The Proton's Absolute Aqueous Enthalpy and Gibbs Free Energy of Solvation from Cluster Ion Solvation Data

Tissandier, Michael D.; Cowen, Kenneth A.; Feng, Wan Yong; Gundlach, Ellen; Cohen, Michael H.; Earhart, Alan; Tuttle, Thomas R.; Coe, James V.

doi:10.1021/jp983807a

Cited by 213 publications

(324 citation statements)

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“…3c The observed trends in barrier energy suggest that the size of the barrier is related to the hydration free energy. The higher charge on divalent ions results in stronger electrostatic attraction between the ion and the surrounding water, and the strength of these interactions is reflected in the magnitude of their experimental hydration free energies (see Supplementary Table S3) 20,21 . Hence, ions with the most negative hydration free energies have the largest barriers to permeation, consistent with permeation data obtained experimentally.…”

Section: Free Energy Barriersmentioning

confidence: 99%

“…However, it is difficult to achieve the high density and uniformity of such pores, which is required for industrial applications, because of the stochastic nature of the involved processes. In contrast, graphene oxide (GO), a chemical derivative of graphene with oxygen functionalities 17 , has attracted wide-spread interest due to its exceptional water permeation and molecular sieving properties [18][19][20] as well as realistic prospects for industrial scale production 21,22 . Molecular permeation through GO membranes is believed to occur along a network of pristine graphene channels that develop between functionalized areas of GO sheets 18 (typically, an area of 40-60% remains free from functionalization 23,24 ), and their sieving properties are defined by the interlayer spacing, d, which depends on the humidity of the surroundings 18,19 .…”

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confidence: 99%

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Tunable sieving of ions using graphene oxide membranes

et al. 2017

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Graphene oxide membranes show exceptional molecular permeation properties, with a promise for many applications. However, their use in ion sieving and desalination technologies is limited by a permeation cutoff of 9 Å, which is larger than hydrated ion diameters for common salts. The cutoff is determined by the interlayer spacing d 13.5 Å, typical for graphene oxide laminates that swell in water. Achieving smaller d for the laminates immersed in water has proved to be a challenge. Here we describe how to control d by physical confinement and achieve accurate and tuneable ion sieving. Membranes with d from  9.8 Å to 6.4 Å are demonstrated, providing the sieve size smaller than typical ions' hydrated diameters. In this regime, ion permeation is found to be thermally activated with energy barriers of 10-100 kJ/mol depending on d. Importantly, permeation rates decrease exponentially with decreasing the sieve size but water transport is weakly affected (by a factor of <2). The latter is attributed to a low barrier for water molecules entry and large slip lengths inside graphene capillaries. Building on these findings, we demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.Selectively permeable membranes with sub-nm pores attract strong interest due to analogies with biological membranes and potential applications in water filtration, molecular separation and desalination [1][2][3][4][5][6][7][8] . Nanopores with sizes comparable to, or smaller than, the diameter D of hydrated ions are predicted to show enhanced ion selectivity 7,9-12 because of dehydration required to pass through such atomic-scale sieves. Despite extensive research on ion dehydration effects 3,7,9-13 , experimental investigation of the ion sieving controlled by dehydration has been limited because of difficulties in fabricating uniform membranes with well-defined sub-nm pores. The realisation of membranes with dehydration-assisted selectivity would be a significant step forward. So far, research into novel membranes has mostly focused on improving the water flux rather than ion selectivity. On the other hand, modelling of practically relevant filtration processes shows that an increase in water permeation rates above the rates currently achieved (2-3 L/m 2 ×h×bar) would not contribute greatly to the overall efficiency of desalination 8,14,15 . Alternative approaches based on higher water-ion selectivity may open new possibilities for improving filtration technologies, as the performance of state-of-the-art membranes is currently limited by the solution-diffusion mechanism, in which water molecules dissolve in the membrane material and then diffuses across the membrane 8 . Recently, carbon nanomaterials including carbon nanotubes (CNT)

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Section: Free Energy Barriersmentioning

confidence: 99%

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confidence: 99%

Tunable sieving of ions using graphene oxide membranes

et al. 2017

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“…4.5.1 in Ref. 1), involving, e.g., setting G • H + ,wat to zero, [6][7][8][9][10] setting the formation parameters of the aqueous proton to those of the gaseous proton, 10,11 setting the formation parameters of the aqueous proton to zero, [10][11][12][13] or setting V • H + ,wat to zero (electrochemical series of redox potentials). The quantitative predictive power of these scales in the context of experimental (i.e., electroneutral) processes is unaffected, but the arbitrariness of the anchoring limits their use for intuitive reasoning in the context of single-ion properties and processes.…”

Section: Introductionmentioning

confidence: 99%

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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“…It should be noted, though, that difficulties arise in the comparison with experiments of homogenous ions as they are not directly accessible and must be conducted in salt solutions. The contributions of anions and cations then must be determined through various schemes such as selfconsistent thermodynamic analysis [60], the TATB assumption [61], or the cluster-pair approximation [62]. The experimental hydration data that we compare with here apply the cluster-pair approximation, which is based on the correlation between ion-water clustering data and aqueous solvation free energies of neutral ion pairs.…”

Section: Solvationmentioning

confidence: 99%

Automation of AMOEBA polarizable force field parameterization for small molecules

Wu¹,

Chattree²,

Ren³

2012

Highlights in Theoretical Chemistry

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A protocol to generate parameters for the AMOEBA polarizable force field for small organic molecules has been established, and polarizable atomic typing utility, Poltype, which fully automates this process, has been implemented. For validation, we have compared with quantum mechanical calculations of molecular dipole moments, optimized geometry, electrostatic potential, and conformational energy for a variety of neutral and charged organic molecules, as well as dimer interaction energies of a set of amino acid side chain model compounds. Furthermore, parameters obtained in gas phase are substantiated in liquid-phase simulations. The hydration free energy (HFE) of neutral and charged molecules have been calculated and compared with experimental values. The RMS error for the HFE of neutral molecules is less than 1 kcal/ mol. Meanwhile, the relative error in the predicted HFE of salts (cations and anions) is less than 3% with a correlation coefficient of 0.95. Overall, the performance of Poltype is satisfactory and provides a convenient utility for applications such as drug discovery. Further improvement can be achieved by the systematic study of various organic compounds, particularly ionic molecules, and refinement and expansion of the parameter database.

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The Proton's Absolute Aqueous Enthalpy and Gibbs Free Energy of Solvation from Cluster Ion Solvation Data

Cited by 213 publications

References 0 publications

Tunable sieving of ions using graphene oxide membranes

Tunable sieving of ions using graphene oxide membranes

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

Automation of AMOEBA polarizable force field parameterization for small molecules

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