PHASE-BEHAVIOR OF DISTEAROYLPHOSPHATIDYLETHANOLAMINE IN GLYCEROL - A THERMAL AND X-RAY-DIFFRACTION STUDY

The phase behaviour of 1,2-distearoylphosphatidylethanolamine in glyce rol has been examined using differential scanning calorimetry and real -time synchrotron X-ray diffraction methods. Dry phospholipid and phos pholipid dispersed in glycerol over the concentration range 2.4%-90% ( w/w) was equilibrated for 30 min at 20 degrees C and thermal and struc tural parameters on the temperature range 60 degrees C to 110 degrees C recorded during an initial heating and subsequent reheating. The cha racteristic feature of the initial heating scan was a direct lamellar crystalline to inverted hexagonal phase transition. In the subsequent cooling scan a lamellar gel structure was formed from the non-lamellar phase which transformed, on reheating, to a lamellar crystalline phas e in which the acyl chain packing was tilted with respect to the bilay er plane, The mechanism of the formation of the two crystalline phases was examined in the context of a relaxation model, where the liquid-c rystal phase below the transition temperature from lamellar crystallin e phase is metastable. A binary phase diagram over the temperature ran ge 60 degrees C to 110 degrees C has been constructed.