Origin of the Hydration Force: Water-Mediated Interaction between Two Hydrophilic Plates

Eun, Changsun; Berkowitz, Max L.

doi:10.1021/jp901747s

Cited by 50 publications

(107 citation statements)

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“…These so-called hydration forces arise from the complex interplay of surface group configurational degrees of freedom, desorption of hydration water from polar surface groups, and ordering of the intersurface water film (4). The understanding of hydration forces has recently been advanced by computer simulations that include explicit water molecules (12)(13)(14).In the absence of direct surface-surface interactions, the transition between cavitation-induced attraction and hydration repulsion should coincide with the contact angle characterizing the border between hydrophilic and hydrophobic surface properties; i.e., θ = 90°. In contrast, experiments probing the interactions between similar neutral surfaces with well-defined contact angles demonstrated that even hydrophilic surfaces exhibit short-range attractions not accountable by vdW forces down to typical adhesive contact angles of θ adh = 65°-80°(15-18).…”

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From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

Kanduč

Netz

2015

Proc. Natl. Acad. Sci. U.S.A.

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Using all-atom molecular dynamics (MD) simulations at constant water chemical potential in combination with basic theoretical arguments, we study hydration-induced interactions between two overall chargeneutral yet polar planar surfaces with different wetting properties. Whether the water film between the two surfaces becomes unstable below a threshold separation and cavitation gives rise to long-range attraction, depends on the sum of the two individual surface contact angles. Consequently, cavitation-induced attraction also occurs for a mildly hydrophilic surface interacting with a very hydrophobic surface. If both surfaces are very hydrophilic, hydration repulsion dominates at small separations and direct attractive force contribution can-if strong enough-give rise to wet adhesion in this case. In between the regimes of cavitation-induced attraction and hydration repulsion we find a narrow range of contact angle combinations where the surfaces adhere at contact in the absence of cavitation. This dry adhesion regime is driven by direct surface-surface interactions. We derive simple laws for the cavitation transition as well as for the transition between hydration repulsion and dry adhesion, which favorably compare with simulation results in a generic adhesion state diagram as a function of the two surface contact angles.A ccording to the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the interaction between hydrated surfaces is given by the sum of van der Waals (vdW) and screened electrostatic interactions (1). Although this approach works well in many situations, subnanometer resolved force measurements between individual surfaces demonstrated that additional watermediated interactions are dominant at small separations and depend crucially on the polarity or wetting properties of the surfaces (2-4). Understanding these solvation-induced interactions is still a central issue in all fields concerned with forces between surfaces, colloids, and macromolecular aggregates in water.As is well known, the water film between two hydrophobic surfaces, characterized by water contact angles θ > 90°, becomes freeenergetically unstable below a critical distance and in equilibrium cavitation leads to vapor bubble-induced long-ranged attraction (5-7). Conversely, polar and overall neutral surfaces, characterized by small or vanishing contact angles, exhibit pronounced shortranged repulsive forces, which decay exponentially with a characteristic length in the subnanometer range (8-11). These so-called hydration forces arise from the complex interplay of surface group configurational degrees of freedom, desorption of hydration water from polar surface groups, and ordering of the intersurface water film (4). The understanding of hydration forces has recently been advanced by computer simulations that include explicit water molecules (12)(13)(14).In the absence of direct surface-surface interactions, the transition between cavitation-induced attraction and hydration repulsion should coincide with the contact angle char...

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confidence: 99%

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From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

Kanduč

Netz

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Although several theoretical (9)(10)(11) and simulation (12)(13)(14)(15)(16)(17)(18) studies elucidated partial aspects of the HR, none treated the full complexity of the problem and could quantitatively reproduce and explain experimental pressure-distance curves, meaning that the HR mechanism remained essentially unclear. The reason for this is obvious: Theory typically only treats one part of the problem, be it the water-water interactions, the water-surface binding, or the configurational entropy of bilayer molecules, whereas current simulation strategies account for the constant water chemical potential either in the form of a large reservoir (13)(14)(15) or by grand-canonical simulations (16,17). Due to limitations in the numerical accuracy, however, both approaches do not enable quantitative comparison of the HR pressure with experimental data.…”

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“…The main question we address with our simulations in essence is: What is it that keeps the bilayers separated even at high pressures of 10 8 Pa or 1,000 atm? To make progress in this direction, the pressure Π ¼ Π dir þ Π ind is first decomposed into the direct membrane-membrane contribution and all other water-mediated forces, in the following denoted as the indirect contribution (13,17). Note that this decomposition is indepen-dent of the position of the surface through which the pressure is calculated as long as it lies entirely inside the water phase.…”

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Hydration repulsion between biomembranes results from an interplay of dehydration and depolarization

Schneck

Sedlmeier

Netz

2012

Proc. Natl. Acad. Sci. U.S.A.

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Hydration repulsion dominates the interaction between polar surfaces in water at nanometer separations and ultimately prevents the sticking together of biological matter. Although confirmed by a multitude of experimental methods for various systems, its mechanism remained unclear. A simulation technique is introduced that yields accurate pressures between solvated surfaces at prescribed water chemical potential and is applied to a stack of phospholipid bilayers. Experimental pressure data are quantitatively reproduced and the simulations unveil a rich microscopic picture: Direct membrane-membrane interactions are attractive but overwhelmed by repulsive indirect water contributions. Below about 17 water molecules per lipid, this indirect repulsion is of an energetic nature and due to desorption of hydration water; for larger hydration it is entropic and suggested to involve water depolarization. This antagonistic nature and the presence of various compensating contributions indicate that the hydration repulsion is less universal than previously assumed and rather involves finely tuned surface-water interactions.solvation | MD simulation | phospholipids H ydration repulsion (HR) universally acts between wellsolvated surfaces in water and balances the van der Waals attraction in the nanometer range. It ultimately prevents the collapse of biological matter and thereby provides macromolecular assemblies with the necessary lubrication for vital functioning, even in the congested cell environment. Although complex in its nature, it is rightfully considered a fundamental force in solution chemistry and structural biology (1). HR was first quantified experimentally for stacks of charge-neutral phospholipid bilayer membranes in terms of pressure-distance curves (2-4), confirmed for two individual bilayers by the surface force apparatus (SFA) (5, 6), and is now known to universally act between nucleic acids, proteins, and polysaccharides alike (7). It exhibits an exponential decay with a decay length of a few Ångstrom (4) and as a heuristic law is nowadays commonly used in modeling the forces between polar surfaces in water (8). Although several theoretical (9-11) and simulation (12-18) studies elucidated partial aspects of the HR, none treated the full complexity of the problem and could quantitatively reproduce and explain experimental pressure-distance curves, meaning that the HR mechanism remained essentially unclear. The reason for this is obvious: Theory typically only treats one part of the problem, be it the water-water interactions, the water-surface binding, or the configurational entropy of bilayer molecules, whereas current simulation strategies account for the constant water chemical potential either in the form of a large reservoir (13-15) or by grand-canonical simulations (16,17). Due to limitations in the numerical accuracy, however, both approaches do not enable quantitative comparison of the HR pressure with experimental data. We solve this problem by introducing the thermodynamic extrapolation method (TE...

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“…correlate the measured repulsion force with the properties of a specic physical system. Molecular dynamics (MD) simulations [14][15][16][17][18][19] can help to understand the interbilayer forces on the molecular level.…”

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Interbilayer repulsion forces between tension-free lipid bilayers from simulation

et al. 2013

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Here we report studies on biologically important intermembrane repulsion forces using molecular dynamics (MD) simulations and experimental (osmotic stress) investigations of repulsion forces between 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine bilayers. We show that the repulsion between tensionfree membranes can be determined from MD simulations by either (i) simulating membrane stacks under different hydration conditions (unrestrained setup) and monitoring the change in the area per lipid upon dehydration or (ii) simulating two single punctured membranes immersed in a water reservoir and controlling the center-of-mass distance between the bilayers using an external potential (umbrella sampling setup). Despite the coarse-grained nature of the (MARTINI) model employed, the disjoining pressure profiles obtained from the simulations are in good agreement with our experiments.Remarkably, the two setups behave very differently in terms of membrane structure, as explained by considerations using elasticity theory, and the balance of interactions. In the unrestrained setup, dehydration decreases the area per lipid and lipid entropy. Dehydration in the umbrella sampling setup, in contrast, leads to an increase in area per lipid and lipid entropy. Hence, in the latter case, entropic effects from protrusion and zippering forces appear to be overcompensated by the entropy gain due to the disorder emerging from the expansion of the bilayers. The balance of interactions involves near cancellation of large opposing terms, for which also intramembrane and water-water interactions are important, and which appears to be largely a consequence, rather than the cause, of the intermembrane repulsion. Hence, care must be taken when drawing conclusions on the origin of intermembrane repulsion from thermodynamic analyses.

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Origin of the Hydration Force: Water-Mediated Interaction between Two Hydrophilic Plates

Cited by 50 publications

References 26 publications

From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

From hydration repulsion to dry adhesion between asymmetric hydrophilic and hydrophobic surfaces

Hydration repulsion between biomembranes results from an interplay of dehydration and depolarization

Interbilayer repulsion forces between tension-free lipid bilayers from simulation

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