Selective resonant diffusion of ions in an artificial analogue of a biological filter

We study selective ionic diffusion in a single-walled carbon nanotube (CNT). The wall is charged so as to mimic the structure of the selectivity filters in biological ion channels. We use all-atom molecular dynamics simulations to demonstrate that a charged CNT can closely reproduce many of the selectivity and conductivity properties of the KcsA biological channel. A K
⁺
/Na
⁺
selectivity ratio ≳150 and a conduction current Ftable ≳50 pA are demonstrated. It is shown that ionic Coulomb blockade is the key phenomenon underlying the CNT conduction properties. Coulomb blockade theory is used to estimate the excess chemical potential of the ions in the channel and the channel capacitance.