Cucurbit[n]urils are a relatively new class macrocyclic host molecules that are formed by the acid-catalyzed condensation of glycoluril and formaldehyde. They are characterized by two carbonyl-lined portals of partial negative charge and a hydrophobic cavity of extremely low polarizability.
The negative charge density on the portals of the cucurbituril host molecule can assist in the stabilization of positive charges. This property of these macrocycles can be exploited to facilitate the protonation of functional groups, thereby shifting their pKa value. These changes can have severe consequences for included guests, e.g. a change in photophysical properties or reactivity.
Example of a product-selective supramolecular tandem enzyme assay for lysine decarboxylase, which converts lysine into cadaverine. The reporter pair used consists of Dapoxyl as dye and Cucurbituril as host.