Alkyl substituted 4-pyrrolidinopyridinium salts encapsulated in the cavity of cucurbit[10]uril

The interaction between cucuribit[10]uril (Q[10]) and a series of 4-pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4-(C4H8N)C5H5NRBr, where R = Et (g1), n-butyl (g2), n-pentyl (g3), n-hexyl (g4), n-octyl (g5), n-dodecyl (g6), has been studied in aqueous solution by 1H NMR spectroscopy, electronic absorption spectroscopy and mass spectrometry. The results revealed that the guests g1–g5 are located completely inside the cavity differing only in the orientation of g1, g4 and g5 which are aligned with the portal, whilst g2 and g3 are perpendicular to it. For g6, the tetrahydropyrrole moiety remains outside of the portal. DFT calculations confirm the stability of the guests in the Q[10] and the possibility of their curved structure inside the Q[10].