Differential scanning calorimetric studies of aqueous dispersions of phosphatidylcholines containing two polyenoic chains.

The thermotropic behavior of aqueous dispersions of phosphatidylcholines (PC) that contain two identical unsaturated acyl chains, either linoleoyl, alpha-linolenoyl, or arachidonoyl chains, has been investigated by differential scanning calorimetry. These dipolyenoic PC displayed very broad thermal transitions, which occurred over a range of approximately 40 C deg, that started between -77 degrees C (20:4-20:4 PC) and -71 degrees C (18:2-18:2 PC). The enthalpy changes associated with the transitions were small (1 to 2 kcal/mol, 4 to 8 kJ/mol). The broad, low-enthalpy transitions suggest that these lipids might have a very disordered gel phase, or that the transitions from the gel to the liquid crystal might proceed through some intermediate states. The temperatures over which the transitions occurred were influenced only slightly by the number of double bonds between two and four per chain.