Heat Capacities of l-Arginine, l-Aspartic Acid, l-Glutamic Acid, l-Glutamine, and l-Asparagine

In an effort to establish reliable thermodynamic data for amino acids, heat capacity and phase behavior is reported for l-arginine (CAS RN: 74-79-3), l-aspartic acid (CAS RN: 56-84-8), l-glutamic acid (CAS RN: 56-86-0), l-glutamine (CAS RN: 56-85-9), and l-asparagine (CAS RN: 70-47-3). Prior to heat capacities measurement, thermogravimetric analysis was performed to determine decomposition temperatures. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval (262–358) K and by power compensation DSC in the temperature interval (215–451) K. Experimental values of this work were combined with the literature data obtained with adiabatic calorimetry. Low temperature heat capacities of l-arginine and l-asparagine, for which no or limited literature data were available, were measured using the relaxation (heat pulse) calorimetry. As a result, reference heat capacities and thermodynamic functions for crystalline phase from near 0 K to 450 K were developed.