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J Magn Reson. 2018 Aug;293:92-103. doi: 10.1016/j.jmr.2018.06.005. Epub 2018 Jun 15.

Uniform signal enhancement in MAS NMR of half-integer quadrupolar nuclei using quadruple-frequency sweeps.

Author information

1
National Center for Magnetic Resonance in Wuhan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, 430071 Wuhan, China.
2
Univ. Lille, CNRS-8181, ENSCL, UCCS-Unit of Catalysis and Chemistry of Solids, 59000 Lille, France.
3
National Center for Magnetic Resonance in Wuhan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, 430071 Wuhan, China; Univ. Lille, CNRS-8181, ENSCL, UCCS-Unit of Catalysis and Chemistry of Solids, 59000 Lille, France; Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, 200062 Shanghai, China.
4
Univ. Lille, CNRS-8181, ENSCL, UCCS-Unit of Catalysis and Chemistry of Solids, 59000 Lille, France; Institut Universitaire de France, 75231 Paris, France.
5
Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, 200062 Shanghai, China.
6
Univ. Lille, CNRS-8181, ENSCL, UCCS-Unit of Catalysis and Chemistry of Solids, 59000 Lille, France; Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, 200062 Shanghai, China; Bruker Biospin, 67166 Wissembourg, France. Electronic address: jean-paul.amoureux@univ-lille1.fr.
7
National Center for Magnetic Resonance in Wuhan, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, 430071 Wuhan, China. Electronic address: dengf@wipm.ac.cn.

Abstract

We introduce two MAS schemes that allow manipulating the satellite-transition (ST) populations of half-integer quadrupolar nuclei, and which both exhibit improved robustness to the quadrupolar coupling constant (CQ). These schemes, called quadruple frequency sweep (QFS) or quadruple WURST (QWURST) are the sums of two DFS or four WURST to efficiently invert the ST populations of nuclei subject to large or small quadrupole interactions, simultaneously. These quadruple sweeps methods only require 6% more rf-power than the double sweeps ones. We demonstrate, both numerically and experimentally, that the QFS and QWURST schemes benefit from robustness to CQ and rf amplitude and offset and hence achieve uniform enhancement of the CT signal for 27Al nuclei subject to different quadrupole interactions. Although the version of QFS with repetitive accumulation can achieve higher enhancement in the S/N of the 27Al MAS spectrum, the final sensitivity gains mainly depend on the longitudinal relaxation time of different 27Al sites. We also confirm that these schemes provide an improved acceleration of the 31P-{27Al} coherence transfer in PT-J-HMQC experiments.

KEYWORDS:

Central transition; Half-integer quadrupolar nuclei; Quadruple-frequency sweeps; Satellite transitions; Signal enhancement

PMID:
29909082
DOI:
10.1016/j.jmr.2018.06.005

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