Solvent molecules trapped in supramolecular organic nanotubes: a combined solid-state NMR and DFT study

When crystallised from water/acetone mixtures, calix[4]hydroquinone (CHQ) forms supramolecular nanotubes which we studied by NMR spectroscopy and DFT calculations, using the 1H and – for the first time – 2H chemical-shift resolution achievable in the solid state under fast (30 kHz) magic-angle spinning. Acetone molecules are trapped in the bowl-shaped CHQ molecules inside the tubes and hydrogen-bonded to an extended chain of hydrogen bonds, which is formed by CHQ and water molecules along the tube axis. Both water and acetone molecules occupy well-defined average positions, but undergo fast reorientation motions during which their protons interchange their positions.