Correlation between salt-induced change in lipid hydration water and inter-space of multi-lamellar vesicles

Salt-induced change in water dynamics inside multi-lamellar vesicles (MLV) is experimentally studied with terahertz (THz) time-domain spectroscopy (TDS). The dielectric constants of lipids dispersed in NaCl solutions with different salt concentrations are measured. We find that the water molecules with fast relaxation time (~100 fs) significantly increase with NaCl concentrations. Furthermore, by combining the THz TDS results with small-angle X-ray scattering (SAXS), we find a strong correlation between multi-lamellar spacing and the fast water fraction. This suggests that long-range hydration might be critical in membrane-membrane communications.