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.