Charge Asymmetry Effect in Ion Transport through Angstrom-Scale Channels

Structural and dynamic properties of ions confined in nanoslits are crucial to understand the fundamental mechanism underlying a wide range of chemical and biological phenomena. K+ and Cl– show similar ion mobilities in a bulk aqueous solution, whereas they exhibit a remarkable difference when transporting through an angstrom-scale channel. Our molecular dynamics simulations uncover that such discrepancy originates from the subtle differences in their hydration structures and preferable locations across the channel. Opposite charge causes different water dipolar orientations around ions, mediating the distance and tribological interactions between hydrated ions and channel’s walls. Hydrated Cl– ions experience a remarkable larger friction force inside the channel and consequently a smaller mobility compared with K+ ions. This charge asymmetry mechanism becomes dominant when the channel size approaches the molecular scale, which takes responsibility for the delicate distinction between dynamic transport be...