title: Calix[4]tubes: a new class of potassium-selective ionophore.
abstract: A new class of cryptand-like ionophore based on a bis calix[4]arene structure has been developed. These molecules proved highly selective for complexation of potassium over all group I metal cations and barium. A range of symmetric and asymmetric calix[4]tubes featuring either alkyl or phenyl substituents at the upper rim have been synthesized in exceptional yield. Alteration of the calix[4]arene upper rim environment enables fine-tuning of the rate of potassium uptake, which can be evaluated through the conformational change on binding by NMR studies. Selectivity of potassium complexation has been demonstrated using NMR and electrospray mass spectral techniques. Molecular modeling studies, derived from crystallographic data, confirm that the potassium metal cation is complexed via the axial route, passing through the calix[4]arene annulus, and provide evidence for complexation rate and selectivity.
authors.affiliation: Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Matthews
authors.forename: Phillipe
authors.initials: P
authors.lastname: Schmitt
authors.forename: Vitor
authors.initials: V
authors.lastname: Felix
authors.forename: Michael G B
authors.initials: MG
authors.lastname: Drew
authors.forename: Paul D
authors.initials: PD
authors.lastname: Beer
mesh_terms: D047250:Calixarenes; D018360:Crystallography, X-Ray; D007476:Ionophores / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D010636:Phenols / Q000138:chemical synthesis / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry*
chemical_list: D007476:Ionophores; D010636:Phenols; C121325:calix(4)arene; D047250:Calixarenes; D011188:Potassium