Elucidating dissociation activation energies in host–guest assemblies featuring fast exchange dynamics†
The ability to mediate the kinetic properties and dissociation activation energies (Ea) of bound guests by controlling the characteristics of “supramolecular lids” in host–guest molecular systems is essential for both their design and performance. While the synthesis of such systems is well advanced, the experimental quantification of their kinetic parameters, particularly in systems experiencing fast association and dissociation dynamics, has been very difficult or impossible with the established methods at hand. Here, we demonstrate the utility of the NMR-based guest exchange saturation transfer (GEST) approach for quantifying the dissociation exchange rates (kout) and activation energy (Ea,out) in host–guest systems featuring fast dissociation dynamics. Our assessment of the effect of different monovalent cations on the extracted Ea,out in cucurbituril:guest systems with very fast kout highlights their role as “supramolecular lids” in mediating a guest's dissociation Ea. We envision that GEST could be further extended to study kinetic parameters in other supramolecular systems characterized by fast kinetic properties and to design novel switchable host–guest assemblies.