Confined Water Organisation in the Fluid Phase of Phospholipid Self-Assemblies: The Three-Water Layer Model

by Prof. Michael Rappolt (University of Leeds)

Monday 8 Dec 2025, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

After an introduction into the history of membrane model fitting, applying both small angle X-ray and neutron scattering, I will focus on the interplay between the lipid bilayer matrix and interfacial water. Despite extensive knowledge on membrane nanostructure and its mechanical properties under various environmental conditions, there is still some lack of understanding on the role membrane hydration. In my presentation, the nature of the confined water between two adjacent bilayers is described in the light of the recently proposed Three-Water Layer model (TWL) [1], discerning (i) ‘headgroup water’, (ii) ‘perturbed water’ near the membrane/water interface, and (iii) a core region of ‘free’, unperturbed water. The interaction of water with lipid leaflets in all three regions is examined in relation to factors such as head-group type and orientation, membrane rigidity, temperature, ion concentration, and membrane curvature. Notably, the thickness of the perturbed water layer increases with temperature and membrane fluidity, whereas the thickness of the free water core exhibits the opposite trend. Finally, the TWL model is discussed in the context of spectroscopic observations of water within soft confinement, highlighting how varying water dynamics affect the interacting forces between adjacent membranes.

 

[1] Vancuylenberg, G., Sadeghpour, A., Tyler, A. I. I. and Rappolt, M. (2023). Planar confined water organisation in lipid bilayer stacks of phosphatidylcholine and phosphatidylethanolamine, Soft Matter 19(27): 5179-5192.