title: Molecular recognition and self-assembly special feature: Self-assembly of dimeric tetraurea calix[4]pyrrole capsules.
abstract: Calix[4]pyrroles having extended aromatic cavities have been functionalized with 4 ureas in the para position of their meso phenyl substituents. This elaboration of the upper rim was completed in 2 synthetic steps starting from the alpha,alpha,alpha,alpha-tetranitro isomer of the calix[4]pyrrole obtained in the acid catalyzed condensation of p-nitrophenyl methyl ketone and pyrrole. In dichloromethane solution and in the presence of 4,4'-bipyridine N-N'-dioxide the tetraurea calix[4]pyrrole dimerizes reversibly forming a cyclic array of 16 hydrogen bonds and encapsulating 1 molecule of bis-N-oxide. The encapsulated guest is bound in the cavity by hydrogen bonding to the 2 endohedral calix[4]pyrrole centers. Further evidence for dimerization of the tetraurea calix[4]pyrroles is provided by (1)H-NMR experiments and by the formation of mixed capsules.
authors.affiliation: Catalan Institution for Research and Advanced Studies, Passeig Lluís Companys, 23 E-08010-Barcelona, Spain. pballester@iciq.es
authors.forename: Pablo
authors.initials: P
authors.lastname: Ballester
authors.forename: Guzmán
authors.initials: G
authors.lastname: Gil-Ramírez
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D019281:Dimerization; D006860:Hydrogen Bonding; D007659:Ketones / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D007659:Ketones; D010087:Oxides; D011166:Porphyrins; D011758:Pyrroles; C469811:calix(4)pyrrole; D047250:Calixarenes; D014508:Urea