Lipid membrane-water partitioning of lysophospholipids and fatty acids

The partition coefficients for the distribution of lysooleylphosphatdylcholine (LOPC) and oleic acid (OA) between water and dioleylphosphatidylcholine (DOPC) bilayer at temperatures of 5 C, 15 C, 37 C and 50 C were determined using a fluorescence assay. The enthalpy and entropy of the partitioning were determined from the temperature dependence of the partition coefficient. The Gibbs free energy decreases and entropy increases upon partitioning into the bilayer for both LOPC and OA, in the temperature region of study. The enthalpy changes of LOPC and OA partitioning are significantly different. LOPC partitioning into the bilayer is endothermic (increase in enthalpy) and OA partitioning is exothermic. This means that LOPC partitioning is entirely driven by entropy. Both enthalpy and entropy contribute favorably to OA partitioning into the lipid bilayer. Entropy contributions for both LOPC and OA are mainly due to the hydrophobic effect of the long hydrocarbon chains of these molecules. The difference between LOPC and OA in the enthalpies of partitioning is due to the difference in the polar characters of their head groups.