Abstract
Proton transport plays an important role in many biological processes due to the ability of protons to rapidly translocate along chains of hydrogen-bonded water molecules. Molecular dynamics simulations have predicted that confinement in hydrophobic nanochannels should enhance the rate of proton transport. Here, we show that 0.8-nm-diameter carbon nanotube porins, which promote the formation of one-dimensional water wires, can support proton transport rates exceeding those of bulk water by an order of magnitude. The transport rates in these narrow nanotube pores also exceed those of biological channels and Nafion. With larger 1.5-nm-diameter nanotube porins, proton transport rates comparable to bulk water are observed. We also show that the proton conductance of these channels can be modulated by the presence of Ca2+ ions. Our results illustrate the potential of small-diameter carbon nanotube porins as a proton conductor material and suggest that strong spatial confinement is a key factor in enabling efficient proton transport.
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Acknowledgements
We thank A.T. Pham for the images used in Fig. 1b,c, and Y. Yu for assistance with cryo-EM imaging. A.B. acknowledges SULI summer internship programme funding from the US Department of Energy. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award SCW0972. Work at the Lawrence Livermore National Laboratory was performed under the auspices of the US Department of Energy under Contract DE-AC52-07NA27344. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.
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R.H.T and A.N. designed the experiments, R.H.T. performed the proton transport experiments. K.K. and R.H.T. performed Raman characterization studies. F.I.A. and R.H.T. performed the TEM and cryogenic TEM characterization. A.B., K.K. and R.H.T. synthesized the CNT porins. R.H.T. and A.N. wrote the manuscript, and all authors commented on it.
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Tunuguntla, R., Allen, F., Kim, K. et al. Ultrafast proton transport in sub-1-nm diameter carbon nanotube porins. Nature Nanotech 11, 639–644 (2016). https://doi.org/10.1038/nnano.2016.43
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DOI: https://doi.org/10.1038/nnano.2016.43
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