Lecithin solubilization

This final proportion also corresponds to the largest quantity of lecithin solubilized in water as an isotropic phase. This system contains only 30% water and 35% lecithin and is represented by point O on Figure 3. All systems with their representative point situated at any place on line WO have the same relative proportion of lecithin and bile salt the relative quantity of water alone increases when moving from O toward W. 

The solubilization of water in lecithin-reversed micelles has been found to be an exothermic process. This finding confirms that water interacts with the zwitterionic head group of lecithin, promoting the formation of strong intermolecular H bonds [104]. 

By IR spectroscopy it was emphasized that the solubilization of amino acids or ohgopeptides in water-containing lecithin-reversed micelles involves structural changes in the aqueous micellar core [159]. 

The vesicular size might go back reversiblly to the original one in the case of nonionic vesicles (Figures 9 and 10) for which the present removal rate may be too slow. A similar behavior was reported by Schurtenberger et al. for their lecithin-bile salt systems vesicle size is reduced to the original dimension after dialysis of remains large when the solubilized is diluted with the buffer solution to very fast reduction of bile salt fast removal of bile salt(22) ... 

The other experiment was performed by Isaksson (5) earlier. He extracted desiccated bile, using different solvents in succession. With chloroform, all of the lecithin was extracted but was accompanied by a large part of the bile salts. While bile salts by themselves are insoluble in chloroform, the extract thus obtained contains a proportion by weight of 2 parts of bile salt to 1 of lecithin—about one molecule of lecithin for three molecules of bile salt. Here, it is the lecithin, soluble in chloroform because of its paraffinic chains, which by association solubilizes the bile salt. It is interesting to inquire how these associations are achieved in both cases—i.e., how the molecules of bile salt are arranged and oriented in relation to the molecules of lecithin and to the polar or non-polar solvent. Let us examine first the state of the bile salt molecules in an aqueous phase. 

Consider first the weight proportion of 77% of Na cholate for 33% lecithin which has to be reached in order to solubilize all the lecithin in water. This corresponds nearly to one molecule of Na cholate for two of lecithin. Taking as a model the one proposed in Figure 2, we can calculate the size which the mixed micelles should have so that the proportion of one molecule of Na cholate for two of lecithin will be obeyed. In other words, we want to know the number of lecithin molecules packed side by side which, surrounded by a ring of adjacent Na cholate molecules, can give the desired proportion. The calculation gives for each... 

Recently Bourges, Small, and Dervichian (5) reported that a para-crystalline lamellar structure of egg lecithin can solubilize cholesterol up to a maximum of one molecule of cholesterol per molecule of lecithin. However, they conclude that this should not be considered as a molecular association but rather the consequence of the relative arrangement of the molecules in the lamellar structure which is a mutual (solid) solution of lecithin and cholesterol. They also reported that the state of compression in the lamellar structure corresponds to that of a highly compressed mixed monolayer of lecithin-cholesterol. The NMR results of Chapman and Penkett (8) also appear to indicate that solubilization of cholesterol in egg lecithin dispersions results in a highly packed structure in which fatty acyl chains possess little molecular motion. Our results from lecithin-cholesterol monolayers also suggest that these mixed mono-layers are two-dimensional solutions with no specific interaction and that the apparent condensation in some instances is caused by the steric factors of the fatty acyl chains and not by the interaction or association between lecithin and cholesterol. 

Naylor et al. (1993) studied the ability of lecithin to modify the rate and mechanism of dissolution of hydrocortisone in the presence of sodium taurocholate (NaTC) solutions. They found that in the presence of lecithin, the CMC of NaTC dropped owing to the more effective solubilization capacity of the mixed micelle. Furthermore, the CMC value dropped more on saturation with hydrocortisone, implying some interaction between hydrocortisone and the NaTC/lecithin micelles. These results indicated that in the NaTC-only system, wetting effects predominated dissolution, whereas in the NaTC/lecithin system, the dissolution rate of hydrocortisone was enhanced mainly through solubilization. 

Rosoff, M., and A. T. M. Serajuddin. 1980. Solubilization of diazepam in bile salts and in sodium cholate-lecithin-water phaseint. J. Pharm.6 137-146. 

Lipids also can be beneficial for cells in culture, since some substances absorbed by the cells need to be solubilized in lipids, or in some cases the toxicity of compounds may be reduced by complexation with lipids. The absence of essential lipids such as linoleic acid, lecithin, cholesterol, ethanolamine, or phosphorylcholine can result in the decrease of cloning efficiency and in reduction in the size of colonies, as shown for insect cells by Echalier (1997). However, one of the difficulties in supplying lipids at reasonable concentrations is their low solubility. To circumvent this limitation, lipids can be emulsified with complexing agents such as Pluronic F68 or cyclodextrin (Maiorella et al., 1998). 

The possible reasons for the different behavior of natural surfactants could include the following. Natural surfactants lead to surface tension values higher than those corresponding to the same concentration of a synthetic surfactant. The ability to nullify the aqueous layer resistance could be related with the surface tension values. However, the micelles of bile salts are smaller and more rigid than the micelles of synthetic surfactants. The solubilization potential of bile salts is increased in the presence of lecithins and fatty acids. For instance, the absorption rate constants obtained in the presence of sodium taurocholate and glycocholate mixed-micelles with lecithin for a series of acids were significantly lower than those obtained in the presence of simple micelles of the same bile salts [29, 30]. 

Answer Lecithin (see Fig. 10-14 for structure), an amphipathic molecule, is an emulsifying agent, solubilizing the fat (triacylglycerols) in butter. Lecithin is such a good emulsifying agent that it... 

Since most drags are insoluble in the propellants, they are usually presented as suspensions. Micronized drag is dispersed with the aid of a surfactant such as oleic acid, sorbitan trioleate or lecithin. At concentrations up to 2% w/w the surfactant stabilizes the suspended particles by adsorption at the drag propellant interface and in addition serves as a valve lubricant. The tendency is to use minimum surfac—tant concentrations to reduce drag solubility within the propellant by solubilization (to reduce Ostwald ripening during the shelf life of the pMDI). Low surfactant concentrations will also avoid substantial reductions in the propellant evaporation rates from aerosolized drops. 

The hydrophilicity of nonionic surfactants can be characterized numerically as their hydrophile-lipophile balance (HLB). An HLB value of 3-6 indicates that the compound is a likely W/O emulsifier 7-9, a wetting agent 8-13, an O/W emulsifier 13-15, a detergent and 15-18, a solubilizer (of oil or other nonpolar compounds) in water. The HLB values of some common compounds are presented in Table 34.12.170 An HLB value of 8.0 is shown in Table 34.12 for lecithin, but manufacturers are able to supply modified lecithins with values of2-12. 

Solubilization. Most lecithins can aid in the production of microemulsions, an example being oil-soluble flavors in aqueous systems. Although standard-grade lecithins do not disperse in water, many modified or fractionated lecithins are water-dispersible, and they can be used to produce microemulsions. Standard-grade lecithin can be blended with other surfactants (e.g., ethoxylated monoglycerides) to produce synergistic emulsifier blends that are also effective in producing microemulsions. 

To act as solubilizing, wetting, or emulsifying agents such as Cremophor EL, sodium desoxy-cholate, Polysorbate 20 or 80, PEG 40 castor oil, PEG 60 castor oil, sodium dodecyl sulfate, lecithin, or egg yolk phospholipid. 

Purified soybean lecithin Dispersing agent, emulsifying agent, solubilizer, stabilizer iv... 

For CFC-based suspension formulations, a surfactant was typically included. A variety of surfactants were used in these systems, e.g., lecithin, oleic acid, sorbitan trioleate. " All these surfactants were freely soluble in the CFC propellants and allowed for a degree of control over the suspension characteristics. Rates of flocculation, sedimentation, and creaming could be controlled and deposition on the internal container components was minimized. The transition to HFA-based MDIs has created significant issues in that none of the surfactants, previously used with the CFC products are soluble in HFA propellants alone. Some formulations have still used these surfactants, but the addition of a cosolvent (ethanol) has been required to solubilize the surfactant. 

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