A redox reaction has been used to move a molecular piston back and forth. It is hoped that this will allow nanomachines to make use of it.

The piston works with a man made molecule called a rotaxne. The rotaxne is a liner molecule with a napthalene complex at one end and sulfur containing group at the other end. The sliding part of the piston is made of six carbon rings, joined to form a hooped shaped positively charged ion.

By made by Togo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

The sliding hoop  prefers to be located at the sulfur end of the molecule. Hover, the rotaxne molecule can be oxidised by an iron compound, which, in removing the electrons makes it positively charged. This results in the hoop being repelled to the other end of the rotaxne molecule.

The opposite happens during a reduction reaction.

It has been noted that the movement of the carbon hoop produces a force of 100 piconewtons, the same as that produced by biological motors! :mrgreen:

Image adapted from an article in New Scientist magazine, page 24, 20th November 2004 titled ‘Molecular piston shuttles into life’.