The mechanism of oxidation-reduction potential

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Abstract
Dixon''s hypothesis of a "steady state," depending on a kinetic equilibrium between the dissociation of H from cysteine and diffusion of H from the surface of the metal electrode, is incorrect. The drift in the reduction potential with a Pt electrode is ascribed to traces of O or other oxidizing agents, adsorbed on the surface of the metal. The steady potential given with a Au electrode is expained by the failure of the Au to adsorb O. The difference in potential between the Au and Hg electrodes in a solution of cysteine cannot be explained by the higher over-voltage of H on Hg. When cysteine is oxidized it does not immediately form cystine, but an intermediate compound exists which is the oxidant of the system and which appears to exist in a low and limited concentration above which it passes into cystine. In the absence of an activating agent, cystine does not affect the Pt electrode and the reduction potential is a function of the logarithm of the concentration of cysteine. In a solution of cysteine and cystine, containing an activating agent, cystine is brought into equilibrium with the oxidant of the system and the reduction potential is determined by the ratio C [image] SH/C [image] SS [image] C groups.

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