Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan.
J Phys Chem A. 2010 Nov 11;114(44):11928-32. doi: 10.1021/jp107930a.
A series of natural circular dichroism (CD) and absorption spectra for films of α-aliphatic amino acids--such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine, and isoleucine--in the vacuum ultraviolet (VUV) region were observed with the absolute values of optical constants at the undulator-based CD beamline TERAS BL5. Preliminary predictions of some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra were found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain--such as valine, leucine, and isoleucine--exhibit strong negative CD peaks in this energy region. In contrast, the corresponding CD peaks were weak or absent in the spectra of amino acids with straight alkyl groups. Our simple calculation, and the absorption spectra of alkanes, suggest that this difference partly originates from the contribution of the alkyl group. Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed; this is probably caused by the different molecular structures in each state. Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules.
我们在基于波荡器的 TERAS BL5 圆二色性光束线（CD 光束线）上，对真空紫外（VUV）区域中α-脂肪族氨基酸（如丙氨酸、氨基丁酸、正缬氨酸、正亮氨酸、缬氨酸、亮氨酸和异亮氨酸）的薄膜进行了一系列自然圆二色性（CD）和吸收光谱的观测，得到了基于光常数的绝对值。此外，还根据晶体结构的量子化学计算，对一些 CD 光谱进行了初步预测。尽管吸收光谱彼此之间具有相似的特征，但在 CD 光谱之间发现了明显的差异，尤其是在 7-8 eV 区域。在具有支链烷基侧链的脂肪族氨基酸（如缬氨酸、亮氨酸和异亮氨酸）的 CD 光谱中，在该能量区域显示出强烈的负 CD 峰。相比之下，在具有直链烷基的氨基酸的光谱中，相应的 CD 峰较弱或不存在。我们的简单计算和烷烃的吸收光谱表明，这种差异部分源于烷基的贡献。在溶液中和固态下，这些氨基酸的 CD 光谱之间也存在明显的差异；这可能是由于每种状态下分子结构的不同。我们的结果清楚地表明，VUV 区域的 CD 光谱对手性分子的构象非常敏感。
