title: Synthetic cation transporters incorporating crown ethers and calixarenes as headgroups and central relays: a comparison of sodium and chloride selectivity.
abstract: An earlier study showed that a calix[4]arene could function as a central relay unit to form an ion conductance pathway through a phospholipid bilayer membrane. The present study expands the range of compounds from calix[4]arene to calix[6]arene and incorporates them either as central units or as headgroups, substituting one or more diaza-18-crown-6 residues in functioning hydraphiles. Ion release was assayed by detecting either Na(+) or Cl(-) release from phospholipid vesicles. The ion transport activity for calix[4]arenes in either position is modest, but is almost non-existent when calix[6] residues were incorporated either as head groups or central relay units. The poor activity of the calix[6]arenes may result from an inability to penetrate to the midplane of the bilayer or pass entirely through it to form a conductance pathway. The transmembrane "flip-flop" may result from high polarity or steric bulk, or both. A hydraphile incorporating a single -NHCOC(6)H(4)OCH(2)CONH- as a central relay proved to be an excellent Na(+) conductor, but less selective for Cl(-). The fact that this new hydraphile molecule shows selectivity for Na (+) over Cl(-) transport and possesses two secondary amide residues in the central relay suggests a means to control ion selectivity in synthetic ion transporters.
authors: Facultad de Ciencias, Departamento de Química Orgánica (C-I), Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors: José Carlos
authors: JC
authors: Iglesias-Sánchez
authors: Wei
authors: W
authors: Wang
authors: Riccardo
authors: R
authors: Ferdani
authors: Pilar
authors: P
authors: Prados
authors: Javier
authors: J
authors: de Mendoza
authors: George W
authors: GW
authors: Gokel