Gs-HSQC-NOESY versus gs-NOESY-HSQC experiments: signal attenuation due to diffusion; application to symmetrical molecules
✍ Scribed by Ruth M. Gschwind; Xiulan Xie; Pattuparambil R. Rajamohanan
- Book ID
- 102529391
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 164 KB
- Volume
- 42
- Category
- Article
- ISSN
- 0749-1581
- DOI
- 10.1002/mrc.1344
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✦ Synopsis
Abstract
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. Copyright © 2004 John Wiley & Sons, Ltd.