Ramped-Amplitude Cross Polarization in Magic-Angle-Spinning NMR

Metz, Guenter; Wu, Xiaoling; Smith, Steven O.

doi:10.1006/jmra.1994.1208

Cited by 1,139 publications

(1,089 citation statements)

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“…First, 15 N spin polarization was prepared by ramped CP 42 . Because of the limited population of the target 15 N species and a broad line width, the signal-to-noise ratio in the direct-detected 15 N CPMAS spectra was low even with 15 N enrichment.…”

Section: Methodsmentioning

confidence: 99%

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

et al. 2012

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Chemically modified graphene platelets, produced via graphene oxide, show great promise in a variety of applications due to their electrical, thermal, barrier and mechanical properties. understanding the chemical structures of chemically modified graphene platelets will aid in the understanding of their physical properties and facilitate development of chemically modified graphene platelet chemistry. Here we use 13 C and 15 n solid-state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy to study the chemical structure of 15 nlabelled hydrazine-treated 13 C-labelled graphite oxide and unlabelled hydrazine-treated graphene oxide, respectively. These experiments suggest that hydrazine treatment of graphene oxide causes insertion of an aromatic n 2 moiety in a five-membered ring at the platelet edges and also restores graphitic networks on the basal planes. Furthermore, density-functional theory calculations support the formation of such n 2 structures at the edges and help to elucidate the influence of the aromatic n 2 moieties on the electronic structure of chemically modified graphene platelets.

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Section: Methodsmentioning

confidence: 99%

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

et al. 2012

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“…The spectra in Fig 2 were processed with Gaussian line broadening of 15 Hz; other spectra were processed with Gaussian line broadening of 25 Hz. 1 H T 1 values were calculated from the data collected by 1 H inversion recovery experiments detected by 13 C CPMAS, where a π-pulse to 1 H spins and the following inversion recovery delay were added prior to the conventional CPMAS sequence with ramped CP [35] and TPPM decoupling [36]. The signal intensities were measured for the highest signals in the 13 CO (160-190 ppm), 13 Cα (40-65 ppm), 13 CH (10-30 ppm) regions to estimate 1 H T 1 ; the average of the 1 H T 1 values estimated for the three regions was used as 1 H T 1 of the sample.…”

Section: Methodsmentioning

confidence: 99%

Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation

Wickramasinghe

Kotecha

Samoson

et al. 2007

Journal of Magnetic Resonance

118

110

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We discuss a simple approach to enhance sensitivity for 13 C high-resolution solid-state NMR for proteins in microcrystals by reducing 1 H T 1 relaxation times with paramagnetic relaxation reagents. It was shown that 1 H T 1 values can be reduced from 0.4-0.8 s to 60-70 ms for ubiquitin and lysozyme in D 2 O in the presence of 10 mM Cu(II)Na 2 EDTA without substantial degradation of the resolution in 13 C CPMAS spectra. Faster signal accumulation using the shorter 1 H T 1 attained by paramagnetic doping provided sensitivity enhancements of 1.4-2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0-8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in 13 C high-resolution solidstate NMR spectroscopy.

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“…The spinning frequency was 14 kHz for all experiments. For the 13 C experiments, a ramped cross polarization [35] with a contact time of 1 ms was used and 1 H decoupling was achieved using the SPINAL64 sequence [36] with a 1 H nutation frequency of 70 kHz. The 13 C pulses used for the excitation and reconversion of triple-quantum (TQ) coherences employed a nutation frequency 57 kHz.…”

Section: Methodsmentioning

confidence: 99%

Triple-quantum correlation NMR experiments in solids using J-couplings

Fayon

Roiland

Emsley

et al. 2006

Journal of Magnetic Resonance

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We show that triple-quantum -single-quantum (TQ-SQ) correlation spectra of crystalline and disordered solids can be obtained under MAS using pulse sequences based on through-bond J-couplings. The feasibility of the experiments in coupled spin-½ systems is demonstrated for fully 13 C-labelled L-alanine and Pb 3 P 4 O 13 crystalline compounds, considered as model three-spin and four-spin systems, respectively. In the case of phosphate glasses, we show that the obtained TQ-SQ correlation spectra provide an improved description of the glass forming network connectivities and of the chain length distribution in the disordered network. IntroductionHomonuclear double-quantum correlation spectroscopy has been shown to be a valuable tool in solid-state NMR for determining atomic connectivities and studying the structure and dynamic of ordered or disordered materials [1,2]. In this context, various experiments have been developed to obtain two-dimensional (2D) double-quantum -singlequantum (DQ-SQ) correlation spectra of coupled spin-½ systems under magic angle spinning (MAS) which is required for enhanced spectral resolution and sensitivity. Many of these methods employ pulse sequences which reintroduce the MAS-averaged through-space homonuclear dipolar interaction, to obtain DQ-SQ correlation spectra which reflect the through-space atomic proximities [3][4][5][6][7][8][9][10]. Alternatively, pulse sequences based on throughbond isotropic J-couplings, like the INADEQUATE [11] and refocused INADEQUATE [12] experiments, have also been applied efficiently to obtain through-bond DQ-SQ correlation spectra for large range of materials [12][13][14][15][16][17][18][19][20][21][22][23].In the case of inorganic glasses, for which the characterization of medium range order remains challenging, the DQ-SQ correlation experiment allows to improve the structural description obtained from NMR spectroscopy by determining the pairwise connectivities between the basic building units of the disordered network. In phosphate glasses, homonuclear through-bond [22,23] and through-space [24-25] DQ-SQ correlation methods have been applied successfully to probe P-O-P connectivities between the various network former PO 4 tetrahedral units (Q n with n bridging oxygen atoms). These experiments provide enhanced spectral resolution relative to the conventional MAS spectra allowing the distinction between Q n units bonded to different types of PO 4 to be made and giving evidence of a chain length distribution in the disordered network [22][23][24][25].Nevertheless, information about longer range order, which could be obtained from a three-spin correlation experiment, remains desirable for a better description of the disordered glassy network. Recently, various dipolar recoupling pulse sequences have been proposed to obtain 1 H and 13 C homonuclear through-space triple-quantum -single-quantum (TQ-SQ) correlation spectra in solids [26][27][28][29][30]. A modified INADEQUATE experiment was also proposed to record 13 C through-bond TQ-SQ correlatio...

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Ramped-Amplitude Cross Polarization in Magic-Angle-Spinning NMR

Cited by 1,139 publications

References 0 publications

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation

Triple-quantum correlation NMR experiments in solids using J-couplings

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