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31.
Jean-François Cavalier Dominique Lafont Paul Boullanger David Houisse Jacqueline Giallo Jean-Michel Ballester Frédéric Carrière 《Journal of chromatography. A》2009,1216(37):6543-6548
A general and easily accessible method for the extraction followed by the simultaneous separation and quantitative determination of triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids has been improved and optimized based on existing protocols using liquid-phase extraction and thin-layer chromatography coupled to flame ionization detection (TLC/FID Iatroscan). After lipid extraction in the presence of a suitable new synthetic internal standard, namely CholE1, a single elution step using n-heptane/diethyl ether/formic acid (55:45:1, v/v/v) was applied. This method was validated in line with international bioanalytical method validation guidelines using two different matrix systems: purified water and human gastro-intestinal fluid. Overall, the assay was found to have high levels of precision with coefficients of variation ranging from 1.48% to 11.0% and accuracy ranging from −13.3% to +5.79% RE. The confidence limits of the lipid mean recovery rates varied between 89.9% and 104%. This method is therefore highly suitable for quantifying the lipolysis products generated in vitro during the hydrolysis of various fats and oils by digestive lipases, as well as those collected from the gastro-intestinal tract in the course of human clinical studies on lipid digestion. 相似文献
32.
N. Z. Mamadalieva L. N. Zibareva R. Lafont L. Dainan Z. Saatov 《Chemistry of Natural Compounds》2004,40(6):574-578
Research results on the isolation and identification of ecdysteroids from plants of the Silene L. genus were presented.Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 472–475, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
33.
Z. Sadikov Z. Saatov M. Garcia J.-P. Girault R. Lafont 《Chemistry of Natural Compounds》2001,37(3):262-265
The ecdysteroid content ofSilene claviformishas been analyzed and the four major compounds have been identified as 20-hydroxyecdysone, 2-deoxy-20-hydroxyecdysone, 2-deoxyecdysone, and integristerone A. Two new minor compounds have also been identified
An erratum to this article can be found at 相似文献
34.
Christos Panagiotopoulos Richard Sempr Raymond Lafont Philippe Kerherv 《Journal of chromatography. A》2001,920(1-2):13-22
The effects of column temperature in the range 10–45°C using high-performance anion-exchange chromatography (HPAEC) and pulse amperometric detection are described for the determination of monosaccharides. The influence of temperature was tested with an isocratic elution of NaOH at concentrations varying from 2.5 to 20 mM and with a post-column addition of 1 M NaOH. The results showed that small changes of temperature greatly affect retention times and resolution (Rs) of monosaccharides and particularly those of the both pairs xylose–mannose and rhamnose–arabinose which cannot be simultaneously detected at usual room temperature (25°C). Our results suggest that a subambient temperature of 17°C and an eluent concentration of 19 mM are the more appropriate conditions for an acceptable separation (Rs rha/ara=1.02, Rs man/xyl=0.70) in a short analytical run time (35 min). The results showed that within the range of temperatures studied, enthalpy and entropy are invariant of temperature indicating that changes in the retention processes are mainly due to temperature than other associated changes in the system. This study demonstrated the importance of controlling temperature during HPAEC of monosaccharides, both to accomplish highly reproducible retention times and to achieve optimal separation of sugars. This method gave acceptable results for detection of marine sugars. 相似文献
35.
Dynamic solubility limits in nanosized olivine LiFePO4 总被引:1,自引:0,他引:1
Wagemaker M Singh DP Borghols WJ Lafont U Haverkate L Peterson VK Mulder FM 《Journal of the American Chemical Society》2011,133(26):10222-10228
Because of its stability, nanosized olivine LiFePO(4) opens the door toward high-power Li-ion battery technology for large-scale applications as required for plug-in hybrid vehicles. Here, we reveal that the thermodynamics of first-order phase transitions in nanoinsertion materials is distinctly different from bulk materials as demonstrated by the decreasing miscibility gap that appears to be strongly dependent on the overall composition in LiFePO(4). In contrast to our common thermodynamic knowledge, that dictates solubility limits to be independent of the overall composition, combined neutron and X-ray diffraction reveals strongly varying solubility limits below particle sizes of 35 nm. A rationale is found based on modeling of the diffuse interface. Size confinement of the lithium concentration gradient, which exists at the phase boundary, competes with the in bulk energetically favorable compositions. Consequently, temperature and size diagrams of nanomaterials require complete reconsideration, being strongly dependent on the overall composition. This is vital knowledge for the future nanoarchitecturing of superior energy storage devices as the performance will heavily depend on the disclosed nanoionic properties. 相似文献
36.
Mallet F. Petit S. Lafont S. Billot P. Lemarchand D. Coquerel G. 《Journal of Thermal Analysis and Calorimetry》2003,73(2):459-471
Solid-solid transformations between solvates of pharmaceutical compounds are investigated under various conditions. In the
case of Roxithromycin, it is shown that starting from single crystals of the acetonitrile solvate, a transformation towards
the monohydrate occurs according to a cooperative mechanism. This smooth exchange of solvent probably involves a transport
of matter within channels, and the comparison of crystal structures is consistent with the persistence of the main features
of the 3D lattice. By contrast, starting from the DMSO solvate of Dexamethasone acetate, the transformation towards the sesquihydrated
form, induced by the immersion of the DMSO solvate in water, is fully destructive and reconstructive. This occurs far-from-equilibrium
and is therefore controlled by kinetic factors. The existence of an intermediate liquid phase within the particle is postulated
to account for the appearance of whisker-like crystals growing first on high-energy sites of the former particle. An extended
analysis of these transformations between solvates shows that they could be classified according to rules previously proposed
in the case of desolvation mechanisms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
37.
This article demonstrates that bicontinuous microemulsions are optimal templates for high yield production of metal nanoparticles. We have verified this for a variety of microemulsion systems having AOT (sodium bis (2-ethyhexyl) sulphosuccinate) or a fluorocarbon (perfluoro (4-methyl-3,6-dioxaoctane)sulphonate) as surfactant mixed with water and oils like n-heptane or n-dodecane. Several types of metal nanoparticles, including platinum, gold and iron, were produced in these microemulsions having a size range spanning 1.8-17 nm with a very narrow size distribution of ±1 nm. Remarkably high mass concentrations up to 3% were reached. Size and concentration of the nanoparticles could be varied with the stoichiometries of the reagents that constituted them. The optimization towards high yield while maintaining low size polydispersity is due to the decoupling of the time scales for the precipitation reaction and for coarsening. In actual fact, coalescence is essentially prevented by the immobilization of nanoparticles within the bicontinuous microemulsion structure. 相似文献
38.
Juan M. Ramírez‐Anguita Àngels González‐Lafont José M. Lluch 《Journal of computational chemistry》2009,30(9):1477-1489
The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO2) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NOx) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO2 from the CH3S(O)(OH)CH3 adduct [including the formation of CH3S(O)(OH)CH3 from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO2 from the CH3S(O2)(OH)CH3 adduct are also studied. The formation of the CH3S(O2)(OH)CH3 adduct from CH3S(OH)CH3 (DMS‐OH) and O2 was analyzed in our previous work. All these pathways due to the presence of NOx (NO and NO2) and also due to the reactions with O2, OH and HO2 are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO2 (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NOx‐dependent pathways leading to the formation of DMSO2, which could explain some of these experimental results in comparison with experimental measurements carried out in NOx‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NOx content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
39.
3-Phenylpyrimido-[3,4-a]-s-triazines exhibit antiparasitic, antibacterial and antifungal activity. In order to study the metabolism of these heterocycles, 9,9-diethyl-3-phenyl-6,8-dioxo-2,3,4,5,6,7,8,9-octahydropyrimido[3 ,4-a]-s- triazine (TZ) was administered to dogs. Three potential metabolites were synthesized, and these models were identified and quantified with gas chromatography-mass spectrometry. The heterobicyclic compounds, TZ and its hydroxy derivative, underwent thermal degradation under chromatographic conditions. Dog urine spiked with the model metabolites was extracted, and the substances were quantified. The urine of dogs treated with TZ was studied, and two of the potential metabolites were recovered, identified and quantified. 相似文献
40.
Summary Thin-layer chromatographic investigations of ecdysteroids have been carried out to monitor their isolation by column chromatography
and droplet countercurrent chromatography as well as to control the homogeneity of the pure products. Isolation scheme and
chemical structure of the 20-hydroxyecdysone-22-benzoate and that of three new ecdysteroid compounds, 2-deoxy-1,20-dihydroxyecdysone,
2-deoxyecdysone-22-acetate and 2-deoxy-20-hydroxyecdysone-22-acetate are also presented. 相似文献