  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, i.e. 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.
