Closed-loop fluid-fluid immiscibility in binary lipid-sterol membranes

We present two binary lipid-sterol membrane systems that exhibit fluid-fluid coex-istence. Partial phase diagrams of binary mixtures of dimyristoylphosphatidylcholine with 25-hydroxyxholesterol and 27-hydroxycholesterol, determined from small-angle X-ray scattering and fluorescence microscopy studies, show closed-loop fluid-fluid immiscibility gaps, with the appearance of a single fluid phase both at higher and lower temperatures. Computer simulations suggest that this unusual phase behavior results from the ability of these oxysterol molecules to take different orientations in the membrane depending on the temperature.

Automated summary

We present two binary lipid-sterol membrane systems that exhibit fluid-fluid coexistence. The partial phase diagrams of the binary mixtures, determined from experimental studies, show closed-loop fluid-fluid immiscibility gaps. Computer simulations suggest that this unusual phase behavior is a result of the different orientations of the oxysterol molecules in the membrane depending on the temperature.