Nanoscale elevators made of two interlinking organic molecules have been built and operated by US and Italian scientists.
They are the most complex molecular machines built yet, consisting of a platform flanked by three rings that thread through three vertical rods.
The force of an acid-base reaction is used to power the “elevator”. Experts say the force produced by the movement of the platform itself is larger than forces produced by previous ‘nanoshuttles’ – single rings that moved up and down a rod. The elevators could be used to tightly control chemical reactions, or as drug-delivery systems.
However, others remain unsure about what the elevators will be used for. “If and in which way such motor molecules will ever be useful, nobody knows at this moment,” says Fred Brouwer of the University of Amsterdam, who built the first light-powered molecular motor in 2001. “The main reason for doing this kind of research is that it is a challenge.”
The nano-elevator consists of a platform molecule – the elevator itself, and a stool-shaped molecule – the shaft. The platform is flat and is flanked by three oxygen-rich rings. The shaft has a flat roof and stands on three vertical prongs. Each prong is threaded through one of the rings.
When the rings slide up the prong, they pull the platform with them. The whole thing stands 2.5 nanometres tall and 3.5 nanometres wide.
In an acidic environment, a nitrogen-containing molecular group near the top of the prongs becomes positively charged and attracts the negatively-polarised oxygen atoms that line the rings. The elevator platform sits in its up position just below the roof of the shaft.
When a base is added, the nitrogen group loses its charge and the rings instead are attracted to atoms situated further down the prong. The elevator platform slides into its down position.
Electricity or light
Brouwer says within the next 10 years the elevator’s most likely application will be in bringing two reactants together, allowing tight control over the timing of a reaction.
Further in the future the elevators could act as pistons for remote-controlled drug delivery inside the body, says Fraser Stoddart a chemist at the University of California, Los Angeles, and one of the team. But this will require that their motion be sparked by electricity or light, rather than a change in pH.
He told New Scientist that the molecules could also endow surfaces with tunable properties. Such surfaces would pull certain molecules from a mixture into the “elevator shaft” when the elevator was in the up position, but then expel that molecule when a different solution was run over the surface. However, researchers will have to find a way to anchor the elevator molecules, which now float free in solution.
Ross Kelly of Boston College, Massachusetts built a chemically-powered molecular motor in 1999 and says he has yet to discover what its applications might be: “I just thought it would be a neat thing to do. Lots of people get turned on by molecular motors.”