E0012

Experimental Evidence for Alkali Metal Cation-pi Interactions. George W. Gokel^*, Leonard J. Barbour, Steven L. De Wall, Jiaxin Hu, and Eric S. Meadows, Program in and Division of Bioorganic Chemistry, Department of Molecular Biology & Pharmacology, Washington University School of Medicine, 660 S. Euclid Avenue, Campus Box 8103, St. Louis, MO 63110, ^*Tel. 314/362-9297, Fax 314/362-9298, e-mail: ggokel@molecool.wustl.edu.

The interactions of benzene, phenol, and indole with sodium and potassium cations are of the profoundest importance in biology. Benzene, phenol, and indole are the respective sidechains of phenylalanine, tyrosine, and tryptophan. Together, they comprise more than 8% of sidechains in all known protein sequences. Sodium and potassium are ubiquitous both intra- and extracellularly. It is reasonable to expect that many cation-pi interactions occur in proteins but they have been little explored. Theoretical work certainly predicts significant interaction energies and mass spectrometric analyses have shown that the enthalpies of interaction for sodium and potassium cations are in the range of 20-30 kcal/mol. Solid state information has largely been lacking until recently. We will present X-ray crystallographic data that demonstrate cation-pi interactions between all three aromatic residues and also show a number of variations in the types of interactions that can occur.