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Emulsion System (emulsion + system)
Selected AbstractsAldol Additions of Dihydroxyacetone Phosphate to N -Cbz-Amino Aldehydes Catalyzed by L -Fuculose-1-Phosphate Aldolase in Emulsion Systems: Inversion of Stereoselectivity as a Function of the Acceptor AldehydeCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2005Laia Espelt Dr. Abstract The potential of L -fuculose-1-phosphate aldolase (FucA) as a catalyst for the asymmetric aldol addition of dihydroxyacetone phosphate (DHAP) to N -protected amino aldehydes has been investigated. First, the reaction was studied in both emulsion systems and conventional dimethylformamide (DMF)/H2O (1:4 v/v) mixtures. At 100,mM DHAP, compared with the reactions in the DMF/H2O (1:4) mixture, the use of emulsion systems led to two- to three-fold improvements in the conversions of the FucA-catalyzed reactions. The N -protected aminopolyols thus obtained were converted to iminocyclitols by reductive amination with Pd/C. This reaction was highly diastereoselective with the exception of the reaction of the aldol adduct formed from (S)- N -Cbz-alaninal, which gave a 55:45 mixture of both epimers. From the stereochemical analysis of the resulting iminocyclitols, it was concluded that the stereoselectivity of the FucA-catalyzed reaction depended upon the structure of the N -Cbz-amino aldehyde acceptor. Whereas the enzymatic aldol reaction with both enantiomers of N -Cbz-alaninal exclusively gave the expected 3R,4R configuration, the stereochemistry at the C-4 position of the major aldol adducts produced in the reactions with N -Cbz-glycinal and N -Cbz-3-aminopropanal was inverted to the 3R,4S configuration. The study of the FucA-catalyzed addition of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde revealed that the 4R product was kinetically favored, but rapidly disappeared in favor of the 4S diastereoisomer. Computational models were generated for the situations before and after CC bond formation in the active site of FucA. Moreover, the lowest-energy conformations of each pair of the resulting epimeric adducts were determined. The data show that the products with a 3R,4S configuration were thermodynamically more stable and, therefore, the major products formed, in agreement with the experimental results. [source] Effect of an anionic monomer on the pickering emulsion polymerization stabilized by titania hydrosolJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2009Xiaomei Song Abstract Polystyrene (PS) nanocomposite particles with high titania content are prepared by Pickering emulsion polymerization. A self-made titania hydrosol modified by an anionic monomer sodium styrene sulfonate (NaSS) is used as a stabilizer and photocatalyst. The stability of the emulsion system is greatly improved by the electrostatic interaction between negatively charged NaSS and positively charged titania nanoparticles. The nanocomposite spheres with the diameter of around 120 nm are highly charged, indicating titania-rich surfaces of latex particles. It is also proven by the field-emission transmission electron microscope and field-emission scanning electron microscope images. The well-defined core-shell structure of the obtained PS/titania composite particles is confirmed by the formation of fragile hollow titania nanospheres after thermogravimetric analysis tests. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5728,5736, 2009 [source] Effect of sodium chloride on the formation and stability of n-dodecane nanoemulsions by the PIT methodASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Jeffery Chin Long Liew Abstract This paper provides a fundamental study of the effect of sodium chloride on the formation and stability of n-dodecane/nonionic surfactant (Brij30)/NaCl nanoemulsions produced by the phase inversion temperature (PIT) method. Nanoemulsions are an emulsion system containing droplets from 20 to 200 nm and widely used in cosmetics and pharmaceutical industries. The PIT method was chosen due to its low energy and surfactant usage to produce the nanoemulsions by heating and quenching an emulsion system. The changes of conductivity with temperatures were continuously monitored to determine phase inversion, and are found to be the same in low surfactant concentrations. PIT point was found to decrease with NaCl concentration especially from 5 to 7 wt% Brij30. At the storage temperature (20 °C), the initial droplet size decreases with NaCl concentration; however, the decrement only occurs from 4 to 7 wt% Brij30 while no nanoemulsions can be produced at 8 wt%. By adding salt, the surfactant concentration needed for the most stable nanoemulsions is reduced to 6 wt% from 7 wt%. Therefore, similar stable nanoemulsions can be produced with less surfactant in a brine system. Furthermore, most of the ageing brine-continuous nanoemulsions could be reproduced to their freshly prepared state by heating process but not for the most stable nanoemulsions. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effects of Fe,AOT complex on the properties of iron oxide particles formed by an AOT isooctane/water emulsion systemASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008J. Oshitani Abstract Formation of iron oxide particles with aerosol-OT (AOT)/isooctane/water emulsion was carried out employing a coprecipitation reaction for Fe3O4 particles. Emulsions containing Fe2+/Fe3+ were mixed with those containing OH,. Iron oxide particles were formed by changing the concentration ratio of AOT to iron ions and maintaining the volume fraction of water in the emulsion at 0.25. Particle formation was also carried out using nonemulsified aqueous solutions as a reference. The morphology, crystal structure, magnetic property and hydration degree of the particles formed under various conditions were compared. The ,-FeOOH or amorphous particles are formed instead of Fe3O4 when the AOT concentration is comparable to, or higher than, the iron ion concentration. These particles contain an OH group and water, and are oxidized to become ,-Fe2O3 by heating in N2. The Fe,AOT complex as the origin of OH-rich particle formation was the focus of this investigation. The IR measurement was carried out for the Fe,AOT complex, separately prepared with the aqueous solution. It was found that the Fe,AOT complex was hydrated, indicating that hydration of the complex affects the properties of particles formed by the emulsion. A possible mechanism for formation of ,-FeOOH or amorphous particles with emulsion is proposed. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Experimental Investigation of Performances of Microcapsule Phase Change Material for Thermal Energy StorageCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2010G. Fang Abstract Performances of microcapsule phase change material (MPCM) for thermal energy storage are investigated. The MPCM for thermal energy storage is prepared by a complex coacervation method with gelatin and acacia as wall materials and paraffin as core material in an emulsion system. A scanning electron microscope (SEM) was used to study the microstructure of the MPCM. In thermal analysis, a differential scanning calorimeter (DSC) was employed to determine the melting temperature, melting latent heat, solidification temperature, and solidification latent heat of the MPCM for thermal energy storage. The SEM micrograph indicates that the MPCM has been successfully synthesized and that the particle size of the MPCM is about 81 ,m. The DSC output results show that the melting temperature of the MPCM is 52.05,°C, the melting latent heat is 141.03 kJ/kg, the solidification temperature is 59.68,°C, and the solidification latent heat is 121.59 kJ/kg. The results prove that the MPCM for thermal energy storage has a larger phase change latent heat and suitable phase change temperature, so it can be considered as an efficient thermal energy storage material for heat utilizing systems. [source] Microencapsulation of n -Eicosane as Energy Storage MaterialCHINESE JOURNAL OF CHEMISTRY, Issue 5 2004Xiao-Zheng Lan Abstract For heat energy storage application, polyurea microcapsules containing phase change material, n -eicosane, were synthesized by using interfacial polymerization method with toluene-2,4-diisocyanate (TDI) and diethylenetriamine (DETA) as monomers in an emulsion system. Poly(ethylene glycol)octyl-phenyl ether (OP), a nonionic surfactant, was the emulsifier for the system. The experimental result indicates that TDI was reacted with DETA in a mass ratio of 3 to 1. FT-IR spectra confirm the formation of wall material, polyurea, from the two monomers, TDI and DETA. Encapsulation efficiency of n -eicosane is about 75%. Microcapsule of n -eicosane melts at a temperature close to that of n -eicosane, while its stored heat energy varies with core material n -eicosane when wall material fixed. Thermo-gravimetric analysis shows that core material n -eicosane, micro- n -eicosane and wall material polyurea can withstand temperatures up to 130, 170 and 250 °C, respectively. [source] Recent advances in controlled/living radical polymerization in emulsion and dispersionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2008Jung Kwon Oh Abstract Effective ways to conduct controlled/living radical polymerization (CRP) in emulsion systems are necessary for commercial latex production without significant modification of current industrial facilities. Conducting CRP in emulsion media is more complicated and more challenging than its application in homogeneous bulk. These challenges come from the intrinsic kinetics of emulsion polymerization. They include mass transport, slow chain growth mechanism, and exit of short radicals from polymeric particles. This review describes the recent developments of CRP in heterogeneous dispersion, including miniemulsion, microemulsion, dispersion, and especially emulsion. Various approaches for conducting emulsion CRP are detailed, including controlled seeded emulsion polymerization, nanoprecipitation, use of short oligomers as macroinitiators for in situ block copolymerization, and RAFT-mediated self-assembly. In addition many remaining challenges of the current methods barring wide spread industrial application of emulsion CRP are also suggested. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6983,7001, 2008 [source] Model salad dressing emulsion stability as affected by the type of the lupin seed protein isolateJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2006Evdoxia Papalamprou Abstract Model salad dressing emulsions of an oil volume fraction of 0.50 were prepared using two types of lupin seed protein isolate (LSPI) differing in the method applied for their isolation and their protein composition. The dressing stability against creaming and droplet coalescence were studied and correlated with data on oil droplet size, rheological characteristics and the amount of protein adsorption at the droplet surfaces. Model salad dressing emulsions containing the isolate, mainly composed of lupin globulins, exhibited higher stability and more pronounced rheological characteristics compared to those prepared with the isolate enriched in albumins or with the mixture of the two isolates. The lupin albumins appeared to displace the globulins from the droplet surfaces, following competitive adsorption from mixtures of the two types of the lupin isolates. The results are discussed in terms of droplet interaction and rearrangement as they are influenced by the presence of the adsorbed protein molecules and aggregates which appear to determine long-term stability of the emulsion systems. Copyright © 2006 Society of Chemical Industry [source] Aldol Additions of Dihydroxyacetone Phosphate to N -Cbz-Amino Aldehydes Catalyzed by L -Fuculose-1-Phosphate Aldolase in Emulsion Systems: Inversion of Stereoselectivity as a Function of the Acceptor AldehydeCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2005Laia Espelt Dr. Abstract The potential of L -fuculose-1-phosphate aldolase (FucA) as a catalyst for the asymmetric aldol addition of dihydroxyacetone phosphate (DHAP) to N -protected amino aldehydes has been investigated. First, the reaction was studied in both emulsion systems and conventional dimethylformamide (DMF)/H2O (1:4 v/v) mixtures. At 100,mM DHAP, compared with the reactions in the DMF/H2O (1:4) mixture, the use of emulsion systems led to two- to three-fold improvements in the conversions of the FucA-catalyzed reactions. The N -protected aminopolyols thus obtained were converted to iminocyclitols by reductive amination with Pd/C. This reaction was highly diastereoselective with the exception of the reaction of the aldol adduct formed from (S)- N -Cbz-alaninal, which gave a 55:45 mixture of both epimers. From the stereochemical analysis of the resulting iminocyclitols, it was concluded that the stereoselectivity of the FucA-catalyzed reaction depended upon the structure of the N -Cbz-amino aldehyde acceptor. Whereas the enzymatic aldol reaction with both enantiomers of N -Cbz-alaninal exclusively gave the expected 3R,4R configuration, the stereochemistry at the C-4 position of the major aldol adducts produced in the reactions with N -Cbz-glycinal and N -Cbz-3-aminopropanal was inverted to the 3R,4S configuration. The study of the FucA-catalyzed addition of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde revealed that the 4R product was kinetically favored, but rapidly disappeared in favor of the 4S diastereoisomer. Computational models were generated for the situations before and after CC bond formation in the active site of FucA. Moreover, the lowest-energy conformations of each pair of the resulting epimeric adducts were determined. The data show that the products with a 3R,4S configuration were thermodynamically more stable and, therefore, the major products formed, in agreement with the experimental results. [source] | ||||||||||