8 results
Now showing1 - 8 of 8
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Water structuring induces nonuniversal hydration repulsion between polar surfaces: quantitative comparison between molecular simulations, theory, and experiments(American Chemical Society (ACS), 2024-04-05); ; ; ; Polar surfaces in water typically repel each other at close separations, even if they are charge-neutral. This so-called hydration repulsion balances the van der Waals attraction and gives rise to a stable nanometric water layer between the polar surfaces. The resulting hydration water layer is crucial for the properties of concentrated suspensions of lipid membranes and hydrophilic particles in biology and technology, but its origin is unclear. It has been suggested that surface-induced molecular water structuring is responsible for the hydration repulsion, but a quantitative proof of this water-structuring hypothesis is missing. To gain an understanding of the mechanism causing hydration repulsion, we perform molecular simulations of different planar polar surfaces in water. Our simulated hydration forces between phospholipid bilayers agree perfectly with experiments, validating the simulation model and methods. For the comparison with theory, it is important to split the simulated total surface interaction force into a direct contribution from surface–surface molecular interactions and an indirect water-mediated contribution. We find the indirect hydration force and the structural water-ordering profiles from the simulations to be in perfect agreement with the predictions from theoretical models that account for the surface-induced water ordering, which strongly supports the water-structuring hypothesis for the hydration force. However, the comparison between the simulations for polar surfaces with different headgroup architectures reveals significantly different decay lengths of the indirect water-mediated hydration-force, which for laterally homogeneous water structuring would imply different bulk-water properties. We conclude that laterally inhomogeneous water ordering, induced by laterally inhomogeneous surface structures, shapes the hydration repulsion between polar surfaces in a decisive manner. Thus, the indirect water-mediated part of the hydration repulsion is caused by surface-induced water structuring but is surface-specific and thus nonuniversal.Publicationtype: Journal Article15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of polar co-solutes and salt on the hydration of lipid membranes(Royal Society of Chemistry (RSC), 2019); ; ; The influence of the co-solutes TMAO, urea, and NaCl on the hydration repulsion between lipid membranes is investigated in a combined experimental/simulation approach. Pressure-hydration curves obtained via sorption experiments reveal that the repulsion significantly increases when the membranes are loaded with co-solutes, most strongly for TMAO. As a result, the co-solutes retain additional water molecules and therefore provide membranes with a fluid and more physiological environment. The experimental data are quantitatively reproduced in complementary solvent-explicit atomistic molecular dynamics simulations, which yield the chemical potential of water. Simulation analysis reveals that the additional repulsion arises from the osmotic pressure generated by the co-solutes, an effect which is maximal for TMAO, due to its unfavorable interactions with the lipid headgroup layer and its extraordinarily high osmotic coefficient.Publicationtype: Journal Article7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effects of Urea and TMAO on Lipid Self-Assembly under Osmotic Stress Conditions(American Chemical Society (ACS), 2018-06-28); ; Most land-living organisms regularly experience dehydration. In nature, one commonly applied strategy to protect against this osmotic stress is to introduce small polar molecules with low vapor pressure, commonly called osmolytes. Two examples of naturally occurring small polar compounds are urea and trimethylamine N-oxide (TMAO), which are known to have counteracting effects on protein stability. In this work, we investigate the effects of urea and TMAO on lipid self-assembly at varying water contents, focusing on dehydrated conditions. By using complementary experimental techniques, including sorption microcalorimetry, NMR, and X-ray scattering, together with molecular dynamics simulations in model systems composed of phosphatidylcholine lipids, water, and solute, we characterize interactions and self-assembly over a large range of hydration conditions. It is shown that urea and TMAO show qualitatively similar effects on lipid self-assembly at high water contents, whereas they have clearly different effects in dehydrated conditions. The latter can be explained by differences in the molecular interactions between the solutes and the lipid headgroups. TMAO is repelled from the bilayer interface, and it is thereby expelled from lipid lamellar systems with low water contents and narrow inter-bilayer regions. In these conditions, TMAO shows no effect on the lipid phase behavior. Urea, on the other hand, shows a slight affinity for the lipid headgroup layer, and it is present in the lipid lamellar system at all water contents. As a result, urea may exchange with water in dry conditions and thereby prevent dehydration-induced phase transitions. In nature, urea and TMAO are sometimes found together in the same organisms and it is possible that their combined effect is to both protect lipid membranes against dehydration and still avoid denaturation of proteins.Publicationtype: Journal Article5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hydration Repulsion Difference between Ordered and Disordered Membranes Due to Cancellation of Membrane-Membrane and Water-Mediated Interactions(American Chemical Society (ACS), 2017-07-06); ; ; ; 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.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Tight cohesion between glycolipid membranes results from balanced water-headgroup interactions(Nature Publishing Group, 2017-04-03); ; 7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Water-Mediated Interactions between Hydrophilic and Hydrophobic Surfaces(American Chemical Society (ACS), 2016-09-06); ; ; All surfaces in water experience at short separations hydration repulsion or hydrophobic attraction, depending on the surface polarity. These interactions dominate the more long-ranged electrostatic and van der Waals interactions and are ubiquitous in biological and colloidal systems. Despite their importance in all scenarios where the surface separation is in the nanometer range, the origin of these hydration interactions is still unclear. Using atomistic solvent-explicit molecular dynamics simulations, we analyze the interaction free energies of charge-neutral model surfaces with different elastic and water-binding properties. The surface polarity is shown to be the most important parameter that not only determines the hydration properties and thereby the water contact angle of a single surface but also the surface-surface interaction and whether two surfaces attract or repel. Elastic properties of the surfaces are less important. On the basis of surface contact angles and surface-surface binding affinities, we construct a universal interaction diagram featuring three different interaction regimes - hydration repulsion, cavitation-induced attraction - and for intermediate surface polarities - dry adhesion. On the basis of scaling arguments and perturbation theory, we establish simple combination rules that predict the interaction behavior for combinations of dissimilar surfaces.Publicationtype: Journal Article9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Physical mechanisms of the interaction between lipid membranes in the aqueous environment(2015-01-15); ; ; ; We review various mechanisms underlying the interaction between biological membranes in their aqueous environment. In the first part we describe van der Waals interactions, derive generally-applicable density functional expressions for solute-mediated interactions with a focus on electrostatic interactions across aqueous electrolytes, and discuss interaction mechanisms involving the overlap of structured interfacial water layers. We then turn our attention to the long-debated hydration repulsion and review its quantitative investigation using classical molecular dynamics simulations.Publicationtype: Journal Article49 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Hydration repulsion between membranes and polar surfaces: Simulation approaches versus continuum theoriesA review of various computer simulation approaches for the study of the hydration repulsion between lipid membranes and polar surfaces is presented. We discuss different methods and compare their advantages and limitations. We consider interaction pressures, interaction thermodynamics, and interaction mechanisms. We take a close look at the influence of the experimental boundary conditions and at repulsion mechanisms due to the unfavorable overlap of interfacial water layers. To this end, we analyze several distinct water order parameters in simulations of interacting polar surfaces and compare the results to the predictions of simple continuum theories. © 2014 Elsevier B.V.Publicationtype: Review Article7