HYDROLYSIS OF THIAMINE

The hydrolysis of thiamine has been studied over the range 0.5 < pH < 10.5 in aqueous solution at 25 degrees C using the stopped-flow techni que. When the backward reaction from thiazolium anion to thiamine is f ollowed, two relaxation effects are observed and the evaluation of the relaxation amplitudes allows us to determine seven independent equili brium constants between thiamine, differently protonated pseudo bases and differently protonated thioles. The results are confirmed by the p H-dependence of the relaxation times. The hydrolysis of thiamine proce eds via the same mechanism as observed for other thiazolium salts, whe n the protonation of the pyrimidine ring of thiamine is also taken int o account for all species.