Aviv Hagit, Nemtsov Irena, Mastai Yitzhak, Tischler Yaakov R
Department of Chemistry and Bar-Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University , Ramat Gan 5290002, Israel.
J Phys Chem A. 2017 Oct 19;121(41):7882-7888. doi: 10.1021/acs.jpca.7b07033. Epub 2017 Oct 4.
We present a new method for differentiating racemic crystals from enantiopure crystals. Recently, developments in optical filters have enabled the facile use of Raman spectroscopy to detect low-frequency vibrational (LFV) modes. Here, for the first time, we use Raman spectroscopy to characterize the LFV modes for crystalline organic materials composed of chiral molecules. The LF-Raman spectra of racemic and enantiopure crystals exhibit a significant variation, which we attribute to different hydrogen-bond networks in the chiral crystal structures. Across a representative set of amino acids, we observed that when comparing racemic versus enantiopure crystals, the available LFV modes and their relative scattering intensity are strong functions of side chain polarity. Thus, LF-Raman can be used as a method that is complementary to the currently used methods for characterizing crystal chirality due to simpler, faster, and more sensitive measurements, along with the small sample size required, which is limited by the laser-beam diameter in the focus.
我们提出了一种区分外消旋晶体和对映体纯晶体的新方法。最近，光学滤波器的发展使得拉曼光谱能够轻松用于检测低频振动（LFV）模式。在此，我们首次使用拉曼光谱来表征由手性分子组成的结晶有机材料的LFV模式。外消旋晶体和对映体纯晶体的低频拉曼光谱表现出显著差异，我们将其归因于手性晶体结构中不同的氢键网络。在一组具有代表性的氨基酸中，我们观察到，在比较外消旋晶体和对映体纯晶体时，可用的LFV模式及其相对散射强度是侧链极性的强函数。因此，由于测量更简单、更快、更灵敏，且所需样品量小（受焦点处激光束直径限制），低频拉曼可作为一种与当前用于表征晶体手性的方法互补的方法。
