Thermodynamics of formation of inclusion compounds in water. a-Cyclodextrin-alcohol adducts at 298.15 K.

The interaction in water of ethanol, n-propanol, n-butanol, isobutanol, s-butanol and t-butanol with a-cyclodextrin (hexacycloamylose, crCD) has been studied calorimetrically at 298.15 K. The results indicate that, with the exception of the t-butanol, these alcohols form inclusion complexes with this dextrin. The calorimetric method employed allows the determination of the thermodynamic parameters characterizing the binding process, namely the enthalpy, APB, the apparent equilibrium constant, I&, and then the free energy, AGE, and entropy, TASOB/. The complexes that result are weak, as shown by the low values of the constants. The absolute values of AIPB and K;3 increase with increasing length of the alkyl chain. Branching of the alkyl chain lowers the value of Kb. Evidence is given to show that t-butanol does not form a complex with aCD, probably because of steric hindrance: for this system the calorimetric data are treated according to an approach derived from the McMillan-Mayer treatment of solutions.