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Proton detection of MAS solid-state NMR spectra of half-integer quadrupolar nuclei

TitleProton detection of MAS solid-state NMR spectra of half-integer quadrupolar nuclei
Publication TypeJournal Article
Year of Publication2017
AuthorsVenkatesh, A, Hanrahan, MP, Rossini, AJ
JournalSolid State Nuclear Magnetic Resonance
Date Published07
Type of ArticleArticle
ISBN Number0926-2040
Accession NumberWOS:000410462800023
Keywords100 khz mas, 2D NMR spectroscopy, angle-spinning nmr, chemistry, correlation, correlation spectroscopy, cross-polarization, Fast MAS, gamma-alumina, laser-polarized xenon, magnetic-resonance, methods, multiple-quantum, physics, point-of-view, quadrupolar nuclei, sensitivity enhancement, Spectroscopy, structure

Fast magic angle spinning (MAS) and proton detection has found widespread application to enhance the sensitivity of solid-state NMR experiments with spin-1/2 nuclei such as C-13, N-15 and Si-29, however, this approach is not yet routinely applied to half-integer quadrupolar nuclei. Here we have investigated the feasibility of using fast MAS and proton detection to enhance the sensitivity of solid-state NMR experiments with half-integer quadrupolar nuclei. The previously described dipolar hetero-nuclear multiple quantum correlation (D-HMQC) and dipolar refocused insensitive nuclei enhanced by polarization transfer (DRINEPT) pulse sequences were used for proton detection of half-integer quadrupolar nuclei. Quantitative comparisons of signal-to-noise ratios and the sensitivity of proton detected D-HMQC and D-RINEPT and direct detection spin echo and quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) solid-state NMR spectra, demonstrate that one dimensional proton detected experiments can provide sensitivity similar to or exceeding that obtainable with direct detection QCPMG experiments. 2D D-HMQC and D-RINEPT experiments provide less sensitivity than QCPMG experiments but proton detected 2D hetero-nuclear correlation solid-state NMR spectra of half-integer nuclei can still be acquired in about the same time as a 1D spin echo spectrum. Notably, the rarely used D-RINEPT pulse sequence is found to provide similar, or better sensitivity than D-HMQC in some cases. Proton detected D-RINEPT benefits from the short longitudinal relaxation times (T,) normally associated with half -integer quadrupolar nuclei, it can be combined with existing signal enhancement methods for quadrupolar nuclei, and t(1)-noise in the indirect dimension can easily be removed by pre-saturation of the H-1 nuclei. The rapid acquisition of proton detected 2D HETCOR solid-state NMR spectra of a range of half -integer quadrupolar nuclei such as O-17, Al-27, Cl-35 and Ga-71 is demonstrated.

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