Molecular Dynamics Simulations of Polypeptoids Reveal the Effects of Chemistry and Topology on Local Water Behavior

Water structure, dynamics, and thermodynamics near surfaces influences the performance of a wide range of engineered systems, spanning water-filtration membranes, catalysis, and protein engineering. Previous computational work with idealized surfaces has shown that spatially patterning chemical functionalities in heterogeneous surfaces can impact water structure and dynamics; however, precised control over spatial surface organization can be challenging to replicate experimentally. Here, we realize spatially-controlled chemical heterogenities using polypeptoids, a class of polymers that can be synthesized sequence-specifically. We use molecular dynamics simulations to probe the effects of heterogeneities encoded in the sequence on local water behavior. Specifically, we observe how the polypeptoid hydration water’s translational, orientational, and hydrogen-bonding structure and dynamics respond to changes in the number and location of hydrophobic and hydrophilic monomers. We furthermore investigate the independent effect of topology on water behavior by comparing conformations with the same sequence. The hydrophobic monomers induce dehydration and dampen the dynamics of water near the polypeptoids, while collapsed conformations of a fully hydrophilic polypeptoid exhibit similar effects. These changes in water behavior provide insight into the way that sequence-specific functionalized surfaces impact their solvation. Ongoing work on polypeptoids tethered to silica surfaces will investigate whether polypeptoid sequence and conformation also modulates water behavior at interfaces, enabling the design of industrially relevant surfaces.