Tiny molecular machines that can build themselves are the futuristic-sounding goal of supramolecular chemists.Ideal candidates for these devices are molecules built out of interlocking rings, known as catenanes. Self-assembly reactions need host and guest molecules and getting them to arrange themselves without some kind of irremovable template guiding them into position is difficult.

Now Stephen Loeb at the University of Windsor in Canada has made a self-assembling catenane with three interlocking rings that very cleverly also acts as a template for itself. In this latest self-assembled twist, the middle of the three rings plays host and binds to two water molecules. In turn they become the guest and are bound centrally into the interlocking rings without the need for a template. As Loeb explains this simplifies the process, '[usually] the actual templating component is incorporated into the final structure and cannot be removed. Using an external guest as the template allows us to remove this component after formation of the catenane'. 

Katharine Sanderson