Landscapes, nonlinearity, and optimality of ion transport in sub-nanoscale pores*

Biological ion channels evolved to have high transport rates and high selectivity, among other functional characteristics. Synthetic nanoscale pores aim to mimic these properties for applications such as desalination and osmotic power generation.¹ In these systems, ion-ion and ion-channel interactions occur at sub-nanometer distances which entails large electrostatic and dehydration energies.² The balance of these energies determines selectivity and permeation rates. Importantly, the susceptibility of transport and selectivity to minute changes in distances—changes on the order of picometers—is enormous resulting in highly-nonlinear behavior. Biological systems can exploit this susceptibility via variations in protein structure that steer the local electrostatic and structural conditions. We demonstrate how this works in a synthetic selectivity filter and discuss how to probe this system, which will help to experimentally quantify optimal transport conditions and will give the foundation for a robust understanding of more complex biological pores.
[1] S. Sahu & M. Zwolak, Rev. Mod. Phys. 91, 021004 (2019).
[2] S. Sahu, J. Elenewski, C. Rohmann, & M. Zwolak, Sci. Adv. 5, eaaw5478 (2019).