UCCS, CNRS-8181, Lille-University, 59652, Villeneuve d'Ascq, France; State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Center for Magnetic Resonance, WIPM, Chinese Academy of Sciences, Wuhan 430071, China; Graduate School of the Chinese Academy of Sciences, Beijing, China.
J Magn Reson. 2010 Mar;203(1):113-28. doi: 10.1016/j.jmr.2009.12.009. Epub 2009 Dec 14.
We describe dipolar recoupling methods that accomplish, at high magic-angle spinning (MAS) frequencies, the excitation of double-quantum (DQ) coherences between spin-1/2 nuclei. We employ rotor-synchronized symmetry-based pulse sequences which are either gamma-encoded or non-gamma-encoded. The sensitivity and the robustness to both chemical-shift anisotropy and offset are examined. We also compare different techniques to avoid signal folding in the indirect dimension of two-dimensional double-quantum<-->single-quantum (DQ-SQ) spectra. This comprehensive analysis results in the identification of satisfactory conditions for dipolar (19)F-(19)F recoupling at high magnetic fields and high MAS frequencies. The utility of these recoupling methods is demonstrated with high-resolution DQ-SQ NMR spectra, which allow probing (19)F-(19)F proximities in powered fluoroaluminates.
我们描述了在高魔角旋转（MAS）频率下实现自旋-1/2核之间的双量子（DQ）相干激发的偶极耦联方法。我们采用基于转子同步的对称脉冲序列，这些序列要么是γ编码的，要么是非γ编码的。我们检查了它们对化学位移各向异性和偏移的灵敏度和鲁棒性。我们还比较了不同的技术来避免二维双量子<-->单量子（DQ-SQ）谱的间接维度中的信号折叠。这种全面的分析导致在高磁场和高 MAS 频率下确定了偶极（19）F-（19）F 耦联的满意条件。这些偶联方法的实用性通过高分辨率的 DQ-SQ NMR 谱得到了证明，这些谱允许探测氟铝酸盐中的（19）F-（19）F 接近度。
