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

Abstract

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-t₁ multiple-quantum magic angle spinning (MQMAS) methods, we have developed a proton-detected 2D ³⁵Cl/¹H T-HMQC-MQMAS pulse sequence under fast MAS (70 kHz) to achieve high-resolution in the indirect dimension of the spin-3/2 (³⁵Cl) nuclei connected via protons. As T-HMQC polarizes not only single-quantum central transition (SQ_CT) but also triple-quantum (TQ) coherences, the proposed 2D pulse sequence is implemented via selection of two coherence pathways (SQ_CT→TQ →SQ_CT and TQ → SQ_CT→TQ) resulting in the ³⁵Cl isotropic dimension and is superior to the existing double-quantum satellite-transition (DQ_ST) T-HMQC in terms of resolution.

Keywords: Fast magic angle spinning; HMQC; Heteronuclear correlations; MQMAS; Nuclear magnetic resonance; Solid-state NMR.