Solubilization of homologous omega-phenylalkanols into gel and liquid-crystalline liposome membranes of dipalmitoylphosphatidylcholine

The gel-to-liquid-crystalline phase transition temperature T-m of dipalmito ylphosphatidylcholine (DPPC) liposome membrane was measured in the presence of homologous omega-phenylalkanols (phenol to 8-phenyl-1-octanol), The dec rease in T-m induced by the alkanols allowed us, by applying the van't Hoff equation for freezing-point depression, to estimate two partition coeffici ents of each alkanol: gel membrane/bulk water K-x(g) and liquid-crystalline membrane/bulk water K-x(l). Shorter alkyl chain alkanols were solubilized only in the liquid-crystalline membrane, ie., K-x(g) = 0, whereas longer-ch ain alkanols were solubilized not only in the liquid-crystalline membrane b ut also in the gel membrane. The former result suggests that the fraction o f liquid-crystalline phase in the liposome membrane is 0.83 at T-m. From th e latter result, the values of the free energy changes of transfer of the a lkanol molecules from bulk water to liposome membrane were estimated to be - 3.46 kJ-mol(-1) (liquid-crystalline membrane) and - 3.85 kJ mol(-1) (gel membrane) per CH2 group in the alkanol molecules.