Interconverting Mirror-Image Molecules
Recent research from scientists at the Universities of York and Durham has developed new concepts about the shape and dynamic nature of molecules.
When a carbon atom forms four bonds to different groups, the molecule can exist in two
mirror image forms. These mirror image forms are vital in medicine because they have
different biological activities. Usually, it is impossible to interconvert between these
‘enantiomers’ because to do so would require a bond to be broken, a process that needs too
much energy.
The team of researchers, led by Dr Paul McGonigal, who recently joined the Department of Chemistry in York as a Reader in the Molecular Materials Group, demonstrated that if the chiral centre was part of a dynamic molecular cage structure, then a simple rearrangement of the cage could lead to inversion of the mirror image form of the molecule. In this way, carbon-based stereochemistry, which is normally considered to be fixed and rigid, became dynamic, fluxional and responsive – a new paradigm in carbon-centred chirality.
The molecular cage has nine carbons atoms in its structure, which are held together by a pair of carbon–carbon double bonds and a three-membered cyclopropane ring (see Figure). This combination of bonds allows some of the bonds in the structure to trade places with one another spontaneously.
Dr Aisha Bismillah, a postdoctoral researcher in the McGonigal Group and the lead investigator of the project, commented: “Our dynamic carbon cages change their shape extremely quickly. They hop back and forth between their mirror image structures millions of times a second. Seeing them adapt to match changes in their environment is truly remarkable.”
Further to uncovering this unique dynamic form of stereochemical interconversion, the researchers demonstrated that the preferences of the cage could be transmitted to nearby metal centres, opening the possibility that this type of responsive chirality might find uses in catalysis, and the synthesis of chiral molecules for biomedical applications.
Reflecting on the way in which these results overturn established ideas, Dr McGonigal said: “The way our dynamic carbon cage interacts with other molecules and ions is fascinating. The cage adapts, giving the mirror-image structure with the ‘best fit’. We hope, in due course that this intriguing bonding concept will be found to apply in other contexts, and potentially used to underpin new applications for more dynamic molecular materials.”
Dr Paul McGonigal works as part of the Molecular Materials Group in the Department of Chemistry at The University of York.
This research has been published in the journal Nature Chemistry. It was funded by the EPSRC and Leverhulme Trust.
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