There’s plenty of room at the bottom,” said Richard P Feynman in his 1960 speech, to which many attribute some of the surging interest in nanotechnology in subsequent decades. He was advocating attempts to manipulate matter at the scale of atoms and molecules to produce functioning devices. The fact that nanoscale cars made from single molecules can now be made with such deft aptitude that a nanocar race has been scheduled, is symptomatic of the huge progress made in this field.

Anyone who has ever threaded a needle can appreciate how much more difficult it becomes to assemble components as the parts get smaller in size. For “bottom-up” synthesis, chemistry is key. However, to produce a molecule that functions as a car takes a number of previously unavailable molecular components that link (catenanes), rotate round an axis (rotaxanes) and provide unidirectional motion. This year’s Nobel Prize for Chemistry celebrates the seminal work by Jean-Pierre Sauvage, now at the University of Strasbourg in France, Sir J Fraser Stobbart, now at Northwestern University in the US, and Bernard (Ben) Feringa, now at the University of Groningen in the Netherlands, that laid the foundations for advances with these components.

Making the right link

In fact, linked molecular ring structures – catenanes, the first step towards a molecular car – had already been achieved at the time of Feynman’s talk. However, the approach had been to use ring-closing reactions that statistically yielded some linked rings, but produced frustratingly low yields that were not significantly increased for decades.

Sauvage in his group adopted a type of template approach with metal ions to coordinate the assembly and reduce the statistical element of chance, thereby improving the yield. In their first report of the approach in 1983, which demonstrated a 42% yield, Sauvage and colleagues already hinted at the general applicability of the approach to other molecules – “á des catenanes multiples, á des rotaxanes et á des ligands variés.”

Finding functions

Stoddart then brought to the fore the potential of such “topologically entangled” molecules with work on rotaxanes, where a molecule shaped as a lasso or bubble wand can be looped around the “axle” of another similarly shaped molecule. In a series of creative molecular inventions that demonstrate what has driven him in chemistry – “its wonderful ability to express yourself in an artistic form”, – he showed how these components could function as artificial muscles and elevators that are activated by light.

Getting a sense of direction

However, the net result of axle motion that occurs evenly in both available directions is likely to sum to zero. Feringa first found that rotation in just one direction could be achieved by using chiral molecules, where two arrangements of the components of a molecule – “isomers” – are possible and one is a mirror image of the other, but cannot be superposed (like the right and left hand). Feringa showed that with certain chiral molecules, rotations could occur in four steps according to specific isomerization reactions. The first two steps effectively block reverse rotation, ensuring a full rotation in one direction takes place.

Feringa has been greatly inspired by biology in his research. When Adam Smith rang Feringa on behalf of the official website for the Nobel Prize, Feringa described how the essential cell functions such as cell division, transport, and the processes for muscle movement, are all controlled by molecular motors, adding “It is fantastic to see how this intricate machinery works.” Many of the molecules in cell processes are also chiral and are primarily “left-handed”, although the origins of this left-handed bias are still the subject of study.

Taking it further

More than miniature curiosities, potential applications abound for the molecular machines emerging in this field of research. For example, in medicine they can be injected into the body and activated by light when they have reached the relevant part of the body for their function.

Yet today’s automobiles and labour-saving devices were beyond the expectations of those viewing exhibits of the then newly devised machine parts at the dawn of the industrial evolution. It has been stressed that similarly the full impact of these functioning molecular nanomachines may far surpass what we can foresee for them today.