Single-Crystal NMR for 17O in Alanine Enantiomers

TL;DR

This study combines single-crystal ssNMR, X-ray diffraction, and DFT calculations to analyze 17O nuclei in alanine enantiomers, revealing detailed electronic structures and tensor parameters crucial for understanding molecular chirality.

Contribution

It is the first comprehensive characterization of 17O NMR tensors in alanine enantiomers, integrating experimental and computational methods to advance chirality analysis.

Findings

Eight 17O resonances observed and assigned in alanine crystals

DFT calculations supported experimental assignments and revealed new tensor components

First detailed 17O NMR tensor characterization in amino acid enantiomers

Abstract

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. 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.