Aggregation and Solubilization Properties of System Based on Glycine-Calix[4]resorcinol and Sodium Dodecyl Sulfate in Aqueous Medium

A complex of physicochemical methods showed that the water-insoluble glycine-based calix[4] resorcinol is solubilized by sodium dodecyl sulfate (SDS) micelles, thus not affecting the character of surfactant aggregation. pH-dependent solubilization of hydrophobic drug 2,2'-bibenzimidazole (BBI) in SDS micellar solutions in the presence of this macrocycle was shown. At acidic conditions the presence of solubilized calix[4] resorcinol in SDS micelles leads to a decrease in the joint solubilization of BBI in aqueous micellar solutions. In this case, the protonation of the nitrogen atom at the upper rim of calixarene favors its solubilization in the SDS micelles due to electrostatic interaction. This leaves little "room" in the hydrophobic part of the micelles to solubilize the drug. In the alkaline medium, the upper rim of calixarene is recharged to negative values due to the dissociation of hydroxyl and carboxyl groups. The electrostatic repulsion between SDS and calixarene molecules frees the hydrophobic part of the surfactant micelles from the macrocycle, which increases the solubilization capacity with respect to BBI. This result is of importance from the viewpoint of the delivery of lipophilic drugs.