Liposome-water and octanol-water partitioning of alcohol ethoxylates

Liposome-water partitioning coefficients, (K(lipw)s), were determined for eight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifugation. Both methods yielded statistically indistinguishable results. The experimentally determined log K(lipw)s were compared with log K-ow values estimated with the fragment method using different literature sources for the fragment constants. Fragments of log K-lipw were calculated for the ethoxy group (EO) and the -CH2- units from the experimentally determined data. An additional -CH2- unit causes an average increase of log K-lipw by 0.45, and an additional EO causes an average decrease of log K-lipw by -0.12. With these fragments, the quality of log K-lipw estimations can be improved significantly as compared to simple linear regression of log K-lipw versus log K-ow. The K-lipw values calculated according to the new fragment method for pure compounds and for commercial mixtures are shown to be adequate descriptors for quantitative structure-activity relationships of bioaccumulation, toxicity, and sorption to natural organic material.