Accelerating the acquisition of high-resolution quadrupolar MQ/ST-HETCOR 2D spectra under fast MAS via 1H detection and through-space population transfers

Abstract

Recently, we established an experimental setup protocol to perform the population transfer from half-integer quadrupolar spin to 1H nuclei under fast MAS in the context of MQ-HETCOR experiments. In this article, we further develop the high-resolution 2D HETCOR methods by ST-based approaches, making use of the sensitivity advantage of STMAS over its MQMAS counterpart. In a similar manner to the previous work, which utilized CP and RINEPT for the population transfer, we also demonstrate the experimental setup protocol for PRESTO. Using {23Na}-1H and {27Al}-1H spin systems of powder samples, we compare a series of MQ/ST-HETCOR 2D spectra to discuss the pros and cons of the distinct MQ/ST-based approaches for spin 3/2 and 5/2 nuclei, respectively. We also incorporate two experimental tricks to reduce the experimental time of such long 2D experiments, the Optimized Rotor-Synchronization (ORS) and the Non-Uniform Sampling (NUS), in the context of high-resolution spectra of half-integer quadrupolar spin nuclei.