The influence of lecithin structure on their monolayer behavior and interactions with cholesterol.

Abstract Pressure-area curves have been measured for monolayers of ten lecithins (16:0–20:0, 16:0–11-methyl-18:0, 16:0–15-methyl-18:0, 16:0–22:1, 16:0–22:6, 18:0–22:6, 20:0–18:2, 18:3–16:0, 18:2–18:2 and 18:3–18:3) and eight fatty acids (18:0, 18:1, 18:2, 18:3, 20:4, 22:5, 11-methyl-18:0 and 15-methyl-18:0). Subtraction of the areas of the consituent fatty acids from the areas of the lecithin molecules in monolayers gave an estimate of the area contributed by the polar group. The effective areas thus obtained were found to range 3-fold in value. This result suggested that the orientation of the polar group in monolayers can vary depending upon the structures of the fatty acid chains in lecithin molecules. Mixed monolayers of each lecithin and cholesterol were investigated in order to find the molecular features of lecithin molecules responsible for condensation in monolayers by cholesterol. Condensation by cholesterol occurred in those lecithins that form expanded films, most strongly with those molecules that have a segment of saturated hydrocarbon chain extending nine or more carbons from the car☐yl group. The condensation between cholesterol and lecithins in monolayers has been interpreted in terms of cohesion between the saturated straight chain hydrocarbon segment of lecithin and either the ring system of cholesterol or other similar saturated segments in lecithin molecules.

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