Pulse sequence NOESY

Figure 1. Pulse sequences of some typical 2D-NMR experiments. COSY = correlation SpectroscopY, DQFCOSY = Double Quantum Filtered COSY, RELAY = RELAYed Magnetization Spectroscopy, and NOESY = Nuclear Overhauser Effect SpectroscopY.

A number of 2D NMR experiments, such as NOESY, have a mixing period incorporated in their pulse sequence. In principle, precession of j magnetization also occurs during the mixing period. Why do we not need to have a third Fourier transformation to monitor the precession frequencies that occur during the mixing period ... 

Figure 5.42 Pulse sequence and vector representation of a NOESY experiment.

Figure 6.10 Pulse sequences for (a) the HMQOCOSY experiments and (b) the HMQC-NOESY experiments. (Reprinted from J. Mag. Reson. 78, S. W. Fesik and E. R. P. Zuiderweg,. 588, copyright (1988), with permission from Academic Press, Inc.)...

The pulse sequences for HMQC-COSY and HMQC-NOESY experiments are presented in Fig. 6.10. The 3D HMQC-COSY spectrum of a N labeled tripeptide is shown in Fig. 6.11. Since the coherence transfer involved in this experiment is N([Pg.362]

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.)...

One problem in recording nOe spectra of proteins in aqueous solutions is the presence of a water signal. Soft NOESY produces minimal excitation of the solvent signal. The pulse sequence used is shown in Fig. 7.18 (Oschki-nat et al, 1988 Oschkinat and Bermel, 1989). 

Pre-saturation In this technique prior to data acquisition, a highly selective low-power rf pulse irradiates the solvent signals for 0.5 to 2 s to saturate them. No irradiation should occur during the data acquisition. This method relies on the phenomenon that nuclei which have equal populations in the ground and excited states are unable to relax and do not contribute to the FID after pulse irradiation. This is an effective pulse sequence of NOESY-type pre-saturation that consists of three 900 pulses RD - 900 - tx - 900 - tm - 90° - FID, where RD is the relaxation delay and t and tm are the presaturation times. 

NOESY NMR spectroscopy is a homonuclear two-dimensional experiment that identifies proton nuclei that are close to each other in space. If one has already identified proton resonances in one-dimensional NMR spectroscopy or by other methods, it is then possible to determine three dimensional structure through NOESY. For instance, it is possible to determine how large molecules such as proteins fold themselves in three-dimensional space using the NOESY technique. The solution structures thus determined can be compared with solid-state information on the same protein obtained from X-ray crystallographic studies. The pulse sequence for a simple NOESY experiment is shown in Figure 3.23 as adapted from Figure 8.12 of reference 19. 

Figure 3.23 The pulse sequence used for NOESY. (Adapted with permission of Nelson Thornes Ltd. from Figure 8.12 of Akitt, J. W. NMR and Chemistry, 3rd ed., 1992.)...

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. 

ID NOESY spectra (b) and (c) were acquired using the pulse sequence of fig. 1(a). A 59.2 ms half-Gaussian pulse was applied to proton H-ld. Mixing time was 25 ms in (b) and 200 ms in (c). Water presaturation was applied during the relaxation delay and the NOE mixing... 

Fig. 17. ID RELAY-NOESY spectra of the oligosaccharide 5 acquired using the pulse sequence of fig. 13(d) with the initial polarization transfer from overlapping anomeric protons of two terminal glucoses in 5. (a) Partial H spectrum of 7 at 600 MHz after 8 scans. The following parameters were used to acquire the two original ID RELAY-NOESY spectra (not shown) rsei = 50 ms, tq = 39 ms, A = 9.09 ms, ti = 120 ms, Tr = 64 ms, r, = 400 ms.

Fig. 18. The pulse sequence of a ID ge-NOESY-TOCSY experiment, tnoe is the NOE mixing time, 5 are optional delays which can be used for z-filtration [81] or for suppression of ROE effects in macromolecules (2 x (5 + Tgrad) = 0.5 x mixing time). DIPSI-2 [78] sequence was used for isotropic mixing. Phases were cycled as follows 0i = 2x, 2(—x) (j)2 = X, —x Ip = X, 2 —x), X. Rectangular PFGs, G = 6 Gauss/cm and Gi = 7 Gauss/cm, were applied along the axis for Xpad = 1 ms.

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