Pierre Lesieur

DSC And X-Ray Diffraction Coupling

A new technique, that allows simultaneous time-resolved synchrotron X-ray diffraction as a function of temperature (XRDT) and high sensitivity DSC to be carried out in the same apparatus, has been developed. Microcalorimetry and XRDT scans can be performed at any rate between 0.01 and 10°C min−1 with a 0.01°C temperature resolution in the temperature range, 30–130°C and at lower cooling rates but the same heating rates in the −30–+30°C range. The use of a single and very small sample (1 to 20 μl) contained in a thin glass capillary for both measurements and simultaneous data collection prevents any temperature shift between recordings and any possible difference in the thermal histories of the samples.

Phase behavior of fully hydrated DMPC-amphiphilic cyclodextrin systems.

With the aim of exploring relationships between the chemical structure and the physico-chemical properties of amphiphilic beta-cyclodextrin, a reappraisal of the obtaining of pure heptakis (2,3-di-O-hexanoyl)-beta-cyclodextrin (beta-CDC(6)) was undertaken. In this paper the chemical characterization of the newly synthesized beta-CDC(6) and its ability to form mixed structures with dimyristoylphosphatidylcholine (DMPC) are reported. Miscibility of the two amphiphiles is examined: (i) in monolayers formed at the air-water interface by analyzing the surface pressure-area isotherms; and (ii) in fully hydrated mixtures by differential scanning calorimetry (DSC) and X-ray diffraction at small and wide angles. Results demonstrate that the beta-cyclodextrin derivative is partially miscible to the phospholipid: intimate mixing occurs at beta-CDC(6) molar ratios smaller than 7-15 mol%, depending on the dimensional scale considered, while beyond these compositions phase separation is observed. At the air-water interface, the miscibility region of the two compounds shows non-ideal behavior characterized by the non-additivity of the molecular areas in the mixed monolayers. At the three-dimension level, the formation of a beta-CDC(6)/DMPC mixed lamellar phase occurs except at beta-CDC(6) molar ratios close to 5 mol% at which a highly ordered structure is depicted below the solid-to-liquid state transition of the DMPC hydrocarbon chains. At beta-CDC(6) contents higher than 7 mol%, the mixed assemblies coexist with excess amphiphilic cyclodextrin which then forms a separated hexagonal structure.

pH-sensitive liposomes as a carrier for oligonucleotides: a physico-chemical study of the interaction between DOPE and a 15-mer oligonucleotide in quasi-anhydrous samples

pH-sensitive liposomes made of dioleoylphosphatidylethanolamine (DOPE)/oleic acid (OA)/cholesterol (CHOL) mixtures were shown to be very promising carriers for oligonucleotides (ON). However, it appeared necessary to clarify the structural consequence of the interactions of ON with the liposome, and especially on DOPE, the lipid responsible for the pH sensitivity. The present study was carried out by differential scanning calorimetry and X-ray diffraction, at low hydration. In such a case, DOPE generally adopt a hexagonal phase. It could be shown that ON increased DOPE transition temperature and increased v/al, as a result of electrostatic interactions between ON and DOPE headgroups. OA was found to have exactly opposite effects, its presence between DOPE molecules inhibiting the formation of hydrogen bonds. The presence of both ON and OA allowed the system to organize in a lamellar phase below the solid/liquid transition, whereas above this temperature ON preferably interacted with DOPE in a hexagonal phase and led OA to separate.

pH-Sensitive liposomes as a carrier for oligonucleotides: a physico-chemical study of the interaction between DOPE and a 15-mer oligonucleotide in excess water

The cytoplasmic delivery of drugs encapsulated into pH-sensitive liposomes is under the control of a lamellar-to-hexagonal transition. In a previous study, under anhydrous conditions, oligonucleotides (ODN) encapsulated in pH-sensitive liposomes composed of dioleoylphosphatidylethanolamine (DOPE)/oleic acid (OA)/cholesterol (CHOL) were shown to modify the phase behaviour of DOPE. In the present study, the lipid/ODN interactions were evaluated in fully hydrated samples by surface tension measurements, differential scanning calorimetry, X-ray diffraction and turbidimetry. Concerning the lipids, it was shown that OA provoked a disorganisation of DOPE lamellar phases and led to the complete disappearance of hexagonal transition along with heating. The addition of CHOL further decreased the lipid packing in the bilayers. Concerning ODN, these molecules provoked an increase in the surface pressure of a DOPE/OA/CHOL monolayer, indicating the existence of molecular interactions with the lipids. At a supramolecular level, ODN induced a more ordered organisation of DOPE molecules in the lamellar and hexagonal phases, and completely abolished the disorganisational effect of OA and CHOL.

Does sucrose influence the properties of DMPC vesicles

Small-angle neutron and X-ray scattering, dynamic light scattering, X-ray diffraction coupled with differential scanning calorimetry, and Raman spectroscopy were applied to investigate unilamellar (ULVs) and multilamellar (MLVs) dimyristoylphosphatidylcholine (DMPC) vesicles in aqueous sucrose solutions with sucrose concentrations from 0 to 60% w/w. In case of ULVs, the addition of sucrose decreases the polydispersity of vesicle population. A minimum value of polydispersity was found at 20% sucrose. For sucrose concentration from 0 to 35% oligolamellar vesicles in the ULV population have a minimum presence. Vesicles with 5-10% sucrose exhibit the best stability in time. For the case of MLVs, sucrose influences the temperature of the phase transitions, but the internal membrane structure remains unchanged.

Dependence of the form factor of ganglioside micelles on a conformational change with temperature

Abstract The gangliosides GM2, GM1 and GD1b, biological amphiphiles with a double tail hydrophobic part and an oligosaccharide chain headgroup, form micelles in solution. Light scattering experiments have shown that ganglioside micelles which have gone through a temperature cycle have a smaller molecular mass and hydrodynamic radius than those which have been kept at room temperature. This fact has been interpreted with the hypothesis that, with temperature, the ganglioside molecules undergo a conformational change which affects their micellar properties appreciably. Careful small angle X-ray experiments, aimed to confirm the light scattering data and to evidence differences in the micellar internal structure are presented. Ganglioside micelles are quite inhomogeneous particles with respect to X-ray scattering, since there is a large contrast variation between the inner lipid part and the external hydrated sugar layer. Experimental form factors are fitted with a double-shell oblate-ellipsoid model.

Sodium Taurocholate-Induced Lamellar-Micellar Phase Transitions of DPPC

The thermotropic transitions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and the structural changes of its lamellar phases have been studied between 0 and 50°C by both DSC and synchrotron small angle X-ray diffraction/scattering as a function of temperature (XRDT) and sodium taurocholate concentration [TC] in the 0–40 mM range ([DPPC]=50 mM) at pH 7.4. The existence of multiple phase transitions (up to 5 peaks within a 5°C interval) in a narrow domain of temperature between 25 and 42°C depending on the [TC]/[lipid] ratio was observed in the DSC curves. XRDT showed that at low ratios they might correspond to transitions between lamellar phases, the structural characteristics of which are given. At higher ratios a lamellar to micellar transition was observed, and the temperature at which it was observed decreased as a function of the TC content. The relationships with DPPC vesicle bilayer permeabilization and solubilization are discussed.

X ray diffraction study of Langmuir-Blodgett mono- and multi-layers

Abstract Langmuir-Blodgett (LB) films are often proposed as candidates for molecular electronics. In fact, the deposition technique allows an easy and good control of the structure along the normal to the surface (B. Belbeoch, M. Roulliay, M. Tournarie, 82 (1985) 701–706). However, only few information has been obtained about in plane structure of LB films. Mono- and multi-layers of docosanoic acid have been studied by X-ray transmission diffraction and infrared spectroscopy. For that purpose, LB layers have been deposited onto collodion membranes which present good mechanical properties and give rise to low background signal for the two characterisation techniques. Deposition of the layers occurred at room temperature and a surface pressure π = 36 mN/m. No salt was added to the underlying water. Different samples were prepared, either with a single monolayer deposited on the upstroke, with a double layer (with first layer deposited on the down stroke) or with multilayers. X-ray diffraction has been performed on beam line D24 at LURE by using a Weissenberg chamber equipped with image plates and infrared absorption was used to control the quality and the number of deposited layers. X-ray diffraction is known to work well with multilayers. In the present work, good signal has been obtained from only 2 layers (one on each side of the collodion membrane). Several diffraction rings have been obtained in these conditions. The structure of the monolayer is compared to that of the multilayers.

Small-angle X-ray scattering structural investigations of starburst dendrimers in solution

A series of polyamidoamine dendrimers (generations 1.5–4.0, with ethylenediamine as the central core) has been investigated in methanol solution by means of the small-angle X-ray scattering technique. The comparative analysis of the structural properties of integer and half-integer generations of the dendrimers seems to be dominated by rather different trends.

Normalisation of linearly collimated ultra-small-angle X-ray scattering (USAXS) data: Influence of crystal resolution and photon energy☆

Abstract A double crystal multiple reflection camera as proposed by Bonse and Hart allows the measurement of ultra-small-angle scattering. Data obtained from this type of camera are linearly collimated unless cross crystals (or very narrow slits) are introduced. The goal of this paper is to give a simple rule of thumb to normalise data (without desmearing) when the infinite slit collimation is practised. Great attention is paid to checking the procedure experimentally. By using biased channel cut crystals, the resolution of the camera is varied and its influence on the data is analysed. Furthermore, experimental scattering data obtained with Cu Kα and Mo Kα radiations are converted to an absolute scale and compared quantitatively.