By Roland Piquepaille
A team of chemists from the University of California at Los Angeles (UCLA) has built the world's first nano valve. This device can trap and release molecules on demand. This mechanical system can control molecules like a water faucet you can open or close at wish. This nano valve has moving parts -- switchable rotaxane molecules -- attached to a piece of porous glass, with pores only a few nanometers in size. As this nano valve is much smaller than living cells, we can imagine a day when we swallow a nano valve combined with bio-molecules to release drugs inside our bodies. But the full potential of artificial molecular machines will take a long time to materialize. Read more..."With the nano valve, we can trap and release molecules on demand. We are able to control molecules at the nano scale," said Jeffrey I. Zink, a UCLA professor of chemistry and biochemistry, a member of the California NanoSystems Institute at UCLA, and a member of the research team.
The image below shows how the nano valve works. And here is a link to a larger version of this diagram.
[On this picture,] "a" shows the structural formula of the rotaxane molecule and the procedure for tethering it to the surface of a tiny piece of glass while "b" shows how the nano valve opens and closes (Credit for image and legend: UCLA).
Now, here are more technical details about this nanofaucet.
This nano valve consists of moving parts -- switchable rotaxane molecules that resemble linear motors designed by California NanoSystems Institute director Fraser Stoddart's team -- attached to a tiny piece of glass (porous silica), which measures about 500 nanometers, and which Thoi Nguyen is currently reducing in size. Tiny pores in the glass are only a few nanometers in size.
The valve is uniquely designed so one end attaches to the opening of the hole that will be blocked and unblocked, and the other end has the switchable rotaxanes whose movable component blocks the hole in the down position and leaves it open in the up position. The researchers used chemical energy involving a single electron as the power supply to open and shut the valve, and a luminescent molecule that allows them to tell from emitted light whether a molecule is trapped or has been released.
The research work has been published in the July 19, 2005 of the Proceedings of the National Academy of Sciences as an "open access article" under the name "A reversible molecular valve." Here is a link to the abstract.
In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways.
These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis).
In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.
And if you really want to read more about this molecular valve, here is a link to the full paper (PDF format, 6 pages, 495 KB). But if you're not a chemist, I doubt you'll understand the contents.
I'll leave the last words to Fraser Stoddart.
"Building artificial molecular machines and getting them to operate is where airplanes were a century ago," Stoddart said. "We have come a long way in the last decade, but we have a very, very long way to go yet to realize the full potential of artificial molecular machines."
And now, I'm waiting for your own comments: what do you think of these future molecular machines?
Sources: UCLA news release, July 15, 2005; and various web sites
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