Glass Transition of a Synthetic Phospholipid in the Lamellar Phase

A synthetic phospholipid, 1-palmitoyl-2-oleoyl- sn -glycero-3-phosphoethanolamine (POPE), was studied by differential scanning calorimetry at different hydration levels. A glass transition was observed in the lamellar gel (L β ) phase but was not detected in a more ordered lamellar crystalline phase. The glassy state of the L β phase of POPE has properties that are typical of other glass-forming materials, i.e., nonexponential relaxation behavior below the glass transition temperature, a broad distribution of relaxation times, and plasticization by water. The significance of the glass transition in biological membranes is discussed.