Silacrown ionophores

A study is reported on the metal ion transport efficiency of various silacrown ether ionophores and their ethyleneoxy glycol hydrolysis products. The silacrowns are modified crown ethers in which an ethylene bridge has been replaced by a difunctional silyl group, e.g. dimethylsilyl. We have studied the relative transport efficiencies of the silacrowns with 4, 5, 6 and 7 oxygen atoms in the macrocycle for the alkali metals ions Li +, Na +, K +, Rb +, and Cs +. We have also performed experiments which illustrate that the silacrowns behave as short-term ion transporters. They will slowly hydrolyse in hydrophobic environments in contact with water to yield ethyleneoxy glycols which partition out of the hydrophobic phase into the hydrophilic phase, This terminates significant transport since the glycols are relatively inefficient ionophores. The potential of such shortterm ionophores is discussed.