Surfactant pKa Calculations using Molecular Dynamics Simulations

Abstract

The protonation state for ionizable surfactants is crucial for self-assembly, phase behavior, and morphology. For example, oleic acid forms vesicles at intermediate pH conditions (∼7-9), micelles at high pH, and oil phases at low pH. The pKa for oleic acid shifts from ∼4.8 as monomers in water to ∼7.5 in model phospholipid vesicles. It remains challenging to accurately model surfactant self-assembly and protonation behavior with molecular dynamics simulations. We use constant pH molecular dynamics simulations and thermodynamic integration calculations for protonating a single fatty acid in different chemical environments.