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141.
[reaction: see text] A new generation of 2,5-dimethylthiolanes with a locked conformation was developed to promote the asymmetric addition of chiral sulfonium ylides to aldehydes. The novel chiral sulfur derivative 4 succeeded the synthesis of trans-stilbene oxide derivatives with enantiomeric ratios ranging from 95:5 to 98:2. This user-friendly organocatalytic process proved to be efficient with 20-10% of sulfide 4 in 1 or 2 days of reaction. An insight into the ylide intermediate conformation is given on the basis of a computational ab initio study. 相似文献
142.
The electrophoretic separation of high-molecular-weight proteins (> 500 kDa) using polyacrylamide is difficult because gels with a large enough pore size for adequate protein mobility are mechanically unstable. A 1% vertical sodium dodecyl sulfate (SDS)-agarose gel electrophoresis (VAGE) system has been developed that allows titin (a protein with the largest known SDS subunit size of 3000-4000 kDa) to migrate over 10 cm in a approximately 13 cm resolving gel. Such migration gives clear and reproducible separation of titin isoforms. Proteins ranging in size from myosin heavy chain ( approximately 220 kDa) up to titin can be resolved on this gel system. Electroblotting of these very large proteins was nearly 100% efficient. This VAGE system has revealed two titin size variants in rabbit psoas muscle, two N2BA bands in rabbit cardiac muscle, and species differences between titins from rat and rabbit muscle. Agarose electrophoresis should be the method of choice for separation and blotting of proteins with very large subunit sizes. 相似文献
143.
Dr. Dominique Marion Dr. Diego F. Gauto Isabel Ayala Karine Giandoreggio-Barranco Dr. Paul Schanda 《Chemphyschem》2019,20(2):276-284
Studying protein dynamics on microsecond-to-millisecond (μs-ms) time scales can provide important insight into protein function. In magic-angle-spinning (MAS) NMR, μs dynamics can be visualized by rotating-frame relaxation dispersion experiments in different regimes of radio-frequency field strengths: at low RF field strength, isotropic-chemical-shift fluctuation leads to “Bloch-McConnell-type” relaxation dispersion, while when the RF field approaches rotary resonance conditions bond angle fluctuations manifest as increased rate constants (“Near-Rotary-Resonance Relaxation Dispersion”, NERRD). Here we explore the joint analysis of both regimes to gain comprehensive insight into motion in terms of geometric amplitudes, chemical-shift changes, populations and exchange kinetics. We use a numerical simulation procedure to illustrate these effects and the potential of extracting exchange parameters, and apply the methodology to the study of a previously described conformational exchange process in microcrystalline ubiquitin. 相似文献
144.
The detection of food allergens has been a challenge because of the increasing need to ensure the absence of undeclared allergens in foods. The current trend in the detection of some food allergens, like peanuts, is based on the detection of multiple allergenic and nonallergenic proteins, and this is the approach that kit manufacturers have adopted. Because commercial kits differ in their ability to detect allergens, regulatory agencies, the food industry, and kit manufacturers are working together to standardize the detection methods. Three kits for the detection of peanuts have been evaluated for performance by the AOAC Research Institute. For this evaluation, a peanut butter suspension was used as a reference material. Several kit components contribute to between-kit analytical variation, even when the same sample is used. One component of commercial kits, which may be contributing to this variability, is the sample extraction buffer. In this study, differences in extractability of 3 allergenic foods were evaluated by using 4 different extraction buffers. The conclusion is that optimum allergen extractability was buffer-dependent, and no single buffer is appropriate for use as a universal extraction solution for all allergenic foods. Therefore, a thorough evaluation of sample preparation buffers needs to be performed for every individual allergenic food. In light of the results obtained, the current approach used for detection of peanut allergens based on the detection of multiple allergenic and nonallergenic proteins is being analyzed. 相似文献
145.
Despite the availability of commercial capillary electrophoresis systems for over ten years, where quantitative analysis is required, capillary zone electrophoresis (CZE) has often failed to replace ion chromatography as the method of choice for a large number of analytes, not least inorganic anions. To investigate the reasons for this apparent failing, a review is presented of work that has been carried out to-date involving the quantitative application of CZE to the determination of inorganic anions in industrial and environmental samples. This review summarizes work both investigating and improving the quantitative aspects of the CZE of inorganic anions. A complete survey of how CZE has been applied to the determination of inorganic anions in real samples is given, including what, if any, analytical performance parameters were investigated and quoted, and if quality assurance data and validation methods were briefly considered, thoroughly investigated or simply ignored. 相似文献
146.
Marion 《Fresenius' Journal of Analytical Chemistry》1928,73(12):472
Ohne Zusammenfassung 相似文献
147.
Mikhail V. Mironenko Steven A. Grant Giles M. Marion 《Journal of solution chemistry》1997,26(5):433-460
We developed a FORTRAN program based on the Pitzer equations to calculate densities of electrolyte solutions at subzero temperatures.
Data from the published literature collected at -28.9, -17.8, -12.2, -6.7, 0, and 25°C were used to calculate the Pitzer-equation
parameters and to evaluate model performance. Three approaches to estimating the molar volume of the solute at infinite dilution
were evaluated: (1) extrapolation of apparent molar volumes to zero square-root ionic strength; (2) calculation with the Tanger
and Helgeson model; and (3) global fit of the data in which the molar volume of the solute at infinite dilution was estimated
along with the Pitzer-equation parameters. The last approach gave parameter estimates that reproduced the experimental data
most accurately. The parameterized model predicted accurately densities of single-electrolyte and multielectrolyte solutions
at -28.9, -17.8, -12.2, -6.7, 0, and 25°C. Available experimental data are generally quite poor. Accordingly, Pitzer-equation
parameters estimated for subzero temperatures should be viewed as conditional until improved measurements of single-electrolyte
solution densities at subzero temperatures are made. 相似文献
148.
149.
J. Bricout R. Viani F. Müggler-Chavan J. P. Marion D. Rwymond R. H. Egli 《Helvetica chimica acta》1967,50(6):1517-1522
Trans-2-penten-1-ol, 1-ethyl-2-formyl-pyrrole, 2-trans, 4-cis-heptadienal, phenyl-acetonitrile, methyl benzoate, 2-phenyl-but-2-enal and the lactone of 2,6,6-trimethyl-2-hydroxy-cyclohexylidene acetic acid have been separated from black tea aroma by gas-liquid chromatography, and identified by infra-red and mass spectrometry. 相似文献
150.
Chiral Phosphate in Rhodium‐Catalyzed Asymmetric [2+2+2] Cycloaddition: Ligand,Counterion, or Both?
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Dr. Marion Barbazanges Dr. Elsa Caytan Dr. Denis Lesage Dr. Corinne Aubert Prof. Louis Fensterbank Prof. Vincent Gandon Dr. Cyril Ollivier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8553-8558
Investigations based on NMR spectroscopy, mass spectrometry, and DFT calculations shed light on the metallic species generated in the rhodium‐catalyzed asymmetric [2+2+2] cycloaddition reaction between diynes and isocyanates with the chiral phosphate TRIP. The catalytic mixture comprising [{Rh(cod)Cl}2], 1,4‐diphenylphosphinobutane (dppb), and Ag(S)‐TRIP actually gives rise to two species, both having an effect on the stereoselectivity. One is a rhodium(I) complex in which TRIP is a weakly coordinating counterion, whereas the other is a bimetallic Rh/Ag complex in which TRIP is a strongly coordinating X‐type ligand. 相似文献