Author: Eleanor Sheekey
Institution: Cambridge University
Date: December 2016
The 2016 Nobel Prize in Chemistry has been awarded to Jean-Pierre Sauvage, Fraser Stoddart, and Bernard Feringa for their pioneering work of molecular machines. The award highlights the promise of their intricate designs in a range of applications from medicine to material science.
The first breakthrough in the field was made by Sauvage and his team in 1983. Whilst focusing on designing molecules that imitate the function of machines, they were able to synthesise interlocking ring shaped molecular chains like the chain of a necklace, otherwise known as catenanes. The major advantage this molecular design had over previous attempts was that the chains were linked non-covalently, conferring a greater degree of flexibility. This structure can then provide the foundation to build more complex motors.
The development of catenanes inspired Stoddard’s subsequent work. In 1991, he created the first molecular shuttle called a rotaxane (Figure 1). A rotaxane consists of a ring shaped molecule threaded onto an axle that can slide sideways according to changes in acidity, light, or temperature. Since then, Stoddard has applied this design to create a molecular lift, artificial muscles, and most impressively a high density memory device.
A high density memory device is of particular interest within the semi-conductor industry. Stoddard’s device stores the information as a binary system in the rotaxane molecules’ two stable configurations. Currently 160,000 bits can be stored in the space of a white blood cell (15 micrometres), 1500 times smaller than a postage stamp. However, before this memory plate can become widely available, a more robust mechanism to switch between the two configurations must be devised. Additionally, recent nanoprinting techniques may permit high-throughput manufacturing of such memory devices in the near future.(2)
However, this is only one application of the nanoscale molecules. Feringa takes his share of the prize for synthesising the first molecular motor back in 1999; it works by connecting four molecular ‘paddle’ units by a carbon-carbon double bond that can be broken with light to allow constant rotation. He famously used these motors to create a Nanocar. The Nanocar depends on electrons tunnelling through the molecule, exciting vibrational and electronic states in the ‘wheels’ causing them to change configuration. One paddlewheel like motion corresponds to 0.7nm propagation, inducing translational movement on the surface. The electrons are dissipated from a scanning tunnelling microscope, a device which was awarded the Nobel Prize for Physics back in 1986(3).
The original idea for the Nanocar was inspired by natural motor proteins that have perfected directional movement through conformational changes. The beauty of Feringa’s design comes from the ability to modify the motion trajectory by modifying the molecule. It is possible to change the chirality—or handedness—of the individual motor units so that the movement can fluctuate from linear to a random orientation. At the moment this serves as a starting point to eventually developing complete control over the movement.
Beyond the novelty of these molecular machines, could they have any functional uses to everyday life? Feringa used the analogy of the Wright brothers, who having powered aircraft more than 100 years ago were asked by the public, ‘Why do we need a flying machine?’. The irony of this statement now shows that there could be an explosion of applications for these creations in the near future.