ARTIFACTS IN GRADIENT ENHANCED HSQC

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The Gradient Enhanced Heteronuclear Single Quantum Correlation (GEHSQC) experiment is widely used, especially as a building block in multi-dimensional NMR, for instance in 3D NOESY HSQC experiments. However, close inspection of GEHSQC spectra reveals a large number of small artifacts. In situations of high dynamic range, these artifacts can interfere with spectral interpretation, since the artifacts associated with intense signals can obscure weak correlations of interest. We have sought to explain the origin of these artifacts and find a method to suppress them. They turn out to be caused by the evolution of proton scalar coupling during the back-transfer portion of the pulse sequence via a relayed coherence transfer mechanism. The artifacts appear as cross-peaks involving remote protons. Product operator analysis of artifact formation and experimental results demonstrate that the magnitude of these artifacts can exceed 10% of the main peak. Therefore, these artifacts represent a significant loss in sensitivity.