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Hydration Repulsion Difference between Ordered and Disordered Membranes Due to Cancellation of Membrane−Membrane and Water-Mediated Interactions

Bartosz Kowalik, Alexander Schlaich, Matej Kanduc,̌ Emanuel Schneck, and Roland R. Netz

J. Phys. Chem. Lett., 2017, 8, pp 2869–2874

News from Jun 19, 2017

ABSTRACT: Hydration repulsion acts between all sufficiently polar surfaces
in water at small separations and prevents dry adhesion up to kilobar
pressures. Yet it remained unclear whether this ubiquitous force depends on
surface structure or is a sole water property. We demonstrate that previous
deviations among different experimental measurements of hydration
pressures in phospholipid bilayer stacks disappear when plotting data
consistently as a function of repeat distance or membrane surface distance.
The resulting pressure versus distance curves agree quantitatively with our
atomistic simulation results and exhibit different decay lengths in the ordered
gel and the disordered fluid states. This suggests that hydration forces are not
caused by water ordering effects alone. Splitting the simulated total pressure
into membrane−membrane and water-mediated parts shows that these
contributions are opposite in sign and of similar magnitude, thus they are
equally important. The resulting net hydration pressure between membranes is what remains from the near-cancellation of these ambivalent contributions. 

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