Hydration Shell Changes in Surfactant Aggregate Transitions Revealed by Raman-MCR Spectroscopy.

Hydration states of many self-assemblies directly relate to their structures and functions. Here, we use Raman multivariate curve resolution (Raman-MCR) assisted by differential scanning calorimetry and nuclear magnetic resonance to explore the hydration properties of aggregates formed by three cationic ammonium surfactants, trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12(Br)2), didodecyldimethylammonium bromide (DDAB), and dodecyltrimethylammonium bromide (DTAB). For 12-3-12(Br)2, the transitions from spherical to rodlike and wormlike micelles lead to about 20% and 60% dehydration and gradually weaken water tetrahedral order and H-bond in hydration shells for both headgroup and hydrophobic chain. As to DDAB, unilamellar vesicles contain two kinds of hydration water species, but multicompartment vesicles exhibit decreased water order and weaker H-bond. DTAB only forms spherical micelles and its hydration structure is similar to that of the 12-3-12(Br)2 spherical micelles. This work provides a basis to explore the hydration states of complex biological self-assemblies.