Molecular motor turns rotor

Gearing up to make even more complex molecular machines, chemists at the University of Groningen have created a molecular motor coupled to a rotor. The motor turns the attached rotor such that the two components’ motions are synchronized, just like that of machines we encounter in everyday life (Science 2017, DOI: 10.1126/science.aam8808).

“This is fundamental research about how to control motion at the molecular level and how then to use it to synchronize motion and amplify motion,” says Ben L. Feringa, who led the Groningen team.

In a commentary that accompanies the paper, University of Bologna chemists and molecular machine makers Massimo Baroncini and Alberto Credi note that the motor-rotor combo “takes an important step forward toward more complex mechanical functions with artificial nanoscale devices.”

The unidirectional motor consists of a fluor­enyl unit attached to an indanyl group via a double bond. The system’s naphthyl rotor is covalently attached to the indanyl half of the motor. When illuminated, the motor’s double bond isomerizes, setting the system into motion. As the motor turns, the naphthyl rotor paddle slides alongside the fluorenyl unit so that the rotor is always facing the motor with the same side—a feat the group accomplished with a complex stereochemical design. Both nuclear magnetic resonance and circular dichroism spectroscopy confirmed this synchronized motion.

It was a delicate balance to achieve the desired movement, Feringa notes. “We had to induce motion, we had to couple motion, and we had to prevent free rotation of the rotor; otherwise we could not have synchronized rotation,” he says.

Next, Feringa’s group would like to create machines that can amplify the molecular machines’ motion to larger movements or transmit motion over longer distances.