[More press releases] Press ReleaseAngewandte Chemie International Edition 2010, 49, 3189–3191 doi: 10.1002/anie.200906753 Nr. 14/2010 April 20, 2010 Biting its Own TailNanocontainer with an integrated switchContact: Julius Rebek, Jr., Scripps Research Institute, La Jolla (USA) Registered journalists may download the original article here: The Ouroborand: A Cavitand with a Coordination-Driven Switching Device The
ouroboros (ancient Greek for “tail devourer”) is a motif found in many
cultures: a snake biting its own tail, it symbolizes eternity and
cycles. Julius Rebek, Jr. and Fabien Durola (The Scripps Research
Institute, La Jolla, USA) have now constructed a molecular tail
devourer, and have named this new class of compound “ouroborand”. As the
researchers report in the journal Angewandte
Chemie,
their tail-biter is a molecular “machine”, which functions as a
nanocontainer with a built-in switch that regulates access to the cavity.
 © Wiley-VCH
Molecular
machines and nanoscopic components imitate—at least theoretically—the functions of their macroscopic analogues. For example,
nanoscopic capsules can act as reaction vessels, molecules with
parts that rotate relative to each other to imitate rotors, and various
types of on/off switches.
The
ouroborand made by the American research duo is a molecule consisting of
multiple parts. A cavity that can take up guest molecules serves as a
container. At its edge, the container has a switchable rotor (a
bipyridyl unit) to which an intramolecular guest is attached like a
hand at the end of a coupling arm of appropriate length. The rotor is
turned so that the hand at the end of the arm sits inside the
container. The container is thus blocked and not accessible to other
molecules; it is switched to closed. In this conformation it is
reminiscent of a snake that is swallowing its own tail, the ouroboros.
If
zinc ions are added to the solution, they trigger a switching mechanism:
the rotor has two binding sites for zinc ions. In order for both to bind
an ion, the rotor must make a half-turn. The coupling arm turns with it,
which causes the hand to be pulled out of the container. The vessel is
now free and accessible to other molecules; it is switched to open. If
the zinc ions are taken back out of the solution, the rotor then turns
back to the starting position and the hand throws the foreign molecule
back out of the container.
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