Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR

Tatton, Andrew S.; Frantsuzov, Ilya; Brown, Steven P.; Hodgkinson, Paul

doi:10.1063/1.3684879

Cited by 8 publications

(9 citation statements)

References 60 publications

(80 reference statements)

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“…This agrees well with the theoretical calculations of heteronuclear third-order terms shown in Fig. S2 and previous results (Tatton et al, 2012).…”

Section: Resultssupporting

confidence: 93%

“…Note that the equation for the third-order contribution differs from the original paper due to a sign mistake in the original work (Ernst et al, 2005). To the best of our knowledge, only one theoretical description of third-order terms under simultaneous rf irradiation and MAS (Tatton et al, 2012) has been published. These terms were shown to cause a shift of the resonance frequency.…”

Section: Theorymentioning

confidence: 99%

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Origin of the residual line width under frequency-switched Lee–Goldburg decoupling in MAS solid-state NMR

et al. 2020

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Abstract. Homonuclear decoupling sequences in solid-state nuclear magnetic resonance (NMR) under magic-angle spinning (MAS) show experimentally significantly larger residual line width than expected from Floquet theory to second order. We present an in-depth theoretical and experimental analysis of the origin of the residual line width under decoupling based on frequency-switched Lee–Goldburg (FSLG) sequences. We analyze the effect of experimental pulse-shape errors (e.g., pulse transients and B1-field inhomogeneities) and use a Floquet-theory-based description of higher-order error terms that arise from the interference between the MAS rotation and the pulse sequence. It is shown that the magnitude of the third-order auto term of a single homo- or heteronuclear coupled spin pair is important and leads to significant line broadening under FSLG decoupling. Furthermore, we show the dependence of these third-order error terms on the angle of the effective field with the B0 field. An analysis of second-order cross terms is presented that shows that the influence of three-spin terms is small since they are averaged by the pulse sequence. The importance of the inhomogeneity of the radio-frequency (rf) field is discussed and shown to be the main source of residual line broadening while pulse transients do not seem to play an important role. Experimentally, the influence of the combination of these error terms is shown by using restricted samples and pulse-transient compensation. The results show that all terms are additive but the major contribution to the residual line width comes from the rf-field inhomogeneity for the standard implementation of FSLG sequences, which is significant even for samples with a restricted volume.

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“…This agrees well with the theoretical calculations of heteronuclear third-order terms shown in Fig. S2 and previous results (Tatton et al, 2012).…”

Section: Resultssupporting

confidence: 93%

Section: Theorymentioning

confidence: 99%

Origin of the residual line width under frequency-switched Lee–Goldburg decoupling in MAS solid-state NMR

et al. 2020

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“…† These were determined from the cross-peaks at short-contact time, where present, or otherwise from clear and distinctive long-range correlation peaks, noting that small differences can be observed in apparent 1 H shifts from short vs. long-range correlation peaks. 34,35 Deuterated samples prepared by recrystallisation from D 2 O or exchange in a D 2 O-saturated atmosphere had identical 13 C NMR spectra. HETCOR spectra of either deuterated sample showed no correlation peaks above 1 H shifts of 10 ppm, indicating that all exchangeable hydrogens on the citrate and N5/N26 of the sildenafil are indeed exchanged.…”

Section: First Principles Calculationsmentioning

confidence: 99%

Characterising the role of water in sildenafil citrate by NMR crystallography

et al. 2016

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“…SI.3), at 9.1 ppm (predicted by GIPAW to be at 11.5 ppm), the other assignments possibly being complicated by spin diffusion (despite the use of Lee–Goldburg CP conditions). Exact quantitative agreement between predicted 1 H shifts and those derived from HETCOR experiments is not expected because, apart from any deficiencies in the computing protocol, there are difficulties in obtaining robust shifts under homonuclear decoupling, especially from short‐range 1 H, 13 C correlation peaks . Moreover, it often happens that the relation of computed to observed shifts does not have the ideal slope of unity, although the order of the shifts is usually reproduced correctly.…”

Section: Structural Characterisationmentioning

confidence: 99%

NMR characterisation of structure in solvates and polymorphs of formoterol fumarate

Apperley

Markwell

Harris

et al. 2012

Magnetic Reson in Chemistry

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The solid-state structures of two polymorphs and two alcoholates (ethanol and isopropanol) of formoterol fumarate have been investigated by a combination of NMR techniques. First-principles shielding computations are combined with NMR data to successfully relate peaks to their crystallographic positions for the solvates, including atoms that are in equivalent molecular positions. The uncharacterised structure of the asolvate form C is found to contain a single formoterol ion and half a fumarate ion in its asymmetric unit. HETCOR experiments for the ethanolate and form C allow proton chemical shifts to be determined and give improved (13)C resolution for the former compound. Desolvation of the solvates to form C has been monitored under the conditions of the NMR experiment. Differential rates of phenylene ring flipping are observed in the different forms. Carbon-13 relaxation times and (2)H NMR are used to probe dynamics of the fumarate ion.

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Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR

Cited by 8 publications

References 60 publications

Origin of the residual line width under frequency-switched Lee–Goldburg decoupling in MAS solid-state NMR

Origin of the residual line width under frequency-switched Lee–Goldburg decoupling in MAS solid-state NMR

Characterising the role of water in sildenafil citrate by NMR crystallography

NMR characterisation of structure in solvates and polymorphs of formoterol fumarate

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