TPPM sequence

Solid-state C variable-amplitude cross polarization magic-angle spinning (VACP/MAS) nuclear magnetic resonance (NMR) spectra were acquired for the sorbitol samples. Proton decoupling was achieved by a two-pulse phase modulation (TPPM) sequence. Identical C spectra were measured for the y-form sorbitol samples, and a representative spectrum is shown in Figure 9. 

Using the OPENCORE NMR spectrometer, standard solid-state NMR experiments have been demonstrated in Ref. 2. They include 1H-13C CPMAS with TPPM decoupling, 13C-15N dipolar recoupling under MAS, 1H FSLG, 13C-13C 2D exchange, and so on. Here we show two more examples, where the spectrometer was used to implement standard pulse sequences, but in somewhat demanding circumstances in terms of sensitivity. 

The spectrometer supports phase cycling, asynchronous sequence implementation, and parameter-array experiments. Thus, most standard solid-state NMR experiments are feasible, including CPMAS, multiple-pulse H decoupling such as TPPM, 2D experiments, multiple-quantum NMR, and so on. In addition, the focus of development is on its extension of, or modification to, the hardware and/or the software, in the spirit of enabling the users to put their own new ideas into practice. In this paper, several examples of such have been described. They include the compact NMR and MRI systems, active compensation of RF pulse transients, implementation of a network analyzer, dynamic receiver-gain increment,31 and so on. 

Fig. 5 Radio frequency pulse sequences for measurements of Sj and Si in DSQ-REDOR experiments. The MAS period rR is 100 ps. XY represents a train of 15N n pulses with XY-16 phase patterns [98]. TPPM represents two-pulse phase modulation [99]. In these experiments, M = Nt 4, N2+ N3 = 48, and N2 is incremented from 0 to 48 to produce effective dephasing times from 0 to 9.6 ms. Signals arising from intraresidue 15N-13C DSQ coherence (Si) are selected by standard phase cycling. Signal decay due to the pulse imperfection of 15N pulses is estimated by S2. Decay due to the intermolecular 15N-I3C dipole-dipole couplings is calculated as Si(N2)/S2(N2). The phase cycling scheme can be found in the original figure and caption. (Figure and caption adapted from [45])...

Proton-proton homonuclear decoupling has been performed by the ESLG decoupling sequence [46]. Quadrature detection in coj was achieved by using the time proportional phase increment method (TPPI) [47]. During the acquisition period, two pulse phase modulation (TPPM) heteronuclear decouphng ]48] was applied (Figure 7.6). 

The new decoupling pulse sequences CNvn as shown in Fig. 4 were found to be competitive with TPPM. Furthermore, as can be seen from Fig. 5, they... 

Figure 7 31P CP spectra for O-phospho-L-threonine spun at 60 kHz and recorded employing different decoupling sequences (A) cw (B) tppm (C) spinal and (D) xix.

Figure 13 Pulse sequence for the solid-state 31P—1H frequency-switched Lee-Goldburg (FSLG) experiment. Proton-proton homonuclear decoupling was performed by using the FSLG decoupling sequence. Quadrature detection in Wi was achieved by using the TPPI method. During the acquisition period, TPPM heteronuclear decoupling was applied.

It has been shown that appropriate modulation of the r.f. amplitude in the two-pulse phase-modulation (TPPM) H decoupling sequence provides an... 

In solid-state NMR experiments, a central theme is that of resolution. For C CP MAS NMR, a critical factor in this respect is the efficiency of H decouphng. The simplest method, which is termed continuous wave (CW) decoupling, involves the application of a continuous rf pulse of fixed phase for the duration of the acquisition of the FID [28]. Recently, more sophisticated decoupling methods, such as TPPM [29] or other sequences possessing a RN symmetry [30], have been introduced an explanation of why these methods yield narrower C hnewidths than... 

In the range Vr < v dec < 2fR, strong decoupUng sidebands are observed [104]. Several sequences for decoupUng have been successfoUy tested at ultrafast MAS low-power XiX [107], low-power TPPM [HI], swept low-power TPPM [105], and low-ampUtude PISSARO [112],... 

A new scheme for heteronuclear decoupling, phase-inverted supercycled sequence for attenuation of rotary resonance (PISSARRO), designed for fast MAS has been reported. " Its efficiency compares favourably with CW, TPPM, SPINAL and XiX decoupling methods at medium and high rf amplitudes, particularly under conditions where the efficiency of decoupling is affected by undesired rotary resonance effects. 

For heteronuclear decoupling, the TPPM (Two Pulse Phase Modulation) sequence " is now widely employed in solid-state NMR. It was extended to PMFM and FMPM by Gan and Ernst, who also found that the phase inversion in TPPM brings about a secondary averaging that further reduces the heteronuclear coupling. Eden and Levitt revisited the problem of heteronuclear decoupling based on the symmetry consideration of the Hamiltonian. Based on the property of the lower orders of the interaction Hamiltonians, a general theorem on the pulse sequence was conjectured that allows one to predict which terms are eliminated and which are symmetry-allowed without... 

MELODRAMA sequence illustrated in (a). Pulse phase detection in all dimensions is accomplished by standard phase cycling procedures. High-power on-resonance CW decoupling is used during mixing periods, and TPPM decoupling during acquisition. (Adapted, with permission, from Sun et al. )... 

Figure 3-3. Carbon-13 CPMAS spectra (a-c) and the chemical structure of nematic 135 (top). The spectra were obtained using CW (a), TPPM (b) and SP1NAL64 (c) decoupling of protons at 40 °C (10°C above the crystal to nematic phase transition) using a cross-polarization sequence. The C-F interactions degrade the resolution in spectra (a) and (b), while the SPINAL64 enhances the spectral resolution and enables the measurement of C-F dipolar couplings (c). C-F dipolar sphttings are indicated in (c). Reprinted from reference 21, with permission from the Chemical Physics Letters...

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