Sample spinning sidebands

CPMAS NMR spectra were acquired on the same Bruker AMX 400 NMR spectrometer with a standard proton decoupled pulse program with a repetition time of 0.53 s, 8K data points, and Hartmann-Hahn conditions being met. For the whole alginate sample, a spin rate of4300 rps was achieved and 6 scans were taken. No improvement was found for increases in delay time from 0.5 to 5 s. A spin rate of 4600 ips was achieved and 16,000 scans were taken for both depolynierized samples. Spinning sidebands at approximately 115 ppm were identified by varying the sample spin rate. 

Figure 7 Natural abundance Mg static (a), 5 kHz MAS (b) spectra of three microporous a-Mg3(HCOO)g phases, and Mg SPAM 3QMAS (c) spectrum of the activated sample. Spinning sidebands. All the spectra were acquired at 21.1T. The dashed lines correspond to the slices taken for simulation. (Reprinted with permission from Ref 17. 2013, Wiley-VCH Verlag GmbH Co. KGaA, 2007.)...

Figure 2. Cs MAS NMR spectra of Cs-exchanged hectorite sample dehydrated at 500°C before analysis at temperatures from 80 to -80°C. The labeled peaks near -120 and +30 ppm are true center bands, and the other peaks are spinning sidebands. After reference 22.

For kaolinite the sample permeability was very low and the solution was poorly removed. The spectra (Figure 3C) are consequently complex, containing peaks for inner and outer sphere complexes, CsCl precipitate from resMual solution (near 200 ppm) and a complex spinning sideband pattern. Spectral resolution is poorer, but at 70% RH for instance, inner sphere complexes resonate near 16 ppm and outer sphere complexes near 31 ppm. Dynamical averaging of the inner and outer sphere complexes occurs at 70% RH, and at 100% RH even the CsCl precipitate is dissolved in the water film and averaged. 

We have referred to the various interactions which can cause line broadening in the solid state. One of these, which is normally not a problem in liquid state NMR, is due to the fact that the chemical shift itself is a tensor, i.e. in a coordinate system with orthogonal axes x, y and z its values along these axes can be very different. This anisotropy of the chemical shift is proportional to the magnetic field of the spectrometer (one reason why ultra-high field spectrometers are not so useful), and can lead in solid state spectra to the presence of a series of spinning sidebands, as shown in the spectra of solid polycrystalline powdered triphenylphosphine which follows (Fig. 49). In the absence of spinning, the linewidth of this sample would be around 75 ppm ... 

There are a lot of other things in a typical NMR. There are spinning sidebands, small duplicates of stronger peaks, evenly spaced from the parent peak. They fall at multiples of the spin rate, here about 30 Hz. Spin the sample tube faster and these sidebands move farther away slow the tube and they must get closer. 

Use of a natural sample. Cq estimated 150 from spinning sidebands span range. Experimental data compared with first-principles calculations in Ref. 40. 

Fig. 20. H MAS NMR spectra of zeolite HZSM-5 (nsi/ Ai = 21.5) before (a) and after (b) adsorption of 0.33mmol acetone-d per gram. In (c) and (d), the ll MAS NMR spectra of zeolite D,HZSM-5 recorded before and after loading, respectively, with 0.34mmol acetone- C-2 per gram of zeolite are shown. The inset (e) is the C MAS NMR spectrum of the sample in (d). Asterisks denote spinning sidebands. Reproduced with permission from (J33). Copyright 2003 The Royal Society of Chemistry.

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