CPMAS condition

Dynamics of nano- to picosecond proton transfer processes in the N labeled polycrystalline tetraaza[14]annulene have been studied by a combination of 9.1 MHz N Ti relaxation time measurements under CPMAS conditions and by 46 MHz H Ti relaxation time measurements of a static sample of a doubly deuterated sample. 

Nitenpyram and its metabolites. The metabolites of nitenpyram, CPMA and CPMF, are determined by HPLC under the same conditions as for the parent nitenpyram. The retention times of nitenpyram, CPMA, and CPMF are 9.2,7.9 and 5.3 min, respectively. However, these compounds are unstable and need to be derivatized to a more stable compound, CPF, prior to analysis. It is necessary to remove acetone from the extract before derivatization, because a by-product can be formed in the presence of acetone thus impacting the recovery of CPF. Nitenpyram is more effectively determined using HPLC, whereas CPF, as the analyte of nitenpyram and its metabolites, is more effective by gas chromatography/flame thermionic detection (GC/FTD). 

Figure 2 Schematic representation of carbon spin-lattice relaxation time, T,c, and spin-spin relaxation time under CPMAS or DDMAS condition, T2C, as a function of correlation times.

CAL-4 was prepared according to the procedure described in reference 2. Powder XRD confirmed the absence of contaminant phases. 13C MAS NMR spectra were recorded under cross polarization conditions (CPMAS). Single-crystal XRD data were collected at room temperature using MoK radiation. 

Under MAS, the Hartmann-Hahn condition for 3Q-CPMAS of spin-3/2 nuclei can be written as... 

FIGURE 28. 39.758-MHz CPMAS 29Si NMR spectrum of solid 1,1,1-trimethyltriphenyldisilane. (a) Slow spinning (206 Hz), (b) Fast spinning (3.2 kHz). The two spinning sideband manifolds in (a) are indicated by different symbols. Experimental conditions contact time 8 ms, recycle time 10 s, number of transients 2090 (a) and 405 (b). Reproduced by permission of the Royal Society of Chemistry from Reference 140... 

There has been some recent criticism of the Maillard reaction as a possible humification pathway (Burdon, 2001 Sutton and Sposito, 2005 von Liitzow et al., 2006). First, the critics argue that the Maillard reaction results in the formation of heterocyclic N, whereas soil N consists primarily of amide N based on 15N CPMAS NMR (Knicker and Liidemann, 1995 Knicker, 2004) studies. However, Jokic et al. (2004a) clearly showed, using N K-edge XANES, that the Maillard reaction catalyzed by bimessite under ambient temperature conditions and environmentally relevant pH not only produces heterocyclic N but also a significant amount of amide N (Figure 2.8). 

Birnessite (8-Mn02) Condensation of glucose and glycine under soil ambient conditions (measurement of optical density) yields of humic substances XANES study of change in speciation of Mn ESR study of Mn speciation in solution 13C CPMAS NMR spectra of FA fraction resembling spectra of natural FAs Jokic et al. (2001b)... 

Cross polarization under MAS condition (CPMAS) is nowadays a ubiquitous technique in the studies of crystalline and amorphous systems. 31P 1H CPMAS is well suited for the study of biomineralization because... 

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... 

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. 

Conformational characterization of these samples was made on the basis of conformation-dependent C and chemical shifts determined from CPMAS NMR and also from the characteristic bands in the IR spectra. Synthetic conditions and characteristics of these samples are summarized in Table 4. 

The spectrum of the spin-1/2 nucleus will depend on d and on I /iso I, to first order. Here, aa and jSd are the polar angles describing the orientation of the intemuclear vector in the EFG PAS. As the observed spectrum depends on R, intemuclear distance information can also be obtained under favourable conditions. For example, shown in Figure 4 are the CPMAS spectra of the carbonyl carbon of 2-chloro-2-(phenylsulfonyl)-l-phenylpropanone, obtained at 2.35 and... 

Fig. 5. The theoretical (right) and experimental (left) H a CPMAS spectra of NaH2PO4.H20 with wn = 60.0 kHz, to, = 3.5 kHz for different matching conditions (A) wis - 31.0 kHz, (B) = 58.0 kHz with different contact times (all less than one...

Gly-Tyr was synthesized as both the [ C]-amido (90 atom % enrichment and amido-[ C, N] (90 atom % enrichment, respectively) isotopomers by known methods. CPA, purchased from Sigma as a suspension in toluene, was crosslinked and soaked with Gly-Tyr as described previously, and the washed, dried crystals examined by solid-state NMR. The C CPMAS NMR spectrum of the C-enriched Gly-Tyr (Fig. 12) displays residual C- N quadrupolar coupling (8 = 176 ppm). However, the C CPMAS difference spectrum of CPA and the CPA/Gly-Tyr complex (Fig. 12) displays a single resonance (5 = 178 ppm, LW /2 60 Hz) revealing that, under the experimental conditions, the peptide bond of this slow reacting substrate has been cleaved to the extent of > 90%. 

When poly(ethylene oxide) (PEO) powders are y-irradiated under vacuum they are observed [43] to crosslink. The CPMAS/DD and MAS/DD NMR spectra of virgin and vacuum y-irradiated POE (see Figure 5.18) show [44] marked differences. The MAS/DD spectrum of unirradiated PEO shows a well-resolved resonance at 72.36 ppm due to carbons in mobile amorphous regions, which have relatively short values, whilst at 73.43 ppm the CPMAS spectrum shows a weak, broad envelope of resonances due to rigid crystalline carbon environments. The corresponding irradiated PEO sample, on the other hand, presents well-resolved resonances for both crystalline (under CPMAS/DD) and amorphous (under MAS/DD) carbons. Figure 5.18(b) shows that under CP conditions, the crystalline resonances are efficiently cross-... 

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