Chemistry

Chemical Turnstiles

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Science  25 Jul 2003:
Vol. 301, Issue 5632, pp. 439
DOI: 10.1126/science.301.5632.439a

Entrance gates in subways and stadiums work, in part, because they are designed to rotate in only one direction. Leigh et al. have designed interwoven ring molecules (catenanes) in which the overall movement of the smaller chemical rings is in one direction as they hop between binding sites on the much larger guide ring. In these systems, a chemical reaction (which can be induced by light or heat) changes the binding constant for the smaller rings to sites on the larger ring (indicated as site A becoming site A'). Changing the binding constant allows movement, but to achieve a net unidirectional motion, the authors used two smaller rings to block each other from completely reversing direction. Like some biological motors, some individual steps are backtracks (such as the “clockwise” movement of the purple ring in step on the right-hand side). — PDS

Nature 424, 174 (2003).

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