Comparison of inter- and intramolecular cyclodextrin complexes

We present the first comparative steady-state and time-resolved fluorescence studies of inter- and intramolecular cyclodextrin complexes. Specifically, we report equilibrium and kinetic results for dansyl-glycine complexed with β-cyclodextrin (intermolecular) and the dansyl-glycine-β-cyclodextrin adduct (intramolecular). The fluorescence intensity decay profile for the intermolecular system is best described by a discrete triple exponential decay law. This is consistent with stepwise 1:1 and 2:1 (β-cyclodextrin:guest) inclusion complexation. Equilibrium constants are in line with previous results on similar species. In contrast, we found that the intramolecular case was described by a doubly exponential decay law—consistent with a single intramolecular inclusion complex. Displacement experiments, with borneol, confirm thesimplicity of the intramolecular complex. In all cases, continuous distribution models failed to fit the experimental data.