Selective inversion pulse

Figure B2.4.8. Relaxation of two of tlie exchanging methyl groups in the TEMPO derivative in figure B2.4.7. The dotted lines show the relaxation of the two methyl signals after a non-selective inversion pulse (a typical experunent). The heavy solid line shows the recovery after the selective inversion of one of the methyl signals. The inverted signal (circles) recovers more quickly, under the combined influence of relaxation and exchange with the non-inverted peak. The signal that was not inverted (squares) shows a characteristic transient. The lines represent a non-linear least-squares fit to the data.

Fig. 9.2 Schematic representation of the three basic experiments useful for the determination of (A) transient NOE experiment, (B) 2D NOESY and (C) 2D ROESY. The gray-filled half-circle represents a frequency-selective inversion pulse which inverts the spin to which the cross-relaxation...

Fig. 3. Numerical simulations of four different selective inversion pulses. (Top) Pulse shapes. From left to right 180° rectangular, 180° Gaussian truncated at 2.5%, Quaternion cascade Q, and l-BURP-2. (Middle) Trajectories of Cartesian operators in the rotating frame during...

The peak rf amplitude required to achieve optimum inversion with a selective inversion pulse is given in comparison to the rf amplitude required to achieve an on-resonance 90° flip-angle with a selective rectangular pulse, the simplest conceivable shape. 

Selectivity of the selective inversion pulses of table 3, all numbers given for properly... 

Fig. 6. Simulation of the effect of longitudinal and transverse relaxation during a 30 ms selective inversion pulse. The trajectories are shown on a Bloch sphere and in the...

For selective inversion or refocussing, a universal pulse is a good choice. In cases where singlets are to be inverted and where relaxation or exchange during pulses is critical, one may need to use a 180° Gaussian pulse which is the shortest selective inversion pulse available [24]. 

A very efficient suppression of parent resonances can be achieved using the T filter. This, however, requires a rather careful tuning of the relaxation delay T (see Figure 8). If the jump and return inversion pulse is employed, the pulse sequence can be regarded as a selective version of the BIRD experiment [57-59]. Obviously, multiple-frequency selective inversion pulses may be necessary in the case of complex proton spectra. Usually the /-BIRD HMQC experiment gives cleaner spectra as compared with equivalent heteronuclear singlequantum coherence (HSQC) experiments, presumably because of fewer 180° pulses which are frequently a source of various artefacts. 

Sometimes we want to invert the magnetization associated with just one resonance while leaving all the others in the spectrum unaffected such a pulse would be called a selective inversion pulse. Just as for selective excitation, all we need to do is to place the transmitter on the line we wish to invert and reduce the RF field until the other resonances in the spectrum are not affected significantly. Of course we need to adjust the pulse duration so that the on-resonance flip angle is 180°. 

Integrated Solid Effect (ISE) was first introduced by Henstra et al. [17]. It can overcome the low efficiency of SE when the homogeneous width is much larger than the nuclear Larmor frequency (A (Uo v)> in which the polarization effect could be canceled by simultaneous saturation of the forbidden transitions at ct)o fflow-The ISE can preserve the polarization in the case of A coow by inverting a forbidden EPR transition prior to saturation of an allowed transition. This effect can be achieved by using a selective inversion pulse after the irradiation on resonance at cooe i (Oon, or applying CW microwave irradiation at a fix frequency... 

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