Preferential hydration, glycerol

Table I shows that for water/glycerol and water/ trehalose mixtures are negative and 721 for water/urea mixture is positive. Therefore, one can notice a correspondence between the preferential hydration and the sign of 72i- If water is in excess in the vicinity of a protein molecule 72i is positive and when the cosolvent is in excess 72i is negative. 21 depends on the nature of the protein and is expected to depend on the mixed solvent composition as well. However, our calculations based on Eq. (17) and the experimental values of the preferential binding parameter have revealed a weak composition dependence of this parameter. One can see from Fig. 3 that the one-parameter (72i) Eq. (17) can accurately represent the preferential binding parameter by considering J21 as composition independent.

Many characteristics of a protein in aqueous solvents are connected to its preferential solvation (or preferential hydration). The protein stability is a well-known example. Indeed, the addition of certain compounds (such as urea) can cause protein denaturation, whereas the addition of other cosolvents, such as glycerol, sucrose, etc. can stahihze at high concentrations the protein stiucture and preserve its en2ymatic activity [4-7]. The analysis of literature data shows that as a rule Ffor the former and r23 " <0 for the latter compounds. Recently, the authors of the present paper showed how the excess (or deficit) number of water (or cosolvent) molecules in the vicinity of a protein molecule can be calculated in terms of F2 the molar volume of the protein at infinite dilution and the properties of the protein-free mixed solvent [8]. The protein solubility in an aqueous mixed solvent is another important quantity which can be connected to the preferential solvation (or hydration) [9-13] and can help to understand the protein behavior [9-17]. 

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