Thermodynamic Studies of Inclusion Compounds of Cyclodextrin
Cyclodextrin (CD) can accommodate numerous polar and non-polar guest molecules to produce inclusion compounds, which are widely used as drugs, pharmaceutical preparations, food, and architectural materials. CD can also function as a simple enzyme, and its multi-purpose applications are extensively documented in the literature. This chapter deals with the thermodynamic properties of CD inclusion compounds involving simple molecules which differ, systematically, in the size of the aliphatic and functional groups. Most of the systems exhibited entropy-driven inclusion, but contributions of: electrostatic energy, exchange repulsion energy, charge transfer energy, and dispersion force to the enthalpies of inclusion, are also discussed. The van der Waals interactions between hydrophobic parts of guest molecules and the α-CD cavity have a large effect on the stability of inclusion compounds, as shown by the results of quantum chemical calculations. Carboxylic and hydroxyl compounds possess unique thermodynamic properties, and their entropy and enthalpy compensations are also discussed.