| Abstract | Cholesterol affects the motional freedom and orientation of the N-oxyl - 4′, 4′ - dimethyl - oxazolidine derivative of 12-keto stearic acid (I) in dry and hydrated egg lecithin multibilayers. However, cholesterol derivatives with methoxy, carbonyl oxygen or chloro substituents at the 3 position of the cholestene nucleus drastically reduce the condensing effect on the multibilayer structure. The spin labelled stearic acid was found to orientate in dry egg lecithin films with its long axis preferentially perpendicular to the plane of lipid films with considerable wobbling motion along the axis. Hydration abolishes this orientation, presumably due to an increase in membrane fluidity, therefore permitting the random motion of the label. Cholesterol decreases the wobbling motion of the label in dry multibilayers and increases orientation of the label in the hydrated bilayer structure. |
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