Comparison of various NMR methods for the indirect detection of nitrogen-14 nuclei via protons in solids

Shen, Ming, Trébosc, Julien, O'Dell, Luke A., Lafon, Oliver, Pourpoint, Frederique, Hu, Bingwen, Chen, Qun and Amoureux, Jean-Paul 2015, Comparison of various NMR methods for the indirect detection of nitrogen-14 nuclei via protons in solids, Journal of magnetic resonance, vol. 258, pp. 86-95, doi: 10.1016/j.jmr.2015.06.008.

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Title Comparison of various NMR methods for the indirect detection of nitrogen-14 nuclei via protons in solids
Author(s) Shen, Ming
Trébosc, Julien
O'Dell, Luke A.ORCID iD for O'Dell, Luke A.
Lafon, Oliver
Pourpoint, Frederique
Hu, Bingwen
Chen, Qun
Amoureux, Jean-Paul
Journal name Journal of magnetic resonance
Volume number 258
Start page 86
End page 95
Total pages 10
Publisher Elsevier
Place of publication Amsterdam, The Netherlands
Publication date 2015-07-30
ISSN 1090-7807
Keyword(s) 14N isotope
Indirect detection
Solid-state NMR
Through-space HETCOR
Summary We present an experimental comparison of several through-space Hetero-nuclear Multiple-Quantum Correlation experiments, which allow the indirect observation of homo-nuclear single- (SQ) or double-quantum (DQ) 14N coherences via spy 1H nuclei. These 1H-{14N} D-HMQC sequences differ not only by the order of 14N coherences evolving during the indirect evolution, t1, but also by the radio-frequency (rf) scheme used to excite and reconvert these coherences under Magic-Angle Spinning (MAS). Here, the SQ coherences are created by the application of center-band frequency-selective pulses, i.e. long and low-power rectangular pulses at the 14N Larmor frequency, ν0(14N), whereas the DQ coherences are excited and reconverted using rf irradiation either at ν0(14N) or at the 14N overtone frequency, 2ν0(14N). The overtone excitation is achieved either by constant frequency rectangular pulses or by frequency-swept pulses, specifically Wide-band, Uniform-Rate, and Smooth-Truncation (WURST) pulse shapes. The present article compares the performances of four different 1H-{14N} D-HMQC sequences, including those with 14N rectangular pulses at ν0(14N) for the indirect detection of homo-nuclear (i) 14N SQ or (ii) DQ coherences, as well as their overtone variants using (iii) rectangular or (iv) WURST pulses. The compared properties include: (i) the sensitivity, (ii) the spectral resolution in the 14N dimension, (iii) the rf requirements (power and pulse length), as well as the robustness to (iv) rf offset and (v) MAS frequency instabilities. Such experimental comparisons are carried out for γ-glycine and l-histidine.HCl monohydrate, which contain 14N sites subject to moderate quadrupole interactions. We demonstrate that the optimum choice of the 1H-{14N} D-HMQC method depends on the experimental goal. When the sensitivity and/or the robustness to offset are the major concerns, the D-HMQC sequence allowing the indirect detection of 14N SQ coherences should be employed. Conversely, when the highest resolution and/or adjusted indirect spectral width are needed, overtone experiments are the method of choice. The overtone scheme using WURST pulses results in broader excitation bandwidths than that using rectangular pulses, at the expense of reduced sensitivity. Numerically exact simulations also show that the sensitivity of the overtone 1H-{14N} D-HMQC experiment increases for larger quadrupole interactions.
Language eng
DOI 10.1016/j.jmr.2015.06.008
Field of Research 020401 Condensed Matter Characterisation Technique Development
Socio Economic Objective 970103 Expanding Knowledge in the Chemical Sciences
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2015, Elsevier
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