Linear solvation free energy

B. Solvent Effects and Linear Solvation Free Energy Relationships.43... 

Usually, linear solvation free energy relationships adopt the form of Eq. 3, ... 

By the use of the multiple linear regression, Abraham and Rogers [16] determined the parameters of the Abraham linear solvation free energy relationship (LSFER) equation [17,18]... 

Linear solvation free energy relafionship LSFER... 

M. Kamlet and R.W. Taft, Linear Solvation Free Energy Relationships. Local Empirical Rules or Fundamental Laws of Chemistry Acta Chem. Scand., 1985,339,611. 

V. Ventosa, J. Llibre, J. Torras, C. Rovira and J. Veciana, Modeling of the solubilities of organic compounds in supercritical fluids using the linear solvation free energy relationship theory... 

Before analyzing concrete cases, a theoretical introduction with respect to some basic methodological issues will be provided in the next section. The methods to be applied are quantum mechanical calculations, which are different from the use of the linear solvation free energy relationships for predicting the equilibrium constant, as described in Chapter 12 of [1]. It is to be mentioned here that the forthcoming discussion of the theoretical results for the prototropic tautomerism always refers to ground-state processes. 

Part of the motivation behind so straightforward an approach derives from its ready application to certain simple systems, such as the solvation of alkanes in water. Figure 11.8 illustrates the remarkably good linear relationship between alkane solvation free energies and their exposed surface area. Insofar as the alkane data reflect cavitation, dispersion, and the hydrophobic effect, this seems to provide some support for the notion that these various terms, or at least their sum, can indeed be assumed to contribute in a manner proportional to solvent-accessible surface area (SASA). 

Figure 11.8 Approximately linear relationship between solvation free energy and solvent-accessible surface area for linear and branched alkanes. A best fit line passing through zero has a slope of...

The solvation free energy calculated by considering only the bulk electrostatics is somewhat arbitrary because the boundary between the dielectric medium and the solute is not well defined, and in fact the treatment of the solvent as a homogeneous, isotropic, linear medium right up to a definite boundary is not valid. To obtain an accurate solvation... 

The basic features of ET energetics are summarized here for the case of an ET system (solute) linearly coupled to a bath (nuclear modes of the solute and medium) [11,30]. We further assume that the individual modes of the bath (whether localized or extended collective modes) are separable, harmonic, and classical (i.e., hv < kBT for each mode, where v is the harmonic frequency and kB is the Boltzmann constant). Consistent with the overall linear model, the frequencies are taken as the same for initial and final ET states. According to the FC control discussed above, the nuclear modes are frozen on the timescale of the actual ET event, while the medium electrons respond instantaneously (further aspects of this response are dealt with in Section 3.5.4, Reaction Field Hamiltonian). The energetics introduced below correspond to free energies. Solvation free energies may have entropic contributions, as discussed elsewhere [19], Before turning to the DC representation of solvent energetics, we first display the somewhat more transparent expressions for a discrete set of modes. 

Almlof M, Carlsson J, Aqvist J (2007) Improving the accuracy of the linear interaction energy method for solvation free energies. J Chem Theory Comput 3(6) 2162-2175... 

These subtleties sometimes lead to a casual view of detailed molecular calculations such as are suggested by Eq. (4.22). If the potential of the phase is always irrelevant to neutral linear combinations of which are thermodynamically measurable, then perhaps it is unimportant to be precise about an assumed value. Our suggestion is that results obtained by molecularly detailed calculations of solvation free energies of single ions are compared and tabulated. Thus, precision and clarity in the assumptions underlying a calculated or tabulated result are important. Indeed, if calculated or tabulated values based upon different assumptions for the potential of the phase were to be combined, it would be essential that the assumptions be precisely known. Nevertheless, an ultimate thermodynamic test of a calculation should be made on thermodynamically measurable combinations of single ion free energies. 

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