Cited research: Angew. Chem. doi:10.1002/anie.200906753 (2010)

The name Ouroboros, given by the ancient Greeks to a mythological serpent that bites its own tail, has now been bestowed on a molecular capsule that can similarly capture and release the end of its own arm to close and open an internal cavity (pictured).

Fabien Durola and Julius Rebek at the Scripps Research Institute in La Jolla, California, synthesized the ouroborand molecule, which consists of a bucket-shaped cavity and a rotating arm. The arm attaches to a bipyridyl unit on one end and bears a guest molecule on the other. The arm reaches over and places the guest in the cavity, closing it off.

When metal ions such as zinc are added to the mixture, the arm twists around so that the bipyridyl unit can bind to these ions. This arm-twisting pulls the contents out of the box, making the cavity accessible to external molecules. The system could be used as a tiny reaction flask, the authors say.

Credit: WILEY-VCH