Modeling polyelectrolyte hydration from a multi scale polarizable pseudo particle solvent coarse grained approach

Abstract

We investigate the reliability of simulations of polyelectrolyte systems in aqueous environments, simulations that are performed using an efficient multi scale coarse grained polarizable pseudo-particle particle approach, denoted as pppl, to model the solvent water, whereas the solutes are modeled using a polarizable all atom force field. We focus our study on issues tied to two key parameters of the pppl approach, namely the extension of the solvent domain SD at the close vicinity of a solute (domain in which each solvent particle corresponds to a single water molecule) and the magnitude of solute/solvent short range polarization damping effects. To this end we built a new pppl models from which we simulate NaCl aqueous solutions at the molar concentration scale. We also re investigate the hydration of a hydrophobic polyelectrolyte polymer that we showed in an earlier study [J Chem Phys, 114903 (155) 2021] to evolve towards a counter intuitive globular form surrounded by a spherical counter ion cloud along pppl-based simulations. Strong short range damping is pivotal to simulate NaCl aqueous solutions. The extension of the domain SD (as well as short range damping) has a weak effect on the conformation of the polymer, but it plays a pivotal role to compute accurate solute/solvent interaction energies. In all our results lead us to recommend to simulate polyelectrolyte polymers as dissolved alone in pppl fluids (i.e. without explicitly accounting for their counter ions) to investigate their behavior at infinite dilution conditions, and to systematically consider strong solute/solvent polarization short range damping to model charged species.