Ion solvation and water structure in potassium halide aqueous solutions

Soper, A. K.; Weckström, Kristian

doi:10.1016/j.bpc.2006.04.009

Cited by 296 publications

(305 citation statements)

References 31 publications

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“…7 and 8 as well as Table I. For the QM/MM simulations, they are in line with those of previous experimental 269,270 and theoretical 155,219 studies reported in the literature (see also other references in Table I). …”

Section: B Hydration Structure and Dynamicssupporting

confidence: 90%

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

Hofer

Hünenberger

2018

The Journal of Chemical Physics

104

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The absolute intrinsic hydration free energy G • H + ,wat of the proton, the surface electric potential jump χ • wat upon entering bulk water, and the absolute redox potential V • H + ,wat of the reference hydrogen electrode are cornerstone quantities for formulating single-ion thermodynamics on absolute scales. They can be easily calculated from each other but remain fundamentally elusive, i.e., they cannot be determined experimentally without invoking some extra-thermodynamic assumption (ETA). The Born model provides a natural framework to formulate such an assumption (Born ETA), as it automatically factors out the contribution of crossing the water surface from the hydration free energy. However, this model describes the short-range solvation inaccurately and relies on the choice of arbitrary ion-size parameters. In the present study, both shortcomings are alleviated by performing first-principle calculations of the hydration free energies of the sodium (Na + ) and potassium (K + ) ions. The calculations rely on thermodynamic integration based on quantum-mechanical molecular-mechanical (QM/MM) molecular dynamics (MD) simulations involving the ion and 2000 water molecules. The ion and its first hydration shell are described using a correlated ab initio method, namely resolution-of-identity second-order Møller-Plesset perturbation (RIMP2). The next hydration shells are described using the extended simple point charge water model (SPC/E). The hydration free energy is first calculated at the MM level and subsequently increased by a quantization term accounting for the transformation to a QM/MM description. It is also corrected for finite-size, approximate-electrostatics, and potentialsummation errors, as well as standard-state definition. These computationally intensive simulations provide accurate first-principle estimates for G • H + ,wat , χ • wat , and V • H + ,wat , reported with statistical errors based on a confidence interval of 99%. The values obtained from the independent Na + and K + simulations are in excellent agreement. In particular, the difference between the two hydration free energies, which is not an elusive quantity, is 73.9 ± 5.4 kJ mol 1 (K + minus Na + ), to be compared with the experimental value of 71.7 ± 2.8 kJ mol 1 . The calculated values of G • H + ,wat , χ • wat , and V • H + ,wat ( 1096.7 ± 6.1 kJ mol 1 , 0.10 ± 0.10 V, and 4.32 ± 0.06 V, respectively, averaging over the two ions) are also in remarkable agreement with the values recommended by Reif and Hünenberger based on a thorough analysis of the experimental literature ( 1100 ± 5 kJ mol 1 , 0.13 ± 0.10 V, and 4.28 ± 0.13 V, respectively). The QM/MM MD simulations are also shown to provide an accurate description of the hydration structure, dynamics, and energetics. Published by AIP Publishing.

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Section: B Hydration Structure and Dynamicssupporting

confidence: 90%

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

Hofer

Hünenberger

2018

The Journal of Chemical Physics

104

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“…For sodium, the coordination numbers are between 5.3 and 5.9 (Table III). For potassium, the coordination numbers vary from 6.1 to 6.6 neutron diffraction experiments [47][48][49] and ab initio calculations 50 give a coordination number of 5 for sodium and 6 for potassium. Chloride, with a less well-defined coordination shell, shows the largest variation, 5.2-6.3, among the models studied in this paper.…”

Section: Resultsmentioning

confidence: 99%

The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions

Nguyen

Rick

2018

The Journal of Chemical Physics

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A relationship between the effect of uni-univalent electrolytes on the structure of water and on its volatility The Journal of Chemical Physics 148, 222807 (2018) The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions The diffusion rates for water molecules in salt solutions depend on the identity of the ions, as well as their concentration. Among the alkali metal ions, cesium and potassium increase and sodium strongly decreases the diffusion constant of water. The origin of the difference can be understood by examining the simulation results using different potential models. In this work, aqueous solutions of salts are simulated with a variety of models. Commonly used non-polarizable models, which otherwise reproduce many experimental properties, do not capture the trend in the diffusion constant, while models which include polarization and/or charge transfer interactions do. For the non-polarizable models, the diffusion constant decreases too strongly with salt concentration. The changes in the water diffusion constant with increasing salt concentration match the diffusion constant of the ion. The ion diffusion constant is dependent on the residence time for water in the ion solvation shell. The non-polarizable models over-estimate the residence time, relative to the translational diffusion constant and so tend to under-estimate the ion and water diffusion constants. Published by AIP Publishing.

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“…Interpretation of these results for aqueous halide anions has given a picture where the ion's first hydration layer behaves as a rigid shell, which rotates concertedly around the ionic solute and reorients more slowly than does a water molecule in the bulk (7,9). However, the dominance of such a mechanism for the reorientation can be doubly questioned: first, it requires the energetically costly cleavage of many H-bonds between the first and second hydration layers; second, it contradicts numerous viscosity (4,11), NMR (12,13), and neutron scattering (14) studies, which indicate that among the halides, I…”

mentioning

confidence: 99%

Reorientional dynamics of water molecules in anionic hydration shells

Laage

Hynes

2007

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

282

351

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Water molecule rotational dynamics within a chloride anion's first hydration shell are investigated through simulations. In contrast to recent suggestions that the ion's hydration shell is rigid during a water's reorientation, we find a labile hydration sphere, consistent with previous assessments of chloride as a weak structure breaker. The nondiffusive reorientation mechanism found involves a hydrogen-bond partner switch with a large amplitude angular jump and the water's departure from the anion's shell. An analytic extended jump model accounts for the simulation results, as well as available NMR and ultrafast spectroscopic data, and resolves the discrepancy between them.hydrogen bonding ͉ ions ͉ orientational dynamics

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Ion solvation and water structure in potassium halide aqueous solutions

Cited by 296 publications

References 31 publications

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions

Reorientional dynamics of water molecules in anionic hydration shells

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