Rapid acquisition of wideline MAS solid-state NMR spectra with fast MAS, proton detection, and dipolar HMQC pulse sequences

Abstract

The solid-state NMR spectra of many NMR active elements are often extremely broad due to the presence of chemical shift anisotropy (CSA) and/or the quadrupolar interaction (for nuclei with spin I > 1/2). These NMR interactions often give rise to wideline solid-state NMR spectra which can span hundreds of kHz or several MHz. Here we demonstrate that by using fast MAS, proton detection and dipolar hetero-nuclear multiple-quantum (D-HMQC) pulse sequences, it is possible to rapidly acquire 2D spectra which correlate ¹H chemical shifts to the indirectly detected wideline MAS powder patterns of dipolar coupled hetero-nuclei. The D-HMQC pulse sequence enables broadband excitation of the wideline hetero-nuclear NMR spectrum and provides higher sensitivity by detecting the narrower and more sensitive ¹H NMR signal. This approach is demonstrated for the rapid acquisition of 2D ¹H detected ¹⁹⁵Pt solid-state NMR spectra of cisplatin and transplatin and the ⁷¹Ga solid-state NMR spectrum of a self-assembled Ga coordination polymer of unconfirmed structure. This approach should be broadly applicable for the rapid acquisition of wideline MAS solid-state NMR spectra of moderately abundant NMR nuclei.