Modification of attractive and repulsive interactions among proteins in solution due to the presence of mono-, di- and tri-valent ions

Bovine serum albumins, at physiological pH, shows a short-range attraction and in addition a long-range electrostatic repulsion among them. These interactions are modified in presence of different counterions. Small angle neutron scattering study shows that for the equal ionic strength, the interactions are largely modified by the tri-valent (Fe3+) and di-valent (Ni2+) ions and comparatively less by the mono-valent (Na+) ions. The effect is nearly similar for the di- and tri-valent ions in comparison with the mono-valent one. The strength of the attractive and repulsive interactions depends strongly on the type of the dissolved ions and salt concentrations.