Eutectic phase behavior of 1-stearoyl-2-caprylphosphatidylcholine and dimyristoylphosphatidylcholine mixtures.

The thermotropic behavior of aqueous dispersions of C(18):C(10)PC/diC(14)PC mixtures with different molar ratios has been investigated by high-resolution differential scanning calorimetry. C(18):C(10)PC is a highly asymmetric lipid molecule, whereas diC(14)PC is a symmetric species with the same molecular weight. Their packing properties in the bilayer are known to be similar at T greater than Tm, but very dissimilar at T less than Tm. Calorimetric results indicate that C(18):C(10)PC and diC(14)PC are completely miscible in the liquid-crystalline state. In the gel state, however, C(18):C(10)PC and diC(14)PC are only partially miscible. The temperature-composition phase diagram for C(18):C(10)PC/diC(14)PC mixtures has the shape characteristic of a typical eutectic system.