Molecules On Elevator Go Up And Down On Command

Updated: Mar 25 2004, 05:30am hrs
In an elegant bit of nanoscale engineering, chemists at the University of California, Los Angeles, have designed and built what must be the worlds tiniest elevator, a molecular platform on three legs that can be raised or lowered on command.

The device, created by Dr J Fraser Stoddart, a professor of organic chemistry, and colleagues, is about 2.5 nanometers high, and the platform moves less than a nanometer up and down. A nanometer is about one 25-millionth of an inch.)

Although the elevator is more complex and organised than other so-called molecular machines, Stoddart said the work, which is described in the current issue of the journal Science, was only an extremely incremental step toward developing useful molecular-scale devices that might, for example, function as drug-delivery systems. The elevator or something like it, he said, might someday serve as a valve, opening and closing a tiny cavity to allow a few drug molecules to reach a cell.

Stoddart said the elevator was created in conventional reaction vessels like those found in any chemistry laboratory.

But the reaction is not a conventional one, he said. The structure assembles itself, the stool-like legs acting as a template that goes out and searches for the platform. The platform is connected by three ringed molecules that fit over the legs like a childs ringtoss game.

In assembling itself, the structure threads the rings on two of the legs fairly quickly. But it takes a week or so for the third leg to be correctly positioned. Its not a boom-boom-boom event, Stoddart said. Its a boom-boom-and-wait event. It makes mistakes along the way and has to correct itself.

The key to the platforms ability to move up or down is in the legs, molecules called rotaxanes that have two sites along their length where the ringlike platform molecules can bind. Normally, the platform molecules are bound near the tops of the legs, but acid-base reactions can cause them to move. Add a base, and they travel to the lower sites. Add an acid, and they return to the top.

The movement is repeatable, Stoddart said, but all that acid and base eventually cause problems. Far better would be a device that operates with a tiny electrical charge or by shining light on it.

Such developments are part of the future of what is a fledgling field, Stoddart noted.

This science is very new and very exciting, he said. But I think its where the Wright brothers were 100 years ago in relation to flight.

HENRY FOUNTAIN / NY TIMES