title: Transport of alkali halides through a liquid organic membrane containing a ditopic salt-binding receptor.
abstract: A ditopic receptor is shown to have an impressive ability to recognize and extract the ion pairs of various alkali halides into organic solution. X-ray diffraction analysis indicates that the salts are bound in the solid state as contact ion pairs. Transport experiments, using a supported liquid membrane and high salt concentration in the source phase, show that the ditopic receptor can transport alkali halide salts up to 10-fold faster than a monotopic cation or anion receptor and 2-fold faster than a binary mixture of cation and anion receptors. All transport systems exhibit the same qualitative order of ion selectivity; that is, for a constant anion, the cation selectivity order is K+ > Na+ > Li+, and for a constant cation, the anion transport selectivity order is I- > Br- > Cl-. The data suggest that with a ditopic receptor, the polarity of the receptor-salt complex can be lowered if the salt is bound as an associated ion pair, which leads to a faster diffusion through the membrane and a higher maximal flux.
authors.affiliation: Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Mahoney
authors.forename: Gayathri U
authors.initials: GU
authors.lastname: Nawaratna
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Beatty
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Duggan
authors.forename: Bradley D
authors.initials: BD
authors.lastname: Smith