Extended surfaces modulate hydrophobic interactions of neighboring solutes

Patel, Amish J.; Varilly, Patrick; Jamadagni, Sumanth N.; Acharya, Hari; Garde, Shekhar; Chandler, David

doi:10.1073/pnas.1110703108

Cited by 154 publications

(250 citation statements)

References 54 publications

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“…Our results have implications on interface-mediated self-assembly and suggest that water-mediated electrostatic interactions may play an even more important role at soft aqueous interfaces compared with that in bulk water. These results on ions along with the results of recent studies on hydrophobic interactions at aqueous interfaces (16)(17)(18) provide a framework for understanding and manipulating self-assembly of surfactants, peptides, proteins, and other macromolecules at interfaces.…”

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confidence: 99%

Water-mediated ion–ion interactions are enhanced at the water vapor–liquid interface

Venkateshwaran

Vembanur

Garde

2014

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

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108

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There is overwhelming evidence that ions are present near the vapor-liquid interface of aqueous salt solutions. Charged groups can also be driven to interfaces by attaching them to hydrophobic moieties. Despite their importance in many self-assembly phenomena, how ion-ion interactions are affected by interfaces is not understood. We use molecular simulations to show that the effective forces between small ions change character dramatically near the water vapor-liquid interface. Specifically, the water-mediated attraction between oppositely charged ions is enhanced relative to that in bulk water. Further, the repulsion between like-charged ions is weaker than that expected from a continuum dielectric description and can even become attractive as the ions are drawn to the vapor side. We show that thermodynamics of ion association are governed by a delicate balance of ion hydration, interfacial tension, and restriction of capillary fluctuations at the interface, leading to nonintuitive phenomena, such as watermediated like charge attraction. "Sticky" electrostatic interactions may have important consequences on biomolecular structure, assembly, and aggregation at soft liquid interfaces. We demonstrate this by studying an interfacially active model peptide that changes its structure from α-helical to a hairpin-turn-like one in response to charging of its ends. T raditional models of an air-water interface of a salt solution present a picture in which salt ions are excluded from the interfacial region (1). However, recent simulations and experiments have shown that certain chaotropic ions, such as iodide, azide, and thiocyanate, can adsorb to the air-water interface (2-7). Even when ions are depleted from the interface, the extent of depletion is limited to a nanometer length scale (8). Charged species can also be driven to an air-water interface by covalently attaching them to hydrophobic moieties, as in ionic surfactants, or interfacially active proteins (9, 10). Thermodynamics of ion adsorption to interfaces are complex, determined by a balance of energetic and entropic contributions (7,11,12). The net energetic contribution can be favorable or unfavorable, depending on the differences between ion-water, ion-ion, and water-water interactions in bulk and at the interface. The entropic contribution is typically unfavorable due to the restriction of water molecules in the hydration shell of the ion and the corresponding pinning of capillary fluctuations at the interface (7,13,14). Solvent structure and fluctuations at the interface are also known to play an important role in ion dissociation pathways in the transport of ions across liquid-liquid interfaces (15). How these factors govern the effective ion-ion interactions near aqueous interfaces and, in turn, influence interfacial self-assembly and aggregation is, however, not understood.We present results from extensive molecular simulations of ion hydration and ion-ion interactions near a water vapor-liquid interface. Our principal results are that solvent-mediated ...

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mentioning

confidence: 99%

Water-mediated ion–ion interactions are enhanced at the water vapor–liquid interface

Venkateshwaran

Vembanur

Garde

2014

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

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108

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“…Recent simulations have shown that anions at the air-water interface specifically bias the height fluctuations of thermal capillary waves over extended domains. [12][13][14] Given the importance of LR-SIE across many fields, [15][16][17] we deemed pertinent to inquire whether such mechanism is universal and applies to other liquids, 1,18,19 or it is inherent to water. Herein, we report experiments addressing this fundamental question.…”

Section: Introductionmentioning

confidence: 99%

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

Enami

Colussi

2013

The Journal of Chemical Physics

102

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Anions populate fluid interfaces specifically. Here, we report experiments showing that on hydrogenbonded interfaces anions interact specifically over unexpectedly long distances. The composition of binary electrolyte (Na + , X − /Y − ) films was investigated as a function of solvent, film thickness, and third ion additions in free-standing films produced by blowing up drops with a high-speed gas. These films soon fragment into charged sub-micrometer droplets carrying excess anions detectable in situ by online electrospray ionization mass spectrometry. We found that (1) the larger anions are enriched in the thinner (nanoscopic air-liquid-air) films produced at higher gas velocities in all (water, methanol, 2-propanol, and acetonitrile) tested solvents, (2) third ions (beginning at sub-μM levels) specifically perturb X − /Y − ratios in water and methanol but have no effect in acetonitrile or 2-propanol. Thus, among these polar organic liquids (of similar viscosities but much smaller surface tensions and dielectric permittivities than water) only on methanol do anions interact specifically over long, viz.: r i − r j /nm = 150 (c/μM) −1/3 , distances. Our findings point to the extended hydrogenbond networks of water and methanol as likely conduits for such interactions. © 2013 AIP Publishing LLC. [http://dx

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“…1,5,[9][10][11][12][14][15][16]18,20,37,56 To illustrate that the sparse sampling method can capture such marked differences in the respective The response of the average number of interfacial waters, Ñ v φ , to the strength of the linear biasing potential, φ , depends on the hydrophobicity of SAM-water interface. While the response is roughly linear for the hydrophilic OH-terminated SAM surface, it is sigmoidal for the hydrophobic CH 3 -terminated SAM surface.…”

Section: Sam -Water Interfacesmentioning

confidence: 99%

“…[27][28][29][30][31] For example, the fact that P v (N), the probability of observing N water molecules in a small observation volume (v 1 nm 3 ), obeys Gaussian statistics, 3,32 has provided molecular-level insights into the the pressure-induced denaturation of proteins, [33][34][35] as well as the convergence of protein unfolding entropies at a particular temperature. 19,32 Similarly, the LumChandler-Weeks (LCW) theory 5 prediction that P v (N) should develop fat low-N tails for large volumes (v 1 nm 3 ) in bulk water, and near hydrophobic surfaces, 5,15,36 and its verification by simulations, 1,14,18,37 has clarified that water near hydrophobic surfaces is sensitive to perturbations, 18,[38][39][40][41][42][43] and led to the insight that extended hydrophobic surfaces could generically serve as catalysts for the assembly and disassembly of small hydrophobic solutes. 14,44 Importantly, the fact that low-N fluctuations are enhanced near hydrophobic surfaces, also makes them a suitable metric for quantifying the hydrophobicity of a surface, or the strength of its interactions with water.…”

Section: Introductionmentioning

confidence: 99%

“…19,32 Similarly, the LumChandler-Weeks (LCW) theory 5 prediction that P v (N) should develop fat low-N tails for large volumes (v 1 nm 3 ) in bulk water, and near hydrophobic surfaces, 5,15,36 and its verification by simulations, 1,14,18,37 has clarified that water near hydrophobic surfaces is sensitive to perturbations, 18,[38][39][40][41][42][43] and led to the insight that extended hydrophobic surfaces could generically serve as catalysts for the assembly and disassembly of small hydrophobic solutes. 14,44 Importantly, the fact that low-N fluctuations are enhanced near hydrophobic surfaces, also makes them a suitable metric for quantifying the hydrophobicity of a surface, or the strength of its interactions with water. 1,16,18,20 Fluctuations are particularly useful in characterizing the hydrophobicity of complex surfaces with molecular-level heterogeneities, wherein conventional macroscopic measures, such as the water droplet contact angle, break down.…”

Section: Introductionmentioning

confidence: 99%

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Sparse Sampling of Water Density Fluctuations in Interfacial Environments

Remsing

Patel

2016

J. Chem. Theory Comput.

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The free energetics of water density fluctuations near a surface, and the rare low-density fluctuations in particular, serve as reliable indicators of surface hydrophobicity; the easier it is to displace the interfacial waters, the more hydrophobic the underlying surface. However, characterizing the free energetics of such rare fluctuations requires computationally expensive, non-Boltzmann sampling methods like umbrella sampling. This inherent computational expense associated with umbrella sampling makes it challenging to investigate the role of polarizability or electronic structure effects in influencing interfacial fluctuations. Importantly, it also limits the size of the volume, which can be used to probe interfacial fluctuations. The latter can be particularly important in characterizing the hydrophobicity of large surfaces with molecular-level heterogeneities, such as those presented by proteins. To overcome these challenges, here we present a method for the sparse sampling of water density fluctuations, which is roughly two orders of magnitude more efficient than umbrella sampling. We employ thermodynamic integration to estimate the free energy differences between biased ensembles, thereby circumventing the umbrella sampling requirement of overlap between adjacent biased distributions. Further, a judicious choice of the biasing potential allows such free energy differences * To whom correspondence should be addressed 1 arXiv:1511.01518v1 [cond-mat.stat-mech] 4 Nov 2015 to be estimated using short simulations, so that the free energetics of water density fluctuations are obtained using only a few, short simulations. Leveraging the efficiency of the method, we characterize water density fluctuations in the entire hydration shell of the protein, ubiquitin; a large volume containing an average of more than six hundred waters.

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Extended surfaces modulate hydrophobic interactions of neighboring solutes

Cited by 154 publications

References 54 publications

Water-mediated ion–ion interactions are enhanced at the water vapor–liquid interface

Water-mediated ion–ion interactions are enhanced at the water vapor–liquid interface

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

Sparse Sampling of Water Density Fluctuations in Interfacial Environments

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