Theoretical study on the protonation of cucurbit[7]uril.

By using quantum mechanical DFT calculations, the most probable structures of the cucurbit[7]urilH3O+ and cucur-bit[7]uril'(H3O+)2 cationic complex species were derived. In these two complexes having a plane symmetry, each of the considered H3O+ cations is bound by relatively strong hydrogen bonds to the corresponding carbonyl oxygens of the parent cucurbit[7]uril macrocycle.