title: Interactions of macromolecules with salt ions: an electrostatic theory for the Hofmeister effect.
abstract: Salting-out of proteins was discovered in the nineteenth century and is widely used for protein separation and crystallization. It is generally believed that salting-out occurs because at high concentrations salts and the protein compete for solvation water. Debye and Kirkwood suggested ideas for explaining salting-out (Debeye and MacAulay, Physik Z; 1925;131:22-29; Kirkwood, In: Proteins, amino acids and peptides as ions and dipolar ions. New York: Reinhold; 1943. p 586-622). However, a quantitative theory has not been developed, and such a theory is presented here. It is built on Kirkwood's idea that a salt ion has a repulsive interaction with an image charge inside a low dielectric cavity. Explicit treatment is given for the effect of other salt ions on the interaction between a salt ion and its image charge. When combined with the Debye-Hückel effect of salts on the solvation energy of protein charges (i.e., salting-in), the characteristic curve of protein solubility versus salt concentration is obtained. The theory yields a direct link between the salting-out effect and surface tension and is able to provide rationalizations for the effects of salt on the folding stability of several proteins.
authors.affiliation: Department of Physics and Institute of Molecular Biophysics and School of Computational Science, Florida State University, Tallahassee 32306, USA. zhou@sb.fsu.edu
authors.forename: Huan-Xiang
authors.initials: HX
authors.lastname: Zhou
mesh_terms: D000818:Animals; D003080:Cold Temperature; D006454:Hemoglobins / Q000737:chemistry; D006736:Horses; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D011489:Protein Denaturation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D012492:Salts / Q000737:chemistry*; D012995:Solubility; D055672:Static Electricity
chemical_list: D006454:Hemoglobins; D007477:Ions; D011506:Proteins; D012492:Salts