Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid‐Crystalline‐Based Medium

Abstract

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self‐assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD3OD, [D6]DMSO, and D2O. The preparation of the OPA‐based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.

Chirality Sensing of N-Heterocycles via 19F NMR

“…Nuclear magnetic resonance (NMR) spectroscopy is a classic method for determining optical purity, which utilizes chiral reagents to generate diastereomeric complexes of distinct spectroscopic signatures through covalent modification or transient intermolecular interactions. − In practice, its widespread adoption in chiral analysis is hampered by the complicated derivatization/purification step, the tedious signal assignments, and the overlap of NMR resonances. These challenges are partially addressed by strategies using chiral oriented solvents, which allow NMR to probe the stereochemical information of a molecule with anisotropic NMR data. − Recently, 19 F NMR-based chemosensing has emerged as a burgeoning subfield in chiral analysis, where the reversible bindings between the 19 F-labeled probe and the target chiral analytes are transduced into simplified 19 F NMR signals of discrete chemical shifts. − As such, enantiomers of different configurations are simultaneously identified, allowing reliable ee determination by ratiometric analysis. This approach has been successfully applied to the chiral differentiation of diverse analytes, including primary amines, alcohols, amides, etc. − N-Heterocyclic compounds are ubiquitously found in natural products and drug molecules, exhibiting a wide spectrum of biological activities .…”

Weak Alignment Liquid Crystal Media from Colloidal Dispersion and Self-assembled Oligopeptide for Anisotropic NMR

“…Very recently, we programmed the hydrophobic tails of oligopeptide amphiphiles instead of de novo design on peptide sequence to construct multiple independent LC media. 45…”

Spatially Resolved Anisotropic Natural Abundance Deuterium 2D-NMR Spectroscopy Using Bimesophasic Lyotropic Chiral Systems

“…In practice, it can be of interest to determine anisotropic data (RCSAs, RDCs, or RQCs or their combination) in more than one ordered solvent to increase the reliability of a structural assignment, − to reduce the number of predetermined structural information or for the purpose of structure refinements ( e.g. , the treatment of conformational flexibility of analytes). − As an alternative to historical, monomesophasic chiral LLCs, it has recently been reported the concept of polymer-based thermoresponsive lyotropic systems which provide two different types of aligning environments at two different temperatures due to a significant molecular reorganization of the polymer (or possibly the phase director) in the NMR sample leading to independent anisotropic data usable for structure elucidation purposes. , …”