Marteau C.,University Lille1 and |
Favier D.,International Flavors and Fragrances Research and Development |
Nardello-Rataj V.,University Lille1 and |
Aubry J.-M.,University Lille1 and
Food Chemistry | Year: 2014
During the DPPH scavenging assay carried out in non polar and non protic solvents, such as toluene, BHT regenerates α-tocopherol from tocopheryl radical, whereas in polar and protic solvents, like methanol, no regeneration is observed due to a fast electron transfer reaction from the tocopheryl radical to the reactive DPPH radical. Surprisingly, in the presence of a small amount of alcohol, the synergy is exalted and BHT regenerates twice as much α-tocopherol due to a nucleophilic addition of short alcohols on the BHT oxidation product, giving a new phenolic co-antioxidant. © 2014 Elsevier Ltd. All rights reserved.
De Viguerie L.,Marcoule Institute for Separative Chemistry |
Mouret A.,University Lille1 and |
Brau H.-P.,Marcoule Institute for Separative Chemistry |
Nardello-Rataj V.,University Lille1 and |
And 2 more authors.
CrystEngComm | Year: 2012
The present study investigates the deposition of hybrid organic/inorganic monolayers composed of polyoxometalate (POM) of the Keggin-type [PW 12O40]3- electrostatically linked to three alkylammonium surfactants. The surface pressure dependence, i.e. Langmuir isotherm, as well as their 2D self-assembly has been investigated with mono- and double-chained surfactants and by varying the alkyl chain length. Stable monolayers were obtained for the hexadecyltrimethylammonium and the didodecyldimethylammonium POM surfactants, called respectively C16POM and 2C12POM. It was found that increasing the surface pressure led to the formation of crystallized nano- and micro-domains in coexistence with the monolayer. The crystallites formed were monodisperse in their size repartition and showed various shapes and sizes: oblate nanoparticles of nanometric size (height ca. 7 nm, diameter ca. 140 nm) for C16POM and micrometric 2D-hexagonal crystallites for 2C12POM. The monolayers and the micro-(nano-) crystallites have been characterized after transfer on silicon wafers by means of atomic force microscopy (AFM), transmission electron microscopy (TEM) and surface-enhanced ellipsometric contrast (SEEC). High crystallinity of the hexagonal aggregates was revealed by electron diffraction (ED). For 2C12POM the monolayer formed before crystallisation is in a 2D-liquid state with the alkyl chains pointing out of the water with an average angle of the alkyl chains to the normal of the plane estimated at 50°. It is shown that the surface pressure induced crystallization of the POM surfactant results in the change of the ammonium surfactant arrangement around the POM with the alkyl chains pointing up and down the POM units showing a reverse bilayer-like structure. This change in the ammonium surfactant arrangement in response to the increase of the surface pressure enables (i) to reduce the molecular area and (ii) the formation of a 2D-hexagonal crystalline lattice of POM units. On the other hand for C16POM the formation of oblate nanoparticles is driven by a three-dimensional growth at the water surface. This journal is © The Royal Society of Chemistry.
Rauwel G.,Laboratoires Anios |
Rauwel G.,University of Lille Nord de France |
Leclercq L.,University of Lille Nord de France |
Leclercq L.,University Lille1 and |
And 5 more authors.
Journal of Colloid and Interface Science | Year: 2012
Mixed aggregate formation and synergistic interactions of binary surfactant mixtures of di-n-decyldimethylammonium chloride, [DiC 10][Cl], with polyoxyethylene alkyl ethers, C iE j (i= 10, 12, j= 4, 6, 8), have been investigated for various [DiC 10][Cl]/C iE j ratios. The critical aggregation concentration of the binary mixtures has been determined by tensiometry, and the aggregate characteristics (i.e., size and composition, free ammonium concentration) have been estimated using the pulsed field gradient NMR spectroscopy and a [DiC 10]-selective electrode. Diffusion coefficient measurements of micelles confirmed the synergistic interaction between the surfactants. It is thus shown that the formation of surface monolayers and mixed aggregates from [DiC 10][Cl]/C 10E j mixtures is driven by both tail/tail and head/head interactions, whereas [DiC 10][Cl]/C 12E j co-aggregation is mainly driven by tail/tail interactions. As a consequence, the co-aggregation phenomenon notably influences the biocidal activity of [DiC 10][Cl] on the Candida albicans fungi. In the presence of C 12E j, the biocidal activity of the ammonium salt is inhibited due to the trapping of the cationic surfactants in the mixed aggregates, whereas in the presence of C 10E j, the biocidal activity of the surfactant mixture is maintained. The mode of action is also confirmed by a faster increase in the zeta potential of a C. albicans suspension in the presence of [DiC 10][Cl]/C 10E 8 than in the presence of [DiC 10][Cl]/C 12E 8. Therefore, a judicious adjustment of the alkyl (i) and polyoxyethylene (j) chain lengths of C iE j avoids its antagonistic effect on the biocidal activity of [DiC 10][Cl]. © 2012 Elsevier Inc.