Biomimetic Knock-on of Ion Transport through Crown Ether-embedded Filter Membranes

Designing a filter membrane that can separate Na+ and K+ ions is of great significance for the study of biomimetic ion channels. Using nonequilibrium molecular dynamics simulations, we investigated monolayer and quadrilayer graphene-embedded 18-crown-6 ether nanopores under different external voltages in solution. We showed that the crown ether nanopores exhibit Na+ ion selectivity at low electric field but turn to K+ ion selectivity at high electric field. Ion translocation time of K+ ions is longer than that of Na+ ions in the monolayer crown ether nanopore, while in the quadrilayer crown ether nanopore, ion translocation time of K+ ions is shorter than that of Na+ ions. We demonstrated a synergetic mechanism for ion transport through the filter membrane from two perspectives: free energy through the nanopore and peeling of ion hydration layer. Partially dehydrated ions pass through the nanopore in a ‘knock-on’ manner due to electrostatic repulsion. Our work highlights the application of crown ether nanopores in the field of artificial biomimetic ion channels and ion filtration.