Modulation of dansyl moiety fluorescence in systems containing cyclodextrins

Abstract

The present study reports on the changes in dansyl moiety fluorescence due to the interactions with the β-cyclodextrin cavity observed by steady-state fluorescence spectroscopy. First, the interaction of a guest molecule, dansyl-TEMPO (DT), which has in its structure a dansyl group as a fluorescent moiety and a paramagnetic fragment (TEMPO), with β-cyclodextrin was studied. Analysis of the EPR spectral parameters provided additional information on the host–guest interaction, suggesting that the cyclodextrin cavity accommodates dansyl rather than a TEMPO moiety. Second, the affinity between 1-adamantol or adamantane end-capped polyethylene glycols – A2Pnn – (as guests) and dansyl-β-cyclodextrin (D-β-CD, as a host) was investigated. In the presence of adamantol, the intensity of fluorescence of D-β-CD decreases and a hypsochromic effect was noticed. The same behaviour was observed in the presence of A2Pnn. Using Benesi–Hildebrand and Stern–Volmer equations and also the sensitivity factor made possible to obtain quantitative data on the interaction between the dansyl moiety and the cyclodextrin cavity. The formation of inclusion complexes in the solid state between D-β-CD and A2Pnn was evidenced analysing the DSC curves of the pure solids, physical mixture and prepared solid complexes. In addition, the use of D-β-CD for fluorescent labeling of a covalently based network hydrogel and diffusion of dansyl derivatives into a gel are shown as possible further application of this study.