Correlation of the formation constant of ferrocene–cyclodextrin complexes with dielectric properties of the aqueous DMSO solution

The host–guest interactions between ferrocene and α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), Heptakis(2,6-di-O-methyl)-β-cyclodextrin (2-β-CD) and Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (3-β-CD) in aqueous DMSO solution were studied by means of cyclic voltammetry. The complex formation constant K was determined in the solutions of various values of the relative permittivity ɛr of DMSO:water mixture. The dependence of K on dielectric properties of the mixtures ɛr for all type of cyclodextrin utilized was found. Furthermore, the dependence of K   on the cyclodextrin type was also found. As an additional feature the different dependencies of the Gibbs energy of the complex formation, ΔGCF0 for different CDs on the volume ratio of DMSO, φDMSO were observed.

Dielectric properties of the solution strongly affect the ability of ferrocene to form host–guest complexes with cyclodextrin. The Gibbs energy of the complex formation depends on the type of cyclodextrin and on the degree of methylation of the CD.Figure optionsDownload as PowerPoint slideHighlights
► Dielectric properties of the solution strongly affect the ability of ferrocene to form host–guest complexes.
► The Gibbs energy of the complex formation depends on the type of cyclodextrin molecule and on the degree of methylation of the CD.
► The value of the complex formation constant is a function of both the type of the cyclodextrin cavity and the mixture composition.