Estimation of internuclear couplings in the solid-state NMR of multiple-spin systems. Selective spin echoes and off-magic-angle sample spinning

Internuclear couplings between selected homonuclear spin pairs in a multiply-labelled spin system are determined by NMR spin echo experiments in the solid-state. The spin echoes are induced by an amplitude-modulated shaped pulse. The time shift in the echo modulation curve is treated by average Hamiltonian theory and verified by numerical simulation. The J-couplings may be estimated by experiments on samples spinning at the magic-angle, while the direct dipole–dipole couplings may be estimated by off-magic-angle spinning. The concept is tested on a uniformly 13C-enriched sample of l-histidine hydrochloride monohydrate.