“η6”‐Type anion–π in Biomolecular Recognition

Theoretical and compelling experimental evidence indicates that the interaction between an anion and an aromatic π system when the anion is directly above the ring face (“η6”‐type anion–π), can be attractive. This may play an important role in the formation and recognition of biomolecular structures. We examined high‐resolution structures of proteins and nucleic acids for the presence of “η6”‐type anion–π. Though less frequent than its counterpart cation–π, “η6”‐type anion–π is observed unambiguously, occurring in protein/nucleic acid loops and often involving conserved/coevolving sites in proteins, suggesting it plays an important role in macromolecular folding and function