Moggach Stephen A, Allan David R, Parsons Simon, Sawyer Lindsay, Warren John E
School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, UK.
J Synchrotron Radiat. 2005 Sep;12(Pt 5):598-607. doi: 10.1107/S0909049505019850. Epub 2005 Aug 16.
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...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 A and (iii) a further shortening of an already short S...S contact from 3.444 (4) A to 3.264 (4) A.
已在室温下、0.4至3.7吉帕的压力范围内测定了六方L-胱氨酸的晶体结构；在高达6.4吉帕的压力下测量了晶胞尺寸。该相的结构由两性离子形式的分子组成，结晶于六方空间群P6(1)22中。该结构由氢键层组成，这些氢键层与α-甘氨酸中的氢键层极为相似，且由R_4;4(16)氢键环基序组成。这些层在一侧通过胱氨酸分子内的二硫键相连，在另一侧通过NH...O氢键与其他类甘氨酸层相连。晶胞中最易压缩的尺寸以及结构中应变最大的方向沿c轴，施加压力会使各层靠得更近。压缩在层间氢键区域和二硫键区域大致等量发生；在后者中，C-S-S-C扭转角的变化使胱氨酸分子起到弹簧的作用。压力的影响可以从结构中孔隙的闭合角度来解释，这导致：(i) N-C-C-O和C-S-S-C扭转角减小；(ii) N-H...O氢键缩短0.10 - 0.60埃；(iii) 原本就较短的S...S接触进一步从3.444(4)埃缩短至3.264(4)埃。
