Montmorillonite catalyzed peptide bond formation: The effect of exchangeable cations

The effect of exchangeable cations, namely, alkali and alkaline metal, ammonium and aluminum ions, on montmorillonite (M) catalyzed peptide formation was investigated. Amino acid (AA) dimerization and peptide chain elongation proceed with relatively low yields on macroscopically swelling montmorillonites (Li-,Na-M) due to redistribution and insufficient concentration of reactant molecules on the clay surface. Cyclic anhydride (CA) formation, proceeding by monomolecular mechanism, is primarily affected by the accessibility of catalytic sites for dimer activation. Weaker sorbed exchangeable cations do not block catalytic sites, and thus favor CA formation.