This year’s Nobel Laureates in chemistry have developed molecules whose movements can be controlled and that can perform a task when power is supplied. Simply put, it can be said that the world’s smallest machine came about when France’s Jean-Pierre Sauvage figured out how two molecular rings could be linked to each other and form a chain without involving chemical bonds. Scotland’s Sir J. Fraser Stoddart later discovered how to move the rings and the Netherlands’ Bernard L. Feringa found a way to set the rings in motion in a specific direction.
We asked chemist Mate Erdelyi to describe this year’s Nobel Prize for those who are particularly interested in chemistry.
The Nobel Prize in chemistry this year recognizes the development of molecular tools that are capable of converting energy, in form of light or heat, into a controlled one-directional movement. As this concept shows some similarities to the machines of our everyday life, such as cars or elevators that convert the energy stored in electricity or petrol into controlled physical movement, it is often marketed as ‘the development of molecular machines’. These could possibly find applications in energy storage, medicinal chemistry and computing or as new types of functional nanomaterials.
In the early 1980’s Jean-Pierre Sauvage, today professor emeritus at the University of Strasbourg, made the first fundamental discoveries providing the basis for further developments by efficiently creating interlocked rings providing catenanes, a type of mechanically linked molecules (Figure 1), whose possible existence was first proposed by the Nobel Laurate of 1915, Richard Willstätter of ETH Zürich. The breakthrough of Sauvage was to recognize that the orthogonal arrangement of bidentate ligands in tetrahedral Cu(I) complexes (Figure 2) are applicable for generation of crossing points that are necessary for formation of catenanes. This approach, so called template synthesis, has been the basis for forming interlocked compounds ever since.
Fraser Stoddart, today employed at the Northwestern University in the USA, created rotaxane, a ring shaped molecule threaded onto an ’axle’ allowing the light, acidity or pH-controlled movement of the first back and forth between the endpoints of the second linear molecule (Figure 3). This molecular complex can be seen as a controlled shuttle system, the prototype of artificial linear molecular motors or switches stimulating a vigorous activity along the same lines towards the construction of memory and logic units in electronic devices. Using millions of rotaxanes a memory device was created, in which molecular switches can be turned between an ‘on’ and an ‘off’ state. Later, the Stoddart group has also created molecular ‘muscles’ that, i.e. rotaxanes, can bend a thin sheet, and developed a molecular ‘lift’ that can raise itself by nearly a nanometer.
Ben Feringa, active at the University of Groningen in the Netherlands, has further developed the above concept by creating a molecular system that is capable of a light induced unidirectional stepwise motion by photoisomerisation of a carbon-carbon double bond (Figure 4) in an interlocked system. He has demonstrated that this ‘molecular motor’ could be used to provide macroscale motion, for example is applicable to rotate a glass rod put on the top of a series of them.
His most famous molecular system is often referred to as a ‘nanocar’, which is capable of converting the energy of light into a controlled motion of the entire molecule on a surface, due to the unidirectional motion of four double bonds similar to the motion of the four wheels of a car. The main impact of the work of Sauvage, Stoddart and Feringa is that they have initiated the development of smart, functional materials that can change their properties based on external signals. There are countless possible applications, which have already been initiated. To mention an example, Morten Grötli at the Department of Chemistry and Molecular Biology has, in collaboration with Joakim Andréasson at Chalmers, recently developed photoswichable RET kinase inhibitors, making use of azo-functionalized pyrazolopyrimidines, which enable the light control of a transmembrane receptor tyrosine kinase activity (Sci. Rep. 2015, 5, 9769).
Following similar lines, I have worked at Uppsala University, under the supervision of Professor Gogoll, on the establishment of a photoswitchable beta-hairpin mimetic (Chem. Eur. J. 2005, 12, 403), whose stilbene-type molecular switch was subsequently utilized in the photocontrol of the activity of an artificial hydrolase enzyme (Chem. Eur. J. 2009, 15, 501). Besides controlling bioactivity, the same concept may be applied in countless other fields, for example for controlling the enantioselectivity of chiral catalysts.