Solvation of beta-lactoglobulin in alkylurea solutions

Solvation of beta-lactoglobulin in aqueous solutions of urea, methyl-, N,N'-dimethyl- and ethylurea was studied by density measurements. From the densities at constant chemical potential and constant molality, the preferential solvation parameters and the partial specific volumes of beta-lactoglobulin in these solutions were determined. In urea and methylurea solutions urea is preferentially bound, whereas in N,N'-dimethyl- and ethylurea solutions at higher concentration water is preferentially bound. From preferential solvation data and partial specific volumes of protein Gibbs free energies of transfer from water to alkylurea solutions were calculated. Since the enthalpies of transfer were determined previously the entropies of transfer could also be obtained so that a complete thermodynamic description is available. An attempt is made to interpret the values of the thermodynamic quantities in terms of various interactions involved in solvation. In salvation of alkylureas the hydrophobic nature of alkyl groups is clearly reflected.