A novel method for measuring membrane-water partition coefficients of hydrophobic organic chemicals: comparison with 1-octanol-water partitioning.

A novel method of measuring membrane-water partitioning characteristics of very hydrophobic organic chemicals is described. Partition coefficients are reported for a series of halogenated aromatic hydrocarbons of varying molar volume between water and L-a-phosphatidylcholine dimyristoyl (DMPC) membrane vesicles and two solvents, n-hexane and 1-octanol. The results indicate that n-hexane and 1-octanol are satisfactory surrogates for DMPC membranes for chemicals with 1-octanol-water partition coefficients (log KOW) less than 5.5 or molar volumes less than 230 cm3/mol. Chemicals with higher log KOW or molar volume values display marked differences in membrane-water, 1-octanol-water, and n-hexane-water partitioning. Implications for lipid- and organism-water partitioning of hydrophobic chemicals are discussed.