Single-Crystal NMR for 17O in Alanine Enantiomers

Single-crystal solid-state nuclear magnetic resonance (ssNMR) spectroscopy, which enables detailed analysis of the electronic structures of crystalline molecules, offers a unique opportunity to investigate molecular chiralityan essential feature with broad implications for understanding the origin and function of life. In this study, we employ single-crystal ssNMR spectroscopy, in combination with X-ray diffraction and density functional theory (DFT) calculations, to examine the electronic structure of 17O nuclei in crystalline forms of alanine enantiomers. Eight magnetically nonequivalent 17O resonances within the unit cell were observed and successfully assigned, and their corresponding NMR tensor parameters were determined. These resonances are comprised of pairs of chemically distinct oxygens in each of four symmetrically related sites. The experimental findings were compared with previous NMR studies as well as with DFT calculations performed in this work. The DFT results not only supported the assignment of crystallographically distinct 17O sites but also revealed previously unobserved antisymmetric components of the chemical shift tensors. This study presents the first comprehensive characterization of 17O NMR tensors in alanine enantiomers and underscores the power of integrating single-crystal ssNMR with X-ray diffraction and DFT calculations to advance our understanding of molecular chirality in amino acids.

单晶固态核磁共振（solid-state nuclear magnetic resonance, ssNMR）技术可实现晶体分子电子结构的精细化解析，为研究分子手性提供了独特契机——分子手性是理解生命起源与功能的核心特征，具有广泛的研究意义。本研究结合单晶固态核磁共振、X射线衍射与密度泛函理论（density functional theory, DFT）计算，对丙氨酸对映体晶体形式中¹⁷O原子核的电子结构展开系统性研究。研究团队在晶胞内观测到8个磁不等价的¹⁷O共振峰并完成精准归属，同时测定了其对应的核磁共振张量参数。这些共振峰对应4个对称相关位点中各一对化学环境存在差异的氧原子。本研究将实验结果与既往核磁共振研究及本次工作中的DFT计算结果进行了对比分析。DFT计算结果不仅佐证了晶体学上互不相同的¹⁷O位点归属，还揭示了此前未被观测到的化学位移张量反对称分量。本研究首次实现了丙氨酸对映体中¹⁷O核磁共振张量的全面表征，并凸显了将单晶固态核磁共振与X射线衍射、DFT计算相结合的研究范式，可深化我们对氨基酸分子手性的认知。