DFT calculations can be used to find out why chiral-at-metal complexes lose their chirality and how this can be prevented, reports Chemistry A European Journal. ‘Knowing how it works gives you the opportunity to do something with it.’

Almost all biomolecules (from sugars to amino acids) are chiral, and many drugs work because they act on chirality. But to make chiral molecules, you also need chiral molecules or catalysts. ‘In metal catalysis, you use metal complexes to which a chiral ligand is attached’, says Koop Lammertsma, professor emeritus at the Vrije Universiteit Amsterdam and the University of Johannesburg. ‘But this is rather strange: the metal in such a complex is often already chiral, so it is somewhat redundant to add a chiral substituent. In addition, such ligands are often expensive or difficult to synthesise.’

Racemisation

But there is a reason why researchers are doing it, says Lammertsma. ‘Complexes in which the metal itself is chiral (chiral-at-metal) are not stable. Complexes with five or six substituents or ligands can twist and turn. Hexa-coordinated complexes in particular turn into their mirror-image isomer. If you start with one mirror-image isomer, but some of it turns into the other mirror-image isomer, this is called racemisation.’ Together with George Dhimba and Alfred Muller from the University of Johannesburg, Lammertsma investigated what causes racemisation and what can be done to stop it. ‘With this paper, we wanted to understand more about how these processes work. Knowing how it works gives you the opportunity to do something with it.’