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991.
Jacqueline Moreira de Morais Orlando David Henrique dos Santos Tatiani Delicato Pedro Alves da Rocha‐Filho 《Journal of Dispersion Science and Technology》2013,34(7):1009-1014
Emulsion stability is controlled by the physicochemical properties of the adsorbed layers formed on the surface of the droplets. Zeta potential and droplet size measured initially and during storage can estimate O/W emulsion stability. The aim of this study was to characterize and evaluate the effects of different hydrolyzable compounds employed in pharmaceutical and cosmetic preparations on the zeta potential and droplet size of canola O/W nano‐emulsions and, consequently, the emulsion stability. The samples containing additives demonstrated significant change in zeta potential, but in spite of that, no macroscopic instability was observed. Yet the droplet size values did not undergo significant change. 相似文献
992.
Monica Maruno Pedro Alves da Rocha-Filho 《Journal of Dispersion Science and Technology》2013,34(1):17-22
The application of nanoemulsions is due to have good stability, uniform spreading and enhance active penetration upon skin. Nanometer emulsions can be obtained by low-energy emulsification method. The required hydrophilic and lipophilic balance indicates the better balance of emulsifier for optimum system emulsification. Emulsion stability is evidently controlled for the properties of the adsorbed layer formed in the surface of its globules, know as potential zeta. The aim of this work was to evaluate the oil/water nanoemulsion of formulation obtained after 15 years of preparation. The results suggested that the nanoemulsion have performed stability for many years. 相似文献
993.
Pedro Merino Graziella Greco Tomás Tejero Ramon Hurtado-Guerrero Rosa Matute Ugo Chiacchio Antonino Corsaro Venerando Pistarà Roberto Romeo 《Tetrahedron》2013
Diastereoselective asymmetric 1,3-dipolar cycloadditions of N-(alkoxycarbonylmethyl) nitrones derived from glycine, alanine and phenylalanine have been studied both experimentally and theoretically. Asymmetric induction is evaluated by either introducing a chiral group at the nitrone nitrogen atom or by using Oppolzer's sultam acrylamide. In both cases the sense of the asymmetric induction is the same, the (3R,5R)-isomer being preferentially obtained. The best results were observed with the chiral dipolarophile, which afforded an only isomer in all cases. The obtained isoxazolidines are easily transformed into the corresponding 5-substituted-3-hydroxypyrrolidin-2-ones. DFT studies are in a qualitative agreement with the observed experimental results. 相似文献
994.
Joana R. Bernardo Sara C.A. Sousa Pedro R. Florindo Mariusz Wolff Barbara Machura Ana C. Fernandes 《Tetrahedron》2013
This work describes the catalytic activity of 17 oxo–rhenium complexes containing heterocyclic ligands in the direct reductive amination of 4-nitrobenzaldehyde with 4-chloroaniline, using phenylsilane as reducing agent. In general, all of the catalysts tested gave excellent yields of the secondary amine, although, the best result was obtained with the catalytic system PhSiH3/ReOBr2(Hhmpbta)(PPh3) (2.5 mol %). This system was also applied to the synthesis of a large variety of secondary amines in good to excellent yields and tertiary amines in moderate yields, with tolerance of different functional groups. 相似文献
995.
Proton nuclear magnetic resonance (1H NMR) relaxometry, over about five decades in Larmor frequency, and pulsed field gradient NMR were used to study the molecular dynamics in the chromonic nematic and isotropic phases of stacked molecules of the binary mixture composed by Edicol Sunset Yellow (ESY) and deuterated water. Our results evidence that in both phases collective motions are responsible for the spin-lattice relaxation dispersion in the Larmor frequency range below 1 MHz. In the nematic phase, the collective motion are attributed to columnar undulations within the stacked molecules, while, in the isotropic phase, the results are explained by local order fluctuations due to the formation of the stacks. The high frequency dispersion was explained by individual molecular motions like rotations around and perpendicular to the stack axis, and also self-diffusion. 相似文献
996.
In this work, a thin, flexible and mechanically stable polymer conducting material (Silk‐Ion Jelly) was developed though application of Ion Jelly on to silk fabrics. Ion Jelly was prepared through jellification of a room temperature ionic liquid, 1‐butyl‐3‐methyl‐imidazolium dicyanamide ([bmim][dca]) using gelatin and water and applied to silk fabrics using two different processes: impregnation and in‐situ. Various parameters influencing ionic conductivity such as Ion Jelly composition (ratio of [bmim][dca], water and gelatin) and incorporation as well as the type of application process were thoroughly investigated. It was observed that the Ion Jelly compositions containing lower gelatin and water ratio as well as application through in‐situ process at high temperature (200 °C) led to considerable improvement in conductivity, mainly due to increased [bmim][dca] concentration, structural flexibility and reduced silk crystallinity. Silk‐Ion Jelly prepared using optimized conditions showed excellent mechanical stability and possessed high room temperature conductivity (2.9 × 10?3 S. cm?1), similar to [bmim][dca], and therefore, this novel ion conducting material may find potential applications in electrochemical devices due to its eco‐friendly preparation route using biomaterials and green solvents. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
997.
Pedro J. Sánchez Gómez 《Foundations of Chemistry》2013,15(1):103-116
In this paper we present a semantic analysis of the application of didactic constructivism to chemical education. We show that the psychological basis of constructivism yield, when applied to chemistry, an internalist semantics for the chemical names. Since these names have been presented as typical examples of an externalism for kind terms, a fundamental incompatibility ensues. We study this situation, to conclude that it affects chemical education at every level. Finally, we present a preliminary analysis of this problem from the point of view of physics. 相似文献
998.
Miguel Espinosa Prof. Dr. Gonzalo Blay Prof. Dr. Luz Cardona Prof. Dr. José R. Pedro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(44):14861-14866
The asymmetric conjugate addition of malonate esters to α,β‐unsaturated N‐sulfonyl imines is catalyzed by PyBOX/La(OTf)3 complexes in the presence of 4 Å MS. The reaction gives the corresponding E enamines bearing a stereogenic center at the allylic position with good yields and enantiomeric ratios up to 97:3. This reaction provides a synthetic entry to chiral δ‐aminoesters and piperidones. 相似文献
999.
Eloy Ramos‐Cordoba Dr. Pedro Salvador Prof. Dr. Markus Reiher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15267-15275
The electronic structure of main‐group diatomic molecules is discussed in the light of local spin analysis. A deep investigation into the origin of local spins and their coupling is presented. It is shown that the presence of significant local spins in bonded molecules flags deviations from the classical bonding prototypes. For the notorious example of the C2 molecule, the local spin analysis indicates that its ground state has all ingredients to be categorized as a diradical. 相似文献
1000.
Inexpensive γ-alumina-based nickel-copper bimetallic catalysts were studied for the hydrogenolysis of levulinic acid,a key platform molecule for biomass conversion to biofuels and other valued chemicals,into γ-valerolactone as a first step towards the production of 2-methyltetrahydrofurane.The activities of both monometallic and bimetallic catalysts were tested.Their textural and chemical characteristics were determined by nitrogen physisorption,elemental analysis,temperature-programmed ammonia desorption,and temperature-programmed reduction.The monometallic nickel catalyst showed high activity but the highest bγ-product production and significant amounts of carbon deposited on the catalyst surface.The copper monometallic catalyst showed the lowest activity but the lowest carbon deposition.The incorporation of the two metals generated a bimetallic catalyst that displayed a similar activity to that of the Ni monometallic catalyst and significantly low bγ-product and carbon contents,indicating the occurrence of important synergetic effects.The influence of the preparation method was also examined by studying impregnated- and sol-gel-derived bimetallic catalysts.A strong dependency on the preparation procedure and calcination temperature was observed.The highest activity per metal atom was achieved using the sol-gel-derived catalyst that was calcined at 450 ℃.High reaction rates were achieved;the total levulinic acid conversion was obtained in less than 2 h of reaction time,yielding up to 96%γ-valerolactone,at operating temperature and pressure of 250 ℃ and 6.5 MPa hydrogen,respectively. 相似文献