2D ROESY

Fig. 9.2 Schematic representation of the three basic experiments useful for the determination of (A) transient NOE experiment, (B) 2D NOESY and (C) 2D ROESY. The gray-filled half-circle represents a frequency-selective inversion pulse which inverts the spin to which the cross-relaxation...

Fig. 9.4 The fixation of the Ala proton in cyclosporin A via ROE-derived distance restraints as an illustrative example for NMR structure determination. (A) The amide region of the 2D ROESY spectrum of cyclosporin A at room temperature with the cross-peaks to...

The results obtained have suggested a sandwich conformation of the host-guest complex in which DABCO was protected from the solvent and other molecules. The cross-peaks between coordinated DABCO and complex protons in the 2D ROESY spectra have indicated the accommodation of the DABCO molecule in the host cavity and confirmed the sandwich binding mode. 

Combining 2D-NOESY and 2D-ROESY NMR experiments with molecular modelling protocols, Kuhn and Kunz32 have been able to study the saccharide-induced peptide conformational behaviour of the recognition region of Ll-Cadherin. The detailed conformational analysis of this key biomolecule not only proves that the saccharide side chain exerts a marked influence on the conformation of the peptide chain, but also that the size and type of the saccharide indeed strongly affects the conformation of the main chain. 

A complete NMR approach has been employed to evaluate the complexation process of catechin A with p-CD and synthetic analogues.125 The analysis of the variation of the proton chemical shifts indicated the formation of a 1 1 stoichiometric complex. 2D-ROESY provided detailed spatial information of the complex while the binding constants were obtained by using diffusion-order spectroscopy (DOSY) techniques. 

Various studies were focusing on the conformational behavior of the cinchonan carbamate selectors in free and complexed form, which could readily be derived from the dihedral coupling constant of the Hs-Hg protons ( /hsh9) and intramolecular NOEs as measured by 2D-NOESY [92,93] or two-dimensional rotating frame Overhauser effect spectroscopy (2D-ROESY) [65] spectra. 

The data of ID NOE experiments yield qualitative or quantitative information on proton-proton distances within or between molecules. The experiment is used for detecting one or a few dipolar proton-proton interactions and is especially useful in solving stereochemical problems. If a large number of dipolar interactions or even all protons in a molecule are of interest, it is more efficient to use the 2D NOESY or 2D ROESY experiment (section 3.4.1.3). The 2D method is hampered however by the fact that only the inherently less intense transient rather than the stronger steady-state effects can be measured. 

The 2D NOESY and the 2D ROESY experiments may also be used to measure NOE-or ROE- build-up rates. This is accomplished using a series of experiments, where the mixing period D9 or the length of the spin-lock period respectively is incremented from experiment to experiment. From build-up rates relative internuclear distances may be estimated and calculated. 

A further field of application for the 2D NOESY and the 2D ROESY experiment.s are dynamic systems, where exchange processes may be recognized and may be analysed quantitatively (EXCSY-spectroscopy). 

Fig. 3.25 The 2D spectrum of peracetylated glucose from a 2D ROESY experiment. Both the positive cross peaks and the negative diagonal peaks are shown.

Load the 2D NOESY spectrum of peracetylated glucose D NMRDATA GLUCOSE 2D HH GHHNO 001999.RR. Process it and set up a layout according to the procedure outlined above for the 2D ROESY spectrum. Plot the spectrum according to your preferred layout ideas. Compare the results with the results obtained with the 2D ROESY and the 1D NOE experiments. 

Fig. 64. 2D-ROESY spectrum of 103a in CDCI3 solution at 315 K, C-Me region. Positive cross signals represent chemical exchange between corresponding methyl groups.88 Reproduced with permission from the American Chemical Society.

The x-CyD and /1-CyD ICs were analyzed using 111 NMR,14 including 2D ROESY 15 ICD 17 and microanalysis.133 The structures of the CyD ICs were concluded to be 45 (a-CyD)2 and (45 / -CyD)2. This denotes that diazirine 45 is sandwiched between two a-CyD units but that it forms a twofold 1 1 complex with /1-CyD.18 It has been demonstrated that a guest must have an electronegative group, like —F or —OH,15 18 to effect an opposite inclusion orientation within CyD in the... 

D-ROESY measurements can be evaluated along with the constitution of the complexes (Fig. 2) [23], Cross peaks can be detected between the protons of the guest molecule and the inner protons of the Me-p-CD torus. 

Figure 8.45. The 2D ROESY sequence. The mixing time, tm. is defined by the duration of the low-power spin-lock pulse.

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. 

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