Complexation of phenols with beta- and gamma-cyclodextrins: determination of the association constants by using the isomerization of spiropyran

As a chemical indicator, the isomerization rate of so-called 6-SO3--spiropy ran was used to estimate the equilibrium constants for the inclusion comple x formation of beta- and gamma-cyclodextrins (beta and gamma-CDs). The asso ciation constants for inclusion complexes of beta- and gamma-CDs with vario us kinds of phenols were determined. It was found that beta- and gamma-CDs form 1:1 and 1:2 inclusion complexes with phenols, respectively. The substi tuent effects on the association constants for the 4-substituted phenols-be ta-CD system can be interpreted in terms of the geometry of the inclusion c omplex. The magnitude of the association constants for the inclusion comple x is related to molecular polarizability of the guest molecule. Based on th e results, the dominant factor for CD complexation with phenols is discusse d. Copyright (C) 1999 John Wiley & Sons, Ltd.