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Imaging the dynamic behaviour of individual retinal chromophores confined inside carbon nanotubes


Retinal is the molecule found in photoreceptor cells that undergoes a change in shape when it absorbs light. Specifically, the cis/trans isomerization of a carbon–carbon double bond in this chromophore sets in motion the chain of biochemical processes responsible for vision1,2,3. Here, we obtain atomically resolved images of individual structural isomers of the retinal chromophore attached to C60 molecules and study their dynamic behaviour inside a confined space—that is, inside single-walled carbon nanotubes—using high-resolution transmission electron microscopy (HR-TEM). Sequential HR-TEM images with sub-second time resolution directly reveal the isomerization between the cis and all-trans forms of retinal, as well as conformational changes and volume-conserving effects. This work opens up the possibility of investigating in vitro the biological activities of these photoresponsive molecules on an individual basis, and the molecular imaging technique described here is a general one that can be applied to a wide range of systems.

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Figure 1: Isomerization of the retinal chromophore is the initial step in the sequence of molecular processes responsible for vision.
Figure 2: Isomerization of Ret-C60.
Figure 3: Time-averaged HR-TEM images of Ret-C60 molecules within the SWNTs.
Figure 4: Dynamic behaviour of the retinal chromophores recorded in sequential HR-TEM images.

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Work on electron microscopy was supported by CREST. K.Y. thanks M. Funabashi for his help in a mass spectroscopy experiment. The partial support of a Grant-in-Aid for Scientific Research from MEXT is also acknowledged by K.Y. and H.K.

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K.Y. and H.K. designed the molecules and contributed the materials. Z.L. performed the experiments. Z.L. and K.S. analysed the data. K.S. and S.I. designed and conceived the experiments. Z.L., K.Y. and K.S co-wrote the paper. All authors discussed the results and commented the manuscript.

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Correspondence to Kazu Suenaga.

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The authors declare no competing financial interests.

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Liu, Z., Yanagi, K., Suenaga, K. et al. Imaging the dynamic behaviour of individual retinal chromophores confined inside carbon nanotubes. Nature Nanotech 2, 422–425 (2007).

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