Aircraft and satellite piloting
Machines enclosed in a cage or a casing can have interesting properties. For example, they can convert their energy intake into programmed functions. The mechanical gyroscope is one such system – an intriguing toy with the ability to spin continuously. Some practical applications of gyroscopes include air and satellite navigation systems and wireless computer mice, to name a few. “In addition to the rotor, another advantage of gyroscopes is their housing, which aligns the rotor in a certain direction and protects it from obstacles”, describes Lars Schäfer.
At the molecular level, many proteins act as biological nanomachines. They are found in every biological cell and perform specific and programmed actions or functions in a confined environment. These 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 presents a huge challenge,” says Schäfer.
Built like a ship in a bottle
Working with a team led by Professor Kimoon Kim from the Institute of Basic Sciences in Pohang, South Korea, the researchers succeeded in enclosing a supramolecular rotor in a cube-shaped porphyrin cage molecule. Typically, the installation of a complete rotor in such cages is complicated by the limited size of the cage windows. In an effort to overcome these limitations, synthetic chemists in South Korea developed a new strategy that first introduced a linear axis into the cage, which was then modified with a side arm to build a rotor. “It’s reminiscent of building a ship in a bottle,” says Chandan Das, who along with Lars Schäfer performed molecular dynamics computer simulations to describe the spinning motion of the rotor in the cage in atomic detail.
“Our collaboration partners made the intriguing observation that the movement of the rotor in the cage could be triggered and also extinguished by light as an external stimulus, just like with a remote control,” describes Schäfer. The researchers achieved this by using light in the UV and visible range to anchor a photosensitive molecule to the cage from the outside and detach it again.
How the Molecular Gyroscope Moves
But how does it work and what movements does the molecular gyroscope perform after being turned on in this way? “Molecular dynamics computer simulations show that the rotor molecule in the cage exhibits stochastic dynamics, characterized by random 90-degree jumps of the side arm of the rotor from one side of the cube to an adjacent side,” as Chandan Das explains. the results of the theory calculations, which can thus elucidate the spectroscopic observations.
The researchers hope that the concept of enclosing molecular nanomachines in a molecular cage and remotely controlling their functions will contribute to the understanding of how biological nanomachines work and the development of smart molecular tools.
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Remotely controllable supramolecular rotor mounted inside a porphyrin cage
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