Translational motion inside self-assembled encapsulation complexes

The motion of guests inside a cylindrical self-assembled host is studied through NMR techniques. Small molecules encapsulated alone, such as the gas molecules cyclopropane and butane, are found to exchange locations slowly but measurably on the NMR time scale using 2D techniques. These molecules can move past one another while still inside the capsule. When gases are coencapsulated with longer flexible molecules such as alkanes, less motion is apparent yet these can still slip by one another and folding of the alkanes also can be detected. Activation barriers for these processes are in the range of 15–17 kcal/mol.