Group contribution solvation model

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. 

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. 

We end our contribution to this editorial initiative of the European Academy of Science by recalling the leading role played by the European quantum chemistry community in the development of quantum mechanical (QM) solvation models. We cite, as an example, the first quantum chemistry continuum solvation code developed by Rivail s group in Nancy in 1973 [43], However, this initiative to address the solvation problem from a QM point of view was not entirely out-of-the-blue. It was, on the contrary, a response to the challenges stimulated by a limited number of scientists working in France and in Italy (Paris, Nancy, Pisa), with strong contact, in competition and also in collaboration to each others [44], More than 30 years later, the European quantum chemistry community is still at the forefront in the development of QM continuum solvation models, and we hope that the present contribution can be considered as a testimony of this activity. 

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. 

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]. 

The equilibrium position is mainly dictated by solvent polarity however, there is clearly a specific contribution of solvent acidity from the carbonyl groups of the dione. 10.3.7.3 Mixtures of solvents. Understanding the preferential solvation model... 

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 ... 

The second group of studies tries to explain the solvent effects on enantioselectivity by means of the contribution of substrate solvation to the energetics of the reaction [38], For instance, a theoretical model based on the thermodynamics of substrate solvation was developed [39]. However, this model, based on the determination of the desolvated portion of the substrate transition state by molecular modeling and on the calculation of the activity coefficient by UNIFAC, gave contradictory results. In fact, it was successful in predicting solvent effects on the enantio- and prochiral selectivity of y-chymotrypsin with racemic 3-hydroxy-2-phenylpropionate and 2-substituted 1,3-propanediols [39], whereas it failed in the case of subtilisin and racemic sec-phenetyl alcohol and traws-sobrerol [40]. That substrate solvation by the solvent can contribute to enzyme enantioselectivity was also claimed in the case of subtilisin-catalyzed resolution of secondary alcohols [41]. 

---