Temperature effect on the small-to-large crossover lengthscale of hydrophobic hydration

Abstract

Abstract.The thermodynamics of hydration is expected to change gradually from entropic for small solutes to enthalpic for large ones. The small-to-large crossover lengthscale of hydrophobic hydration depends on the thermodynamic conditions of the solvent such as temperature, pressure, presence of additives, etc... We attempt to shed some light on the temperature dependence of the crossover lengthscale by using a probabilistic approach to water hydrogen bonding that allows one to obtain an analytic expression for the number of bonds per water molecule as a function of both its distance to a solute and solute radius. Incorporating that approach into the density functional theory, one can examine the solute size effects on its hydration over the entire smallto-large lengthscale range at a series of different temperatures. Knowing the dependence of the hydration free energy on the temperature and solute size, one can also obtain its enthalpic and entropic contributions as functions of both temperature and solute size. These function can provide some interesting insight into the temperature dependence of the crossover lengthscale of hydrophobic hydration. The model was applied to the hydration of spherical particles of various radii in water in the temperature range from T = 293.15 K to T = 333.15 K. The model predictions for the temperature dependence of the hydration free energy of small hydrophobes are consistent with the experimental and simulational data on the hydration of simple molecular solutes. Three alternative definitions for the small-to-large crossover length-scale of hydrophobic hydration are proposed, and their temperature dependence is obtained. Depending on the definition and temperature, the small-to-large crossover in the hydration mechanism is predicted to occur for hydrophobes of radii from one to several nanometers. Independent of its definition, the crossover length-scale is predicted to decrease with increasing temperature.

Principles for Tuning Hydrophobic Ligand–Receptor Binding Kinetics

“…One of the greatest advances in our understanding of hydrophobicity is the recognition that the hydration structure and thermodynamics of non-polar solutes is length scale dependent [7,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Although the length scale dependence of solvation is not unique to water [20,[28][29][30][31][32], arguably it is most pronounced for water because of the self-associated or "sticky" nature due to its H-bond network.…”

Curvature Dependence of Hydrophobic Hydration Dynamics

“…After equilibration the box lengths of the cubic boxes are roughly 5.65 nm and 7.15 nm for the small (6000 SPC/E) and big (12000 SPC/E) setups respectively. In order to gather enough statistics to probe long-time dynamics within the thin solvation shell comprised of O (10) to O(10 2 ) water molecules subsequent production runs have a length of 200 ns for the small systems and 100 ns for the big systems with a time step of 2 fs and writing period of 200 fs. Energy divergence is prevented by simulation in NVT ensemble (T = 300 K) applying the Nosé-Hoover thermostat with a coupling period of 1 ps.…”

“…One of the greatest advances in our understanding of the hydrophobic effect is the recognition that the hydration structure and thermodynamics of apolar solutes is qualitatively length scale dependent [1][2][3][4][5][6][7][8][9][10][11]. The microscopic reason is that water structures very differently at small (convex) solutes, where the bulk H-bond network is only moderately deformed, as compared to large solutes, which significantly distort the tetrahedral bulk structure.…”

“…Additionally, we find an apparently anomalous diffusion for water moving parallel to the surface of small solutes, which, however, can be explained by topology effects. The intimate connection between solute curvature, water structure and dynamics has implications for our understanding of hydration dynamics at heterogeneous biomolecular surfaces.One of the greatest advances in our understanding of the hydrophobic effect is the recognition that the hydration structure and thermodynamics of apolar solutes is qualitatively length scale dependent [1][2][3][4][5][6][7][8][9][10][11]. The microscopic reason is that water structures very differently at small (convex) solutes, where the bulk H-bond network is only moderately deformed, as compared to large solutes, which significantly distort the tetrahedral bulk structure.…”

On the Correlation between Pair Hydrophobicity and Mixing Enthalpies in Water–Alcohol Binary Mixtures

“…It is important to note that hydrophobicity plays a pivotal role in a number of key physical and biological processes and often it has been found that hydrophobicity is length-scale dependent. − Here, we expand our recent work on water–ethanol binary mixtures by systematically exploring the role of the chain length of alcohol (methanol to butanol) on the composition-dependent pair hydrophobicity in their aqueous mixtures. We have shown that the composition at which the pair hydrophobicity is highest is dependent on the alcohol chain length in water–alcohol binary mixtures.…”