A polarizable MARTINI model for monovalent ions in aqueous solution

Area of Science:

• Computational chemistry
• Molecular dynamics simulations
• Physical chemistry

Background:

• Accurate modeling of electrostatic properties in aqueous electrolyte solutions is crucial for understanding various chemical and biological processes.
• Existing coarse-grained models often struggle to precisely capture the behavior of ions, especially in complex systems.
• Polarization effects, essential for electrostatic interactions, are challenging to implement in coarse-grained force fields.

Purpose of the Study:

• To introduce refIon, a novel polarizable coarse-grained Martini force field for monovalent ions.
• To accurately reproduce electrostatic properties, mass density, and static dielectric permittivity of aqueous electrolyte solutions.
• To validate the force field's performance in various systems, including polyelectrolytes and lipid bilayers.

Main Methods:

• Development of a new polarizable coarse-grained Martini force field (refIon) for monovalent ions.
• Inclusion of full long-range Coulomb interactions and satellite charges to model polarization.
• Parameterization against experimental data for aqueous NaCl solutions (mass density, dielectric permittivity).
• Validation using analytic solutions, atomistic simulations, and experimental data for polyelectrolytes and lipid bilayers.

Main Results:

• refIon accurately reproduces experimental values for mass density and dielectric permittivity of NaCl solutions up to moderate concentrations.
• Improved agreement with experimentally measured ionic conductivities.
• Successful validation for ion distribution around polyelectrolytes and structural properties of lipid bilayers.
• Elimination of heuristic scaling factors, leading to better simulation-experimental agreement.

Conclusions:

• The refIon force field offers a significant improvement for simulating electrostatic properties in aqueous electrolyte solutions.
• It provides a reliable tool for studying highly charged systems like DNA, polyelectrolytes, and their complexes.
• The model enhances the accuracy of molecular dynamics simulations for charge transport and electrostatic effects.