Several water nanopores, including single-wall carbon nanotube (SWNT), Y-shaped carbon nanotube (Y-CNT), nanoporous 2D Fe phthalocyanine (FePc), have been studied with large scale molecular dynamics simulations on their capability in water permeation, desalination, gating and even signal transduction. The water permeation across a SWNT can be controlled with a single electron/proton. The effect on the water flow and net flux in the confined nanotube is found to be negligible when the external charge of value is beyond a critical distance from the wall of the SWNT. This designed nanopore shows an excellent on-off gating behavior by a single charge. Meanwhile, one signal at single-electron level can be converted and multiplied into two or more stable signals by water chains confined in a narrow Y-CNT. This remarkable transduction capability of molecular signal by Y-CNT is found to be attributable to the surprisingly strong dipole-induced ordering of such water chains, such that the concerted water orientations in the two branches of the Y-CNT can be modulated by the water orientation in the main channel. The response to the switching of the charge signal is very rapid, from a few nanoseconds to a few hundred nanoseconds. As for the FePc nanopore, interestingly, we find that it not only conducts fast water flow, with a water conductivity up to 6.5 L/cm2/day/MPa, but also can fully exclude the permeation of Na+ ions, and also limit the Cl- ions' transduction rate to be four orders of magnitude smaller than water. Such remarkable selectivity is attributed to the unique feature of FePc nanopores which is distinct from traditional steric exclusion mechanism. In addition, the number of protonated nitrogen atoms in FePc pores can be modulated by adjusting the pH value of the solution. The extent of the anion trapping and occupancy can thus be regulated, giving rise to the control of the water flow.

Water permeation, desalination, gating, and dipole signal transduction with nanopores

248th National Meeting (2014)

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