Preferential solvation definition

Remarkable data on primary hydration shells are obtained in non-aqueous solvents containing a definite amount of water. Thus, nitrobenzene saturated with water contains about 0.2 m H20. Because of much higher dipole moment of water than of nitrobenzene, the ions will be preferentially solvated by water. Under these conditions the following values of hydration numbers were obtained Li+ 6.5, H+ 5.5, Ag+ 4.4, Na+ 3.9, K+ 1.5, Tl+ 1.0, Rb+ 0.8, Cs+0.5, tetraethylammonium ion 0.0, CIO4 0.4, NO3 1.4 and tetraphenylborate anion 0.0 (assumption). 

All the definitions of the local composition and preferential solvation are applicable for any mixture, including electrolyte solutions. Suppose for simplicity we have a solution of an electrolyte D in water W. Viewing this system as a mixture of a two-component system, we can apply all the equations of the previous section. 

Third, to obtain the spatial profiles for the preferential solvation around a solute molecule, we proposed another definition of the KB integral around the solute molecule with finite dimensions, i.e., the surficial KB integral, to systematically examine the solvation on the distance from the molecular surface of the solute molecule. With the aid of surficial KB treatment, the present MD simulations of chymotrypsin inhibitor 2 (CI2) showed the preferential exclusion of ectoine (i.e., a CS) near the protein surface, while it is generally considered that CSs are preferentially excluded from the surface of proteins [28,29], On the other hand, the preferential exclusion of ectoine was found to be significantly weakened near the surface of much smaller solute met-enkephalin (M-Enk) in its bent structure [39,40]. 

Binary mixtures of water with water-miscible solvents show a balance between the self-association and the mutual association of the components. This aspect has been studied by the use of many methods, but the most definite information is given by the preferential solvation parameter 5w(s>=. w(S) — w, where jcw(S) is the local mole fraction of W around S. Obviously, what is excess in one component must be deficiency in the other, so that 5w(S) = — S(S) and 5w(W> = —5s(w>. Also, 5w(S)( w = 0) = 0=5w(s)(.xw = 1) and necessarily also 5w(s) <. xw The experimental errors in the data required for the calculation of the preferential solvation parameters lead to values 5w(s)l < 0.010 to be insignificant, but larger values mean that water is preferred around S rather than S molecules, i. e., self-associated S. Similarly, Sw(w) > 0.010 means that self-association of water is preferred over mutual association with the co-solvent S. Another manner of presenting this information is in terms of the solvent sorting parameter Pss. ... 

Binary systems have been the most common system of interest when applying FST. Most investigations of closed binary systems have involved the determination and examination of the three KBIs, possibly followed by some description of local composition or preferential solvation (see Section 1.3.4), all of which is composition dependent. The equations provided in the previous section are more commonly expressed and simpMed by the definition of two additional variables (Ben-Naim 1977),... 

The availability of the local compositions allows one to calculate a quantity called preferential solvation. There is no generally established definition of preferential solvation (see Section 3.1 in Chapter 3). For a binary mixture, the excess local molar fraction has been usually considered synonymous with preferential solvation the more positive the higher the preference of i to be solvated by j than by... 

If we examine the literature works that use the KBI and the local composition or preferential solvation to obtain information on the type and strength of the interactions in mixtures, we realize that in most of these works the KBIs have not been used directly, but rather after subtraction of a quantity called the ideal contribution, or volume correction, or excluded volume contribution (MatteoU and Lepori 1995 Matteoli 1997 Marcus 2001 Ruckenstein and Shulgin 2001a Vergara et al. 2002 Aparicio et al. 2008). The last definition comes from the always-negative contribution to the KBI from zero to the distance of maximum approach. See also Section 2.7.2... 

In contrast to this equal propensity toward formation of a H-bond, there is a definite preference for a proton to locate on the syn side when coming much closer and forming a covalent bond. That is, the syn conformer of RCOOH is more stable than the anti structure by about 5 kcal/mol in the gas phase. If this is the case, why then is there so little apparent pK difference between the syn and anti structures The answer to this question resides in solvation phenomena. The presence of the polarizable medium preferentially stabilizes the anti conformer of the carboxylic acid due to its higher dipole moment. 

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