Cholesterol ternary systems

Figure 7. The ternary system cholesteryl oleate-cholesterol-triolein (CO-C-TO) at different temperatures (10). The darkened region corresponds to one isotropic phase whereas the remainder consists of two or three phases.

Lamellar arrangements were detected by polarised light microscopy. DSC and XRD confirmed that chains of emulsifier were in the crystalline state. Ternary systems with liquid paraffin were isotropic, homogenous o/w creams for a wide composition range. Incorporation of 50 mol % cholesterol lead to the separation of a gel-liquid crystalline phase within the layer [174]. The transition energies, derived from DSC, decreased linearly with increasing cholesterol concentration. Optical microscopy should be used to confirm phase separation in creams [175]. 

When alamethicin is added to a ternary vesicle system comprising PDA, phospholipid, and lipopolysaccharide (LPS), the addition of polymyxin, an LPS-binding antibiotic, sensitizes the vesicles to alamethicin (Katz et al. 2003). Cholesterol-containing PDA liposomes have been used to colorimetrically detect streptolysin O, a cholesterol-dependent pore-forming toxin (Ma and Cheng 2005). 

For mixtures of lecithin plus Na cholate it appears possible to infer the molecular arrangement in the dispersed micelles from the most likely structure of the liquid crystalline phase suggested by x-ray analysis. However, there are cases where dispersion is not possible because neither component is sufficiently hydrophilic to be dispersed even when alone in water. This is shown by the association of cholesterol and lecithin in the presence of water. The ternary diagram of Figure 4 is relative to these systems. Here only the lamellar liquid crystalline phase is obtained (region 1< in Figure 4). This phase is already given by lecithin alone, which can absorb up to 55% water. Cholesterol can be incorporated within this lamellar phase up to the proportion of one molecule of choles-... 

Figure 4. Ternary phase diagram for system lecithin (L), cholesterol (Choi), and water (W)...

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).

The phase behavior of mixtures of polyoxyethylene phytosterol surfactants and paraiSn as well as ternary mixtures of the surfactants, water, and paraiSn has also been studied [18]. The objective of this work was to find creamy mixtures to be used in topical preparations. Uchegbu et al. investigated the phase behavior of cholesterol with 24 oxyethylene units with free cholesterol and hexadecyldiglycerol in order to find phases that can be used as drug delivery systems [25]. No liquid crystalline phases were found. 

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... 

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... 

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