Cryptophanes represent an exciting class of xenon-encapsulating molecules that
can be exploited as probes for nuclear magnetic resonance imaging. The 1.70 A
resolution crystal structure of a cryptophane-derivatized benezenesulfonamide
complexed with human carbonic anhydrase II shows how an encapsulated xenon atom
can be directed to a specific biological target. The crystal structure confirms
binding measurements indicating that the cryptophane cage does not strongly
interact with the surface of the protein, which may enhance the sensitivity of
129Xe NMR spectroscopic measurements in solution.