Anomalous dynamics of interfacial water around micelles

Fundamental understanding of water at the interface of biological membranes and proteins has been important to understand various functions and processes in biological systems. Here, the dynamics of hydration water around sodium dodecyl sulphate micelles has been studied using molecular dynamics (MD) simulation technique. On a fundamental level, this is important as the dynamics of the micelle is governed by the dynamics of the surrounding water as indicated in our neutron scattering measurements. Moreover, the micelles are a simple model system to study the macromolecule-water interface. In this study, we find that both the rotational and translational motion of interfacial water around the micelle is significantly slowed down in comparison to bulk water. It is found that in the first hydration shell, the translational diffusion is anomalous in nature and rotation is anisotropic. Existence of bimodal relaxation (slow and fast) for the rotational motion of the water molecules in the first hydration layer suggests that there are two different species of water molecules - bound and free. Gibb's free energy of transition from bound to free is estimated to be similar to 0.8 kcal/mol. It is expected that this computational study can offer essential insight to complement possible future experimental studies using neutron scattering on similar system.