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catenane
A catenane, consisting of two interlocked rings.

What’s the smallest machine you’ve seen? Can you imagine machines so small that you can’t even see them, complete with movable parts, motors, and switches? They do, in fact, exist; these nanoscale machines are sometimes composed of just a few molecules. Called “molecular machines,” these systems have a rather surprising story, beginning with a serendipitous start.

Jean-Pierre Sauvage, a professor at the University of Strasbourg, made the first discovery of a molecular machine in 1983, when he coincidentally linked together two molecules into a chain when building a photochemistry model. The process of linking the molecules together was centered on a copper ion that the molecules were mutually attracted to. After removing the copper ion, researchers obtained two chained molecules, now known as a catenane. Molecular machines were further developed by Fraser Stoddart of Northwestern University in 1991: he was able to build a “molecular axle,” (known as a rotaxane) in which a ringed, electron-poor molecule was fitted around an axle. When heat was applied, the ring was able to jump along the axle between electron-rich areas. These rotaxanes constitute the moving parts to the molecular machine, and the motion of the ring can be controlled quite precisely. In 1999, Ben Feringa of the University of Groningen discovered how to make a molecular motor—a molecule that can continually spin in the same direction—by placing together two molecular “rotor blades” and exposing the machine to UV light. Light pulses created tension on the rotor blades, causing them to rotate in a particular direction.

The discoveries of these three scientists were groundbreaking in the development of a variety of molecular machinery. As a result of these contributions, Sauvage, Stoddart, and Feringa won 2016’s Nobel Prize in Chemistry. Their unique chemical structures (the chained molecule, the molecular axle, and the motor) form a molecular toolbox of sorts that allow researchers to develop increasingly complex contraptions.

Now, you’re probably wondering how all of this is useful. As it turns out, molecular machines have many different applications, from synthesizing proteins and polymers to drug delivery and cleaning up pollution. The possibilities are endless.

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rotaxane
A rotaxane, or molecular axle.

For example, a team of researchers at the University of Manchester have produced a machine that mimics the role of the ribosome, which translates the body’s genetic code in the form of RNA into chains of amino acids. The machine relies on the rotaxane, or the molecular axle, which has a sulfur-containing thiol group able to pluck amino acids preloaded onto the axle and attach them to a moving ring. While this method is still primitive, since amino acids must be preloaded onto the axle, this machine is promising and might allow chemists to quickly construct materials with specific molecule sequences.

Researchers have also created tiny motors that can move through liquids at phenomenal speeds (like miniscule rockets). These motors can contain a catalyst to propel them or utilize light or external magnetic or electric fields. Of course, there are promising applications for these motors, such as fast drug delivery or cheap methods of cleaning up environmental pollutants.

Their unique chemical structures (the chained molecule, the molecular axle, and the motor) form a molecular toolbox of sorts that allow researchers to develop increasingly complex contraptions.

Research into molecular machines has come a long way, and scientists today are incorporating the array of tools developed by Sauvage, Stoddart, and Feringa into diverse fields. Machines on the nanoscale are incredibly powerful: combining a small number of them can accomplish tiny, molecular jobs that otherwise couldn’t be achieved; using billions of them together could change the properties of a material itself. Just as the miniaturization of computer technology has revolutionized our lives, the development of these small machines may have opened the door to a new forefront, the beginning of a new era. The future for these tiny gadgets is exciting indeed!

About The Author

Yusha Sun