The encapsulation of biologically important compounds in the cavity of cucurbiturils (CB7) brings about a variety of effects. The binding of lumichrome to CB7 promotes the tautomerization from alloxazine- to isoalloxazinetype structure in the ground-state, leading to substantial changes in the absorption and fluorescence properties. Even partial embedding in CB7 macrocycle is able to protect sanguinarine, a natural alkaloid, against nucleophilic addition and photooxidation. The inclusion of berberine in CB7 results in about 500-fold enhancement of its fluorescence intensity, and the change in its fluorescence decay characteristics indicates ternary complex formation with cations. DAPI (4',6-diamidino-2-phenylindole dication) is an excellent fluorescent probe for the study of the CB7 complex formation with ionic liquids, surfactants, and biologically important compounds. The binding of 1-alkyl-3-methylimidazolium ions to CB7 is strongly exothermic; both the enthalpy and the entropy change in the reaction go through a minimum when the 1-alkyl group is lengthened, reaching the smallest values for the hexyl derivative.
- Supramolecular chemistry
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