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

DOI: 10.1107/S0909049505019850 DOI Help
PMID: 16120983 PMID Help

Authors: Stephen Moggach (The University of Edinburgh) , Dave Allan (Diamond Light Source) , Simon Parsons (School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , Lindsay Sawyer (School of Biological Sciences and Centre for Science at Extreme Conditions, The University of Edinburgh, U.K.) , John E. Warren (University of Liverpool; Daresbury)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Synchrotron Radiation , VOL 12 , PAGES 598-607

State: Published (Approved)
Published: September 2005

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 P6(1)22. The structure consists of hydrogen-bonded layers which are strongly reminiscent of those seen in alpha-glycine, and consist of R-4(4)(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 center dot center dot center dot 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 center dot center dot center dot O hydrogen bonds by 0.10 - 0.60 angstrom and (iii) a further shortening of an already short S center dot center dot center dot S contact from 3.444 (4) angstrom to 3.264 (4) angstrom.

Journal Keywords: Amino Acid; Hydrogen Bonding; High-Pressure Single-Crystal Diffraction.

Subject Areas: Chemistry

Facility: Daresbury laboratory

Added On: 01/04/2012 13:26

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