COMPENSATION EFFECTS IN THE COMPLEXATION REACTIONS OF α- AND β-CYCLODEXTRIN

摘要

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) + [42.1( ± 1.2)]AS. 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 ± 0.2 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.