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
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