Impact of Ions on Individual Water Entropy

Saha, Debasis; Mukherjee, Arnab

doi:10.1021/acs.jpcb.6b04033

Cited by 23 publications

(23 citation statements)

References 67 publications

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“…In particular, at comparable sizes, anions induce a more pronounced perturbation of their hydration shells compared to cations, because they are hydrogen-bond acceptors. 17,50,113,268,282,294,[296][297][298][299][300][301][302] The same applies to small or/and multivalent ions, because they generate a stronger electric field at their surface. This more important perturbation may require the inclusion of the second hydration shell into the QM region.…”

Section: Discussionmentioning

confidence: 97%

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: Discussionmentioning

confidence: 97%

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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“…This result also agrees with a theoretical analysis on individual water entropy around ions, which showed that the rotational entropy reduction of the first solvation shell water molecules near Cl À is almost half compared to that around Mg 2 + . [93] The retardation of the water dipole reorientation near ions, including Mg 2 + , [94] has also been discussed in the "jump model" by Stirnemann et al to explain the long-and short-range effects of Mg 2 + on the orientation time correlation function. Our finding that subpopulations such as W 211 and W 212 in MgCl 2 (aq) have a slow reorientation dynamics compared to bulk behaviour supports previous investigations of electrolyte solutions reporting on the long-range effects of ions, beyond their first hydration shell.…”

Section: Reorientation Dynamics In Different Subpopulationsmentioning

confidence: 99%

Hydrogen‐Bond Structure and Low‐Frequency Dynamics of Electrolyte Solutions: Hydration Numbers from ab Initio Water Reorientation Dynamics and Dielectric Relaxation Spectroscopy

et al. 2020

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We present an atomistic simulation scheme for the determination of the hydration number (h) of aqueous electrolyte solutions based on the calculation of the water dipole reorientation dynamics. In this methodology, the time evolution of an aqueous electrolyte solution generated from ab initio molecular dynamics simulations is used to compute the reorientation time of different water subpopulations. The value of h is determined by considering whether the reorientation time of the water subpopulations is retarded with respect to bulk-like behavior. The application of this computational protocol to magnesium chloride (MgCl 2) solutions at different concentrations (0.6-2.8 mol kg À 1) gives h values in excellent agreement with experimental hydration numbers obtained using GHz-to-THz dielectric relaxation spectroscopy. This methodology is attractive because it is based on a well-defined criterion for the definition of hydration number and provides a link with the molecular-level processes responsible for affecting bulk solution behavior. Analysis of the ab initio molecular dynamics trajectories using radial distribution functions, hydrogen bonding statistics, vibrational density of states, water-water hydrogen bonding lifetimes, and water dipole reorientation reveals that MgCl 2 has a considerable influence on the hydrogen bond network compared with bulk water. These effects have been assigned to the specific strong Mg-water interaction rather than the Cl-water interaction.

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“…The latter allows computing a local covariance matrix for each solvent molecule to estimate its configurational entropy. This approach can be extended to allow for solvation entropy estimations and to include spatial resolution of local contributions via the reference positions of the solvent molecules …”

Section: Solvation Entropy and Spatial Resolutionmentioning

confidence: 99%

“…However, PRPCA was shown to reproduce experimental data for the solvation entropy of various ions with good accuracy, demonstrating that quantitative descriptions are feasible in such systems. 45 To evaluate the performance of each approach in terms of accuracy as well as computational efficiency, it would be highly desirable to compare them side by side using identical simulation trajectories with converged thermodynamic integration data as a reference. Such an approach is more insightful than comparisons to experimental data, because intrinsic errors of the underlying force field model cancel out in the comparison.…”

Section: Solvation Free Energiesmentioning

confidence: 99%

Disassembling solvation free energies into local contributions—Toward a microscopic understanding of solvation processes

Heyden

2018

WIREs Comput Mol Sci

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Solvation free energies contribute to the driving force of molecular processes in solution and play a significant role for the relative stability of biomolecular conformations or the formation of complexes. Changes in solvation free energy are the origin of solvent‐mediated interactions such as the hydrophobic effect in water. However, an accurate description of solvation free energies, specifically in aqueous solution, without explicit representation of the solvent is a challenging task in computer simulations. To improve existing models detailed microscopic information on solute–solvent interactions is required, which is not directly accessible from experiments. Explicit solvent simulations include solvent‐mediated effects, however, at a considerable computational cost. Computational tools have been proposed in recent years to extract information on solvation free energies and solute–solvent interactions from explicit solvent simulations. The latter includes spatial decompositions of the solvation enthalpy and entropy, which may eventually lead to an improved theoretical understanding of solvation thermodynamics. This article is categorized under: Molecular and Statistical Mechanics> Free Energy Methods Theoretical and Physical Chemistry > Statistical Mechanics Structure and Mechanism > Computational Biochemistry and Biophysics

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Impact of Ions on Individual Water Entropy

Cited by 23 publications

References 67 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

Hydrogen‐Bond Structure and Low‐Frequency Dynamics of Electrolyte Solutions: Hydration Numbers from ab Initio Water Reorientation Dynamics and Dielectric Relaxation Spectroscopy

Disassembling solvation free energies into local contributions—Toward a microscopic understanding of solvation processes

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