Hydroxypropyl-beta-cyclodextrins: Induced circular dichroism spectra of included phenolphthalein as a function of the degree of substitution

The hydroxypropylation of beta-cyclodextrin does not change the essential nature of its interaction with phenolphthalein but the pattern and degree of substitution do alter both the stability constant of the inclusion complex and its induced circular dichroism spectrum. The reason for this phenomenon is that substitution of the hydroxy groups (especially that of the primary ones) in cyclodextrin may cause increased steric hindrance and provide modified possibilities for hydrogen bonding.