Circular Dichroism of Crystals

每种手性有机晶体都具有固有的光学活性。有机晶体的旋光活性的符号和大小应该反映分子结构以及堆积排列，因为分子的自由度在晶格中受到严格限制，这与分子在溶液中的高迁移率非常不同。然而，有机晶体的旋光性几乎没有被测量过，因此直到现在才与晶体结构相关联。其原因是，由于双折射率是回转张量的10^3倍，因此测量晶体的旋光性非常困难，因此在这种情况下，后者的影响被掩盖了。几年前，我们首次在化学中引入了高精度通用旋光仪（HAUP）。最近，我们制备了一种新的HAUP，用于测量晶体的圆二色性光谱。本文采用HAUP法测定了色胺与对氯苯甲酸形成的螺旋型共晶的旋光度。经过反复试验，我们用软质Fe_2O_3抛光剂解决了样品抛光问题，得到了满意的色胺-对氯苯甲酸共晶的旋光度。结果表明，螺旋排列的芳香族π电子以及晶体中的螺旋离子和氢键网络有助于这些旋转幅度的增强。这是首次对由两种不同的非手性分子形成的有机-有机共晶的旋光性进行测量。

Every chiral organic crystal has inherent optical activity. The sign and the magnitude of the optical activity of an organic crystal should reflect the molecular structure as well as the packing arrangement because the freedom of molecules is severely restricted in the crystal lattice, which is very different from the high mobility of molecules in solution. However, the optical activity of organic crystals has been scarcely measured and therefore never correlated with the crystal structure until the present time. The reason for this is that the measurement of optical activity of a crystal is accompanied with much difficulty due to birefringence being 10^3 times larger birefringence than the gyration tensor, so in this case the latter effect is masked. A few years ago, we first introduced a high accuracy universal polarimeter (HAUP) in chemistry. Recently, we prepared a new version of HAUP in order to measure circular dichroism spectra of crystals. Now the check of performance is in progress.Herein the rotatory powers of helical-type cocrystal formed between tryptamine and 4-chlorobenzoic acid were determined by the HAUP method. After much trial and error, we could overcome the sample polish problem by using soft Fe_2O_3 polish agent and obtain satisfactorily the rotatory powers of the cocrystal from tryptamine and 4-chlorobenzoic acid. The results revealed that the helically arranged aromatic π electrons as well as the helical ionic and hydrogen bond networks in the crystal contributed to the enhancement of the magnitude of these rotations. This is the the first measurement of the optical activity of organic-organic cocrystal formed from two different achiral molecules.