Pulse sequence triple-resonance

After the N, C-labelled NBD peptide was obtained, the triple-resonance experiment developed to measure rNHC dipole-CSA CCR-rates [41] was performed as a 2-dimensional experiment. The spectra are obtained by applying a pulse sequence that was developed by Kay and co-workers [41] to measure /nhc with increased sensitivity. The experiment is one of the sensitive triple-resonance experiments, and is therefore suitable to test the feasibihty of CCR measurements and to optimize sample conditions. The pulse sequence is derived from an HNCOCA and the double and zero-quantum co-... 

In addition to the above-mentioned challenges of all triple resonance experiments, pulse sequences for 3D experiments are demanding to develop and test as well as to run... 

To illustrate how a complex triple-resonance pulse sequence can be understood relatively easily using the concepts developed in this book, consider the HNCO experiment. The Hn and 15N chemical shifts of one residue are correlated with the chemical shift of the carbonyl group of the previous residue (Fig. 12.56). This is accomplished by a simple out-and-back scheme of coherence transfer (Fig. 12.57) xHn 15N 13C (H) 15N fe) xHn... 

FIGURE 12.16 Pulse sequence for the triple resonance 3D NMR experiment HNCO. H and N denote H and 15N, C denotes 13C=0, and K denotes 13C . Pulses at times 1, 2, and 3 constitute an INEPT sequence that transfers coherence from H to. V, where it precesses during q. Pulses at times 6, 7, and 8 represent an HMQC sequence that creates multiple quantum coherence in C (where it precesses during and transfers coherence back to N. Pulses 10 and 11 are an inverse INEPT sequence that transfers coherence back to H for detection during f3.The other 180° pulses refocus heteronuclear spin couplings. Note that coherence is not transferred to spin K. 

Figure 9 Davies TRIPLE pulse sequence. The uppermost level indicates the microwave pulses and immediately helow, delay times are indicated. The two lower levels indicate the rf pulses. The first rf energy (rft) is fixed and corresponds to a resonant nuclear transition and the second rf (rf2) is swept over a range of frequencies to yield an ENDOR spectrum. The rft pulse would he omitted to provide the control for a difference TRIPLE spectrum. The timing would be similar to a standard Davies sequence see Figure 7). A Mims TRIPLE pulse sequence hkewise would he the same as in Figure 6, except with two rf pulses as shown here...

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... 

Figure 14 Contour plot (adapted with permission from Ref. 85) of the 2D inverse, pseudo triple-resonance H %n( experiment for cyclopentadien dn, (t -C5H5>2Sn, using the phase sensitive version of a -BIRD HS pulse sequence (25 C, IS mg in 0.5ml of C D. The splitting in F2 is due to y(, H)=168Hz, V( Sn, H)= 16Hz and "/( H, H). The coupling constant V(" n l 1. 2 can be read from F, and the positive tilt proves that the signs of iC( C, H) (>0) and (" Sn, C) are alike...

Fig. iL Pulse sequences for pseudo triple-resonance experiments with passive selection of satellites (a) z-filtered 2D-"X, H( "Y) INEPT. (b) -BIRD H,"X( "Y) HMQC. (c) H,"X( "Y) HMQC experiment with biselective excitation pulse (bis) biselective excitation may be achieved with DANTE or P-BIRD sequences, binomial pulses, or shaped pulses. (d) H, X( "Y) HEED-INEPT." ... 

The name TROSY [5.226, 5.227] has now became an pseudonym for relaxation optimized pulse sequences and as such, nearly all triple resonance experiments are now available with a TROSY variant allowing the selection of the slowest relaxing component in a multiplet. Consequently, large bio-molecules can now be studied using triple resonance experiments. Check it 5.9.2.2 simulates a 2D [l N, IH] TROSY-HSQC experiment, the original experiment used to illustrate spin-state selection for fast relaxing spin systems. 

In this work the applications of three dimensional (3D) solution NMR techniques for characterizing the structures of synthetic polymers and dendrimers are illustrated, including the characterization of polymer chain-end structure, monomer sequence, stereosequence, and branching. The utility of triple resonance and pulsed field gradient NMR techniques in these research endeavors are discussed. 

Figure 7. Pulse sequence diagram for an HXY triple resonance 3D-NMR, open rectangles represent 180°pulses and solid rectangles represent 90°...

NMR has been a powerful technique for structural analyses of macromolecules. However, ID NMR spectra of PDMS are usually complicated due to signal overly. Their complete characterization often requires combinations of several techniques. Multidimensional NMR techniques, especially inversely detected 3D heteronuclear shift correlation experiments, offer the opportunity to obtain the complete structural characterization by using NMR experiments alone. Biological 3D-NMR experiments are usually performed in conjunction with uniform and isotopic labeling. In polymer chemistry, when isotopic labeling is possible, it is often very difficult and expensive. By modifying the 3D-pulse sequence used for biopolymers, triple resonance 3D-NMR techniques have been adapted for sbufying the structures of polymers, which involve H- C- P, H- C- Si spin... 

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