Characterization of cation receptors and synthetic anion transporters

Reported here are studies of noncovalent interactions that occur between and among small molecules as well as at the surface of a cell membrane. Synthetic crown ether receptors were used to study cation-pi interactions between potassium ions and benzene, the side chain of the amino acid phenylalanine. Absorbance and fluorescence spectroscopy characterized the solution behavior of crown ether receptors in the presence of cations. Amphiphilic heptapeptides can function as synthetic anion transporter (SAT) molecules. Previous work showed that SATs formed anion-selective pores in bilayer membranes. Monolayer behavior of amphiphilic SATs at the air-water interface reveal polar interactions at the membrane surface and hydrophobic interactions in the membrane interior. Studies using a Langmuir trough and Brewster angle microscope (BAM) probed and characterized the self-assembly of synthetic anion transporters in monolayers, which directly models behavior in bilayer membranes. Dynamic light scattering experiments in aqueous solution and transmission electron microscopic images correlated well with the Langmuir trough and BAM results obtained at the air-water interface.