Occurrence of Glass Transitions in Long-Chain Phosphatidylcholine Mesophases

Several phosphatidylcholine (PC) species were studied by differential scanning calorimetry at different levels of hydration. A glass transition was observed in both lamellar gel and nonlamellar phases, with the glass transition temperature, T g, decreasing as water content was increased. The structure of the lipid mesophase has a major impact on T g, with the lamellar gel phase having a higher T g than that of nonlamellar phases of the same lipid. While the headgroup has a noticeable influence on the T g, changing the chain length, on the other hand, has less of an impact. The values of the calorimteric T g were compared with other measures of molecular mobility in the PC species at comparable water contents reported in the literature. Observation of a T g in different phosphatidylethanolamines (PE), as previously reported, and PC species in this study suggests that a glass transition can be expected to be a common feature of biological membranes and phospholipid bilayer preparations, such as liposomes.