The Folded Conformation of Perezone Revisited. Long Range nOe Interaction in Small Molecules: Interpretable Small Signals or Useless Large Artifacts?

The nuclear Overhauser effect (nOe) is a consequence of the cross-relaxation and it involves the transfer of nuclear spin polarization from one population to another intra or inter-molecularly. It is generally accepted that a proton-proton distance between 4 and 5 A is the upper limit for the occurrence of measurable nOe´s in small molecules. However, we herein show how detectable nOe´s may, in fact, take place between alkyl groups of quinones with substitutions at 1-4 relative positions, showing distances longer than 6 A. Although the signals of interest are very small, of the order of 1% of a normal nOe, so a priori are considered artifacts originated by decoupling modulation, they maintain, properties that make them interesting and give them coherence as interpretable signals. If the signals of interest are not artifacts these observations represent an important breakthrough with impact on the standard protocols that are commonly used for determination of molecular structure and conformation.