399,405, 2006. © 2006 Society of Plastics Engineers [source] | |||||||||||||||||||||||||