The Studies on Brdicka's Catalytic Hydrogen-Wave II, Polarography of α-Lipoic Acid in Co(II) or Co(III)-Ammoniacal Ammonium Chloride Solution.

Abstract

It was reported by Shinagawa, et al. that some onium compounds and miscellaneous compounds have also shown similar catalytic waves to that by cysteine in ammoniacal cobalt solution, but a consideration for this effect brings more complicate relation on studying the mechanism of Brdicka's catalytic hydrogen-wave. In the series of this study, therefore, a compound containing sulf hydryl or disulfide group and the related compound are discussed mainly. The catalytically acting part of the compound lowering the hydrogen overvoltage in the ammoniacal cobalt solution is, in most instances, the sulfhydryl group, which is either present in solution or is formed by the reduction of disulfide group at more positive potential before the catalytic process gives rise. The relations between the structure of the compound given a catalytic wave and the catalytic effect in ammoniacal Co(II) or Co(II) solution are summarized as follows:1) The compounds containing amino, sulf hydryl or disulfide, and carboxyl groups in a molecule ; such as cysteine, cystine, glutathione, cystinylglycine, penicillamine (dimethylcysteine), ergothioneine and thiolhistidine are amino acids and peptides, and give a similar wave to the catalytic wave shown by cysteine in ammoniacal cobaltous solution . In the ammoniacal cobaltic solution, cystine or homocystine at high concentration give a catalytic wave, but other compounds stated above were not tested in cobaltic solution .2) The compounds containing amino and sulfhydryl group in a molecule; such as β-aminoethylmercaptan, diethylaminoethylmercaptan, vitamin B1, thiothiamine, ethylthiamine', benzothiamine give catalytic wave in both cobaltous and cobaltic ammoniacal ammonium chloride solution.3) The compound containing sulf hydryl or disulfide and carboxyl group in a molecule; such as thioglycolic acid, thiomasalate1 or dithiodiglycolic acid give a catalytic wave in ammoniacal cobaltous solution. Thioglycolic acid in cobaltic solution is inactive (10-3-10-4M).4) The compounds containing sulf hydryl or disulfide and other group e.g ., hydroxyl, aldehyde etc., such as ethylendithiol, or 2, 3-dimercaptopropanol (BAL) give a catalytic wave in ammoniacal cobaltous solution, BAL gave catayltic waves in both cobaltic and cobaltous ammoniacal ammonium chloride solution,