Carboxylated pillar[5]arene cavity accommodates organic cations in the host-guest complexes

National Science Centre of Poland (grant PRELUDIUM 14 nr 2017/27/N/ST5/01931); Polish high-performance computing infrastructure PLGrid (HPC Centers: ACK Cyfronet AGH) computational grant no. PLG/2024/016926

The electron-rich cavity of carboxylated pillar[5]arene efficiently encapsulates cationic guest molecules within supramolecular assemblies. In this study we provide evidence of the host-guest complexation between carboxylated pillar[5]arene and benzamidine, a competitive inhibitor of serine proteases. We show the unexpected inclusion of the polar amidinium functionality within the central cavity of the macrocyclic host sustained by N+-H⋅⋅⋅π and cation⋅⋅⋅π interactions. In addition to the incavity complexation, simultaneous external binding of bipyridinium guests with varying stoichiometries has been observed. The interesting aspect is the inclusion of a hydrogen bonded pair of 1,2-bis(4-pyridyl)ethylene guests into pillar[5]arene cavity. Additional insights into inclusion characteristics are provided by NMR and ion mobility mass spectrometry (IM-MS) studies, offering information for the solution/gas phase and enabling a comprehensive description of the complexation process across different phases. This work expands the portfolio of cationic guest molecules capable of being encapsulated by carboxylated pillar[5]arene, showing new promises and directions for their inclusion and self-assembly behavior.