Will You Ride This Nano-Elevator?

By Roland Piquepaille

Chemists from Italy and at the University of California, Los Angeles (UCLA) have built the world's smallest elevator. It is a molecular elevator, about 2.5 nanometers high and 3.5 nanometers wide. The molecular platform sits on three legs which can move up and down by one nanometer. The New Scientist and the New York Times (free registration needed) are both reporting about this nano-elevator. The researchers think this system might be used as a drug delivery system. Even if they're right, it will not happen before at least ten years.

Let's start with the New Scientist introduction.

Nanoscale elevators made of two interlinking organic molecules have been built and operated by US and Italian scientists.

They are the most complex molecular machines built yet, consisting of a platform flanked by three rings that thread through three vertical rods.

Here is how it works.

The nano-elevator consists of a platform molecule -- the elevator itself, and a stool-shaped molecule -- the shaft. The platform is flat and is flanked by three oxygen-rich rings. The shaft has a flat roof and stands on three vertical prongs. Each prong is threaded through one of the rings.

When the rings slide up the prong, they pull the platform with them. The whole thing stands 2.5 nanometres tall and 3.5 nanometres wide.

Here is a schematical representation of the chemical equilibrium between the two co-conformations of the molecular elevator (Credit: UCLA).

The New York Times adds that the process is not perfect.

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. "It's not a boom-boom-boom event," said Dr. J. Fraser Stoddart, a professor of organic chemistry at UCLA. "It's a boom-boom-and-wait event. It makes mistakes along the way and has to correct itself."

So will these nano-elevators be used as drug-delivery systems as Stoddart envisions? Here is a skeptical answer provided by the New Scientist.

However, others remain unsure about what the elevators will be used for. "If and in which way such motor molecules will ever be useful, nobody knows at this moment," says Fred Brouwer of the University of Amsterdam, who built the first light-powered molecular motor in 2001. "The main reason for doing this kind of research is that it is a challenge."

Even Stoddart is not so sure about the future of this molecular elevator, he's still excited about it, as reports the New York Times.

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

The research work has been published by Science on March 19. Here is the abstract of the paper, simply named "A Molecular Elevator."

We report the incrementally staged design, synthesis, characterization, and operation of a molecular machine that behaves like a nanoscale elevator. The operation of this device, which is made of a platformlike component interlocked with a trifurcated riglike component and is only 3.5 nanometers by 2.5 nanometers in size, relies on the integration of several structural and functional molecular subunits. This molecular elevator is considerably more complex and better organized than previously reported artificial molecular machines. It exhibits a clear-cut on-off reversible behavior, and it could develop forces up to around 200 piconewtons.

Sources: Celeste Biever, New Scientist, March 18, 2004; Henry Fountain, The New York Times, March 23, 2004; Science, Vol. 303, Issue 5665, Pp. 1845-1849, March 19, 2004