Nicole Kamenka

Some aspects on the hydration of surfactant micelles

A review of the hydration properties of surfactant micelles is presented. Water self-diffusion studies are foundto give global hydration numbers corresponding approximately to the hydration of the counterions and the polar head-groups. The hydration numbers are inconsistent with water penetration into micelles and other arguments against such an effect are discussed as well. Furthermore, the hydration of counterions and the effect of solubilization on hydration are discussed. Sodium cholate differs considerably in its self—association behaviour from micelle-forming amphiphiles and this is found to apply also for the hydration characteristics.

Aggregation, aggregate composition, and dynamics in aqueous sodium cholate solutions

The translational mobility of aggregates formed in aqueous sodium cholate solutions was obtained from the self-diffusion coefficient of solubilized decanol, which was determined using the capillary tube method with radioactive labeling. Combining these results with the self-diffusion coefficients of cholate ions, sodium ions, and water molecules the following quantities were determined as a function of cholate concentration: the fraction of cholate aggregated, the ratio of counterions and cholate ions in the aggregates, and the hydration number of the aggregates. All the quantities considered differ in their concentration dependences from those of typical micelle forming long chain ionic surfactants. There seems to be no distinctly favored aggregate size but rather the aggregate radius and aggregation number increase progressively with increasing concentration. The aggregation number is much smaller than for typical surfactant micelles. The deduced fraction of aggregated cholate shows that association progresses continuously over a wide concentration range without a well-defined critical micelle concentration. Sodium ion binding to cholate aggregates is highly variable with a rapid increase taking place above 0.1 mole/kg, a conclusion which may also be drawn from 23Na chemical shift and relaxation data. The counterion binding is discussed in relation to the so-called ion condensation model, found to apply with good approximation for simple surfactant aggregates, and in relation to the progressive cholate aggregation. The aggregates are rather strongly hydrated and the hydration number shows a peculiar concentration dependence. Information on the orientation of cholate within the aggregates is deduced by combining deuterium NMR relaxation data of deuterated cholate with the diffusion results. The order parameter is rather insensitive to concentration and points to a packing of cholate in the aggregates which does not change appreciably with concentration and which corresponds to a marked mobility of cholate within the aggregates.

Translational motion and association in aqueous sodium cholate solutions

Abstract Self-association in aqueous sodium cholate solutions was studied at 25°C by determining the translational self-diffusion coefficients of water molecules, cholate ions, and sodium ions. Association was found to be much more gradual than for simple surfactants. Thus association starts at a concentration of about 0.014 mole/kg and progresses continuously up to the highest concentrations studied (0.5 mole/kg). The counterion association degree, which was derived from the sodium ion diffusion coefficient, is much lower than for typical micelle-forming substances. From the concentration dependence of the water self-diffusion coefficient the micellar hydration number was estimated. Hydration was found to be much more extensive than for simple surfactant micelles.

Mixed micelle-to-vesicle transition in aqueous nonionic phospholipid systems

Abstract We have investigated the aggregation behavior in aqueous solutions of mixed systems formed by one nonionic surfactant (Triton X-100 or C12E8) and one phospholipid (egg lecithin or dipalmitoylphosphatidylcholine) by means of quasiclastic light scattering and tracer self-diffusion using radioactive labeling. The size of the mixed micellar aggregates depends on the surfactant lipid ratio and increases with phospholipid content. Dilution of the solutions with the highest phospholipid nonionic surfactant ratio induces a transition from mixed micelles to vesicles.

Dodecylbetaïne micelle formation from fourier transform 1H NMR and tracer self-difusion studies

Abstract Micellization of a zwitterionic surfactant, n -dodecylbetaine, was investigated in multicomponent NMR and tracer self-diffusion studies. Self-diffusion coeffecients were measured for amphiphile ion, water molecules, and solubilized decane and decanol molecules. The aggregated are spherical in a large concentration range, the free amphiphile concentration remains equal to the CMC, and the hydration numbers are low. These results are compared with the micellization of ionic surfactants.

Solution behaviour of hydrophilic bile salts: pathophysiological implications

Abstract A series of bile salt solutions were investigated in order to determine the hydrophilic-hydrophobic balance of individual bile salts. Potentiometric titration, cholesterol and bile acid solubilization and surface tension were employed. Hydrophilicity greatly depended on the number, position and orientation of hydroxyl groups. It decreased as follows: β muricholate (3α,6β,7β triOH) > ursodeoxycholate (3α,7β diOH) > hyocholate (3α,6α,7α triOH)≈hyodeoxycholate (3α,6α diOH) > chenodeoxycholate (3α,7α diOH). Taurochenodeoxycholate, tauroursodeoxycholate and β muricholate were infused in bile fistula rats to evaluate their acute effects on liver and bile secretion. Taurochenodeoxycholate infusion led to severe cholestasis. In contrast, the hydrophilic species tauroursodeoxycholate and β muricholate were hypercholeretic, were not hepatotoxic and were able to protect the liver against the cytotoxicity of the hydrophobic bile salt. Ursodeoxycholic acid was also found to be hepatoprotective when given for 1 year to patients suffering from cystic fibrosis and hepatopathy. It improved standard liver function tests by decreasing both cholestasis and cytolysis.

Micellar Structure in Intestinal Bulk — Relations with Mucosal Uptake

From measurements of translational self-diffusion coefficients and from solubility characteristics of bile salt mixed micelles, we have investigated some molecular associations between the major lipids of the intestinal aqueous content in an attempt to correlate the cholesterol flux into the intestinal mucosal cells with the structure of micellar solutions.