Self-refocusing pulses

The double-selective TOCSY-ROESY and TOCSY-NOESY techniques are particularly useful. They allow one to measure NOE and ROE correlations in spectra with high degree of overlap as often found in carbohydrates. In addition to the DANTE, DANTE-Z [66], and Gaussian pulses as described earlier for selective excitation, self-refocusing shaped pulses such as BURP (EBURP and UBURP) [67] have also been used for this purpose [64]. 

McCoy et a/. have proposed a method termed ERASER based on self-refocused and hard rectangular pulses. The scheme does not generate phase roll. Moy et alP have demonstrated the use of frequency shifted, self-refocused top hat pulses to observe amide resonances, that they termed selective-excitation-corrected spectroscopy (SelECSy). This method, although not providing exceptional water suppression, overcomes the dynamic range problem and produces uniform amide proton excitation... 

Liu et al have developed shaped self-refocusing irl2 RF pulses with a duration of 1-3 ms that provide a flat null (i.e. a notch ) at a narrow band (several hundred hertz) of resonance frequencies with uniform excitation and minimum phase distortion at the other frequencies ( 5000 Hz). 

Edwards MW, Daly JW, Myers CW (1988) Akaloids from a Panamanian poison frog, Dendrobates speciosus identification of pumiliotoxin-A and allopumiliotoxin class alkaloids, 3,5-disubstituted indolizidines, 5-substituted 8-methylindolizidines, and a 2-methyl-6-nonyl-4-hydroxypiperidine. J Nat Prod 51 1188-1197 Emsley L, Bodenhausen G (1989) Self-refocusing effect of 270° Gaussian pulses. Applications to selective two-dimensional exchange spectroscopy. J Magn Reson 82 211-221... 

After a time r, a 180° RF pulse reverses the spin precession. A second gradient pulse of equal duration 8 and magnitude g follows to tag the spins in the same way. If the spins have not changed their position in the sample, the effects of the two applied gradient pulses compensate each other, and aU spins refocus. If the spins have moved due to self-diffusion, the effects of the gradient pulses do not compensate and the echo-amplitude is reduced. The decrease of the amplitude A with the applied gradient is proportional to the movement of the spins and is used to calculate the self-diffusion coefficient. 

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