Polarographic Study of Bis-cysteinatodiaquocobaltate (III)

The Brdicka catalytic reduction of hydrogen at the dropping mercury electrode fundamentally differs from the reduction in the case of usual diffusion currents. This phenomenon has been studied in detail by many authors for the last thirty years. Despite the vast experimental data thus accumulated, no decisive conclusion seems to have been drawn as to the nature of the species in the electrolytic solutions. This catalytic reduction apparently requires the presence of sulfhydryl group and is best observed in an ammoniaammonium chloride buffer solution containing cobalt. Compound such as cysteine or cystine produces under these conditions a single wave with a rounded maximum. The most difficult point in the interpretation of the whole catalytic electrode process is in the elucidation of the role of cobalt. Brdicka has assumed that the cysteinatocobaltate complex formed in the electrolytic solution might facilitate the deposition of hydrogen from the solution. This assumption is based on the structure of cysteinatocobaltate which was given by Schubert in 1931. But Brdicka did not show any experimental evidence to verify the assumption. As the catalytic action of bis-cyteinatocobaltate does not seem to have been firmly established, this paper describes a work carried out to learn more about this complex. On the basis of polarographic and spectrophotometric methods, it is suggested that the cysteinatocobaltate (II) chelate is the essential substance to produce the catalytic wave of cysteine in ammoniacal solution containing divalent cobalt.