Xe-129 NMR spectroscopy of deuterium-labeled cryptophane-A xenon complexes: Investigation of host-guest complexation dynamics
We have discovered the ability of Xe-129 NMR spectroscopy to discriminate between the xenon complexes of cryptophane-A1 and its deuterated congeners 2-6 in solution. At 238 K, under slow exchange conditions, the upfield shift experienced by the xenon atom upon complexation by 1 (190 ppm) is increased (up to similar to 0.6%) when the hosts are deuterated. By using mixtures of deuterated and nondeuterated hosts, such as 1 and 6, the dynamics of a xenon atom can thus be traced between three different sites (one free and two bound states). We have demonstrated that some of the dynamic features of the exchange between these sites can be extracted from 2D-EXSY experiments, using a suitable kinetic model. We conclude that the exchange of a xenon atom between different hosts occurs by travelling through the solution rather than upon collision of two hosts.