Simulations predict water mobility and ion rejection in biomimetic pore membranes

Biomimetic pore embedded membranes can mimic highly efficient water filtration processes occurring in nature. In this work, we simulate peptide appended pillar[5]arene (PAP[5]) pore molecules embedded in polybutadiene-polyethylene oxide (PB-PEO) membranes, which imitate aquaporin water channels in cell membranes. These systems offer a possible high-permeability alternative to conventional reverse osmosis membranes. Because of their rigid pore dimension and surface chemistry, PAP[5] molecules have excellent water permeability and high selectivity. In this study, we systematically varied the PB and the PEO block lengths to discover the effect of membrane architecture on water mobility. We measured short-time water diffusivity in these designs and obtained a diffusivity comparable to that inferred from experiments. Further, a long-time water diffusivity for the best design was computed from the random entrances and exits of water molecules from the PAP[5], which was in good agreement with the short-time diffusivity. Finally, to quantify the ion rejection characteristics of the PAP[5] molecule, we measured the work to drag Na⁺ and Cl^- ions into and out of the pore. Our simulation techniques can be readily applied to other candidate structures, to aid in pore design.