Halogen Bonding Improves the Performance of Small Molecular Machines

Professor David Bryce is standing in his lab next to his PhD student Patrick Szell

Professor David Bryce with PhD candidate Patrick Szell and undergraduate student Scott Zablotny

Department of Chemistry and Biomolecular Sciences

Molecules in solids (e.g., crystals, powders) are not static – they often are moving very rapidly even though we cannot see this motion with our eyes. This motion (dynamics) has a profound impact on the functionality of the molecules and the molecular machines that can be built to accomplish specific tasks. Professor David Bryce, PhD candidate Patrick Szell and undergraduate student Scott Zablotny demonstrated that a special interaction with halogen atoms, termed ‘halogen bonding’, can improve the performance of small molecular machines.

This is the first experiment to show that this type of chemical interaction has an impact on how molecules move, not only on their static structures. This finding opens up a new world parallel to ubiquitous hydrogen bonding. Their results showed that this interaction actually facilitates dynamics in the solid state, rather than hindering it. Until now, this type of ‘dynamics catalysis’ had not been explored; however, Prof. Bryce’s work could have implications for dynamic processes which play key roles in enzymatic reactions involved in disease and health. Dynamics are also essential to the functioning of molecular machines (the 2016 Nobel Prize in Chemistry was awarded for the design and production of molecular machines), and thus the discovery that halogen bonding can improve molecular dynamics is particularly exciting. Prof. Bryce and his team used a method his lab developed, called cosublimation, as well as mechanochemistry to prepare a series of chemical cocrystals. This method consists of taking two powders, vaporizing them, and creating a new cocrystal, in this case using a heavy isotope of hydrogen called deuterium. They then carried out deuterium nuclear magnetic resonance relaxation experiments to see how fast certain parts of the molecules in the crystals were moving. These parts, called methyl groups, behave like spinning tops and their spinning rate was easily modified when particular chemical interactions were introduced in their vicinity. Furthermore, Prof. Bryce’s research revealed that halogen bonds outperform traditional hydrogen bonds, and that halogen bonding plays a direct role as a supramolecular dynamics catalyst. Dynamic processes have many implications in functional molecules, including catalysts, enzymes, host-guest complexes, and molecular machines. There are therefore broad implications for the improved design of enzymes and molecular machines in the future.

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