A comparison of through-space population transfers from half-integer spin quadrupolar nuclei to 1H using MQ-HETCOR and MQ-SPAM-HETCOR under fast MAS.

In this article, we compare the various schemes of magnetization transfer from half-integer quadrupolar spins to 1H nuclei and we establish an efficient protocol to perform these transfers under MQMAS high-resolution with the MQ-HETCOR and MQ-SPAM-HETCOR experiments under fast MAS. The MQMAS efficiencies are analyzed with SIMPSON simulations, and the CPMAS and RINEPT magnetization transfers are compared at 62.5 kHz MAS using {23Na}-1H and {27Al}-1H MQ-HETCOR and MQ-SPAM-HETCOR experiments performed on NaH2PO4, Na2HPO4, Na citrate dihydrate and ipa-AlPO-14 powder samples. We discuss the pros and cons of these approaches, aiming to record 2D spectra of the best possible quality under fast MAS. We also incorporate some experimental approaches to reduce the total experiment time of such long 2D experiments.