Thermodynamic Analysis of Inclusion Complexation between α-Cyclodextrin-Based Molecular Tube and Sodium Alkyl Sulfonate

Abstract

Thermodynamics on inclusion complexation of α-cyclodextrin-based molecular tube (MT) with sodium octyl-, decyl-, and dodecylsulfonates (C8-, C10-, and C12SO3Na) were measured by isothermal titration calorimetry (ITC) to evaluate the effects of alkyl chain length of CnSO3Na and temperature. It was found that CnSO3Na with a longer alkyl chain formed more stable inclusion complex with MT. The association constant of inclusion complexation between MT and C12SO3Na at 298 K was found to be on the order of 105. The stoichiometric number ([host]/[guest] ratio) was found to be 0.50 ± 0.05. This result indicates that one MT forms an inclusion complex with two CnSO3Na molecules, regardless of the alkyl chain length of CnSO3Na. Enthalpy−entropy compensation was also observed in MT/CnSO3Na systems, and it was confirmed that the free energy change was not affected by the change in temperature (288−308 K). From the thermodynamic parameters, it was considered that both hydrophobic interaction and van der Waals interactio...