Molecular dynamics simulations of ionic and nonionic surfactant micelles with a generalized Born implicit-solvent model

In recent years, all-atom and coarse-grained models have been developed and applied to simulations of micelles and biological membranes. Here, we explore the question of whether a combined all-atom representation of surfactant molecules and continuum description of solvent based on the generalized Born model can be used to study surfactant micelles. Specifically, we report the parameterization of the GBSW model with a surface-area dependent nonpolar solvation energy term for dodecyl sulfate, dodecyl tetramethylammonium, and dodecyl triethyleneglycol ether molecules. In the parameterization procedure,the atomic Born radii were derived from the radial distribution functions of solvent charge and refined targeting the potential of mean force of dimer interactions from explicit-solvent simulations. The optimized radii were then applied in molecular dynamics simulations of the ionic and nonionic micelles.We found that the micelles are stable but more compact and rigid than in explicit solvent as a consequence of the drastic reduction in solvation and mobility of surfactant monomers within the micelle. Based on these data and our previous work, we suggest that in addition to a more accurate description of the nonpolar solvation energy, the ruggedness in the short-range interactions due to solvent granularity is a critical feature that needs to be taken into account to accurately model processes such as micelle formation and protein folding in implicit solvent. Finally, the explicit-solvent data presented here offers new insights into different conformational behavior of ionic and nonionic micelles which is valuable for understanding hydrophobic assemblies and of interest to the detergent industry.