The Limited Contribution of the Analyte Partition to the Water-Rich Layer in Immobilized Artificial Membrane Chromatography with an Acetonitrile-Rich Binary Mobile Phase

Abstract

Drug-induced phospholipidosis, a side effect of drugs, is associated with drug–membrane binding. Hydrophobic interactions of the drug with the membrane and polar interactions of the drug with the membrane are involved. For risk predictions, membrane binding studies often give false results for strongly hydrophobic compounds and basic hydrophilic compounds because the effects of the hydrophobic interactions overshadow the effects of the polar interactions. Therefore, separate assessments of hydrophobic partitioning and polar interactions are needed. However, a screening method focusing on the polar interactions between drugs and membranes has not yet been reported. In the present study, the retention behavior of an immobilized artificial membrane (IAM) column using a binary mobile phase with a high acetonitrile content was studied to clarify the contribution of the analyte partition to the water-rich layer on the surface of the packed material, which may interfere with the assessment of the polar interactions with the membrane. For acetonitrile contents greater than 50%, the retention factor of propranolol increased as a result of the hydrophilic interactions. The Van’t Hoff plot suggested that the adsorptive retention of the analyte became dominant with high acetonitrile content in the mobile phase, in contrast to the hydrophobic partitioning that occurred for low acetonitrile content. Hydrophilic neutral compounds (e.g., thiourea and mesityl oxide) were not retained. The addition of salts to the mobile phase decreased the propranolol retention. Even with the addition of a kosmotropic salt, the decreased retention indicated that hydrophilic partitioning to the water-enriched layer was unlikely to be the major mechanism. In addition to ionic interactions, other polar interactions were presumed to be involved. The relationships between the retention factor and the log P or pKa values also supported this conclusion. The results of this study suggest that there is potential for IAM chromatography to be used as a tool to estimate the contribution of the polar interactions in overall drug–membrane interactions, which can aid in predicting the risk of phospholipidosis.