Another first for Feringa: chemically powered rotary motor

University of Groningen chemist Ben Feringa has done it again. After the first molecular motor, the first molecular car (both powered by light) and other firsts, he has now presented a rotary motor driven by chemical energy. An article on the new motor was published in Nature Chemistry on 6 June.

Our cells are full of molecular motors, and nature knows very well how to make them. But chemists and materials scientists want to design their own motors, to power molecular machines. University of Groningen chemist Ben Feringa is a world leader in the field of molecular motors. Most of his motors are powered by light. But if they need to work inside the body or an opaque solution, that is not the most efficient method.

So he started looking for a way to power a motor with chemical fuel. Again, it would be a rotary motor, based on two chemical rings, one of which makes a unidirectional 360-degree rotation. The two rings are connected by two carbon atoms, which act as a pivot. The upper ring is kept in the same position by weak interactions between atoms within the molecular structure.

Feringa and his colleagues reasoned that by binding a metal catalyst to the molecule, the stabilizing interaction would be broken and the molecule would change its configuration, basically making a half turn. At that point, another metal catalyst would give it a ‘push’ to complete the circle.

Feringa then came up with the novel idea of using one and the same metal catalyst: a palladium catalyst would first oxidize and then reduce the ring, giving it the two pushes it needed. As it turned out, this is possible by changing the reaction conditions. Feringa and his colleagues showed that it does indeed work, albeit slowly: in the first attempt, it took about a day for a batch of motor molecules in solution to proceed through one rotary motion. They also needed to change the temperature and the reagents.

His next step was to tweak the reaction to speed up and simplify the procedure – although this reduced the percentage of molecules going through the motion. But it is a proof of principle: a unidirectional rotary motor driven by chemical energy. And after all, this is how the first light-driven motor started off: slow and cumbersome, but now it rotates at dazzling speed. To be continued…

Reference: Beatrice S. L. Collins, Jos C. M. Kistemaker, Edwin Otten & Ben L. Feringa, A chemically powered unidirectional rotary molecular motor based on a palladium redox cycle. Nature Chemistry, 6 June 2016, DOI 10.1038/nchem.2543