Abstract
We have used the isomerization of 1',3',3'-trimethyl-spiro[2H-1-benzopyran-2,2'-indoline]-6-sulfonic acid (6-SO3--spiropyran) as a chemical indicator determining the unbound cyclodextrin (CD) concentration in solution, and have evaluated the equilibrium constants for the inclusion complex formation of heptakis-(2,6-di-O0methyl)-β-cyclodextrin (DM-β-CD) with 4-substituted phenols. The equilibrium constants for inclusion complexation tend to increase with an increase in the bulkiness of the 4-substituted group. The effects of pressure were examined for the inclusion complexation of DM-β-CD with 4-substituted phenols. The reaction volume for the DM-β -CD inclusion complexation with 4-substituted phenols was estimated from the pressure dependence of the inclusion equilibria. The pressure dependences for the DM-β-CD inclusion of 4-substituted phenols except 4-CH3(CH2)5-phenol were small (ΔV=0 cm3 mol-1). The difference in the reaction volumes for the inclusion complexation is explained in terms of the volume contributions of a few different factors in analogy with the inclusion complexation of β-CD. Based on the results, we undertook a volumetric study to clarify the inclusion behaviour of DM-β-CD.
