Decoupling sequence

Many variations of this experiment are known. Some of the pulse sequences used for recording heteronuclear 2D/resolved spectra are shown in Fig. 5.8. In a modified gated decoupler sequence (Fig. 5.8b), the decoupler is off during the first half of the evolution period and is svdtched on during the second half. Any C resonances that are folded over in the F, domain may be removed by employing the fold-over corrected gated decoupler sequence (FOCSY) (Fig. 5.8c) or the refocused fold-over corrected decoupler sequence (RE-FOCSY) (Fig. 5.8d). 

Finally, it is important for optimal resolution and thus sensitivity to use a proper decoupling sequence when necessary, during both the evolution and detection... 

Fig. 14. SeqHNCA-TROSY experiment for establishing sequential 1HN(i), 15N(i), 13Ca(i— 1) correlations in 13C/15N/2H enriched proteins. Durations of transfer delays A = 1/(4/Hn) 2Ta = 20-27 ms, depending on rotational correlation time of protein 2Tc = 5-7 ms S = gradient + field recovery delay 0 < k < Ta/t2,max- Phase cycling i = y (j>2 = y, — y + States-TPPI 0 = x 0ret. = x, — x. Semi-selective decoupling of 13C spins is attained using a SEDUCE-1 decoupling sequence.95...

Fig. 19 a, b. Nuclear spin decoupling in ENDOR. a) ENDOR spectrum of Cu(gly)2 in a-glycine vp free proton frequency, b) Decoupling sequence of the doublet structure of the proton H2 (I nucleus) for various pumping fields B2eff at H3 (K nucleus). (Ref. 40)... 

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 inclusion of average Hamiltonian theory derived pulse sequence building blocks specifically designed for the measurement of RDCs is highly desirable. The homonuclear dipolar decoupling sequences used in ref. 190 lead to the less complex multiplet structures observed in isotropic samples with the chemical shift resolution reduced by a factor of 2-3, depending on the multiple pulse... 

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.

Some of the pulse sequences involve additional refocusing pulses in the l3C channel, the proton channel, or both channels. This discussion and examples presented here are confined to the simplest of interrupted-decoupling sequences, as illustrated in Fig. 4.5.2, since the reader may not have access to the computer code for the more sophisticated versions. 

Fig. 5.4.4a-c. nC NMR sequences a Routine sequence with broad band H decoupling, b Inverse gated decoupling sequence (1GD) for quantitative analysis c Time sequence for 1-D and 2-D pulse NMR experiments... 

The 180° 13C pulse at the middle of the evolution period interchanges the precession frequencies of the a and /3 spins (see Fig. 9.2, bottom) and effectively decouples the spins during tu and a broadband decoupling sequence, such as WALTZ or GARP, is applied during f2.Thus, the 13C spectrum in the F2 dimension is decoupled, and the H spectrum in the Fx dimension retains homonuclear couplings but is also decoupled from 13C, as illustrated in Fig. 10.106. 

The CP can be used with different decoupling sequences during the acquisition (these should also be optimized). 

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