Application of the MIMS Technique to Study the Stability Constants of Small Organic Guest Molecules into Cyclodextrin Hosts in Aqueous Medium

In this work the potential of MIMS (Membrane Introduction Mass Spectrometry) for studying the inclusion of small organic guest molecules into cyclodextrin hosts in aqueous medium was investigated. MIMS profiles showed that the inclusion of benzene in cyclodextrins is favored in the following order: -CD HO-propyl--CD> -CD> -CD with equilibrium constants of K -CD = 404; K_HO-propyl-CD = 395, K _-CD = 335 and K _-CD = 210 M^-1 at 25 °C. Kinetic experiments suggested that under the conditions employed the inclusion process has a pseudo first-order dependence on the guest benzene concentration with the following order: -CD > -CD HO-propyl--CD> -CD. MIMS inclusion profiles of chlorobenzene and toluene showed that the presence of substituents in benzene makes the inclusion in -CD more difficult. Experiments with ferrocene--CD have also been carried out, showing that the complex rapidly dissociates in water and the resulting free -CD can complex with benzene present in the solution.