薬品のポーラログラフ的研究 (第24報)

Thiamine関連物質のポーラログラフィー (v) Thiamineの直流および交流ポーラログラフィー

抄録

Principle of polarographic waves indicated by thiamine under various conditions have been revealed. The cathodic wave of E_1/2 -1.1V at pH 1 has the properties of a diffusion current and shows diffusion current constant, k_D, of 12.5 (μA⋅mM^-1mg.^-2/3⋅sec.^1/2) and its temperature coefficient is 1.8% deg^-1. This is due to electrolytic reduction of the thiazole and pyrimidine rings, and hydrogen sulfide, ammonium chloride, and 3-acetyl-3-mercapto-1-propanol are obtained by the controlled potential electrolysis. This wave height decreases with increasing pH above 5. This wave is ascribed to reduction of the cation of thiamine. The anodic wave (E_1/2≅Ep=-0.32, -0.4V) indicated by the thiol-type thiamine in alkaline solution at the dropping mercury electrode is due to the formation of mercurithio thiamine and the wave of Ep -0.14, -1V, is due to adsorption and desorption of thiol-type thiamine. The anodic wave at +0.2V shown by thiamine mononitrate in acid solution at the dropping mercury electrode is due to formation of thiamine mercury (I) complex. The use of rotating platinum electrode gives the oxidation wave due to 2B₁-S^-→ thiamine disulfide+2e at E_1/2+0.3V. From its wave height-pH curve, apparent pK′ 10 is calculated. The greater value of pK′ than pK 9.33 for the thiol-type thiamine is considered to be due to kinetic current.