Madhu P K, Johannessen Ole G, Pike Kevin J, Dupree Ray, Smith Mark E, Levitt Malcolm H
Department of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
J Magn Reson. 2003 Aug;163(2):310-7. doi: 10.1016/s1090-7807(03)00159-9.
We report pulse sequences for the sensitivity enhancement of magic-angle spinning and multiple-quantum magic-angle spinning spectra of spin-72 systems. Sensitivity enhancement is obtained with the use of fast amplitude-modulated (FAM) radiofrequency pulses. In one-dimensional magic-angle spinning experiments, signal enhancement of 3 is obtained by a FAM pulse followed by a soft 90 degrees pulse. In two-dimensional multiple-quantum magic-angle spinning experiments, FAM pulses are used for both the excitation of multiple-quantum coherences and for their conversion into observable single-quantum coherences. The observed signal enhancements are 2.2 in 3Q experiments, 3.1 in 5Q experiments, and 4.1 in 7Q experiments, compared to the conventional two-pulse scheme. The pulse schemes are demonstrated on the 45Sc NMR of Sc2(SO4)3 x 5H2O and the 139La NMR of LaAlO3. We also demonstrate the generation of FAM pulses by double-frequency irradiation.
我们报道了用于增强自旋 - 7/2 体系魔角旋转（MAS）和多量子魔角旋转（MQMAS）谱灵敏度的脉冲序列。通过使用快速幅度调制（FAM）射频脉冲实现了灵敏度增强。在一维魔角旋转实验中，由一个FAM脉冲后跟一个软90度脉冲可使信号增强3倍。在二维多量子魔角旋转实验中，FAM脉冲用于激发多量子相干以及将其转换为可观测的单量子相干。与传统双脉冲方案相比，在3Q实验中观测到的信号增强为2.2倍，5Q实验中为3.1倍，7Q实验中为4.1倍。这些脉冲方案在Sc2(SO4)3·5H2O的45Sc NMR和LaAlO3的139La NMR上得到了验证。我们还展示了通过双频辐照产生FAM脉冲。
