Molecular dynamics simulations of sodium dodecyl sulfate micelle in water: The behavior of water

Using a 5 ns explicit atom molecular dynamics simulation of a 60 monomer sodium dodecyl sulfate micellar system containing 7579 TIP3P water molecules, the behavior of water in different electrostatic environments was examined. Structural evaluation of the system revealed that penetration of water molecules into the micelle was restricted to the headgroup region, leaving a 12 Angstrom water-free hydrocarbon core. Water molecules near the headgroup exhibit a distortion of the water-water hydrogen bonding network due to headgroup oxygen-water hydrogen bond formation. The dynamic implications of this distortion are manifested in the decay of the dipole autocorrelation function, Phi(t) and translational diffusion coefficient. We observe that while the translational diffusion coefficient of water molecules in the first solvation shell of the micelle is reduced by less than a half of its value in bulk water, the slow component of the reorientational correlation function is slowed by one or two orders of magnitude.