129Xe and 1H NMR Study of the Reversible Trapping of Xenon by Cryptophane-A in Organic Solution

Abstract

The interaction of xenon with cryptophane-A in 1,1,2,2-tetrachloroethane-d2 is investigated by 129Xe and 1H NMR spectroscopy. Xenon is reversibly trapped into the cavity of this host to form a 1 to 1 host−guest complex with an apparent association constant K of the order of at least 3 × 103 M-1 at 278 K. The exchange between the free and bound xenon is slow on the 129Xe NMR time scale, and the bound xenon resonance is shifted by approximately 160 ppm to lower frequencies with respect to the free xenon resonance. The xenon complex is at least 4 and 20 times more stable, respectively, than the corresponding chloroform and methane complexes under the same conditions. The stability of this xenon complex appears to be much greater than that of the previously described xenon complex of α-cyclodextrin in water. This is probably due to the combination of three favorable effects: (i) good size matching between the guest and the cryptophane cavity in its most relaxed conformation, resulting in the optimization of ...