An enormous challenge to science is the generation of two individual molecules that are not chemically bound to each other but are mechanically wedged together to form a tight link. A team of British and American researchers now has developed an entire new family of such mutually interlocked molecules. The team is headed by J. Fraser Stoddart -- director of the California NanoSystems Institute (CNSI), who holds UCLA's Fred Kavli Chair in Nanosystems Sciences -- and David J. Williams, emeritus professor of chemistry at Imperial College, London.
The researchers have named these novel compounds "suitanes," based on their resemblance to a "torso" with two or more "limbs" that is completely enveloped in a one-piece "suit." The number of limbs is indicated by a number inserted into the name of the compound --for example, a suit[2]ane has two limbs and a suit[3]ane has three.
"Discovering the way to dress a molecule with another one is a prelude to constructing artificial systems reminiscent of the living cell," Stoddart said.
A suit[5]ane -- a suitane with five limbs -- looks like a doll wearing a one-piece romper enclosing all five limbs: two legs, two arms and the head, said Stoddart, a pioneer in supermolecular chemistry who grew up in Scotland.
"The inspiration for the name came from looking at my grandson in a onesie, an American term I had never heard before," he said.
The team of chemists has successfully synthesized the simplest representative of this class of compounds: a suit[2]ane. They first used computer simulations to develop a plan of attack. The inner molecule, the "body," should be relatively stiff and oblong, Stoddart said. The suit must be a flexible molecule that can be assembled around the body from a few individual components.
"Like a well-tailored suit, all of the individual components must be perfectly coordinated with each other regarding their shape, size and functional groups," Stoddart said. The research is published this month in the German chemistry journal, Angewandte Chemie.
The chemists first produced a stiff, linear molecular framework. A slim center (a central aromatic ring) was hooked to two bulging "shoulders" (anthracene ring systems), each attached to an "arm." Next, the molecule was dressed in its suit. The suit was put on piece-by-piece and "sewed" together in a final step: in a self-organization process, two large ring-shaped molecules (crown ethers) slipped like sleeves onto the molecular "arms."
The torso, arms and sleeves were chemically outfitted to provide strong interactions to hold the sleeves tightly in place. In the next step, another smaller type of molecule (aromatic ring) was added. These molecules each contained two groups of atoms (amino groups) located across from each other, designed to each enter into attractive interactions with one spot on each sleeve. In the final step, chemical bonds were formed at these four points of contact; the aromatic rings thus linked the two sleeves into a single large molecule that completely enclosed the torso molecule without binding to it chemically.
The CNSI, a joint enterprise between UCLA and the University of California, Santa Barbara, is exploring the power and potential of organizing and manipulating matter to engineer "new devices and systems that will extend the scope of many existing technologies and foster commercial development far beyond anything we might have contemplated up until now," Stoddart said. Its mission is to encourage university collaboration with industry and to enable the rapid commercialization of discoveries in nanosystems.
For more information about Stoddart's research, please see http://stoddart.chem.ucla.edu/. For more about the CNSI, please see http://www.cnsi.ucla.edu/.
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