Nanomachines enable mechanical work to be carried out on the smallest of scales, were awarded the Nobel Prize in Chemistry in the year 2016. However, at such minute dimensions, molecular motors can finish the work only in a single direction.
A research team from the CNRS’s Institut Charles Sadron, headed by Nicolas Giuseppone, a professor from the Université de Strasbourg, working in collaboration with the Laboratoire de mathématiques d’Orsay (CNRS/Université Paris-Sud), has been successful in creating highly complex molecular machines that can work not only in one direction but also in a direction opposite to it.
Similar to a gearbox, the system can also be accurately controlled. The research was reported in the journal Nature Nanotechnology on 20 March 2017.
Molecular motors use an external energy source, such as a light or chemical source, in combination with Brownian motion - random and disorganized movement of surrounding molecules - to produce cyclical mechanical movement.
Yet, nanomotors are prone to molecular collisions on all the sides, making the production of directed and thus useful mechanical work more complicated. The earlier molecular motors developed in the 2000s were based on the principle of the “Brownian ratchet,” which is similar to a notch on a cogwheel that blocks the backward movement of a mechanism and might bias the Brownian movement such that the motor operates only in a single direction.
Although this enables production of usable work, it does not enable a change in direction.
The researchers started their search for a solution for interchanging the movement. They achieved this by connecting the motors to molecular modulators, or clutch subunits, with the help of polymer chains, that is, transmission subunits. They have also come up with a mathematical model to interpret the behavior of the network.
Upon exposure to ultraviolet radiation, the motors turn and the modulators are rendered immobile. The polymer chains get wound around themselves and contract like a rubber band that gets shortened when twisted. This phenomenon can be detected on a macroscopic scale because the molecules together form a material that can contract.
Upon exposure to visible light, the motors cease to work while the modulators get activated. Here, the mechanical energy stored in the polymer chains is used to rotate the modulators in a direction opposite to direction of the original movement. As a result, the material gets expanded.
Even more striking is the fact that the research team was successful in demonstrating that the speed and rate at which the work is produced can be cautiously controlled by using a combination of visible and UV light, similar to a gearbox that functions as a result of modulations in frequency between the modulators and motors. At present, efforts are on to use this research to create photomechanical devices with the ability to carry out mechanical work regulated by light.
The ERC and the ANR financially supported the study.
Nanomachines at real work: a molecular motor with a transmission-clutch system
(© Gad Fuks / Nicolas Giuseppone / Mathieu Lejeune)