Nuclear magnetic resonance homonuclear correlation experiments

On a system equipped with multiple RF channels and receivers several such schemes can be executed in parallel. Let s consider one of the simplest NMR experiments - the two-dimensional COSY experiment. The basic homonuclear COSY pulse sequence consists of an excitation pulse followed by the evolution period, t, a read pulse and an acquisition period, t2 (see Fig. 2a). The same scheme can be executed in parallel on two or more RF channels (Fig. 2b). If the cross-talk between the different nuclear species could be avoided, such an experiment would produce two independent 2D COSY spectra. However, in practise the magnetically active and in particular spin 1/2 nuclei from the same molecule are usually coupled via the scalar spin-spin couplings and in such a simple pulse scheme cross-talk is unavoidable. Therefore we should also observe heteronuclear correlations arising ffran coherence transfer A X and X A, i.e. in total four two-dimensional spectra in a single measurement Indeed, all the correlations can be observed in instances where the gyrranagnetic ratios of the nuclei and their natural abundances are similar. In fact, as a cmisequence of the close proximity of the H-1 and F-19 resonance frequencies at the Earth magnetic field, their two-dimensional correlation spectra can be observed even with a single receiver [29]. 

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