We study the sponge phase of the mixed non-ionic/ionic surfactant system C₁₄DMAO–TTAB–hexanol–brine. Our aim is to determine if this phase exists in this mixed system and if it preserves or changes its structure when the relative amount of the charged surfactant is increased in the mixture. SAXS, FFEM, and conductivity results show that for the same bilayer volume fraction the sponge phase preserves its global structure. We propose a method to determine the geometrical obstruction factor from electrical conductivity measurements in ionic sponge phases. Analysis of lamellar phases in the same system shows that the bilayer thickness increases when the ionic surfactant concentration is increased.

The forced Rayleigh light scattering technique has been applied to measurements of thermal diffusivity in liquid crystalline phases. In the nematic phase of p-methoxy benzylidene p-n-butyl aniline (MBBA), our results are in good agreement with the data obtained by classical methods. The thermal diffusivity anisotropy in smectic A and B phases has been measured here for the first time in p-butoxy benzylidene p-n-butyl aniline (BBOA). As in the nematic phase, the thermal diffusivity parallel to the long molecular axis is greater than perpendicular to it, i.e. D _| > D _⊥. It is particularly striking that the thermal properties do not change significantly at the nematic to smectic phase transition. This suggests that the thermal diffusivity does not depend on the long range order properties of the various mesophases in a crucial manner, contrary to other transport properties such as the electrical conductivity. A tentative description of the thermal transport in terms of high frequency phonons seems adequate to explain our observations.

Interactions between hydrophobic chains of lipid monolayers and interactions between hydrophilic headgroups of lipid bilayers (with or without a molecular recognition step) are now well documented, especially for commonly used lipids. Here, we report force measurements between a new class of fluorinated lipid layers whose headgroups (synthetic ligands of retinoid receptors) display a very unusual polar/apolar character and can interact via a combination of hydrophobic forces and hydrogen bonds. Although these two interactions produce adhesion and are therefore not easily distinguishable, we show that it is possible to extract both contributions unambiguously. Experiments are performed both in pure water, where the adhesion is a combination of hydrophobic forces and hydrogen bonds, and in Tris buffer, where the hydrophobic effect is the dominant short-range attractive force. The contribution of hydrophobic forces scaled down to molecular interactions is deduced from force versus distance profiles, and the same value is found independently in pure water and Tris buffer, about 1 k_BT. We also show that retinoid lipid layers attract each other through a very long-range (100 nm) exponential force, which is insensitive to the pH and the salinity. The origin of this long-range attraction is discussed on the basis of previously proposed mechanisms.

We have observed large pores in the membrane of giant vesicles in an aqueous medium. The lifetime of the pores can reach 2min and their size (a few micrometers) enables their visualization by fluorescence microscopy. These pores are obtained thanks to a destabilization of the membrane due to the synergistic action of a cone-shaped and nitrobenzodiazole (NBD) labeled phospholipid illuminated in the presence of dithionite. The opening of the pore occurs immediately after illumination starts so that it can be accurately triggered. A concomitant decrease of the vesicle radius is observed; we interpret it as a solubilization of the membrane. Depending on the rate of this solubilization, long- or short-lived pores were observed. At the transition between both regimes for a 30μm vesicle, the solubilization rate was about 1/300s−1. In order to interpret these observations, we have revisited the current model of pore opening to take into account this solubilization. This proposed model along with simulations enables us to prove that solubilization explains why the large long-lived pores are observed even in an aqueous medium. The model also predicts the solubilization rate at the transition between a single long-lived pore and a cascade of short-lived pores.

Serum albumin is the most abundant protein in the circulatory system. The ability of albumins to undergo a reversible conformational transition, observed with changes in pH, is conserved in distantly related species, suggesting for it a major physiological role possibly related to the transport of small molecules including drugs. We have followed changes of bovine serum albumin (BSA) in volume by densimetry and in adiabatic compressibility during its conformational transition from pH 7–2, using ultrasound measurements. In parallel, circular dichroism was measured. The volume and adiabatic compressibility decrease from pH 4 to 2. The change in ellipticity shows a decrease over the same pH range from 70% to 40% of its α-helix content. Sorbitol, at concentrations from 0 to 2 M, led to the progressive restoration of BSA volume and compressibility values, as well as a substantial recovery of its original α-helix content. This finding implies that the compressibility variation observed reflects the conformational changes during the transition. The mutual interactions of the mechanical properties and structural features of BSA reported here are important in biotechnology for research in material sciences and for the design and the development of new, tailor-made drug carriers.