Dimerization reactions of amino acids by pyrolysis

20 amino acids mixed with silica and tetramethylammonium hydroxide (TMAH) were pyrolyzed and the pyrolysis products formed from dimerization reactions of amino acids were analyzed using GC/MS and GC. Among them, asparagine, aspartic acid, proline, and serine generated only cyclic dimerized products, whereas cysteine, isoleucine, methionine, and valine generated only non-cyclic dimerized products. Alanine and glycine generated both cyclic and non-cyclic dimerized products. Most amino acids which do not generate the dimerized pyrolysis products have a long side chain or a ring group except threonine. Variations of the intensity ratios of the dimerized products with the pyrolysis temperature were examined. Variations of the product intensity ratios with the amino acid and TMAH concentrations were also investigated.