THERMOGRAVIMETRY STUDY OF AROMATIC AMINO ACIDS AND ALIPHATIC PEPTIDES

Aromatic alpha-amino acids (L-phenylalanine, L-tyrosine, L-tryptophan) and aliphatic peptides (glycyl-glycine, triglycine, beta-alanyl-glycine, beta-alanyl-beta-alanine, glycyl-DL-alanine, DL-alanyl-glycine, L-alanyl-L-alanine, DL-alanyl-DL-alanine, DL-alanyl-DL-valine) were investigated by methods of thermogravimetry (TG) and differential thermal analysis (TGA) in temperature ranges 50-700 degrees C and 50-450 degrees C, correspondingly. The thermal degradation of the substances was studied. It has been shown that the differences in the spatial structure of the solid amino acids and aliphatic peptides have an influence on the character of phase transformations. The characteristics of thermal destruction stages were defined. The thermal stability of the amino acids with aromatic rings in the side chain structure was higher than the aliphatic amino acids. For two linear dipeptides (beta-alanylglycine and beta-alanyl-beta-alanine), the melting process is accompanied by chemical decomposition. Melting stage does not occur on heating of other dipeptides. The tendency of the decomposition temperature increase with the increase of heat capacities of crystalline amino acids and peptides is established.