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

2020 ◽  
Vol 1 (1) ◽  
pp. 13-25 ◽  
Author(s):  
Johannes Hellwagner ◽  
Liam Grunwald ◽  
Manuel Ochsner ◽  
Daniel Zindel ◽  
Beat H. Meier ◽  
...  
Keyword(s):  
Solid State ◽  
Line Width ◽  
Floquet Theory ◽  
Pulse Sequence ◽  
Second Order ◽  
Magic Angle ◽  
Line Broadening ◽  
Third Order ◽  
Order Error ◽  
Error Terms

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.

scholarly journals Origin of the Residual Linewidth Under FSLG-Based Homonuclear Decoupling in MAS Solid-State NMR

2019 ◽  
Author(s):  
Johannes Hellwagner ◽  
Liam Grunwald ◽  
Manuel Ochsner ◽  
Daniel Zindel ◽  
Beat H. Meier ◽  
...  
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Floquet Theory ◽  
Pulse Sequence ◽  
Field Inhomogeneity ◽  
Line Broadening ◽  
Third Order ◽  
Order Error ◽  
Homonuclear Decoupling ◽  
Error Terms

Abstract. Homonuclear decoupling sequences in solid-state NMR under magic-angle spinning (MAS) show experimentally significantly larger residual linewidth than expected from Floquet theory to second order. We present an in-depth theoretical and experimental analysis of the origin of the residual linewidth in frequency-switched Lee-Goldburg (FSLG) based decoupling 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 static rf-field inhomogeneity 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 linewidth comes from the rf-field inhomogeneity for the standard implementation of FSLG sequences, which is significant even for samples with a restricted volume.

scholarly journals Residual dipolar line width in magic-angle spinning proton solid-state NMR

2021 ◽  
Vol 2 (1) ◽  
pp. 499-509
Author(s):  
Matías Chávez ◽  
Thomas Wiegand ◽  
Alexander A. Malär ◽  
Beat H. Meier ◽  
Matthias Ernst
Keyword(s):  
Chemical Shift ◽  
Line Width ◽  
Magic Angle Spinning ◽  
Spin Systems ◽  
Second Order ◽  
Magic Angle ◽  
Line Broadening ◽  
Third Order ◽  
Angle Spinning ◽  
Effective Hamiltonians

Abstract. Magic-angle spinning is routinely used to average anisotropic interactions in solid-state nuclear magnetic resonance (NMR). Due to the fact that the homonuclear dipolar Hamiltonian of a strongly coupled spin system does not commute with itself at different time points during the rotation, second-order and higher-order terms lead to a residual dipolar line broadening in the observed resonances. Additional truncation of the residual broadening due to isotropic chemical-shift differences can be observed. We analyze the residual line broadening in coupled proton spin systems based on theoretical calculations of effective Hamiltonians up to third order using Floquet theory and compare these results to numerically obtained effective Hamiltonians in small spin systems. We show that at spinning frequencies beyond 75 kHz, second-order terms dominate the residual line width, leading to a 1/ωr dependence of the second moment which we use to characterize the line width. However, chemical-shift truncation leads to a partial ωr-2 dependence of the line width which looks as if third-order effective Hamiltonian terms are contributing significantly. At slower spinning frequencies, cross terms between the chemical shift and the dipolar coupling can contribute in third-order effective Hamiltonians. We show that second-order contributions not only broaden the line, but also lead to a shift of the center of gravity of the line. Experimental data reveal such spinning-frequency-dependent line shifts in proton spectra in model substances that can be explained by line shifts induced by the second-order dipolar Hamiltonian.

scholarly journals Residual Linewidth in Magic-Angle Spinning Solid-State NMR

2021 ◽  
Author(s):  
Matías Chávez ◽  
Thomas Wiegand ◽  
Alexander A. Malär ◽  
Beat H. Meier ◽  
Matthias Ernst
Keyword(s):  
Line Width ◽  
Solid State Nmr ◽  
Magic Angle Spinning ◽  
Spin Systems ◽  
Second Order ◽  
Magic Angle ◽  
Line Broadening ◽  
Third Order ◽  
Angle Spinning ◽  
Effective Hamiltonians

Abstract. Magic-angle spinning is routinely used to average anisotropic interactions in solid-state NMR. Due to the fact, that the Hamiltonian of a strongly-coupled spin system does not commute with itself at different time points during the rotation, second-order and higher-order terms lead to a residual line broadening in the observed resonances. Additional truncation of the residual broadening due to isotropic chemical-shift differences can be observed. We analyze the residual line broadening in coupled proton spin systems based on theoretical calculations of effective Hamiltonians up to third order using Floquet theory and compare these results to numerically obtained effective Hamiltonians in small spin systems. We show that at spinning frequencies beyond 50 kHz, second-order terms dominate the residual line width leading to a 1/ωr dependence of the second moment which we use to characterize the line width. However, chemical-shift truncation leads to a partial ωr-2 dependence of the line width which looks as if third-order effective Hamiltonian terms are contributing significantly. We show that second-order contributions not only broaden the line but also lead to a shift of the center of gravity of the line. Experimental data reveals such spinning-frequency dependent line shifts in proton spectra in model substances that can be explained by line shifts induced by the second-order dipolar Hamiltonian.

Multinuclear solid-state NMR of square-planar platinum complexes — Cisplatin and related systems

2011 ◽  
Vol 89 (7) ◽  
pp. 919-937 ◽  
Author(s):  
Bryan E.G. Lucier ◽  
Alex R. Reidel ◽  
Robert W. Schurko
Keyword(s):  
Hydrogen Bonding ◽  
Solid State ◽  
First Principles ◽  
Density Functional ◽  
Pulse Sequence ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
First Principles Calculations ◽  
Dipolar Relaxation ◽  
Square Planar

Multinuclear solid-state nuclear magnetic resonance (SSNMR) experiments have been performed on cisplatin and four related square-planar compounds. The wideband uniform rate smooth truncation – Carr–Purcell–Meiboom–Gill (WURST–CPMG) pulse sequence was utilized in NMR experiments to acquire 195Pt, 14N, and 35Cl ultra-wideline NMR spectra of high quality. Standard Hahn-echo and magic-angle spinning 195Pt NMR experiments are also performed to refine extracted chemical shielding (CS) tensor parameters. Platinum magnetic shielding (MS) tensor orientations are calculated using both plane-wave density functional theory (DFT) and standard DFT methods. The tensor orientations are shown to be highly constrained by molecular symmetry elements, but also influenced to some degree by intermolecular interactions. 14N WURST–CPMG experiments were performed on three compounds and electric field gradient (EFG) parameters (the quadrupolar coupling constant, CQ, and the asymmetry parameter, ηQ) are reported. First principles calculations of the 14N EFG tensor parameters and orientations and affirm their dependence on the local hydrogen bonding environment. 35Cl WURST–CPMG experiments on cisplatin and transplatin are reported, using two different static magnetic fields to extract EFG and CS tensor parameters, and 35Cl EFG tensor magnitudes and orientations are predicted using first principles calculations. Transverse (T2) relaxation data for all nuclei are used to investigate heteronuclear dipolar relaxation mechanisms, as well as the nature of the local hydrogen bonding environments.

A carbon-13 nuclear magnetic resonance study of solid tetracyclines

1987 ◽  
Vol 65 (2) ◽  
pp. 357-362 ◽  
Author(s):  
Sandra Mooibroek ◽  
Roderick E. Wasylishen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Pulse Sequence ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Magic Angle ◽  
X Ray Diffraction ◽  
Magic Angle Sample Spinning ◽  
Nuclear Magnetic

Magic angle sample spinning and proton/carbon-13 cross-polarization techniques have been used to obtain high resolution solid state 13C nuclear magnetic resonance spectra of several tetracycline antibiotics. Carbon-13 resonances in the solid state are assigned by measuring the extent of dipolar broadening due to neighbouring quadrupolar nuclei and by using a pulse sequence that suppresses non-quaternary carbon resonances. The observed 13C chemical shifts are discussed in light of the known solid state structures derived from X-ray diffraction, and are compared with those in solution. It is shown that the solid state nuclear magnetic reosnance technique is capable of clearly distinguishing between the neutral and zwitterionic forms of the tetracycline free bases.

Two-dimensional proton-detected 35Cl/1H correlation solid-state NMR experiment under fast magic angle sample spinning: application to pharmaceutical compounds

2016 ◽  
Vol 18 (8) ◽  
pp. 6209-6216 ◽  
Author(s):  
Manoj Kumar Pandey ◽  
Hiroshi Kato ◽  
Yuji Ishii ◽  
Yusuke Nishiyama
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Pulse Sequence ◽  
Pharmaceutical Compounds ◽  
Magic Angle ◽  
Two Dimensional ◽  
Active Pharmaceutical Ingredients ◽  
Pharmaceutical Ingredients ◽  
Fast Mas ◽  
Magic Angle Sample Spinning

In this study, we have measured 35Cl/1H correlations in hydrochloride salts of active pharmaceutical ingredients (HCl APIs) using the D-HMQC pulse sequence at fast MAS.

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