Accordion-like tuning of composite pulse dipolar recoupling in solid-state NMR

Solid-state nuclear magnetic resonance (NMR) spectroscopy, being an important analytical tool in materials science and structural biology, typically relies on magic-angle-spinning (MAS). Often, it is combined with dipolar recoupling to reintroduce effects from dipole-dipole coupling interactions for polarization transfer or for distance measurements. A large variety of dipolar recoupling methods have been presented over the past decades. However, most of them are heavily constrained to certain application regimes defined by the MAS frequency, the static magnetic field, radio frequency pulse power capabilities, and combinations with efficient 1H decoupling. In this work, we exploit recent findings in pulsed dynamic nuclear polarization and its combinations with MAS solid-state NMR to propose an accordion-like method for tuning periodic composite pulse dipolar recoupling sequences to different experimental conditions, thereby improving the experimental flexibility of dipolar recoupling experiments to adapt optimally to applications in chemistry, materials science, and structural biology.