The use of immobilized artificial membrane chromatography to predict bioconcentration of pharmaceutical compounds

The potential of immobilized artificial membrane chromatography (IAM) to predict bioconcentration factors (BCF) of pharmaceutical compounds in aquatic organisms was studied. For this purpose, retention factors extrapolated to pure aqueous phase, logk_w(IAM), of 27 drugs were measured on an IAM stationary phase, IAM.PC.MG type. The data were combined with retention factors on two IAM columns, IAM.PC.MG and IAM.PC.DD2 types, reported previously by our research group and correlated with logBCF values predicted by Estimation Program Interface (EPI Suite) Software. Linear models were established upon exclusion of ionic or highly hydrophilic nonionic drugs, for which a constant value of logBCF equal to 0.50 was arbitrarily assigned by EPI Suite Software. As additional physicochemical parameter BioWin5 proved to be statistically significant, expressing the decrease of bioaccumulation potential as a result of biodegradation in the aquatic environment. The constructed IAM model was successfully validated by application to a set of pharmaceuticals, whose experimental BCF values are available. Better predictions compared to EPI Suite Software were achieved for the dataset under study. Since bioconcentration process involves electrostatic interactions, IAM retention may be a better measure for BCF values, especially for ionic species, compared to octanol-water partition coefficients widely implemented in environmental sciences. The developed approach can be considered as a novel tool for the prediction of bioconcentration of pharmaceutical compounds in aquatic organisms in order to minimize further experimental assays in the future.

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.