title: The role of the concentration scale in the definition of transfer free energies.
abstract: The Gibbs free energy of transferring a solute at infinite dilution between two solvents quantifies differences in solute-solvent interactions - if the transfer takes place at constant molarity of the solute. Yet, many calculation formulae and measuring instructions that are commonly used to quantify solute-solvent interactions correspond to transfer processes in which not the molarity of the solute but its concentration measured in another concentration scale is constant. Here, we demonstrate that in this case, not only the change in solute-solvent interactions is quantified but also the entropic effect of a volume change during the transfer. Consequently, the "phenomenon" which is known as "concentration-scale dependence" of transfer free energies is simply explained by a volume-entropy effect. Our explanations are of high importance for the study of cosolvent effects on protein stability.
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany. Electronic address: Beate.Moeser@ur.de.
authors.forename: Beate
authors.initials: B
authors.lastname: Moeser
authors.affiliation: Institute of Physical and Theoretical Chemistry, University of Regensburg, 93040 Regensburg, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Horinek
mesh_terms: D004735:Energy Transfer; D019277:Entropy; D008956:Models, Chemical; D055550:Protein Stability; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D012996:Solutions / Q000737:chemistry; D012997:Solvents / Q000737:chemistry
chemical_list: D011506:Proteins; D012996:Solutions; D012997:Solvents
keywords: Concentration scale; Cosolvent and osmolyte effects on proteins; Preferential interaction; Solute–solvent interaction; Thermodynamics of solvation; Transfer free energy