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991.
Stabilization of Catalytically Active Cu+ Surface Sites on Titanium–Copper Mixed‐Oxide Films
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Dr. Ashleigh E. Baber Dr. Xiaofang Yang Dr. Hyun You Kim Dr. Kumudu Mudiyanselage Markus Soldemo Dr. Jonas Weissenrieder Dr. Sanjaya D. Senanayake Dr. Abdullah Al‐Mahboob Dr. Jerzy T. Sadowski Dr. Jaime Evans Dr. José A. Rodriguez Dr. Ping Liu Dr. Friedrich M. Hoffmann Dr. Jingguang G. Chen Dr. Darío J. Stacchiola 《Angewandte Chemie (International ed. in English)》2014,53(21):5336-5340
The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper‐based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu+ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu2O film leads to the formation of a stable mixed‐metal oxide with a Cu+ terminated surface that is highly active for CO oxidation. 相似文献
992.
Separation of triglyceride and diglyceride positional isomers by silver ion high-performance liquid chromatography coupled with an evaporative light-scattering detector is described. The triglyceride isomers had a fatty acid composition of CLC and CCL, where C and L were caprylic acid and linoleic acid, respectively. Diglyceride isomers, 1,2(2,3)-diglyceride and 1,3-diglyceride, which contained caprylic acid were separated too. A solvent system based on n-hexane, 2-propanol, ethyl acetate, and acetonitrile with a flow-rate of 0.8 ml/min was developed. Calibration curves of CLC and CCL were achieved with triolein as internal standard. Using this method, the incorporation of linoleic acid onto specific a position of glycerol backbone can be monitored. 相似文献
993.
Tom Mortier André Persoons Thierry Verbiest 《Central European Journal of Chemistry》2006,4(1):160-165
We describe a very simple, two-step synthetic method to prepare gold nanorods with extremely high aspect ratios (> 20) and
average lengths of more than 1000 nm. The method is based on a seed-mediated growth in presence of the surfactant cetyltrimethylammonium
bromide. The length and aspect ratios of the nanorods can be manipulated by varying the surfactant concentration. 相似文献
994.
Illanes A Wilson L Caballero E Fernández-Lafuente R Guisán JM 《Applied biochemistry and biotechnology》2006,133(3):189-202
Crosslinked enzyme aggregates (CLEAs) of a partially purified penicillin acylase from a recombinant Escherichia coli strain have been produced as a novel type of biocatalysts well endowed to perform in organic media. Different protein precipitants
were studied and glutaraldehyde was used as the crosslinking agent. Precipitation curves were obtained for all precipitants
to determine the concentrations at which all the protein precipitated out of the solution. The effect of the glutaraldehyde-to-protein
ratio was studied with respect to process recovery and the specific activity and stability of the biocatalyst. Recovery of
penicillin acylase activity was moderately high, about 50%; major losses of enzyme activity were produced at the precipitation
step. Specific activities of all CLEAs were very high, which is one of the advantages of using nonsupported biocatalysts.
Ammonium sulfate and tert-butyl alcohol were the best precipitants at a glutaraldehyde-protein mass ratio of 2 and were selected to perform the kinetically
controlled synthesis of ampicillin in 60% (v/v) ethylene glycol medium. At comparable conversion yields, volumetric and specific
antibiotic productivity were much higher for CLEAs than for carrier-bound penicillin acylases. 相似文献
995.
Inmaculada García Cuesta José Sánchez-Marín Alfredo M J Sánchez de Merás 《Chemphyschem》2006,7(2):508-513
Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2- has D2d symmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved. 相似文献
996.
A membrane-assisted solvent extraction (MASE) method is presented for the extraction of several non-ionic organophosphorus chemicals from wastewaters samples followed by LC-MS/MS determination. The method was developed for a variety of chlorinated phosphates (trichloroethyl, tichloropropyl) and non-chlorinated phosphates (triphenyl, tributyl) used as flame retardants and for plasticizers such as triethylhexyl and tris-butoxyethyl phosphate. Parameters such as extracting solvent, sample volume and ionic strength, extraction temperature and time were optimized. The final method provides good quantification limits (1-25 ng L(-1)) and linearity (R2>0.9978). Method precision was also good at high concentrations (5% mean RSD at the 500 ng L(-1) level) but decreased at lower concentrations (20% mean RSD at the 20 ng L(-1) level). MASE yields lower matrix effects than SPE in a successive LC-MS/MS analysis of these compounds, avoiding the need for standard addition for quantification. When applied to wastewater samples comparable results were obtained using either MASE with internal standard calibration or SPE with standard addition. 相似文献
997.
Karina González‐Segura Paulina Cañete‐Rosales Rodrigo del Rio Claudia Yáñez Nancy F. Ferreyra Gustavo A. Rivas Soledad Bollo 《Electroanalysis》2012,24(12):2317-2323
The electrochemical response of a glassy carbon electrode modified with carbon nanotubes (CNT) dispersed in two solvents, water and DMF, and two polymers, chitosan and Nafion is reported. The films were homogeneous when the dispersing agent was water or DMF. In the case of polymers, the surfaces present areas with different density of CNTs. A more sensitive electrochemical response was obtained when CNTs are dispersed in the solvents. In the case of CNT dispersed with polymers, the nature of the polymer demonstrated to be a critical parameter not only for dispersing the nanotubes but also for the electrochemical activity of the resulting electrodes. 相似文献
998.
Iannucci NB Navarro del Cañizo AA Cascone O 《Applied biochemistry and biotechnology》2003,104(3):173-183
Twenty triazinic dyes were assayed as ligands for the chromatographic affinity purification of a neutral protease from Flavourzyme™, a commercial preparation. Screening at pH 4.0 allowed the selection of eight dyes on the basis of their high protease adsorption.
When the pH was set to 5.0 in order to increase selectivity, only Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A maintained
protease adsorption at high values. Neither maximum capacities nor dissociation constants calculated from isotherms measured
at 8 and 25°C showed great differences. By contrast, a strong temperature effect was evidenced in the elution step: elution
at 8°C allowed 70, 81, and 98% recovery of adsorbed protease with Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A, respectively,
whereas only 20% recovery was attained at 25°C. Based on the results obtained, a purification process for the neutral protease
contained in Flavourzyme with Cibacron Blue F3G-A as the affinity ligand was developed, yielding 96% of electrophoretically
pure enzyme in a single step, the specific activity rising from 850 to 3650 U/mg. 相似文献
999.
An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3. 相似文献
1000.
Ferreira H Lúcio M Lima JL Matos C Reis S 《Analytical and bioanalytical chemistry》2005,382(5):1256-1264
In this work the interaction of a non-steroidal anti-inflammatory drug (NSAID), diclofenac, with egg yolk phosphatidylcoline (EPC) liposomes, used as cell-membrane models, was quantified by determination of the partition coefficient. The liposome/aqueous phase partition coefficient was determined by derivative spectrophotometry, fluorescence quenching, and measurement of zeta-potential. Theoretical models based on simple partition of the diclofenac between two different media, were used to fit the experimental data, enabling the determination of Kp. The three techniques used yielded similar results. The effects of the interaction on the membranes characteristics were further evaluated, either by studying membrane potential changes or by effects on membrane fluidity. The liposome membrane potential and the size and size-homogeneity of liposomes were measured by light scattering. The effects of diclofenac on the internal viscosity or fluidity of the membrane were determined by use of spectroscopic probes—a series of n-(9-anthroyloxy) fatty acids in which the carboxyl terminal group is located at the interfacial region of the membrane and the fluorescent anthracene group is attached at different positions along the fatty acid chain. The location of the diclofenac on the membrane was also evaluated, by fluorescence quenching using the same series of fluorescent probes. Because the fluorescent anthracene group is attached at different positions along the fatty acid chain, it is possible to label at a graded series of depths in the bilayer. The interactions between the drug and the probe are a means of predicting the location of the drug on the membrane. 相似文献