Bile salts ternary systems

The ternary diagrams in Fig. 4.37 indicate the complexity of the bile salt-lecithin systems especially in the presence of cholesterol which limits the extent of the isotropic micellar phase (IV) in particular. Intense interest in these systems has been generated in the search for the cause of cholelithiasis. Of great importance in understanding gallstone formation is how cholesterol, which is a major... 

KP and v can, in contrast to kp, not be determined via the concentration gradient for binary and ternary mixed micelles, because for the calculation of the Nemstian distribution a constant CMC and an almost constant partial molar volume must be assumed. The calculation of aggregation constants of simple bile salt systems based on Eq. (4) yields similar results (Fig. 8b). Assuming the formation of several concurrent complexes, a brutto stability constant can be calculated. For each application of any tenside, suitable markers have to be found. The completeness of dissolution in the micellar phase is, among other parameters, dependent on the pH value and the ionic strength of the counterions. Therefore, the displacement method should be used, which is not dependent on the chemical solubilization properties of markers. For electrophoretic MACE studies, it is advantageous for the micellar constitution (structure of micelle, type of phase micellar or lamellar) to be known for the relevant range of concentrations (surfactant, lipids). 

When a bicontinuous cubic lipid-water phase is mechanically fragmented in the presence of a liposomal dispersion or of certain micellar solutions e.g. bile salt solution), a dispersion can be formed with high kinetic stability. In the polarising microscope it is sometimes possible to see an outer birefringent layer with radial symmetry (showing an extinction cross like that exhibited by a liposome). However, the core of these structures is isotropic. Such dispersions are formed in ternary systems, in a region where the cubic phase coexists in equilibrium with water and the L(x phase. The dispersion is due to a localisation of the La phase outside cubic particles. The structure has been confirmed by electron microscopy by Landh and Buchheim [15], and is shown in Fig. 5.4. It is natural to term these novel structures "cubosomes". They are an example of supra self-assembly. 

Small, D. M., Bourges, M., and Dervichian, D. G., Ternary and quartemary aqueous systems containing bile salt, lecithin and cholesterol. Nature (London) 211, 816-818... 

In an earlier review [3], mixed micelles formed by bile salts were classified into those with (i) non-polar lipids (e.g., linear or cyclic hydrocarbons) (ii) insoluble amphiphiles (e.g., cholesterol, protonated fatty acids, etc.) (iii) insoluble swelling amphiphiles (e.g., phospholipids, monoglycerides, acid soaps ) and (iv) soluble amphiphiles (e.g., mixtures of bile salts with themselves, with soaps and with detergents) and the literature up to that date (1970) was critically summarized. Much recent work has appeared in all of these areas, but the most significant is the dramatic advances that have taken place in our understanding of the structure, size, shape, equilibria, and thermodynamics of bile salt-lecithin [16,18,28,29,99-102,127, 144,218,223,231-238] and bile salt-lecithin-cholesterol [238,239] micelles which are of crucial importance to the solubihty of cholesterol in bile [1]. This section briefly surveys recent results on the above subclasses. Information on solubilization, solubilization capacities or phase equilibria of binary, ternary or quaternary systems or structures of liquid crystalline phases can be found in several excellent reviews [5,85,207,208,210,211,213,216,217] and, where relevant, have been referred to earlier. 

Fig. 56. Cholesterol-sodium cholate-water ternary phase diagram. The structure of the bile salt micelles is indicated in the inset. These micelles remain small in the presence of cholesterol (Section IX. E). It will be noted that the micellar zone is smalt and that no liquid crystalline phases are formed in this system (2, 6, 47).

We begin this section with a discussion of the bile salts as biological detergents, concentrating first on their physico-chemical properties and some of their interactions with other solutes and with membranes. There then follows a brief look at the phospholipids and a consideration of ternary bile salt-phospholipid-water systems and quaternary cholesterol-bile salt-phospholipid-water systems which play an important role in various biological processes. The chapter ends with a survey of some miscellaneous amphipathic compounds of biological interest. 

Ternary and quaternary systems of lecithin, cholesterol, and bile salts... 

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