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Notes:
In the last lecture, we have seen how we can use 2D-NMR to transfer magnetization between spins, and connect resonances by different properties. In COSY and DQF-COSY spectra, we connect spins through bonds. There is only one transfer step (mixing pulse ) in both experiments. Hence, magnetization is transferred from one nucleus to another one which is coupled to it ( 2IxSz - 2IzSx), which means we obtain cross peaks for vicinal or geminal protons only. These can be used to stepwise connect all protons coupled to another (spin system), but this is in practice often difficult. Next to signal overlap, in (DQF)COSY spectra small coupling constants, (i.e. smaller than the peptide/protein line widths) will lead to low signal intensity or even lack of some cross peaks due to their antiphase structure.
