title: Selective self-organization of guest molecules in self-assembled molecular boxes.
abstract: This article describes the synthesis and binding properties of highly selective noncovalent molecular receptors 1(3).(DEB)6 and 3(3).(DEB)6 for different hydroxyl functionalized anthraquinones 2. These receptors are formed by the self-assembly of three calix[4]arene dimelamine derivative molecules (1 or 3) and six diethylbarbiturate (DEB) molecules to give 1(3).(DEB)6 or 3(3).(DEB)6. Encapsulation of 2 occurs in a highly organized manner; that is, a noncovalent hydrogen-bonded trimer of 2 is formed within the hydrogen-bonded receptors 1(3).(DEB)6 and 3(3).(DEB)6. Both receptors 1(3).(DEB)6 and 3(3).(DEB)6 change conformation from staggered to eclipsed upon complexation to afford a better fit for the 2(3) trimer. The receptor selectivity toward different anthraquinone derivatives 2 has been studied using 1H NMR spectroscopy, X-ray crystallography, UV spectroscopy, and isothermal microcalorimetry (ITC). The pi-pi stacking between the electron-deficient center ring of the anthraquinone derivatives 2a-c and 2e-g and the relatively electron-poor melamine units of the receptor is the driving force for the encapsulation of the guest molecules. The selectivity of the hydrogen-bonded host for the anthraquinone derivatives is the result of steric interactions between the guest molecules and the calix[4]arene aromatic rings of the host.
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Jessica M C A
authors.initials: JM
authors.lastname: Kerckhoffs
authors.forename: Mattijs G J
authors.initials: MG
authors.lastname: ten Cate
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Mateos-Timoneda
authors.forename: Fijs W B
authors.initials: FW
authors.lastname: van Leeuwen
authors.forename: Bianca
authors.initials: B
authors.lastname: Snellink-Ruël
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Huub
authors.initials: H
authors.lastname: Kooijman
authors.forename: Mercedes
authors.initials: M
authors.lastname: Crego-Calama
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
mesh_terms: D000880:Anthraquinones / Q000737:chemistry*; D001463:Barbiturates / Q000737:chemistry; D047250:Calixarenes / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000138:chemical synthesis* / Q000737:chemistry; D014227:Triazines / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000880:Anthraquinones; D001463:Barbiturates; D010636:Phenols; D014227:Triazines; C121325:calix(4)arene; D047250:Calixarenes; C011907:melamine