We report sublimation enthalpies of sulfur-containing amino acids, l- and dl-methionine, investigated by Knudsen's effusion method with mass spectrometric vapor composition control. The fragmentation of molecules under electron ionization (EI) was discussed. For these compounds, the molar sublimation enthalpies were derived from the Clausius-Clapeyron equation. Using the isobaric heat capacities in the crystal phases of the compounds the standard molar enthalpies of sublimation at T = 298.15 K, were obtained. In addition, conformational analysis of methionine (Met) was performed by hybrid DFT and MP2 calculations. Analysis of natural bond orbitals (NBO) carried out for the three low-energetic conformers of Met revealed intramolecular hydrogen bonds in one of these. The average interaction energies between a lone electron pair (donor) of nitrogen and "antibonding" orbital of O-H bond (acceptor) were obtained and used in the interpretation of the structure.
Compounds
#
Formula
Name
1
C5H11NO2S
L-methionine
2
C5H11NO2S
DL-2-amino-4-(methylthio)butanoic acid
3
C7H6O2
benzoic acid
Datasets
The table above is generated from the ThermoML associated json file (link above).
POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied;
the numbers refer to the table of compounds on the left.
Type
Compound-#
Property
Variable
Constraint
Phase
Method
#Points
POMD
1
Molar enthalpy of vaporization or sublimation, kJ/mol ; Crystal
Temperature, K; Crystal
Crystal
Gas
Derived by Second law
1
POMD
2
Molar enthalpy of vaporization or sublimation, kJ/mol ; Crystal
Temperature, K; Crystal
Crystal
Gas
Derived by Second law
1
POMD
2
Molar heat capacity at constant pressure, J/K/mol ; Crystal
Temperature, K; Crystal
Pressure, kPa; Crystal
Crystal
DSC
44
POMD
3
Molar heat capacity at constant pressure, J/K/mol ; Crystal