Recovering Invisible Signals by Two-Field Nuclear Magnetic Resonance Spectroscopy

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Recovering Invisible Signals by Two-Field Nuclear Magnetic Resonance Spectroscopy, Angew.Chem.Int. Ed.2016, 55, 9886-9889

 

The ability of Nuclear Magnetic Resonance (NMR) to probe the chemical and physical properties of matter at atomic resolution makes it a universal spectroscopic tool for molecular chemistry, material science, structural biology and medicine. The ubiquity of NMR has greatly benefitted from the enhanced resolution and sensitivity offered by high magnetic fields and the introduction of two- and multi-dimensional NMR experiments. Severe line broadening due to micro- to millisecond dynamics (known as “chemical exchange”) occurs in many chemical and biological systems. Such line-broadening effects are often exacerbated at high fields. Hence, chemists and biologists face a dilemma: they must choose between good sensitivity and resolution at high fields, or more favorable line-widths and relaxation rates at lower fields.

 

 

Magnetic-field dependent properties can be probed by a broad range of NMR techniques that explore two or more fields in a single experiment, as in fast field-cycling relaxometry, zero-field NMR, dynamic nuclear polarization, and other methods. However, to the best of our knowledge, no experiment has ever been proposed that allows one to correlate chemical shifts at two different fields. The requirement that both fields should be homogeneous has so far been a formidable obstacle. Here, we introduce a two-field NMR spectrometer and illustrate its potential for high-resolution two-field NMR spectroscopy. The benefits of high fields (sensitivity and resolution) and those of low fields (line-narrowing when chemical exchange occurs) can thus be combined. This approach can yield high-resolution chemical shift correlations between high and low fields, for example in heteronuclear (e.g. 1H-13C) spin systems. We show that signals of methyl groups that cannot be observed at 14.1 T because of chemical exchange can be recovered by two-field correlation spectroscopy. This work is important because it shows how a wide range of molecules and biomolecules prone to excessive broadening by chemical exchange can be studied by NMR. Two-field NMR spectroscopy paves the way to a new generation of NMR spectrometers, where multiple fields can be explored in the course of a single experiment in order to achieve an optimal combination of sensitivity, resolution, and spectral information.

 

N'hésitez pas à consulter le communiqué de presse associé à cet article : Le futur de la résonance magnétique nucléaire à haut champ? La RMN à deux champs 

 

Résumé: 

Angew.Chem.Int. Ed., 2016, 55, 9886-9889

 

Nuclear Magnetic Resonance has benefited tremendously from the steady increase of magnetic fields. Spectacular improvements in both sensitivity and resolution have allowed the investigation of molecular systems of rising complexity. At very high fields, this progress may be jeopardized by line broadening due to chemical exchange or relaxation by chemical shift anisotropy. Here, we introduce a two-field NMR spectrometer designed for both excitation and observation of nuclear spins at two distinct magnetic fields in a single experiment. NMR spectra were obtained, with two dimensions acquired at vastly different magnetic fields. We show that signals of exchanging groups broadened beyond recognition at high field can be sharpened up to narrow peaks in a low-field dimension. Two-field NMR makes it possible to measure chemical shifts at optimal fields, allows the observation of molecular systems that suffer from internal dynamics, and opens new avenues for NMR at very high magnetic fields.

 

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Recovering Invisible Signals by Two-Field Nuclear Magnetic Resonance Spectroscopy

 

S. F. Cousin, P. Kadeřávek, B. Haddou, C. Charlier, T. Marquardsen, J.-M. Tyburn, P.-A. Bovier, F. Engelke, W. Maas, G. Bodenhausen, P. Pelupessy, and Fabien Ferrage

 

Angew.Chem.Int. Ed., 2016, 55, 9886-9889

 

DOI : 10.1002/anie.201602978