A calorimetric study of binary mixtures of 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphoethanolamine and dimyristoyl phosphatidylethanolamine.

Model membranes composed of 1-octadecanoyl-2-decanoyl-sn-glycero-3- phosphoethanolamine and dimyristoyl phosphatidylethanolamine have been studied calorimetrically. 1-Octadecanoyl-2-decanoyl-sn-glycero-3- phosphoethanolamine is a highly asymmetric mixed-chain lipid, whereas dimyristoyl phosphatidylethanolamine is an identical-chain lipid with the same molecular weight. Calorimetric results indicate that these two lipids with a common molecular weight are completely miscible in the two-dimensional plane of the lipid bilayer in the liquid-crystalline state and that they are only partially miscible in the gel-state bilayer. Specifically, binary mixtures of these two lipids form eutectic phase diagrams at pH 7.4 and 10.0.