Homonuclear 2D TOCSY

Figure 5 Cross-peaks in homonuclear 2D TOCSY spectra arising due to ROESY effects. Clean TOCSY spectra were acquired with the MLEV-17 spin-lock sequence, (a) Base proton H6-to-methyl correlations in a 27-nt AT-rich DNA stem-loop structure 93 the spectrum was recorded with the 50-ms mixing sequence, (b) and (c) TOCSY spectra acquired for a 31 -nt stem-loop RNA (unpublished data), (b) H5-H6 cross-peaks in pyrimidines and a H1 -H8 cross-peak (boxed) in the syn guanine from the tetraloop UACG the spectrum was recorded with the 30-ms mixing sequence, (c) Sequential H2 -H6/H8 cross-peaks the spectrum was recorded with the 90-ms mixing sequence.

The enormous simplification of crowded spectra in this manner makes this a very powerful technique. However, a point to bear in mind when considering applying these methods is that crosspeaks in the C-edited experiment originate only from C satellites because of the initial HMQC/HSQC step, and the experiment is therefore of significantly lower sensitivity than homonuclear 2D TOCSY, in which all protons may participate. The experiment will generally find use after initial stages of investigation of complex spectra... 

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