Cation-Pi Interactions
- Cation-p interaction is a noncovalent molecular interaction between the face of an electron-rich p system (e.g. benzene, ethylene) with an adjacent cation (e.g. Li+, Na+). This unusual interaction is an example of noncovalent bonding between a monopole (cation) and a quadrupole (p system). Cation-p interaction energies are of the same order of magnitude as hydrogen bonds or salt bridges and play an important role in molecular recognition.
Cation-p interaction between benzene and a sodium cation.
In a protein Lys and Arg have the cationic side chains, so when they are near the aromatic side chains of Phe, Tyr or Trp they show cation-pi interactions.
When a cationic side chain (Lys or Arg) is near an aromatic side chain (Phe, Tyr, or Trp) within 6Å separation they account for cation-pi interactions.
REFERENCES :
[1] Eric V. Anslyn, Dennis A. Dougherty (2004). Modern Physical Organic Chemistry. University Science Books. ISBN 9-78-891389-31-3
[2] R.Satyapriya and Saraswathi Vishveshwara, Nucleic Acid Research , 2004, Vol 32, pg.4109Â4118.