Compensation effects in the complexation reactions of α‐ and β‐cyclodextrin

Analysis of temperature dependent equilibrium constant data for the complexation of α‐cyclodextrin with approximately 70 different substrates demonstrates the existence of a general compensation effect. Enthalpies (kJ mol−1) and entropies (J K−1 mol−1) of complexation are related by ΔH = −5·70(±0·05) + [421·1(±1·2)]ΔS. A few substrates deviate from the general effect, possibly owing to reorganization of internal hydrogen bonding interactions. Complexation reactions involving β‐cyclodextrin are found to divide into two groups. Eleven small molecule or ion substrates undergo isoentropic complexations with ΔS = −5·7±2 J K−1 mol−1. Fourteen larger substrate species exhibit a compensation effect with ΔH = −23·5(±0·2) + [634(±26)]ΔS. The compensation behavior of the two cyclodextrins is discussed in terms of bonding mechanisms and cavity size.