Pulse sequence DANTE

An analytical solution for the DANTE pulse sequence was found by Canet et a/.50 that might be useful for designing new selective pulse sequences. Goldman et a/.51 analysed the NMR frequency shift induced by sample spinning. For spin-i systems in solids, it was shown that the intensities of the two MAS-induced RF fields are only about one-thousandth of the real RF field, hence causing no problems in most experiments. However, it becomes important in NQR experiments, for example in the appearance of geometric phase.52... 

In some spectrometers it is not feasible to generate BURP or related tailored soft pulses. A useful alternative is the DANTE pulse sequence (delays alternating with nutation for tailored excitation). Normal high excitation power is used, but rather than apply a single 90° pulse, the DANTE method uses a sequence of small angle pulses that sum to 90° but with a short time between pulses during which nuclei... 

FIGURE 9.7 Trajectories for the on-resonance magnetization and several off-resonance magnetizations from a DANTE pulse sequence consisting of 18 pulses along the x axis, each of 5°. From Free-... 

DANTE pulse sequences do not require spectrometers equipped with shaped pulses. 

The DANTE pulse sequence is shown in Figure 20b. A peak that is exactly on-resonance or an integral multiple of l/d2 Hz off-resonance, experiences the cumulative effect of the n pi pulses. Other resonances see a random excitation that effectively sums to zero. In exchange experiments, a variable delay (vd) is inserted between the end of the DANTE pulse train and the read pulse, p2. During vd, magnetization is transferred between exchanging sites. 

Figure 20 Saturation transfer experiment using (a) Selective inversion by a shaped pulse or (b) a DANTE pulse sequence. Do not use the DANTE-Z sequence, Section 3.3, in saturation transfer experiments...

In a related paper, WATERGATE and DANTE pulse sequences were used under MAS condition to selectively excite or suppress peaks in H solid state spectra. As known from solution NMR studies, signal selection or suppression... 

Fig. 12. 5 P-NMR spectra (121.47 MHz) of a phosphonolipid - DPPC mixture (1 4, w/w) in water at pH 7.0 at S0°C. (A) 90° pulses, 2400 accumulations at 1 scan s. (B) As in (A) but using a DANTE pulse sequence at the indicated frequency (arrow) with 4° pulses separated by SO fts and a total saturation time of800 ms. (Q Difference spectrum of (A)- (B). (D) Computer simulation of spectrum (A) in terms of two axially symmetric powder patterns characterized by a difference in isotropic chemical shift of 28 ppm, angular-independent and angular-dependent linewidths of 70 Hz, chemical-shift anisotropies of +46 and +30 ppm for phospho- and phosphonolipid, respectively. From Jarrell et al. (1981).

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