Polarographic Studies of Dithiothreitol
1980 Volume 1980 Issue 5 Pages 722-728
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1980 Volume 1980 Issue 5 Pages 722-728
Dithiothreitol (DTT) gave two anodic waves at d. m. e. in buffer solution of pH 1 to 12. The first wave (E1/2=-0.434V vs. SCE) at pH4.5 had the nature of adsorption wave and was assigned from DC and AC polarographic studies to a reversible anodic oxidation of DTT to form a monolayer of mercury salt of DTT on d. m. e. surface;
R(SH)2 + 2Hg ←→ [R(SHg)2]ad + 2H+ + 2e+
The application of Brdicka equation to the saturation current of first wave gave the surface area of 4.9×103(nm2) per [R(SHg)2]ad salt. From the Ed (dissolution potential of the first wave) vs. pH curve, the acid dissociation constants (pKa) of DTT were determined as pKa1=9.3 and pKa2=10.6.
In acetate buffer solution of pH4.5, DTT was subjected to the anodic electrolysis on mercury pool electrode, the potential of which was controlled precisely 2 to 3 mV more positive than Ed. The electrolysis proceeded only very slowly and the product was identified to be cyclic disulfide form of oxidized DTT (OX-DTT) by means of spectrophotometry and polarography. This result can be explained only by assuming a sluggish formation of OX-DTT either from [DTT-Hg2(I)]ad through the eq. (1′) or from DTT through the eq. (3) on mercury electrode covered by [DTT-Hg2(I)]ad. The 2nd wave (E1/2=-0.228V vs. SCE) at pH4.5 was assigned to the anodic multi-layer formation of DTT-Hg2(I). Its limiting current was nearly diffusion-controlled. The electrolysis of the solution of pH4.5 at the potential of limiting current more positive than -0.344V made the solution turbid due to the formation of mercury salt.
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