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Is Perfection Ever Attainable? Strong Coupling Effects in the Perfect Echo.
Magnetic Resonance in Chemistry ( IF 1.9 ) Pub Date : 2019-08-19 , DOI: 10.1002/mrc.4927 Peter W A Howe 1
Magnetic Resonance in Chemistry ( IF 1.9 ) Pub Date : 2019-08-19 , DOI: 10.1002/mrc.4927 Peter W A Howe 1
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The Perfect Echo sequence, originally proposed in the late 1980s, has recently been popularised with many applications in the field of small‐molecule proton NMR spectroscopy. The Perfect Echo refocuses all homonuclear J‐couplings for AX spin systems and refocuses magnetization in‐phase for more complex weakly coupled spin systems, albeit with some intensity reduction. In contrast to suggestions in previous publications, spectra acquired in our laboratory showed that the Perfect Echo caused intensity distortions in strongly coupled systems where the chemical shift difference between the coupled spins was not large compared to the J‐coupling. This paper reports experimental observations and theoretical analysis of strongly coupled spins to confirm the distortions are real and that they originate principally from transfer of magnetization caused by the final inversion pulse of the Perfect Echo. The intensity changes are not large, but because of them, identifications of coupling partners based on resonance intensities (“roofing”) can no longer be relied on when the Perfect Echo is used. However, theory and experiment confirm that adding an orthogonal excitation pulse at the end of the Perfect Echo greatly reduces the distortions.
中文翻译：
完美永远可以实现吗？完美回声中的强耦合效应。
Perfect Echo 序列最初是在 1980 年代后期提出的，最近在小分子质子核磁共振光谱领域的许多应用中得到了推广。Perfect Echo 为 AX 自旋系统重新聚焦所有同核 J 耦合，并为更复杂的弱耦合自旋系统重新聚焦同相磁化，尽管强度有所降低。与之前出版物中的建议相反，我们实验室获得的光谱表明，完美回波在强耦合系统中引起强度失真，与 J 耦合相比，耦合自旋之间的化学位移差异不大。本文报告了强耦合自旋的实验观察和理论分析，以确认失真是真实的，并且它们主要源自完美回波的最终反转脉冲引起的磁化转移。强度变化不大，但正因为如此，当使用 Perfect Echo 时，不再依赖于基于共振强度（“屋顶”）的耦合伙伴识别。然而，理论和实验证实，在完美回波的末尾添加一个正交激励脉冲可以大大减少失真。
更新日期：2019-08-19
中文翻译：
完美永远可以实现吗？完美回声中的强耦合效应。
Perfect Echo 序列最初是在 1980 年代后期提出的，最近在小分子质子核磁共振光谱领域的许多应用中得到了推广。Perfect Echo 为 AX 自旋系统重新聚焦所有同核 J 耦合，并为更复杂的弱耦合自旋系统重新聚焦同相磁化，尽管强度有所降低。与之前出版物中的建议相反，我们实验室获得的光谱表明，完美回波在强耦合系统中引起强度失真，与 J 耦合相比，耦合自旋之间的化学位移差异不大。本文报告了强耦合自旋的实验观察和理论分析，以确认失真是真实的，并且它们主要源自完美回波的最终反转脉冲引起的磁化转移。强度变化不大，但正因为如此，当使用 Perfect Echo 时，不再依赖于基于共振强度（“屋顶”）的耦合伙伴识别。然而，理论和实验证实，在完美回波的末尾添加一个正交激励脉冲可以大大减少失真。
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