Crowded spectra

The COSY pulse sequence can be modified to provide a 2D spectrum that is decoupled in the a)t dimension while retaining coupling in chemical shifts are clearly revealed. Although this experiment is not widely used as such, it serves as a prototype for a building block in other more complex 2D and 3D experiments. 

Finally, broadband and multiple-step selective Hartmann-Hahn transfer can be of assistance in the determination of long-range heteronuclear coupling constants in crowded spectra, van Halbeek and co-workers used broadband and multiple-step selective Hartmann-Hahn transfer in onedimensional experiments to determine long-range heteronuclear coupling constants in oligosaccharides (Poppe and van Halbeek, 1991 Poppe et al., 1994). 

Correlating coupled heteronuclear spins across a single bond and hence identifying directly connected nuclei. Employs detection of high-sensitivity nuclide e.g. H, F, P (an inverse technique ). Provides improved resolution over HM(JC so is better suited for crowded spectra but is more sensitive to experimental imperfections. 

When the aim is to study the very crowded spectra characteristic of large biomolecules such as proteins, the overriding concern is to reduce the amount of data to... 

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... 

J-Resolved Spectroscopy. In J-resolved spectra, the chemical shifts are displayed on one axis while on the other axis the coupling information is displayed. These spectra can be obtained both for protons and carbon-13. They can be useful in the case of crowded spectra. 

HQQC Assignment of methyl groups in crowded spectra, when folding is not feasible... 

---