COSMO-RS Model

QuantlogP, developed by Quantum Pharmaceuticals, uses another quantum-chemical model to calculate the solvation energy. As in COSMO-RS, the authors do not explicitly consider water molecules but use a continuum solvation model. However, while the COSMO-RS model simpUfies solvation to interaction of molecular surfaces, the new vector-field model of polar Uquids accounts for short-range (H-bond formation) and long-range dipole-dipole interactions of target and solute molecules [40]. The application of QuantlogP to calculate log P for over 900 molecules resulted in an RMSE of 0.7 and a correlation coefficient r of 0.94 [41]. 

Having recognized the theoretical inadequacy of the dielectric theory for polar solvents, I started to reconsider the entire problem of solvation models. Because the good performance of dielectric continuum solvation models for water cannot be a result of pure chance, in some way there must be an internal relationship between these models and the physical reality. Therefore I decided to reconsider the problem from the north pole of the globe, i.e., from the state of molecules swimming in a virtual perfect conductor. I was probably the first to enjoy this really novel perspective, and this led me to a perfectly novel, efficient, and accurate solvation model based upon, but going far beyond, the dielectric continuum solvation models such as COSMO. This COSMO for realistic solvation (COSMO-RS) model will be described in the remainder of this book. 

As mentioned earlier, I was not aware of the details of the chemical engineering models and Guggenheim s QUAC approximation, when I developed the COSMO-RS model. From a brief glance at that part of the literature I had got the impression that all these models are basically lattice theories, while I wanted to... 

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. 

Recognizing that the continuum solvent calculations are the weakest link in pKa calculations, Ho and Coote [3] used the CPCM (with UAKS and UAFH radii), SM6, IPCM, and COSMO-RS models to predict pKa values for a common data set of neutral organic and inorganic acids. They used four different thermodynamic cycles, and in general found that the COSMO-RS, CPCM, and SM6 models worked best depending on the thermodynamic cycle used. We turn to a discussion of thermodynamic cycles in the next section. 

The PSP approach [39-43] is a novel predictive thermodynamic framework, which combines elements from the solubility parameter approach [112,114,116,126] detailed earlier, the solvatochromic/ LSER approach [127-133], and the COSMO-RS theory of solutions [134-136]. It retains the simplicity of the solubility parameter approach, it uses molecular descriptors that can be mapped one to one to the Abraham/LSER descriptors, and these descriptors are derived from the moments of the a-profiles of the quantum mechanics-based COSMO-RS model. Because of this combination, the PSP approach has a broader range of applications compared to each of the earlier three... 

The above exemplary consideration of repre.sentative solvents within the COSMO-RS approach reveals significant differences between them and gives instructive explanations for several of the differences in their solvation behaviour. It demonstrates the capability of the COSMO-RS model to shed new light on solvation phenomena. 

Calculations were carried out with the COSMO-RS model to account for the solvent effects of PhCl for very reactive species like alkoxide monomers or dissociated Na and RO ions, deprotonation next to the lactone carbonyl group is clearly feasible. The formation of such ions, however, is endergonic by more than 100 kj/mol, and cubane-Hke alkoxide tetramers" have a computed free binding energy of 90 kJ/mol per monomer. 

The density of RTILs, and more generally their P-V-T properties have been described by several models. The COSMO-RS model was applied by Palomar et al. [47] for the prediction of the densities and molar volumes of 40 -imidazolium-based RTILs. The predicted densities had a small positive bias (2.5 %) relative to the experimental values. The Sanchez-Lascombe equation of state (SL-EoS) was applied by Machida et al. [48] to the P-V-T properties of C4mim+... 

The modeling of the (temperature dependent) densities is described briefly in Sect. 6.1.2, using equations of state (EoS) derived from various modifications of the statistical associated fluid theory (SAFT), the COSMO-RS model, the Sanchez-Lascomb lattice fluid model (SL), or the perturbed hard sphere model (PHS). Each... 

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