Chemical gatekeepers that admit only certain kinds of molecules could be used
to build better sensors for chemical weapons or pollutants. These 鈥渁ccess ports鈥�
will guide target molecules to an inner sanctum, where they can be trapped and
identified.
To make the access ports, Ken Suslick and his colleagues at the University of
Illinois at Urbana-Champaign tinkered with dendrimers, self-assembling polymers
that branch out in all directions from a single molecule. They attached
dendrimers to a porphyrin, an organic molecule with a metal binding site that
can trap other substances.
Zinc is the metal at the active site of the team鈥檚 artificial porphyrin. It
works in the same way as haemoglobin, which contains iron for transporting
oxygen in mammals.
Advertisement
Suslick鈥檚 dendrimers formed two types of access port leading to the porphyrin
binding site. One, shaped like a chimney, let in molecules only if they were
slender. The other, shaped like a cave, admitted only short, chubby molecules.
鈥淲e can choose between short fat molecules or long skinny ones,鈥� says Suslick.
The porphyrins changed colour when they bound to their chosen targets, in the
same way that haemoglobin turns red when it binds to oxygen and blue when the
oxygen is released. The team鈥檚 results will appear in this week鈥檚 Journal of
the American Chemical Society.
The new molecules show that the concept works, but they have no direct
application yet. However, Suslick鈥檚 team is now working towards 鈥渁rtificial
noses鈥�. 鈥淚t鈥檚 the sort of thing you could use in the food industry, in the
chemicals industry or as detectors for chemical warfare agents,鈥� says Suslick.
鈥淵ou could have them in arrays for detecting all sorts of things.鈥� The ports
could also be used to control specific molecules鈥� access to catalysts in
chemical reactions.
Jean Fr茅chet, a dendrimer specialist at the University of California
at Berkeley, is impressed. 鈥淭hey鈥檝e shown that by using the sheer bulk of the
dendrimer, they can control what you let into the binding site,鈥� says
Fr茅chet. 鈥淚t鈥檚 very much like the cavity in an enzyme.鈥� He believes that
the idea could be applied to create a new generation of designer enzymes.