Developing and Validating a Set of All-Atom Potential Models for Sodium Dodecyl Sulfate.

Abstract

We present a set of novel all-atom potential models for sodium dodecyl sulfate (SDS), developed within the framework of the widely used OPLS-AA and General AMBER force fields. The choice of the parameters for the models is made by rigorously following the methodology of the used force fields to ensure full compatibility with the models for other compounds. For the GAFF model, extensive quantum-chemical computations are performed to obtain reliable Boltzmann-averaged atomic point charges, and the latter are compared with the single-conformation charges. For representation of the hydrocarbon tail, we use recently published improved parameters that correctly reproduce the properties of lipids and long alkanes. The models are validated on the basis of correct reproduction of the main properties of micelles (size, degree of counterion binding) as well as diffusion coefficient of the SDS monomer. As an extended test, a simulation of a micelle with a high aggregation number (382) and unnatural initial shape is performed, and a restructuring to the correct shape is observed. This proves the suitability of the developed models for simulations of concentrated SDS solutions containing large micelles and also emphasizes importance of hydrocarbon tail parameters for the micelle properties. Finally, the developed DS- models are tested in combination with several common Na+ and water models. Their effect on the properties of SDS micelles is discussed, and suitable combinations are determined.