Journal of Synchrotron Radiation

Volume 12, Part 5 (September 2005)

SXD at Mbar pressures

J. Synchrotron Rad. (2005). 12, 598-607 [ doi:10.1107/S0909049505019850 ]

The effect of pressure on the crystal structure of hexagonal L-cystine

S. A. Moggach, D. R. Allan, S. Parsons, L. Sawyer and J. E. Warren

Abstract: 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 P6₁22. The structure consists of hydrogen-bonded layers which are strongly reminiscent of those seen in [alpha] -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 NHO 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-HO hydrogen bonds by 0.10-0.60 Å and (iii) a further shortening of an already short SS contact from 3.444 (4) Å to 3.264 (4) Å.

Keywords: amino acid; hydrogen bonding; high-pressure single-crystal diffraction.


	Structure factor file (CIF format) (49.7 kbytes) Contains datablock cystin00

	Structure factor file (CIF format) (28.0 kbytes) Contains datablock cystin04

	Structure factor file (CIF format) (26.4 kbytes) Contains datablock cystin14

	Structure factor file (CIF format) (25.3 kbytes) Contains datablock cystin23

	Structure factor file (CIF format) (24.4 kbytes) Contains datablock cystin37

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