High-resolution solid-state<sup>13</sup>C μMAS NMR with long coherence life times

Vasa, Suresh K.; Janssen, Hans; Eck, Ernst R. H. van; Kentgens, A.P.M.

doi:10.1039/c0cp01929a

Cited by 17 publications

(22 citation statements)

References 15 publications

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“…An interesting side note is that the measured R 1ρ of 0.18 s -1 for CH 2 in glycine should correspond to R 2 ' (minus the exchange contribution) under perfect heteronuclear decoupling conditions. Currently the smallest reported R 2 ' for CH 2 in glycine measured using 400 kHz SPINAL decoupling is ~4 s -1 , 23 which is still >20 times larger than the R 1ρ measured in this study. This result suggests that, even though it may be difficult to achieve, there is still plenty of room for improvement in heteronuclear decoupling methodology before the relaxation limit for coherence lifetimes is reached.…”

Section: Resultscontrasting

confidence: 70%

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Lamley

Lougher

Sass

et al. 2015

Phys. Chem. Chem. Phys.

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Typically, protein dynamics involve a complex hierarchy of motions occurring on different time scales between conformations separated by a range of different energy barriers. NMR relaxation can in principle provide a site-specific picture of both the time scales and amplitudes of these motions, but independent relaxation rates sensitive to fluctuations in different time scale ranges are required to obtain a faithful representation of the underlying dynamic complexity. This is especially pertinent for relaxation measurements in the solid state, which report on dynamics in a broader window of time scales by more than 3 orders of magnitudes compared to solution NMR relaxation. To aid in unraveling the intricacies of biomolecular dynamics we introduce (13)C spin-lattice relaxation in the rotating frame (R1ρ) as a probe of backbone nanosecond-microsecond motions in proteins in the solid state. We present measurements of (13)C'R1ρ rates in fully protonated crystalline protein GB1 at 600 and 850 MHz (1)H Larmor frequencies and compare them to (13)C'R1, (15)N R1 and R1ρ measured under the same conditions. The addition of carbon relaxation data to the model free analysis of nitrogen relaxation data leads to greatly improved characterization of time scales of protein backbone motions, minimizing the occurrence of fitting artifacts that may be present when (15)N data is used alone. We also discuss how internal motions characterized by different time scales contribute to (15)N and (13)C relaxation rates in the solid state and solution state, leading to fundamental differences between them, as well as phenomena such as underestimation of picosecond-range motions in the solid state and nanosecond-range motions in solution.

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Section: Resultscontrasting

confidence: 70%

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Lamley

Lougher

Sass

et al. 2015

Phys. Chem. Chem. Phys.

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“…5 It has also been demonstrated that solid-state NMR experiments on single crystals can also reduce ABMS broadening. 10,11 Hexamethylbenzene (HMB) is the prototypical sample displaying ABMS broadening; both the methyl and aromatic carbon 13 C peaks have a FWHM greater than 1 ppm, and the FWHM of the peaks (in ppm) is independent of the applied field (vide infra). 5,6,12 Substantial ABMS broadening has also been clearly observed in the 13 C solid-state NMR spectra of porphyrins, 10 glycine, 11 metal-organic frameworks (MOF), 13 APIs with aromatic groups such as ibuprofen 7 and piroxicam HCl, 14 the 19 F solid-state NMR spectrum of octafluoronapthalene 8 and in the high resolution 1 H solid-state NMR spectra of organic materials obtained with combined rotation and multiple pulse spectroscopy (CRAMPS) 15 or ultrafast MAS (ν r > 100 kHz).…”

Section: Introductionmentioning

confidence: 99%

Enhancing the resolution of¹H and¹³C solid-state NMR spectra by reduction of anisotropic bulk magnetic susceptibility broadening

Hanrahan

Venkatesh

Carnahan

et al. 2017

Phys. Chem. Chem. Phys.

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We demonstrate that natural isotopic abundance 2D heteronuclear correlation (HETCOR) solid-state NMR spectra can be used to significantly reduce or eliminate the broadening of H andC solid-state NMR spectra of organic solids due to anisotropic bulk magnetic susceptibility (ABMS). ABMS often manifests in solids with aromatic groups, such as active pharmaceutical ingredients (APIs), and inhomogeneously broadens the NMR peaks of all nuclei in the sample. Inhomogeneous peaks with full widths at half maximum (FWHM) of ∼1 ppm typically result from ABMS broadening and the low spectral resolution impedes the analysis of solid-state NMR spectra. ABMS broadening of solid-state NMR spectra has previously been eliminated using 2D multiple-quantum correlation experiments, or by performing NMR experiments on diluted materials or single crystals. However, these experiments are often infeasible due to their poor sensitivity and/or provide limited gains in resolution. 2D H-C HETCOR experiments have previously been applied to reduce susceptibility broadening in paramagnetic solids and we show that this strategy can significantly reduce ABMS broadening in diamagnetic organic solids. Comparisons of 1D solid-state NMR spectra and H andC solid-state NMR spectra obtained from 2D H-C HETCOR NMR spectra show that the HETCOR spectrum directly increases resolution by a factor of 1.5 to 8. The direct gain in resolution is determined by the ratio of the inhomogeneous C/H linewidth to the homogeneous H linewidth, with the former depending on the magnitude of the ABMS broadening and the strength of the applied field and the latter on the efficiency of homonuclear decoupling. The direct gains in resolution obtained using the 2D HETCOR experiments are better than that obtained by dilution. For solids with long proton longitudinal relaxation times, dynamic nuclear polarization (DNP) was applied to enhance sensitivity and enable the acquisition of 2DH-C HETCOR NMR spectra. 2D H-C HETCOR experiments were applied to resolve and partially assign the NMR signals of the form I and form II polymorphs of aspirin in a sample containing both forms. These findings have important implications for ultra-high field NMR experiments, optimization of decoupling schemes and assessment of the fundamental limits on the resolution of solid-state NMR spectra.

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“…Obtaining high-resolution solid-state NMR spectra relies on many facts in addition to the decoupling sequence, including local order in the sample (as explored through production of nano-or microcrystals and highly order fibers [21][22][23][24] ), nuclear spin relaxation properties, 25 and multiple-spin effects. 26 While the former is an intrinsic property of the sample that only can be altered through sample preparation, the two latter may be influenced through the use of fast sample spinning serving to reduce, e.g., 1 H-1 H interactions.…”

Section: Introductionmentioning

confidence: 99%

Refocused continuous-wave decoupling: A new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy

Vinther

Nielsen

Bjerring

et al. 2012

The Journal of Chemical Physics

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A novel strategy for heteronuclear dipolar decoupling in magic-angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy is presented, which eliminates residual static high-order terms in the effective Hamiltonian originating from interactions between oscillating dipolar and anisotropic shielding tensors. The method, called refocused continuous-wave (rCW) decoupling, is systematically established by interleaving continuous wave decoupling with appropriately inserted rotor-synchronized high-power π refocusing pulses of alternating phases. The effect of the refocusing pulses in eliminating residual effects from dipolar coupling in heteronuclear spin systems is rationalized by effective Hamiltonian calculations to third order. In some variants the π pulse refocusing is supplemented by insertion of rotor-synchronized π/2 purging pulses to further reduce the residual dipolar coupling effects. Five different rCW decoupling sequences are presented and their performance is compared to state-of-the-art decoupling methods. The rCW decoupling sequences benefit from extreme broadbandedness, tolerance towards rf inhomogeneity, and improved potential for decoupling at relatively low average rf field strengths. In numerical simulations, the rCW schemes clearly reveal superior characteristics relative to the best decoupling schemes presented so far, which we to some extent also are capable of demonstrating experimentally. A major advantage of the rCW decoupling methods is that they are easy to set up and optimize experimentally.

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High-resolution solid-state¹³C μMAS NMR with long coherence life times

Cited by 17 publications

References 15 publications

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Enhancing the resolution of¹H and¹³C solid-state NMR spectra by reduction of anisotropic bulk magnetic susceptibility broadening

Refocused continuous-wave decoupling: A new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy

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High-resolution solid-state13C μMAS NMR with long coherence life times

Cited by 17 publications

References 15 publications

Unraveling the complexity of protein backbone dynamics with combined 13C and 15N solid-state NMR relaxation measurements

Unraveling the complexity of protein backbone dynamics with combined 13C and 15N solid-state NMR relaxation measurements

Enhancing the resolution of1H and13C solid-state NMR spectra by reduction of anisotropic bulk magnetic susceptibility broadening

Refocused continuous-wave decoupling: A new approach to heteronuclear dipolar decoupling in solid-state NMR spectroscopy

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High-resolution solid-state¹³C μMAS NMR with long coherence life times

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Unraveling the complexity of protein backbone dynamics with combined ¹³C and ¹⁵N solid-state NMR relaxation measurements

Enhancing the resolution of¹H and¹³C solid-state NMR spectra by reduction of anisotropic bulk magnetic susceptibility broadening