title: Complexation of phenolic guests by endo- and exo-hydrogen-bonded receptors.
abstract: This article describes the complexation of phenol derivatives by hydrogen-bonded receptors. These phenol receptors are formed by self-assembly of calix[4]arene dimelamine or tetramelamine derivatives with 5,5-diethylbarbiturate (DEB) or cyanurate derivatives (CYA). The double rosette assemblies 3(3).(DEB)6/(CYA)6 have their phenol-binding functionalities (ureido groups) at the top and at the bottom of the double rosette (exo-receptors). The tetrarosette assemblies 4(3).(DEB)12/(CYA)12 form a cavity with binding sites between the two double rosettes for guest encapsulation (endo-receptors). An intrinsic binding constant Ka of 202 M-1 and 286 M-1 for the binding of 4-nitrophenol to the ureido functionalized exo- and endo-receptors, respectively, was observed. For the exo-receptor a 1:6 stoichiometry was observed while for the endo-receptor 1:4 binding stoichiometry was determined by Job plot and MALDI-TOF MS. The important role that the hydroxy group's acidity plays in the complexation of 4-nitrophenol is clarified by binding studies with different phenol derivatives. The hydrogen-bonded receptors showed a much smaller response towards less acidic phenol derivatives.
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology, MESA Research Institute, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Jessica M
authors.initials: JM
authors.lastname: Kerckhoffs
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Ishi-i
authors.forename: Vasile
authors.initials: V
authors.lastname: Paraschiv
authors.forename: Peter
authors.initials: P
authors.lastname: Timmerman
authors.forename: Mercedes
authors.initials: M
authors.lastname: Crego-Calama
authors.forename: Seiji
authors.initials: S
authors.lastname: Shinkai
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
mesh_terms: D001463:Barbiturates / Q000737:chemistry; D001665:Binding Sites; D047250:Calixarenes; D006860:Hydrogen Bonding; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010636:Phenols / Q000737:chemistry*; D011955:Receptors, Drug / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D014227:Triazines / Q000737:chemistry
chemical_list: D001463:Barbiturates; D010636:Phenols; D011955:Receptors, Drug; D014227:Triazines; C476540:calix(6)arene; D047250:Calixarenes; C011907:melamine