Open AccessThe effect of pressure on the crystal structure of hexagonal l ‐cystine
Author(s) -
Moggach Stephen A.,
Allan David R.,
Parsons Simon,
Sawyer Lindsay,
Warren John E.
Publication year - 2005
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049505019850
Subject(s) - crystallography , hydrogen bond , molecule , cystine , chemistry , crystal structure , hydrogen , hexagonal crystal system , stereochemistry , cysteine , organic chemistry , enzyme
The crystal structure of hexagonal l ‐cystine has been determined at room temperature at pressures between 0.4 and 3.7 GPa; unit‐cell dimensions were measured up to 6.4 GPa. The structure of this phase consists of molecules in their zwitterionic form, and crystallizes in the hexagonal space group P 6 1 22. The structure consists of hydrogen‐bonded layers which are strongly reminiscent of those seen in α‐glycine, and consist of (16) hydrogen‐bonded ring motifs. These layers are connected on one side by the disulfide bridges within the cystine molecules, and on the other by NH⋯O hydrogen bonds to other glycine‐like layers. The most compressible unit‐cell dimension, and the direction of greatest strain in the structure, is along the c ‐axis, and application of pressure pushes the layers closer together. The compression occurs approximately equally in the regions of the interlayer hydrogen bonds and the disulfide bridges; in the latter, changes in the C—S—S—C torsion angles allow the cystine molecules to act like springs. The effects of pressure can be interpreted in terms of closing‐up of voids in the structure, and this leads to (i) a lessening of the N—C—C—O and C—S—S—C torsional angles, (ii) shortening of the N—H⋯O hydrogen bonds by 0.10–0.60 Å and (iii) a further shortening of an already short S⋯S contact from 3.444 (4) Å to 3.264 (4) Å.