NMR study of the reversible complexation of xenon by cucurbituril

Abstract

The interaction of xenon with cucurbituril, a synthetic receptor, in aqueous solutions is investigated by 129Xe and 1H NMR spectroscopy. Xenon is reversibly trapped into the cavity to form a 1 ∶ 1 host–guest complex. The exchange between the free and the complexed xenon is slow on the 129Xe NMR chemical shift time scale but fast on the 1H NMR chemical shift time scale. The apparent association constant of xenon for cucurbituril can be obtained from analysis of the 1H spectra and is estimated to be around 200 M−1 at 298 K. Interestingly, even though no H-bonding or electrostatic interactions play a role in the stabilisation of the complex, its stability is comparable to the stability of cucurbituril complexes with certain aryl- and alkyl-ammonium ions.