Bile salts micellar shape

Under these considerations, the analysis of the energetics of size and shape of the micelles becomes of interest. The spherical shape would be the most stable structure if the monomers aggregate with a minimum of other constraints needed to satisfy the forces as described under Chap. 2.3, because this gives the minimum surface area of contact between the micelle and the solvent. On the other hand, if large constraints exist, other possible shapes, e.g. ellipsoids, cylinders or bilayers would be present [1,4]. It is obvious that micelles as formed by non-linear surfactants, e.g. bile salts etc., can not be analyzed by these theories, because steric hinderance gives rise to rather small aggregation numbers [1,3,4, 12,32,33,34,35,36,37,38,39,40]. In the case of spherical micelles of linear alkyl chain surfactants, with aggregation numberm, the radius, R, and total volume, V, and micellar surface area, A, we have ... 

Ekwall and Baltcheffsky [265] have discussed the formation of cholesterol mesomorphous phases in the presence of protein-surfactant complexes. In some cases when cholesterol is added to these solutions a mesomorphous phase forms, e.g. in serum albumin-sodium dodecyl sulphate systems, but this does not occur in serum albumin-sodium taurocholate solutions [266]. Cholesterol solubility in bile salt solutions is increased by the addition of lecithin [236]. The bile salt micelle is said to be swollen by the lecithin until the micellar structure breaks down and lamellar aggregates form in solution the solution is anisotropic. Bile salt-cholesterol-lecithin systems have been studied in detail by Small and coworkers [267-269]. The system sodium cholate-lecithin-water studied by these workers gives three paracrystalline phases I, II, and III shown in Fig. 4.37. Phase I is equivalent to a neat-soap phase, phase II is isotropic and is probably made up of dodecahedrally shaped lecithin micelles and bile salts. Phase III is of middle soap form. The isotropic micellar solution is represented by phase IV. The addition of cholesterol in increasing quantities reduces the extent of the isotropic... 

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