The standard enthalpies of formation of l-asparagine and l-α-glutamine

The energies of combustion of l-asparagine and l-α-glutamine were measured in a static bomb adiabatic calorimeter. Corrections were made for the heats due to the ignition of sample and for the nitric acid formation. The derived enthalpies of formation in solid state of asparagine monohydrate, nonhydrated asparagine and glutamine are respectively −1084.1 ± 3.0, −788.1 ± 4.7 and −834.3 ± 4.6 kJ mol−1. The data of enthalpy of formation are compared with the literature values and with estimated values by means of group additivity, using parameters recommended by Domalski and Hearing. The discrepancies between experimental and calculated values are explained by considering the number and strength of intermolecular hydrogen bonds. The dehydration of asparagine monohydrate and the possible melting of the three amino acids were investigated by means of DSC. Glutamine melts without considerable decomposition at about 182 °C, while asparagines decompose during the fusion process (208 °C).