Search results for "liquid"
showing 10 items of 4351 documents
Isotropic-nematic interface in suspensions of hard rods: Mean-field properties and capillary waves
2006
We present a study of the isotropic-nematic interface in a system of hard spherocylinders. First we compare results from Monte Carlo simulations and Onsager density functional theory for the interfacial profiles of the orientational order parameter and the density. Those interfacial properties that are not affected by capillary waves are in good agreement, despite the fact that Onsager theory overestimates the coexistence densities. Then we show results of a Monte Carlo study of the capillary waves of the interface. In agreement with recent theoretical investigations (Eur.Phys.J. E {\bf 18} 407 (2005)) we find a strongly anistropic capillary wave spectrum. For the wave-numbers accessed in o…
Application of the 6-aminoquinolyl-N-hydroxysccinimidyl carbamate (AQC) reagent to the RP-HPLC determination of amino acids in infant foods.
2005
The validation of a pre-column derivatization procedure with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) to the determination of the amino acid content by RP-HPLC with fluorescence detection (lambda excitation 250 nm, lambda emission 395 nm) in milk-cereal based infant foods was carried out. The analytical parameters: linearity (0.0025-0.2mM), precision of the method (0.2-3.5% variation coefficients), accuracy (derivatization: 86-106% average recovery and method: 88.3-118.2% average recovery) and the limits of detection (0.016-0.367 microM) and quantification (0.044-1.073 microM) were determined. Glutamic acid, proline and leucine were the most abundant amino acid whereas the lowe…
Ionic Liquid Binary Mixtures, Zeolites, and Ultrasound Irradiation: A Combination to Promote Carbohydrate Conversion into 5-Hydroxymethylfurfural
2019
The efficient conversion of biomass into value-added compounds under mild and safer conditions is a cornerstone of present research efforts to meet the needs of the chemical industry with sustainable development. In this work, we studied the dehydration of fructose, glucose, and sucrose into 5-hydroxymethylfurfural (5-HMF), catalyzed by HY zeolite, in three ionic liquid mixtures differing for the cation, aromatic, or aliphatic. We investigated the effect of several operational parameters such as temperature, catalyst loading, zeolite counterion, solvent mixture, and added chloride. In the optimal experimental conditions, we obtained good conversions to 5-HMF especially for fructose and sucr…
Absolute and relative quantification of RNA modifications via biosynthetic isotopomers
2014
In the resurging field of RNA modifications, quantification is a bottleneck blocking many exciting avenues. With currently over 150 known nucleoside alterations, detection and quantification methods must encompass multiple modifications for a comprehensive profile. LC-MS/MS approaches offer a perspective for comprehensive parallel quantification of all the various modifications found in total RNA of a given organism. By feeding (13)C-glucose as sole carbon source, we have generated a stable isotope-labeled internal standard (SIL-IS) for bacterial RNA, which facilitates relative comparison of all modifications. While conventional SIL-IS approaches require the chemical synthesis of single mod…
Covalently Supported Ionic Liquid Phases: An Advanced Class of Recyclable Catalytic Systems
2016
In this review, the most recent advances in the synthesis and catalytic applications of covalently supported ionic liquid (IL) phases will be discussed. This class of recyclable catalytic materials is based on the covalent attachment of several types of ammonium salts, usually imidazolium, but also thiazolium, triazolium, and pyrrolidinium salts, on the surface of different supports, for example, silica, periodic mesoporous organosilica, polystyrene, magnetic-based materials, carbon nanotubes (NTs), halloysite NTs, polyhedral oligomeric silsesquioxane (POSS), and fullerenes. Moreover, poly(ionic liquid) materials, in which the IL-based structure also acts as a support, will be considered. T…
Direct HPLC Monitoring of Lipase Activity in Reverse Micellar Media
1995
Given the profusion of biotechnological applications of the nonaqueous use of lipases, we have evaluated the possibilities of exploiting the inherent advantages of high performance liquid chromatography (HPLC) for a simple, rapid assay of lipase activity in reverse micellar media, as a convenient alternative to previously reported spectroscopic methods, using both a model system and esterification reaction, and different commercial lipases. The results obtained after a screening for optimized chromatographic conditions in the reverse-phase mode indicate that a satisfactory resolution of the reaction components can be obtained following a straightforward protocol, which permits an accurate, …
Highly efficient separation of amines by electrokinetic chromatography using resorcarene-octacarboxylic acids as pseudo-stationary phases
1998
Abstract Resorcarene-octacarboxylic acids, macrocyclic molecules built up by four alkylidene-bridged resorcinol units, were synthesized and used as pseudostationary phases in electrokinetic chromatography (EKC). Resorcarenes provide a stable structure and good solubility in electrolytes even with organic modifiers. The high electrophoretic mobility of the resorcarene-octacarboxylic acids introduced here as pseudostationary phases is based on the eight partly deprotonated carboxylic groups. This offers a broad migration time window, which is the main parameter for the resolution of peaks. From three compounds with different alkyl chain lengths (C 1 , C 5 , C 11 ), the C 11 -resorcarene-octa-…
Cytotoxic effects and degradation products of three mycotoxins: Alternariol, 3-acetyl-deoxynivalenol and 15-acetyl-deoxynivalenol in liver hepatocell…
2015
This work is focused in studying the cytotoxic effects on HepG2 cells of the mycotoxins alternariol (AOH), 3-acetyl-deoxynivalenol (3-ADON) and 15-acetyl-deoxynivalenol (15-ADON) by the MTT assay, as well as in the identification of the degradation products and/or metabolites originated after treatment by liquid chromatography tandem mass spectrometry (LC-MS/MS) equipment and extracted from culture media. HepG2 cells were treated at different concentrations over 24, 48 and 72 h. The IC50 values were from 65 to 96 μM, from 3.6 to 6.2 μM and from 5.2 to 8.1 μM for AOH, 3-ADON and 15-ADON, respectively. Among all three mycotoxins assayed, deoxynivalenol (DON) derivated presented the highest to…
Identification and quantification of carotenoids including geometrical isomers in fruit and vegetable juices by liquid chromatography with ultraviole…
2004
A method was established for the identification and quantification of carotenoids including geometrical isomers in fruit and vegetable juices by liquid chromatography with an ultraviolet−diode array detector, using a C18 Vydac 201TP54 column. The mobile phase used was the ternary methanol mixture (0.1 M ammonium acetate), tert-butyl methyl ether and water, in a concentration gradient, and a temperature gradient was applied. Retinol palmitate was added as an internal standard. An extraction process (ethanol/hexane, 4:3, v/v) was performed, followed by saponification with diethyl ether/methanolic KOH (0.1%, w/v, BHT) (1:1, v/v) for 0.5 h at room temperature. Seventeen different (cis and trans…
High pressure processing of carrot juice: Effect of static and multi-pulsed pressure on the polyphenolic profile, oxidoreductases activity and colour.
2020
Abstract The aim of this study was to determine the influence of static and multi-pulsed hydrostatic pressure processing (HPP) treatments on the polyphenolic profile, oxidoreductase activity, colour, and browning index of carrot juice. Phenolic acids, flavonoids, lignans and other polyphenols were the predominant polyphenols detected with Triple-TOF-LC-MS/MS. The highest concentration of ferulic acid, didymin, dihydro-p-coumaric acid, sesaminol and matairesinol isomers were found among all the compounds detected. After HPP treatment, irrespective of the pressures applied, new simple polyphenols like oleuropein, 4-vinylsyringol, isocoumarin, and 4-hydroxybenzaldehyde were detected. Both phen…