Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers

Abstract

Pyridine[4]arenes have previously been considered as anion binding hosts due to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected and studied by multiple gas-phase techniques, ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, as well as DFT calculations. The comparison of classical resorcinarenes with pyridinearenes by MS and NMR experiments reveals clear differences in their host–guest chemistry and implies that cation encapsulation in pyridine[4]arene is an anion-driven process.

Solution- and gas-phase study of binding of ammonium and bisammonium hydrocarbons to oxacalix[4]arene carboxylate

“…IM-MS is a versatile gas-phase method that has been used for evaluating host-guest complex conformation, structures and geometries. [39][40][41][42][43] In IM-MS, the collision cross section (CCS) value for analyte ions is measured. Additionally, in the presence of two or more binding modes, their respective structures can be separated.…”

Reaction Monitoring and Structural Characterisation of Coordination Driven Self-Assembled Systems by Ion Mobility-Mass Spectrometry

“…However, these complicated behaviours are only of value if they are understood. IMS-MS can be a powerful tool for developing that understanding, as these behaviours often yield mass or shape differences ( Nortcliffe et al, 2015 ; Kiesilä et al, 2017 ; Schröder et al, 2017 ; Kiesilä et al, 2019 ).…”

Thermodynamically driven self-assembly of pyridinearene to hexameric capsules

“…6 Recently, conformational analysis for the tautomers also revealed that the hydroxy-oxo tautomer (Scheme 1) is ∼150 kJ mol −1 lower in energy than the dihydroxy tautomer. 7 The cavity of pyridinearene was earlier considered electron deficient and suitable to bind anionic guests. 8,9 Recently, instead of encapsulation of anions, the pyridinearene dimers were shown to actually favour encapsulation of neutral guests of matching size, and hence maximizing dispersion interactions.…”

“…6 Although the cavity of pyridinearenes is most suitable for neutral guests, also anion-driven encapsulation of cations inside the pyridinearene dimers was recently demonstrated. 7 In one of the earliest reports concerning the self-assembly of pyridinearene, two species were observed in chloroform solution which were initially erroneously assigned as a mixture of monomers and dimeric assemblies. 9 Cohen et al later proved these as dimeric and hexameric species using diffusion ordered (DOSY) NMR spectroscopy experiments.…”