Aqueous solutions Free energy

Cieplak, P., Caldwell, J. W., Kollman, P. A., Molecular mechanical models for organic and biological systems going beyond the atom centered two body additive approximation aqueous solution free energies of methanol and IV-methyl acetamide, nucleic acid base, and amide hydrogen bonding and chloroform/water partition coefficients of the nucleic acid bases, J. Comput. Chem. 2001, 22, 1048-1057... 

It is useful to know, that for a given type of crystals (oxides, sulfates, carbonates), the interfacial mineral-aqueous solution free energy, y (or ycw), increases with decreasing solubility (Schindler, 1967). Nielsen (1986) cites the following empirical relationship... 

Mechanical Models for Organic and Biological Systems Going Beyond the Atom Centered Two Body Additive Approximation Aqueous Solution Free Energies of Methanol and N-Methyl Acetamide, Nucleic Acid Base, and Amide Hydrogen Hydrogen Bonding and Chloroform/Water Partition Coefficients of the Nucleic Acid Bases. 

Table 2 contrasts the free energy cycle for association of a proton with NH3 (a very strong gas phase electrostatic dominated interaction) with that of two methane molecules (a very weak gas phase association). As one can see, the aqueous solution free energies are very different from those in the gas phase. 

Using the same theoretical model, Karelson et al. [269] and later Rzepa et al. [270] examined 4-nitroimidazole. The latter work corrected incomplete geometry optimizations present in the former study. In this instance, AMI predicts 5 to be 1.4 kcal/mol lower in relative energy than 6. However, the D02 model predicts the aqueous solvation free energies to be -25.3 and -7.1 kcal/mol for 6 and 5, respectively, rendering 6 considerably lower in energy than 5 in solution, which agrees with the experimental situation. 

C. P. Kelly, C. J. Cramer and D. G. Truhlar, SM6 A density functional theory continuum solvation model for calculating aqueous solvation free energies of neutrals, ions, and solute-water clusters, J. Chem. Theory Comput., 1 (2005) 1133-1152. 

Aqueous Solvation Free Energies from Properties of Solute Molecular Surface Electrostatic Potentials. 

Murray, JS., Abu-Awwad, F. and Politzer, P. (1999). Prediction of Aqueous Solvation Free Energies from Properties of Solute Molecular Surface Electrostatic Potentials. Journal of Physical Chemistry A, 103,1853-1856. 

According to Memming and Schwandt, surface states are always present on silicon electrodes in acidic aqueous solutions. The energy levels depend on whether fluoride ions are present the surface states in acidic fluoride solutions are associated with the dissolution of the silicon. The quantity of the surface states depends on the type of silicon and the illumination intensity. When fluoride ions are present in the solution, the n-Si surface, being oxide free and terminated by hydrogen, exhibits a low density of surface states. ... 

The calculated individual contributions to the total aqueous solvation free energies of 30 organic compounds are given in Table 1. The electrostatic (SCRF) contributions were calculated using semiempirical AMI (Austin Model 1 [60,61]) method. The dispersion energies were calculated using INDO/1 parameterization [62] and AMI optimized molecular geometries in solution. A comparison of different columns in Table 1 with the experimental solvation... 

Murray JS, Abu-Awwad F, Politzer P. Prediction of aqueous solvation free energies from properties of solute molecular surface electrostatic potentials. J Phys Chem, A 1999 103 1853-1856. 

The solutus curve, in binary SSAS systems with ideal or positive solid-solution free-energies of mixing and with large differences (more than an order of magnitude) in end-member solubility products, will closely follow the pure-phase saturation curve of the least soluble end-member (except at high aqueous activity fractions of the more soluble component, e . figure 1). In contrast, ideal solid-solutions with very close end-member solubility products (less than an order of magnitude apart) will have a solutus curve up to 2 times lower in EH than the pure end-member saturation curves. The factor of 2 is obtained for the case where the two end-member solubility products are equal and can be derived from equations 4, 16 and 17. 

It would be superfluous to review here the story of e aq in the radiation chemistry of aqueous solutions. High energy radiations cause ionizations and the free electrons so generated dissipate their excess energy and are eventually trapped in solvation shells. The discovery of hydrated electrons showed that electrons in water were chemical entities (as distinct from possessing purely physical characteristics) in having diffusion properties, size and sphere of influence, associated ion atmosphere, and reaction rate parameters all of which are comparable to normal chemical reagents. 

If two immiscible phases are placed adjacent to each other, with one containing a solute soluble in both phases, the solute will distribute itself between two immiscible phases until equilibrium is attained therefore, no further transfer of solute occurs. At equilibrium, the chemical potential of the solute (free energy of the solute in solvent) in one phase is equal to its chemical potential in the other phase. If we consider an aqueous (w) and an organic (o) phase, we write according to theory ... 

The distribution equilibria of a neutral solute is governed by the difference in the solution free energies in aqueous and organic phases ... 

Aqueous Interfaces Force Fields A Brief Introduction Force Fields A General Discussion Free Energy Changes in Solution Free Energy Simulations Intermolecular Interactions by Perturbation Theory Monte Carlo Simulations for Complex Fluids Monte Carlo Simulations for Polymers OPLS Force Fields Supercritical Water and Aqueous Solutions Molecular Simulation. 

A Density Functional Theory Continuum Solvation Model for Calculating Aqueous Solvation Free Energies of Neutrals, Ions, and Solute-Water Clusters. 

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