Adsorption of Cytochrome c on Mesoporous Molecular Sieves: Influence of pH, Pore Diameter, and Aluminum Incorporation

The adsorption of cytochrome c onto different mesoporous molecular sieves (C12-MCM-41, C16-MCM-41 and SBA-15) is studied at different solution pHs. Adsorption isotherms were recorded up to final solution concentrations of ca. 250 mol/L and were found to be of the pseudo-Langmuir type. Cytochrome c (cyt c) adsorption was observed to be pH-dependent with maximum adsorption near the isoelectric point of the protein. SBA-15 showed a larger amount of cyt c adsorption as compared to MCM-41. The increased cyt c adsorption capacity may be due to the larger pore volume and pore diameter as compared to C12- and C16MCM-41. It has been discovered that the amount of cyt c adsorption can be increased by the introduction of aluminum into the pure silica materials. The observed increase is most likely a consequence of the strong electrostatic interaction between the negative charges on the aluminum sites and the positively charged amino acid residues of cyt c. Furthermore, the rate of cyt c adsorption has been studied and no significant differences in adsorption rate were found for the mesoporous materials with different pore diameters between 3 and 9 nm. While the adsorption capacity is reduced upon bead formation (due to the reduction in specific pore volume), the rate of adsorption is mainly unchanged