C&EN: TODAY'S HEADLINES - Molecular Motor Has Novel Three-Ring Design

BETHANY HALFORD

A new type of molecular motor, a supramolecular structure with components that rotate in only one direction, incorporates two small rings threaded onto a 63-membered macrocycle to create a [3] catenane [Nature, 424, 174 (2003)].

The charm-bracelet-like structure--designed and built by chemistry professor David A. Leigh and grad student Jenny K. Y. Wong at the University of Edinburgh and coworkers at the University of Bologna, in Italy--is the first molecular motor to be made of components that do not share covalent bonds. Previous synthetic molecular motors spin around a single bond or a sequentially isomerized double bond.

"Leigh's mechanically interlocked molecular rotary motor is one of the most sophisticated examples of its kind to emerge so far," UCLA chemistry professor J. Fraser Stoddart says. Boston College chemistry professor T. Ross Kelly adds, "The experimental achievement--both the syntheses of the ingenious system and the studies demonstrating that the idea works--are magnificent accomplishments."

Hydrogen-bonding interactions hold each small ring at one of four chemically distinct sites on the macrocycle. Light, heat, or chemical stimuli drive the rings around by altering those sites and consequently the rings' affinity for them. Each small ring blocks movement of the other, ensuring that rotation occurs in only one direction.

In terms of potential applications, "nature uses molecular motion all the time," Leigh notes. "If we can get control over molecular motion, it would give us a whole new dimension of chemical technology."