Proton–nitrogen-14 overtone two-dimensional correlation NMR spectroscopy of solid-sample at very fast magic angle sample spinning

Abstract

1H–14N overtone (OT) heteronuclear multiple quantum coherence (HMQC) experiment at very fast magic angle spinning (MAS) is reported. The 14N OT coherence is excited and reconverted by 14N OT pulses at twice the 14N Larmor frequency. The OT coherence is free from the first order quadrupolar broadening. MAS further removes the broadening due to chemical shift anisotropy (CSA). With a small 0.75mm MAS rotor and coil system, very fast MAS up to 90kHz and very strong rf field are achieved, enhancing the sensitivity of indirect 14N OT observation via protons. In comparison with 1H–14N double-quantum HMQC, an enhancement factor of 1.8 is obtained for glycine with the 14N OT irradiation. The bandwidth in the 14N OT dimension is limited due to long 14N OT pulses.