Investigation of phase transitions of lipids and lipid mixtures by sensitivity differential scanning calorimetry.

High sensitivity differential scanning calorimetry is applied to the study of the thermotropic behavior of mixtures of synthetic phospholipids in multilamellar aqueous suspensions. The systems dimyristoylphosphatidylcholine dipalmitoylphosphatidylcholine, and dimyristoylphosphatidylethanolamine-distearoylphosphatidylcholine, although definitely nonideal, exhibit essentially complete miscibility in both gel and liquid crystalline states, while the system dilauroylphosphatidylcholine-distearoylphosphatidylcholine is monotectic with lateral phase separation in the gel state. Comparison of the observed transition curves with theoretical curves calculated from the calorimetrically determined phase diagrams supports a literal interpretation of the phase diagrams.