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

Abstract

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.

Molecular enantiodiscrimination by NMR spectroscopy in chiral oriented systems: Concept, tools, and applications

“…Besides to reduce the experimental time (T exp ) of ANAD QUOSY nD experiments that required a large number of scans for each t 1 transient, a new type of data acquisition in the direction dimension t 1 as the nonuniform sampling (NUS) approaches combined with an adapted reconstruction such as the covariance (Cov) method or compressed sensing (CS) processing can be applied. [47][48][49] F I G U R E 5 Schematic description of homonuclear and heteronuclear 2 H-QUOSY 2D/3D experiments: (A) echotype schemes (Q-resolved sequences and δ-resolved), (B) COSY-type scheme (Q-COSY), (C) double quantumtype scheme (Q-DQ), (D) Heteronuclear HETCORtype sequence (CDCOM or NASDAC or 2D Refocussed-NASDAC), and (E) homonuclear 3D-type sequence (3D Q-DQ). Figure adapted from reference 23 with permission…”

“…To experimentally fight the inherent low sensibility of ANAD 2D NMR, the use of higher magnetic fields (> 9.4 T) and selective 2 H probes (standard probe or better, a cryogenic probe 46 ) is a simple way to increase the sensitivity of NAD 1D/2D experiments. Besides to reduce the experimental time ( T exp ) of ANAD QUOSY nD experiments that required a large number of scans for each t 1 transient, a new type of data acquisition in the direction dimension t 1 as the nonuniform sampling (NUS) approaches combined with an adapted reconstruction such as the covariance (Cov) method or compressed sensing (CS) processing can be applied 47–49 …”

Recent developments in MAS DNP-NMR of materials

“…The sensitivity of the NMR detection has been significantly increased by the introduction of Fourier Transform NMR spectroscopy [7]. More recently, the sensitivity per spin of NMR detection for solids has also been increased using techniques, such as Magic-Angle Spinning (MAS) NMR probes with cryogenic detection systems, also termed cryoprobe [8], microcoils [9] and non-uniform sampling of the indirect dimensions of multidimensional NMR experiments [10].…”

Multinuclear NMR in polypeptide liquid crystals: Three fertile decades of methodological developments and analytical challenges

“…36a,b, respectively. In short, the analysis of these results has shown that: i) the combination of NUS-Cov allows spectral resolution to be enhanced and measurement time to be reduced by a factor of 4 with respect to US-FT and by a factor of 2 with respect to US-Cov techniques [256]; ii) for the NUS-CS schedule, it was shown that the highest spectral fidelity is obtained for T S ≈ 0.5-0.6 × T 2 * in the case of exponentially decaying NUS [257], and this sampling scheme enhances the sensitivity and resolution of anisotropic NAD 2D-NMR experiments compared to US-FT classical combination [258]. [256] and [257], with permission.…”

“…The acquisition of multidimensional NMR spectra of solutes in isotropic samples can be accelerated by various strategies. Among them, we can include for instance: i) the enhancement of the population difference across the excited transition using high magnetic field, DNP [250], low and ultralow temperatures [251] ; or polarization transfer methods [9,10,15]; ii) the use of more sensitive detection schemes through the indirect detection of abundant nuclei ( 1 H, 19 F); iii) the minimization of the recycling delay (T R ), by using band-selective 1 H or 13 on spectral resolution and sensitivity was examined [256,257,258].…”