Utility of microcalorimetry in the characterization of the browning reaction

An isothermal microcalorimeter was utilized to characterize a model solid-state interaction. The degradation of the HIV protease inhibitor, DMP 450, in a binary mixture with hydrous lactose was followed in the presence of 5% additional water. Heat produced in the microcalorimeter sample vessel from either chemical or physical change is channeled through extremely sensitive thermopile blankets and is measured as it flows into infinite heat sinks. Solid-state 1:1 mixtures of DMP 450 and hydrous lactose each with 5% water added were analyzed in the microcalorimeter at 50, 60 and 65 degrees C. The resulting heat flow profiles were consistent with an autocatalytic rate law. An activation energy of 26.12 kcal mol(-1) for the DMP 450:lactose mixture was determined from the slope of the Arrhenius plot of the microcalorimetry heat flow maximum value versus the reciprocal of the absolute temperature. The activation energy determined by the traditional method with HPLC analysis was found to be in excellent agreement with the microcalorimetry value at 26.38 kcal mol(-1).