Additives and Hydraphiles

The concept of channels has been with us more than a century. For half a century, biologists have studied the remarkable workings of protein and peptide channels that permit various cations and small molecules to pass through the phospholipid bilayer membrane. During the past decade, attempts have been made by chemists and biochemists to examine the action of channel compounds from the chemical point of view and to model their function using synthetic structures.

Shuttlilng of Cations

Calix[4]arenes in their 1,3-alternate conformation are particularly convenient scaffolds for the construction of extended tubes. These molecules can act as polytopic cation receptors and have the fascinating property of allowing cation transport |("shuttling") along the tube by passing through the "π-basic tube" formed by the macrocyclic rings of the calixarene units. Although calix tubes can also influence anion transport, this does not appear to involve anion shuttling.