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Concept

Amphiphile

Résumé

Une espèce chimique (que ce soit une molécule ou un ion) est dite amphilyophile, amphiphile, amphipathique ou bien amphipolaire lorsqu'elle possède à la fois un groupe hydrophile et un groupe hydrophobe. Structure

Le groupe hydrophobe est généralement une longue chaîne carbonée de la forme : :CH3(CH2)n, avec n compris entre 4 et 16.
Le groupe hydrophile, quant à lui, détermine la famille à laquelle appartient l'espèce amphiphile :

Espèces ioniques :

#Anioniques : #* Les carboxylates, formant des acides gras : RCO2−Na+ ; #** Les sulfates : RSO4−Na+ ; #** Les sulfonates : RSO3−Na+; #* Cationiques, généralement bactéricides et non biodégradables ;

Espèces amphotériques, par exemple les phospholipides ;

Espèces non-ioniques : un petit polymère est greffé sur un segment hydrophobe ;

Des copolymères en blocs ;

Des additifs ;

Rôle biologique Les phospholipides, une classe de molécules amphiphiles, sont les principaux composants des membranes biologiqu

Source officielle

https://fr.wikipedia.org/wiki/Amphiphile

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Séances de cours associées (23)

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Séances de cours associées

Chargement

In this work, fluorescent-based chemosensors for the detection of important analytes in aqueous solution are described. The sensors are based on different detection concepts, including analyte-induced aggregation/de-aggregation, pattern-based sensing and micelle-based sensing. In chapter 2, we present an analyte-induced aggregation-type chemosensor for the sensing of spermine. A charge-frustrated amphiphile composed of a highly fluorescent pyrene-1,3,6-trisulfonate head group and an eicosane side chain was used as a fluorescence chemosensor. Analyte-induced aggregation of the dye upon addition of spermine results in pronounced fluorescence quenching. The sensor enables the detection of spermine down to the nanomolar concentration range with good selectivity over closely related biogenic amines such as spermidine. In chapter 3, we describe a conceptually new âone-cuvetteâ sensing system for the pattern-based analysis of seven aminoglycosides antibiotics. The antibiotics include amikacin, apramycin, gentamicin, kanamycin A and B, neomycin, and paromomycin. A mixture of two amphiphiles with fluorescent head groups was used as a sensing ensemble. In buffered aqueous solution, the amphiphiles form a dynamic mixture of micellar aggregates. In the presence of aminoglycosides, the relative amount and the composition of the micelles is modified. Accurate differentiation in the low micromolar concentration range is achieved by a principal component analysis of the spectral data. Also, the sensing system allows the differentiation of pure aminoglycosides from their mixtures. In chapter 4, a fluorescent chemosensor based on analyte-induced aggregation/de-aggregation is described for the sensing of Al3+ and citric acid. In buffered aqueous solution, the amphiphilic dye can form aggregates and the aggregation of the dye is associated with a strong quenching of its fluorescence. The Al3+-induced aggregation is used to sense Al3+ in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that the non-fluorescent dye-Al3+ complex can be used as a sensing ensemble for the detection of citric acid. The assay is able to quantify the citric acid content of commercial beverages such as energy drinks. A simple micelle-based assay for the fluorescence sensing of vitamin K1 is described. In the following chapter 5, the assay enables the detection of vitamin K1 in the low micromolar concentration range. As a sensing ensemble, a mixture of the surfactant triton X-100 and 1 aminopyrene in buffered aqueous solution is employed. Vitamin K1 co-localizes with the fluorescent pyrene dye in the micelle, resulting in fluorescence attenuation by dynamic quenching. The assay displays good selectivity and can be used to determine the concentration of vitamin K1 in a commercial preparation. In chapter 6, a fluorescent-based sensor array for the optical analysis of purine derivatives is described. The array is composed of four polysufonated fluorescent dyes. The complexation of the analytes results in partial quenching of the fluorescence. The Sensor array enables the identification of ten purine derivatives including caffeine, theophylline, theobromine, purine, hypoxanthine, paraxanthine, 8-chlorotheophylline, 6-mercaptopurine, cladribine and penciclovir at low millimolar concentration. Furthermore, it is possible to use the array for obtaining information about the quantity and the purity of samples.

EPFL2015

Chargement

Interactions of highly charged polyelectrolytes with monolayers of oppositely charged amphiphiles

Vesela Malinova, Christine Wandrey

Poly(vinylbenzylammonium chloride) (PVBAC) polyelectrolytes possessing defined chain lengths, narrow chain length distributions, uniform charge d., but substituents of different hydrophilicity and size at the quaternary ammonium group were used as model compds. to study the influence of the chain length and the substituent type on the interaction with oppositely charged monolayers. Langmuir monolayers were formed from dimyristoylphosphatidic acid (DMPA). Pressure-area and pressure-time isotherms revealed an increase of both the area per amphiphile mol. and the surface pressure at const. area as a function of time if the polyelectrolyte adsorbs on the amphiphile. The compressibility of the DMPA/PVBAC complex layers is much higher than the compressibility of the DMPA monolayer. Also, the results clearly indicate the influence of the chain length and the substituent type. Larger and more hydrophobic substituents at the quaternary ammonium group significantly increase the area per amphiphile mol., from 0.42 nm2 for the amphiphile up to 0.97 nm2 for the complex. This parameter also increases with decreasing chain length. Incorporation of the hydrophobic substituents into the monolayer as well as end group effects probably are the reason for the monolayer extension. [on SciFinder (R)]

2004

Chargement

Interaction of polyelectrolytes with oppositely charged surfaces

Vesela Malinova

Despite progress during the last decade, the behavior of charged macromolecules, polyelectrolytes, including their interactions is not yet completely understood. In particular, interactions with oppositely charged surfaces, which play a significant role in many practical applications and are of central importance in life processes, need more investigation. This situation has motivated the selection of the topic of this doctoral thesis. The study is dedicated to interactions of positively charged polyelectrolytes with negatively charged surfaces considering two types of surfaces, flat amphiphile monolayers and porous surfaces of microspheres. The research aimed at quantitative evaluation of the influence of macromolecular dimensions, chemical structure, electrostatic parameters, and surface characteristics on the adsorption process. As a prerequisite, a series of poly(vinylbenzyltrialkylammonium chloride) model polyelectrolytes has been synthesized. The characteristics were five defined contour lengths with three different types of substituents at the quaternary ammonium group each in addition to uniform charge density and narrow chain length distribution. The final polyelectrolytes were the quaternization products of precursors synthesized by controlled radical polymerization. Two experimental techniques were employed to quantify the influence of chemical, macromolecular, and electrostatic parameters as well as geometrical characteristics on the adsorption of polyelectrolytes on porous microsphere surfaces. These were adsorption on microspheres suspended in aqueous phase and microspheres packed in a chromatography column. During the first technique the total surface comes immediately in contact with the polyelectrolyte molecules, whereas the second technique followed the rules of chromatography. For the first time, the contour length of the polyelectrolyte, the Debye length, the pore dimensions, as well as the chemical structure were likewise considered in a comprehensive study to describe the interaction of polyelectrolytes with well-characterized porous surfaces. A polyelectrolyte charge to surface charge ratio was defined and served to classify different adsorption behavior. Three models have been proposed to illustrate the adsorption behavior based on experimental findings and model calculations. The first one identifies the Debye length in addition to the contour length as dominating parameter, which decides whether a polyelectrolyte molecule can enter a pore or not. The second quantifies the influence of the contour length. Finally, the third describes the concentration influence on the type of molecule organization, layer formation, on the outer surface or inside of pores with diameters exceeding considerably the contour length. For amphiphile monolayer, for the first time, the influence of chain length and substituent at the quaternary ammonium group on the adsorption process was quantified. Based on the surface pressure, pressure-area and pressure-time isotherms measured, a model describing the monolayer arrangement on polyelectrolyte solutions was proposed. A second model correlates the increase of the area per amphiphile molecule and the decrease of the surface pressure with the size and hydrophobicity of the substituents. In addition chain length influence was evident. The results of the thesis contribute to progress in basic research in the field of polyelectrolytes, while also an impact on technical applications such as surface modification, chromatographic processes or improvement of materials is expected. Precise data for comparison with theoretical model calculations are provided, which were not available before.

EPFL2005

Chargement

EPFL2015

Interaction of polyelectrolytes with oppositely charged surfaces

Vesela Malinova

EPFL2005