Improving solid-state NMR dipolar recoupling by optimal control

We present the first solid-state NMR experiments developed using optimal control theory. Taking heteronuclear dipolar recoupling in magic-angle-spinning NMR as an example, it proves possible to significantly improve the efficiency of the experiments while introducing robustness toward instrumental imperfections such as radio frequency inhomogeneity. The improvements are demonstrated by numerical simulations as well as practical experiments on a ¹³C^α,¹⁵N-labeled powder of glycine. The experiments demonstrate a gain of 53% in the efficiency for ¹⁵N to ¹³C_α coherence transfer relative to the typically double-cross-polarization experiments.