Abstract
Diffraction data were taken from the contribution named 'β-dl-Me-thio-nine at 105 K' by Alagar et al. [Acta Cryst. (2005 ▶). E61, o1165-o1167]. Refinement of the coordinates of the three amino H atoms, previously constrained to an idealized geometry, shows that the amino group is in fact rotated 13.5° from the perfectly staggered orientation. This apparently modest change has a profound impact on the calculated hydrogen-bond geometries.
Highlights
Redetermined structure of b-DL-methionine at 105 K: an example of the importance of freely refining the positions of the amino-group H atoms
Refinement of the coordinates of the three amino H atoms, previously constrained to an idealized geometry, shows that the amino group is rotated 13.5 from the perfectly staggered orientation
Upon comparing the hydrogen-bond geometries of the hightemperature -phase of the amino acid racemate dl-methionine (Gorbitz et al, 2014) with the best published structure of the -phase [Alagar et al, 2005; refcode DLMETA05 in the Cambridge Structural Database (CSD), Version 5.35; Allen, 2002], we noted that HÁ Á ÁO distances surprisingly appeared to get shorter at 340 K than at 105 K
Summary
Diffraction data were taken from the contribution named ‘ -dl-Methionine at 105 K0 by Alagar et al [Acta Cryst. (2005). Upon comparing the hydrogen-bond geometries of the hightemperature -phase of the amino acid racemate dl-methionine (Gorbitz et al, 2014) with the best published structure of the -phase [Alagar et al, 2005; refcode DLMETA05 in the Cambridge Structural Database (CSD), Version 5.35; Allen, 2002], we noted that HÁ Á ÁO distances surprisingly appeared to get shorter at 340 K than at 105 K. This was judged to be an artefact resulting from different ways of handling the amino H atoms. C5H11NO2S 149.21 Monoclinic, I2/a 105 9.877 (2), 4.6915 (10), 32.603 (6) 106.25 (1) 1450.4 (5) 8 Mo K 0.38 0.32 Â 0.24 Â 0.22
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