Off-resonance proton-decoupling in overtone NMR spectroscopy of solids

An off-resonance proton-decoupling method is presented for the measurement of H–N dipolar couplings in 14N-overtone NMR spectroscopy of solids. This one-dimensional method employs magic-angle radio-frequency irradiation of protons in order to suppress the 1H–1H dipole interactions during the 14N-overtone signal acquisition. The one-dimensional dipolar-overtone-shift spectrum obtained allows the direct measurement of N–H dipolar couplings for the structure determination of single crystalline or uniaxially oriented peptides. Results are presented from experiments on a single crystal sample of N-acetyl-D,L-valine. The proposed method is easy to implement experimentally and the results are simple to interpret. This experiment is less time-consuming and therefore useful for the study of biological solids as compared to two-dimensional separated-local-field methods.