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J Magn Reson. 2015 Feb;251:36-42. doi: 10.1016/j.jmr.2014.11.013. Epub 2014 Dec 11.

Observation of 1H-13C and 1H-1H proximities in a paramagnetic solid by NMR at high magnetic field under ultra-fast MAS.

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, Wuhan 430071, China.
2
Univ. Lille North of France, Unit of Catalysis and Chemistry of Solids (UCCS), CNRS UMR 8181, ENSCL, Univ. Lille 1, Villeneuve d'Ascq 59652, France.
3
Univ. Lille North of France, Unit of Catalysis and Chemistry of Solids (UCCS), CNRS UMR 8181, ENSCL, Univ. Lille 1, Villeneuve d'Ascq 59652, France. Electronic address: olivier.lafon@univ-lille1.fr.
4
Univ. Lille North of France, Unit of Catalysis and Chemistry of Solids (UCCS), CNRS UMR 8181, ENSCL, Univ. Lille 1, Villeneuve d'Ascq 59652, France; Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China.
5
Univ. Lille North of France, Unit of Catalysis and Chemistry of Solids (UCCS), CNRS UMR 8181, ENSCL, Univ. Lille 1, Villeneuve d'Ascq 59652, France; Physics Department & Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China. Electronic address: jean-paul.amoureux@univ-lille1.fr.
6
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, Wuhan 430071, China. Electronic address: dengf@wipm.ac.cn.

Abstract

The assignment of NMR signals in paramagnetic solids is often challenging since: (i) the large paramagnetic shifts often mask the diamagnetic shifts specific to the local chemical environment, and (ii) the hyperfine interactions with unpaired electrons broaden the NMR spectra and decrease the coherence lifetime, thus reducing the efficiency of usual homo- and hetero-nuclear NMR correlation experiments. Here we show that the assignment of (1)H and (13)C signals in isotopically unmodified paramagnetic compounds with moderate hyperfine interactions can be facilitated by the use of two two-dimensional (2D) experiments: (i) (1)H-(13)C correlations with (1)H detection and (ii) (1)H-(1)H double-quantum↔single-quantum correlations. These methods are experimentally demonstrated on isotopically unmodified copper (II) complex of l-alanine at high magnetic field (18.8 T) and ultra-fast Magic Angle Spinning (MAS) frequency of 62.5 kHz. Compared to (13)C detection, we show that (1)H detection leads to a 3-fold enhancement in sensitivity for (1)H-(13)C 2D correlation experiments. By combining (1)H-(13)C and (1)H-(1)H 2D correlation experiments with the analysis of (13)C longitudinal relaxation times, we have been able to assign the (1)H and (13)C signals of each l-alanine ligand.

KEYWORDS:

2D correlation spectra; Chemical shift assignment; Paramagnetic solid; Solid state NMR

PMID:
25557861
DOI:
10.1016/j.jmr.2014.11.013

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