Trying to answer the intriguing and fundamental question related to chiral induction/amplification at the origin of homochirality in Nature: “Is there a relationship between enantiomeric and isotopic fractionation of carbon 13 in chiral molecules?” is a difficult but stimulating challenge. Although isotropic ¹³C-PSIA NMR is a promising tool for the determination of (¹³C/¹²C) ratios capable of providing key ¹³C isotopic data for understanding the reaction mechanisms of biological processes or artificial transformations, this method does not provide access to any enantiomeric ¹³C isotopic data unless mirror-image isomers are first physically separated. Interestingly, ¹³C spectral enantiodiscriminations can be potentially performed in situ in the presence of enantiopure entities as chiral-europium complexes or chiral liquid crystals (CLCs). In this work, we explored for the first time the capabilities of the anisotropic ¹³C-{¹H} NMR using PBLG-based lyotropic CLCs as enantiodiscriminating media in the context of the enantiomeric position-specific ¹³C isotope fractionation (EPSIF), within the requested precision of the order of the permil. As enantiomeric NMR signals are discriminated on the basis of a difference of ¹³C residual chemical shift anisotropy (¹³C-RCSA) prior to being deconvoluted, analysis of enantiomeric mixtures becomes possible. The analytical potential of this approach when using poly-γ-benzyl-L-glutamate (PBLG) is presented, and the preliminary quantitative results on small model chiral molecules obtained at 17.5 T with a cryogenic NMR probe are reported and discussed.

Graphical abstract

中文翻译：

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探索对映体 13C 位置特定同位素分馏：挑战和基于各向异性核磁共振的分析策略

试图回答与自然界同手性起源处的手性诱导/扩增相关的有趣和基本问题：“手性分子中碳 13 的对映异构和同位素分馏之间是否存在关系？” 是一个困难但刺激的挑战。尽管各向同性¹³ C-PSIA NMR 是确定 ( ¹³ C/ ¹² C) 比率的一种很有前途的工具，能够提供关键的¹³ C 同位素数据以了解生物过程或人工转化的反应机制，但该方法无法提供任何对映异构体¹³ C 同位素数据，除非首先物理分离镜像异构体。有趣的是，¹³C 光谱对映体区分可能在对映体纯实体存在下进行，如手性铕配合物或手性液晶 (CLC)。在这项工作中，我们首次探索了各向异性¹³ C-{ ¹ H} NMR的能力，使用基于 PBLG 的溶致 CLC 作为对映体位置特异性¹³ C 同位素分馏 (EPSIF)背景下的对映体区分介质，在要求的 permil 顺序的精度。由于对映体 NMR 信号是根据¹³ C 残留化学位移各向异性 ( ¹³C-RCSA) 在解卷积之前，对映异构体混合物的分析成为可能。介绍了这种方法在使用聚-γ-苄基-L-谷氨酸 (PBLG)时的分析潜力，并报告和讨论了使用低温 NMR 探针在 17.5 T 下获得的小模型手性分子的初步定量结果。

图形概要