Spectrophotometric determination of the stability constant of the inclusion complexes of some catechol derivatives with β-cyclodextrin based on their reaction with iodate

The effects of beta-cyclodextrin (beta-CD) inclusion on the kinetics of the oxidation of several cathechol derivatives, including 4-tert-butylcatechol, 3-methylcatechol and 3-methoxycatechol, with iodate was studied spectrophotometrically. The rate of the oxidation reactions decreased by increasing beta-CD concentration as a result of inclusion. The stability constants for the inclusion complexes of the investigated compounds were determined based on the changes in the rate constants as a function of beta-CD concentration at pH 3.0. The rate constants for the free and complexed forms and also the stability constants for the inclusion complexes were calculated. The role of the hydrophobic effect was evaluated by studying the influence of the presence of different amounts of ethanol on the beta-CD: guest interaction. In a given H2O-EtOH mixture the stability of beta-CD complexes shows the order of 4-tert-butylcatechol approximate to 3-methylcatechol approximate to 3-methoxycatechol. Increasing ethanol content caused a decrease in the stability constant of the inclusion complexes and an increase in observed rate constants.