Effects of external pressure and solvent polarity on inclusion complexations of phenothiazine dyes and trans-4-[4-(dimethylamino)styryl]-1- methylpyridinium with water-soluble p-sulfonatocalix[8]arene in alcohol-water mixtures

The effects of pressure and solvent were examined for the inclusion complexation of phenothiazine dyes and trans-4-[4-(dimethylamino)styryl]-1- methylpyridinium (St-4Me) with water-soluble p-sulfonatocalix[8]arene (Calix-S8). Depending on the bulkiness of the guest dyes, external pressures and solvent polarity increase the inclusion equilibrium constants of dyes with Calix-S8. From the pressure dependence of the inclusion equilibria, the reaction volumes for inclusion by Calix-S8 in the alcohol-water mixtures were estimated to be negative values (-19.8 to -5.29 cm³ mol^-1 for the phenothiazine dyes and -13.1 to -9.85 cm³ mol^-1 for St-4Me). Analysis of the results of the high pressure indicated that the intrinsic volume change related to inclusion into the Calix-S8 cavity plays an important role in the inclusion of Calix-S8, depending on the bulkiness of the guest molecules. Based on ¹H NMR measurements, the structures of the inclusion complexes of Calix-S8 with phenothiazine dyes have been established and the differences in the inclusion behaviors of the phenothiazine dyes and St-4Me are discussed.