Critical Evaluation of Enthalpies of Formation and Phase Transitions of Amino Acids with a New Approach Based on Solution Calorimetry, Quantum Cluster Growth, COSMO-RS, and PC-SAFT

The determination of thermochemical data for amino acids has always been a challenging endeavor for the scientific community. Due to the very low vapor pressure at room temperature and thermal decomposition at higher temperatures, enthalpies of sublimation and fusion, in particular, are difficult to measure. Existing enthalpy data have been evaluated to determine which values can be considered reliable. Furthermore, recommendations are provided regarding which data should be remeasured. For this purpose, thermodynamic consistency between the standard enthalpies of formation and the phase transition enthalpies, group additivity, and a new method based on solution calorimetry, PC-SAFT, quantum cluster growth, and COSMO-RS were used. It was shown that the thermodynamic data for the amino acids Glycine, l -Alanine, l -Threonine, l -Serine, and l -Tyrosine can be assumed reliable within chemical accuracy of 4 kJ·mol –1, but new measurements are required for all other amino acids. The results of this work provide the basis for future experimental work to develop a valid data set of the thermodynamic properties of amino acids. This data set can then be used in other disciplines to investigate the behavior of amino acids in the environment, technology, and living organisms.