Scientists are a step closer to the precise control of chirality at the molecular level thanks to a quantum chemical study.  

Dominik Kröner and Bastian Klaumünzer at Potsdam University, Germany, have shown that a pre-oriented achiral molecule, possessing no chirality at all, can be selectively switched into both its left- and right-handed chiral forms using a finely-tuned sequence of laser pulses.

'We were wondering how to affect the chirality of a molecule by laser pulses and how to describe it in terms of quantum mechanics,' said Kröner. 'Changing the chirality of a molecule being used as a chiral catalyst or a medical drug can alter the outcome of a chemical or biochemical process.'

The researchers carried out quantum simulations on the effect of sequences of infrared and ultraviolet laser pulses on a fluorinated styrene derivative. Internal rotation around the carbon-carbon single bond that connects the benzene ring and ethenyl group revealed three conformations, one being achiral, the most stable form of the molecule, and two being chiral, namely the two mirror images of left- and right-handed forms of the molecule.

Swapping a molecule from left- to right-handed could be as easy as flipping a switch

In effect, the molecule can switch between a true 'off' (achiral) state and two different chiral 'on' states. And by toggling between the two enantiomeric forms, the chirality of the compound can not only be 'turned on', but the handedness can also be chosen. 

According to Kröner, if such a chiral molecular switch could be applied as a catalyst in asymmetric synthesis, it would be able to control the stereoselectivity of the reaction depending on its 'chiral switching status'.

The biggest challenge for Kröner is the experimental realisation of this stereoselective laser control. 'While in theory we rely on rather simplified models to describe the molecular system in terms of the underlying chemical and physical interactions and processes, in experiment many other effects, which cannot easily be covered by theory, may play an important role,' he said. 'We need to extend our model to include other influences like more degrees of freedom, energy dissipation or temperature effects.'

Stephen Wilkes