Alumina catalyzed reactions of amino acids

Thermal reactions of glycine (Gly), alanine ( Ala), leucine (Leu), valine (Val) and proline ( Pro) adsorbed on activated alumina were studied by means of thermal analysis. In the absence of alumina, decomposition of amino acids was detected as a sharp endotherm above 200 degreesC, whereas no thermal effects were detectable by differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for amino acid/alumina mixtures. This could be explained by a continuous amino acid condensation to peptides and simultaneous absorption of formed water by alumina, the latter being gradually released at higher temperatures. Thermogravimetry (TG) and differential thermogravimetry (DTG) measurements revealed that the reactions of the amino acids adsorbed on alumina surface were spread over a wide range of temperatures. The catalysis of peptide bond formation on alumina surface at 85 degreesC was proven directly by the identification of the reaction products, mainly dipeptides and cyclic anhydrides.