Five decades of homonuclear dipolar decoupling in solid-state NMR: Status and outlook

Mote, Kaustubh R.; Agarwal, Vipin; Madhu, Perunthiruthy K.

doi:10.1016/j.pnmrs.2016.08.001

Cited by 61 publications

(50 citation statements)

References 192 publications

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“…Highly optimized modern 1 H CRAMPS solid-state NMR spectra typically give 1 H peaks with homogeneous linewidths around 200 Hz in rigid crystalline organic solids (0.5 ppm at 9.4 T). 40,[49][50][51][52] DNP Enhanced Solid-State NMR Experiments on Salicylic Acid Diluted in Lactose. DNP enhanced solid-state NMR experiments were also performed on salicylic acid diluted into lactose to determine if 2D HETCOR experiments on pure salicylic acid or a 1D 13 C CPMAS experiment on the diluted sample provides better resolution and sensitivity.…”

Section: Resultsmentioning

confidence: 99%

“…0.5 ppm at 9.4 T). 40,[49][50][51][52] A homogeneous 1 H linewidth of 200 Hz would correspond to 2D HETCOR slices with 1 H and 13 C NMR spectra with peaks with FWHM of 0.5 ppm at 9.4 T and 0.25 ppm at 18.8 T. Therefore, in order for the 2D 1 H-13 C HETCOR approach to be able to improve resolution, the inhomogeneous broadening due to ABMS likely must be greater than 0.5 ppm. Note that the refocused 13 C transverse relaxation time (T 2 ') of rigid protonated organic solids is usually longer than 20 ms and this corresponds to a homogeneous 13 C linewidth less than 15 Hz.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

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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“…The major obstacle is the presence of strong 1 H-1 H homonuclear dipolar interactions that are difficult to suppress at slow or moderate MAS. Tremendous efforts have been put into the development of methods to get rid of the 1 H-1 H homonuclear dipolar interactions (Hodgkinson, 2011;Mote et al, 2016). The combined rotation and multiple pulse spectroscopy (CRAMPS) technique is one of the most widely used methods at slow or moderate MAS to remove homonuclear interactions by spin rotations.…”

Section: Sample Preparationmentioning

confidence: 99%

Solid-state NMR meets electron diffraction: determination of crystalline polymorphs of small organic microcrystalline samples

Oikawa¹,

Okumura

Kimura

et al. 2017

Acta Crystallogr C

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A combination of solid-state NMR (ssNMR) and electron diffraction (ED) has been used to determine the crystalline polymorphs in small-organic microcrystalline molecules. Although C cross-polarization magic angle spinning (CPMAS) is a widely used method for determining crystalline polymorphs, even in a mixture, it sometimes fails if the molecular conformations are similar. On the other hand, ED can, in principle, differentiate crystalline forms with different lattice parameters, even when they have very similar molecular conformations. However, its application is usually limited to inorganic molecules only. This is because the ED measurements of organic molecules are very challenging due to degradation of the sample by electron irradiation. We overcame these difficulties by the use ofH double-quantum/single-quantum correlation experiments at very fast magic angle spinning, together with ED observations under mild electron irradiation. The experiments were demonstrated on L-histidine samples in L-histidine·HCl·HO, orthorhombic L-histidine and monoclinic L-histidine.

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“…In solids, however, high-resolution proton studies are hampered by the significant line-broadening effects due to the presence of strong homonuclear H NMR in the solid state has found numerous applications, particularly in studies of small natural abundance organic molecules and their crystal polymorphs that are pharmaceutically relevant [1] but also, increasingly, for elucidation of structure and dynamics of biomolecules [2][3][4][5][6][7]. To combat the broadening effects of 1 H-1 H dipolar couplings and improve spectral resolution in 1 H observed spectra, studies usually employ either dilution of the dense networks of protons with deuterium atoms [8][9][10], combined rotation and multiple pulse spectroscopy (CRAMPS) techniques to decouple the homonuclear dipolar couplings [11][12][13] or combination of these two solutions [14]. The first of these approaches is most commonly used for proteins where incorporation of 2 H is achieved by biosynthetic methods [15].…”

Section: Introductionmentioning

confidence: 99%

1H line width dependence on MAS speed in solid state NMR – Comparison of experiment and simulation

Sternberg

Witter

Kuprov

et al. 2018

Journal of Magnetic Resonance

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b s t r a c tRecent developments in magic angle spinning (MAS) technology permit spinning frequencies of !100 kHz. We examine the effect of such fast MAS rates upon nuclear magnetic resonance proton line widths in the multi-spin system of b-Asp-Ala crystal. We perform powder pattern simulations employing Fokker-Plank approach with periodic boundary conditions and 1 H-chemical shift tensors calculated using the bond polarization theory. The theoretical predictions mirror well the experimental results. Both approaches demonstrate that homogeneous broadening has a linear-quadratic dependency on the inverse of the MAS spinning frequency and that, at the faster end of the spinning frequencies, the residual spectral line broadening becomes dominated by chemical shift distributions and susceptibility effects even for crystalline systems.

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Five decades of homonuclear dipolar decoupling in solid-state NMR: Status and outlook

Cited by 61 publications

References 192 publications

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

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

Solid-state NMR meets electron diffraction: determination of crystalline polymorphs of small organic microcrystalline samples

1H line width dependence on MAS speed in solid state NMR – Comparison of experiment and simulation

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Five decades of homonuclear dipolar decoupling in solid-state NMR: Status and outlook

Cited by 61 publications

References 192 publications

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

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

Solid-state NMR meets electron diffraction: determination of crystalline polymorphs of small organic microcrystalline samples

1H line width dependence on MAS speed in solid state NMR – Comparison of experiment and simulation

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

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