The effect of pressure on the crystal structure of hexagonal L-cystine.
The effect of pressure on the crystal structure of hexagonal L-cystine.
复制标题
压力对六方L-胱氨酸晶体结构的影响。
DOI：
10.1107/s0909049505019850
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发表时间：
2005
影响因子：
2.5
通讯作者：
John E. Warren
中科院分区：
文献类型：
--
作者：
S. Moggach;David R. Allan;S. Parsons;Lindsay Sawyer;John E. Warren
六方L-胱氨酸的晶体结构已确定在室温下在0.4和3.7 GPa之间的压力，晶胞尺寸测量高达6.4 GPa。该相的结构由两性离子形式的分子组成，并且在六方空间群P6（1）22中结晶。该结构由氢键层组成，这些氢键层强烈地让人联想到在α-甘氨酸中所看到的那些，并且由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桥连接，在另一侧通过NH连接。O氢键到其他甘氨酸类层。最可压缩的晶胞尺寸和结构中最大应变的方向是沿着c轴，并且施加压力将层推得更靠近在一起。压缩发生在层间氢键和二硫桥的区域中大致相等;在后者中，C-S-S-C扭转角的变化允许胱氨酸分子像弹簧一样起作用。压力的作用可以解释为结构中空洞的闭合，这导致（i）N-C-C-O和C-S-S-C扭转角减小，（ii）N-H-O和C-S-S-C扭转角缩短。O氢键由0.10-0.60 A和（iii）进一步缩短已经短的S…S接触从3.444（4）A到3.264（4）A。
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.