Research ArticleBIOPHYSICS

Water-ion permselectivity of narrow-diameter carbon nanotubes

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Science Advances  16 Sep 2020:
Vol. 6, no. 38, eaba9966
DOI: 10.1126/sciadv.aba9966
  • Fig. 1 Water permeability of CNTPs.

    (A) Schematics of dye-encapsulating liposome exposed to hypertonic buffer upon mixing; the escape of water causing vesicle shrinkage and responsible for self-quenching of encapsulated dyes. (B) Representative normalized CF fluorescence curves from the stopped-flow water transport measurements (CNTP-LUVs contained, on average, 16 CNTPs per vesicle). a.u., arbitrary unit. (C) Comparison of the unitary water permeabilities of CNTPs and aquaporin 1 (AQP1) (22).

  • Fig. 2 Water transport activation energy in CNTPs.

    (A) Normalized fluorescent curves indicative of water transport across DOPC membranes at five different temperatures. (B) Arrhenius plots of the water permeability for DOPC LUVs, with corresponding activation energies indicated on the graph. (C) Normalized fluorescent curves indicative of water transport across CNTP-embedded DOPC membranes at five different temperatures. (D) Arrhenius plots of the water permeability Pf (in units of μm/s) for CNTP-LUVs after subtraction of the background water permeability for DOPC-LUVs, with corresponding activation energies indicated on the graph.

  • Fig. 3 Simulation of water transport in CNTPs.

    (A) Snapshot from a WT-MetaD simulation showing the model system consisting of two water reservoirs, two graphene sheets, and a CNT. (B) 1D PMF of a water molecule transporting through the CNTP with respect to the length of the minimum free energy path. “0” and “1” correspond to the bulk water found in two reservoirs, and “0.5” corresponds to the center of the CNTP. The error bars are estimated from the SD of three independent replicas. (C) 2D PMF of a water molecule transporting through the CNTP computed from an average of three independent simulations. The black line represents the minimum free energy path. (D) 1D free energy profile of a water molecule transporting through the CNTP as obtained from hybrid quantum-continuum simulations, where the interaction between the permeated water molecule and CNTP was explicitly described using DFT and the rest of the liquid was treated by an implicit solvation model (see Materials and Methods for more details). The vertical dashed line indicates the position of the CNTP entrance. PES, potential energy surface. (E) Snapshots from a WT-MetaD simulation showing the process of water entering the CNTP at different time points in the simulation. (F) Evolution of the total number of hydrogen bonds (black lines and markers) formed by a water molecule transitioning the CNTP. Water-water (red lines and markers) and water-COO bonds (blue lines and markers) correspond to the number of hydrogen bonds formed with other water molecules and the COO groups at the entrance of the CNTP.

  • Fig. 4 Cl ion transport and water-salt permselectivity of CNTP.

    (A) Schematic of the chloride ion permeation assay showing lucigenin dye encapsulated in a liposome and Cl ion diffusion into the liposome through CNTP channels in the liposome wall. Valinomycin (VA) ionophore is added to the lipid bilayer to ensure that counterion (K+) transport does not impede anion diffusion. (B) Representative lucigenin fluorescence traces obtained in the Cl permeability measurements for CNTPs-LUVs, which contained, on average, 10 CNTPs per vesicle, and control LUVs. In both experiments, vesicles were exposed to 15 mM Cl gradient. (C) Chloride flux plotted as a function of chloride concentration gradient for CNTPs-LUVs and control LUVs. (D) Projected seawater desalination performance of composite lipid-CNTP (blue hexagon symbols) for different CNTP area fractions in the membrane (the corresponding numbers on the plot, where 0 corresponds to pure lipid membrane and 1 to pure CNTP). The performance of commercial desalination membranes (black open triangles), Turing-type polyamide membranes, TS-I and TS-II (solid inverted triangle), and graphene-nanomesh/single-walled CNT hybrid membrane (brown open circle) are adapted from (5759). Dashed red and solid black lines indicate the trade-off line and upper-bound line (3, 60). TS, turing structure.

Supplementary Materials

  • Supplementary Materials

    Water-ion permselectivity of narrow-diameter carbon nanotubes

    Yuhao Li, Zhongwu Li, Fikret Aydin, Jana Quan, Xi Chen, Yun-Chiao Yao, Cheng Zhan, Yunfei Chen, Tuan Anh Pham, Aleksandr Noy

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    The PDF file includes:

    • Determination of lucigenin dye quenching constant
    • Calculation of water and salt permeabilities of membranes with CNTPs
    • Figs. S1 to S8
    • Legend for movie S1

    Other Supplementary Material for this manuscript includes the following:

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