Solubilization of Homologous ω-Phenylalkanols into Gel and Liquid-Crystalline Liposome Membranes of Dipalmitoylphosphatidylcholine

Abstract

The gel-to-liquid-crystalline phase transition temperature T _m of dipalmitoylphosphatidylcholine (DPPC) liposome membrane was measured in the presence of homologous ω-phenylalkanols (phenol to 8-phenyl-1-octanol). The decrease in T _m induced by the alkanols allowed us, by applying the van't Hoff equation for freezing-point depression, to estimate two partition coefficients of each alkanol: gel membrane/bulk water K ^g_x and liquid-crystalline membrane/bulk water K ¹_x . Shorter alkyl chain alkanols were solubilized only in the liquid-crystalline membrane, i.e., K ^g_x =0, whereas longer-chain alkanols were solubilized not only in the liquid-crystalline membrane but also in the gel membrane. The former result suggests that the fraction of liquid-crystalline phase in the liposome membrane is 0.83 at T _m. From the latter result, the values of the free energy changes of transfer of the alkanol 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.