Journal
SOLID STATE NUCLEAR MAGNETIC RESONANCE
Volume 84, Issue -, Pages 171-181Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ssnmr.2017.03.005
Keywords
Fast MAS; Quadrupolar nuclei; Structure; Methods; 2D NMR spectroscopy
Categories
Funding
- Iowa State University
- Ames Laboratory (Royalty Account)
- U.S. DOE [DE-AC02-07CH11358]
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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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