Measuring amide nitrogen quadrupolar coupling by high-resolution 14N/13C NMR correlation under magic-angle spinning.

The measurement of amide nitrogen 14N quadrupolar coupling by two-dimensional 14N/13C correlation experiment is presented with a natural abundant polypeptide. Directly bonded 14N/13C pairs are correlated through J and residual dipolar coupling under magic-angle spinning using a HMQC-type pulse sequence. The 14N quadrupolar coupling is measured from the isotropic second-order quadrupolar shift obtained by comparing the 14N peak positions with the 15N chemical shifts. The high spectral resolution and sensitivity through 13C detection make this method applicable to many organic, inorganic, and biological molecules for the measurement and the use of 14N quadrupolar coupling as a probe for molecular structure and dynamics.