Indirect measurement of NMR scalar coupling constants under inhomogenous magnetic fields

Abstract

Scalar coupling constant is an important parameter in structure analysis from nuclear magnetic resonance (NMR) spectra. However, it is difficult to obtain in inhomogeneous fields using general NMR techniques due to broadened line-width. Since the line-widths of intermolecular zero quantum coherence (iZQC) spectrum only depend on the relative inhomogeneity within the correlation distance in the sample, scalar coupling constants can be gained though one-dimensional spectra from the projection of two-dimensional iZQC spectra onto the indirect dimension. However, the existing pulse sequences are not suitable for various spin systems because of the great difference in scalar coupling constants and line denseness in spectra. To solve this problem, a new pulse sequence, which can scale scalar coupling constants, was designed by adding a refocusing π pulse in the indirect detection period (corresponding to indirect dimension). According to specific spin coupled system and spectral condition, precise coupling constants can be indirectly measured by selecting a compromise scaling factor for coupling constant.