Chemical shift anisotropy in powdered solids studied by 2D FT CP/MAS NMR

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

doi:10.1016/0022-2364(83)90292-5

Cited by 48 publications

(50 citation statements)

References 2 publications

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“…Some methods are distortionless only for very small scaling factors (<0.1) (16), while most other CSA recoupling pulse sequences are notoriously sensitive to pulselength imperfections or off-resonance effects (18,19,22,23) or suffer from low sensitivity (24). The techniques that yield the best powder patterns require unconventional hardware for angle switching (15,17,25), for slow spinning, and/or for special rotor synchronization throughout the pulse sequence (12,20,21).…”

Section: Introductionmentioning

confidence: 98%

“…A few techniques for obtaining undistorted quasi-static CSA powder patterns under standard MAS conditions have been described (16,18,19), while others provide unusual powder patterns (22)(23)(24). Some methods are distortionless only for very small scaling factors (<0.1) (16), while most other CSA recoupling pulse sequences are notoriously sensitive to pulselength imperfections or off-resonance effects (18,19,22,23) or suffer from low sensitivity (24).…”

Section: Introductionmentioning

confidence: 98%

“…With suitable rotationsynchronized radiofrequency pulses, such static powder patterns can also be produced in the first dimension of a 2D MAS experiment (12,(15)(16)(17)(18)(19)(20)(21). Such undistorted quasi-static powder patterns have several major advantages over MAS sideband patterns.…”

Section: Introductionmentioning

confidence: 99%

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A Robust Technique for Two-Dimensional Separation of Undistorted Chemical-Shift Anisotropy Powder Patterns in Magic-Angle-Spinning NMR

Schmidt‐Rohr

2002

Journal of Magnetic Resonance

199

274

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

A Robust Technique for Two-Dimensional Separation of Undistorted Chemical-Shift Anisotropy Powder Patterns in Magic-Angle-Spinning NMR

Schmidt‐Rohr

2002

Journal of Magnetic Resonance

199

274

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“…Equation [26] also provides the relationship between the metric tensors in two different representations as follows:…”

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confidence: 99%

Metric spaces in NMR crystallography

Grant

Halling

2009

Concepts Magnetic Resonance

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ABSTRACT:The anisotropic character of the chemical shift can be measured by experiments that provide shift tensor values and comparing these experimental components, obtained from microcrystalline powders, with 3D nuclear shielding tensor components, calculated with quantum chemistry, yields structural models of the analyzed molecules. The use of a metric tensor for evaluating the mean squared deviations, d 2 , between two or more tensors provides a statistical way to verify the molecular structure governing the theoretical shielding components. The sensitivity of the method is comparable with diffraction methods for the heavier organic atoms (i.e., C, O, N, etc.) but considerably better for the positions of H atoms. Thus, the method is especially powerful for H-bond structure, the position of water molecules in biomolecular species, and other proton important structural features, etc. Unfortunately, the traditional Cartesian tensor components appear as reducible metric representations and lack the orthogonality of irreducible icosahedral and irreducible spherical tensors, both of which are also easy to normalize. Metrics give weighting factors that carry important statistical significance in a structure determination. Details of the mathematical analysis are presented and examples given to illustrate the reason nuclear magnetic resonance are rapidly assuming an important synergistic relationship with diffraction methods (X-ray, neutron scattering, and high energy synchrotron irradiation).

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“…Several types of experiments have been proposed to facilitate the measurement of chemical shift anisotropy (1-9). All have the common feature that the sample is rotated about the magic-angle axis (1-8) or an axis very close to the magic angle (9), either by rapid sample spinning (1)(2)(3)(4)(5)(6)(7)9) or by rotating the sample in three discrete steps (8).…”

mentioning

confidence: 99%

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

Bax

Szeverenyi

Maciel

1983

Journal of Magnetic Resonance (1969)

Self Cite

111

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Information about chemical shift anisotropy is usually difficult to extract from the spectrum of a nonspinning powdered sample because of the usually extensive overlap of the powder patterns from the chemically different sites in the molecule. Several types of experiments have been proposed to facilitate the measurement of chemical shift anisotropy (1-9). All have the common feature that the sample is rotated about the magic-angle axis (1-8) or an axis very close to the magic angle (9), either by rapid sample spinning (1)(2)(3)(4)(5)(6)(7)9) or by rotating the sample in three discrete steps (8).We propose a new two-dimensional approach for obtaining the anisotropy information. In this new experiment, the spinning axis of the sample is flipped from 90 to 54.7" between the evolution and detection periods. The experiment appears to be widely applicable and has great promise for the study of complex samples.The experimental scheme is set out in Fig. 1. Cross polarization of, in our case, 13C nuclei is performed while the sample is spun about an axis that makes an angle of 90" with the static magnetic field. It can be shown (IO) that the powder anisotropy pattern that obtains under these conditions is reversed and collapsed to half the width of the static nonspinning case, but keeps the same shape. At the end of the evolution period (t,), the x component of the transverse 13C magnetization is stored along the z axis, parallel to the static magnetic field, by means of a 90," 13C pulse. The orientation of the spinning axis of the sample is then changed to the magic angle. The sample is spun fast compared with the width of the anisotropy patterns, so that spinning sidebands have negligible intensities. A final 90 o 13C pulse rotates the z-stored 13C magnetization back into the transverse plane, where it precesses in the time domain, tZ, with the corresponding isotropic chemical shift frequencies.Cycling of the phase of the first 90 o 13C pulse alternately along +y and -y, together with adding and subtracting of the acquired data, is used to eliminate spurious signals. The detected isotropic spectrum, S(tl , F2) obtained by Fourier transformation with respect to t2, is modulated in amplitude with the frequencies existing during the evolution period, t,. Hence, the powder anisotropy information and the isotropic chemical shifts will appear in the F, dimension. Because of the amplitude modulation, a pure 2D absorption spectrum can be obtained by calculating the cosine Fourier transform, P (F,, FJ (II,12).

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Chemical shift anisotropy in powdered solids studied by 2D FT CP/MAS NMR

Cited by 48 publications

References 2 publications

A Robust Technique for Two-Dimensional Separation of Undistorted Chemical-Shift Anisotropy Powder Patterns in Magic-Angle-Spinning NMR

A Robust Technique for Two-Dimensional Separation of Undistorted Chemical-Shift Anisotropy Powder Patterns in Magic-Angle-Spinning NMR

Metric spaces in NMR crystallography

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

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