Protomer of Imipramine Captured in Cucurbit[7]uril

Small molecules possessing multiple proton-accessible sites are important not only to many biological systems but also to host–guest chemistry; their protonation states are causal to boosting or hindering specific host–guest interactions. However, determining the protonation site is not trivial. Herein, we conduct electrospray ionization ion mobility spectrometry–mass spectrometry to imipramine, a known molecule with two protonation sites, based on the introduction of cucurbit[7]­uril as a host molecule. For protonated imipramine, the proposed strategy allows clear distinction of the two protomers as host–guest complex ions and can be leveraged to capture the energetically less preferable protomer of the protonated imipramine.