Hybrid Particle-Field Molecular Dynamics Simulations of Charged Amphiphiles in an Aqueous Environment

Abstract

We develop and test specific coarse-grained models for charged amphiphilic systems such as palmitoyloleoylphosphatidylglycerol (POPG) lipid bilayer and sodium dodecyl sulfate (SDS) surfactant in an aqueous environment, to verify the ability of the hybrid particle-field method to provide a realistic description of polyelectrolytes. According to the hybrid approach, the intramolecular interactions are treated by a standard molecular Hamiltonian, and the nonelectrostatic intermolecular forces are described by density fields. Electrostatics is introduced as an additional external field obtained by a modified particle-mesh Ewald procedure, as recently proposed [Zhu et al. Phys. Chem. Chem. Phys. 2016 , 18 , 9799 ]. Our results show that, upon proper calibration of key parameters, electrostatic forces can be correctly reproduced. Molecular dynamics simulations indicate that the methodology is robust with respect to the choice of the relative dielectric constant, yielding the same correct qualitative behavior for a broad range of values. In particular, our methodology reproduces well the organization of the POPG bilayer, as well as the SDS concentration-dependent change in the morphology of the micelles from spherical to microtubular aggregates. The inclusion of explicit electrostatics with good accuracy and low computational cost paves the way for a significant extension of the hybrid particle-field method to biological systems, where the polyelectrolyte component plays a fundamental role for both structural and dynamical molecular properties.

Supramolecular Packing Drives Morphological Transitions of Charged Surfactant Micelles

“…The relationship between the change in the morphology of SDS micelles and the total concentration of electrolytes was investigated by a set of hybrid particle‐field/molecular dynamics (hPF‐MD) computer simulations at different SDS and salt concentrations, using the same protocol as in ref. , which reproduced the qualitative trends observed in the experiment.…”

“…In fact, for concentrations much larger than the cmc, the micelles undergo a morphological transition, transforming into cylindrical structures spanning lengths on the order of ≈100–1000 nm . Moreover, both experiments and simulation studies show that such a transition can be drastically enhanced by the presence of a significant excess of salts in the solution. The physical origin of such a behavior may be attributed to non‐linear electrostatic effects involving both the surfactants, the free ions, and the solvent, as also suggested by all‐atom molecular dynamics simulation studies on pre‐micellar aggregates …”

Atomistic hybridparticle‐fieldmolecular dynamics combined withslip‐springs: Restoring entangled dynamics to simulations of polymer melts

“…More details about the density‐functional potential and its implementation can be found in former publications. [ 2,5,10–12,14,15 ]…”

“…[ 5,6 ] More recently, the hPF‐MD model was validated in describing the conformational and dynamical properties of biological systems such as lipid bilayers [ 7–9 ] and biosurfactants. [ 10,11 ] After the integration of electrostatics, [ 12,13 ] the hPF‐MD method was further successfully applied in charged systems particularly of polyelectrolytes, charged amphiphiles [ 14 ] and polypeptides. [ 15 ]…”

“…validated in describing the conformational and dynamical properties of biological systems such as lipid bilayers [7][8][9] and biosurfactants. [10,11] After the integration of electrostatics, [12,13] the hPF-MD method was further successfully applied in charged systems particularly of polyelectrolytes, charged amphiphiles [14] and polypeptides. [15] The hPF-MD method has, therefore, been around for a decade, and its capabilities and shortcomings are well-known.…”