Hydrolysis of thiamine

Abstract

The hydrolysis of thiamine has been studied over the range 0.5 < pH < 10.5 in aqueous solution at 25 °C using the stopped-flow technique. When the backward reaction from thiazolium anion to thiamine is followed, two relaxation effects are observed and the evaluation of the relaxation amplitudes allows us to determine seven independent equilibrium constants between thiamine, differently protonated pseudo bases and differently protonated thioles. The results are confirmed by the pH-dependence of the relaxation times. The hydrolysis of thiamine proceeds via the same mechanism as observed for other thiazolium salts, when the protonation of the pyrimidine ring of thiamine is also taken into account for all species.