Adsorption and binding of peptides on homoionic montmorillonite and kaolinite

The adsorption and binding (amount retained after extensive washing) of peptides (two, three or four amino acids with isoelectric points ranging from pH 3.31 to 6.81) on montmorillonite (M) and kaolinite (K) made homoionic to H, Na, Ca, Zn, Al or La were studied. The amount of peplide adsorbed or bound varied with the type of clay, the type of cation saturating the clay, and the constitutive amino acids of the peptides. Di-, tri- and tetraglycine were adsorbed to a greater extent on M than on K. A larger amount of the basic peptide, l-alanyl-l-lysine, than of the acidic peptide, l-aspartylglycine, was adsorbed. The heterocyclic peptides, l-histidylglycine and l-prolyl-l-phenylalanylglycyl-l-lysine, were preferentially adsorbed on M homoionic to di- and trivalent cations. Only l-aspartylglycine, l-histidylglycine. l-alanyl-l-lysine and l-prolyl-l-phenylalanylglycyl-l-lysine were bound on M, and only diglycine, tetraglycine and l-prolyl-l-phenylalanylglycyl-l-lysine were bound on K.