BIRD pulse decoupling

FIGURE 9.8 (a) Bilinear rotation decoupling (BIRD) pulse sequence, (b) Behavior of the H magnetization from a proton coupled to 13C. (c) Behavior of the H magnetization from a proton not coupled to 13C. See text for details. 

In 1986 Bax and Subramanian [10] proposed the utilization of the discriminatory power of the Bilinear Rotational Decoupling [36] (BIRD) pulse cluster to achieve an even better suppression of unwanted H- C signals (Figure 13). 

Heteronuclear coupling constants (1,b7c,h) are most commonly measured from heteronuclear 2D experiments. The 3/c H couplings can be easily extracted from /-resolved spectra as well as from f or F2 proton coupled HSQC spectra. The undesired evolution of "/CH during q can be eliminated with use of an appropriate bilinear rotation decoupling (BIRD) pulse, such as BIRDd,x in. /-resolved spectroscopy35 and 111RD in Fi-coupled HSQC.36 Spin-state selective excitation techniques, S3E and S3CT37 38 (spin-state-selective coherence transfer), can also be used for the measurement of... 

A) evolves in variable time - F, modulation (A) decoupled by BIRD pulse ... 

Subsequently, Uhrinova et al.29 reconsidered the problem using both proton-and carbon-detected experiments. For example, couplings of anomeric carbons were measured from the 13C satellites in proton NMR spectra. The critical factor in these methods is the suppression of signals from protons bound to, 2C atoms. In the pulse-sequence proposed, these protons were selectively inverted by a BIRD (Bilinear Rotation Decoupling) pulse,30 and the spin-echo method introduced by Bendall et al.31 was used. 

This is the simple heteronuclear -X COSY (or HETCOR) pulse sequence adapted to long-range correlations simply by adjustment of the Ai and A2 delays. Small coupling constants rule out the use of broad-band proton decoupling during evolution time t by BIRD, and thus the correlation cross-peaks display the structure of proton multiplets, which reduces further the sensitivity of the experiment. 

These filters are usually employed to suppress strong and undesirable resonances, e.g. parent signals of isotopically diluted spin systems. In a typical experiment the undesirable magnetization is inverted and allowed to relax until the equilibrium state is reached. At this point the inverted magnetization is not observable and the basic experiment may be started. In the simplest case a jump and return inversion pulse or binomial pulses can provide the necessary selective inversion. A simple example of application of a T relaxation filter is the J/-BIRD (BI linear Rotation Decoupling) HMQC... 

Figure 8 The /-BIRD HMQC pulse sequence. The delay T is tuned to minimize the appearance of the parent proton resonance and the delay A is set to 0.5//hx sel = selective pulse Dec. = decoupling...

BIRD-HMQC. The most difficult aspect of implementing the HMQC experiment is the suppression of signals from protons attached to C (the center-band or single quantum coherences) in favor of the protons attached to C (the satellites or double quantum coherences). The use of pulse field gradients (PFG, Section 6-6) is the most effective technique, but relatively few spectrometers are equipped with the hardware required for their generation. Fortunately, there is an effective alternative for the suppression of center bands by means of the BIRD Bilinear Rotation Decoupling) sequence, which is outlined by the vector... 

Not every NMR spectrometer or probehead is equipped with pulsed field gradient capabilities, yet it may still be possible to execute the basic heteronu-clear shift correlation experiments described above. In such cases it is desirable to employ an alternative scheme to remove the interfering parent resonances and produce spectra devoid of objectionable artefacts. In the BIRD (bilinear rotation decoupling) variant (Fig. 6.12), unwanted resonances are... 

HMQC). The initial part of the sequence, labeled BIRD, is a pulse scheme for removing from the spectrum the H resonances of protons attached to nuclei. The filled symbols denote 90° pulses and the open symbols denote 180° pulses, x, y, and 0 refer to RF pulse phases. The delay A is set to 1/(2 x u/ch)- GARP denotes a pulse method of spin decoupling all nuclei. 

Figure 2 Pulse sequences used in this article. All experiments can be acquired in the phase-sensitive mode, using either TPPI or the States method. Sequences 12 and 13 are best displayed in the magnitude mode because of phase modulation owing to homo-nuclear couplings in F2. All inverse correlations, except for sequences 12 and 13, can be preceded by a BIRD (bilinear rotating decoupling) pulse sandwich to allow for a fast repetition rate of scans. For simplicity gradients are not given here in most cases.

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