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.