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 H-1 and - for the first time - H-2 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. (C) 2004 Elsevier B.V. All rights reserved.