Figure 3.

Thermodynamics of preferential exclusion. In water a) upon addition of a soluble protein the chemical potential μ is raised by the hydration energy ΔG_h. A solution of solutes in water b) in general has a lower chemical potential. Depending on whether a solute preferredly binds b1) is inert b2) or is preferredly excluded hydration energies are lower (ΔG_h^b) equal (ΔG_hⁱ) or higher (ΔG_h^x) than ΔG_h. Thus, in a theoretical experiment of transferring a protein from water into a solute solution we either gain energy ΔΔG^b, have no energetic effect or have to put energy into the system ΔΔG^x.