Computer Simulation of Solubilization

Abstract

In order to clarify the solubilization at a molecular level, free energy of transfer of methane, ethane, butane, hexane, and octane as well as amphiphilic molecule such as methylamine, octylamine, methanol, and octanol from water phase to a sodium dodecyl sulfate (SDS) micelle has been calculated by thermodynamic integration method combined with molecular dynamics calculations. The free energy of transfer of all alkanes was negative, that is, the alkanes in the SDS micelle are more stable than in the water phase avoiding contact with water molecules. Further, the free energy decreases almost linearly as a function of the number of carbon atoms of alkanes with a decrement of 3.3 kJ mol^-1 per one methylene group. The free energy of methylamine, octylamine, methanol, and octanol from the water phase to the SDS micelle is all negative. Further the methane and octane molecule are found in the SDS micelle core. The methylamine was adsorbed on the SDS micelle surface. The methanol is found everywhere in the system from the SDS micelle core to the water phase. The octylamine and octanol are solubilized in the SDS micelle with palisade layer structure.