Enhanced ion transfer rate due to the presence of zwitterionic phospholipid monolayers at the ITIES

The transfer of cations across phospholipid monolayers at ITIES is studied both experimentally and theoretically. Further evidence of the enhanced rate for cation transfer due to the presence of the monolayer is presented, and a theoretical model that can explain these observations is worked out. The system considered experimentally is Li+ ion transfer across a hemispherical water ∣ 1,2-dichloroethane interface covered by distearoyl phosphatidylcholine. The theoretical description is based on the electrical double layer correction to the Butler–Volmer equation, coupled with a solution of the Poisson–Boltzmann equation across the interfacial region. The phospholipid monolayer is modelled as two parallel planes of charge, with the negative charge located at the ITIES and the positive charge located at a distance d into the aqueous phase. The enhancement factors predicted are found to be in agreement with our experimental results as well as with those obtained by other authors.