Chemistry

Rotaxane Receptor

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Science  28 Mar 2008:
Vol. 319, Issue 5871, pp. 1735
DOI: 10.1126/science.319.5871.1735b

A rotaxane is a molecular mimic of a wheel and axle—a large ring-shaped molecule that can translate and rotate along a second linear molecule, until its path is blocked bulky end groups. Frey et al. examined the application of rotaxanes bearing two macrocyclic groups as receptors in a functional arrangement resembling bookends. Each macrocycle was tethered through a long fused aromatic arm to a Zn porphyrin group, which could be used to bind pyridine molecules. The authors explored the binding of two different guest substrates—one comprising two pyridine rings bonded back-to-back at the 4 position and the other connecting two pyridines through a flexible 10-carbon-atom alkyl bridge—and found that both had nearly the same association constant for insertion into the gap between the Zn centers. Even when the macrocycles were anchored on the axle through copper coordination, the tethered Zn complexes retained sufficient flexibility to bind the guests with similar association constants. — PDS

J. Am. Chem. Soc. 130, 10.1021/ja7110493 (2008).

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