title: Bipyrrole-strapped calix[4]pyrroles: strong anion receptors that extract the sulfate anion.
abstract: Cage-type calix[4]pyrroles 2 and 3 bearing two additional pyrrole groups on the strap have been synthesized. Compared with the parent calix[4]pyrrole (1), they were found to exhibit remarkably enhanced affinities for anions, including the sulfate anion (TBA(+) salts), in organic media (CD2Cl2). This increase is ascribed to participation of the bipyrrole units in anion binding. Receptors 2 and 3 extract the hydrophilic sulfate anion (as the methyltrialkyl(C(8-10))ammonium (A336(+)) salt) from aqueous media into a chloroform phase with significantly improved efficiency (>10-fold relative to calix[4]pyrrole 1). These two receptors also solubilize into chloroform the otherwise insoluble sulfate salt, (TMA)2SO4 (tetramethylammonium sulfate).
authors.affiliation: Department of Chemistry, The University of Texas at Austin , 105 E. 24th Street, Stop A5300, Austin, Texas 78712-1224, United States.
authors.forename: Sung Kuk
authors.initials: SK
authors.lastname: Kim
authors.forename: Juhoon
authors.initials: J
authors.lastname: Lee
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Williams
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Lynch
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Hay
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Moyer
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler