Indirect high-resolution detection for quadrupolar spin-3/2 nuclei in dipolar HMQC solid-state NMR experiments

We present a new kind of NMR pulse sequences to observe heteronuclear correlation (HETCOR) specifically between spin-1/2 and spin-3/2 nuclei with isotropic resolution on the quadrupolar channel. These methods, called HMQC-ST, feature a STMAS filter during the evolution period of the HMQC scheme. Compared to existing HETCOR techniques involving quadrupolar nuclei, the HMQC-ST combines high-resolution and high efficiency and allows indirect detection of spin-3/2 nuclei via sensitive nuclei. We study analytically and using simulations how through-bond and through-space HMQC-ST perform compared to regular HMQC sequence. HMQC-ST potential is demonstrated experimentally by recording through-space HETCOR 2D spectra of Na₂HPO₄ and NaH ₂PO₄.