Deuterium NMR of Liquid-crystalline Samples at Natural Abundance

Lesot, Philippe

doi:10.1002/9780470034590.emrstm1318

Cited by 14 publications

(30 citation statements)

References 60 publications

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“…First, it gives access to new anisotropic NMR interactions, as the 2 H quadrupolar interaction ( I = 1) generates a better spectral distribution of 2 H resonances, and these are predisposed to minimize excessive peak overlaps on 1D‐NMR spectra. Second, the analysis of complex 2 H 1D spectra can be simplified by recording specific 2 H 2D‐NMR experiments …”

Section: Anisotropic 2h 2d‐nmr Psiamentioning

confidence: 99%

“…Second, the analysis of complex 2 H 1D spectra can be simplified by recording specific 2 H 2D-NMR experiments. 18,26 Theoretically, the anisotropic 2 H-{ 1 H} NMR spectra of solutes are dominated by two NMR observables: the anisotropic 2 H chemical shifts, d D aniso , and the 2 H residual quadrupolar couplings (RQCs). 15,23 In practice, each non-equivalent 2 H site gives rise to quadrupolar doublets (QDs) centred on d D aniso ; 16,18 the splitting between components, Dm Q , is equal (in Hz) to:…”

Section: Molecular Order and 2 H Nmr Consequencesmentioning

confidence: 99%

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Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin

Texier–Bonniot

Berdagué

Robins

et al. 2018

Flavour & Fragrance J

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The evaluation of intramolecular 2H or 13C isotopic composition of vanillin by liquid‐state nuclear magnetic resonance (NMR) is an illustrative example of the analytical challenges associated with molecular authenticity/traceability investigations in food products, and the determination/understanding of metabolic/synthetic pathways. Although isotopic ratio monitoring by 13C NMR (irm‐13C NMR) provides a valuable new source of isotopic information, the analysis of position‐specific (2H/1H) isotopic fractionation of vanillin remains incomplete because of the overlap of two aromatic 2H resonances, and the impossibility of separating these fortuitous isochronous nuclei by isotropic NMR. Exploiting the analytical potential of 2H 2D‐NMR in media containing polypeptide‐based liquid crystals, we show that all aromatic monodeuterated isotopomers can be spectrally discriminated on the basis of 2H residual quadrupolar couplings, ΔνQ(2H), thus enabling the determination of their relative proportions for the first time. After discussing the multiple relevant cofactors leading to the best discrimination and optimization of experimental conditions for reliable quantitative measurements by anisotropic 2D‐NMR, a comparative analysis of six vanillin samples from diverse origins is reported. How the 2H distribution might relate to the biosynthesis of vanillin is discussed.

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Section: Anisotropic 2h 2d‐nmr Psiamentioning

confidence: 99%

Section: Molecular Order and 2 H Nmr Consequencesmentioning

confidence: 99%

Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin

Texier–Bonniot

Berdagué

Robins

et al. 2018

Flavour & Fragrance J

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“…Indirect covariance has been applied to 31 P{ 27 Al} MQ‐HETCOR experiments on crystalline aluminophosphates . For aligned solutes, covariance has been successfully applied for processing 2 H autocorrelation symmetrical 2D spectra of isotopically unmodified organic solutes aligned in a polypeptide chiral liquid crystals, and 15 N homonuclear 1Q–1Q correlation 2D spectrum of proteins aligned in macrodiscs . Nevertheless, as explained above, covariance processing only allows the reconstruction of spectra with specific symmetries, such as the homonuclear 2D spectra.…”

Section: Sparse Samplingmentioning

confidence: 99%

Fast acquisition of multidimensional NMR spectra of solids and mesophases using alternative sampling methods

Lesot

Kazimierczuk

Trébosc

et al. 2015

Magnetic Reson in Chemistry

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Unique information about the atom-level structure and dynamics of solids and mesophases can be obtained by the use of multidimensional nuclear magnetic resonance (NMR) experiments. Nevertheless, the acquisition of these experiments often requires long acquisition times. We review here alternative sampling methods, which have been proposed to circumvent this issue in the case of solids and mesophases. Compared to the spectra of solutions, those of solids and mesophases present some specificities because they usually display lower signal-to-noise ratios, non-Lorentzian line shapes, lower spectral resolutions and wider spectral widths. We highlight herein the advantages and limitations of these alternative sampling methods. A first route to accelerate the acquisition time of multidimensional NMR spectra consists in the use of sparse sampling schemes, such as truncated, radial or random sampling ones. These sparsely sampled datasets are generally processed by reconstruction methods differing from the Discrete Fourier Transform (DFT). A host of non-DFT methods have been applied for solids and mesophases, including the G-matrix Fourier transform, the linear least-square procedures, the covariance transform, the maximum entropy and the compressed sensing. A second class of alternative sampling consists in departing from the Jeener paradigm for multidimensional NMR experiments. These non-Jeener methods include Hadamard spectroscopy as well as spatial or orientational encoding of the evolution frequencies. The increasing number of high field NMR magnets and the development of techniques to enhance NMR sensitivity will contribute to widen the use of these alternative sampling methods for the study of solids and mesophases in the coming years.

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“…Solutes dissolved in such liquids exhibit high‐resolution NMR spectra with features resulting from isotropic interactions, as well as residual anisotropic terms in the Hamiltonian . The latter include the anisotropic chemical shift, anisotropic scalar coupling, dipolar coupling and for I ≥ 1 also quadrupolar interaction . Although the degree of the solutes' alignment in these solvents is rather small, the extent of the anisotropic interaction is often large enough to render the effect of these anisotropic interactions conveniently measurable.…”

Section: Introductionmentioning

confidence: 99%

“…[14] The latter include the anisotropic chemical shift, anisotropic scalar coupling, dipolar coupling and for I ≥ 1 also quadrupolar interaction. [15][16][17] Although the degree of the solutes' alignment in these solvents is rather small, the extent of the anisotropic interaction is often large enough to render the effect of these anisotropic interactions conveniently measurable. More important is the fact that the ordering of solutes in such solvents may be strongly enantioselective, that is, different enantiomers acquire different degrees of ordering.…”

Section: Introductionmentioning

confidence: 99%

NMR discrimination in nonrigid prochiral solutes dissolved in chiral liquid crystals: symmetry considerations

Lesot

Luz

Aroulanda

et al. 2014

Magnetic Reson in Chemistry

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Enantiodiscrimination in the NMR spectra of flexible prochiral solutes dissolved in chiral liquid crystals (CLCs) is reviewed and compared with the analog phenomenon in such rigid solutes. In rigid prochiral solutes, the discrimination is brought about by the cancellation of improper symmetry elements upon dissolving in CLC within the frame of solute-solvent ordering mechanisms. If this reduction in symmetry renders the ordering of enantiotopic sites dissimilar, spectral discrimination may be observed. Symmetry considerations indicate that this is only possible for improper nonaxial groups lacking inversion symmetry. Nonrigid prochiral solutes consist of rapidly (on the NMR timescale) interconverting enantiomers, in which the racemization is accompanied by exchange of nonequivalent sites. These sites become, on the average, enantiotopically related, and in CLC, they exhibit spectral discrimination. The mechanism of the effect and the symmetry selection rules are different for the two cases. Specifically, the discrimination in flexible prochiral compounds results from the different ordering of the interchanging enantiomers in CLC. Using Altman's definition of average symmetry (Proc. R. Soc. A, 1967, 298, 184), selection rules for the phenomenon are derived. It follows that chiral discrimination in nonrigid prochiral solutes is much more abundant and can occur in all symmetry types except those possessing inversion. In particular, contrary to earlier thoughts, the effect can occur in compounds with axial symmetry. Illustrative examples of such studies with particular emphasis on compounds with average axial symmetry of the type D(3h), C(3v) and C(3h) are reviewed in this contribution.

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Deuterium NMR of Liquid-crystalline Samples at Natural Abundance

Cited by 14 publications

References 60 publications

Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin

Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin

Fast acquisition of multidimensional NMR spectra of solids and mesophases using alternative sampling methods

NMR discrimination in nonrigid prochiral solutes dissolved in chiral liquid crystals: symmetry considerations

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Deuterium NMR of Liquid-crystalline Samples at Natural Abundance

Cited by 14 publications

References 60 publications

Analytical contribution of deuterium 2D‐NMR in oriented media to 2H/1H isotopic characterization: the case of vanillin

Analytical contribution of deuterium 2D‐NMR in oriented media to 2H/1H isotopic characterization: the case of vanillin

Fast acquisition of multidimensional NMR spectra of solids and mesophases using alternative sampling methods

NMR discrimination in nonrigid prochiral solutes dissolved in chiral liquid crystals: symmetry considerations

Contact Info

Product

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Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin

Analytical contribution of deuterium 2D‐NMR in oriented media to ²H/¹H isotopic characterization: the case of vanillin