Nanomachinery gets a spring in its step

Molecular springs that always twist the same way are the latest addition to the nanomachinery toolbox. Developed by Japanese researchers, the springs can rotate microscopic objects in specific directions - something which may be useful in chiral systems such as liquid crystals. 

Several muscle-like molecules have been developed that can move objects at the nanoscale - but reliably twisting in a single direction, to the left or right, is more difficult. 

’The extension and contraction motion of our molecule is exactly like a macroscopic spring,’ says Yoshio Furusho, who worked on the project with Eiji Yashima at Nagoya University in Japan. ’Extension is accompanied by a twisting that maintains the left or right handedness, so it will always twist in the same direction.’ 

The spring was made from two polymer strands that are bridged by negatively-charged borate groups. When positively-charged sodium ions are added, they complex with the borate groups, sliding into the molecule and pulling the borate groups closer together. This causes the molecule to contract to around half its original length. 

Meanwhile, the two polymer strands twist to resemble a double helix - which causes the molecule to be rotated. By isolating only one chiral isomer of the bridged molecule, the team ensures that it always twisted to the right. To return the molecule to its original form, a multidentate ligand, such as cryptand, can be used to remove the sodium ions, which allows the molecule to spring back to its original form. 

’We are now working on incorporating this double helical spring into organogels and liquid crystalline materials,’ Furusho told Chemistry World. ’We are aiming to reflect the nanoscopic changes in macroscopic systems.’ 

’This is a clever piece of chemistry,’ says Jonathan Nitschke at the University of Cambridge, UK. ’The suggestion to embed these structures into a liquid crystal matrix - scaling up the properties - should also work, so this is quite exciting.’ 

Ben Feringa, who has designed similar compounds at the University of Groningen in the Netherlands, is also impressed by the work and suggests that applications may range from molecular actuators to artificial membranes that respond when twisted or compressed. 

’More importantly, we can learn from these designs how to control motion and dynamic function at the molecular scale - which is a challenging and still largely mysterious area of contemporary science,’ he told Chemistry World. ’Molecular motors play key roles in nearly every biological process, so there is great incentive to learn how to govern this in synthetic systems.’ 

Lewis Brindley