How to tame random motion inside a molecule? Scientists can do it with light
Molecules are never still. Driven by thermal energy, they are constantly moving through space, while their individual parts also rotate relative to one another. Scientists at IOCB Prague have now shown that random motion within a molecule can be dramatically suppressed. Using light, they can slow down the relative rotation of two different parts of a single molecule by up to five orders of magnitude, paving the way for more complex molecular machines.
Driven by thermal energy, individual parts of molecules are constantly vibrating, rotating, and changing their positions – a phenomenon known as Brownian motion. Unlike conventional engineers, scientists building molecular machines therefore work with components that are constantly in motion. To assemble them into a functioning mechanism, they need to be able to control this motion. This is precisely what the team of Jiří Kaleta at IOCB Prague has achieved.
The scientists created a molecular system incorporating two key components: a light-controlled molecular motor and a rotor that randomly rotates around its axis because of thermal motion. “When we shine light on the molecule, the motor changes its spatial arrangement, which in turn affects the motion of the rotor. In the ‘unbraked’ state, the rotor can rotate easily, while in the ‘braked’ state, the motor physically obstructs its motion and significantly increases the energy barrier the rotor must overcome to turn,” explains Lukáš Severa, first author of the study.
The principle can be pictured as a hand freely mounted on an axis and constantly jostled by tiny vibrations. If nothing stands in its way, it can rotate easily. But when an obstacle is placed in its path, its rotation slows dramatically. In the molecule, this obstacle is created by the moving part of the molecular motor.
Up to a 300,000-Fold Slowdown
The difference between the two states is striking. “In previous similar systems, it was possible to change the rotation rate by no more than a factor of one hundred. With our approach, we have achieved a slowdown of approximately 300,000-fold, which represents a major breakthrough,” says Jiří Kaleta.
The difference between the two states becomes even more dramatic as the temperature decreases. If, at a very low temperature, the unbraked rotor completed one rotation per second, under the same conditions the braked rotor would take approximately 350 billion years to complete a single rotation – about twenty-five times the current age of the universe.
The ability to control the motion of individual components is essential for constructing more complex molecular machines. “If you want to build a more complex mechanism, having a motor alone is not enough. You also need elements that can regulate and coordinate the motion of individual components. We are demonstrating one principle for achieving this at the molecular level,” concludes Jiří Kaleta.
Read the paper:
- Severa, L., Bezděková, K., Majerová Varga, K., Bastien, G., Stroka, M., Císařová, I., Dračínský, M., & Kaleta, J. (2026). Light-Gated Control of Brownian Rotation by a Molecular Motor. Angewandte Chemie International Edition, e7061287. https://doi.org/10.1002/anie.7061287
