The 3D HCCH-TOCSY and HCC(CO)NH-TOCSY experiments provide through bond connectivity and are used for side-chain chemical shift assignment by solution-state NMR. Careful design and implementation of the pulse sequence are key to the successful application of the technique particularly when trying to extract the maximum information out of challenging biomolecules. Here we investigate the source of and propose solutions for abnormal peak splitting ranging from 152 to 80 Hz and below that were found in three popular TOCSY-based experiment types: H(F1)-C(F2)-DIPSI-H(F3), C(F1)-DIPSI-C(F2)-H(F3), and C(F1)-DIPSI-N(F2)-HN(F3). Peak splitting occurs in the indirect C(F1) or C(F2) dimension before DIPSI and analyses indicate that the artifacts are resulted mainly from the DIPSI transforming a double spin order [Formula: see text] from 13C-13C scalar 1JCC coupling during t1 into observable megnetization. The splitting is recapitulated by numerical simulation and approaches are proposed to remove it. Adding a pure delay of 3.7 ms immediately before DIPSI is a simple and effective strategy to achieve 3D HCCH-TOCSY and HCC(CO)NH-TOCSY spectra free of splitting with full crosspeak intensity.

中文翻译：

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了解和解决3D HCCH-TOCSY和HCC（CO）NH-TOCSY中的异常峰分裂。

3D HCCH-TOCSY和HCC（CO）NH-TOCSY实验通过键连接提供，并通过溶液态NMR用于侧链化学位移分配。精心设计和执行脉冲序列是成功应用该技术的关键，特别是在尝试从具有挑战性的生物分子中提取最大信息时。在这里，我们调查了三种常见的基于TOCSY的实验类型：H（F1）-C（F2）-DIPSI-H（F3），从152至80 Hz及以下的异常峰分裂的来源，并提出了解决方案。 C（F1）-DIPSI-C（F2）-H（F3）和C（F1）-DIPSI-N（F2）-HN（F3）。峰值分裂发生在DIPSI之前的间接C（F1）或C（F2）维度上，分析表明，伪影主要是由DIPSI转换了双自旋阶数引起的[公式：[参见文字]从t1期间的13C-13C标量1JCC耦合变为可观察到的磁化。通过数值模拟概括了该分裂，并提出了消除该分裂的方法。在DIPSI之前立即添加3.7 ms的纯延迟是一种简单而有效的策略，可实现3D HCCH-TOCSY和HCC（CO）NH-TOCSY光谱，且不产生完全的交叉峰强度。