Ion transport in biological ion channels beyond classical electrostatics. Nanoscale confinement, non-linear concentration patterns and interfacial effects.

Membrane transport has been the subject of intense investigation during decades in diverse scientific disciplines like physical chemistry, biophysics, and electrochemistry. While simplified models derived from continuous electrostatics generally hold, nanometer-sized channels often exhibit unexpected behaviors that stem from a variety of factors including the molecular nature of the solvent or the charge-charge correlations involving both the permeating ions and fixed charges within the membrane-pore system. In this short review, we summarize recent work focusing on two different salt concentration regimes with behaviors that contradict classical models. First, at low concentrations, critical interfacial effects such as access resistance occur involving a non-trivial interplay between membrane and protein charges. Second, in concentrated solutions, many ion transport properties show non-monotonic concentration patterns compatible with underscreening. Understanding these nanoscale deviations from typical microscale behavior is essential for accurately predicting the function of biological ion channels and designing advanced, atomic-sized fluidic devices for industry.