(15)N-(1)H bond length determination in natural abundance by inverse detection in fast-MAS solid-state NMR spectroscopy.

A solid-state 15N-1H correlation NMR experiment is presented, which provides a substantial gain in signal sensitivity by 1H inverse detection under fast MAS conditions and allows for the precise determination of NH bond lengths via heteronuclear 1H-15N dipole-dipole couplings on samples naturally abundant in 15N. Pulsed-field gradients or, alternatively, radio frequency pulses ensure suppression of unwanted 1H signals. In this way, natural-abundance 15N-1H correlation NMR spectroscopy becomes feasible in the solid state with experiment times of a few hours. The dipole-dipole coupling constants are extracted from spinning sideband patterns generated by recently developed recoupling strategies. The information on 15N/1H chemical shifts and quantitative 15N-1H couplings can readily be combined in a single two-dimensional spectrum using a split-t1 approach.