Ionization of cucurbiturils as a pathway to more stable host–guest complexes

Abstract

Cucurbiturils are particularly interesting to chemists, because these macrocyclic molecules are suitable hosts for many neutral and cationic species. Allegedly, the host–guest binding originates from hydrophobic effects and ion–dipole interactions in the case of cationic guests. An elementary unit of cucurbiturils (glycoluril unit) consists of two fused imidazole rings. Each of these rings can be ionized. We report ionized cucurbiturils and discuss their binding to C60 fullerene using an electronic-structure approach. We assert that the ionization of cucurbiturils fosters C60 – cucurbituril binding due to significant polarization of electron density in C60. Our results suggest a previously unexplored pathway to additionally increase stability of the host–guest complexes.