Sucrose dependence of solute inclusion in surfactant micelles: hydrophobiceffect and geometrical considerations

In high performance liquid chromatography (HPLC) using a poly(octadecylsilo xane) as a stationary phase, a series of imidazole derivatives (IDs) as sol utes, and a surfactant as a mobile phase modifier, a study on the surface t ension of sugar on the inclusion of IDs in surfactant micelles was carried out by varying the salting out agent concentration. A mathematical treatmen t was developed to calculate the degree of inclusion, n(c) (the percentage of included guest solute) and the number of sucrose molecules excluded from the solute-micelle interface during the inclusion process. The thermodynam ic parameters for solute inclusion processing the surfactant micelles were determined from Vant'Hoff plots. It was shown that the decrease in solute i nclusion accompanying the sucrose concentration increase was principally go verned by a decrease in the micelle radius due to the increased surface ten sion effects. This behavior caused a decrease in the hydrophobic interactio n for ligand inclusion in the surfactant micelle explaining the observed th ermodynamic trends. (C) 2001 Elsevier Science B.V. All rights reserved.