The effects of small amounts of enantiomeric impurities on the vibrational modes of polycrystalline L-histidine (His) were examined using high-frequency-accurate terahertz (THz) spectroscopy. Samples of polycrystalline L-His in its monoclinic form (form B) were grown from an ethanol-rich solvent. D-histidine, ranging from 0.05 to 10.0% in content, was added to the L-His/ethanol-rich solution prior to recrystallization. The crystal forms of all recrystallized samples were first confirmed by high-frequency-accurate THz spectra recorded at 70 K and room-temperature powder X-ray diffraction spectra. A detailed analysis of two spectral features (1.54 and 1.80 THz) measured at 10 K showed that the absorption lines had a narrow linewidth, as well as broad spectral components that could be fitted by Gaussian curves corresponding to defects within the crystals. The shifts in peak frequency with varying amounts of D-His additive in the polycrystalline L-His samples were examined in detail. It was observed that the peak frequency shifted to lower frequencies when small amounts of D-histidine were present and then to higher frequencies when relatively large amounts were present. At low concentrations, D-His molecules are thought to act as impurities that disturb the normal mode vibrations of L-His crystals; however, above certain concentrations, D-His contributes to the formation of a DL racemic crystal. Although the effects of small amounts of D-His molecules in L-His crystals were detectable, quantitative determination of trace amounts of impurity was limited by the complex crystallography of L-His, which includes defects and racemic compounds.

中文翻译：

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使用高频精确太赫兹光谱法精确评估L组氨酸B型晶体中少量D组氨酸的作用

使用高频精确太赫兹（THz）光谱检查了少量对映体杂质对多晶L-组氨酸（His）振动模式的影响。从富含乙醇的溶剂中生长单斜晶型（B型）多晶L-His样品。在重结晶之前，将含量范围为0.05至10.0％的D-组氨酸添加到L-His /富含乙醇的溶液中。首先通过70 K记录的高频精确THz光谱和室温粉末X射线衍射光谱确认所有重结晶样品的晶型。对在10 K下测量的两个光谱特征（1.54和1.80 THz）进行的详细分析表明，吸收线的线宽较窄，以及可以由高斯曲线拟合的与晶体内缺陷相对应的广谱分量。详细检查了多晶L-His样品中D-His添加剂含量不同时峰值频率的变化。观察到，当存在少量D-组氨酸时，峰值频率移至较低频率，而当存在相对大量时，移至较高频率。在低浓度下，D-His分子被认为是干扰L-His晶体正常模式振动的杂质。但是，在一定浓度以上，D-His有助于DL外消旋晶体的形成。尽管可以检测到L-His晶体中少量D-His分子的作用，