Unraveling the mechanism of selective ion transport in hydrophobic subnanometer channels

Hui Li, Joseph S. Francisco, Xiao Cheng Zeng

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

Recently reported synthetic organic nanopore (SONP) can mimic a key feature of natural ion channels, i.e., selective ion transport. However, the physical mechanism underlying the K+/Na+ selectivity for the SONPs is dramatically different from that of natural ion channels. To achieve a better understanding of the selective ion transport in hydrophobic subnanometer channels in general and SONPs in particular, we perform a series of ab initio molecular dynamics simulations to investigate the diffusivity of aqua Na+ and K+ ions in two prototype hydrophobic nanochannels: (i) an SONP with radius of 3.2 Å, and (ii) single-walled carbon nanotubes (CNTs) with radii of 3-5 Å (these radii are comparable to those of the biological potassium K+ channels). We find that the hydration shell of aqua Na+ ion is smaller than that of aqua K+ ion but notably more structured and less yielding. The aqua ions do not lower the diffusivity of water molecules in CNTs, but in SONP the diffusivity of aqua ions (Na+ in particular) is strongly suppressed due to the rugged inner surface. Moreover, the aqua Na+ ion requires higher formation energy than aqua K+ ion in the hydrophobic nanochannels. As such, we find that the ion (K+ vs. Na+) selectivity of the (8, 8) CNT is ∼20x higher than that of SONP. Hence, the (8, 8) CNT is likely the most efficient artificial K+ channel due in part to its special interior environment in which Na+ can be fully solvated, whereas K+ cannot. This work provides deeper insights into the physical chemistry behind selective ion transport in nanochannels.

Original languageEnglish (US)
Pages (from-to)10851-10856
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume112
Issue number35
DOIs
Publication statusPublished - Sep 1 2015

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Keywords

  • Ion
  • Molecular-dynamics
  • Nanotubes
  • Selective
  • Transport

ASJC Scopus subject areas

  • General

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