CP/MAS 13C NMR

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. 

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.

Quantitative solid state 13C CP/MAS NMR has been used to determine the relative amounts of carbamazepine anhydrate and carbamazepine dihydrate in mixtures [59]. The 13C NMR spectra for the two forms did not appear different, although sufficient S/N for the spectrum of the anhydrous form required long accumulation times. This was determined to be due to the slow proton relaxation rate for this form. Utilizing the fact that different proton spin-lattice relaxation times exist for the two different pseudopolymorphic forms, a quantitative method was developed. The dihydrate form displayed a relatively short relaxation time, permitting interpulse delay times of only 10 seconds to obtain full-intensity spectra of the dihydrate form while displaying no signal due to the anhydrous... 

The 13C CP/MAS NMR spectrum taken 30 min after recrystallization of THY is shown in Figure 36A, and the 13C chemical shift values of this spectrum together with those of the THY monomer in CDCI3 solution are summarized in Table 35. 

Shea KJ, Sasaki DY. An analysis of small-molecule binding to functionalized synthetic polymers by 13C CP/MAS NMR and FT-IR spectroscopy. J Am Chem Soc 1991 113 4109-4120. 

C CP/MAS NMR SPECTRAL ANALYSIS AND CONFORMATIONAL CHARACTERIZATION OF HOMOPOLYPEPTIDES AND THEIR .ENDS... 

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.

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