- Researchers develop the world’s fastest molecular machine using the harpoon mechanism.
- It is 4000 times faster than myosin, the fastest biological motor protein.
- These artificial machines could perform tasks essential for life such as ATP synthesis and DNA replication.
One of the great challenges in today’s nanotechnology is controlling motion on a molecular scale. This has led to the development of mechanically interlocked molecular architectures that performs certain functions in response to external stimuli.
The most explored class of such molecules is rotaxanes. It consists of a ‘dumbbell-shaped molecule’ that is threaded through a macrocycle (ring).
Since the dumbbell’s ends (stations) are bigger than the ring’s internal diameter (macrocycle), both components are kinetically trapped. Unthreading these two components would require substantial distortion of covalent bonds.
Rings Can Move Through Wire
Most of the studies concerning rotaxanes have emphasized on their utilization as artificial molecular machines. These machines could perform tasks essential for life such as ATP synthesis and DNA replication.
The ring of a rotaxane can travel from one end of the wire to the other. The sliding ring, however, doesn’t have a particular direction: it moves randomly over the wire.
Structure of a rotaxane | Wikipedia
In the recent decade, scientists have been able to develop rotaxane-based molecular motors. In advanced versions, the stations of rotaxanes can be chemically altered with the help of light so that they can attract the ring toward them.
It is now possible to move the ring from one station to another by flashing light of the right wavelength on a nanometre length scale.
Molecular machines, however, are still in their infancy. With existing techniques, the ring takes too much time to travel from one station to another.
For instance, if you make a particular station more attractive (by flashing light), the ring first spontaneously leaves its starting station and walks over the wire toward the stronger binding station. It takes a significant time to reach the destination, especially if the wire is long.
Now, researchers at the University of Amsterdam have developed a molecular machine in which the terminal station comes to the ring. In this so-called harpoon mechanism, the terminal station with strong attraction deforms the wire, grabs the ring, and then drags it over the wire toward the destination.
Working of the ‘harpoon effect’ | Credit: Van ‘t Hoff Institute for Molecular Sciences / Maximilian Paradiz
This mechanism drastically reduces the time the ring takes to move from one station to another. Researchers were able to create the fastest molecular shuttle the world has ever seen.
They induced movement of the ring using a short pulse of ultraviolet light, and then followed its motion (to measure the speed of the molecular shuttle) via the second pulse of infrared light.
The ring covered 1 nanometer distance in 30 nanoseconds, equivalent to an average speed of 3 cm/s. This is 4000 times faster than myosin, the fastest biological motor protein, which is responsible for muscle contraction.
The next challenging task would be making these artificial motor molecules work together so they can mimic complex biological machines and perform tasks essential for life.