STABILITY AND STRUCTURE OF THE INCLUSION COMPLEXES OF ALKYL-SUBSTITUTED HYDROXYPHENYLAZO DERIVATIVES OF SULFANILIC ACID WITH ALPHA-CYCLODEXTRIN AND BETA-CYCLODEXTRIN

The dissociation constants for inclusion reactions, Kd and Kd′, of alkyl-substituted hydroxyphenylazo derivatives of sulfanilic acid with α- and β-cyclodextrins are determined spectrophotometrically. In most cases, stabilities of the inclusion complexes with β-cyclodextrin are found to be lower than those of the corresponding inclusion complexes with α-cyclodextrin. The values of Kd and Kd′ for β-cyclodextrin complexes to some extent depend on the shape and the size of the alkyl substituents in the guest azo molecules, whereas those for α-cyclodextrin are almost the same except for the guests having bulky alkyl substituents. On the basis of 1H NMR measurements, we propose a possible structure of the final inclusion complexes and the intermediate species in the two-step inclusion between the guest azo molecules and cyclodextrins. © 1990 American Chemical Society.