Newly designed molecules can spontaneously snap together to form three interlocking rings. The molecular knot--a chemical incarnation of a symbol from Norse mythology, early Christianity, and 15th century Italian heraldry--may signal the way to new nanotechnologies.
For decades, practitioners of "topological chemistry" have sought ways to intertwine molecules in ever more elaborate patterns. In particular, researchers have striven to synthesize a molecular version of the Borromean rings--three rings laced together in such a way that cutting any one allows the other two to fall apart. Yet that knot, which adorns the crest of the Borromeo family of Renaissance Tuscany, has proved difficult to tie. In 1997, researchers succeeded in fashioning a version from specially coded DNA, but even then the twisted molecule looked more like a wadded up rubber band than three distinct rings.
More aesthetically pleasing Borromean rings can emerge spontaneously from a jumble of carefully engineered parts, nanochemists Kelly Chichak and J. Fraser Stoddart of the University of California, Los Angeles, and colleagues report in the 28 May issue of Science. The researchers first sketched out a hypothetical molecule with the right structure. To figure out how to synthesize it, they worked backwards, using a computer to break the virtual molecule into parts.Each ring was made of four parts. Zinc ions linked the rings in the desired configuration. Moreover, the parts were designed so that the only thermodynamically stable arrangement was a Borromean ring. The team then synthesized the parts from real molecules, mixed them in solution, and generated copy after copy of molecular Borromean rings."It is an absolutely magnificent piece of work," says Jean-Pierre Sauvage, a chemist at the University Louis Pasteur in Strasbourg, France. "It will stand as a masterpiece of molecular science." Jay Siegel, a stereochemist at the University of Zürich in Switzerland, says the results demonstrate the kind of control that may someday allow nanotechnologists to design molecular nanoparticles and even molecular machines: "This is exactly the kind of technology you need."
Chichak and colleagues' Science paper 
Stoddart group home page 
Much more about Borromean rings