Proton decoupling, high-power

In the case of pharmaceutical solids that are dominated by carbon and proton nuclei, the dipole-dipole interactions may be simplified. The carbon and proton nuclei may be perceived as dilute and abundant based upon then-isotopic natural abundance, respectively (Table 1). Homonuclear 13C—13C dipolar interactions essentially do not exist because of the low concentration of 13C nuclei (natural abundance of 1.1%). On the other hand, H—13C dipolar interactions contribute significantly to the broad resonances, but this heteronuclear interaction may be removed through simple high-power proton decoupling fields, similar to solution-phase techniques. 

Fig. 3 Solid state 31P NMR spectra of fosinopril sodium acquired under single pulse, high-power proton decoupling and various conditions of magic-angle spinning (A) static, (B) 2.5 kHz, (C) 4.0 kHz, (D) 5.0 kHz, and (E) 6.0 kHz. The isotropic chemical shift is designated by an asterisk. (From Ref. 15.)...

Figure 6. Magic angle spinning, high-power proton decoupling, FT C-13 NMR spectrum of cured, carbon-black-loaded polyisoprene at ambient temperature, FT of normal FID without proton enhancement.

Fig. 30. Spectra of filled natural rubber obtained under various conditions without MAS and decoupling (A) with high power proton decoupling but no MAS (B) with MAS but no proton decoupling (C) with MAS and multiple pulse MREV-8 decoupling (D) with MAS and high power proton decoupling (E). Resonance at 43 ppm arises from an antioxidant and it is not a subject of the study (adapted from Ref. 191 )...

Fig. 31. Stacked plot of the heteronuclear two-dimensional J-resolved spectrum of cured, carbon black filled, natural rubber. The proton flip experiment was used with high-power proton decoupling during the detection time. The experiment was performed with the sample spinning at the magic angle (reprinted from Ref. 1911 with permission)...

Quite early on, cross-polarization was used by Chang et al. (352) to improve the quality of the 13CNMR spectrum (Fig. 74) of the surface of chrysotile asbestos (Ch) derivatized with vinylmethyldichlorosilane (Scheme 2). When high-power proton decoupling, magic-angle spinning, and... 

The original development of the basis for SSNMR by Schaefer and Stejskal (1976) through the combination of high power proton decoupling with magic angle spinning and cross-polarization SSNMR techniques for is demonstrated in Fig. 4.32. 

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.)...

Dipolar Coupling and High-Power Proton Decoupling... 

Figure 3.2.11 The experimental 13C spectra of a powder of 99%- 3C2-labeled glycine, acquired at a magnetic field of 9.4 T. High-power proton decoupling was employed during the acquisition, (a) The spectrum of a static sample, (b-d) Spectra for a sample rotating at the magic angle and recorded at a spinning frequency equal to (b) 2.50, (c) 5.30, and (d) 10.00 kHz. Reproduced with permission from Ref. [23],...

One consequence of high-power proton decoupling during observation of F spectra is that resonance frequencies will be affected by the Bloch-Siegert effect [11]. This has been thoroughly investigated by Vierkotter [12] for some nonpolymeric fluorinated compounds, and has been observed for polymeric systems [13]. The shift (expressed as a fraction) is given by ... 

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