Liposome-water and octanol-water partitioning of alcohol ethoxylates

Liposome-water partitioning coefficients, (K(lipw)s), were determined for e ight pure alcohol ethoxylates using equilibrium dialysis and ultracentrifug ation. Both methods yielded statistically indistinguishable results. The ex perimentally determined log K(lipw)s were compared with log K-ow values est imated 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 t hese fragments, the quality of log K-lipw estimations can be improved signi ficantly 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 descrip tors for quantitative structure-activity relationships of bioaccumulation, toxicity, and sorption to natural organic material.