Bile salt aggregates

The kinetic studies indicated that the rate of equilibrium between large monoolein-bile salt aggregates and small monolein-bile salt aggregates was very fast. Information is needed on the rate of exchange of polar lipids between micelles since these aggregates have different structures than soap micelles, where the exchange rates are believed to be rapid (15, 21). 

Warren, DB, Chalmers, DK, Hutchison, K, Dang, W, and Pouton, CW. Molecular dynamics simulations of spontaneous bile salt aggregation. Colloids Surfaces A Physiochem Eng Aspects 2006 280 182-193. 

Measurement of the influence of different micellar environments on proton transfer from excited states of 3-hydroxyflavone allows estimates to be made of micelle concentrations from measurement of the tautomer emission yield. Proton transfer reactions of benzimidazole excited singlet states have also been studied in ionic micelles. Magnetic fields are found to affect the behaviour of radicals generated by the photodissociation of benzil in micellar media. The starburst dendrites which are formed by anionic macromolecules in interaction with both anionic and cationic surfactants have been examined by pyrene fluorescence. Benzo[k]fluoranthrene fluorescence has served as a probe of the effects of metal salts on bile salt aggregation. The incorporation and distribution of benzoquinone into liposomes containing amphilic Zn(II) porphyrin has been followed by its effect on the quenching of the excited state °. A comparison of the photochromism of spirobenzpyran derivatives in unilamellar surfactant vesicles and solvent cast surfactant films has also been reported. ... 

Figure 4 Schematic diagram of bile salt aggregates. The dark areas indicate the polar moieties of the bile salt monomer.

In conclusion, bile salt aggregates are self-assembled systems with a more defined structure than conventional micelles, as they provide less access to molecules from the aqueous environment. 

This chapter covered the use of excited states as probes for dynamic studies involving supramolecular stmctures. It was shown that excited singlet and triplet states provide complementary capabilities for these studies. Micelles are the best characterized structures, and most of the methodology currently in use was developed when studying these supramolecular systems. Other self-assemblies, such as vesicles and bile salt aggregates, have been studied to some extent, but the dynamics of guest complexation has not been fully described and will undoubtedly be explored in the future. Cyclodextrins are widely employed as... 

Megyesi M, Biczok L (2007) Berberine alkaloid as a sensitive fluorescent probe for bile salt aggregates. J Phys (Them B 111 5635-5639... 

Certain surface-active compounds [499], when dissolved in water under conditions of saturation, form self-associated aggregates [39,486-488] or micelles [39,485], which can interfere with the determination of the true aqueous solubility and the pKa of the compound. When the compounds are very sparingly soluble in water, additives can be used to enhance the rate of dissolution [494,495], One can consider DMSO used in this sense. However, the presence of these solvents can in some cases interfere with the determination of the true aqueous solubility. If measurements are done in the presence of simple surfactants [500], bile salts [501], complexing agents such as cyclodextrins [489 191,493], or ion-pair-forming counterions [492], extensive considerations need to be applied in attempting to extract the true aqueous solubility from the data. Such corrective measures are described below. 

Figure 7.13 Examples of bile salts and aggregate structures formed in aqueous solutions.

Other aqueous aggregates (trialkylammonium aggregates, bile salt micelles and microemulsions) 439... 

OTHER AQUEOUS AGGREGATES (TRIALKYLAMMONIUM AGGREGATES, BILE SALT MICELLES AND MICROEMULSIONS)... 

McKenna et al. (1977) found that a bis steroid [10] can bind perylene without micellization. Interestingly, the corresponding monosteroid did not bind perylene in the absence of micellization. The bis-steroid may assume a conformation which is related to the aggregate structure of bile salts. An... 

The aggregation behavior of C21-DA salt in dilute electrolyte medium appears to resemble that of certain polyhydroxy bile salts (25,16). That C21-DA, with a structure quite different from bile acids, should possess solution properties similar to, e.g., cholic acid is not entirely surprising in light of recent conductivity and surface tension measurements on purified (i.e., essentially monocarboxylate free) disodium salt aqueous solutions, and of film balance studies on acidic substrates (IX) The data in Figure 3 suggest that C21-DA salt micelles Incorporate detergents - up to an approximate weight fraction of 0.5 -much like cholate Incorporates lecithin or soluble... 

Micelles tend to aggregate, and there are many ways to measure their concentration, including surface tension measurements. The midpoint of the concentration range over which micellar aggregation occurs is called the critical micellar concentration (CMC). Below the CMC, added bile-salt molecules dissolve in the form of monomers above the CMC, added bile-salt molecules form micelles, leaving the monomeric concentration essentially constant. The pH at which CMC formation occurs is called the critical micellar pH, (CMpH). Table 1.1 lists values for some of the bile acids mentioned in this review. 

Szoekoe et al. (23) assume several parallel complex formation equilibria with different aggregates [the number of degrees of association is dependent on the bile salts (BS) concentration]. Each micelle with an iden-... 

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). 

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