Mobility of a One-Dimensional Confined File of Water Molecules as a Function of File Length

Confinement of water by pore geometry to a one-dimensional file of molecules interacting with the pore alters the diffusion coefficient $D_W$. Here we report an exponential dependence of $D_W$ on the number of water positions in the pore. The result is based on measurements of single channel water permeabilities of structurally similar peptidic nanopores of different length. The inconsistency with predictions from continuum or kinetic models indicates that pore occupancy is reduced in single file transport. In longer pores (e.g., in aquaporins) the presence of charged residues increases $D_W$.