Hofmeister effects: Why protein charge, pH titration and protein precipitation depend on the choice of background salt solution

Protein solubility, protein charge and acid–base titration in protein solutions depend strongly on the choice of background salt solution. Hofmeister effects, or sequences, refer to the relative effectiveness of anions or cations on a wide range of phenomena. Understanding this ion specificity is vital for biology, biotechnology, and colloid chemistry but the reason has, until very recently, not been clear. We present calculations using the Poisson–Boltzmann equation that includes not only electrostatic interactions but also many-body ion–protein dispersion potentials, originated from polarizabilities of ions and proteins. These calculations reveal that is possible to qualitatively predict different Hofmeister effects observed in protein solutions. Our results enable us to give an explanation for the Hofmeister series observed in the measured pH in protein and buffer solutions, protein charge and ion adsorption on protein surface.