Kinetic effects of methyl-β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin and their mixtures on the reaction [Fe(CN)5(4-phepy)]3− + [Co(NH3)4(H2O)2]3+

Oxidation (electron transfer) of [Fe(CN)5(4-phepy)]3− with [Co(NH3)4(H2O)2]3+ has been studied in solutions containing methyl-β-cyclodextrin (MβCD) and 2-hydroxypropyl-β-cyclodextrin (HβCD) as well as mixtures of these CDs. The results can be explained by using the Brönsted equation after an adequate formulation of the activity coefficients appearing in this equation. The non-additivity of the effects of the CDs in these mixtures is also shown here.