A polarizable MARTINI model for monovalent ions in aqueous solution

Abstract

We present a new polarizable coarse-grained martini force field for monovalent ions, called refIon, which is developed mainly for the accurate reproduction of electrostatic properties in aqueous electrolyte solutions. The ion model relies on full long-range Coulomb interactions and introduces satellite charges around the central interaction site in order to model molecular polarization effects. All force field parameters are matched to reproduce the mass density and the static dielectric permittivity of aqueous NaCl solutions, such that experimental values are well-reproduced up to moderate salt concentrations of 2 mol/l. In addition, an improved agreement with experimentally measured ionic conductivities is observed. Our model is validated with regard to analytic solutions for the ion distribution around highly charged rod-like polyelectrolytes in combination with atomistic simulations and experimental results concerning structural properties of lipid bilayers in the presence of distinct salt concentrations. Further results regarding the coordination numbers of counterions around dilute poly(styrene sulfonate) and poly(diallyldimethylammonium) polyelectrolyte chains also highlight the applicability of our approach. The introduction of our force field allows us to eliminate heuristic scaling factors, as reported for previous martini ion models in terms of effective salt concentrations, and in consequence provides a better agreement between simulation and experimental results. The presented approach is specifically useful for recent martini attempts that focus on highly charged systems—such as models of DNA, polyelectrolytes or polyelectrolyte complexes—where precise studies of electrostatic effects and charge transport processes are essential.

Mechanistic insight into the early stages of amyloid formation using an anuran peptide

“…Recently, Michalowsky and coworkers have developed new polarizable models for water and monovalent ions, consistent with the MARTINI force‐field, for obtaining a more accurate description of the electrostatic properties of highly charged polyelectrolytes and lipid bilayers. Density and ionic conductivity values for monovalent aqueous electrolytes, calculated using these polarizable models showed excellent agreement with experimental data . However, the MARTINI description used here appears to be adequate in correctly describing the qualitative changes in electrostatic effects at different salt concentrations.…”

“…Density and ionic conductivity values for monovalent aqueous electrolytes, calculated using these polarizable models showed excellent agreement with experimental data. [26,27] However, the MARTINI description used here appears to be adequate in correctly describing the qualitative changes in electrostatic effects at different salt concentrations. Periodic boundary conditions were applied along all three orthonormal directions.…”

Theoretical and Computational Insight into Solvent and Specific Ion Effects for Polyelectrolytes: The Importance of Local Molecular Interactions

“…In terms of highly polar aqueous solutions, most often a decrease of the dielectric constant can be observed for increasing co-solvent concentrations which strengthens electrostatic interactions between charged species and hence a stronger counterion condensation behavior for polyelectrolytes. Comparable conclusions can be also drawn with regard to semi-coarse-grained MD simulations with the MARTINI force field and for concentrated polyelectrolyte solutions, high salt conditions as well as dense polyelectrolyte solutions [33,59]. However, with regard to the fact that most binary solutions reveal non-ideal effects due to the presence of clustering tendencies, a non-linear variation of the dielectric constant can be observed instead (Figure 7).…”

“…In consequence, one usually observes a locally varying dielectric constant in close vicinity of charged species. In addition to linear respone relations [19,20,58,59], a simple expression for the global dielectric constant r reads [60][61][62]…”

Phase-Transferable Force Field for Alkali Halides

“…A common approach is to parameterise alkali halides in connection to established water models, using for example ion-water distances or hydration free energies in the parameterisation procedure. 16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Other research focuses the parameterisation on physico-chemical properties from alkali halides only, or even just uses parameters that are extracted from density functional theory calculations. 17,[34][35][36][37][38][39][40] Furthermore, there are force fields that are parameterised for describing both the physico-chemical properties of ions in a crystal lattice and ions solvated by water.…”