The influence of dielectric saturation on the thermodynamic properties of aqueous ions

1957 ◽  
Vol 241 (1224) ◽  
pp. 80-92 ◽  
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Small Radius ◽  
Free Energies ◽  
Born Model ◽  
First Approximation ◽  
Born Equation ◽  
Electrostatic Contribution ◽  
Aqueous Ions ◽  
Dielectric Saturation

An examination is made of the applicability of the simple electrostatic (Born) model for ions in aqueous solutions, with special reference to the expressions for free energy, z 2 e 2 /2 r ϵ , and entropy, ( z 2 e 2 /2 r ϵ ) (∂ ln ϵ /∂T). The model is found to be valid to a useful first approximation, but the deviations are significant, particularly for ions of high charge and small radius. Theories of the dielectric constant of water and of its variation with field strength are applied to the case of monatomic ions in aqueous solution, and give rise to an interpretation of the experimental free energies and entropies that is more satisfactory than the simple model. If S͞ 0 e. s. is the electrostatic contribution to the entropy, S͞ 0 e. s. / z 3/2 is found to be a continuous function of z ½ / r , and the Born equation is closely applicable to entropies for values of z ½ / r less than about 0·4. In the case of free energy the Born equation applies over a wider range, up to z ½ / r values of about 0·8.

scholarly journals Thermodynamics of ester and orthoester formation from trifluoroacetic acid

1976 ◽  
Vol 54 (2) ◽  
pp. 202-209 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constant ◽  
Trifluoroacetic Acid ◽  
Sodium Methoxide ◽  
Standard Free Energy ◽  
Steric Effects ◽  
Addition Reactions ◽  
Free Energies ◽  
Acetic Acids

The equilibrium constant for the addition of sodium methoxide to methyl trifluoroacetate, in methanol as solvent, has been measured by 19F nmr, and is 7 M−1. From this was calculated an equilibrium constant, 2 × 10−4 M−1, for addition of methanol to the ester. The equilibrium constant for formation of methyl trifluoroacetate in aqueous solutions is 0.06 M−1. These results, with literature data, permit calculation of the free energies of formation in aqueous solution of orthotrifluoroacetic acid and its mono-, di-, and trimethyl esters. These in turn permit calculation of the standard free energy changes for addition of water and methanol to trifluoroacetic acid and its methyl ester. These combined with the analogous values for formic and acetic acids permit evaluation of ρ* values for these addition reactions. Linear plots are obtained if correction is made for steric effects, and the ρ* values are somewhat larger, 2.1–2.9, than was observed for the analogous carbonyl addition reactions.

Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and pKa values for ionization of the P—H bond in phosphonic acid and phosphonic esters

1979 ◽  
Vol 57 (2) ◽  
pp. 236-239 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Equilibrium Constants ◽  
Phosphorous Acid ◽  
Triethyl Phosphite ◽  
Ethyl Esters ◽  
Free Energies ◽  
Phosphonic Acids ◽  
Hydroxy Compounds ◽  
Energy Relations

From data in the literature the free energies of formation in aqueous solution of triethyl phosphite and diethyl phosphonate can be calculated as −138.4 ± 1.7 and −165.1 ± 2.0 kcal mol−1, respectively. From these values, by application of free energy relations which we have published, the free energies of formation of the corresponding hydroxy compounds can be calculated and thence the equilibrium constants for tautomerization, which are 107.2, 108.7, and 1010.3 in favor of the tetracoordinate phosphonate tautomer for P(OEt)2OH, P(OEt)(OH)2, and P(OH)3, respectively. Using estimated pKa values for the tricoordinate phosphite species the tautomerization equilibria for the anions could also be calculated, as could the pKa values from the P—H bonds: 13, 26, and 38 for H—PO(OEt)2, H—PO2(OEt)−, and H—PO32−, respectively.

Conformational analysis in carbohydrate chemistry. I. Conformational free energies. The conformations and α : β ratios of aldopyranoses in aqueous solution

1968 ◽  
Vol 21 (11) ◽  
pp. 2737 ◽  
Author(s):  
SJ Angyal
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Conformational Analysis ◽  
Reasonable Agreement ◽  
Anomeric Effect ◽  
Interaction Energies ◽  
Free Energies ◽  
Carbohydrate Chemistry ◽  
Predominant Conformation

The relative free energies of the aldopyranoses in aqueous solution have been calculated, taking non-bonded interaction energies and the anomeric effect into account. It is shown that the calculated free-energy values correctly predict the predominant conformation of the α- and β-pyranose forms of each aldose. The α- to β-pyranose ratios of the aldoses in aqueous solution, calculated from these values, are in reasonable agreement with those determined experimentally.

Reactivity differences between haemoglobins. II. Electrostatic contribution to the free energy and enthalpy of ionization of methaemoglobins

1964 ◽  
Vol 277 (1370) ◽  
pp. 414-422 ◽  
Keyword(s):  
Free Energy ◽  
Amino Acid ◽  
Amino Acid Composition ◽  
Acid Composition ◽  
Linear Relation ◽  
Electrostatic Interactions ◽  
Free Energies ◽  
Reactive Site ◽  
Electrostatic Contribution ◽  
Enthalpy Of Ionization

It was concluded in part I that the differences between the free energies, enthalpies, and entropies of ionization of methaem oglobins A, S , and C are the result of different electrostatic interactions between the protein and the reactive site, and that this arises because of the small differences in their amino acid composition. In this paper the electrostatic contribution to the differences in the free energies of ionizations are calculated, using as a basis for calculation Kirkwood’s model for a protein. These calculations show that the observed differences in free energies may be accounted for quantitatively by the different electrostatic interactions between the protein and reactive site for the three methaemoglobins. The linear relation between Δ H ° and T Δ S °, reported in part I, is also shown to be the consequence of the electrostatic origin of the differences between these quantities. Other abnormal haemoglobins are considered in the light of the conclusions reached in this paper, and predictions are made concerning the thermodynamics of ionizations of their met forms.

Conformational Preference and Configurational Equilibria of the Methyl 3-Deoxy-3-nitro-pentopyranosides and their Nitronates

1971 ◽  
Vol 49 (11) ◽  
pp. 1940-1952 ◽  
Author(s):  
Hans H. Baer ◽  
Jan Kovář
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Hydroxyl Group ◽  
Free Energies ◽  
Conformational Preference ◽  
Early Stages ◽  
Kinetically Controlled ◽  
Group A

The conformations of four methyl 3-deoxy-3-nitropentopyranosides and their sodium nitronates in aqueous solution were examined by n.m.r. spectroscopy, and the results are explained by calculation of free energies of non-bonded interactions. It is shown that protonation of glycoside nitronates is a kinetically controlled process. The β-epimerization of nitronates was investigated, and relative thermodynamic stabilities of epimers were determined and correlated with conformations. The non-bonded interaction between the nitronate grouping and an adjacent, equatorial hydroxyl group (A(1,3) effect) must be associated with a free energy in excess of 2 kcal/mol. The influence of this effect upon conformational and configurational equilibria in glycoside nitronates and upon nitromethylene acidity is emphasized. The compounds were found to differ in their behavior during early stages of the β-epimerization reaction, which was linked to differential nitromethylene acidities. Mechanisms for the reaction are discussed.

The enol content of simple carbonyl compounds: a thermochemical approach

1979 ◽  
Vol 57 (2) ◽  
pp. 240-248 ◽  
Author(s):  
J. Peter Guthrie ◽  
Patricia A. Cullimore
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Carbonyl Compounds ◽  
Free Energy Change ◽  
Energy Change ◽  
Free Energies ◽  
Enol Ethers ◽  
Free Energy Of Formation ◽  
Hydrolysis Of ◽  
Energy Of Formation

From the heats of hydrolysis of enol ethers, the heats of formation of the enol ethers, and thence the free energies of formation of the enol ethers in aqueous solution can be calculated. For this calculation it was necessary to determine the free energies of transfer from the gas phase to aqueous solution. By methods previously published it was possible to estimate the free energy change for the hypothetical hydrolysis reaction leading from the enol ether to the enol, which in turn made possible calculation of the free energy of formation of the enol. Finally the free energy change for enolization in aqueous solution could be calculated using the known free energy of formation of the corresponding keto tautomer. In this way the following were determined: carbonyl compound, pKenol = −log ([enol]/[keto]): acetaldehyde, 5.3; propionaldehyde, 3.9; isobutyraldehyde, 2.8; acetone, 7.2; 2-butanone, 8.3; 3-pentanone, 7.8; cyclopentanone, 7.2; cyclohexanone, 5.7; acetophenone, 6.7.

SAMPL6 Octanol-Water Partition Coefficients from Alchemical Free Energy Calculations with MBIS Atomic Charges

2019 ◽  
Author(s):  
Maximiliano Riquelme ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Free Energy ◽  
Electron Density ◽  
Free Energy Calculations ◽  
Basis Set ◽  
Energetic Cost ◽  
Atomic Charges ◽  
Free Energies ◽  
Energy Calculations ◽  
Alchemical Free Energy ◽  
Alchemical Free Energy Calculations

In molecular modeling the description of the interactions between molecules forms the basis for a correct prediction of macroscopic observables. Here, we derive atomic charges from the implicitly polarized electron density of eleven molecules in the SAMPL6 challenge using the Hirshfeld-I and Minimal Basis Set Iterative Stockholder(MBIS) partitioning method. These atomic charges combined with other parameters in the GAFF force field and different water/octanol models were then used in alchemical free energy calculations to obtain hydration and solvation free energies, which after correction for the polarization cost, result in the blind prediction of the partition coefficient. From the tested partitioning methods and water models the S-MBIS atomic charges with the TIP3P water model presented the smallest deviation from the experiment. Conformational dependence of the free energies and the energetic cost associated with the polarization of the electron density are discussed.

Molecular orientation of liquid aliphatic hydrocarbons on the surface and at the interface with water

1989 ◽  
Vol 54 (12) ◽  
pp. 3171-3186 ◽  
Author(s):  
Jan Kloubek
Keyword(s):  
Free Energy ◽  
Surface Free Energy ◽  
Molecular Orientation ◽  
Phase Changes ◽  
Aliphatic Hydrocarbons ◽  
Water Molecules ◽  
Free Energies ◽  
Dispersion Component ◽  
System Water ◽  
Orientation Of Molecules

The validity of the Fowkes theory for the interaction of dispersion forces at interfaces was inspected for the system water-aliphatic hydrocarbons with 5 to 16 C atoms. The obtained results lead to the conclusion that the hydrocarbon molecules cannot lie in a parallel position or be randomly arranged on the surface but that orientation of molecules increases there the ration of CH3 to CH2 groups with respect to that in the bulk. This ratio is changed at the interface with water so that the surface free energy of the hydrocarbon, γH, rises to a higher value, γ’H, which is effective in the interaction with water molecules. Not only the orientation of molecules depends on the adjoining phase and on the temperature but also the density of hydrocarbons on the surface of the liquid phase changes. It is lower than in the bulk and at the interface with water. Moreover, the volume occupied by the CH3 group increases on the surface more than that of the CH2 group. The dispersion component of the surface free energy of water, γdW = 19.09 mJ/m2, the non-dispersion component, γnW = 53.66 mJ/m2, and the surface free energies of the CH2 and CH3 groups, γ(CH2) = 32.94 mJ/m2 and γ(CH3) = 15.87 mJ/m2, were determined at 20 °C. The dependence of these values on the temperature in the range 15-40 °C was also evaluated.

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