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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Weak Hydrogen Bonds Formed by Thiol Groups in N-Acetyl-L-Cysteine and Their Response to the Crystal Structure Distortion on Increasing Pressure
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Weak Hydrogen Bonds Formed by Thiol Groups in N-Acetyl-L-Cysteine and Their Response to the Crystal Structure Distortion on Increasing Pressure

机译：N-乙酰基-L-半胱氨酸中硫醇基形成的弱氢键及其对压力升高时晶体结构变形的响应

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The effect of hydrostatic pressure on single crystals of N-acetyl-L-cysteine was followed at multiple pressure points from 10~4 to 6.2 GPa with a pressure step of 0.2-03 GPa by Raman spectroscopy and X-ray diffraction. Since in the crystals of N-acetyl-L-cysteine the thiol group is involved in intermolecular hydrogen bonds not as a donor only (bonds S—H---O) but also as an acceptor (bonds N—H---S), increasing the pressure does not result in phase transitions. This makes a contrast with the polymorphs of l-and DL-cysteine, in which multiple phase transitions are observed already at relatively low hydrostatic pressures and are related to the changes in the conformation of the thiol side chains only weakly bound to the neighboring molecules in the structure and thus easily switching over the weak S—H—O and S-H---S hydrogen bonds. No phase transitions occur in N-acetyl-L-cysteine with increasing pressure, and changes in cell parameters and volume vs pressure do not reveal any peculiar features. Nevertheless, a more detailed analysis of the changes in intermolecular distances, in particular, of the geometric parameters of the hydrogen bonds based on X-ray single crystal dim-action analysis, complemented by an equally detailed study of the positions of all the significant bands in Raman spectra, allowed us to study the fine details of subtle changes in the hydrogen bond network. Thus, as pressure increases, a continuous shift of the hydrogen atom of the thiol group from one acceptor (a carboxyl group) to another acceptor (a carbonyl group) is observed. Precise single-crystal X-ray diffraction and polarized Raman spectroscopy structural data reveal the formation of a bifurcated S—H—O hydrogen bond with increasing pressure starting with ~ 1.5 GPa. The analysis of the vibrational bands in Raman spectra has shown that different donor and acceptor groups start "feeling" the formation of the bifurcated S—H---0 hydrogen bond in different pressure ranges. The results are discussed in relation to some of the previously published data on the effect of high pressure on the polymorphs of L-cysteine, DL-cysteine, and glutathione, that show similarity with the effects reported here for N-acetyl-i.-cysteine. The results obtained in this work allow one to suggest new models for the pressure-induced structural rearrangements in the whole family of cysteine-containing crystals.
机译：通过拉曼光谱和X射线衍射，在10〜4至6.2 GPa的多个压力点，以0.2-03 GPa的压力阶跃跟踪静水压力对N-乙酰基-L-半胱氨酸单晶的影响。由于在N-乙酰基-L-半胱氨酸的晶体中，硫醇基团不仅作为供体（键SH --- O）参与分子间氢键，而且还作为受体（键NH --- S）参与分子间氢键。 ），增加压力不会导致相变。这与L-和DL-半胱氨酸的多晶型形成对比，在L-和DL-半胱氨酸的多晶型中，已经在相对较低的静水压力下观察到了多个相变，并且与硫醇侧链构象的变化仅弱结合到与之相邻的分子有关。结构，因此很容易切换弱的S-HO和SH--S氢键。随着压力的增加，N-乙酰基-L-半胱氨酸中不会发生相变，并且细胞参数和体积与压力的变化不会显示出任何奇特的特征。然而，基于X射线单晶调光分析，更详细地分析了分子间距离的变化，特别是氢键的几何参数，同时还对所有重要谱带的位置进行了同样详细的研究，在拉曼光谱中，我们可以研究氢键网络中细微变化的细节。因此，随着压力增加，观察到硫醇基团的氢原子从一个受体（羧基）到另一种受体（羰基）的连续移动。精确的单晶X射线衍射和偏振拉曼光谱结构数据显示，从〜1.5 GPa开始，随着压力增加，分叉的S-H-O氢键形成。拉曼光谱中振动带的分析表明，不同的供体和受体基团开始“感觉”在不同压力范围内分叉的SH--0氢键的形成。讨论了有关高压对L-半胱氨酸，DL-半胱氨酸和谷胱甘肽多晶型物影响的一些先前公开数据的结果，这些结果与此处报道的N-乙酰基-i.-相似。半胱氨酸。这项工作中获得的结果使人们可以提出一种新的模型，用于对整个含半胱氨酸晶体家族进行压力诱导的结构重排。

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