Heteronuclear Overhauser experiments for symmetric molecules

The nuclear Overhauser effect (NOE) arises from dipolar interactions between magnetic moments associated with nuclear spins and it has become a powerful tool to extract relevant pieces of structural information about small molecules, as well as in molecules of biological interest. As a consequence, accurate NOE measurement is a very crucial issue. Here, we present a comparison between direct and a new inverse HOESY experiment aimed at the detection of heteronuclear NOE between H-1 and C-13, which is particularly well suited for symmetric compounds. It transpires that directly detected data are more suitable for quantitative assessment even if they suffer from lower sensitivity, whereas inverse detection is quite appropriate for a quick and qualitative assessment. In the latter experiment, unwanted cross-correlation effects may hide valuable NOE data (cross-relaxation), this drawback can be circumvented by a slight modification of the pulse sequence. Copyright (C) 2003 John Wiley Sons, Ltd.