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Tiny ''elevator'' most complex nanomachine yet.
19:00 18 March 2004
Nanoscale elevators made of two interlinking organic molecules have been built and operated by US and Italian scientists.
are the most complex molecular machines built yet, consisting of a
platform flanked by three rings that thread through three vertical
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.
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."
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 slide up the prong, they pull the platform with them. The
whole thing stands 2.5 nanometres tall and 3.5 nanometres wide.
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.
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
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.
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
which now float free in solution.
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."
Journal reference: Science (vol 303, p 1845)