Systems magnetic resonance homonuclear couplings

Grage SL and Ulrich AS (1999) Structural parameters from homonuclear dipolar couplings, obtained by multipulse solid state NMR on static and oriented systems. Journal of Magnetic Resonance 138 98-106. 

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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