Calorimetric Investigations of Phase Transitions of Sonicated Vesicles of Dimyristoylphosphatidylcholine and Their Stabilities.

概要

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The process of transformation of a large multilamellar vesicle (MLV) composed of dimyristoylphosphatidylcholine (DMPC) into a small unilamellar vesicle (SUV) brought about by ultrasonic irradiation was calorimetrically investigated. It was found that the final state of SUV is attained by way of a large vesicle of unilamellar-like packing, which appears with an increase in length of the irradiation. Representative three types of vesicles of different sizes and lamellar multiplicities, i. e., sonicated SUV, sonicated large unilamellar-like vesicle, and unsonicated MLV, showed a characteristic thermotropic behavior of the phase transition of the gel to liquid crystal (Tm transition). The enthalpy and entropy changes, and also the transition temperature associated with the Tm transition increased in the order SUV < large unilamellar-like vesicle < MLV. Furthermore, the annealing treatment at approximately -5°C caused the SUV to transform finally into a vesicle of multilamellar packing by way of the large unilamellar-like vesicle. The schematic diagram of Gibbs energy (G)-vs-temperature (T) curves for the gel phase were revealed to lower in the order SUV < large unilamellar-like vesicle < MLV, similar to the enthalpy (H)-vs-temperature (T) curves for this phase. This fact indicated that DMPC vesicles are thermodynamically stabilized by the enthalpy effect resulting from a closely packed aggregation of the lipid molecules.
日本熱測定学会の論文