Physical properties of insect cuticular hydrocarbons: model mixtures and lipid interactions

Cuticular lipids include a diverse array of hydrophobic molecules that play an important role in the water economy of terrestrial arthropods. Their waterproofing abilities are believed to depend largely on their physical properties, but little is known about interactions between different surface lipids to determine the phase behavior of the total lipid mixture. I examined the biophysical properties of binary hydrocarbon mixtures, as a model for interactions between different epicuticular lipids of insects. The midpoint of the solid/liquid phase transition (Tin) for mixtures of n-alkanes differing in chain length equaled the weighted average of the/'ms of the component lipids. This was also true for n-alkane-methylalkane mixtures. However, alkane-alkene mixtures melted at temperatures up to 17°C above the temperature predicted from the weighted average of component lipid T m values. Hydrocarbon mixtures did not exhibit biphasic melting transitions indicative of independent phase behavior of the component lipids. Instead, melting occurred continuously, over a broader temperature range than pure hydrocarbons.