Résumé:

It is well acknowledged that clay minerals can retain proteins dependently on pH and ionic strength of the aqueous solution in which they are dropped1. However, little is known about the influence of the extra-framework cations (EFC) located into the interlayer space of swelling clays. So, the questions concerning the role plays by EFC on hard or soft proteins regarding their adsorption kinetics and loading, as well as their conformation at the clay outer or inner surface remain posed. In the present study, we investigate the adsorption of different hard and soft proteins (lysozyme, BSA, -chymotrypsin, and trypsin) on a series of homoionic montmorillonite (CMS reference clay SWy-2) exchanged by various monovalent and bivalent EFC, i.e. Li+, Na+, K+, Rb+, Cs+, Ba2+, Ca2+ and Mg2+. Figure 1 shows the lysozyme and BSA loadings at equilibrium under room experimental conditions in two buffer, i.e. Na+ and K+ phosphate, solutions. As expected, it can then be seen that the protein loading is strongly influenced by the buffer solution. However, it can also be observed a protein loading decrease with the EFC radius except for Li+. This result could be correlated to the EFC exchange capacity that is to the EFC hydration2 Nevertheless the particular case of lithium can be explained by its inhibitor effect on protein adsorption3.