Recording ¹³C-¹⁵N HMQC 2D sparse spectra in solids in 30 s

We propose a dipolar HMQC Hadamard-encoded (D-HMQC-H_n) experiment for fast 2D correlations of abundant nuclei in solids. The main limitation of the Hadamard methods resides in the length of the encoding pulses, which results from a compromise between the selectivity and the sensitivity due to losses. For this reason, these methods should mainly be used with sparse spectra, and they profit from the increased separation of the resonances at high magnetic fields. In the case of the D-HMQC-H_n experiments, we give a simple rule that allows directly setting the optimum length of the selective pulses, versus the minimum separation of the resonances in the indirect dimension. The demonstration has been performed on a fully ¹³C,¹⁵N labelled f-MLF sample, and it allowed recording the build-up curves of the ¹³C-¹⁵N cross-peaks within 10 min. However, the method could also be used in the case of less sensitive samples, but with more accumulations.