김도의 (POSTECH)

김도의 (POSTECH)

서종철 (POSTECH)

Supramolecular chemistry relies on non-covalent interactions for the formation of host–guest complexes. In the case of macrocyclic hosts—such as cucurbiturils (CBs), pillararenes, and cyclodextrins—the stability of these assemblies is governed not only by host–guest interactions but also solvation behavior of the guest molecules in bulk solution. For cucurbiturils, the encapsulation process is driven by the expulsion of so-called “high-energy water” molecules that contributes to the free energy of complexation.

In contrast, under gas-phase conditions where solvent effects are absent, host–guest complexes may adopt significantly different structural conformations compared to those observed in solution.  This deviation is especially notable in complexes involving CBs and cationic guests, where electrostatic interactions are substantially enhanced in the gas phase. These amplified interactions can give rise to unique complex isomers that are not observed in solvated environments.

In  this work, we conducted a thermodynamic and structural analysis of CB[6] and CB[7] complexes with three bipyridine isomers (2,2′-, 3,3′-, and 4,4′-) through a combination of density functional theory (DFT) calculations and ion mobility spectrometry–mass spectrometry (IMS-MS) under gas-phase conditions. Solution-phase structures were characterized using nuclear magnetic resonance (NMR) spectroscopy, highlighting the significant influence of phase on complex stability and conformation.