Resolution-Enhanced Solid-State NMR ¹³C−¹³C Correlation Spectroscopy by Optimal Control Dipolar-Driven Spin-State-Selective Coherence Transfer

Using optimal control, we have designed spin-state-selective coherence transfer experiments for biological solid-state NMR based on transfer via dipole−dipole coupling interactions. This enables combined coherence transfer and spin-state-selective excitation using very short pulse sequences compared to previous J_CC coupling-based methods, which have not so far been developed for transfer of coherence between spins but only for spin state selection on the origin spin. Furthermore, coherence transfer through the much larger dipole−dipole couplings renders the experiments more forgiving with respect to the demand of very intense proton decoupling during the long excitation periods of J_CC-based methods. The optimal control dipolar-driven spin-state-selective coherende transfer (^OCDDS₃CT) experiment doubles the resolution in the detection dimension of 2D CACO and 3D NCACO experiments, as demonstrated experimentally using uniformly ¹³C,¹⁵N-labeled amino acids, ubiquitin, and fibrils of the SNNFGAILSS fibrillating core of human islet amyloid polypeptide with the FGAIL part labeled with ¹³C and ¹⁵N.