Influence of the Structural Characteristics of Amino Acids on Direct Methylation Behaviors by TMAH in Pyrolysis

Abstract

Direct methylation behaviors of 20 amino acids with tetramethylammonium hydroxide (TMAH) were studied under diluted conditions with silica. Amino acid concentration was controlled by dilution with silica (SiO2) and the molar ratios of amino acid/silica were 0.20, 0.50, and 2.0. The molar ratios of amino acid/TMAH (0.51 -4.64) also varied. It was found that arginine, asparagine, aspartic acid, cysteine, glutamic acid, and glutamine did not generate any directly methylated pyrolysis products, whereas alanine, glycine, isoleucine, leucine, methionine, phenylanaline, valine, and proline generated all the directly methylated pyrolysis products. Tri-and tetra methylated products of lysine consisted of two types. Histidine and threonine hardly generated the partly methylated products. Mono-and dimethylated products of serine, tryptophan, and tyrosine were not observed. Relative intensities of the methylated products varied with the amino acid concentration, TMAH concentration, and pyrolysis temperature. Direct methylation behaviors of amino acids were explained by the structural characteristics of amino acids.