Application of viscosity-enhanced NMR spectroscopy to complex mixtures such as essential oils

Complex mixture investigations by liquid-NMR is a subject as old as NMR itself and for which only a few solutions have been developed, such as LC-NMR hyphenation, diffusion-ordered spectroscopy (DOSY), multi-quantum spectroscopy combined with broadband homonuclear decoupling, sparse sampling, ultrafast data acquisition, multiple selective excitation, or tensor decomposition methods. The recent use of viscous solvents has provided a promising approach called ViscY (Viscosity-enhanced spectroscopY) to investigate complex mixtures by slowing down the tumbling rate of mixed analytes [1] [2] [3]. As a result, the molecules present a negative NOE regime, and their resonances can be grouped in relation to their capability to exchange magnetisation through intramolecular spin diffusion. The 2D ¹H NOESY spectrum of a complex mixture shows correlations between all ¹H resonances of each compound when recorded in spin diffusion conditions, thus giving access to the individual ¹H NMR spectra of the mixture components. In this context, we applied 1D & 2D ViscY NMR experiments (1D, 2D ¹H NOESY, 2D ¹H-¹³C-HSQC-NOESY, ¹H/¹³C NOAH BSCN) to complex mixtures such as essential oils: Vanilla, Lemon, Cumin, Niaouli and Lemon Eucalyptus, by considering viscous chlorotrifluoroethylene polymer. We assessed information gain compared to the usual non-viscous solvent CDCl₃ regarding the number of chemical shifts, NOEs and structures elucidated.

 

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• References

• 1 Pedinielli F., Nuzillard J.-M., Lameiras P. Anal. Chem. 2020; 92 (07) 5191-5199
• 2 Pedinielli F., Leroy R., Martinez A., Nuzillard J.M., Lameiras P.. Analyst. 2021; 146: 5316-5325
• 3 Leroy R., Pedinielli F., Bourbon G., Nuzillard J.-M., Lameiras P.. Anal. Chem. 2022; 94 (26) 9278-9286

Publication History

Article published online:
16 November 2023