High-resolution heteronuclear correlations between spin-1/2 and half-integer quadrupolar nuclei under fast MAS solid-state NMR.

High isotropic resolution is essential for the structural elucidation of samples with multiple sites. In this study, utilizing the benefits of TRAPDOR-based heteronuclear multiple quantum coherence (T-HMQC) and a pair of one rotor period long cosine amplitude modulated low-power (cos-lp) pulse-based symmetric-split-t multiple-quantum magic angle spinning (MQMAS) methods, we have developed a proton-detected 2D Cl/H T-HMQC-MQMAS pulse sequence under fast MAS (70 kHz) to achieve high-resolution in the indirect dimension of the spin-3/2 (Cl) nuclei connected via protons. As T-HMQC polarizes not only single-quantum central transition (SQ) but also triple-quantum (TQ) coherences, the proposed 2D pulse sequence is implemented via selection of two coherence pathways (SQ→TQ →SQ and TQ → SQ→TQ) resulting in the Cl isotropic dimension and is superior to the existing double-quantum satellite-transition (DQ) T-HMQC in terms of resolution.