Chemical shift anisotropy in powdered solids studied by 2D FT NMR with flipping of the spinning axis

Bax, Ad; Szeverenyi, Nikolaus M.; Maciel, Gary E.

doi:10.1016/0022-2364(83)90134-8

Cited by 112 publications

(91 citation statements)

References 8 publications

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“…This expression could be modified to include multiple components with different diffusion properties, which could then be resolved in the experimental data if they have significantly different values of the isotropic diffusivity D iso . Such a separation and correlation of the isotropic and anisotropic features are analogous to the variable-angle spinning 51 and switched-angle spinning 52 techniques in solidstate NMR spectroscopy.…”

Section: Discussionmentioning

confidence: 99%

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

Eriksson

Lasič

Nilsson

et al. 2015

The Journal of Chemical Physics

173

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We introduce a nuclear magnetic resonance method for quantifying the shape of axially symmetric microscopic diffusion tensors in terms of a new diffusion anisotropy metric, DΔ, which has unique values for oblate, spherical, and prolate tensor shapes. The pulse sequence includes a series of equal-amplitude magnetic field gradient pulse pairs, the directions of which are tailored to give an axially symmetric diffusion-encoding tensor b with variable anisotropy bΔ. Averaging of data acquired for a range of orientations of the symmetry axis of the tensor b renders the method insensitive to the orientation distribution function of the microscopic diffusion tensors. Proof-of-principle experiments are performed on water in polydomain lyotropic liquid crystals with geometries that give rise to microscopic diffusion tensors with oblate, spherical, and prolate shapes. The method could be useful for characterizing the geometry of fluid-filled compartments in porous solids, soft matter, and biological tissues.

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Section: Discussionmentioning

confidence: 99%

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

Eriksson

Lasič

Nilsson

et al. 2015

The Journal of Chemical Physics

173

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“…Data were collected on samples rotating at angles different from the magic angle, restricted between 0 • and 54.7 • (MAS). SAS has been used in the past to obtain similar correlations, with the constraint of one angle being the magic angle [9][10][11][12], and also in the context of Dynamic Angle Spinning (DAS) [13,14] for high resolution NMR of quadrupolar nuclei. Our goals here are quite different; we are interested in recording the full isotropic and anisotropic spectroscopic information by spinning the sample or the magnetic field around axes making angles with the static magnetic field away from the magic angle.…”

Section: Introductionmentioning

confidence: 99%

High-resolution NMR of anisotropic samples with spinning away from the magic angle

Sakellariou

Meriles

Martin

et al. 2003

Chemical Physics Letters

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High-resolution NMR of samples in the solid state is typically performed under mechanical sample spinning around an axis that makes an angle, called the magic angle, of 54.7 degrees with the static magnetic field. There are many cases in which geometrical and engineering constraints prevent spinning at this specific angle. Implementations of in-situ and ex-situ magic angle field spinning might be extremely demanding because of the power requirements or an inconvenient sample size or geometry. Here we present a methodology based on switched angle spinning between two angles, none of which is the magic angle, which provides both isotropic and anisotropic information. Using this method, named Projected Magic Angle Spinning, we were able to obtain resolved scaled isotropic chemical shifts in spinning samples where the broadening is mostly inhomogeneous.

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“…In the case of restricted diffusion, the diffusion tensor should be interpreted as an apparent one, being given by the pore size and shape, the local diffusivity within the pore space, as well as the timing parameters of the used pulse sequence [39][40][41][42][43][44]. A more in-depth analysis of the validity of this approximation is given in the Supplemental Material [45].Here, we propose a diffusion NMR experiment to resolve distinct water components using inspiration from 2D solid-state NMR techniques correlating isotropic and anisotropic chemical shifts [50][51][52]. In these techniques, the NMR signal is sampled in a 2D time-domain space (t 1 , t 2 ) where the spins evolve under both isotropic and anisotropic chemical shifts in the first time dimension t 1 , and exclusively under the isotropic chemical shift in the second dimension t 2 .…”

mentioning

confidence: 99%

“…The expression in Eq. (5) corresponds to the 2D line shape for an axially symmetric chemical shift tensor in the solid-state NMR experiments for correlating isotropic and anisotropic chemical shifts [50][51][52]. According to Eq.…”

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confidence: 99%

Two-Dimensional Correlation of Isotropic and Directional Diffusion Using NMR

Martins

Topgaard

2016

Phys. Rev. Lett.

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Diffusion nuclear magnetic resonance (NMR) is a powerful technique for studying porous media, but yields ambiguous results when the sample comprises multiple regions with different pore sizes, shapes, and orientations. Inspired by solid-state NMR techniques for correlating isotropic and anisotropic chemical shifts, we propose a diffusion NMR method to resolve said ambiguity. Numerical data inversion relies on sparse representation of the data in a basis of radial and axial diffusivities. Experiments are performed on a composite sample with a cell suspension and a liquid crystal. DOI: 10.1103/PhysRevLett.116.087601 Many porous materials of biological, geological, and synthetic origin contain water in a range of microscopic environments with different local pore geometries. Information about the structure of the pore space can be inferred from nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) measurements of the self-diffusion of the pore water [1,2]. The diffusion MRI approach has been especially powerful for noninvasive studies of the living human brain [3], allowing for quantification of axon diameter [4], mean orientation [5], and orientation distribution [6]. Although useful, classical diffusion MRI protocols relying on the Stejskal-Tanner experiment [7] suffer from the fact that the effects of distributions in pore size, anisotropy, and orientation are intrinsically entangled. A partial solution to this problem is provided by the double diffusion encoding (DDE) family of NMR methods [8], which can give estimates of the pore size and shape even in the presence of orientational disorder [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Current in vivo versions of DDE permit detection of anisotropy in areas of the human brain that are macroscopically isotropic [24] and the assignment of metabolitespecific compartment shapes in animal models [25]. Despite these impressive feats, DDE yields ambiguous results if the investigated volume element comprises several types of water environments, the presence of which has been inferred by fitting multicomponent biophysical models [26][27][28][29] to in vivo data acquired with the StejskalTanner method [30,31]. Selection of a single model from all the ones that are able to reproduce the experimental data remains a challenge [29]. The key to future progress in diffusion NMR and MRI of heterogeneous anisotropic materials lies in designing a method to unambiguously resolve and quantify water compartments with respect to their size and anisotropy, irrespective of the details of their orientations. Once this goal has been achieved, the obtained information could be used as input for existing methods to estimate distributions of axon diameters [4] and orientations [32][33][34].In solid-state NMR spectroscopy [35], the eigenvalues and eigenvectors of the chemical shift tensors can be determined through the dependence of the nuclear spin Hamiltonian on the orientation of the tensors with respect to the static magnetic field. We have recently poin...

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Chemical shift anisotropy in powdered solids studied by 2D FT NMR with flipping of the spinning axis

Cited by 112 publications

References 8 publications

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

NMR diffusion-encoding with axial symmetry and variable anisotropy: Distinguishing between prolate and oblate microscopic diffusion tensors with unknown orientation distribution

High-resolution NMR of anisotropic samples with spinning away from the magic angle

Two-Dimensional Correlation of Isotropic and Directional Diffusion Using NMR

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