The permeation of potassium and chloride ions through nanotubes: a molecular simulation study

Abstract

The permeation of K⁺ and Cl⁻ ions across (7,7) and (8,8) carbon and boron nitride nanotubes was studied by the molecular dynamics simulation method. The simulated systems consist of a carbon or boron nitride nanotubes inserted in a silicon nitride membrane immersed in an aqueous ionic solution. The considered nanotubes were fixed in a silicon–nitride membrane and an external electrical field was applied on the systems along the axis of the nanotubes. Some of the simulated properties including the ionic current, the water structure inside the nanotubes, the retention time of the ions, ion-water radial distribution functions, numbers of hydrogen bonds, density of water molecules inside the nanotube, and the normalized transport rate of water with respect to the number of transported ions were calculated. The results show that the permeation of ions across the nanotubes is dependent on the diameter of the considered nanotubes and the applied electrical field. We find that the (7,7) and (8,8) nanotubes are exclusively selective to ions. A (7,7) nanotube can selectively conduct K⁺ ions. In contrast, a (8,8) nanotube can selectively conduct Cl⁻ ions. By calculating the potential of mean force for ions, we show that K⁺ and Cl⁻ ions face a large energy barrier and will not pass through the (8,8) and (7,7) nanotubes. Hence, based on the present study, these systems can be suggested as preliminary models for ion-channels and water desalinating devices because they broadly mimic some of the permeation characteristics of gramicidin and chloride channels.

Graphical Abstract