Ion-triggered spring-like motion of a double helicate accompanied by anisotropic twisting

Author:  ["Kazuhiro Miwa","Yoshio Furusho","Eiji Yashima"]

Publication:  Nature Chemistry

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Tags:  Supramolecular chemistry   Chemistry

Abstract

Molecules that extend and contract under external stimuli are used to build molecular machines with nanomechanical functions. But although common in biological systems, such extension and contraction motions with helical molecules have rarely been accompanied by unidirectional twisting in synthetic systems. Here we show that sodium ions can trigger the reversible anisotropic twisting of an enantiomeric double-stranded helicate, without racemization. An optically active helicate consisting of two tetraphenol strands bridged by two spiroborate groups sandwiches a sodium ion. On removal of the central sodium—through addition of a cryptand [2.2.1] in solution—the double helicate extends. Crystallographic and nuclear magnetic resonance studies reveal that the extended helicate is over twice as long as the initial molecule, and is twisted in the right-handed direction. Circular dichroism analysis suggests that the twisting doesn't affect the helicate's handedness. This anisotropic extension–contraction process is reversibly triggered by the successive addition and removal of sodium ions in solution. Helical molecules in biological systems commonly undergo extension, contraction and unidirectional twisting motions, but such twisting — promising for the construction of molecular machines — has rarely been achieved in synthetic systems. Now, a chiral double helix has been prepared whose spring-like motion is accompanied by an anisotropic twist under the control of sodium ions.

Cite this article

Miwa, K., Furusho, Y. & Yashima, E. Ion-triggered spring-like motion of a double helicate accompanied by anisotropic twisting. Nature Chem 2, 444–449 (2010). https://doi.org/10.1038/nchem.649

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