Nuclear magnetic resonance decoupling

Résumé

Nuclear magnetic resonance decoupling (NMR decoupling for short) is a special method used in nuclear magnetic resonance (NMR) spectroscopy where a sample to be analyzed is irradiated at a certain frequency or frequency range to eliminate fully or partially the effect of coupling between certain nuclei. NMR coupling refers to the effect of nuclei on each other in atoms within a couple of bonds distance of each other in molecules. This effect causes NMR signals in a spectrum to be split into multiple peaks. Decoupling fully or partially eliminates splitting of the signal between the nuclei irradiated and other nuclei such as the nuclei being analyzed in a certain spectrum. NMR spectroscopy and sometimes decoupling can help determine structures of chemical compounds. Explanation NMR spectroscopy of a sample produces an NMR spectrum, which is essentially a graph of signal intensity on the vertical axis vs. chemical shift for a certain isotope on the horizontal axis. The sign

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https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_decoupling

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vignette|redresse=1.5|alt=specte RMN|spectre RMN H de l'éthanol. La RMN du proton est la spectroscopie RMN du proton (1H), un isotope de l'hydrogène. L'analyse d'un spectre RMN du proton peut se situe

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Fast remote correlation experiments for 1H homonuclear decoupling in solids

David Lyndon Emsley, Pinelopi Moutzouri, Bruno Simões de Almeida

In 1H MAS spectra, the residual homogeneous broadening under MAS is due to a combination of higher-order shifts and splittings. We have recently shown how the two-dimensional anti-z-COSY experiment can be used for the removal of the splittings. However, this requires spectra with high resolution in the indirect dimension (t1), leading to experiment times of hours. Here, we show how anti-z-COSY can be adapted to be combined with the two-dimensional one pulse (TOP) transformation which leads to significantly reduced experimental time while retaining the line narrowing effect. The experiment is demonstrated on a powdered sample of L-histidine monohydrochloride monohydrate, where the new TAZ-COSY sequence at 100 kHz MAS, yields between a factor 1.6 and 2.3 increase in resolution compared with the equivalent one-pulse experiment, in just 20 min. The same methodology is also adapted for the acquisition of liquid state 1H homodecoupled data, and an example is given for testosterone.

2020

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Homonuclear Decoupling in H-1 NMR of Solids by Remote Correlation

David Lyndon Emsley, Pinelopi Moutzouri, Federico Maria Paruzzo, Bruno Simões de Almeida, Gabriele Stevanato

The typical linewidths of H-1 NMR spectra of powdered organic solids at 111 kHz magic-angle spinning (MAS) are of the order of a few hundred Hz. While this is remarkable in comparison to the tens of kHz observed in spectra of static samples, it is still the key limit to the use of H-1 in solid-state NMR, especially for complex systems. Here, we demonstrate a novel strategy to further improve the spectral resolution. We show that the anti-z-COSY experiment can be used to reduce the residual line broadening of H-1 NMR spectra of powdered organic solids. Results obtained with the anti-z-COSY sequence at 100 kHz MAS on thymol, beta-AspAla, and strychnine show an improvement in resolution of up to a factor of two compared to conventional spectra acquired at the same spinning rate.

2020

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Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP

Geoffrey Bodenhausen, Aurélien Bornet, Diego Carnevale, Srinivas Chinthalapalli, Sami Jannin

Complex overlapping multiplets due to scalar couplings (n)J(C-13, C-13) in fully C-13-enriched molecules can be simplified by polychromatic irradiation of selected spins. The signal intensities of the remaining non-irradiated signals are proportional to the concentrations, as shown in this work for the anomeric C-13 signals of the alpha- and beta-conformers of glucose. Homonuclear decoupling can therefore be useful for quantitative NMR studies. The resulting decoupled lineshapes show residual fine structures that have been investigated by means of numerical simulations. Simulations also show that homonuclear decoupling schemes remain effective despite inhomogeneous static fields that tend to hamper in cellulo and in vivo studies. Homonuclear decoupling schemes can be combined with dissolution DNP to obtain signal enhancements of more than four orders of magnitude. Polychromatic irradiation of selected spins does not cause significant losses of hyperpolarization of the remaining non-irradiated spins.

Royal Society of Chemistry2016

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