Measurements of host-guest interaction energies in a calixarene supramolecular complex

We report the results of NMR relaxometry measurements on the p-tert-butyl-calix[4]arene and the p-tert-butyl-calix[4]arene(1:1)toluene supramolecular systems in the solid state. Relevant information on the dynamics of the p-tert-butyl groups of the host cage is obtained, and the variation produced by the toluene guest molecule in the activation energy characterizing the reorientation of the methyl groups is determined. This variation provides an estimate of the host-guest interaction energy, part of which is attributed to a noncovalent, attractive force between CH₃ groups of the host and the π system of the guest molecule.