Solubilities, Fugacities and All That in Solution Chemistry

Wilhelm, Emmerich

doi:10.1007/s10953-014-0279-8

“…The free energy costs of (de-)solvation are quantified by its solvation free energy, which corresponds to the transfer free energy of the molecule from the gas phase to solution [ 21 , 22 , 23 , 24 , 25 ]. In aqueous solution, the solvation free energy is also known as hydration free energy (

).…”

Section: Introductionmentioning

confidence: 99%

A Comparison of QM/MM Simulations with and without the Drude Oscillator Model Based on Hydration Free Energies of Simple Solutes

König

¹

,

Pickard

²

,

Huang

³

et al. 2018

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Maintaining a proper balance between specific intermolecular interactions and non-specific solvent interactions is of critical importance in molecular simulations, especially when predicting binding affinities or reaction rates in the condensed phase. The most rigorous metric for characterizing solvent affinity are solvation free energies, which correspond to a transfer from the gas phase into solution. Due to the drastic change of the electrostatic environment during this process, it is also a stringent test of polarization response in the model. Here, we employ both the CHARMM fixed charge and polarizable force fields to predict hydration free energies of twelve simple solutes. The resulting classical ensembles are then reweighted to obtain QM/MM hydration free energies using a variety of QM methods, including MP2, Hartree–Fock, density functional methods (BLYP, B3LYP, M06-2X) and semi-empirical methods (OM2 and AM1 ). Our simulations test the compatibility of quantum-mechanical methods with molecular-mechanical water models and solute Lennard–Jones parameters. In all cases, the resulting QM/MM hydration free energies were inferior to purely classical results, with the QM/MM Drude force field predictions being only marginally better than the QM/MM fixed charge results. In addition, the QM/MM results for different quantum methods are highly divergent, with almost inverted trends for polarizable and fixed charge water models. While this does not necessarily imply deficiencies in the QM models themselves, it underscores the need to develop consistent and balanced QM/MM interactions. Both the QM and the MM component of a QM/MM simulation have to match, in order to avoid artifacts due to biased solute–solvent interactions. Finally, we discuss strategies to improve the convergence and efficiency of multi-scale free energy simulations by automatically adapting the molecular-mechanics force field to the target quantum method.

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“…One of the most important functions in solution chemistry is the fugacity coefficient π i T, P, x π i of component i in solution in phase π [66]. It is related to the isobaric residual chemical potential, which may be obtained either by applying the partial molar derivative prescription to the expression for the molar isobaric residual Gibbs energy of the mixture in phase π, or by substituting the expression for the chemical potential of component i in a perfect-gas mixture…”

Section: Isobaric Residual Properties Fugacities and Fugacity Coefficientsmentioning

confidence: 99%

“…Consider a liquid equilibrium phase with composition x i ≡ x L i at uniform temperature and pressure. Using the idealized composition dependence of the component fugacity as represented by the Lewis-Randall (LR) rule [17,66,151], one obtains for the partial molar Gibbs energy.…”

Section: Property Changes On Mixing and Excess Propertiesmentioning

confidence: 99%

“…239 with canonical variables T, P and n i supplies complete information on excess properties. It is of central importance in solution chemistry because H E , and its temperature dependence C E P , the molar excess heat capacity at constant pressure (molar excess isobaric heat capacity) the molar excess volume V E and ln LR i are experimentally accessible quantities: excess enthalpies and excess isobaric heat capacities may be obtained more or less directly via calorimetry, and excess volumes may be obtained more or less directly via dilatometry, or pycnometry, or vibrating-tube densimetry, or buoyancy methods (exploiting the Archimedes principle), respectively [37,46,66,68,[152][153][154][155][156][157][158][159][160]. The excess Gibbs energy, in principle the key excess property, is a conceptual property that cannot be measured directly (nor can the excess entropy), though it can be quantitatively deduced from vapor-liquid equilibrium (VLE) measurements via determination of LR activity coefficients [17,20,46,[161][162][163][164][165][166][167][168][169][170][171][172].…”

Section: Property Changes On Mixing and Excess Propertiesmentioning

confidence: 99%

“…The corresponding activity coefficient HL i measures how much the component fugacity of i in the real solution differs from the component fugacity of i corresponding to the HL-idealization Eq. 296 (ratio measure) [17,66,169]. Thus, The value of the Henry fugacity depends on T and P and also on the identity of the solvent (the other component), hence the double subscript i, j has been added; and h i,j (T, P) has to be determined for each binary system.…”

Section: Henry's Law: An Alternative Ideal-solution Model For Liquid Systemsmentioning

confidence: 99%

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Solutions, in Particular Dilute Solutions of Nonelectrolytes: A Review

Wilhelm¹

2021

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The liquid state is one of the three principal states of matter and arguably the most important one; and liquid mixtures represent a large research field of profound theoretical and practical interest. This topic is of importance in many areas of the applied sciences, such as in chemical engineering, geochemistry, the environmental sciences, biophysics and biomedical technology. First, I will concisely present a review of important concepts from classical thermodynamics of nonelectrolyte solutions; this will be followed by a survey of (semi-)empirical approaches to representing the composition and temperature dependence of selected thermodynamic mixture properties, and finally the focus will be on dilute binary nonelectrolyte solutions where one component, a supercritical solute, is present in much smaller quantity than the other component, called the solvent. Partial molar properties in the limit of infinite dilution (indicated by a superscript ∞) are of particular interest. For instance, activity coefficients (Lewis–Randall (LR) convention) are customarily used to characterize mixing behavior, and infinite-dilution values $$\gamma_{i}^{{{\text{LR,}}\infty }}$$ γ i LR, ∞ provide a convenient route for obtaining binary parameters for several popular solution models. When discussing solute (j)—solvent (i) interactions in solutions where the solute is supercritical, the Henry fugacity $$h_{j,i} \left( {T,P} \right)$$ h j , i T , P , also known as Henry’s law (HL) constant, is a measurable thermodynamic key quantity. Its temperature dependence yields information on the partial molar enthalpy change on solution $$\Delta H_{j}^{\infty } \left( {T,P} \right)$$ Δ H j ∞ T , P , while its pressure dependence yields information on the partial molar volume $$V_{j}^{{{\text{L,}}\infty }} \left( {T,P} \right)$$ V j L, ∞ T , P of solute j in the liquid phase (superscript L). I will clarify issues frequently overlooked, touch upon solubility data reduction and correlation, report a few recent high-precision experimental results on dilute aqueous solutions of supercritical nonelectrolytes, and show the equivalency of results for caloric quantities (e.g. $$\Delta H_{j}^{\infty }$$ Δ H j ∞ ) obtained via van ’t Hoff analysis of high-precision solubility data with directly measured calorimetric data.

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