Bile salt-swelling amphiphile micelles

TDC-L system there is an initial decrease in size and in the TC-L system an initial increase in size. Beyond the vertical dashed lines in the center of the plots the micellar sizes are seen to increase strongly to 80 A as the L/BS values reach the phase limit (broad dashed line). It is apparent that these micellar sizes are much larger than the sizes based on the micellar structures proposed by Small and Dervichian [5,6] (Fig. 17). This finding led us to propose a new molecular model (the mixed disk micelle) for these BS-L particles in which BS both coat the perimeter and are solubilized (probably as reverse dimers) within the disk-like fragments of L bilayers (Fig. 17). The marked divergence in micellar sizes as the phase limit is approached provides an explanation for the existence of the limit since at these lipid ratios the micelles become maximally swollen with L. As the L to BS ratio is increased beyond the phase limit, the excess L plus BS constitute a second lecithin-rich liquid ctystalline phase [102,236,251]. 

The values to the left of the narrow-dashed vertical lines (Fig. 16) show dissimilar behavior between the two systems. In addition, there is a pronounced 

The intermicellar BS concentration (IMC) is a key parameter in such systems since it is decreased in proportion to swelling amphiphile to BS ratios [99,100], is critically influenced by micelle size [102], and determines the swelling amphiphile-BS phase limit since it controls the lipid ratio in the micellar particles [102]. As a corollary, it is greatly influenced by BS species, being much higher with the more hydrophilic C and UDC than the less hydrophilic DC and CDC [99,100,254]. The actual values have been measured directly by surfactant ion electrodes [16,144], QLS-monitored dilution effects on preserving [ 02], Sephadex G-10 exclusion 

The interior microenvironment of BS-L micelles has been probed by fluorescence spectroscopy using a variety of large probes with both common BS-egg and -synthetic L micelles as functions of temperature [223,232,238], NMR of [ H]lecithins [235,237] differential scanning calorimetry [236], X-ray scattering [233], and electron spin resonance of spin-labels incorporated into lecithin and fatty acid chains [232]. 

---

Bile salt-swelling amphiphile-insoluble amphiphile micelles... 

Fig. 17. Longitudinal and cross-sectional views of the proposed molecular models for the structure of bile salt-lecithin (BS-L) mixed micelles. All recent experimental data for BS-swelling amphiphile micelles are consistent with model B. In this model, reverse BS aggregates are present in high concentrations within the hydrophobic domains of L or other swelling amphiphile bilayers. BS also coat the perimeter of the disks as a bilayered ribbon . (From ref. 102 with permission.)...

Lecithin (Lee) is a swelling insoluble amphiphile having truncated-cone shape complementary to Ch in water it forms liquid crystals which can dissolve high proportions of cholesterol. A bilayer of lecithin is destroyed by bile salt (BS) simple micelles. 

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. 

---