1960 年 80 巻 9 号 p. 1222-1226
The pyrimidine portion of thiamine, 2, 5-dimethyl-4-aminopyrimidine (I), shows one-step reduction wave in E1/2=(-1.06-0.076 pH) at pH 1-8. Its diffusion current constant, kD, is 4.8 (μA⋅mM-1⋅mg.-2/3⋅sec.1/2) at pH 3-6, and becomes one-half at pH 8. This reduction wave is due to hydrogenation of the proton adduct of (I) in the course of three-electron reduction. The formation of ammonia and amine was observed by controlled potential electrolysis.
The thiazole portion of thiamine, 3, 4-dimethyl-5-(2-hydroxyethyl) thiazolium iodide (II), undergoes electrolytic reduction at pH 6.8 to be decomposed into hydrogen sulfide, amine, alcohol, and sulfur-containing compound. Cathodic wave of E1/2 -1.4V and kD 8.6 is due to reduction of the thiazole ring and the cathodic wave of E1/2 -1.7V is ascribed to catalytic hydrogen wave of the reduction product. (II) takes the thiol type at pH above 9 and shows anodic wave (E1/2 -0.43V) due to the reaction of thiol-+Hg→ thiol-Hg+e. From the ie-pH and titration curves, pK of the thiol type was calculated as 10.3. Formation velocity of the thiol type is proportional to the concentration of OH- and k1 is 0.18 (min.-1) at pH 10.5. The reaction of the thiol type and p-chloromercuribenzoate, and oxidation of thiol type to the disulfide were examined by polarography.