  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.
