Two pulse phase modulation

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). 

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. 

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

Solid-state C NMR was used to compare differences in mobility of the cell wall polysaccharides of apples after 20 weeks of storage. Ng et al. used two Pulse Phase Modulation (TPPM) decoupling was combined with CP and SPE experiments. 

Zujovic et al investigated the mobility of veiy mobile polysaccharides in plant cell walls by NMR method. Mobility of such polysaccharides as arabinan and galactan side chains of pectic polysaccharide rhamnoga-lactouronan I in two apple cultivars was evaluated by the solid-state C NMR. The authors used two pulse phase modulation (TPPM) decoupling which improved the resolution of cross polarisation (CP) and single pulse excitation (SPE) NMR spectra. This methodology facilitated the mobility estimation of mobile polysaccharides in apples cell walls. 

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... 

---