Rapid¹H{¹³C}-Resolved Diffusion and Spin-Relaxation Measurements by NMR Spectroscopy

Abstract

Hadamard-encoded heteronuclear-resolved NMR diffusion and relaxation measurements allow overlapping signal decays to be resolved with substantially shorter measuring times than are generally associated with 2D heteronuclear cross-correlation experiments. Overall measuring time requirements can be reduced by approximately an order of magnitude, compared to typical 2D heteronuclear single-quantum correlation-resolved diffusion or relaxation measurements. Specifically, in cases where chemical shift correlation information provides enhanced spectral resolution, the use of Hadamard encoding can be used to overcome uniqueness challenges that are associated with the analysis of concurrent dynamic processes and the extraction of time constants from overlapping exponential signal decays. This leads to substantially improved resolution of similar time constants than can be achieved solely through the use of post-acquisition processing techniques. In the ideal case of complete spectral separation of the signal decays, the usual constraint that time constants must be sufficiently different to resolve by exponential analysis can be circumvented entirely. Hadamard-based pulse sequences have been used to determine 1H[13C]-resolved diffusion coefficients and spin-relaxation time constants for the chemically similar components of an aqueous solution of ethanol, glycerol, and poly(ethylene glycol), and a dye-containing block-copolymer solution, which exhibit significant spectral overlap in their 1H NMR spectra.

Selective oxidation of methanol over supported vanadium oxide catalysts as studied by solid-state NMR spectroscopy

“…The signal at 53 ppm is due to the physisorbed methanol [20], which can be easily removed by vacuum pumping. The resonance at 69 ppm is likely due to the ethylene glycol (HOCH 2 CH 2 OH) [47], and the signal at 97 ppm arises from the methylene of dimethoxymethane (DMM) [48]. The appearance of the new signal at 162 ppm (due to formic acid) [49] and a small signal at 90 ppm (due to paraformaldehyde) [20] indicates that methanol has been further oxidized as the temperature is elevated to 423 K. When the reaction temperature further increases, the intensity of the 162 and 97 ppm decreases, indicating that high temperature does not favor the formation of formic acid and DMM.…”

Solid-state Hadamard NMR spectroscopy: Simultaneous measurements of multiple selective homonuclear scalar couplings

“…. The smart NMR spectral-tailoring approach has been successfully incorporated into various other experimental schemes, for example, excitation sculpting [33], DOSY [34,35], multi voxel/slice-selective imaging [36,37], single-scan TOCSY [38], and also applied to quantum computations [39,40]. As shown below, we have extended this approach for Hadamard encoded multiplex refocusing in the solid-state.…”

Disentangling diffusion information of individual components in a mixture with a 3D COMPACT‐IDOSY NMR experiment

“…Proton 3D DOSY experiments suffer from signal overlap although carbon 3D DOSY experiments offer better resolution but suffer from poor signal‐to‐noise ratios and very long experimental times . Several variants of the 3D DOSY technique have been suggested to overcome the limitation of long experimental times, such as internally encoded (I‐DOSY) schemes, spectral aliasing in the indirect dimension, and Hadamard‐encoded diffusion measurements . In I‐DOSY experiments, the diffusion encoding gradients are intertwined with the main 2D correlation pulse sequence, leading to a substantial reduction in experimental time.…”

“…[12][13][14][15][16][17][18] Several variants of the 3D DOSY technique have been suggested to overcome the limitation of long experimental times, such as internally encoded (I-DOSY) schemes, [19][20][21][22] spectral aliasing in the indirect dimension, [23] and Hadamard-encoded diffusion measurements. [24,25] In I-DOSY experiments, the diffusion encoding gradients are intertwined with the main 2D correlation pulse sequence, leading to a substantial reduction in experimental time. Although I-DOSY schemes have the advantage of taking less time, they have the limitation that the diffusion-encoding gradient pulses need to be fitted into the polarization transfer intervals.…”