title: Bidentate urea derivatives of p-tert-butyldihomooxacalix[4]arene: neutral receptors for anion complexation.
abstract: Three new bidentate ureidodihomooxacalix[4]arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound p-tert-butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by (1)H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F(-) (log K(assoc) = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO(-) and BzO(-). Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.
authors.affiliation: Centro de Ciências Moleculares e Materiais, Faculdade de Ciências da Universidade de Lisboa , Edifício C8, 1749-016 Lisboa, Portugal.
authors.forename: Paula M
authors.initials: PM
authors.lastname: Marcos
authors.forename: Filipa A
authors.initials: FA
authors.lastname: Teixeira
authors.forename: Manuel A P
authors.initials: MA
authors.lastname: Segurado
authors.forename: José R
authors.initials: JR
authors.lastname: Ascenso
authors.forename: Raul J
authors.initials: RJ
authors.lastname: Bernardino
authors.forename: Sylvia
authors.initials: S
authors.lastname: Michel
authors.forename: Véronique
authors.initials: V
authors.lastname: Hubscher-Bruder
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D014508:Urea / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: C000591318:p-tert-butyldihomooxacalix(4)arene; D047250:Calixarenes; D014508:Urea