A CATALYTIC PRE-WAVE OF COBALT IN PRESENCE OF SELENOCYSTINE

In the presence of seleno-cystine we have established the formation of a catalytic pre-wave of cobalt for which the half-wave potential is about -0.94 V. The pre-wave forms from seleno-cystine concentrations of 10-6 M; at 2.10-5 M the cobalt wave (10-3 M) is completely displaced into the region of the pre-wave. The concentration of adsorbing substances has an important effect on the catalytic pre-wave. In the absence of gelatine there is no splitting of the wave in ammoniacal buffer. At a gelatine concentration of 0.004% the wave are completely separated, the cobalt maximum is suppressed, but the pre-wave maximum remains very strong. When the concentration of gelatine increases, a decrease in the height of the pre-wave is observed; it practically disappears at 0.02% gelatine. The height of the pre-wave is not influenced by variation of the height of the mercury reservoir; this behaviour shows the kinetic character of the pre-wave. The reservoir height influences the pre-wave maximum, which is suppressed at large heights. The variation of the concentration of the ammoniacal buffer and of its components demonstrates the existence of equilibria between ammoniacal complexes and the complex which produces the catalytic pre-wave. The ionic strength has little influence on the half-wave potentials, but the height of the pre-wave reaches a maximum value at a certain salt concentration. Since seleno-cystine is reduced to seleno-cysteine at a half-wave potential of -0.06 V, the cobalt pre-wave must be produced by a complex formed between cobalt and seleno-cysteine. © 1969.