Study of Inclusion Complexes of Cyclodextrins with Orange II

Inclusion reactions of α- and β-CD with Orange IIwere measured by means of a stopped-flow method and UV-spectra. The forward rate constants (k+), backward rateconstants (k-) and the equilibrium constants (K) for the inclusion reactions were determined. Theinclusion processes of CD with Orange II follow a one-step reaction mechanism. The value of the forward rate constantat neutral and alkaline conditions for Orange II binding to α-CD cavity was large. This suggests that thenaphthalene side is partially included in the final complex form. In the case of β-CD, only marginal differenceis shown.It is probable that inclusion covers the whole naphthalene group and part of the azo group as well,resulting ina small effect from the pH variation. The results show that the equilibrium constant at pH 7 for the binding ofOrange II to α-CD is the largest because the included part of Orange II matches the cavity of α-CD well.