Research Project

Development of novel recoupling and decoupling techniques in solid-state NMR spectroscopy

Solid state nuclear magnetic resonance (NMR) can unveil the local chemical structure of the observed nuclei, including electron distribution, internuclear distance, the mobility of atoms and groups, etc. It is therefore a powerful tool to investigate solid materials and to gain insight into heterogeneous catalytic process.

The main concern of our research is recoupling/decoupling technique based on R-symmetry pulse sequence. The R-symmetry pulse sequences consist of a series of strictly designed, rotor-synchronized, phase-alternating π sequences applied under magic angle spinning (MAS) condition. Because of its strict selection rules, a particular R-symmetry pulse sequence can reintroduce the symmetry-allowed interaction (i.e. recouple) while effectively suppress those interaction prohibited by the selection rules (i.e. decouple).

In order to investigate the local chemical structure of catalysts and adsorbates, we need to design appropriate R-symmetry pulse sequences to selectively recouple some vital interactions of the nuclei of interest, such as chemical shift anisotropy (CSA), dipolar coupling constant (DCC), etc. The CSA describes the electron distribution around the nuclei and it is sensitive to the local chemical environment. By taking use of the dipolar recoupling sequences, we can calculate the heteronuclear distances, as well as accomplish effective polarization transfer to enhance the signal. And because the condition of NMR hardware always deviates from ideal, for example the magnetic field inside the coil generated by radiofrequency pulse is more or less inhomogeneous, the pulse sequence should be robust enough to resist those hardware imperfection.