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Synthetic molecular motor performs real work

21 December 2021

In nature, molecular machines do several different jobs: they translate our genetic code into proteins, transport cargo in our body or store energy in form of high energy molecules. In a new publication in Nature Nanotechnology, researchers from University of Groningen with colleagues from the Freien Universität Berlin (Germany) show that a synthetic molecular machine can also perform work, by driving a chemical reaction.

First author Michael Kathan explains: ‘We have developed a light-driven molecular motor containing two loops. Under normal conditions these loops are stable and are not intertwined: they are in equilibrium.’ But when the system is irradiated with light, the motor rotates and winds the loops into tight knots. This way, light energy is converted into chemical energy and pushes the system out of equilibrium. Kathan: ‘At a certain point a chemical reaction occurs: the loops break temporarily. Once they are broken, the loops automatically unwind and repair, so we can repeat the process. Basically, our machine is reminiscent of a tiny wind-up toy that is operated with light energy.’

A photo-responsive molecular motor is constrained by two loops. Crossings in the system can be established by either thermal nucleophile exchange (brown), leading to temporary ring-opening of one loop, or by light-driven unidirectional rotation of the molecular motor (blue), which increases the number of crossings per half-turn by +1. | Illustration Feringa Group, University of Groningen
A photo-responsive molecular motor is constrained by two loops. Crossings in the system can be established by either thermal nucleophile exchange (brown), leading to temporary ring-opening of one loop, or by light-driven unidirectional rotation of the molecular motor (blue), which increases the number of crossings per half-turn by +1. | Illustration Feringa Group, University of Groningen

Biological machines

This work was done by the Synthetic Organic Chemistry group led by Ben Feringa, and the micromechics group led by Giuseppe Portale, both at the University of Groningen, together with the Supramolecular Cemistry in Berlin, led by Christoph Schalley.

Making synthetic molecular motors perform useful work and convert light energy into chemical energy is a big step towards the application of molecular motors. This form of energy conversion is one of the main reasons why life on earth is possible in the first place. Plants use a similar principle in photosynthesis to produce ATP, a small molecule that acts as the ‘energy currency’ of a living cell, with the molecular machine ATP synthase. Breaking up ATP frees up energy to fuel other biological machines, for example those that control muscle contraction.

Synthetic molecular machines are like natural molecular machines: they can do their job if they are properly designed and the right source of energy is provided. The only problem is that sophisticated systems to exchange different types of energy are rare, because they are difficult to make in the lab. However, these new experiments bring such a system a little closer. Like ATP synthase in photosynthesis, the twisting loops can convert one form of energy into another – in this case light into chemical energy.

.| Illustration University of Groningen
Thermal equilibration (brown) takes place by temporary ring-opening of the loops and will populate all accessible, wound states so that the (Gibbs free) energy of the system is minimized. The expected population is indicated by the brown bar diagram. Light-driven winding (blue) twists the loops and increases the number of crossings in the system above its equilibrium level until mechanical resistance hinders further winding. The expected population is indicated by the blue bar diagram. | Illustration Feringa Group, University of Groningen

Unique achievement

The ultimate goal would be to build a molecular factory that is as complex as a living cell. This is not easy, because most chemical processes want to reach equilibrium at a certain point. The defining feature of life is that it is out of equilibrium – when your body reaches equilibrium, it means you are dead. Molecular motors offer unique potential here because as long as they are supplied with energy, they can keep moving and stay out of equilibrium, as well as every process that is coupled to them.

‘What our team achieved here is very important’, says professor Ben Feringa. ‘What molecular motors do in in our body is to bring something out of equilibrium. Michael and his co-workers show here that a synthetic motor, which is fueled by light energy, can take a chemical system out of equilibrium too. That is a unique achievement.’

Reference: Michael Kathan, Stefano Crespi, Niklas O. Thiel, Daniel L. Stares, Denis Morsa, John de Boer, Gianni Pacella, Tobias van den Enk, Piermichele Kobauri, Giuseppe Portale, Christoph A. Schalley & Ben L. Feringa: A light-fuelled nanoratchet shifts a coupled chemical equilibrium. Nature Nanotechnology, 16 December 2021.

Last modified:05 January 2022 11.15 a.m.
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