Protein adsorption into mesopores: a combination of electrostatic interaction, counterion release, and van der Waals forces.

Bovine heart cytochrome c has been immobilized into the mesoporous silica host material SBA-15 in both its native folded and urea-unfolded state. The comparison of the two folding states' behavior casts doubt on the commonly used explanation of cytochrome c adsorption, that is, the electrostatic interaction model. A detailed investigation of the protein binding as a function of pH and ionic strength of the buffer solution reveals the complex nature of the protein-silica interaction. Electrostatic interaction, van der Waals forces, and entropic contributions by counterion release each contribute to adsorption on the silica pore walls.