Cation-pi interactions in chemistry and biology: a new view of benzene, Phe, Tyr, and Trp.
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.
Dougherty
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Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125, USA.
D000109:Acetylcholine / Q000378:metabolism; D001554:Benzene / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002412:Cations / Q000737:chemistry / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007473:Ion Channels / Q000378:metabolism; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism*; D014867:Water / Q000737:chemistry / Q000378:metabolism
D002412:Cations; D007473:Ion Channels; D011506:Proteins; D011950:Receptors, Cholinergic; D013256:Steroids; D014867:Water; D014443:Tyrosine; D010649:Phenylalanine; D014364:Tryptophan; D001554:Benzene; D000109:Acetylcholine