Orchestrated approaches using pure shift NMR: Extraction of spectral parameters, ultra‐high resolution, and sensitivity enhancement

Abstract

The limited chemical shift range of protons and pairwise interaction among all the abundant nuclear spins of a molecule makes H spectrum too complicated. As a consequence, the straightforward analysis and the accurate extraction of their interaction strengths from the H spectrum of a complex spin system are formidably difficult or often impossible. This problem persists in the determination of scalar couplings be it between two abundant homonuclear spins or between H and an abundant heteronuclear spin (viz., F and P). Such problems are encountered in many situations where the determination of homonuclear and heteronuclear couplings is challenging. The several pure shift based one-dimensional and two-dimensional NMR strategies recently developed in our laboratory for the straightforward extraction of homonuclear and heteronuclear interaction parameters in diverse situations are discussed. Initially, the unique application of pure shift technique that paves the way for easy and straightforward extraction of magnitudes of heteronuclear couplings, namely, J (where X stands for F, P, etc.), is discussed. Subsequently, several pure shift edited one-dimensional and two-dimensional NMR strategies that are developed for the direct extraction of homonuclear and heteronuclear couplings and for achieving ultra-high-resolved H spectra with complete eradication of zero frequency peaks and the evolution of unwanted couplings. The enhancement in the sensitivity has also been achieved in the slice-selective pure shift experiments by the rapid acquisition of proton spectrum where the polarization from the adjacent protons is transferred to the selectively excited proton.

Combining pure shift and J‐edited spectroscopies: A strategy for extracting chemical shifts and scalar couplings from highly crowded proton spectra of oligomeric saccharides

“…The combination of pure shift and J ‐edited spectroscopies proposes a unique way to perform a systematic—though site specific—and fully resolved analysis of 1 H– 1 H scalar coupling networks in highly crowded spectra and also constitutes a supplementary—though not redundant—way to assign correlations, compared with the well‐established protocols that are routinely implemented for such purpose. We also note that several improvements of the pulse sequences implemented in this work have been introduced over the last years, either based on a spatial frequency encoding or a PSYCHE method . The resolution and/or sensitivity enhancements that are provided by these recent experiments will contribute to increase the robustness of this approach.…”

“…As a result, only a limited number of multidimensional spectra can provide to date the combined benefit of the high resolution offered by broadband homonuclear decoupling and the invaluable added value of correlation spectroscopy . On the other hand, it has been shown that it is also possible to generate J ‐edited spectra allowing for a straightforward assignment and measurement, within a single acquisition, of the whole scalar coupling network involved around a selected proton site . Among the different approaches explored to provide chemists with a simplified analytical content, strategies on the basis of a spatial frequency encoding of the sample proved to be particularly robust and flexible, despite their intrinsic lower sensitivity …”

Monitoring Conformational Changes in an Enzyme Conversion Inhibitor Using Pure Shift Exchange NMR Spectroscopy

“…Finally, we note that different improvements can be made as regards implementation of pure shift methods in EXSY experiments. On the one hand, a number of interesting developments based either on the PSYCHE or the Zangger‐Sterk method have been introduced recently to remove artefacts from pure shift data, and notably overcome the general issue of strongly coupled protons . The SAPPHIRE method has notably been shown to lead to a significant improvement of the quality of pure shift spectra by averaging to zero artefacts that arise from residual J evolutions.…”

“…On the one hand, a number of interesting developments based either on the PSYCHE or the Zangger-Sterk method have been introduced recently to remove artefacts from pure shift data, and notably overcome the general issue of strongly coupled protons. [37][38][39][40][41][42] The SAPPHIRE method [43] has notably been shown to lead to a significant improvement of the quality of pure shift spectra by averaging to zero artefacts that arise from residual J evolutions. It should be noted however that this latter method is time consuming because several scans should be acquired for each data point in order to perform the averaging process.…”

G‐SERF Editing in Two‐Dimensional Pure‐Shift Total Correlation Spectroscopy: Scalar Coupling Measurements for a Group of Spins in Organic Molecules

“…At the same time, it only facilitates scalar coupling measurements for one particular spin at a time. Another experiment, which utilizes COSY type of spin‐filtration to remove the axial peaks, and incorporates homodecoupling (PS‐Clean‐G‐SERF) has also been developed.…”