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. Keywords Crystalline phase • Heat capacity •This article is part of the Special Issue in Memory of Professor Talgat Khasanshin.

As a follow-up to our effort to establish reliable thermodynamic data for amino acids, the heat capacity and phase behavior are reported for N-acetyl glycine amide (CAS RN: 2620-63-5), N-acetyl-L-alanine amide (CAS RN: 15962-47-7), N-acetyl-L-valine amide (CAS RN: 37933-88-3), N-acetyl-L-isoleucine amide (CAS RN: 56711-06-9), and N-acetyl-L-leucine amide (CAS RN: 28529-34-2). Prior to heat capacity measurement, thermogravimetric analysis and X-ray powder diffraction were performed to determine decomposition temperatures and initial crystal structures, respectively. The crystal heat capacities of the five N-acetyl amino acid amides were measured by Tian–Calvet calorimetry in the temperature interval (266–350 K), by power compensation DSC in the temperature interval (216–471 K), and by relaxation (heat-pulse) calorimetry in the temperature interval (2–268 K). As a result, reference heat capacities and thermodynamic functions for the crystalline phase from 0 K up to 470 K were developed.