Abstract
One mg % thiamine in buffered solutions over pH 11 showed absorption maximum at 340 mμ which faded out quickly, and the intensity of the absorption was highest at pH 13 and slowly fading. Formation of thiochrome by ferricyanide in these ranges of pH was also proportional to the intensity of absorption at 340mμ. Thiamine in NaOC_2H_5 or NaOCH_3 also showed the absorption at 340mμ which was lasting for many hours, while its formation of thiochrome by ferricyanide was rather diminishing on standing. If water was added into thiamine solutions in NaOCH_3,absorption at 340mμ and formation of thiochrome were quickly decreased. The absorption maximum at 340mμ would indicate an cyclic thiol form (I) of thiamine but its absorption was not always correlated to formation of thiochrome.
