13C CP-MAS NMR spectra

Szlyk et al.109 have studied the di-Schiff bases Zn(II) complexes, being derivatives of (7R/2R)-l,2-diaminocyclohexane and 5-bromo- or 5-chloro-salicylaldehydes by means of 1H and 13C NMR in CDCI3 and 13C CP MAS NMR spectra. 

Noteworthy NMR studies involving nuclei other than phosphorus have been carried out for some P-chloro-NHPs where the possible occurrence of spontaneous P-Cl bond dissociation was probed by II NMR titrations and 35C1 NMR [20], and for P-cyclopentadienyl derivatives where measurement of solid-state 13C CP-MAS NMR spectra allowed one to substantiate the preservation of the circumambulatory ring migration of cyclopentadienyl groups in the solid state [47], Several neutral and cationic derivatives have also been studied by 15N NMR [20, 53],... 

X-ray studies showed that all the complexes listed in Table 4 are crystalline and displayed the diffraction patterns as predicted from the molecular models, in which the a-CD cavity is threaded by an OE chain but not by a squalane chain, and also from the experimental finding that a-CD forms complexes with the former but not with the latter. The fact that neither jS-CD nor y-CD can complex with OE may be ascribed to the thickness of the OE chain that is too thin to interact effectively with the inner surfaces of these CD rings. The 13C CP/MAS NMR spectra of the a-CD-OE complexes were similar to those of a-CD-PEG complexes, exhibiting each carbon atom of glucose as a single peak. Thus, the a-CD molecules in the complex with OE assume a symmetrical conformation and each glucose unit finds itself in a similar environment. 

The observed 13C CP/MAS NMR spectra of pure PLA and pure PLV are shown in Fig. 3 (a) and (d), respectively. The assignments of these spectra are straightforwardly made by using reference data of polypeptides with the a-helix and p-sheet forms reported previously.21,22,26 The 13C chemical shift values of these polypeptide samples are listed together with reference data of PLA and PLV with the right-handed a-helix form and the p-sheet form in Table 3. The three intense peaks at 177.0, 53.2, and 15.8 ppm which appear in the spectrum of pure PLA (Fig. 3 (a)) can be assigned to the C=0, Ca and Cp carbons, respectively. From these 13C chemical shift values, it is found that PLA takes the right-handed a-helix form. There are no peaks which come from the P-sheet form. On the other hand, in the spectrum of PLV (Fig. 3 (d)), the four intense peaks appear at 172.4, 58.9, 33.2 and... 

The observed 13C CP/MAS NMR spectra of PLA, PLIL and the PLA/PLIL (20/80, 50/50 and 80/20 wt/wt%) blend samples, prepared by adding a TFA solution with a 2.0 wt/wt% amount of H2S04 to alkaline water (Method 5), are shown in Fig. 7. In the spectra, homopolypeptides of PLA (a-helix) and PLIL ((3-sheet) are treated using the same condition as for the mixture of PLA/PLIL blend samples. The assignments of these spectra are made by the above mentioned method. The 13C chemical shift values of these polypeptide samples are listed together with the reference data of PLA in the right-handed a-helix form and the (3-sheet form, and PLIL in the (3-sheet form in Table 6.21,22,26 The reference 13C chemical shift data were used... 

Fig. 6. Expanded 13C CP/MAS NMR spectra for the carbonyl-carbon region and for the Ca, Cp and Cy carbons region of PLA/PLV (50/50) blend sample.

Fig. 10. 13C CP/MAS NMR spectra of PG (O), PLV (A) and PG/PLV blend samples which were prepared by adding their TFA solutions with a 2.0 wt/wt% amount of H2S04 to alkaline water (Method 5). Homopolypeptides of PG (3 -helix) and PLV (P-sheet) are prepared using same condition as PG/PLV (80/20, 50/50, 20/80) blend samples. The symbols of star ( / ) show the new signals that were produced by this blend condition, (a) PG, (b) PG/PLV (80/20), (c) PG/PLV (50/50), (d) PG/PLV (20/80) and (e) PLV.

Fig. 65. 13C CP/MAS NMR spectra of offretite and blocked ofTretite containing TMA+ cations (345).

In figure 9.29, 13C CP MAS NMR spectra for APTS modified silica, cured at 423 K on air and under vacuum are given. Corresponding peak positions are displayed in table 9.7. 

A considerable amount of work has been done on comparing free radicals in humic substances and melanoidins by ESR,539 as well as by 13C-CP/MAS NMR spectra and <513C and <515N values. These studies have not been able to define the role played by the melanoidins, but do not exclude their participation either. 

Figure 4. C 1FI [ DEPT NMR spectra for DVB and St monomers and 13C CP/MAS NMR spectra for DVB-St copolymers filled with methyl- (/) and methyl,hydride-containing silicas (2).

Figure 6. C II jDF.PT NMR spectra for MEDDE monomers and 13C CP/MAS NMR spectra for MEDDE-DVB copolymer filled with methyl,hydride-containing silica.

Maciejewska et a/.87 have published 13C CP/MAS NMR spectra of nine 4 -substituted-4-dimethylamino-tra/Ji-azobenzenes 27 (Table 13). The nonequivalence of C2/C6 and of C2 /C6 was observed and the difference in 13C chemical shifts was 14.0-22.0 ppm for C2/C6 and 12.2-22.5 for C2 /C6. The 13C CP/MAS NMR spectra of the compound with 4 -CHO substituent were measured in the temperature range 298-373 K but the spectra did not exhibit any substantial changes except for a small high-frequency shift of all resonances. These results confirm the lack of ring dynamics in the above-mentioned temperature range. 

Maciejewska" has published 13C CP/MAS NMR spectra of 2-methyl-4-(4-X-phenylazo)imidazoles. Proton transfer phenomena can occur in imidazoles. Depending on the nature and orientation of the substituent X it was possible to identify one tautomer for X = H, Br and N02 and two tautomers for X = OCH3. Solid 2-methyl-4-(4-X-phenylazo)imidazoles form hydrogen-bonded chains with N—H- N bonds and C—H- O or C—H- N interactions. 

The nonequivalence of some signals that are equivalent in solution NMR complicates the interpretation of the 13C CP/MAS NMR spectra of azo dyes, even for simple compounds where the chemical shifts measured in solution and their interpretation are available. The dipolar dephasing experiment permits the selective measurement of nonprotonated carbon (i.e. with no directly bound hydrogen). We have used Q,Ds deuterated isotopomers88 in the analysis of the 13C CP/MAS spectra of azo dyes. I3C CP/MAS NMR spectra of 4-[/V,/V-bis(2-hydroxyethyl)amino]azobenzene (28), 2-hydroxy-5-ter -butylazo-benzene (29) 4-(Ar,A-dimethylamino)azobenzene (30), 4-methoxyazobenzene (31) and 4-hydroxybenzene (32) were recorded. 

Harris et al.9i used C. I. Pigment Red 57 1 as a model compound in testing a pulse sequence for generating 13C CP/MAS NMR spectra of proton-bearing carbons only. The sequence is based on difference spectroscopy and enables the observation of peaks that are otherwise severely overlapped by others. 

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