Biomimetic Ion Transport: Pores and Channels in Vesicle Membranes

Summary

Two approaches to biomimetic membrane transport systems for vesicle membranes are discussed. The first seeks to mimic the pore-forming antibiotic amphotericin, while the second involves the construction of a unimolecular ion channel.

Pore-forming antibiotics are proposed to form aggregates in the membrane by self association. The aggregate is proposed to present a hydrophobic exterior to the membrane, yet contain a hydrophilic interior for transport of ions and small molecules. The mimic system is based on side-discriminated bola form amphiphiles possessing hydrophilic and hydrophobic edges. Transport accross the visicle wall is followed by the pH dependent flourescence of a fluorescein bolaamphile embedded in the visicle wall. Even though the visicles are leaky, specific structural effects can be discerned.

The channel forming structures are constructed on a central crown framework with functionalized arms projecting towards the two faces of a bilayer membrane. In response to a pH gradient, the channel mediates the collapse of the gradient by mediating the cation-proton antiport. Structural effects, and the effects of carrier additives are consistent with the channel providing a mechanism for cation translocation.