1992 Volume 41 Issue 462 Pages 336-341
Phospholipid bilayers and surfactant micelles have been used as a model for biological membranes. The temperature-pressure phase diagram of dipalmitoylphosphatidylcholine (DPPC) bilayer liposomes has been constructed. Four states, i.e., liquid crystal (Lα), gel I (Pβ'), gel II (Lβ') and interdigitated (LβI) phases, were observed in the pressure range up to 200MPa. The present study proposes a novel method for the estimation of the partition coefficient of drugs between the aqueous and the lipid phases. Two kinds of partition coefficients of an inhalation anesthetic were estimated from the depression of the main- and pre-transition temperature of DPPC liposome. The Lα phase/water and Pβ' phase/water partition coefficients of halothane were 3390 and 820, respectively. The effect of pressure on the partition coefficient was determined, and then the transfer volume of halothane was estimated.
The critical temperature-pressure lines for the micellar dissolution, which represent the pressure dependence of Krafft temperature, were determined for a homologous series of cationic surfactants. The depression of Krafft temperature by solubilization can be used for the estimation of the partition coefficient of solubilizate between the aqueous phase and the micellar phase.
