Static and Kinetic Studies on the Phase Transition of Single Lamellar Liposomes

Abstract

Uniformly sized L-a-dipalmitoylphosphatidylcholine liposome dispersions were prepared in different molecular weights ranging from 2×10⁶ to 3×10⁷ daltons by means of molecular sieve column chromatography on a Sepharose 2B gel in order to investigate the static and kinetic behaviors of the phase transition of the single lamellar liposomes.
The phase transition was monitored by the fluorescence intensity of N, N′-dioctadecyloxacarbocyanine incorporated in the liposomes. The single lamellar liposomes exhibit only single transition which depends on the liposome size. Decrease in the liposome size results in the drop of the transition temperature and in the decrease of the cooperativity of the transition.
The rate of the phase transition was also studied by the temperature-jump method as a function of the liposome size. The relaxation is characterized by single process and its time constant exhibits a maximum at the midpoint of the transition. The maximum values increase with increasing size of the liposomes. Theoretical results obtained from a kinetic model based on two-dimensional Ising lattice were compared with the experiments.