Hexagonal phases in phospholipids with saturated chains: phosphatidylethanolamines and phosphatidic acids.

The structure of phospholipids with saturated chains was investigated by differential scanning calorimetry and by X-ray diffraction. It is shown that both phosphatidylethanolamines and phosphatidic acids can exhibit a hexagonal phase at high temperature. The temperature of the transition to the hexagonal phase is dependent on chain length and sodium salt concentration. Increasing the chain length or the sodium salt concentration results in a decrease in the transition temperature. In addition to this transition at high temperature, a calorimetric transition at low temperature, a calorimetric transition at low temperature is detected in some phospholipids.