Occurrence of Glass Transitions in Long-Chain Phosphatidylcholine Mesophases

Abstract

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.