Design-driven trends in transport properties of artificial water channels

Peptide-appended pillar arenes (PAP) are a family of tubular molecules that allow rapid and selective transport of water. These artificial water channels embedded in self-assembled polymer bilayers can serve as desalination membranes, with potential for reverse osmosis because of their rigid pore dimension and favorable surface chemistry. In this work, we use atomistic molecular dynamics simulations to study the water mobility and ion rejection characteristics of a range of PAP channels with varying tube diameter, embedded in self-assembled polybutadiene-polyethylene oxide membranes. From our prior work, we know that PAP channels reject ions through hydration shell stripping.  An ion must partially dehydrate to be able to pass through the narrow pore; this incurs a significant free energy penalty, so the pore is able to reject ions. As the pore diameter increases, the water mobility goes up, while the ion rejection drops. By our simulations, we determine the limiting size of the PAP channel that offers enhanced water transport while still rejecting ions.