Chemical changes… directed by mechanical forces

Theoretical and Computational Chemistry Institute (IQTC)
  • Researchers find a new factor influencing the outcome of chemical reactions
  • Mechanical stress is found to be capable of directing the reactions towards different products
  • This discovery may have implications in fields as nanotechnology, engineering, as well as chemistry and biochemistry


A collaboration from the Ruhr region to Barcelona

A study with the participation of the University of Barcelona (UB) and the Ruhr University cast light onto a series of chemical changes that can be caused by the application of mechanical tension forces on molecules. The work, with participation of Dr. Jordi Ribas Ariño of the Theoretical and Computational Chemistry Institute of the UB (IQTC) and the Physical Chemistry and Materials Science dept. of the UB, showcases the reduction of disulphide molecules linked to polymeric networks under such mechanically-modified conditions.

The study, with the participation of  Professor Dominik Marx of the Ruhr University Bochum, made use of computer simulation to describe how mechanical stress can influence chemical reactivity, becoming a milestone being published in the journal Nature Chemistry. From the industrious region of the Ruhr river in Germany comes a collaboration resulting in an advance with manifold ramifications.


A shift of a paradigm?

So far, heat, light and electricity have been regarded as the main key tools or levers to use in order to drive and fine-tune chemical reactions. The result of mixing the right components in the right proportions and conditions is the conversion of reagent molecules into one or more products with new, different properties –and eventually, added value-.

Purified sulfur. Disulphides arise when one or more molecules containing sulfur atoms form a sulfur-sulfur bond.

Years ago, it was yet found that certain molecules, upon exposure to mechanical stress or tension forces had a particular behaviour. It was found that such molecules could in those conditions undergo chemical modifications that would not take place under other circumstances. A field of chemistry arose, that studies such chemical processes and how they are influenced by the mechanical force applied to the involved molecules. That field was called covalent mechanochemistry, which has yet become a thriving field of research.

Dr. Ribas Ariño and Prof. Marx found an unexpected complexity into a particular chemical reaction: in the reduction reaction of disulphide links into alkaline medium, the breaking of a covalent link between carbon and sulphide atoms was not happening, if the reaction was activated by an external mechanical force.

Disulphides, molecules formed by the covalent link between two sulphur atoms, show quite particular mechanochemical properties when inside an alkaline solution. For instance, when they are exposed to a mechanical tension they undergo structural changes that completely modify their reactivity. These changes were described in detail in their article published in 2013 in Nature Chemistry.

Proteins contain typical examples of disulphides and their importance: they can change radically their structure and function.

The discovery of force-induced conformational changes steering chemical reactivity was suggested to play roles in the understanding of aspects of protein regulation, or in the design of mechanoresponsive materials.


A finding with profound consequences

Using computer simulations, the researchers found that, while applying force on the system accelerates the reaction, it also enforces a distorsion of the chemical bond angles. This is effect is responsible for “steering” the reaction into a particular direction, while preventing certain products from appearing. This has the consequence of opening new potential ways for controlling chemical reactivity, and confirms that mechanical tension can potentially be used to control the products resulting of certain chemical reactions.

Dr. Ariño said, “the results open the door to design specific applications for these small molecules, such as synthesis of materials that become more rigid when stressed (as happens with muscles and bones) or elastic bands that become shorter when pulled at, or on the other hand, the application of ultrasounds to activate selective chemical reactions” says Prof. Ariño of the Faculty of Chemistry of the UB, member of the Reference Network in Theoretical and Computational Chemistry (XRQTC).

The finding has implications in fields extending outside the domains of chemistry or the chemical industry.

Furthermore, the results allow predicting properties and behaviour of mechanophores, which are molecules that can undergo a chemical reaction when exposed to external mechanical stress. The prospects opened by these advances are potentially enormous. For instance, numerous sub-fields of engineering, nanotechnology or chemistry may find application to the implications of this notable breakthrough in basic research.


Image credits:

Purified sulfur picture was downloaded from Wikipedia and is in the public domain.

Bacyllus anthracis protein, by Argonne Laboratory, was downloaded from Wikipedia and licensed via a Creative Commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) license.

Picture of Chemical factory in Antwerp (Belgium) is in the public domain and was downloaded from Pixabay.

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