The effect of clay structure on peptide bond formation catalysis

The catalytic efficiency in peptide bond formation of various clays was tes ted by reactions of glycine (gly), diglycine (gly(2)), glycine + alanine (a la), gly(2) + ala. The main effects of clay structure and composition resul ted as following: (1) Clay composition influences the activation of reactan t molecules at clay particle edges. (2) Acidity (basicity) of the clay surf ace can change on the state of the reactant. (3) The clay structure is rela ted to suspension stability and thus accessibility of clay catalytic sites. Mg-rich trioctahedral clays hectorite (smectite) and talc are the most eff icient catalysts. Oligomerization of gly and gly(2) proceeds on all clays, whereas oligopeptides including ala units are formed with much lower yields and only on the most efficient catalysts. Besides dipeptides and other lin ear peptides, also cyclic anhydride (diketopiperazine) is formed with relat ively high yields from diglycine. Cyclic anhydrides can directly act in the formation of the linear oligopeptides by ring opening molecular rearrangem ent and addition of another amino acid (oligopeptide). (C) 1999 Elsevier Sc ience B.V. All rights reserved.