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971.
C. Gaucher P. Legentilhomme P. Jaouen J. Comiti J. Pruvost 《Experiments in fluids》2002,32(3):283-293
The wall shear stress is determined at the surface of a plane sheet of Plexiglas, taking the place of a membrane, using an
electrochemical method. Several microelectrodes are mounted flush to this plane plate, and maps of shear stress are determined
for two inlet and outlet configurations and three channel heights. The heterogeneity of the wall shear stress is observed
for both configurations. Furthermore, the study of the turbulence features of the flow shows a decreasing fluctuating rate
of velocity gradient when the channel height is decreased. The wall velocity gradients and turbulent intensity rates analysis
are confirmed by a flow visualization using the particle image velocimetry method.
Received: 25 September 2000 / Accepted: 23 April 2001 相似文献
972.
Direct Umpolung of Glycals and Related 2,3‐Unsaturated N‐Acetylneuraminic Acid Derivatives Using Samarium Diiodide
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Tien Xuan Le Caroline Papin Gilles Doisneau Jean‐Marie Beau 《Angewandte Chemie (International ed. in English)》2014,53(24):6184-6187
The umpolung of glycals with samarium diiodide offers a simple route to novel carbohydrate‐derived nucleophilic reagents in a single step using a readily available reductant. The corresponding allyl samarium reagent that arises from the hexose series reacts with ketones at the C3 position with high stereoselectivity; carbon–carbon bond formation takes place only anti to the substituent at the C4 position of the dihydropyran ring. For the sialic acid series, the completely regio‐ and stereoselective coupling process of the samarium reagent occurs at the anomeric carbon atom and provides a new approach to the α‐C‐glycosides of N‐acetyl neuraminic acid. 相似文献
973.
Caroline Barrère Marie Hubert-Roux Carlos Afonso Majed Rejaibi Nasreddine Kebir Nicolas Désilles Laurence Lecamp Fabrice Burel Corinne Loutelier-Bourhis 《Analytica chimica acta》2014
The structural characterization of polyamides (PA) was achieved by tandem mass spectrometry (MS/MS) with a laser induced dissociation (LID) strategy. Because of interferences for precursor ions selection, two chemical modifications of the polymer end groups were proposed as derivatization strategies. The first approach, based on the addition of a trifluoroacetic acid (TFA) molecule, yields principally to complementary bn and yn product ions. This fragmentation types, analogous to those obtained with peptides or other PA, give only poor characterization of polymer end-groups [1]. A second approach, based on the addition of a basic diethylamine (DEA), permits to fix the charge and favorably direct the fragmentation. In this case, bn ions were not observed. The full characterization of ω end group structure was obtained, in addition to the expected yn and consecutive fragment ions. 相似文献
974.
Development of Experiment and Theory to Detect and Predict Ligand Phase Separation on Silver Nanoparticles
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Zachary Farrell Steve Merz Jon Seager Caroline Dunn Dr. Sergei Egorov Dr. David L. Green 《Angewandte Chemie (International ed. in English)》2015,54(22):6479-6482
MALDI mass‐spectrometry measurements are combined with self‐consistent mean‐field (SCF) calculations to detect and predict ligand phase separation on Ag nanoparticles. The experimental and theoretical techniques complement each other by enabling quantification of the nearest‐neighbor distribution of a ligand mixture in a monolayer shell. By tracking a characteristic metallic fragment family, analysis of a MALDI spectrum produces a frequency distribution corresponding to specific ligand patterning. Inherent to the SCF calculation is the enumeration of local interactions that dictate ligand assembly. Interweaving MALDI and SCF facilitates a comparison between the experimentally and theoretically derived frequency distributions as well as their deviation from a well‐mixed state. Thus, we combine these techniques to detect and predict phase separation in monolayers that mix uniformly or experience varying degrees of de‐mixing, including microphase separation and stripe formation. Definition of MALDI removed as this is a commonly recognized technique. 相似文献
975.
Modification of the Optical Spectrum of Cytosine by the Formation of an Ordered Monolayer of Molecules at a Au(110)/Electrolyte Interface
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Dr. Andrew Bowfield Dr. Caroline I. Smith Dr. Christopher P. Mansley Prof. Peter Weightman 《Chemphyschem》2015,16(7):1535-1541
An analysis of the reflection anisotropy spectrum (RAS) of an ordered monolayer of cytosine adsorbed at a Au(110)/electrolyte interface is found to contain optical contributions from both the substrate and the cytosine. The spectrum of cytosine in an aqueous environment is significantly broadened by the interaction between the molecule and the Au(110). Successful simulations of the Au(110)/cytosine interface consisting of two additional molecular transitions, which sit in the middle of previously observed molecular absorption bands, are produced by an empirical Lorentzian transition model that is consistent with previous theoretical and experimental studies. While this analysis alone cannot determine the number of π→π* dipole transitions, it confirms that the only cytosine transitions that contribute to the optical response of the Au(110)/cytosine interface are located in the plane of the molecule, which is vertical to the gold surface with the long axis along the [1$\bar 1$ 0] direction. 相似文献
976.
Alesandra Oriente Robson Tramontina Diandra de Andrades Caroline Henn Jose L. C. Silva Rita C. G. Simão Alexandre Maller Maria de Lourdes T. M. Polizeli Marina K. Kadowaki 《Chemical Papers》2015,69(8):1050-1057
Properties of beta-glucosidase produced by Aspergillus niger URM 6642 recently isolated from the Atlantic rainforest biome and its potential tolerance to saccharification of lignocellulosic biomass products and fermentation inhibitors was evaluated. The fungus was cultivated under solid state culture conditions at 37°C with different agro-industrial wastes. High levels of beta-glucosidase (3778.9 U g?1)from A. niger were obtained with rice meal as substrate under solid state culture conditions after ten days. Optimum pH for this particular beta-glucosidase activity was 4.0 although it was stable in the range of 4.0 to 7.0. The half-life (T½) of beta-glucosidase at 55°C is 3 h. However, at the optimum temperature of the enzyme, 65°C, T½ is 20 min. The enzyme showed tolerance to various compounds such as glucose, xylose, 5-hydroxymethyl furfural, furfural, coumarin, ethanol and acetic acid. Therefore, beta-glucosidase from the novel A. niger species may be of potential use in the saccharification of lignocellulosic biomass, as well as an additional enzyme supplement in cellulase cocktails used to increase the yield of fermentable sugars. 相似文献
977.
Dr. Jose M. González‐Domínguez Ana Santidrián Dr. Alejandro Criado Dr. Caroline Hadad Dr. Martin Kalbáč Prof. Tatiana Da Ros 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18631-18641
In the vast field of functionalization routes to carbon nanoforms, the fulfillment of such critical requirements as quick and nonharsh methods, good dispersibility, introduction of reactive groups, short reaction time, and low cost can be quite challenging. Traditional thermally induced diazonium chemistry on single‐walled carbon nanotubes (SWCNTs) is revisited by using commercial anilines and providing useful insight into the versatility of this approach. Functionalized SWCNTs with multiple controllable features, such as degree (and ratio) of coverage, orthogonalization, doping, and high water dispersibility, are obtained by introducing benzenesulfonic acid and benzylamine moieties. The scenario opens up an avenue to address relevant applications in which most functionalization methods could not be applied in a straightforward way. 相似文献
978.
A simple micro‐extraction plate assay for automated LC‐MS/MS analysis of human serum 25‐hydroxyvitamin D levels
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Timon Geib Florian Meier Pascal Schorr Frank Lammert Caroline S. Stokes Dietrich A. Volmer 《Journal of mass spectrometry : JMS》2015,50(1):275-279
This short application note describes a simple and automated assay for determination of 25‐hydroxyvitamin D (25(OH)D) levels in very small volumes of human serum. It utilizes commercial 96‐well micro‐extraction plates with commercial 25(OH)D isotope calibration and quality control kits. Separation was achieved using a pentafluorophenyl liquid chromatography column followed by multiple reaction monitoring‐based quantification on an electrospray triple quadrupole mass spectrometer. Emphasis was placed on providing a simple assay that can be rapidly established in non‐specialized laboratories within days, without the need for laborious and time consuming sample preparation steps, advanced calibration or data acquisition routines. The analytical figures of merit obtained from this assay compared well to established assays. To demonstrate the applicability, the assay was applied to analysis of serum samples from patients with chronic liver diseases and compared to results from a routine clinical immunoassay. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
979.
Bell AF Feng Y Hofstein HA Parikh S Wu J Rudolph MJ Kisker C Whitty A Tonge PJ 《Chemistry & biology》2002,9(11):1247-1255
Enoyl-CoA hydratase catalyzes the hydration of trans-2-crotonyl-CoA to 3(S)- and 3(R)-hydroxybutyryl-CoA with a stereoselectivity (3(S)/3(R)) of 400,000 to 1. Importantly, Raman spectroscopy reveals that both the s-cis and s-trans conformers of the substrate analog hexadienoyl-CoA are bound to the enzyme, but that only the s-cis conformer is polarized. This selective polarization is an example of ground state strain, indicating the existence of catalytically relevant ground state destabilization arising from the selective complementarity of the enzyme toward the transition state rather than the ground state. Consequently, the stereoselectivity of the enzyme-catalyzed reaction results from the selective activation of one of two bound substrate conformers rather than from selective binding of a single conformer. These findings have important implications for inhibitor design and the role of ground state interactions in enzyme catalysis. 相似文献
980.
The title compounds BaIn3.1Hg3.9 (x = 3.1) (I) and BaInxHg11‐x (x = 0—2.8) (II) are prepared from stoichiometric mixtures of the elements (Ta crucible, 825 K, cooling rate of 5 K/h). 相似文献