Molecular dynamics study of solubilization of immiscible solutes by a micelle: Free energy of transfer of alkanes from water to the micelle core by thermodynamic integration method.

Free energy of transfer, DeltaG(w-->m), from water phase to a sodium dodecyl sulfate (SDS) micelle core has been calculated for a series of hydrophobic solutes originally immiscible with water by thermodynamic integration method combined with molecular dynamics calculations. The calculated free energy of transfer is in good correspondence to the experiment as well as the theoretical free energy of transfer. The calculated DeltaG(w-->m)'s are all negative, implying that the alkane molecules are more stable in the micelle than in the water phase. It decreases almost linearly as a function of the number of carbon atoms of the alkanes longer than methane with a decrement of 3.3 kJ mol(-1) per one methylene group. The calculated free energy of transfer indicates that, for example, at the micelle concentration of 50 CMC (critical micelle concentration), about only 1 of 6 micelles or 1 of 32 000 micelles does not contain a solute methane or n-octane molecule, respectively.