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Bulk protonic conductivity in a cephalopod structural protein

Abstract

Proton-conducting materials play a central role in many renewable energy and bioelectronics technologies, including fuel cells, batteries and sensors. Thus, much research effort has been expended to develop improved proton-conducting materials, such as ceramic oxides, solid acids, polymers and metal–organic frameworks. Within this context, bulk proton conductors from naturally occurring proteins have received somewhat less attention than other materials, which is surprising given the potential modularity, tunability and processability of protein-based materials. Here, we report proton conductivity for thin films composed of reflectin, a cephalopod structural protein. Bulk reflectin has a proton conductivity of ~2.6 × 10–3 S cm–1 at 65 °C, a proton transport activation energy of ~0.2 eV and a proton mobility of ~7 × 10–3 cm2 V–1 s–1. These figures of merit are similar to those reported for state-of-the-art artificial proton conductors and make it possible to use reflectin in protein-based protonic transistors. Our findings may hold implications for the next generation of biocompatible proton-conducting materials and protonic devices.

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Figure 1: Electrochemical impedance spectroscopy of reflectin films.
Figure 2: Electrical properties of reflectin films contacted with palladium hydride electrodes.
Figure 3: Comparison of the electrical properties of wild-type and mutant reflectins.
Figure 4: Electrochemical impedance spectroscopy of reflectin films as a function of temperature.
Figure 5: Electrical characteristics of protonic transistors from reflectin.

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Acknowledgements

We thank S. Hess at the California Institute of Technology Proteome Exploration Laboratory for assistance with the tryptic digestion and mass spectrometry experiments. We thank Professor Albert Yee's Laboratory for the use of their optical microscope. We thank J. Angle in Professor Martha Mecartney's Laboratory for the use of custom-built EIS equipment during the temperature-dependent measurements and S. Yang in Professor John Kymissis' Laboratory for the use of EIS equipment during the deuterium oxide measurements. We thank the Penner and Law Laboratories for the use of their atomic force microscope. We also thank P. Sheehan and the Naval Research Laboratory and Professor Zhibin Guan's Laboratory for the use of their thermogravimetric analysis instruments. A.A.G. acknowledges the Air Force Office of Scientific Research (FA9550-14-1-0144) and the University of California, Irvine, for financial support. W.G.W. acknowledges the National Science Foundation Postdoctoral Research Fellowship in Biology (DBI1306188) for financial support.

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Experiments were conceived by D.D.O. and A.A.G. Experiments were carried out by D.D.O., L.P., E.K., J-M.J. and N.H. Biological samples were produced by L.P. and W.G.W. The manuscript was written by A.A.G., D.D.O., L.P. and W.G.W.

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Correspondence to Alon A. Gorodetsky.

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Ordinario, D., Phan, L., Walkup IV, W. et al. Bulk protonic conductivity in a cephalopod structural protein. Nature Chem 6, 596–602 (2014). https://doi.org/10.1038/nchem.1960

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