Phase NOESY

Phase-sensitive NOESY spectra are generally significantly superior in resolution to absolute-mode spectra. As in phase-sensitive COSY spectra. 

Figure 5.44 (a) Phase-sensitive absorption-mode NOESY spectrum of bovine phos-... 

The reason for this is that our experiments are phase-sensitive. What do we mean by this You will remember that in the DEPT and APT spectra the CH/CHj and CH2 peaks are in one case positive (up) and in the other negative (down), which we also refer to as in opposite phase. Here in COSY and NOESY our experiments include such phase information, which is read off from the way the signals look in the plot. 

Thus all the signals in the COSY spectrum are of the same phase, while in NOESY the diagonal and cross peaks have opposite phase. 

Fig. 10.11. 2D NOESY data of astemizole (5). The mixed phase correlations in the aromatic region (boxed) are examples of the artifacts described in the text.

This review describes experimental techniques, then gives some selected results of H, and NMR studies of pressure effects on the structure, dynamics and phase transitions of phospholipid bilayers. Other examples deal with 2D-NOESY experiments on lipid vesicles and pressure effects on the interaction of anaesthetics with phospholipid bilayers. Furthermore, we discuss... 

Four diastereomers of 2-ethynyl-7a-hydroxy-3a,7-dimethyl-4,6-diphe-nylperhydropyrrolo[3,2-c]pyridine (58B) were recently isolated (92KGS-903). It was established by means of H-NOESY and C-NMR spectroscopy that the stereochemical differences in the structures of the diastereomers involve cis and transfusion of the rings and different configurations at C(2). In solution and in the gas phase, the corresponding ring-chain equilibrium 58A 58B was detected, with two open-chain epimers (different configurations at C—NH2). 

The ID NOESY-TOCSY experiment [39] shown in fig. 1(c) is a straighffor-ward concatenation of ID NOESY and TOCSY experiments [34] (figs 1(a), (b)). Since the NOE transfer takes place along the z axis, and thus has no phase memory, no phase correction for the second selective pulse is needed to compensate for the change of the r.f. frequency during the tnoe interval. Nevertheless, any possible phase differences between the selective and consecutive nonselective pulses must be taken into account in both steps, by adjusting the phase of soft pulses. 

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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