Differential Effects of Substituent and Pressure on Induced Inclusion Complexation of 6-O-α-D-Glucosyl-β-Cyclodextrin with 4-Substituted Phenols

The inclusion complexation of 6-O-α-D-glucosyl-β-cyclodextrin (G-β-CD), in which the glucosyl side chain is introduced to β-CD, with various kinds of phenols was studied spectrophotometrically at high pressures. The characteristic effects of substituent and pressure were found for the inclusion complexation of G-β-CD. The association constants K for the G-β-CD inclusion complexation increased with an increase in the bulkiness of the 4-substituent groups in phenols. As the external pressure increases, the inclusion constants for the G-β-CD complexation increased and the reaction volumes were estimated to be −3.8 to −19.4 cm³ mol⁻¹ from their pressure dependences. From analysis of the effect of pressure on the inclusion complexation with G-β-CD, the number of water molecules included in the G-β-CD cavity in water was estimated. The number of water molecules repelled from the CD cavity plays an important role in the change in volume upon inclusion. In addition, the structures of the inclusion complexes of G-β-CD with phenols have been established by 1D and 2D NMR measurements. Based on the results, we suggested that the ability of the G-β-CD inclusion complexation is enhanced by the interaction between guest molecules and the glucosyl side chain of G-β-CD.