Molecular echoes of Kekule

Julius Rebek, Jr. and Fabien Durola of The Scripps Research Institute, La Jolla, USA, have constructed a molecular tail devourer, which they have named an ouroborand after the Greek ouroboros. The system functions as a molecular machine, that can encapsulate a smaller molecule but has a built-in switch that regulates access to the cavity. A switchable rotor, a bipyridyl unit, on its edge acts as a zinc-activated access control, In the presence of zinc ions, this rotates so that it opens entry to the cavity and can allow smaller molecules inside. Remove the zinc and the molecule once again bites its own tail.