MEMBRANE WATER PARTITIONING OF POLYCHLORINATED-BIPHENYLS IN SMALL UNILAMELLAR VESICLES OF 4 SATURATED PHOSPHATIDYLCHOLINES

Experimental data are presented on the partition coefficients of 14 polychlorinated biphenyls (PCBs) between four species of saturated 1,2-diacyl-sn-glycero-3-phosphocholine membrane vesicles and aqueous buffer. Small unilamellar vesicles of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), distearoylphosphatidylcholine (DSPC), and diarachidoylphosphatidylcholine (DAPC) show a high affinity for extreme hydrophobic xenobiotics such as the PCBs in this study. Observed membrane-water partition coefficients K-mw of the PCBs, with log K-ow values ranging from 5.3 to 8.26, in membrane lipid vesicles were in the following order: DPPC > DMPC > DSPC > DAPC. Beside the hydrophobicity of the PCBs, the order of the K-mw values is primarily determined by the fluidity of the membrane bilayer. At the experimental temperature of 37 degrees C for every PCB, a correlation exists between log K-mw and the membrane lipid main phase transition temperature T-m. In comparison to the bulk solvent 1-octanol, the membrane lipid phase is highly structured and the correlation between log K-mw and both the molar liquid volume MLV of the PCBs and their log K-ow is nonlinear.