Researchers have discovered that a heart-shaped molecule will jump in straight lines when receiving an electrical shock.
Introduction
In a room in the basement of Graz University in Austria, there is a collection of steel tanks and pipes covered in ice. A scanning tunneling microscope can capture images of individual atoms and molecules. It is extremely sensitive, working best at night when there is no one walking, talking, or causing vibrations to the building.
Discovery of the Nanoscale Bulldozer Molecule
The computer screen next to the device shows images of small heart-shaped blocks arranged on a copper surface. Those hearts are individual molecules: ditholyl-ATI molecules, to be precise. Earlier this year, Grant Simpson, a chemist at the microscopy lab, was playing with them in hopes of stimulating them to function as very small mechanical switches.
The New Nanoscale Molecule
The jumping hearts represent an entirely new type of molecular nanoscale motors – tiny machines that expend energy to move purposefully against the random tide that pulls the minuscule world into random and futile motion. Some man-made nanoscale motors can rotate in place, but few can move reliably from point A to point B. The mechanical magic of the new motor comes from the interaction between the molecule and the copper surface it moves on – as if it has car engine parts in the vehicle and integrated into the path below.
Challenges in Developing Nanoscale Technology
Chemist David Lee from the University of Manchester indicates that the problem with nanoscale technology is that familiar mechanics in the macroscopic world simply do not work at the molecular level. At such small scales, randomness prevails. If properties like temperature, energy, and pressure are held constant, processes at the nanoscale – including chemical reactions or particle motion – are likely to occur with equal probability in all directions. Moving from point A to point B at the nanoscale is like rolling dice and taking steps forward, backward, or sideways depending on the outcome. “You cannot use Newtonian mechanics” in nanoscale technology, Lee says. “This essentially rules out all the engineering processes we have built as civilizations over the past 5,000 years.”
Nanoscale Technology and Examples from Nature
Why do scientists believe that nanoscale machines can be developed at all? Lee says the answer is that there is already a mature and functioning example at work, “what we call biology.” The complex natural enzymes that move bacterial flagella, the contraction of animal muscles, and the harnessing of chemical energy in cell mitochondria are all molecular machines.
Molecular Nanoscale Motors
In 1999, scientists synthesized the first true molecular nanoscale motor, a light-driven rotary motor that was later honored with the Nobel Prize in Chemistry. Since then, scientists have developed many types of motors with different capabilities. Recently, chemist Nathalie Katsonis of the University of Groningen and her colleagues stuck trillions of nanoscale motors together and tore them apart to move a macroscopic polymer. Lee and his colleagues developed rotary nanoscale motors that move by harnessing the energy from chemical reactions catalyzed by the motor itself.
Challenges in Building Linear Nanoscale Motors
Building rotary nanoscale motors in place; molecular motors that move in straight lines, like trains on tracks, have posed a larger challenge for construction. Some researchers have synthesized ring-shaped molecules that can rotate and slide on dumbbell-shaped platforms. Then there is “DNA walking,” which has legs and moves in steps, like some vital motile proteins. However, DNA walking is relatively heavy (not strictly “nano,” Lee says) and can take only a few steps on carefully engineered pre-formed DNA tracks. Nonetheless, the new heart-shaped motor is very small and will continue to jump along its path of copper atoms as long as the surface is not disrupted.
Discovery
The New Motor
Simpson and Greal discovered the motor largely by accident – it’s “pure luck,” according to Greal. Initially, the scientists were interested in how the dithiol-ATI molecule throws one of its hydrogen atoms between the nitrogen atoms, a behavior that scientists believe could make it a nanoscale switch. After years of work, Simpson tried placing the molecules on a specific type of copper surface where the atoms are arranged in linear rows. To his surprise, an electric shock sent the hearts jumping along the copper tracks. Researchers then confirmed that the molecules move in only one direction and can even push other particles like nanoscale bulldozers.
The New Motor as a Nanoscale Machine
Katsounis, who was not involved in the study, states that this new motor is a “power switch,” using energy – here an electric shock – to switch between two states, each with a different set of energy potentials. Activating the molecule makes it transition to its more impressive excited state, where moving forward on the copper track is favored. When the molecule returns to its unimpressive original state, it jumps forward by one step on the track.
Importance of the New Nanoscale Molecule
Katsounis mentions that it is interesting for two reasons. Firstly, the molecules interact with something larger than themselves, in this case, the surface. Secondly, they move in a line on an atomic pathway – which is key to mastering directional movement at the nanoscale, and she notes that, after all, many linear molecular motors in biology travel on platforms to move in the right direction.
Conclusion
Lee states that this is really beautiful because it moves in one direction in a one-dimensional manner, in a very simple system. The new motor may not drive at a nanoscale pace or gather an ear of corn anytime soon. However, it can be easily studied using scanning tunneling microscopes, making it an ideal test system for future experiments with energy switches, tracks, and directional movement – and Katsounis and Lee agree that this is a major step in the right direction.
Elise Katz is a freelance science journalist covering earth and life sciences.
Source: The original article “Nanoscale Bulldozer” in Scientific American, Vol. 329, No. 5 (December 2023), p. 14
Source: https://www.scientificamerican.com/article/nanoscale-bulldozer/
Source: https://www.scientificamerican.com/article/this-molecule-is-a-nanoscale-bulldozer/
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