Hydrophobic Hydration in an Orientational Lattice Model

Guisoni, Nara; Henriques, Vera B.

doi:10.1021/jp060729f

Cited by 4 publications

(3 citation statements)

References 43 publications

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“…The mean-field limit is that in which Z → ∞ and ǫ 11 → 0 with the product Zǫ 11 ≡ φ fixed. In this limit, from t in (1) and from (8),…”

Section: Mean-field and Low-temperature Limitsmentioning

confidence: 98%

“…We study this in a lattice model on a Bethe lattice (Cayley tree), for which the Bethe-Guggenheim "quasichemical" approximation [1,2] becomes exact. The Bethe-Guggenheim and related approximations have been used before for lattice models of water and hydrophobic solvation [3][4][5][6][7][8] and the approximation is used extensively in continuum models of solutions as well [9,10]. Models of water and aqueous solutions on other hierarchical lattices have also been extensively studied [11,12].…”

Section: Introductionmentioning

confidence: 99%

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Molecular correlations and solvation in simple fluids

Barbosa

Widom

2010

The Journal of Chemical Physics

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We study the molecular correlations in a lattice model of a solution of a low-solubility solute, with emphasis on how the thermodynamics is reflected in the correlation functions. The model is treated in the Bethe-Guggenheim approximation, which is exact on a Bethe lattice (Cayley tree). The solution properties are obtained in the limit of infinite dilution of the solute. With h(11)(r), h(12)(r), and h(22)(r) the three pair correlation functions as functions of the separation r (subscripts 1 and 2 referring to solvent and solute, respectively), we find for r > or = 2 lattice steps that h(22)(r)/h(12)(r) is identical with h(12)(r)/h(11)(r). This illustrates a general theorem that holds in the asymptotic limit of infinite r. The three correlation functions share a common exponential decay length (correlation length), but when the solubility of the solute is low the amplitude of the decay of h(22)(r) is much greater than that of h(12)(r), which in turn is much greater than that of h(11)(r). As a consequence the amplitude of the decay of h(22)(r) is enormously greater than that of h(11)(r). The effective solute-solute attraction then remains discernible at distances at which the solvent molecules are essentially no longer correlated, as found in similar circumstances in an earlier model. The second osmotic virial coefficient is large and negative, as expected. We find that the solvent-mediated part W(r) of the potential of mean force between solutes, evaluated at contact, r = 1, is related in this model to the Gibbs free energy of solvation at fixed pressure, DeltaG(p)(*), by (Z/2)W(1) + DeltaG(p)(*) is identical with pv(0), where Z is the coordination number of the lattice, p is the pressure, and v(0) is the volume of the cell associated with each lattice site. A large, positive DeltaG(p)(*) associated with the low solubility is thus reflected in a strong attraction (large negative W at contact), which is the major contributor to the second osmotic virial coefficient. In this model, the low solubility (large positive DeltaG(p)(*)) is due partly to an unfavorable enthalpy of solvation and partly to an unfavorable solvation entropy, unlike in the hydrophobic effect, where the enthalpy of solvation itself favors high solubility, but is overweighed by the unfavorable solvation entropy.

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“…The mean-field limit is that in which Z → ∞ and ǫ 11 → 0 with the product Zǫ 11 ≡ φ fixed. In this limit, from t in (1) and from (8),…”

Section: Mean-field and Low-temperature Limitsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Molecular correlations and solvation in simple fluids

Barbosa

Widom

2010

The Journal of Chemical Physics

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“…These rotor lattices are motivated by phase transitions of water where the geometric nature of neighbor interactions between molecules dictates their transition behavior and ordering in liquid and solid phases. 22 2D lattices of rotors should be simple to image and provide a 2D model system which could eventually inform the organization of 3D systems. Rotary elements can only form a finite number of bonds, which can give rise to behaviors such as termination and the formation of switchable shapes and patterns that can be toggled between their phases by modulating the interaction strength.…”

Section: Introductionmentioning

confidence: 99%

Thermally reversible pattern formation in arrays of molecular rotors

et al. 2023

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Solvation theory to provide a molecular interpretation of the hydrophobic entropy loss of noble-gas hydration

Irudayam¹,

Henchman²

2010

J. Phys.: Condens. Matter

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An equation for the chemical potential of a dilute aqueous solution of noble gases is derived in terms of energies, force and torque magnitudes, and solute and water coordination numbers, quantities which are all measured from an equilibrium molecular dynamics simulation. Also derived are equations for the Gibbs free energy, enthalpy and entropy of hydration for the Henry's law process, the Ostwald process, and a third proposed process going from an arbitrary concentration in the gas phase to the equivalent mole fraction in aqueous solution which has simpler expressions for the enthalpy and entropy changes. Good agreement with experimental hydration free energies is obtained in the TIP4P and SPC/E water models although the solute's force field appears to affect the enthalpies and entropies obtained. In contrast to other methods, the approach gives a complete breakdown of the entropy for every degree of freedom and makes possible a direct structural interpretation of the well-known entropy loss accompanying the hydrophobic hydration of small non-polar molecules under ambient conditions. The noble-gas solutes experience only a small reduction in their vibrational entropy, with larger solutes experiencing a greater loss. The vibrational and librational entropy components of water actually increase but only marginally, negating any idea of water confinement. The term that contributes the most to the hydrophobic entropy loss is found to be water's orientational term which quantifies the number of orientational minima per water molecule and how many ways the whole hydrogen-bond network can form. These findings help resolve contradictory deductions from experiments that water structure around non-polar solutes is similar to bulk water in some ways but different in others. That the entropy loss lies in water's rotational entropy contrasts with other claims that it largely lies in water's translational entropy, but this apparent discrepancy arises because of different coordinate definitions and reference frames used to define the entropy terms.

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Hydrophobic Hydration in an Orientational Lattice Model

Cited by 4 publications

References 43 publications

Molecular correlations and solvation in simple fluids

Molecular correlations and solvation in simple fluids

Thermally reversible pattern formation in arrays of molecular rotors

Solvation theory to provide a molecular interpretation of the hydrophobic entropy loss of noble-gas hydration

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