Gschwind Ruth M, Xie Xiulan, Rajamohanan Pattuparambil R
Kekulé Institute of Organic Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany.
Magn Reson Chem. 2004 Mar;42(3):308-12. doi: 10.1002/mrc.1344.
Gradient-selected (gs) HSQC-NOESY type experiments are often applied in order to obtain NOE cross peaks in symmetrical molecules or in complex organic molecules, e.g. carbohydrates. Since the coherence-selecting gradients in these pulse sequences are separated by several delays, including the mixing time, the gs-HSQC-NOESY spectra exhibit severe signal attenuation due to diffusion effects. The respective NOE information unaffected by diffusion effects can be obtained by X-half-filtered gs-NOESY-HSQC spectra. In this paper, an X-half-filtered version of the gs-NOESY-HSQC experiment is presented and the NOE cross peak integrals of its spectra are compared with those of a standard gs-HSQC-NOESY experiment. With phenanthrene as an example of symmetrical molecules, it is shown that the relative signal attenuation of gs-HSQC-NOESY cross peaks versus gs-NOESY-HSQC cross peaks is caused by diffusion effects and follows the Stejskal-Tanner equation. In contrast, the X-half-filtered gs-NOESY-HSQC experiment provides NOE cross peaks with reasonable signal-to-noise ratios even for long-range interactions in the presence of quadrupolar relaxation. This is demonstrated by the spectra of lithium dimethylcuprate.
梯度选择（gs）HSQC - NOESY类型的实验通常用于在对称分子或复杂有机分子（如碳水化合物）中获取NOE交叉峰。由于这些脉冲序列中的相干选择梯度被包括混合时间在内的几个延迟隔开，gs - HSQC - NOESY谱会因扩散效应而出现严重的信号衰减。不受扩散效应影响的相应NOE信息可通过X半滤波的gs - NOESY - HSQC谱获得。本文介绍了gs - NOESY - HSQC实验的X半滤波版本，并将其谱的NOE交叉峰积分与标准gs - HSQC - NOESY实验的进行了比较。以菲作为对称分子的例子表明，gs - HSQC - NOESY交叉峰相对于gs - NOESY - HSQC交叉峰的相对信号衰减是由扩散效应引起的，并且遵循斯泰斯卡尔 - 坦纳方程。相比之下，即使在存在四极弛豫的情况下对于长程相互作用，X半滤波的gs - NOESY - HSQC实验也能提供具有合理信噪比的NOE交叉峰。这通过二甲基铜锂的谱得到了证明。
