The HSQC-TOCSY Experiment

Parameters for the HSQC-TOCSY experiment are the same as for the component HSQC and TOCSY experiments  

7-10 Homonuclear Chemical-Shift Correlation Via Dipolar Coupling 

Nuclei that undergo mutual relaxation via dipolar coupling are said to be dipolar coupled and give rise to the nuclear Overhauser effect. Whether the nuclei in question also may be scalar (or spin) coupled is not pertinent to the discussion (Section 5-4). NOE experiments can be either homonuclear or heteronuclear in nature, although the former, involving protons, are much more common. One-dimensional homonuclear Overhauser experiments are discussed in Section 7-3 their 2D versions, NOESY and ROESY, are treated in this section. 

Similar to the COSY experiments, contour plots for NOESY and ROESY are symmetric, with both the spectral widths and the data point resolutions almost always identical. Linear prediction can, again, help greatly in making DRi equal to DR2 by keeping the data 

It should also be remembered that the results of 2D NOE experiments are averaged (i.e., an AB cross peak represents the average of the enhancement of Hb when is irradiated, and vice versa). As we saw in Section 7-3, the two enhancements (A B) and B(A ) usually are different, sometimes very much so. The resulting averaged cross peaks can thus be small and difficult to detect. 

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A second natural product study reported in 2003 that used the sensitivity of cryogenic probe capabilities and the HSQC-TOCSY experiment to advantage was the report by Preiss et al.25S that detailed the elucidation of the structure of two new asterosaponins from the starfish Asterias rubens. The structure of one of the molecules characterized (110) of which only 0.3 mg was isolated, is shown. 

Nolls, P., Parella, T. Spin-edited 2D HSQC-TOCSY experiments for the measurement of homonuclear and heteronuclear coupling constants application to carbohydrates and peptides. /. Magn. Reson. 2005, 176, 15-26. 

If 2-D NMR techniques are really useful then 3-D ones must be even more so... shouldn t they A number of 3-D experiments have been devised which are in fact, produced by merging two, 2-D experiments together. The results could never be plotted in true 3-D format since etching them into an A3-sized block of glass would not be practical and viewing them as some sort of holographic projection, would probably not be feasible In essence, 3-D spectra have to be viewed as slices through the block which effectively yield a series of 2-D experiments. It is possible to combine techniques to yield experiments such as the HMQC-COSY and the HSQC-TOCSY. 

Load the spectrum of the gradient-assisted, inverse detected, 2D CH-HSQC-TOCSY experiment acquired with the echo-antiecho technique, D NMRDATA GLUCOSE 2D CH GCHICOTO 001999.RR. Check and if necessary correct its calibration in both dimensions. Set up a layout as for the basic HSQC spectrum. Compare the spectrum with the spectra of the basic HSQC and HMQC experiments. Use the same rows or columns to identify the additional TOCSY-peaks. 

Their work was based, in part, on the ID HSQC-TOCSY experiment. In general, the authors have utilized the Preservation of Enhanced Pathways (PEP) approach in the development of the sequences that they have described. The HSQC-TOCSY based experiments, of course, mandate a protonated resonance. The authors have, however, also proposed a HSQMBC experiment in which the heteronuclear... 

Clearly the homonuclear and the heteronuclear experiments could be combined in the reverse order i.e. HSQC-NOESY and HSQC-TOCSY. The main advantage in these schemes relates to N-edited experiments in which the narrower amide proton spectral width is sampled during f and the full proton spectral width is collected during t. On the other hand water suppression is more effective when HSQC follows NOESY. Also the sensitivity enhancement can be incorporated into the NOESY-HSQC experiment. Eor the TOCSY-HSQC or HSQC-TOCSY it does not matter because both the TOCSY and HSQC sequences can be implemented with the sensitivity enhancement. It should be mentioned that the TOCSY type of transfer is more effective between C nuclei than between protons and therefore the HCCH-TOCSY experiment is preferred when a doubly labeled sample is available. 

There are a number of possible variants and modifications of the HMQC-TOCSY experiment. One obvious modification would be to use HSQC rather than HMQC to label protons with the chemical shift of the carbon to which they are directly bound. To the best of our knowledge, applications of... 

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