Small molecular ion adsorption on proteins and DNAs revealed by separation techniques

Ion binding is a term that assumes that the ion is included in the solvation sphere characterising the biomolecule. The binding forces are not clearly stated except for electrostatic attraction; weak forces (hydrogen bonds and Van der Waals forces) are likely involved. Many publications have dealt with ion binding to proteins and the consequences over the past 10 years, but only a few studies were performed using high-performance liquid chromatography (HPLC: ion exchange, reversed phase without the well-identified immobilised metal affinity chromatography) and capillary zone electrophoresis (CZE). This review focuses on the binding of proteins and DNAs mainly to the oxyanions (phosphate, borate, citrate) and amines used as buffers for both the HPLC eluent and the background electrolyte of CZE. Such specific ion adsorption on biomolecules is evidenced by physico-chemical characteristics such as the mobility or retention volume, closely associated with the net charge, which differ from the expected or experimental data obtained under the conditions of an indifferent electrolyte. It is shown that ion binding to proteins is a key parameter in the electrostatic repulsion between the free protein and a fouled membrane in the ultrafiltration separation of a protein mixture.