Hydrophobic Effects on a Molecular Scale

Hummer, Gerhard; Garde, Shekhar; Garcı́a, Angel E.; Paulaitis, Michael E.; Pratt, Lawrence R.

doi:10.1021/jp982873+

Cited by 370 publications

(451 citation statements)

References 104 publications

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“…In contrast to the temperature dependence of macroscopic interfacial free energy, ΔG hyd for a hydrophobic solute increases at low temperature, reaches a maximum and decreases at high temperature. This temperature dependence has been observed for small hydrocarbon molecules (36), and has been reproduced by many theoretical studies (19,21,23,28). This anomalous increase in the hydration free energy before the turnover point is believed to originate from the lowered entropy of water molecules adjacent to the small hydrophobic molecules, as the degrees of freedom of these water molecules are reduced by the formation of more ordered, dynamic structures.…”

Section: Resultssupporting

confidence: 64%

“…However, it was argued that the correction to the effective surface tension to maintain the correlation between ΔG hyd and SASA at small length scales lacked a clear physical meaning (16). Instead of depending on a scaling relation with SASA, theories and simulations were developed predicting that ΔG hyd has nontrivial size dependence: Below approximately 1 nm radius, ΔG hyd of a spherical solute scales roughly with the solute volume; whereas above this value, ΔG hyd scales with SASA and asymptotically approaches the behavior described by macroscopic interfacial thermodynamics (6,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). These treatments correctly predict the trend for the temperature dependence of ΔG hyd for small molecules.…”

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confidence: 99%

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Signature of hydrophobic hydration in a single polymer

Walker

2011

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

156

158

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Hydrophobicity underpins self-assembly in many natural and synthetic molecular and nanoscale systems. A signature of hydrophobicity is its temperature dependence. The first experimental evaluation of the temperature and size dependence of hydration free energy in a single hydrophobic polymer is reported, which tests key assumptions in models of hydrophobic interactions in protein folding. Herein, the hydration free energy required to extend three hydrophobic polymers with differently sized aromatic side chains was directly measured by single molecule force spectroscopy. The results are threefold. First, the hydration free energy per monomer is found to be strongly dependent on temperature and does not follow interfacial thermodynamics. Second, the temperature dependence profiles are distinct among the three hydrophobic polymers as a result of a hydrophobic size effect at the subnanometer scale. Third, the hydration free energy of a monomer on a macromolecule is different from a free monomer; corrections for the reduced hydration free energy due to hydrophobic interaction from neighboring units are required.H ydrophobic hydration involves the minimization of the free energies of water molecules near nonpolar surfaces. Hydrophobic hydration of macromolecules is central to understanding protein folding (1-6) and advancing materials science and biotechnologies (7-9). A detailed methodology has been developed to study hydrophobic hydration by the mechanical unfolding of a collapsed single hydrophobic polymer (10). Typically, the hydration free energy (ΔG hyd ) is assumed to scale with the solvent accessible surface area (SASA) of molecules according to macroscopic interfacial thermodynamics, which is supported by the linear correlation between the SASA and the free energy to transfer hydrocarbons from a hydrophobic solvent (such as hexadecane) to water (11). Despite a strong correlation, the experimentally measured small hydrocarbon ΔG hyd is smaller than that predicted by the calculated SASA (12), showing the breakdown of macroscopic interfacial thermodynamics at the microscopic scale and suggesting that the origin of the correlation goes beyond SASA. In addition, the temperature dependence of ΔG hyd (the signature of hydrophobic hydration) varies according to the size of the solute; such temperature dependence cannot be explained simply by the macroscopic interfacial free energy. In an earlier attempt to address these issues, Tolman (13) developed a thermodynamic treatment that lowers the surface tension of water at the solutewater interface by taking into account the cavity curvature. Later developments included temperature dependence of the Tolman length using simulations to address the temperature dependence of ΔG hyd (14, 15). However, it was argued that the correction to the effective surface tension to maintain the correlation between ΔG hyd and SASA at small length scales lacked a clear physical meaning (16). Instead of depending on a scaling relation with SASA, theories and simulations were developed predic...

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Section: Resultssupporting

confidence: 64%

mentioning

confidence: 99%

Signature of hydrophobic hydration in a single polymer

Walker

2011

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

156

158

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“…This is also the result for the solvation free energy of the theory of Hummer, Pratt and coworkers [6,23]. Fig.…”

Section: A Small Length Scale Regimesupporting

confidence: 76%

“…As the occupation statistics is Gaussian for small volumes, the insertion probability P (N = 0; v ex ), and hence the solvation free energy of small solutes, can be obtained from a Gaussian theory. Examples of such Gaussian theories are the PrattChandler theory of hydrophobicity [3,5] and the theory of Hummer, Pratt and coworkers [6,23]. For larger volumes the situation changes significantly.…”

Section: Density Fluctuations At Small and Large Length Scalesmentioning

confidence: 99%

Hydrophobic interactions: an overview

Wolde¹

2002

J. Phys.: Condens. Matter

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We present an overview of the recent progress that has been made in understanding the origin of hydrophobic interactions. We discuss the different character of the solvation behavior of apolar solutes at small and large length scales. We emphasize that the crossover in the solvation behavior arises from a collective effect, which means that implicit solvent models should be used with care. We then discuss a recently developed explicit solvent model, in which the solvent is not described at the atomic level, but rather at the level of a density field. The model is based upon a lattice-gas model, which describes density fluctuations in the solvent at large length scales, and a Gaussian model, which describes density fluctuations at smaller length scales. By integrating out the small length scale field, a Hamiltonian is obtained, which is a function of the binary, large-length scale field only. This makes it possible to simulate much larger systems than hitherto possible as demonstrated by the application of the model to the collapse of an ideal hydrophobic polymer. The results show that the collapse is dominated by the dynamics of the solvent, in particular the formation of a vapor bubble of critical size. Implications of these findings to the understanding of pressure denaturation of proteins are discussed.

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“…10,11 Nevertheless, the molecular origin of the entropy convergence phenomenon in the hydration ͑i.e., gas-towater transfer͒ thermodynamics of nonpolar solutes has deeply been investigated with the aim to shed light on some aspects of hydrophobic hydration. Garde et al 13 and Hummer et al 14 provided an explanation of entropy convergence grounded on an information theory approach for cavity thermodynamics and emphasized that ⌬S · ͑T S * ͒ is a negative quantity. The occurrence of entropy convergence in cavity thermodynamics with ⌬S · ͑T S * ͒ Ͻ 0 was demonstrated also in an isotropic model of water 15 and in an analytical model combining a van der Waals treatment of excluded volume with the small coordination number characteristic of water.…”

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confidence: 99%