Journal
CHEMPHYSCHEM
Volume 21, Issue 9, Pages 938-951Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.202000078
Keywords
amino acids; Knudsen effusion; phase transitions; sublimation enthalpies; thermodynamics
Funding
- Ministry of Education, Youth and Sports of the Czech Republic [LTAUSA18011]
- European Social Fund (ESF) [UID/QUI/0081/2020]
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This work presents a new Knudsen effusion apparatus employing continuous monitoring of sample deposition using a quartz-crystal microbalance sensor with internal calibration by gravimetric determination of the sample mass loss. The apparatus was tested with anthracene and 1,3,5-triphenylbenzene and subsequently used for the study of sublimation behavior of several proteinogenic amino acids. Their low volatility and thermal instability strongly limit possibilities of studying their sublimation behavior and available literature data. The results presented in this work are unique in their temperature range and low uncertainty required for benchmarking theoretical studies of sublimation behavior of molecular crystals. The possibility of dimerization in the gas phase that would invalidate the effusion experiments is addressed and disproved by theoretical calculations. The enthalpy of sublimation of each amino acid is analyzed based on the contributions in two hypothetical sublimation paths involving the proton transfer in the solid and in the gas phase.
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