Mechanical twisting of a guest by a photoresponsive host

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Abstract

Molecular analogues of a variety of mechanical devices such as shuttles, brakes, unidirectional rotors and tweezers have been created1,2,3,4,5,6,7,8,9,10,11. But these ‘molecular machines’ have not yet been used to mechanically manipulate a second molecule in a controlled and reversible manner. Here we show that light-induced scissor-like conformational changes of one molecule5 can give rise to mechanical twisting of a non-covalently bound guest molecule. To realize this coupling of molecular motions, we use a previously designed system5: a ferrocene moiety with an azobenzene strap, each end of which is attached to one of the two cyclopentadienyl rings of the ferrocene unit, acts as a pivot so that photoisomerization of the strap rotates the ferrocene rings relative to each other and thereby also changes the relative position of two ‘pedal’ moieties attached to the ferrocene rings. We translate this effect into intermolecular coupling of motion by endowing the pedals with binding sites, which allow the host system to form a stable complex with a bidentate rotor molecule. Using circular dichroism spectroscopy, we show that the photoinduced conformational changes of the host are indeed transmitted and induce mechanical twisting of the rotor molecule. This design concept, which significantly extends the successful coupling of motion beyond the intramolecular level seen in synthetic allosteric receptors12, might allow for the remote control of molecular events in larger interlocked molecular systems.

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Figure 1: Design and concept of light-powered molecular pedal.
Figure 2: Binding of rotary guest 2 with molecular pedal trans -1.
Figure 3: Circular dichroism (CD) visualization of the motions of guest–binding molecular pedals 2·(+ )-1 and 2·(- )-1 triggered by light.
Figure 4: Configurational aspects of the zinc porphyrin units of molecular pedal trans -1 and rotary guest 2 in 2· trans -1.

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Acknowledgements

T.M. thanks the JSPS Young Scientist Fellowship. This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research on Priority Areas ‘Life-Surveyors’ (to K.K.). We thank Y. Casta and S. Nara for cooperation in synthesis, and N. Tamai and M. Irie for discussion on photophysics.

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Correspondence to Kazushi Kinbara or Takuzo Aida.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Notes

This file contains the Supplementary Methods (experimental details for synthesis and measurements) and Supplementary Figures 1-12. (PDF 1867 kb)

Supplementary Movie 1

This movie represents computer-generated 3D molecular models of 2otrans-1 and 2ocis-1 viewed from various angles. (MOV 9094 kb)

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Muraoka, T., Kinbara, K. & Aida, T. Mechanical twisting of a guest by a photoresponsive host. Nature 440, 512–515 (2006) doi:10.1038/nature04635

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