Electrochemical Oxidative Decomposition of Cyclic Amino Acids

Masaharu KOBAYASHI*, Yoshiaki MIHO†, Masaharu NAKAYAMA†† and Kotaro OGURA††

Water Environment Research Laboratory, Kyushu Matsushita Electric Co., Ltd.;
4-1-62 Minoshima Hakata-ku Fukuoka-shi 812-8531 Japan
† Sasakura Co., Ltd.; 4-7-32 Takeshima Nishiyodogawa-ku, Osaka-shi
555-0011 Japan
†† Department of Applied Chemistry, Yamaguchi University; 2557 Tokiwadai,
Ube-shi 755-8611 Japan

Anodic oxidation of cyclic amino acids was performed in a strong basic solution by galvanostatic and potentiostatic methods. 1 mM(1 M = 1 mol dm−3) tryptophan, tyrosine, histidine and proline were completely decomposed within 100 min at a constant current of +1.15 mA cm−2, and converted to CO2, NH3, HCOOH etc. Rate constants for potentiostatic oxidation of these amino acids (1.29 × 10−2 min−1 for tryptophan) at +1.8 V vs. Ag/AgCl were larger than those for aliphatic amino acids (6.82 × 10−3 min for lysine) indicating that the adsorption of the cyclic amino acids to electrode surface promotes their decomposition. Adsorption and decomposition processes of cyclic amino acids were studied by in situ FT-IR. In the oxidation of tyrosine, it was suggested that phenolic and carboxylic moieties start to be adsorbed on electrode at +0.3 and +0.4 V, respectively, followed by the decarboxylation at higher potential than +1.1 V.


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