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14 N– 1 H heteronuclear multiple-quantum correlation (HMQC) solid-state magic-angle spinning (MAS) NMR spectra recorded at a  1 H Larmor frequency of 850 MHz are presented for the dipeptide  β -AspAla. A modified version of the pulse sequence presented by Gan  et al.  (Chem. Phys. Lett. 435 (2007) 163) that utilises rotary resonance recoupling (R 3 ) at the  n  = 2   condition ( ν  1  = 2 ν  R   ) is employed. Spectra recorded with a short recoupling period (under 200 μs) show two correlation peaks corresponding to the NH and NH 3  moieties in the dipeptide. The quadrupolar product,  P  Q  =  C  Q  √ [1 + ( η  Q  2 /3)]  , is determined experimentally as 3.1 MHz (NH) and 1.0 MHz (NH 3 ) by a comparison of the  14 N and  15 N isotropic chemical shifts which differ due to the isotropic second-order quadrupolar shift for the spin  I  = 1  14 N   nucleus. It is shown that the peak sensitivities increase markedly upon increasing the MAS frequency from 30 to 45 to 60 kHz due to a combination of the reduced residual dipolar broadening of the  1 H resonances and a lengthening of the coherence lifetimes under R   3    recoupling. Increasing the recoupling period leads to the observation of additional peaks corresponding to longer range intra- and intermolecular NH proximities. Reasonable agreement is evident upon comparing the experimental build-up of correlation peak intensity to that observed for eight-spin density-matrix simulations.

14 N– 1 H Heteronuclear Multiple-Quantum Correlation Magic-Angle Spinning NMR Spectroscopy of Organic Solids