PARTITION-COEFFICIENTS OF OMEGA-PHENYLALKANOLS BETWEEN WATER AND LIPOSOME MEMBRANES OF PHOSPHOLIPIDS

For the liposome of two types of phospholipids (zwitterionic dipalmitoylphosphatidylcholine (DPPC) and anionic dimyristoylphosphatidic acid (DMPA)), the partition coefficient K(x) for partition of homologous omga-phenylalkanols (C6H5(CH2)mpOH; m(p) = 0 - 8) between bulk water and the liposome membrane was determined on the basis of the gel to liquid crystalline phase transition temperature T(m) of the liposome membrane. The plot of log K(x) vs. mp gave a break at m(p) = 7 for both phospholipids, and a second break at m(p) = 4 was observed for DPPC. The local polarity of the surface region and the orderliness of phospholipid molecules in the liposome membrane were estimated from ESR spectra of two spin probes solubilized in the membrane. The results suggest that the hydration of DPPC liposome membrane is relatively restricted to its surface region, but for DMPA the hydration spreads not only along the surface but also to the inside of the membrane. The main factor controlling the partitioning of the alkanols is the local polarity. The higher alkanols (m(p) = 7, 8) are solubilized not only in the liquid crystalline phase but also in the gel phase, although the other lower alkanols are solubilized in the liquid phase only.