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Persistent URL http://purl.org/net/epubs/work/35149
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Record Id 35149
Title High-pressure polymorphism in L-cysteine: the crystal structures of L-cysteine-III and L-cysteine-IV
Abstract The crystal structure of the orthorhombic phase of l-cysteine (hereafter l-cysteine-I) consists of chains of molecules linked via NH O hydrogen bonds. The chains are linked into a layer by other NH O hydrogen bonds, forming R44 ð16Þ ring motifs. The layers are linked by further NH O and disordered SH S/SH O interactions. The main effects of compression to 1.8 GPa are to contract voids in the middle of the R44 ð16Þ rings and to reduce S S distances from 3.8457 (10) to 3.450 (4) A ° . The latter is at the lower limit for S S distances and we suggest that strain about the S atom is responsible for the formation of a new phase of l-cysteine, lcysteine- III, above 1.8 GPa. The phase transition is accompanied by a change in the NCCS torsion angle from ca 60 to ca 60 and small positional displacements, but with no major changes in the orientations of the molecules. The structure of l-cysteine-III contains similar R-type ring motifs to l-cysteine- I, but there are no S S contacts within 3.6 A ° . l-Cysteine-III was found to be stable to at least 4.2 GPa. On decompression to 1.7 GPa, another single-crystal to single-crystal phase transition formed another previously uncharacterized phase, l-cysteine-IV. This phase is not observed on increasing pressure. The structure consists of two crystallographically independent cysteine molecules in the same conformations as those found in l-cysteine-I and l-cysteine-III. The structure separates into zones with are alternately phase I-like and phase III-like. l-Cysteine-IV can therefore be thought of as an unusual example of an intermediate phase. Further decompression to ambient pressure generates l-cysteine-I.
Organisation CCLRC , ISIS , ISIS-SXD
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Language English (EN)
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Journal Article Acta Crystallogr B 62 (2006): 296-309. doi:10.1107/S0108768105038802 2006