ROESY transverse

T-ROESY Transverse- Rotating Frame Overhauser Effect SpectroscopY... 

A 2002 review by Reynolds and Enriquez describes the most effective pulse sequences for natural product structure elucidation.86 For natural product chemists, the review recommends HSQC over HMQC, T-ROESY (transverse rotating-frame Overhauser enhancement) in place of NOESY (nuclear Over-hauser enhancement spectroscopy) and CIGAR (constant time inverse-detected gradient accordion rescaled) or constant time HMBC over HMBC. HSQC spectra provide better line shapes than HMQC spectra, but are more demanding on spectrometer hardware. The T-ROESY or transverse ROESY provides better signal to noise for most small molecules compared with a NOESY and limits scalar coupling artefacts. In small-molecule NMR at natural abundance, the 2D HMBC or variants experiment stands out as one of the key NMR experiments for structure elucidation. HMBC spectra provide correlations over multiple bonds and, while this is desirable, it poses the problem of distinguishing between two- and three-bond correlations. 

Tr-ROESY Transverse rotating-frame Overhauser effect spectroscopy 8.8... 

The ROESY spectrum affords homonuclear transverse nOe interactions as cross-peaks between the various dipolarly coupled hydrogens. This... 

The effects due to enhanced transverse relaxation can be experimentally determined from a CPMG pulse experiment [15, 16], although the determination of T1(, (by ROESY-type experiments) is more attractive from a practical point of view. Usually it suffices to record relaxation-weighted experiments using the methods described above to reveal binding. 

The third complicating factor specific to ROESY is the attenuation of cross-peak intensities as a function of resonance offset from the transmitter frequency [69]. Off-resonance spins experience a spin-lock axis that is tipped out of the x-y plane (Section 3.2.1) resulting in a reduction in observable transverse signal in addition to a reduction in cross-relaxation rates. This is more of a problem for quantitative measurements, although fortunately mid-sized molecules show the weakest dependence of ROE cross-relaxation rates on offset. The so-called compensated ROESY sequence [69] eliminates these frequency-dependent losses should quantitative data be required. 

This structure was clearly supported by the data obtained by irradiation of the protons of HDA-j8-CyD and observing the response for the protons of CL [60]. Thus, upon irradiation of the H-3 protons of HDA-j8-CyD an intermolecular NOE was observed only for the protons of the fert-butyl moiety of CL. In combination with the NOE response observed for the aromatic protons of CL upon irradiation of the acetyl group of HDA-j8-CyD these data indicate that the fert-butyl moiety is included in the cavity and the phenyl moiety is located outside the cavity close to the secondary rim of HDA-j8-CyD. Thus, the ROESY experiment shows a significant difference between the structures of the CL complexes with fi-CyD and HDA-j8-CyD. ID and 2D transversal ROESY (T-ROESY) experiments confirmed that the effect observed in the ID ROESY spectra were solely of intermolecular origin and that there was no significant contribution due to intramolecular TOCSY (total correlation spectroscopy) magnetization transfer. Thus, all ROESY experiments clearly indicated that CL forms intermolecular inclusion complexes with -CyD and HDA-jS-CyD. The CL molecule is included in the cavity of both CyDs from the secondary wider rim. The most distinct difference between the two complexes is that the phenyl moiety of CL is most likely included in the cavity of j8-CyD whereas the fert-butyl moiety is included in the cavity of HDA- 8-CyD. 

Detailed knowledge of the architecture of KS chains will continue to be an important factor in eliciting the modes of action and biological roles for these species. The structural and NMR assignment data currently available for these systems now provide a base for the assessment of KS epitope molecular shapes. This is a difficult process because of the inherent spectral complexity, but is being aided by the application of a modified transverse-ROESY method. However, the structural features present within the recently discovered members of this diversely distributed KS family, which would be anticipated to contribute specific behavioural properties or to permit selective interactions with other, noncarbohydrate, molecular sites, are still largely unexplored. Recent KS structural studies are reviewed in depth in a forthcoming article (76). 

To overcome this limitation, a different type of NOE experiment was introduced by Bothner-By with the name CAMELSPIN, although it is now commonly known by the name ROESY. In this experiment, noneqnilibrium states are locked in the transverse plane and the tumbling... 

Similar relationships can be derived for ROESY. In this case, the cross peaks are generated by cross relaxation of transverse magnetization. In the rotating frame, o is given by Equation [4]... 

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