Drebushchak Tatiana N, Bizyaev Sergey N, Boldyreva Elena V
Institute of Solid State Chemistry and Mechanochemistry, SB Russian Academy of Sciences, Kutateladze 18, Novosibirsk 128, 630128 Russian Federation.
Acta Crystallogr C. 2008 Jun;64(Pt 6):o313-5. doi: 10.1107/S0108270108012341. Epub 2008 May 14.
In the title compound, 2C3H8NO2S+.C2O4(2-), the oxalate anion occupies an inversion centre and is coordinated to cysteine molecules of different chirality (L and D) via O-H...O and N-H...O hydrogen bonds, the resulting cysteine-oxalate stoichiometry in the crystal structure being 2:1. The oxalate anion is completely deprotonated, whereas cysteine has a positively charged -NH3+ group and a neutral protonated carboxyl group. The structure is built from infinite hydrogen-bonded triple layers, consisting of an oxalate layer in the middle with layers of L- and D-cysteine molecules on either side. The thiol groups are at the external sides of the layers and form S-H...O hydrogen bonds with the carboxyl groups of neighbouring cysteine molecules. An interesting feature of the structure is the occurrence of short S...S contacts between SH groups of molecules in neighbouring layers, which form not S-H...S but S-H...O intermolecular hydrogen bonds. Due to the effects of crystal packing and intermolecular hydrogen-bond formation, the conformation of the cysteine cation in the title structure is different from that calculated theoretically for an individual cation, as well as from those of cysteine zwitterions in crystals of pure cysteine.
在标题化合物2C₃H₈NO₂S⁺·C₂O₄²⁻中，草酸根阴离子占据一个反演中心，并通过O—H…O和N—H…O氢键与不同手性（L和D）的半胱氨酸分子配位，晶体结构中得到的半胱氨酸 - 草酸根化学计量比为2:1。草酸根阴离子完全去质子化，而半胱氨酸有一个带正电荷的—NH₃⁺基团和一个中性的质子化羧基。该结构由无限的氢键连接的三层组成，中间是一个草酸根层，两侧是L - 和D - 半胱氨酸分子层。硫醇基团位于层的外侧，并与相邻半胱氨酸分子的羧基形成S—H…O氢键。该结构的一个有趣特征是相邻层中分子的SH基团之间存在短的S…S接触，它们形成的不是S—H…S而是S—H…O分子间氢键。由于晶体堆积和分子间氢键形成的影响，标题结构中半胱氨酸阳离子的构象与理论计算的单个阳离子的构象不同，也与纯半胱氨酸晶体中半胱氨酸两性离子的构象不同。
