NOESY sequence

Figure 7.5 Pulses sequences for ID NOESY and ID relayed NOESY experiments, (a) A ID NOESY sequence with full Gaussian pulses is inferior to the ID NOESY sequence (b) with half-Gaussian excitation, (c) A 90° Gaussian pulse in the pulse sequence of 1D relayed NOESYis appropriate for excitation, since antiphase magnetization is required for the first mixing step. (Reprinted from Mag. Reson. Chem. 29, H. Kessler el al, 527, copyright (1991), with permission from John Wiley and Sons Limited, Baffins Lane, Chichester, Sussex P019 lUD, England.)...

A second class of multidimensional experiments uses through-space interactions perhaps the best-known example is the NOESY sequence, which is as follows ... 

D NOE-pumping experiment. E Reverse NOE pumping experiment (bottom) and reference experiment (top). F e-PHOGSY NOESY sequence. The water-selective 180° pulse sandwiched by the first two gradients has a gaussian shape and a duration of 40-50 ms. The mixing time is approx. 2 s. For further details, see Refs. [29, 30]. 

Fig. 6. Basic scheme of the NOESY sequence which provides essentially homo-nuclear cross-relaxation rates from a double Fourier transform of the signal S( 2)-...

The NOESY and TOCSY polarization transfers can also be arranged so that two NOESY steps are interrupted by one TOCSY transfer. This is useful for situations when a proton which is intended as a starting point for a ID TOCSY-NOESY experiment cannot be selectively excited, nevertheless it has a NOE contact to an isolated proton. The ID NOESY-TOCSY-NOESY sequence [72] (fig. 4(b)) is obtained by appending another NOESY step to the ID NOESY-TOCSY pulse sequence of fig. 1(c). The last NOESY step can be either selective or nonselective depending whether a selective 180° pulse is applied after the nonselective 90° pulse at the end of the TOCSY transfer. 

Replacement of the TOCSY transfer in a ID COSY-TOCSY experiment by the NOESY step yields a ID COSY-NOESY sequence [38] (fig. 13(c)). The experiment is illustrated by the determination of NOEs from the H-7 proton of a terminal 3,6-dideoxy-4-C-(l-hydroxyethyl)-D-xylohexose (6)... 

Results similar to those shown in the slice of Fig. 8.22 can be obtained with the so-called NOE-NOESY sequence [36]. Here a hyperfine shifted signal, e.g. I2-CH3 of the above compound, is selectively saturated, and then the NOESY pulse sequence is applied. The NOESY difference spectrum obtained by subtracting a NOESY spectrum without presaturation of the I2-CH3 signal is shown in Fig. 8.23. Here, some more cross peaks are evident with respect to the 3D NOESY-NOESY experiment because secondary NOEs develop much more when the primary NOEs from the I2-CH3 signal evolve in a steady state experiment like the NOE-NOESY rather than in a transient-type experiment like the NOESY-NOESY. In Fig. 8.23, dipolar connectivity patterns are apparent among protons... 

Fig. 9.1. (A) Gaussian (a) and sine (b) excitation profiles. (B) Composite (G3) Gaussian pulse. (C) Train of soft pulses modified after the DANTE sequence to achieve selective off-resonance excitation. (D) Redfield 21412 sequence. (E) Binomial 11, 121, 1331, 14641 sequences. (F) JR (a) and compensated JR (or 1111) (b) sequences. (G) Watergate sequence. (H) Weft (Superweft) sequence. (I) Modeft sequence. (J) MLEV16 sequence. (K) NOESY sequence with trim pulse. (L) MLEV17 sequence with trim pulses. (M) Clean-TOCSY sequence.

The NOESY sequence proved to be very effective for the reduction of one particular signal such as the methyl group of acetonitrile. However, very often the mobile phase has a composition of several solvents, together with up to six solvent signals. Here, the application of the soft pulse multiple solvent suppression technique is advisable. 

FIGURE 12.13 Pulse sequence for the three-dimensional experiment NOESY-HMQC. The first three 90° H pulses constitute the usual NOESY sequence, with mixing time r.The 180° 15N pulse at time 3 removes the effect of H-15N couplings. The H and 15N pulses at times 7, 9, 11, and 13 constitute the HMQC sequence, with the pulse at time 7 serving as part of both sequences. 

A gradient version is available. EXSY and diagonal peaks are positive, NOESY peaks negative—use the gradient-accelerated NOESY sequence supplied with your instrument. 

NOESY) sequence (see Fig. 26D, Table 3), which was computer-optimized by Kadkhodaei et al. (1993), is based on the MLEV-16 expanded composite pulse R = 15° 75°, 279°45°. In the TOWNY sequence, a 2 1 ratio of and is achieved by the created trajectory of z magnetization during the course of the optimized phase-alternated composite pulse R, without the need for additional delays or modulation of the rf amplitude. Clean Hartmann-Hahn mixing sequences based on shaped pulses were developed by Mayr et al. (1993). The parameters of the shaped MW-1 sequence (Mayr and Warren, 1995) are given in Table 3. 

Suppression sequences are normally used in combination with some form of measurement pulse sequence which could be a multidimensional sequence (e.g. a NOESY sequence). This may change the requirements (less restrictive or more restrictive) of the suppression method. Suppression in multidimensional experiments is considered in Section 5. Suppression techniques, as we have noted above, are influenced/restricted by instrumental limitations and the sample itself and we note that simply by confining the sample to a smaller volume, for example through the use of susceptibility matched microtubes,... 

Many different ways of effecting water suppression in the NOESY sequence have been implemented, for example, presaturation, jump and return, l-T-echo, WATERGATE, SS pulses and excitation sculpting. The basic NOESY sequence using presaturation and two variations using WATERGATE are illustrated in Fig. 24. In the basic NOESY sequence (Fig. 

COSY experiments using Bi gradient-based water suppression have been presented. In a later work Brondeau et have successfully combined Bx gradient suppression (i.e. their DEBOG sequence see B gradient-based suppression methods, p. 320) with a NOESY sequence, which they termed NOESY-DEBOG (see Ftg. 27),... 

Figure 8.34. The 2D NOESY sequence and the associated coherence transfer pathway. The optional use of a pulsed field gradient (shown greyed) during the mixing time is described in the text.

In parallel with the ID NOESY sequences above, the 2D ROESY experiment also has its ID equivalent (in fact, this was the original ROE experiment [60]) and gradient-selected analogues [70-72] all of which incorporate selective excitation of the target spin. These can be derived from ID NOESY sequences by incorporation of a suitable spin-lock in place of the 90-Tm-90 segment of NOESY, and thus require no further elaboration. 

Although these results have been derived for the NOESY sequence, they are in fact general for any two-dimensional experiment. Summarising, we find... 

The key to this method is the ability to record a cosine modulated data set and a sine modulated data set. The latter can be achieved simply by changing the phase of appropriate pulses. For example, in the case of the NOESY experiment, all that is required to generate the sine data set is to shift the phase of the first 90° pulse by 90° (in fact in the NOESY sequence the pulse needs to shift from x to -y). The two data sets have to kept separate. 

It was noted above that shifting the phase of the first pulse in the NOESY sequence from x to -y caused the modulation to change from cos Qtx) to sin j). One way of expressing this is to say that shifting the pulse causes a phase shift (j) in the signal modulation, which can be written cos + (pi). Using the usual trigonometric expansions this can be written... 

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