Influence of Unsaturations on the Organization and Air Reactivity of Triglyceride Monolayers.

The behavior of Langmuir monolayers of saturated and unsaturated C18 triglycerides (TAGs) was studied as two-dimensional (2D) models for paint systems at the air-water interface or transferred onto solid films. The organization of saturated tristearin (C18:0) monolayer was probed thanks to grazing incidence X-ray diffraction: one observes a hexagonal packing of the chains perpendicular to the air-water interface, in contrast to what is described in the literature. Conversely, the mono- and polyunsaturated TAGs (triolein C18:1, trilinolein C18:2, and trilinolenin C18:3) monolayers do not present any organization at the air-water interface but do exhibit peculiar reactivity regarding the air atmosphere. The obtained results derived from the evolution of surface pressure-molecular area isotherms and monolayer compressibility under different atmospheres over time, combined with ultrahigh-vacuum infrared (UHV-FTIR) spectroscopy, showed the adsorption of O2 molecules in the monolayer together with chemical reactions with hydrocarbon chains. The kinetic effect of lead ions, known to be efficient siccative agents in oil paints, was also assessed: the addition of Pb2+ in the subphase induces an increase of the O2 adsorption.

Self-assembly of hydrophobin protein rodlets studied with atomic force spectroscopy in dynamic mode.

We have investigated the self-assembling properties of the class I hydrophobin Vmh2 isolated from the fungus Pleurotus ostreatus. Five different hydrophobin self assembled samples including monolayers, bilayers, and rodlets have been prepared by Langmuir technique and studied at the nanoscale. Local wettability and visco-elasticity of the different hydrophobins samples were obtained from atomic force spectroscopy experiments in dynamic mode performed at different, controlled relative humidity (RH) values. It was found that hydrophobins assembled either in rodlets or in bilayer films, display similar hydropathicity and viscoelasticity in contrast to the case of monolayers, whose hydropathicity and viscoelasticity depend on the adopted preparation method (Langmuir-Blodgett or Langmuir-Schaeffer). The comparison with monolayers properties evidences a rearrangement of the bilayers adsorbed onto solid substrates. It is shown that this rearrangement leads to the formation of a stable hydrophobic film, and that the rodlets structure consists in fragments of restructured proteins bilayers. Our results support the hypothesis that the observed variations in the viscoelastic properties could be ascribed to the localization of the large flexible loop, typical of Class I hydrophobins which appears free at the air interface for LB monolayers but not for the other samples. These findings should now serve future developments and applications of hydrophobin films beyond the archetypal monolayer.

Experimental evidence for an original two-dimensional phase structure: an antiparallel semifluorinated monolayer at the air-water interface.

We show the spontaneous formation of an antiparallel monolayer of diblock semifluorinated n-alkane molecules spread at the air-water interface. We used simultaneous measurements of surface pressure and surface potential versus molecular area and performed grazing x-ray reflectivity experiments to characterize the studied monolayer, which is obtained at almost zero surface pressure and precedes the formation of a bilayer at higher surface pressure. Its thickness, equal to 2.7 nm, was found to be independent of the molecular area. This behavior may be explained by van der Waals and electrostatic interactions.

Architecture-controlled "SMART" Calix[6]arene self-assemblies in aqueous solution.

Self-assemblies of a calix[6]arene (1) functionalized at the small rim by three imidazolyl arms and at the large rim by three hydrophilic sulfonato groups have been studied in water. Transmission electron microscopy, atomic force microscopy, and in situ dynamic light scattering showed that 1 forms multilamellar vesicles at a concentration equal to or higher than 10(-4) M. At pH 7.8 and 10(-4) M, the multilamellar vesicles present a relatively large polydispersity (50-250 nm in diameter). However, after sonication unilamellar vesicles of much lower polydispersity and smaller size are obtained. The impact of the pH and the presence of Ag+ ions have also been investigated. Whereas increasing the pH led to the formation of giant vesicles (450 nm), monodisperse vesicules of 50 nm were obtained at a pH (6.5) that is only slightly higher than the pKa of the tris(imidazole) core of 1. Most interestingly, in the presence of silver ions, micelles (2.5 nm large) were obtained instead of vesicles. These observations are attributable to the imidazole core in 1 that is not only sensitive to the presence of protons but also can bind a silver cation. The resulting geometrical change in the monomeric units triggers the collapse of the vesicles into micelles. This shows that the implementation of an acid-base functionality such as an imidazole group in the hydrophobic core of the amphiphilic calix[6]arene makes the aggregation architecture responsive to the pH and to metal ions.

Radiation-induced synthesis and cryo-TEM characterization of silver nanoshells on linoleate spherical micelles.

We combine the self-assembly properties of amphiphilic molecules with the radiolysis method to produce specific sizes and shapes of metallic nano-objects. Radiolysis is used to synthesize core--shell structures consisting of nanometric linoleate spherical micelles as the core and silver as the shell. The validity of the technique is asserted by cryoelectron microscopy, which is an adequate technique for low density contrasts and core--shell structures. The shells are found to be homogeneous with a size of a few nanometers. Images are used to bring forward the hypothesis of the fabrication process.