Group contribution solvation

Lin, S.-T. and Sandler, S.l. (1999) Prediction of octanol-water partition coefficients using a group contribution solvation model. Ind. Eng. Chem. Res., 38, 4081 091. 

Correlation methods discussed include basic mathematical and numerical techniques, and approaches based on reference substances, empirical equations, nomographs, group contributions, linear solvation energy relationships, molecular connectivity indexes, and graph theory. Chemical data correlation foundations in classical, molecular, and statistical thermodynamics are introduced. 

One center has been attributed to the central sulfur atom because it is impossible to assign it either to the S-0 bond or the methyl groups, as can be seen in Table I and Fig. 1. As expected, the main contribution to the total dipole moment of DMSO stems from the S-0 bond dipole, see third row of Table I. The methyl groups contribute only in a small way. Whereas the S-0 bond dipole increases, the methyl group dipole moments decrease upon solvation which is in accordance with the observed red-shift and blue-shift from many experiments. The increase of the DMSO dipole moment upon solvation is about 81%. This increase can only partly be explained by the 23% increase of the S-0 bond dipole. A much larger share is due to the reduction of about 35% of the methyl group. 

It is very satisfying and useful that the COSMO-RS model—in contrast to empirical group contribution models—is able to access the gas phase in addition to the liquid state. This allows for the prediction of vapor pressures and solvation free energies. Also, the large amount of accurate, temperature-dependent vapor pressure data can be used for the parameterization of COSMO-RS. On the other hand, the fundamental difference between the liquid state and gas phase limits the accuracy of vapor pressure prediction, while accurate, pure compound vapor pressure data are available for most chemical compounds. Therefore, it is preferable to use experimental vapor pressures in combination with calculated activity coefficients for vapor-liquid equilibria predictions in most practical applications. 

Viswanadhan VN, Ghose AK, Wendoloski JJ. Estimating aqueous solvation and lipophilicity of small organic molecules A comparative overview of atom/group contribution methods. Perspect Drug Discov Des 2000 19 85-98. 

Ghose-Crippen descriptors were successfully used also to model —> molar refractivity [Ghose and Crippen, 1987] and solvation free energies [Viswanadhan, Ghose et al, 1999] by —> group contribution methods. 

Structure/Response Correlations, Hansch analysis, Hammett equation, Free-Wilson analysis. Linear Solvation Energy Relationships, Linear Free Energy Relationships, group contribution methods, substituent descriptors, extrathermodynamic approach, and biological activity indices. 

A recent alternative to group-contribution activity-coefficient estimation methods is based on interactions between surface charge distributions (determined by quantum-mechanical calculations) of molecules in solution. The solvation model used for the charge-distribution calculation is known as COSMO the most widely used method based on this technique is called COSMO-RS [47]. 

Apart from methods based on continuum approaches, methods based on the division of the total solvation energy by atom or group contributions that are independent from each other are quite popular. The solvation free energy in these methods is computed as a sum of products of an empirical constant depending on the nature of atom or group (wy), and a solvent accessible area of this atom or group (Si) ... 

Researchers in solvation thermodynamics have long attempted to assign group contributions of various parts of a solute molecule to the thermodynamic quantities of solvation. In this section we examine the molecular basis of such a group-additivity approach. As we shall see, the problem is essentially the same as that treated in the previous section i.e., it originates from a split of the solute-solvent intermolecular potential function into two or more parts. 

The Achard model combines the UNIFAC group contribution model modified by Larsen et al. [LAR 87], the Pitzer-Debye-Hiickel equation [PIT 73a, PIT 73b] and solvation equations (Figure 2.1). The latter are based on the definition of the number of hydration for each ion, which corresponds to the assumed number of water molecules chemically related to the charged species. It divides the activity coefficient into two terms ... 

Revelli, A.-L. Mutelet, F. Jaubert, J.-N. (2010a). Prediction of partition coefficients of organic compounds in ionic liquids Use of a linear solvation energy relationship with parameters calculated through a group contribution method. Ind. Eng. Chem. Res., 8,49, 3883-3892. 

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