Štěpánek Petr, Coriani Sonia, Sundholm Dage, Ovchinnikov Vasily A, Vaara Juha
NMR Research Unit, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland.
Institute of Organic Chemistry and Biochemistry, AS CR, Flemingovo nam. 2, 166 10 Prague, Czech Republic.
Sci Rep. 2017 Apr 24;7:46617. doi: 10.1038/srep46617.
The recently theoretically described nuclear spin-induced circular dichroism (NSCD) is a promising method for the optical detection of nuclear magnetization. NSCD involves both optical excitations of the molecule and hyperfine interactions and, thus, it offers a means to realize a spectroscopy with spatially localized, high-resolution information. To survey the factors relating the molecular and electronic structure to the NSCD signal, we theoretically investigate NSCD of twenty structures of the four most common nucleic acid bases (adenine, guanine, thymine, cytosine). The NSCD signal correlates with the spatial distribution of the excited states and couplings between them, reflecting changes in molecular structure and conformation. This constitutes a marked difference to the nuclear magnetic resonance (NMR) chemical shift, which only reflects the local molecular structure in the ground electronic state. The calculated NSCD spectra are rationalized by means of changes in the electronic density and by a sum-over-states approach, which allows to identify the contributions of the individual excited states. Two separate contributions to NSCD are identified and their physical origins and relative magnitudes are discussed. The results underline NSCD spectroscopy as a plausible tool with a power for the identification of not only different molecules, but their specific structures as well.
最近在理论上描述的核自旋诱导圆二色性（NSCD）是一种用于光学检测核磁化强度的很有前景的方法。NSCD涉及分子的光学激发和超精细相互作用，因此，它提供了一种实现具有空间局域化、高分辨率信息的光谱学的手段。为了研究与分子和电子结构相关的因素对NSCD信号的影响，我们从理论上研究了四种最常见核酸碱基（腺嘌呤、鸟嘌呤、胸腺嘧啶、胞嘧啶）的20种结构的NSCD。NSCD信号与激发态的空间分布及其之间的耦合相关，反映了分子结构和构象的变化。这与核磁共振（NMR）化学位移形成了显著差异，后者仅反映基态电子态中的局域分子结构。通过电子密度的变化和态叠加方法对计算得到的NSCD光谱进行了合理化分析，该方法能够确定各个激发态的贡献。确定了对NSCD的两种不同贡献，并讨论了它们的物理起源和相对大小。结果强调了NSCD光谱学是一种合理的工具，不仅具有识别不同分子的能力，还具有识别其特定结构的能力。
