C. Taupin

Spin labelled sarcoplasmic reticulum vesicles: Ca2+-induced spectral changes.

A growing number of reports dealing with transport ATPases, either (Na + + K+)-activated or Ca2+-activated Mg2+-dependent ATPase, support the hypothesis that reactivity of their active center for phosphorylation is controlled by the bound cations [1--5]. To investigate this hypothesis we prepared rabbit skeletal muscle sarcoplasmic reticulum fragments [6 8], since these membranes are easily isolated as vesicles in which a CaZ+-dependent ATPase is the major protein. We labelled these vesicles with a paramagnetic iodoacetamide analog [9,10], and found that the bound label exhibits an e.s.r, spectrum which is insensitive to magnesium but sensitive to calcium concentration. The spectral change occurred between 1 and 3/~M at pH 8.0 and 4°C; when the same metal buffers were used to measure the K M of formation of the phosphorylated intermediate, the value of 1.3 #M was found. We discuss the possibility that this Ca 2÷ binding-induced spectral change indeed reveals a conformational change of the ATPase molecule upon Ca binding.

Pressure—area curves of single and mixed monolayers of phospholipids and the possible relevance to properties of lung surfactant☆

Abstract This paper presents a study of the dynamic surface pressure-area (II- A ) behavior of surface film made with the major lipidic components of the pulmonary surfactant namely l -α-dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG). A Langmuir trough is used under temperature and dynamical conditions very similar to the physiological state as a model system. Several mixtures (DPPC-PG 9:1, 8:2, 7:3, and 6:4) were used and the effect of temperature was studied particularly in the gel-liquid crystalline phase transition region of the mixtures as determined by DSC. DPPC alone permits the obtainment of high surface pressures in dynamic conditions, PG itself having good respreading properties. In the transition range of the mixtures, we observed new effects; there were two pressure plateaux at compression corresponding to two collapses and one plateau at expansion. After the first cycle, a permanent cycling regime settles down. This suggests an interesting effect concerning the exogenous replacement therapy in neonatal Respiratory Distress Syndrome (RDS). This new effect is also very important in the understanding of the mechanism of action of PG and its role.

Structure of concentrated winsor microemulsions by SANS

We have performed contrast variation SANS experiments in Winsor microemulsions. We discuss the results in terms of film curvature, shown to be related to the film-water partial structure factor experimentally measured. We thus evidence that the Winsor microemulsion studied are random and bicontinuous as predicted by recent theories.

Pressure—area curves of phospholipid monolayers in relation to pulmonary surfactant

Abstract In this paper is presented a study of the dynamic surface pressure—area (Π— A ) curves of monolayers at the air—water interface. These were made with the major lipidic components of the alveolar surfactant. The synthetic phospholipids are L-α-dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG). The experiments consist of successive compression—expansion cycles of pure and mixed phospholipid surface films on a modified Langmuir balance, used under temperature and dynamical conditions very similar to those of the physiological pulmonary state. The studies were carried out at different temperatures between 22 and 37°C. The effect of temperature was particularly studied in the gel—liquid crystalline phase-transition region of the DPPC—PG mixtures, as determined by differential scanning calorimetry (DSC). From our results, we can see that pure DPPC permits the obtention of high surface pressure under dynamic conditions, whereas pure PG presents good re-spreading properties. In the transition range of the mixtures, the shape of the Π— A curves is quite different; we observe one intermediate pressure plateau on compression, and a slightly different one on expansion. In this temperature region, from the second cycle, the cycling behaviour settles down to a stable regime under the present conditions. This new effect is very interesting with regard to the mechanism of action of PG in the pulmonary surfactant and suggests a favourable effect for an exogenous replacement therapy in neonatal respiratory distress syndrome (RDS).

Interfacial transfers through an ultrathin network of variable mesh size

Abstract We study the permeabilities of a polymerized surfactant film at an oil-water interface. The molecules crossing the interface are paramagnetic spin labels, and their concentrations in the two phases are monitored by an ESR technique. The results are interpreted in terms of an average pore size S (τ) which is a decreasing function of the UV irradiation time τ for polymerization. Measurements with two labels of different size and polarity give the same pore size S (τ). The dependance of S on τ can be correlated with our earlier data on polymerization kinetics in Langmuir troughs. At large τ, however, a new effect appears, probably a thickening of the polymerized sheet.

Diffuse Interface in Oil-in-Water Microemulsions at Low Surfactant Concentration of the Brine-Toluene-n-Butanol-Sodium Dodecyl Sulfate System

The system brine (65.74%, with NaCl salinity of 6.5%), toluene (31.9%), n-butanol (2.3%) and SDS (0.04%) displays at room temperature a new type of phase equilibrium between an upper oily transparent phase and a lower oil-in-water microemulsion domain; the latter exhibits two regions different in composition and structure. The oil-microemulsion interface is sharp, while the microemulsion-microemulsion interface is diffuse, the diffuse region being a few millimeters thick. Results on the composition and structural investigations are shown in terms of index of refraction, gaschromatography and diffusion coefficient (quasi-elastic light scattering analysis). To account for the observed results, an interpretation is proposed in terms of structural change of the o/w microemulsion (droplet coalescence).

Film Flexibility of Amphiphilic Layers and Structure of Middle-Phase Microemulsions

Two applications of recent theories about microemulsions are presented. In the first part, the theoretical ideas are applied to birefringent microemulsions, leading to the first determination of the rigidity constant of the interfacial surfactant film and the demonstration of the role of the cosurfactant as decreasing this rigidity. In the second part, the structure of Winsor microemulsions is investigated by small-angle X-ray and neutron scattering, which leads to the demonstration of the existence of random bicontinuous microemulsions.

Experimental Evidence of a Nonuniform Microemulsion in the Low Surfactant Concentration Range

The sodium dodecyl sulfate (or SDS)/ n-butanol/toluene/ brine system has been selected for investigation in the low surfactant concentration range. For a 6.5% NaCl salinity and the following proportions of the other components: brine 65.74%, toluene 31.90%, n-butanol 2.30% and SDS 0.04%, the sample is composed of a transparent upper oily region, an intermediate turbid microemulsion region, and a lower transparent one. The oil-microemulsion interface is sharp; the intermediate and lower regions are separated by a diffuse interface, a few millimeters thick. Index of refraction and gas chromatographic analyses plus quasielastic light scattering (QELS) characterize the sample as composed of a non uniform vertical composition aqueous domain of microemulsion type and an excess oily solution. In the aqueous domain, two regions with constant but different index of refraction (n) and mutual diffusion coefficient (D) correspond approximately to the intermediate and lower regions and are separated by a region with progressive n and D variation. The composition and structure results at a given temperature suggest an alcohol-rich composition of the microemulsion interfacial film, the n-butanol/SDS ratio becoming larger than for usual SDS/n-butanol/toluene/brine systems. Due to this fact, an unusually low value of the rigidity constant of the interfacial film is expected. Preliminary experimental results define the thermal range in which the sample displays a diffuse interface, and show that the surfactant is near its solubilization limit for the given proportions of the other components.

Winsor Microemulsions: Evidence for Bicontinuous Structure By X-Rays and Neutron Scattering

Since the early model of ordered bicontinuous structures generated by minimal surfaces proposed by Scriven[1], two models of random bicontinuous structures[2–4] have been published in which the local curvature of the surfactant film strongly fluctuates.

Determination of the Rigidity Constant of the Amphiphilic Film in Birefringent Microemulsions, Spin-Labeling and Quasielastic Light Scattering Experiments

Much activity has been devoted to the intensive study of lyotropic systems and more specifically of microemulsions[1] because of their practical applications: oil enhanced recovery, cosmetic industry, pharmacology etc.[2]. From a more fundamental point of view, these systems are very interesting because of their fascinating properties: critical behavior[3,4], percolation transition[5], ultralow interfacial tensions[6] and extraordinarily rich phase diagrams[7,8]. The usual application of micro-emulsions recovers isotropic thermodynamically stable dispersions of water in oil (or oil in water) whose characteristic size is of order of one hundred A and thus are transparent to visible light. These systems are stabilized by a surfactant forming an interfacial film separating oil and water often associated to a cosurfactant (usually a short-tail alcohol).