Lord of the molecular rings created

By Maggie McKee The Borromean ring, an icon of Nordic and Christian traditions, has been self-assembled at the molecular scale level for the first time. The new molecule, composed of three interlocking rings, provides another new component for future nano-devices. For decades, chemists have been creating molecules with ever more complicated shapes. Two rings had already been made to interlock, by creating one ring and then building a second around it. A five-link chain has also been strung together. But the Borromean ring - three rings entwined such that breaking one separates the other two - has proved elusive. It has been moulded in DNA, but only in a very wound-up form. "The molecular Borromean rings became a kind of Holy Grail in recent years," says Fraser Stoddart, director of the California NanoSystems Institute in Los Angeles, where the molecular rings were created.

"There was a bit of a friendly race going on to see who would get there first." Holy trinity Borromean rings have symbolised the holy trinity in Christian iconography, the heart of a giant in Nordic mythology, and the crest of the Borromeo family in 15th-century Tuscany. "Our inspiration was partly the sheer beauty of the molecules and partly their potential to be turned into some of the smallest possible machines and switches you can design at the molecular level," Stoddart told New Scientist . "Chains and links are important for making gears and switching devices," agrees Jay Siegel, a chemist at the University of Zurich, Switzerland, who was not part of the team. "But the real advance here is the synthetic skills that allow a whole variety of ringed structures to be made." Spontaneous assembly Rather than building the rings one at a time, Stoddart's team used zinc ions to nudge three component parts to come together spontaneously. The result was a Borromean ring with a diameter of 2.5 nanometres and an inner chamber lined with 12 oxygen atoms. "The compound makes itself because it is very much more stable than any of its competitors," he says. Computer modelling played a vital role in the molecule's design. "Not one atom changed its type or place in the molecular structure between going from the computer to the laboratory. This experience is still an extremely rare one," says Stoddart, whose results are published in Science . In the same issue of Science , a team led by Leyong Wang of Johannes Gutenberg University in Mainz, Germany, report creating two molecules, each made of four interlinked rings. Applications from the research are still a long way off, says Stoddart. "But as soon as we have a clear line of sight to a widget, we will head straight for it with a vengeance." Journal reference: Science (vol 304, pp 1308 and 1312)