The organization of n-alkanes in lipid bilayers.

The interaction of n-alkanes (C6--C16) with phosphatidylcholine has been studied by the combined use of differential scanning calorimetry, X-ray diffraction and monolayer techniques. It has been found that the thermal properties and ultrastructure of lipid-alkane vesicles are strongly dependent on the length of the n-alkanes. Long alkanes, such as tetradecane and hexadecane, increase the transition temperature of dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine, while the X-ray data indicate that these long alkanes align parallel to the lipid acyl chains. In contrast, shorter alkanes, such as hexane and octane, decrease and broaden the thermal transition and electron density profiles show that these alkanes increase bilayer width by partitioning between the apposing monolayers of the bilayer. For lipids in the gel and liquid crystalline states, the short alkanes form an alkane region in the geometric center of the bilayer.