  We report for the first time real time in situ and quantitative measurements
of the mutarotation reaction of lactose in the solid state. The experiments
have been performed by 13C NMR. We show that mutarotation is initiated on
heating the amorphous state, and reaches chemical equilibrium close above the
glass transition temperature Tg. We do not observe this transformation when
starting from stable crystalline states. The final ratio of <alfa> and <beta>
anomers is 1:1, which suggests that the energy profile of the mutarotation
reaction pathway in the solid state is actually different from the mechanism
proposed for aqueous solution. This chemical equipartition is reached before
the crystallization into the corresponding 1:1 molecular compound. These new
data clearly illustrate the interrelation between the chemical molecular
properties, the physical state of the material, and the relaxational dynamics
of the glass.
