Canadian chemists have used interlocked molecules to create a mechanical switch that is sensitive to its solvent.

Stephen Loeb and colleagues at the University of Windsor have made a mechanically interlocked molecule, known as a rotaxane, which switches between two different molecular arrangements depending on the solvent in which it is dissolved. 

The rotaxane is made of two parts - a bis(pyridinium) axle and a crown ether wheel. Bulky stoppers at either end of the axle keep the wheel in place.

Loeb said the structure can exist in two states, which differ in the relative positions of the wheel and axle, because the interlocked components are asymmetric. 

Fraser Stoddart, an expert in molecular machines at the University of California, Los Angeles, welcomed the findings. 'The Canadian chemists have come up with an intriguing variation of bistable rotaxane-based switches,' he said. 'Although the bias between the two different states of the switch is 4:1 in the best situation, and the barrier to switching is low . it should be possible to increase the bias and slow down the rate of switching.'

Stoddart added, 'conceptually, this work represents a significant contribution, adding another extremely valuable approach to the design and construction of molecular switches.' 

Alison Stoddart