Decoupling high power

Fig. 7. Nmr spectra of quinine [103-95-0] C2QH24N2O2, acquired on a Bruker 300AMX spectrometer using a Bmker broadband CP/MAS probe, (a) Proton-decoupled spectmm of quinine in CDCl (b) the corresponding spectmm of solid quinine under CP/MAS conditions using high power dipolar decoupling (c) soHd-state spectmm using only MAS and dipolar decoupling, but without cross-polarization and (d) soHd quinine mn using the...

Many components of food are in the solid state and possess very short T2. The linewidths from solid components are generally too wide to be observed directly by solution state NMR methods. However, these components can be detected by the special techniques of solid state NMR. These techniques involve the use of cross polarization excitation (from 3H to 13C), high power 3H decoupling (to inhibit... 

DD (1) Dipole-dipole interactions (2) Decoupling/double resonance (high power 1H decoupling) (3) Direct deposition... 

Carbon-13. The molecular structure of phosphino-thioformamides (27) and their chalcogenides have been studied in the solid and liquid states.57 The, 3C n.m.r. spectra of solid methylphenyl phosphonium salts have been studied using high power decoupling cross-polarisation and slow magic angle rotation. 

In the early days of carbon-13 spectroscopy, high power decoupling was used and NOE measurements had to be carried out in such a way that temperature was identical for both experiments (interleaved experiments with shift of the proton frequency). With modem spectrometers, such... 

However, typical polarization transfer efficiency reported for 13C-13C TOBSY measurements of polypeptides is significantly less than the theoretical maximum. One of the major reasons is due to the requirement of high power 1H decoupling during the polarization transfer, which is usually set to be three times larger than the recoupling field [37, 77]. 

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.)...

The basic components of the solid state spectrometer are the same as the solution-phase instrument data system, pulse programmer, observe and decoupler transmitters, magnetic system, and probes. In addition, high-power amplifiers are required for the two transmitters and a pneumatic spinning unit to achieve the necessary spin rates for MAS. Normally, the observe transmitter for 13C work requires broadband amplification of approximately 400 W of power for a 5.87-T, 250-MHz instrument. The amplifier should have triggering capabilities so that only the radiofrequency (rf) pulse is amplified. This will minimize noise contributions to the measured spectrum. So that the Hartmann-Hahn condition may be achieved, the decoupler amplifier must produce an rf signal at one-fourth the power level of the observe channel for carbon work. 

The methods of high power decoupling, cross-polarization and magic angle spinning produce useful spectra from intractable polymers. In a rather rigid material... 

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