Magic Angle Spinning MAS NMR

When the MAS experiment is appHed to quadrupolar nuclei such as Al, the quality of the NMR spectrum depends dramatically on the magnitude of compared with both the MAS spin rate and the magnetic field, Bq. Excellent spectra are obtained for small Cq sites when studied with high-speed MAS spin rates at high Bg. Conversely, Al sites can be invisible for high Cq values and modest MAS spin rates and Bo, note the evolution in line shapes for the Al MAS NMR spectra in Fig. 7.11. Likewise, the four-coordinate AIO4 sites in an aluminum isoproxide complex, with Cq = 12.3 MHz, are observable at 20 kHz and 19.6 T while three-coordinate aluminum sites in related complexes, with Cq 30 MHz, are not observable [14], 

There are many relaxation paths and experiments to measure the relaxation kinetics. Three common relaxation pathways are  

Solid-state NMR is, among techniques which measure molecular motion, capable of measuring an extremely wide range of motional rates. When Tj measurements are included, rate constants of more than 10 orders of magnitude are accessible. In addition to methyl group rotation, the combination of deuteration and solid-state NMR has yielded molecular dynamic information on phenyl groups, aliphatic chains, and ethene bound to transition metal centers. 

In any imaging experiment, the critical issues are sample preparation, image contrast, spatial resolution, field of view, and total time of the experiment Relative to other imaging techniques, the NMR spectroscopists s control over the image contrast mechanisms is exceptional. Of course, MRI images are affected by the number of nuclei in each volume element In addition, the NMR relaxation dynamics, Ti and T2, can be used to control image contrast, especially for the soft tissues in the human body. Sample preparation is perfectly simple for the patient remove metal objects and lie still. For inanimate objects, sample preparation of 

To visualize the effect of a pulse sequence with the rotating frame description, one makes the following assumptions  

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A. R. Tate, P. J. D. Foxall, E. Holmes, D. Molca, M. Spraul, J. K. Nicholson, J. C. Lindon 2000, (Distinction between normal and renal cell carcinoma kidney cortical biopsy samples using pattern recognition of H-l magic angle spinning (MAS) NMR spectra), NMR Biomed. 13, 64-71. 

Although limited by sensitivity, chemical reaction monitoring via less sensitive nuclei (such as 13C) has also been reported. In 1987 Albert et al. monitored the electrochemical reaction of 2,4,6-tri-t-butylphenol by continuous flow 13C NMR [4]. More recently, Hunger and Horvath studied the conversion of vapor propan-2-ol (13C labeled) on zeolites using 1H and 13C in situ magic angle spinning (MAS) NMR spectroscopy under continuous-flow conditions [15]. 

The A1 Magic Angle Spinning (MAS)-NMR spectra were obtained in a Bruker MSL-400 spectrometer (N =104.25 MHz). A 2 s pulse (30° degree) was used with a repetition time of 2 s between pulses in order to avoid saturation effects. Zircona cylindrical sample... 

Mainly during the last decade structural information regarding flavonoids associated with other molecules has been reported. High-resolution H magic angle spinning (MAS) NMR spectroscopy has been used to investigate the structural basis for the antioxidative effects of... 

Modified mesoporous materials are usually characterised by various methods, such as elemental analysis (EA). This often involves studying the loading of the metal and performing powder X-ray diffraction (XRD), N2 adsorption, magic angle spinning (MAS) NMR spectroscopy ( C, Si), IR spectroscopy and in some cases EXAFS spectroscopy. 

TS-1 has been obtained by the hydrothermal crystallization of a gel obtained from TEOS and TEOT in the presence of tetrapropylammonium hydroxyde (TPA-OH). The structure of TS-1 has been demonstrated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), microprobe analysis, and 29Si magic-angle spinning (MAS) NMR spectroscopy. Furthermore, an absorption band in the IR spectrum at 960 cm-, present in TS-1 and absent from that of silicalite, was initially considered a fingerprint for the characterization of TS-1. However, later work (discussed below) has shown that this band is also present in many other silica compounds, and therefore its relation to framework Tilv is not straightforward. 

Structure identification, quantifying relative cage occupancies. 1II NMR has been used for ethane, propane, and isobutane hydrates (Davidson et al., 1977 Garg et al., 1977), while 2H, 19F, 31P, and 77 Se NMR have been used for several si guests (Collins et al., 1990). 13C cross-polarization and magic angle spinning (MAS) NMR techniques have been applied to study hydrates of carbon dioxide, methane, and propane (Ripmeester and Ratcliffe, 1988, 1999 Wilson et al., 2002 Kini et al., 2004). 

Correlating positively with the hydrophobicity of the solvent, different fractions of inactivated active centers were measured in different solvents with solid-state NMR spectroscopy (13C-cross-polarization/magic angle spinning (MAS) NMR) (Burke, 1992). Just as with tritiated water (see above), immediate desorption of water molecules from the protein surface was observed after addition to the organic solvent. 

Magic angle spinning (MAS) NMR brings the power of H NMR to solid-phase chemistry [2,25], A simple MAS spectrum, that of the reaction product of succinic anhydride and TentaGel S NH2, is shown in Fig. 2. Presaturation of the PEG resonance at 3.6 ppm is critical to spectral quality. The complex peaks from 3.4 to 3.9 ppm are due to residual PEG, 13C satellites and the terminal CH2 of the PEG chain. The characteristic doubling of the solution-phase CDC1, and TMS resonances can be seen. 

We report (i) isomorphous substitution of boron, by secondary synthesis, into silicalite and into highly siliceous (Si/Al>400) ZSM-5 and (ii) an improved direct synthesis of zeolite (Si,B) -ZSM-5. The chemical status of B in die boronated products depends upon reaction conditions. Careful control of the concentration of the base, the borate species and of die duration of treatment, allows the preparation of samples containing only 4-coordinated B or a mixture of 3- and 4-coordinated B in various relative concentrations. The products were characterized by magic-angle-spinning (MAS) NMR and infrared (IR) spectroscopies and by powder x-ray diffraction (XRD). 

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