DIPSI pulse sequence

Fig. 18. The pulse sequence of a ID ge-NOESY-TOCSY experiment, tnoe is the NOE mixing time, 5 are optional delays which can be used for z-filtration [81] or for suppression of ROE effects in macromolecules (2 x (5 + Tgrad) = 0.5 x mixing time). DIPSI-2 [78] sequence was used for isotropic mixing. Phases were cycled as follows 0i = 2x, 2(—x) (j)2 = X, —x Ip = X, 2 —x), X. Rectangular PFGs, G = 6 Gauss/cm and Gi = 7 Gauss/cm, were applied along the axis for Xpad = 1 ms.

Fig. 1. Basic pulse sequence and CP diagram for gradient-based spin-locked ID exf>eriments. A 1 (— 1) 2 gradient ratio selects N-type data (solid lines) while 1 (— 1) (—2) selects P-type data (dashed lines). When SL stands for a -filtered DIPSI-2 pulse train, a ge-lD TOeSY is performed. On the other hand, when SL stands for a T-ROESY pulse train, a GROESY experiment is performed. S stands for the gradient length.

Phase-modulated multiple-pulse sequences with constant rf amplitude form a large class of homonuclear and heteronuclear Hartmann-Hahn sequences. WALTZ-16 (Shaka et al., 1983b) and DIPSI-2 (Shaka et al., 1988) are examples of windowless, phase-alternating Hartmann-Hahn sequences (see Table II). 

Only recently, new multiple-pulse sequences that were developed specifically for broadband heteronuclear Hartmann-Hahn experiments in liquids were reported. The SHR-1 sequence developed by Sunitha Bai et al. (1994) consists of a windowless phase-alternated composite pulse R, which is expanded according to the MLEV-8 supercycle. R was optimized based on a phase-distortionless single-spin 180° composite pulse and is related to the composite pulses used in DIPSI-1 (Shaka et al., 1988) and the composite pulses in the homonuclear IICT-1 sequence (Sunitha Bai and Ramachandran, 1993). The bandwidth of the SHR-1 sequence is comparable to the bandwidth of DIPSI-3, albeit with a slightly reduced transfer efficiency (Sunitha Bai et al., 1994 Fig. 33F). 

Broadband Hartmann-Hahn sequences, such as DIPSI-2 or WALTZ-16, can be made band-selective by reducing the rf amplitude of the sequences (Brown and Sanctuary, 1991). Richardson et al. (1993) used a low-amplitude WALTZ-17 sequence for band-selective heteronuclear Hartmann-Hahn transfer between N and in order to minimize simultaneous homonuclear Hartmann-Hahn transfer between and The DIPSI-2 sequence was successfully used by Gardner and Coleman (1994) for band-selective Hartmann-Hahn transfer between C d and H spins. So far, no crafted multiple-pulse sequences have been reported that were optimized specifically for band-selective heteronuclear Hartmann-Hahn transfer. Based on the results of Section X, it is expected that such sequences with well defined regions for coherence transfer and effective homonuclear decoupling will result in increased sensitivity of band-selective heteronuclear Hartmann-Hahn experiments. 

Spectra were recorded on Bruker AMX-500 and DMX-750 NMR spectrometers at 30 C. All triple resonance experiments and the HCCH-TOCSY experiment were performed on a single sample of 15N, l3C-ubiquitin in 90% H2O/10% D20 buffer. HCCH-TOCSY spectra were obtained using the pulse sequence described by Bax et al. (1990) and utilized a 27 ms DIPSI-3 mixing sequence. The HCCH-TOCSY data sets were composed of 92 complex points in the... 

The performance of multiple-pulse sequences can be calculated using average Hamiltonian theory. For WALTZ and DIPSI the average Hamiltonian up to first order is given by... 

Fig. 20. (Top) SPIROE-TOCSY pulse sequence comprised of proton saturation, adabatic CHIRP transfer, and proton magnetization buildup during and TOCSY using the DIPSI-2 mixing sequence. (Bottom) 2D SPIROE-TOCSY performed in deuterated 1,1,2,2-tetra-chloroethane. Broken line indicates the diagonal. The inset shows the region of the camp-hanic ester protons. The total experiment time is only 4.5min. (Courtesy of Herve Desvaux. Reprinted from ref. 313 with permission. Copyright 2004, Elsevier SAS.)...

Other strategies to achieve this task are provided by the broadband (BB) saturation sequences (like MLEV16 (Fig. 9.1J) [21], WALTZ16 [22], GARP [23], DIPSI [24], etc.). The power of the BB saturation pulse can be adjusted in such a way as to effectively saturate the slowly relaxing signals and only maiginally the... 

A markedly increased bandwidth of heteronuclear Hartmann-Hahn transfer for a given average rf power can be achieved with the MGS-1 and MGS-2 sequences developed by Schwendinger et al. (1994) (see Fig. 33G and H). The sequences are MLEV-4 and MLEV-8 expansions of new composite pulses R, which consist of square pulses with rf phases of 0 or 180° and different rf amplitudes that are separated by delays (see Fig. 34). Figure 35 shows HCCH-COSY spectra of a fully C-labeled protein using DIPSI-2 and MGS-2 for the initial polarization transfer from H to (prepolarization) as well as for back-transfer from to H (Majumdar et al., 1993). Note that the absolute bandwidth of MGS-2 is markedly increased compared to DIPSI-2, even though the average power... 

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