Damien Sluysmans, FNRS postdoctoral researcher at the NanoChem laboratory (UR MolSys / Faculty of Sciences), has designed a molecule allowing the quantification of the mechanical resistance of weak π-interaction at the single-molecule level. This research has been published and featured as a Cover of the Journal of the American Chemical Society.
Proteins and DNA are examples of biological molecules stabilized by a large number of non-covalent interactions. These non-covalent interactions include electrostatic, hydrophobic or π-interactions (mainly between aromatic compounds). The multiplicity of these weak interactions confers high stability to these biomolecules. Moreover, these interactions are used by biological molecular machines, these nanomachines present in our cells. The ease of breaking and recreating non-covalent interactions is at the basis of conformational changes, i.e. a modification of the molecular structure, in order to perform a mechanical or chemical task. Synthetic chemists also take advantage of such weak interactions. For example, π-interactions between a donor and an acceptor are commonly used for the synthesis of supramolecules or artificial molecular machines, capable of performing a task in response to an external stimulus.
Although the interactions between π-donors and π-acceptors are well characterized in solution, their mechanical resistance is rarely studied. This information is crucial for their integration into complex molecular structures subjected to controlled molecular motions.
Damien Sluysmans, FNRS postdoctoral researcher at the NanoChem laboratory (UR MolSys) at ULiège conducted this research in collaboration with the group of Prof. Stoddart (2016 Nobel laureate in Chemistry) at Northwestern University (USA). We started from a very simple concept: a molecular tweezer," explains Damien Sluysmans, the first author of the publication. We have synthesised a molecule containing two π-acceptor units connected by a loop. In solution, the tweezer is open but when we add π-donors, the molecular tweezer closes and the π-donor compound is trapped between the two π-acceptors as a result of the formation of a π-interaction. Using an Atomic Force Microscope (AFM), we were able to catch one molecule between the AFM tip and a surface and mechanically open it. In this way, we were able to measure the force required to break one π-interaction. »
The Nanochemistry and Molecular Systems group, led by Pr Anne-Sophie Duwez, has a large AFM expertise, particularly in single-molecule force spectroscopy experiments. Usually, they observe the behaviour of a single molecule trapped between an AFM tip and a surface by exerting successive mechanical stretches on it. This research has enabled us to compare the force of interaction between several π-donors and our molecular tweezer," says the researcher. We were also able to exchange one π-donor compound by another in situ. »
This strategy could be applied to a wider range of chemical interactions. The authors of this publication also show the power of single-molecule techniques, capable of accurately quantify the mechanical resistance and the work performance of artificial molecules, a crucial information in the race for functional artificial molecular machines.
Damien Sluysmans, Long Zhang, Xuesong Li, Amine Garci, J. Fraser Stoddart, Anne-Sophie Duwez, Viologen Tweezers to Probe the Force of Individual Donor Acceptor π-Interactions, JACS 2020, 142, 21153-21159 (DOI : 10.1021/jacs.0c10339)
Spotlight: https://pubs.acs.org/doi/10.1021/jacs.0c12720
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