L3C CP/MAS NMR

Kg. 35. l3C CP MAS NMR spectra and peak assignments of a cured polystyrylpyridine resin. Stick spectra are drawn from 13C NMR spectra of the model compounds CTC and BP2 in solution (reprinted from Ref. 2391 with permission)... 

As expected, the l3C CP/MAS NMR spectrum of the l3C-enriched Gly-Tyr crystals displays the characteristic doublet (Fig. 91 A). However, the l3C CP/MAS difference spectrum between the CPA (which is also rich in C—N bonds, but which is not13C-enriched) and the CPA/Gly-Tyr complex (Fig. 91B) displays a single resonance. This signifies that, under the experimental conditions, the peptide bond of the Gly-Tyr has been cleaved. To confirm this result, the authors took the 1SN CP/MAS NMR spectrum of the... 

Fig. 43. Transformation of protonated ethanol dimer in HjPWuO, by heat treatment. Solid-state l3C CP/MAS NMR spectra were obtained by using high purity, 3C ethanol (a) Dimer, (b) 333 K, (c) 343 K, (d) 363 K, (e) 373 K, (f) 423 K. Reprinted with permission from Ref. 169. Copyright 1992 American Chemical Society.

Table 1 Observed 13C NMR chemical shifts of the L-alanine residue Cp-carbons for peptides and polypeptides containing the L-alanine residues from l3C CP/MAS NMR measurements, and their main chain dihedral angles and hydrogen-bond length for the L-alanine residues determined by X-ray diffraction studies.

Willis JM, Jagannathan NR, Herring FG (1986) The potential of l3C CP/MAS NMR in the study of kraft pulping kinetics. J Wood Chem Technol 6 249-267... 

Fig. 13. Comparison of l3C CP-MAS NMR (left) and DD-MAS NMR spectra (right) of D85N mutant (black traces) and wild type (dotted traces).153 Reproduced with permission from the Biophysical Society.

Maciel et al. (370,371,374) combined l3C and 15N CP/MAS NMR to study the adsorption of pyridine on silica-alumina. Hydrogen bonding was found to be the dominant interaction at high loading levels (0.5 to 1 monolayer). At lower coverages, a Lewis acid-base complex dominates and the pyridine is significantly less mobile. Bronsted complexes are found when the surface has been pretreated with HC1 gas. 

For /er/-butyl alcohol, we have observed (8f) with l3C CP/MAS and 2H NMR spectroscopy, the formation of tert-butyl silyl ether (TBSE) at temperatures as low as 296 K. In these experiments,, 3C and 2H-labeled tert-butyl alcohols were used ... 

Figure 7. 13CP alanine shielding tensor results. A, 11 Tesla 13C CP-MAS NMR spectrum of crystalline ala-[l3C]ala-ala,vr =1.2 kHz. B, graph showing experimental shift tensor elements versus computed shieldings slope = 1.07, R2 = 0.99. 

Infrared spectra of the unfilled and filled copolymers were measured using a Perkin-Elmer model 1700 FTIR spectrometer. The 13C CP/MAS NMR measurements were conducted on a Bruker 300 instrument operating at 75.51 MHz. The samples were rotated with a spectra width of 40.0 Hz, the CP time was 5 ms. l3C lI distortionless enhancement by polarization transfer (DEPT) technique was applied for analysis of monomers. The process was performed at 75.51 MHz, rotated with a spectral width of 0.75 Hz and a CP time of 15 ms. Atomic force microscopy measurements were carried out using a Nanoscope Ilia controlled Dimension 3000 AFM (Digital Instrument, Santa Barbara, CA). 

In general, l3C CP/MAS techniques depend on the mathematical manipulation which is employed to enhance the resolution of solid state NMR coal spectra.27 The several methods that have been implemented include ... 

This section reports studies on item (1) using solid-state NMR methods ( H CRAMPS, l3C CP/MAS and 13C DD/MAS) and NMR imaging methods. The behaviour from 300 to 550 °C of preheated coals is described using the newly developed high temperature in situ imaging system to clarify the effects of rapid heating on coal properties.98... 

For the 13C CP/MAS measurement and dipolar-dephasing CP/MAS NMR the experimental conditions were 3 ms contact time, 5 s repetition time, 40 kHz spectral width, and 8 k data points. The l3C chemical shifts were calibrated through the hexamethylbenzene peak (17.3 ppm relative to tetramethylsilane). The l3C relaxation measurements were performed with Torchia s pulse sequence."... 

Coal is a very complex material. Although l3C CP/MAS can provide much information on coals, there are very similar molecular structures in coals, so that an approach using multinuclear NMR is very helpful in understanding... 

Fig. 26. I3C CP-MAS NMR spectra of [l-l3C]Val-labeled wild type (A) and D85N (B and D) and D85N/D96N (C and E) recorded at pH 7 and 10. It is noteworthy that the arrowed peaks from the transmembrane helices are displaced to higher frequencies by protonation of Asp 85 at neutral pH and suppressed at pH 10 taking the M-like state.117 The peak at 177.81 ppm is ascribed to Val 213.88 Reproduced with permission from the American Chemical Society.

Fig. 27. I3C DD-MAS NMR spectra of enzymatically cleaved [3-l3C]Ala-labeled C-2 fragment (1-71) incorporated into the DMPC bilayer (A) and lipids from Halobacterium (B) with reference to the CP-MAS NMR spectrum of intact bacteriorhodopsin.16...

Fig. 6. CP-MAS l3C-NMR spectra of polydimethylsiloxane at 75.47 MHz above and below the melting transition. Chemical shifts refer to TMS = 0 ppm and correspond to the scale at the bottom (Ref.10))...

Fig. 8. Slow exchange-fast exchange transition for the conformational interconversion of crystalline cyclotetraeicosane in CP-MAS l3C-NMR spectra at 75.47 MHz. Chemical shifts refering to TMS = 0 ppm and temperatures in K are indicated at the spectra. (Ref.7 )...

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