Hydrophobic Interactions and Dewetting between Plates with Hydrophobic and Hydrophilic Domains (original) (raw)
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Characterizing hydrophobicity at the nanoscale: A molecular dynamics simulation study
The Journal of Chemical Physics, 2012
We use molecular dynamics (MD) simulations of water near nanoscopic surfaces to characterize hydrophobic solute-water interfaces. By using nanoscopic paraffin like plates as model solutes, MD simulations in isothermal-isobaric ensemble have been employed to identify characteristic features of such an interface. Enhanced water correlation, density fluctuation and position dependent compressibility apart from surface specific hydrogen bond distribution have been identified as characteristic features of such interfaces. Orientational distributions of the dipole moment vector and the molecular plane vector of the water molecule do not show much sensitivity to the nature of the surface, whereas that of OH bond vector shows enhanced structuring with increasing hydrophobicity. Tetrahedral order parameter that quantifies the degree of tetrahedrality in the water structure and an orientational order parameter, which quantifies the orientational preferences of the second solvation shell water around a central water molecule, have also been calculated as a function of distance from the plate surface. In the vicinity of the surface these two order parameters show considerable sensitivity to the surface hydrophobicity. The potential of mean force (PMF) between water and the surface as a function of the distance from the surface has also been analyzed in terms of direct and induced contributions, which shows unusual effect of plate hydrophobicity on the solvent induced PMF. In order to investigate hydrophobic nature of these plates, we have also investigated interplate dewetting when two such plates are immersed in water.
Sitting at the edge: How biomolecules use hydrophobicity to tune their interactions and function
2011
Water near extended hydrophobic surfaces is like that at a liquid–vapor interface, where fluctuations in water density are substantially enhanced compared to those in bulk water. Here we use molecular simulations with specialized sampling techniques to show that water density fluctuations are similarly enhanced, even near hydrophobic surfaces of complex biomolecules, situating them at the edge of a dewetting transition.
Bulletin of Materials Science, 2008
We have performed a series of molecular dynamics simulations of water containing two nanoscopic hydrophobic plates to investigate the modifications of the density and hydrogen bond distributions of water in the vicinity of the surfaces. Our primary goal is to look at the effects of plate thickness, solutesolvent interaction and also interplate separation on the solvent structure in the confined region between two graphite-like plates and also near the outer surfaces of the plates. The thickness of the plates is varied by considering single and triple-layer graphite plates and the interaction potential is varied by tuning the attractive strength of the 12-6 pair interaction potential between a carbon atom of the graphite plates and a water molecule. The calculations are done for four different values of the tuning parameter ranging from fully Lennard-Jones to pure repulsive pair interactions. It is found that both the solvation characteristics and hydrogen bond distributions can depend rather strongly on the strength of the attractive part of the solute-water interaction potential. The thickness of the plates, however, is found to have only minor effects on the density profiles and hydrogen bond network. This indicates that the long range electrostatic interactions between water molecules on the two opposite sides of the same plate do not make any significant contribution to the overall solvation structure of these hydrophobic plates. The solvation characteristics are primarily determined by the balance between the loss of energy due to hydrogen bond network disruption, cavity repulsion potential and offset of the same by attractive component of the solute-water interactions. Our studies with different system sizes show that the essential features of solvation properties, e.g. wetting and dewetting characteristics for different interplate separations and interaction potentials, are also present in relatively smaller systems consisting of a few hundred atoms.
Adhesive water networks facilitate binding of protein interfaces
Nature Communications, 2011
Water structure has an essential role in biological assembly. Hydrophobic dewetting has been documented as a general mechanism for the assembly of hydrophobic surfaces; however, the association mechanism of hydrophilic interfaces remains mysterious and cannot be explained by simple continuum water models that ignore the solvent structure. Here we study the association of two hydrophilic proteins using unbiased extensive molecular dynamics simulations that reproducibly recovered the native bound complex. The water in the interfacial gap forms an adhesive hydrogen-bond network between the interfaces stabilizing early intermediates before native contacts are formed. Furthermore, the interfacial gap solvent showed a reduced dielectric shielding up to distances of few nanometres during the diffusive phase. The interfacial gap solvent generates an anisotropic dielectric shielding with a strongly preferred directionality for the electrostatic interactions along the association direction.
Developing a General Interaction Potential for Hydrophobic and Hydrophilic Interactions
Langmuir, 2014
We review direct force measurements on a broad class of hydrophobic and hydrophilic surfaces. These measurements have enabled the development of a general interaction potential per unit area, W(D) = −2γ i Hy exp(−D/D H ) in terms of a nondimensional Hydra parameter, Hy, that applies to both hydrophobic and hydrophilic interactions between extended surfaces. This potential allows one to quantitatively account for additional attractions and repulsions not included in the wellknown combination of electrostatic double layer and van der Waals theories, the so-called Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. The interaction energy is exponentially decaying with decay length D H ≈ 0.3−2 nm for both hydrophobic and hydrophilic interactions, with the exact value of D H depending on the precise system and conditions. The pre-exponential factor depends on the interfacial tension, γ i , of the interacting surfaces and Hy. For Hy > 0, the interaction potential describes interactions between partially hydrophobic surfaces, with the maximum hydrophobic interaction (i.e., two fully hydrophobic surfaces) corresponding to Hy = 1. Hydrophobic interactions between hydrophobic monolayer surfaces measured with the surface forces apparatus (SFA) are shown to be well described by the proposed interaction potential. The potential becomes repulsive for Hy < 0, corresponding to partially hydrophilic (hydrated) interfaces. Hydrated surfaces such as mica, silica, and lipid bilayers are discussed and reviewed in the context of the values of Hy appropriate for each system.
Extended surfaces modulate hydrophobic interactions of neighboring solutes
Proceedings of the National Academy of Sciences, 2011
Interfaces are a most common motif in complex systems. To understand how the presence of interfaces affects hydrophobic phenomena, we use molecular simulations and theory to study hydration of solutes at interfaces. The solutes range in size from subnanometer to a few nanometers. The interfaces are self-assembled monolayers with a range of chemistries, from hydrophilic to hydrophobic. We show that the driving force for assembly in the vicinity of a hydrophobic surface is weaker than that in bulk water and ...
Influence of surface morphology and nano-structure on hydrophobicity: A molecular dynamics approach
Applied Surface Science, 2019
In this study, water droplet behavior on hydrophobic and superhydrophobic surfaces with different morphologies and geometries has been investigated using molecular dynamics method. The contact angle and potential energy of water droplet on nanostructured surfaces has been evaluated as criteria of hydrophobicity. Results show that surface morphology, distance between columns, void fraction and the growth angle are the main parameters that significantly influence surface hydrophobicity. Wetting transition from Cassie-Baxter state to Wenzel state of simulated structures show that contact the angle decreases with increasing the distance between the columns. Superhydrophobic thin films with different shapes and dimensions, namely tetragonal helical sculptured, gecko feet and lotus leaves were designed and simulated. A contact angle of 155.7° for tetragonal helical sculptured structure is achieved. Interestingly, gecko feet and lotus leaves structures show oscillatory behavior of potential energy curves. It implies that these surfaces are more hydrophobic than other simulated films.
Consequences of Water between Two Hydrophobic Surfaces on Adhesion and Wetting
Langmuir, 2015
The contact of two hydrophobic surfaces in water is of importance in biology, catalysis, material science, and geology. A tenet of hydrophobic attraction is the release of an ordered water layer, leading to a dry contact between two hydrophobic surfaces. Although the waterfree contact has been inferred from numerous experimental and theoretical studies, this has not been directly measured. Here, we use surface sensitive sum frequency generation spectroscopy to directly probe the contact interface between hydrophobic poly-(dimethylsiloxane) (PDMS) and two hydrophobic surfaces (a selfassembled monolayer, OTS, and a polymer coating, PVNODC). We show that the interfacial structures for OTS and PVNODC are identical in dry contact but that they differ dramatically in wet contact. In water, the PVNODC surface partially rearranges at grain boundaries, trapping water at the contact interface leading to a 50% reduction in adhesion energy compared to OTS−PDMS contact. The Young−Dupréequation, used extensively to calculate the thermodynamic work of adhesion, predicts no differences between the adhesion energy for these two hydrophobic surfaces, indicating a failure of this well-known equation when there is a heterogeneous contact. This study exemplifies the importance of interstitial water in controlling adhesion and wetting.
Extended surfaces modulate and can catalyze hydrophobic effects
2011
Interfaces are a most common motif in complex systems. To understand how the presence of interfaces affect hydrophobic phenomena, we use molecular simulations and theory to study hydration of solutes at interfaces. The solutes range in size from sub-nanometer to a few nanometers. The interfaces are self-assembled monolayers with a range of chemistries, from hydrophilic to hydrophobic. We show that the driving force for assembly in the vicinity of a hydrophobic surface is weaker than that in bulk water, and decreases with increasing temperature, in contrast to that in the bulk. We explain these distinct features in terms of an interplay between interfacial fluctuations and excluded volume effects---the physics encoded in Lum-Chandler-Weeks theory [J. Phys. Chem. B 103, 4570--4577 (1999)]. Our results suggest a catalytic role for hydrophobic interfaces in the unfolding of proteins, for example, in the interior of chaperonins and in amyloid formation.