Prediction of the carrier-mediated cation flux through polymer inclusion membranes via fundamental thermodynamic quantities: complexation study of bis(dodecyloxy)calix[4]arene-crown-6 with alkali metal cations

In a systematic study of alkali metal cation transport through a polymer in clusion membrane (PIM) with calixcrown carriers, a model that postulates di ffusion-limited flux successfully describes PIM transport behavior. The mod el developed herein is based on an ion-pair extraction equilibrium at the P IM interface and provides a convenient tool for the quantitative understand ing and interpretation of the transport data. Cation permeability coefficie nts can be easily determined and used for the quantitative correlation of f luxes employing a range of aqueous and PIM compositions. The described appr oach can be readily extended to competitive-transport experiments. Transpor t of a single cation as well as several cations in a competitive experiment was related to the stability constants of the carrier-metal complexes and the Gibbs energies of ion partitioning between source and membrane phases. The expected dependence of Cs+ ion transport on the Gibbs energy of anion p artitioning was validated in a series of 8 univalent anions. Accordingly, t he permeability coefficient once determined for a given metal salt, carrier , and PIM provides the basis for the prediction of the transport fluxes und er different initial conditions if the thermochemical quantities which gove rn the complexation and distribution of the metal species into the membrane phase are known or can be estimated. In support of these efforts, a calori metric study was carried out to obtain thermodynamic parameters for the com plexation of bis(dodecyloxy)calix[4]arene-crown-6 with alkali metal ions in acetonitrile.