PYSICOCHEMICAL PROPERTIES OF THIAMINIC ACIDS

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The physicochemical properties of thiaminic acid (TnA) and O-benzoylthiaminic acid (BTnA) were investigated and the following results were obtained.1. Each monohydrate crystal is relatively stable in drying in vacuo but by refluxing with ethanol, it is converted into anhydride.2. Ultraviolet absorption spectra are similar to those of thiamine disulfide and O-benzoylthiamine disulfide, respectively. The spectra vary according to pH, owing to the resonance in the pyrimidine ring. Each compound has isosbestic point at about 273mμ.3. Each compound is hardly soluble in organic solvents. Thiaminic acid is readily soluble in water, while BTnA is a little soluble at pH above the isoelectric point. However, it is hardly soluble in lower pH levels.4. Both of them are almost negative to the Dragendorff reagent and also negative for thiochrome reaction even after treatment with cysteine or thiosulfate. On paper chromatogram they can be detected by tert-butyl hypochlorite method as a violet spot. The Rf values of TnA and BTnA with n-butanol-acetic acid-water are 0.25 and 0.54, respectively. These values are a little higher than the corresponding compounds, thiamine (0.17) or O-benzoylthiamine (0.5).5. By paper electrophoresis, thiamine and O-benzoylthiamine migrate toward the cathode at pH 1.0-8.0, as a cationic form, while TnA and BTnA migrate toward the cathode at pH 1, do not move at pH 3.0-5.0, and toward the anode at pH sending its amphoteric character.6. From the pontentiometric titration curve, the apparent dissociation index was determined at 25±1°. pK1 (-SO3H) was 2.2 (TnA) and 2.3 (BTnA), and pK2 (-NH3+) was 6.2 (TnA) and 6.1 (BTnA). The isoelectric points are both at pH 4.2.7. By HCl-hydrolysis of TnA, formic acid and 2-methyl-4-amino-5-aminomethyl-pyrimidine were formed, whereas in the case of BTnA, benzoic acid was additionally formed.
日本ビタミン学会の論文

PYSICOCHEMICAL PROPERTIES OF THIAMINIC ACIDS

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