Correlation between salt-induced change in water structure and lipid structure of multi-lamellar vesicles observed by terahertz time-domain spectroscopy

Highlights: • Complex dielectric constant of lipids in NaCl solutions is measured in 0.3–1.2 THz. • Fast water fraction inside multi-lamellar vesicles increased with NaCl concentrations. • Correlation between salt-induced change in water structure and lipid structure is observed. Salt-induced change in the structure of water molecules inside multi-lamellar vesicles is experimentally studied with terahertz time-domain spectroscopy. The complex dielectric constant of 1, 2-ditetradecanoyl-sn-glycero-3-phosphocholine model membranes dispersed in NaCl solution with different salt concentrations are measured. Structure of water molecules in the solution is characterized from the measured dielectric constant using Debye relaxation model. Combined with small-angle X-ray scattering observation, it is found that salt-induced change of water structure, especially fast water fraction, show strong correlation with the increase in nanometer-scale multi-lamellar repeat space. This suggests that water could be critical in nanometer-scale membrane-membrane communications.