Towards selective recoupling and mutual decoupling of dipolar-coupled spin pairs in double-quantum magic-angle spinning NMR experiments on multiply labelled solid-state samples

In solid-state magic-angle spinning NMR experiments, the combination of selective inversion and dipolar recoupling schemes, such as DANTE and C7, allows double-quantum coherences to be selectively generated between distinct types of spins, as is experimentally demonstrated here. In such selective inversion and multiple quantum excitation experiments, the double quantum coherences are excited between spins with identical polarisation, but not between spins with opposite polarisation. By investigating the decay of longitudinal magnetisation or the build-up of double-quantum coherences, the respective dipolar pair couplings can be individually measured in the presence of perturbing couplings, which may even significantly exceed the coupling of interest.