Search results for "aqueous solution"
showing 10 items of 1610 documents
Preferential localization of Lactococcus lactis cells entrapped in a caseinate/alginate phase separated system.
2013
International audience; This study aimed to entrap bioprotective lactic acid bacteria in a sodium caseinate/sodium alginate aqueous two-phase system. Phase diagram at pH = 7 showed that sodium alginate and sodium caseinate were not miscible when their concentrations exceeded 1% (w/w) and 6% (w/w), respectively. The stability of the caseinate/alginate two-phase system was also checked at pH values of 6.0 and 5.5. Lactococcus lactis subsp. lactis LAB3 cells were added in a 4% (w/w) caseinate/1.5% (w/w) alginate two-phase system at pH = 7. Fluorescence microscopy allowed to observe that the caseinate-rich phase formed droplets dispersed in a continuous alginate-rich phase. The distribution of …
Modelling of proton and metal exchange in the alginate biopolymer.
2005
Acid-base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1or=I/mol l(-1)or=1.0) and in different supporting electrolytes (Et4NI, NaCl, KCl, LiCl, NaCl+MgCl2), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H+]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (alpha) using different models (Henderson-Hasselbalch modified, Högfeldt three parameter…
Investigation of the aqueous transmetalation of π-allylpalladium with indium salt: the use of the Pd(OAc)2–TPPTS catalyst
2005
pi-Allylpalladium complexes could be generated in water by the palladium(0) water soluble catalyst prepared in situ from palladium acetate and TPPTS. These complexes were transmetalated with indium to react with benzaldehyde. The aqueous solution of Pd(0)(TPPTS)(n) could be reused without deterioration of the catalyst in the first and second recycling. The system proved to be efficient with primary and secondary allylic substrates. The stereochemical outcome of the allylation through umpolung of allylpalladium, was also studied using models with a restraint conformation.
Reduction of Dinitrogen to Ammonia in Irradiated Heterogeneous Systems
1988
The recent developments of the research in the field of dinitrogen reduction to ammonia at mild conditions of pressure and temperature are reported. After a brief historical recapitulation of the traditional thermal process, the new routes for NH3 synthesis (biological photosynthesis, direct electrochemical reduction, and photocatalytic reduction) are presented and critically discussed. A particular attention is devoted to heterogeneous photocatalytic reduction performed by irradiating pure, mixed, and doped semiconducting catalysts in gas-solid and liquid-solid systems. The fixation of dinitrogen in aqueous solutions containing complexes and photoactive particulate systems is also reported…
Imidazolsynthesen, 8. Mitt.: N-Substituierte Imidazole nach Weidenhagen
1976
Die Weidenhagen-Synthese N-unsubstituierter Imidazole aus α-substituierten Carbonylverbindungen 1, Aldehyden 3, wasrigem Ammoniak (4) und Kupfer(II)-salzen als Oxidationsmittel ist in Gegenwart primarer Amine 5 auch zur Darstellung N-substituierter Imidazole 6 geeignet. Weidenhagen Synthesis of N-Substituted Imidazoles The Weidenhagen synthesis of N-unsubstituted imidazoles from α-substituted carbonyl compounds 1, aldehydes 3, and aqueous ammonia (4) with copper (II) salts as oxidizing agents is also usable for the synthesis of N-substituted imidazoles 6 through the addition of primary amines 5.
Thioflavin T Hydroxylation at Basic pH and Its Effect on Amyloid Fibril Detection
2008
The fluorescent dye thioflavin T (ThT) is commonly used for in situ amyloid fibril detection. In this work, we focused on the spectroscopic properties and chemical stability of ThT in aqueous solution as a function of pH, temperature, and dye concentration. A reversible hydroxylation process occurs in alkaline solutions, which was characterized using a combination of UV-vis absorption spectroscopy, proton NMR, and density functional theory (DFT). On the basis of these studies, we propose a chemical structure for the hydroxylated form. Finally, by means of fluorescence spectroscopy, ThT hydroxylation effects on in situ amyloid detection have been investigated, providing new insights on the e…
Fully Automated Electric-Field-Driven Liquid Phase Microextraction System with Renewable Organic Membrane As a Front End to High Performance Liquid C…
2019
This article reports for the first time a programmable-flow-based mesofluidic platform that accommodates electric-field-driven liquid phase microextraction (μ-EME) in a fully automated mode. The miniaturized system is composed of a computer-controlled microsyringe pump and a multiposition rotary valve for handling aqueous and organic solutions at a low microliter volume and acts as a front-end to online liquid chromatographic separation. The organic membrane is automatically renewed and disposed of in every analytical cycle, thus minimizing analyte carry-over effects while avoiding analyst intervention. The proof-of-concept applicability of the automated mesofluidic device is demonstrated b…
Application of solid-phase microextraction combined with derivatization to the determination of amphetamines by liquid chromatography
2004
This work evaluates the utility of solid-phase microextraction (SPME) in the analysis of amphetamines by liquid chromatography (LC) after chemical derivatization of the analytes. Two approaches have been tested and compared, SPME followed by on-fiber derivatization of the extracted amphetamines, and solution derivatization followed by SPME of the derivatives formed. Both methods have been applied to measure amphetamine (AP), methamphetamine (MA), and 3,4-methylenedioxymethamphetamine (MDMA), using the fluorogenic reagent 9-fluorenylmethyl chloroformate (FMOC) and carbowax-templated resin (CW-TR)-coated fibers. Data on the application of the proposed methods for the analysis of different kin…
Automated Photo-Induced Fluorescence Determination of Flumetsulam
2009
The present article deals with a new procedure for determination of the herbicide flumetsulam. The fluorimetric procedure is performed on the basis of photo-increased fluorimetric emission of the pesticide solution and by means of a multicommutation continuous-flow assembly. The alkaline solution containing the analyte is irradiated online and then directly forced through the fluorimeter flow cell. The analysis of different samples is completely automated, as the analyte separation was performed online by including a separation cartridge in the manifold. When dealing with solid samples (such as soil samples), the automation was completed by adding to the manifold the corresponding device fo…
Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.
2005
Abstract The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o -phthaldialdehyde (OPA)– N -acetyl- l -cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA–NAC derivatives formed. The proposed conditio…