Monday, January 31, 2022

Molecular machine in the nanocontainer

Lars Schäfer from Theoretical Chemistry examined a nanocreis with colleagues from South Korea. Credit: Ruhr University Bochum / Marquard

What a toy: A tiny gyro that has space in a cell and can be controlled from the outside.

The theoretical chemists Dr. have a molecular gyroscope that can be controlled remotely by light. Chandan Das and Prof. Dr. Lars Schäfer from the Ruhr University Bochum (RUB) constructed together with an international team at the Institute for Basic Science in South Korea. In addition, they managed to characterize the rotary movements of this synthetic nanomachine with computer simulations. The authors describe their results in the journal Chem.

Navigation of aircraft or satellites

Machines that are enclosed in a cage or housing can have interesting properties. You can convert any energy supplied into programmed functions. One such system is the mechanical gyroscope. This toy fascinates with its constant rotation. Gyroscopes are also used in practice, for example in navigation systems of aircraft or satellites and in wireless computer mice. "What makes these gyroscopes so advantageous is not only the rotor, but also the housing, which aligns the rotor in a certain direction and protects it from obstacles," says Lars Schäfer.

At the molecular level, many proteins work as biological nanomachines. They are present in every biological cell and perform precise and programmed actions or functions, also within a limited environment. The machines can be controlled by external stimuli. "In the laboratory, the synthesis and characterization of such complex structures and functions in an artificial molecular system is a major challenge," said Schäfer.

Structure like a bottle ship

In collaboration with a team led by Prof. Dr. Kimoon Kim at the Institute for Basic Science in Pohang, South Korea, has now managed to include a supramolecular rotor in a cube-shaped porphyrin cage molecule. The installation of a finished rotor in such cages is typically made difficult by the limited size of the cage windows. To overcome these challenges, the synthetic chemists in Pohang developed a new strategy that first introduces a linear axis into the cage, which was then modified with a side arm to construct a rotor. "This is reminiscent of the construction of a bottle ship," says Chandan Das, who carried out molecular dynamic computer simulations together with Lars Schäfer to describe the rotational movement of the rotor in the cage in atomic detail.

"We were particularly fascinated by the observation of our collaboration partners that the movement of the rotor in the cage could be started by light as an external stimulus and also switched off again, as with a remote control," says Schäfer. The researchers achieved this by docking a photoresponsive molecule to the cage from the outside by light in the UV and visible range and replacing it again.

How the molecular gyroscope moves

But how does that work, and what movements does the molecular gyroscope perform after it is turned on in this way? "Molecular dynamic computer simulations show that the rotor molecule in the cage has a stochastic dynamic, which is characterized by random 90-degree jumps of the rotor side arm from one side of the cube to an adjacent side," explains Chandan Das the results of the theoretical calculations, which can explain the spectroscopic observations.

The researchers hope that the concept of including molecular nanomachinery in a molecular cage and remotely controlling their functions will help to understand how biological nanomachinery works and to develop intelligent molecular instruments.

Source/Credit: Ruhr University Bochum

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