Proton-decoupled CP/MAS

Fig. 38. Proton-decoupled CP/MAS carbon-13 NMR spectrum of an as-cast Fiberite 934 epoxy showing the integration of aromatic and aliphatic carbons...

Fig. 39. Proton-decoupled CP/MAS 14.2-MHz carbon-13 NMR spectra of Fiberite 934 epoxies showing spectral changes due to postcuring and physical aging...

Figure 30. The effect of physical aging on the spectral changes in proton-decoupled CP/MAS carbon-13 NMR measurements.

Figure 6. Proton-decoupled/CP C-13 NMR spectra of PEO at —140°C (a) under MAS conditions (h) nonspinning. The three principal elements of the shielding tensor are indicated in the static spectrum.

Fig. 4.32 Demonstration of the cumulative effects of techniques employed in C CP/MAS SSNMR spectroscopy on a sample of dideoxyinosine. (a) High-power proton decoupling combined with magic-angle spinning (MAS) and cross polarization (CP) (b) high-power proton decoupling and MAS at 5 kHz (c) high-power proton decoupling only and (d) conventional solution phase techniques. (From Bugay 1993, as modified by Byrn et al. 1999.)...

Fig. 6 Centrebands of the proton-decoupled CP and BD NMR spectra (81 MHz) of human trabecular bone, recorded under MAS at 3 kHz [20]. The peaks are presented with the same maximum intensities...

Fig. 8 Proton-decoupled CP NMR spectra (81 MHz) of apatites and BRU recorded with MAS at 1.00 kHz and CT=1 ms [20]. HA was studied as-prepared (hydrated denoted HAh) and calcined (heated at 1073 K denoted HAc). CHA-B contained 9 wt% COf ...

Fig. 7. Nmr spectra of quinine [103-95-0] C2QH24N2O2, acquired on a Bruker 300AMX spectrometer using a Bmker broadband CP/MAS probe, (a) Proton-decoupled spectmm of quinine in CDCl (b) the corresponding spectmm of solid quinine under CP/MAS conditions using high power dipolar decoupling (c) soHd-state spectmm using only MAS and dipolar decoupling, but without cross-polarization and (d) soHd quinine mn using the...

Fig. 9 Examples of simplifying solid state NMR spectra by the TOSS and delayed decoupling pulse sequences. Shown is a comparison of the 31P CP/MAS NMR spectrum of fosinopril sodium utilizing the standard pulse sequence (A) and the TOSS routine (B). Also shown is the full 13C CP/MAS NMR spectrum of fosinopril sodium (C) and the nonprotonated carbon spectrum (D) obtained from the delayed decoupling pulse sequence utilizing a 80 /us delay time. Signals due to the methyl carbon resonances (0-30 ppm) are not completely eliminated due to the rapid methyl group rotation, which reduces the carbon-proton dipolar couplings.

FIGURE 6. The first (proton decoupled) C CP/MAS NMR spectrum of an organolithium spectmm, methylUthium at —150 °C (a) CHjLi, (b) CHjLi, (c) CHjLi with both H and Li high-power decoupling. Reprinted with permission from Reference 95. Copyright 1984 American Chemical Society... 

Fig. 32. CF MAS NMR spectra recorded during the conversion of C-enriched methanol ((U/ F = 100 gh/mol) on calcined zeolite HY (nsi/ Ai = 2.7) at reaction temperatures of 393 K (a), 433 K (b), and 473 K (c). The spectra on the left-hand side were obtained with MAS NMR and proton decoupling (HPDEC), and the spectra on the right-hand side were recorded with the CP technique. Asterisks denote spinning sidebands. Reproduced with permission from (74). Copyright 2001 American Chemical Society.

The resonances observed under MAS and strong proton decoupling were separated and analyzed as a function of the delay between scans to infer the relaxation times, T, and to extrapolate the corresponding intensities to infinite delay. No new spectral features were detected under a Bloch decay experiment, as compared to those under a CP/MAS experiment. The extrapolated Bloch decay intensities were then compared with that of a standard. The results of these measurements are presented in Table 1, The number of surface platinum atoms was also calculated on the basis of the Pt dispersion and Pt loading. Subsequently, the number of chemisorbed carbon atoms per surface platinum atom (Table 1, last column) was calculated. The results indicated that there were 4.0 0.6 chemisorbed carbon atoms per one surface Pt atom and 10.2 1.0 carbon atoms in the highly... 

Most NMR spectrometers have 12 to 18 shim controls (Churmny and Hoult 1990). Each user will adopt their own procedure but the aim is to produce the minimum linewidth consistent with a good lineshape. In practice, some shims are much more significant than others and for particular probes different shims will be important. For solid-state operation, shimming usually needs to be carried out relatively infrequently. One possible procedure for probes tuned to H is to crudely shim on H2O. If there is no proton channel most multinuclear probes will tune to D, so D2O can be used. For CP-MAS probes that tune to - C, adamantane is a useful compound which should be shimmed under spinning and H decoupling conditions. A typical resolution for in admantane of 3-4 Hz at 7.05 T and 10 Hz at 11.7 T should be achieveable. 

Following the first procedure, mineral standards were synthesized and characterized by P MAS NMR [31,42]. BD, CP and DD spectra of mineral standards and bone samples were compared, giving particular attention to chemical shifts (Table 2),linewidths and rotational sideband patterns [35]. A typical set of spectra, acquired for mineral standards, is given in Fig. 7. Each BD spectrum comes from all P-sites, while its CP counterpart exposes a fraction of the P-sites capable of obtaining polarization from surrounding protons. The DD experiment is performed with a time interval without proton decoupling inserted just after CP. This is called a dipolar suppression period (DS), because... 

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