Dynamics of an Inclusion Complex of Chloroform and Cryptophane-E:  Evidence for a Strongly Anisotropic van der Waals Bond

The motional dynamics of a van der Waals inclusion complex of cryptophane-E and chloroform has been investigated by a combined NMR exchange and relaxation study. The kinetics of exchange of chloroform between the bulk solution and the complex was investigated by means of proton EXSY measurements. The carbon-13 relaxation of the cryptophane-E host and of the bound chloroform guest was analyzed using the Lipari−Szabo “model-free” approach. For interpretation of the carbon-13 relaxation measurements for chloroform, the chemical-exchange process of complex formation and dissociation had to be taken into account in terms of the modified Bloch equations. It was found that the complex behaves as a single molecule without any significant guest chloroform motion inside the host's cavity.