CPMAS sample spinning

NMR Experiments 29Si-NMR spectra were obtained on a Bruker CXP-200 solid state high power and high resolution spectrometer equipped with the Bruker 3C-CPMAS accessory. Chemical shifts are reported relative to tetramethylsilane (TMS), to an accuracy better than can be justified from the line-widths (about 2.5 ppm) in these materials. The sample spinning rate was usually between 3 and 4 kHz, and no spinning side bands were observed. 

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. 

For the morphological discussions, NMR measurements must be carried out in the solid state. The cross-polarization and magic angle sample spinning (CPMAS) for and the solid echo pulse sequence for are practical methods. From CPMAS measurements, the spectrum similar to the solution NMR spectrum is observed. NMR chemical shifts are easily obtained from the CPMAS spectrum. Furthermore, the application of the sequence developed by Torchia supplies Tj in the solid state. However, C NMR measurements are time consuming because of the low natural abundance of C nucleus. Tj of H can be observed easily by the solid echo... 

Fig. 9 15N 1H CPMAS spectra of the fibril sample formed by huPrPJ27 i47 (15N labeled at PI 37 and S143) at a spinning frequency of 20 kHz. (a) Contact time of 100 ps. (b) Contact time of 2 ms. (Figure and caption adapted from [50]. Copyright 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim)...

FIGURE 54. 29Si CPMAS NMR spectra of (a) kaolinite and (b) kaolinite-DMSO. The spinning rate of the sample was 3.00 kHz. Reproduced by permission of Elsevier Science from Reference 153... 

By monitoring the H MAS spectra, it has been suggested that the loss of water from bone tissue is an irreversible process under air drying conditions.38 It has been shown that CP transfer within an isolated heteronuclear spin pair will exhibit a characteristic oscillation, from which the dipolar coupling constant can be accurately determined.197 The technique of LG-CPMAS can probe this oscillation pattern due to a dominating 31P-1H interaction in a dipolar coupled network, if any. However, such oscillation is seldom observed in 31P 1H CPMAS measurements of biominerals because of the damping effect of the homonu-clear dipole-dipole interaction. Thus, it is rather remarkable that the buildup curve of 31P 1H LG-CPMAS obtained for a sample of powdered femoral cortical bone, which is partially hydrated, shows a distinctive... 

Solid-state experiments use a dry sample that is packed into a rotor and spun at high frequency inside the spectrometer s magnetic field. This approach is termed cross-polarization magic angle spinning (CPMAS), and is the standard protocol for solids. It relies on transfer of magnetization from protons to C (or other nuclei) in order to achieve rapid analyses with reasonably narrow spectral lines. Cody et al. 

Fig. 18.9. Fluorine-19 CPMAS spectra of PVDF (biaxially stretched film), showing the discriminatory effect of a precontact delay (with H spin-locking) following a 90° proton pulse, combined with the use of a short (100 /as) contact time, (a) Precontact delay zero, (b) Precontact delay 40 ms. The signal for amorphous domains does not appear in (b). The sample contains both a and crystallites. The signals from head-to-head units are also lost in (b) and, therefore, reside principally in amorphous regions. [Figure reproduced with permission from Ref. 72.]...

Fig. 18.10. The effect of crystallite phase on PVDF CPMAS spectra. Top. sample crystallised from the melt (a form). Bottom 9-p.m thick biaxially drawn film ()3 form with a little a). Spectra were obtained using the Tip filter (precontact H spin lock 40 ms, contact time 50 p-s).

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