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.