Solubility of protons in water

Klots, Cornelius E.

doi:10.1021/j150624a013

Cited by 110 publications

(144 citation statements)

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“…Adding this value to our SPC/E estimate we obtain -256.7 kcal/mole for the hydration free energy of the proton in the presence of the potential of the phase. This greatly improves the agreement with the value of the value of -265.9 kcal/mole obtained by Coe and coworkers [19,50,59] and -264.3 kcal/mole obtained by Klots [34]. Consistent with this but probably more significantly, the consensus results of TABLE II suggest a value that is negative and somewhat greater than 10 kcal/mole-e in magnitude.…”

Section: Discussionsupporting

confidence: 89%

“…3 could be solved for eφ(w) + µ H + (w) = ∆µ H + (w), corresponding to the same standard state as for H + in compiling the conventional ion hydration free energies. The evidence presented [19,34] suggests that this procedure is successful to an interesting degree, and remarkably so for small values of n. In view of those results and the analysis from Eq. 3, we conclude that the values otained have not separated the absolute hydration free energy µ M + (w) from the potential of the phase in ∆µ H + (w).…”

Section: Analyses Based Upon Ion-water Cluster Datamentioning

confidence: 70%

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Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Asthagiri¹,

Pratt²,

Ashbaugh³

2003

The Journal of Chemical Physics

212

296

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Experimental studies on ion-water clusters have provided insights into the microscopic aspects of hydration phenomena. One common view is that extending those experimental studies to larger cluster sizes would give the single ion absolute hydration free energies not obtainable by classical thermodynamic methods. This issue is reanalyzed in the context of recent computations and molecular theories on ion hydration, particularly considering the hydration of H + , Li + , Na + , and HO − ions and thence the hydration of neutral ion pairs. The hydration free energies of neutral pairs computed here are in good agreement with experimental results, whereas the calculated absolute hydration free energies, and the excess chemical potentials, deviate consistently from some recently tabulated hydration free energies based on ion-water cluster data. We show how the single ion absolute hydration free energies are not separated from the potential of the phase in recent analyses of ion-water cluster data, even in the limit of large cluster sizes. We conclude that naive calculations on ion-water clusters ought to agree with results obtained from experimental studies of ion-water clusters because both values include the contribution, somewhat extraneous to the local environment of the ion, from the potential of the phase.

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Section: Discussionsupporting

confidence: 89%

Section: Analyses Based Upon Ion-water Cluster Datamentioning

confidence: 70%

Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Asthagiri¹,

Pratt²,

Ashbaugh³

2003

The Journal of Chemical Physics

212

296

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“…65 There are several available sets of experimental hydration free energies available for comparison. [75][76][77][78][79][80][81] Hydration free energies and corrections calculated in this study are presented in Table III along with the experimental results of Tissandier et al, 77 Marcus et al, 76 and Schmid et al 75 Our corrected results ͑⌬G hyd real ͒ compare well with the data of Tissandier et al The larger anions ͑Br − and I − ͒ exhibit the greatest deviation from experiment, 7.5% and 3.0%, respectively. This is approximately the same accuracy obtained by Warren et al 82 for analogous anions in TIP4P-FQ.…”

Section: Single Ion Hydration Free Energiessupporting

confidence: 80%

Molecular dynamics simulations of nonpolarizable inorganic salt solution interfaces: NaCl, NaBr, and NaI in transferable intermolecular potential 4-point with charge dependent polarizability (TIP4P-QDP) water

Bauer

Patel

2010

The Journal of Chemical Physics

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We present molecular dynamics simulations of the liquid-vapor interface of 1M salt solutions of nonpolarizable NaCl, NaBr, and NaI in polarizable transferable intermolecular potential 4-point with charge dependent polarizability water ͓B. A. Bauer et al., J. Chem. Theory Comput. 5, 359 ͑2009͔͒; this water model accommodates increased solvent polarizability ͑relative to the condensed phase͒ in the interfacial and vapor regions. We employ fixed-charge ion models developed in conjunction with the TIP4P-QDP water model to reproduce ab initio ion-water binding energies and ion-water distances for isolated ion-water pairs. The transferability of these ion models to the condensed phase was validated with hydration free energies computed using thermodynamic integration ͑TI͒ and appropriate energy corrections. Density profiles of Cl − , Br − , and I − exhibit charge layering in the interfacial region; anions and cation interfacial probabilities show marked localization, with the anions penetrating further toward the vapor than the cations. Importantly, in none of the cases studied do anions favor the outermost regions of the interface; there is always an aqueous region between the anions and vapor phase. Observed interfacial charge layering is independent of the strength of anion-cation interactions as manifest in anion-cation contact ion pair peaks and solvent separated ion pair peaks; by artificially modulating the strength of anion-cation interactions ͑independent of their interactions with solvent͒, we find little dependence on charge layering particularly for the larger iodide anion. The present results reiterate the widely held view of the importance of solvent and ion polarizability in mediating specific anion surface segregation effects. Moreover, due to the higher parametrized polarizability of the TIP4P-QDP condensed phase ͕1.31 Å 3 for TIP4P-QDP versus 1.1 Å 3 ͑TIP4P-FQ͒ and 0.87 Å 3 ͑POL3͒ ͓Ponder and Case, Adv. Protein Chem. 66, 27 ͑2003͔͖͒ based on ab initio calculations of the condensed-phase polarizability reduction in liquid water, the present simulations highlight the role of water polarizability in inducing water molecular dipole moments parallel to the interface normal ͑and within the interfacial region͒ so as to favorably oppose the macrodipole generated by the separation of anion and cation charge. Since the TIP4P-QDP water polarizability approaches that of the experimental vapor phase value for water, the present results suggest a fundamental role of solvent polarizability in accommodating the large spatial dipole generated by the separation of ion charges. The present results draw further attention to the question of what exact value of condensed phase water polarizability to incorporate in classical polarizable water force fields.

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“…This situation may arise from the use of inappropriate cluster models for hydrated species in previous computational studies. Theoretical calculations on the Gibbs free energy of hydration for the proton show that the first hydration shell of the proton requires at least four water molecules, [28,29] and the predicted Gibbs free energy of hydration is about 263 kcal mol À1 , in good agreement with the experimental results of 262.4 [30] and 264.1 kcal mol À1 .[31]On the contrary, simple H 3 O + and H 5 O 2 + models in combination with the dielectric continuum solvent underestimate the Gibbs free energy of hydration of the proton by about 16 and 10 kcal mol À1 , [28] respectively. Such a large deviation can significantly influence the description of thermodynamic and dynamic properties in the proton-transfer process.…”

supporting

confidence: 74%

Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules

Wang

Cao

2011

Angew Chem Int Ed

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Water plays a quite important role in chemical and biological processes, such as acid-base reactions, [1,2] proton transfer in membrane proteins, [3][4][5] keto-enol tautomerization, [6] and the hydration of carbonyl compounds. The hydration of carbonyl compounds has a long standing interest, both experimentally [7][8][9][10] and theoretically. [11][12][13][14][15][16][17][18][19][20][21][22] In most reactions of carbonyl compounds, such as aldehydes, ketones, esters, amides, the carboxylic acids, and their derivatives, the initial hydration or the nucleophilic addition of water at the carbonyl group, leading to a tetrahedral intermediate, is the rate-determining step. For example, the neutral hydrolyses of carboxylic acid derivatives normally proceed through the addition-elimination mechanism, [9] in which the hydration of the carbonyl group to yield a tetrahedral intermediate is the key step for hydrolysis.For the hydration of carbonyl compounds, all the previous ab-initio calculations proposed a concerted mechanism for the rate-determining hydration step, [11][12][13][14][15][16][17][18][19][20] including the nucleophilic attack of one water molecule onto the carbonyl carbon atom coupled with the concerted proton transfer to the carbonyl oxygen atom assisted by one or more water molecules as shown in Scheme 1. However, most of the calculated Gibbs free energies of activation (DG°) for the concerted mechanism exceed the experimental value considerably, [23] although calculations with a relatively small basis set happen to predict activation energies comparable to the experimental value. This unexpected agreement between theory and experiment can be ascribed to use of relatively small basis set (see below). In a recent study the initial water autoionization was assumed to be involved in the hydrolysis of esters, [23] and the predicted Gibbs activation energies by molecular dynamics (MD) simulations for the key steps are comparable to DG°of 23.8 kcal mol À1 for the water autoionization, [24] in agreement with the experimental value of 26.1 kcal mol À1 .[25] However, in this mechanism the water autoionization as the rate-determining step is a prerequisite to hydrolysis, implying that the Gibbs free energies of activation (DG°) are little changed for different esters.Nevertheless, the experimental rate constants for the hydration of esters can vary by 10 7 fold, which approximately corresponds to an activation energy difference of 10 kcal mol À1 . Experimental studies by Bell et al. suggested that the hydration of the carbonyl group may proceed through a stepwise transfer of three protons in a cyclic array of three water molecules, [26] and that an intermediate Eigen ion (H 3 O + ) [27] is most likely involved in hydration. However, to date, there is no computational evidence for H 3 O + as the key intermediate. This situation may arise from the use of inappropriate cluster models for hydrated species in previous computational studies. Theoretical calculations on the Gibbs free energy of hydration for the proton sh...

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Solubility of protons in water

Cited by 110 publications

References 4 publications

Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Molecular dynamics simulations of nonpolarizable inorganic salt solution interfaces: NaCl, NaBr, and NaI in transferable intermolecular potential 4-point with charge dependent polarizability (TIP4P-QDP) water

Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules

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Solubility of protons in water

Cited by 110 publications

References 4 publications

Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Absolute hydration free energies of ions, ion–water clusters, and quasichemical theory

Molecular dynamics simulations of nonpolarizable inorganic salt solution interfaces: NaCl, NaBr, and NaI in transferable intermolecular potential 4-point with charge dependent polarizability (TIP4P-QDP) water

Hydration of Carbonyl Groups: The Labile H3O+ Ion as an Intermediate Modulated by the Surrounding Water Molecules

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Hydration of Carbonyl Groups: The Labile H₃O⁺ Ion as an Intermediate Modulated by the Surrounding Water Molecules