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Science. 1996 Jan 12;271(5246):163-8.

Cation-pi interactions in chemistry and biology: a new view of benzene, Phe, Tyr, and Trp.

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  • 1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.


Cations bind to the pi face of an aromatic structure through a surprisingly strong, non-covalent force termed the cation-pi interaction. The magnitude and generality of the effect have been established by gas-phase measurements and by studies of model receptors in aqueous media. To first order, the interaction can be considered an electrostatic attraction between a positive charge and the quadrupole moment of the aromatic. A great deal of direct and circumstantial evidence indicates that cation-pi interactions are important in a variety of proteins that bind cationic ligands or substrates. In this context, the amino acids phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) can be viewed as polar, yet hydrophobic, residues.

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