Long-range heteronuclear single quantum correlation (LR-HSQC) experiments may be applied for detecting long-range correlations but suffer from two disadvantages, common to all heteronuclear long-range correlation experiments: (i) The information density in LR-HSQC spectra may be too high to be used directly without "filtering out" shorter range correlations, and (ii) often, substantial differences in intensity among cross peaks exist, potentially hampering the visualization of weak, often crucial cross peaks. In this contribution, we propose a modified LR-HSQC experiment, the LR-HTQC experiment (Long-Range Heteronuclear Triple Quantum Correlation) that partially solves the problems aforementioned. We show theoretically and experimentally that the LR-HTQC experiment removes the intense cross peaks of CH spin pairs, substantially reduces the medium intensity of cross peaks originating from CHH' spin systems, whereas the typically weak intensity of cross peaks of CHH'H″ and C(H)n, n > 3 spin systems is less affected. Consequently, the LR-HTQC experiment affords simplified long-range heteronuclear shift correlation spectra and scales down large intensity differences among different types of cross peaks, although a certain general reduction of signal intensities has to be accepted.

中文翻译：

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使用三重量子滤波器简化 LR-HSQC 光谱：LR-HTQC 实验

长程异核单量子关联 (LR-HSQC) 实验可用于检测长程关联，但存在两个缺点，所有异核长程关联实验都有：(i) LR-HSQC 光谱中的信息密度可能太高而不能直接使用而不“过滤掉”较短范围的相关性，并且（ii）通常，交叉峰之间的强度存在显着差异，这可能会阻碍弱的，通常是关键的交叉峰的可视化。在这个贡献中，我们提出了一种改进的 LR-HSQC 实验，即 LR-HTQC 实验（远程异核三重量子相关），它部分解决了上述问题。我们在理论上和实验上表明 LR-HTQC 实验消除了 CH 自旋对的强烈交叉峰，显着降低了源自 CHH' 自旋系统的交叉峰的中等强度，而 CHH'H" 和 C(H)n, n > 3 自旋系统的交叉峰的典型弱强度受到的影响较小。因此，LR-HTQC 实验提供了简化的远程异核位移相关光谱，并缩小了不同类型交叉峰之间的大强度差异，尽管必须接受信号强度的某种普遍降低。