Effect of Solute Size and Solute−Water Attractive Interactions on Hydration Water Structure around Hydrophobic Solutes

Ashbaugh, Henry S.; Paulaitis, Michael E.

doi:10.1021/ja016324k

Cited by 175 publications

(242 citation statements)

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“…The asymptotic approach to the macroscopic thermodynamic description with increasing solute size is consistent with the contact density profiles (19,24) (Fig. 2b).…”

Section: (D) Shown Is the Ratio P N͞supporting

confidence: 71%

“…For example, the blurring of the entropy convergence in thermal unfolding of proteins (21), the drying-induced collapse of hydrophobic polymers (22), or the strong association of nanoscopic solutes in water cannot be explained based on the physics of small-solute hydration alone. Independent molecular simulation studies of various model nanoscopic solutes in water have also reported dewetting of solute surfaces and the resultant strong water-mediated interactions between those solutes (20,(23)(24)(25)(26)(27).LCW theory predicts that the free energy of hydration of hard-sphere solutes increases approximately linearly with solute volume for small solutes, and with solute surface area for large solutes, and the small-to-large crossover occurs over nanoscopic lengthscales (28). The small-solute hydration is governed by microscopic density fluctuations (11,12,(16)(17)(18), whereas largesolute hydration is described by the thermodynamics of interface formation (1,15,19).…”

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confidence: 99%

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confidence: 99%

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Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Rajamani

Truskett

Garde

2005

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

275

329

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Small and large hydrophobic solutes exhibit remarkably different hydration thermodynamics. Small solutes are accommodated in water with minor perturbations to water structure, and their hydration is captured accurately by theories that describe density fluctuations in pure water. In contrast, hydration of large solutes is accompanied by dewetting of their surfaces and requires a macroscopic thermodynamic description. A unified theoretical description of these lengthscale dependencies was presented by Lum, Chandler, and Weeks [(1999) J. Phys. Chem. B 103, 4570 -4577]. Here, we use molecular simulations to study lengthscale-dependent hydrophobic hydration under various thermodynamic conditions. We show that the hydration of small and large solutes displays disparate dependencies on thermodynamic variables, including pressure, temperature, and additive concentration. Understanding these dependencies allows manipulation of the small-tolarge crossover lengthscale, which is nanoscopic under ambient conditions. Specifically, applying hydrostatic tension or adding ethanol decreases the crossover length to molecular sizes, making it accessible to atomistic simulations. With detailed temperaturedependent studies, we further demonstrate that hydration thermodynamics changes gradually from entropic to enthalpic near the crossover. The nanoscopic lengthscale of the crossover and its sensitivity to thermodynamic variables imply that quantitative modeling of biomolecular self-assembly in aqueous solutions requires elements of both molecular and macroscopic hydration physics. We also show that the small-to-large crossover is directly related to the Egelstaff-Widom lengthscale, the product of surface tension and isothermal compressibility, which is another fundamental lengthscale in liquids. molecular dynamics ͉ salt and additive effects ͉ density fluctuations ͉ nonpolar solvation B iological self-assembly processes in aqueous solutions are driven by water-mediated interactions between constituents taking part in the assembly. Of these, hydrophobic interactions have received particular attention because of their relevance to protein folding and interactions, micelle and membrane formation, and molecular recognition (1-5). Theoretical work in this direction has been focused on the modeling of primitive hydrophobic phenomena, such as hydration and association of small hydrophobic particles in water (6-13). However, biological assembly occurs over a spectrum of lengthscales from that of an amino acid to proteins and larger. Naturally, fundamental understanding of the lengthscale dependence of hydration and association of hydrophobic solutes in water will be relevant to the quantitative modeling of realistic macromolecular processes (14,15).Small hydrophobic solutes can be accommodated into the open hydrogen-bonded network of liquid water without significant perturbations. Indeed, theories that model density fluctuations over small lengthscales in pure water provide a quantitative description of the hydration thermodynamics of small...

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“…The asymptotic approach to the macroscopic thermodynamic description with increasing solute size is consistent with the contact density profiles (19,24) (Fig. 2b).…”

Section: (D) Shown Is the Ratio P N͞supporting

confidence: 71%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Rajamani

Truskett

Garde

2005

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

275

329

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“…With increasing solute length scale, the elegant theory by Lum, Chandler, and Weeks (11) as well as computer simulations (12, 13) predict a gradual dewetting of the solute. Near large solutes or a hard-wall, water density is small and vapor-like, and the wall-water interface resembles a water vapor-liquid interface (14).Realistic solutes exert van der Waals and/or electrostatic interactions and pull the water interface closer, wetting the solute surface (12,(15)(16)(17)(18). The extent of wetting depends on the strength of attraction and on the local surface curvature or roughness.…”

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confidence: 99%

“…Realistic solutes exert van der Waals and/or electrostatic interactions and pull the water interface closer, wetting the solute surface (12,(15)(16)(17)(18). The extent of wetting depends on the strength of attraction and on the local surface curvature or roughness.…”

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confidence: 99%

Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations

Godawat

Jamadagni

Garde

2009

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

328

396

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Hydrophobicity is often characterized macroscopically by the droplet contact angle. Molecular signatures of hydrophobicity have, however, remained elusive. Successful theories predict a drying transition leading to a vapor-like region near large hard-sphere solutes and interfaces. Adding attractions wets the interface with local density increasing with attractions. Here we present extensive molecular simulation studies of hydration of realistic surfaces with a wide range of chemistries from hydrophobic (؊CF 3, ؊CH3) to hydrophilic (؊OH, ؊CONH 2). We show that the water density near weakly attractive hydrophobic surfaces (e.g., ؊CF 3) can be bulk-like or larger, and provides a poor quantification of surface hydrophobicity. In contrast, the probability of cavity formation or the free energy of binding of hydrophobic solutes to interfaces correlates quantitatively with the macroscopic wetting properties and serves as an excellent signature of hydrophobicity. Specifically, the probability of cavity formation is enhanced in the vicinity of hydrophobic surfaces, and water-water correlations correspondingly display characteristics similar to those near a vapor-liquid interface. Hydrophilic surfaces suppress cavity formation and reduce the water-water correlation length. Our results suggest a potentially robust approach for characterizing hydrophobicity of more complex and heterogeneous surfaces of proteins and biomolecules, and other nanoscopic objects.hydration ͉ hydrophilic ͉ hydrophobic ͉ wetting ͉ fluctuations H ydrophobicity, reflected in the low solubility of nonpolar solutes or in their tendency to aggregate in water, is known to play an important role in many biological and colloidal self-assembly processes (1-4). Yet defining it precisely is challenging, and its molecular signatures remain unclear. Macroscopically, hydrophobicity is often characterized by measuring the droplet contact angle, with surfaces showing angles greater than 90°termed hydrophobic. Water beads up into droplets on hydrophobic surfaces and spreads on hydrophilic ones. Translating these ideas into the molecular domain presents special challenges. In a recent perspective, Granick and Bae (5) highlight the ambiguity in defining hydrophobicity at molecular length scales, such as near proteins or nanotubes, where droplet contact angle measurements are not possible.At the molecular level, hard-sphere solutes have served as excellent models for studies of hydrophobicity, with their hydration thermodynamics capturing the solubility of noble gases as a function of temperature (6, 7), pressure (8), and salt addition (9, 10). With increasing solute length scale, the elegant theory by Lum, Chandler, and Weeks (11) as well as computer simulations (12, 13) predict a gradual dewetting of the solute. Near large solutes or a hard-wall, water density is small and vapor-like, and the wall-water interface resembles a water vapor-liquid interface (14).Realistic solutes exert van der Waals and/or electrostatic interactions and pull the water interface closer, ...

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Hydrophobic Effect

Lazaridis

2013

Encyclopedia of Life Sciences

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The term 'hydrophobic effect' refers to the poor solubility of nonpolar substances in water compared to organic solvents or to polar substances. The transfer of small nonpolar molecules from the gas phase or organic solvents to water has a characteristic thermodynamic signature: positive free energy, negative enthalpy, large negative entropy and positive heat capacity. This thermodynamic signature can be explained by considering the structure of water around nonpolar substances, which depends on the size and shape of the nonpolar solute. The poor solubility of nonpolar groups in water leads to aggregation of these groups (hydrophobic interaction) and the formation of self-assembled structures such as miscelles and lipid bilayers. The hydrophobic interaction is also the major contributor to protein folding. The origin of the hydrophobic effect lies in the fact that water interacts with itself much more strongly than it does with nonpolar groups.

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Effect of Solute Size and Solute−Water Attractive Interactions on Hydration Water Structure around Hydrophobic Solutes

Cited by 175 publications

References 43 publications

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Hydrophobic hydration from small to large lengthscales: Understanding and manipulating the crossover

Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations

Hydrophobic Effect

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