Low-power homonuclear dipolar recoupling in solid-state NMR developed using optimal control theory

Novel low-power pulse sequences for homonuclear dipolar recoupling in biological solid-state NMR spectroscopy are presented. The pulse sequences are developed numerically using the Simpson simulation program in combination with optimal control procedures. The quality criteria for the experiment optimizations are the achievement of the highest possible sensitivity for powder samples under typical experimental inhomogeneous radio-frequency (rf) field conditions, while keeping the rf field strength sufficiently low to prevent undesirable sample heating in biological applications. The new dipolar recoupling methods are demonstrated numerically and experimentally by double-quantum filtration magic-angle spinning NMR experiments for which sensitivity gains approaching a factor of 2 is observed.