An intramembrane ion trap

Molecular ion channels consisting of covalently stacked crown ether (CE) rings are mounted in a membrane bilayer between two ion-containing aqueous layers. Molecular dynamics shows that because of a large negative electrostatic potential on the axis of the channel, the cations (but not anions) in the electrolyte layers enter the channel from the aqueous layer. Calculations suggest that the cations encounter an energy barrier at the mouth of the channel and occupy approximately axial sites between which they undergo dynamic redistributions. The application of electric fields sweeps the ions to one end of the channel but fields of electrolytic strengths affect neither the exit of the cations nor the admission of anions. The retention of the ion M+ shows that the CE channel acts as a trap for cations from the electrolyte layers.