One of nature’s best strategies for acting on the cellular scale involves powerful molecular motors: complex molecules that convert chemical energy into mechanical energy to complete tasks such as transporting components inside the cell, contracting muscle fibers, and separating strands of DNA.
Since 1999, chemists have been designing synthetic molecules that rotate 360 degrees in response to light or chemical stimuli. These single-function motors can generate forces on a surface, send cargo to sensors and power nanoscale devices. But researchers can’t easily control or monitor them when they’re embedded in opaque biological tissue.
A newly designed molecular engine overcomes these two challenges by switching between spin and fluorescence when different wavelengths of light hit. Science Advances. “Many compounds don’t react in two different ways to light, and this is the first engine to show this property,” says Maxim Pshenichnikov, a spectroscopy expert at the University of Groningen in the Netherlands and co-author of the new study.
Under the guidance of Groningen organic chemist and 2016 Nobel Prize winner Ben Feringa, Pshenichnikov and his colleagues created the bifunctional molecule by attaching a chemical called triphenylamine to a basic molecular motor. This allows the engine to respond in different ways to different light energies. The lower-energy light gave the motor just enough power to spin, while the higher-energy light over-excited the motor, emitting photons, causing it to throw off the excess energy: it became fluorescent. Additionally, unlike typical molecular motors driven by ultraviolet light, which damages tissue, this new compound responded to infrared tones that could penetrate deeper into the skin without being damaged.
An engine like this could help applications that require precise pinpointing. For example, a fluorescent motor can interact with different cellular structures and emit light for tracking while delivering and activating a drug. “How wonderful it would be if we could actually follow the movement of the engine in the cells and use it for mechanical interference, [drug] delivery and detection?” says Feringa.
Chemist Salma Kassem of the City University of New York, who was not involved in the study, says the design is an important step towards light-based pharmacology: two properties that block each other. This work performs the separation of roles in a simple and elegant way.”
The researchers plan to apply the technology to a motor that has a biological function, such as binding to specific cell receptors. They will then test its performance in living cells or tissues. Lukas Pfeifer, lead author of the study, an organic chemist at the Swiss Federal Institute of Technology in Lausanne, says the success of this technique “gives me hope that we can easily transfer it to engines made with different chemical compounds.”