log Pe (2%DOPC+0.5%Cho - Model 1A.0) Figure 7.29 Modified Chugai model compared to 2% DOPC + 0.5% cholesterol model.

7.7.5 Lipid Models Based on Lecithin Extracts from Egg and Soy

Hydrogen bonding and electrostatic interactions between the sample molecules and the phospholipid bilayer membranes are thought to play a key role in the transport of such solute molecules. When dilute 2% phospholipid in alkane is used in the artificial membrane [25,556], the effect of hydrogen bonding and electrostatic effects may be underestimated. We thus explored the effects of higher phospholipid content in alkane solutions. Egg and soy lecithins were selected for this purpose, since multicomponent mixtures such as model 11.0 are very costly, even at levels of 2% wt/vol in dodecane. The costs of components in 74% wt/vol (see below) levels would have been prohibitive. Egg Lecithin from Different Sources

Egg lecithins from two sources were considered: Avanti Polar Lipids (Alabaster, AL) and Sigma-Aldrich (St. Louis, MO). The ''60% lecithin total extract'' grade from Avanti and the ''60% lecithin'' grade from Sigma-Aldrich were tested. Apparently, different procedures are used to extract the lipids from egg yolk, since the permeability properties of the lecithins from the two sources are significantly different. The Avanti catalog identifies their procedure as a chloroform-methanol extraction. The extract is partitioned against deionized water, and the chloroform phase is concentrated. This extraction procedure is expected to remove proteins and polar (e.g., phenolic) substituents. The Avanti principal lipid components are listed in Table 7.1. The Sigma-Aldrich composition was not available.

TABLE 7.10 Egg Lecithin 10% wt/vol in Dodecane PAMPA Models, pH 7.4"
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