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Conformational analysis of DL ‐, L ‐ and D ‐methionine by solid‐state 13 C NMR spectroscopy
Author(s) -
Díaz Luis E.,
Morin Frederick,
Mayne Charles L.,
Grant David M.,
Chang Chingjer
Publication year - 1986
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260240213
Subject(s) - chemistry , conformational isomerism , crystallography , nuclear magnetic resonance spectroscopy , nmr spectra database , methionine , spectroscopy , magic angle spinning , solid state nuclear magnetic resonance , crystallization , crystal structure , molecule , analytical chemistry (journal) , spectral line , stereochemistry , amino acid , nuclear magnetic resonance , organic chemistry , biochemistry , physics , quantum mechanics , astronomy
The conformational analysis of DL ‐, L ‐ and D ‐methionine was studied by solid‐state 13 C NMR with the help of cross‐polarization and magic‐angle spinning techniques. The spectrum of commercial crystalline DL ‐methionine showed two chemical shifts (18.7 and 15.8 ppm) for the methyl carbon. Crystallization from water or water‐ethanol (95 : 5) allowed the separation of two crystalline forms (α and β), of which one had δ (CH 3 ) 18.7 ppm and the other δ (CH 3 ) 15.8 ppm. Therefore, each crystalline form of DL ‐methionine consists of a single conformer, a result in agreement with x‐ray diffraction data. This conformational difference of the two crystalline forms was also reflected in the carbon resonances of C‐β and C‐γ. When L ‐ and D ‐methionine were crystallized from water‐ethanol (3 : 2), the solid‐state 13 C NMR spectra showed that each isomer displayed two methyl carbon peaks at 18.1 and 16.2 ppm of equal intensities, while the α‐carbon resonances showed a broad peak due to two unresolved doublets. These results suggest that the L ‐ or D ‐methionine crystal contains two different conformers in one unit cell, a conclusion that is also supported by the x‐ray data.