title: Dimeric capsules by the self-assembly of triureidocalix
abstract: A number of calix[6]arenes bearing ureas at the upper rim positions of alternate rings 1, 3 and 5 were prepared and studied in detail by NMR spectroscopy and gel permeation chromatography. N-Unsubstituted ureas were shown to dimerize through a cyclic array of hydrogen bonds to give cylindrical cavities capable of encapsulating small molecules such as dichloromethane, benzene and fluorobenzene. Slow equilibria between dimer and monomer were observed in [D6]DMSO-CDCl3 mixtures. By contrast, N-substituted ureas are monomeric. All urea monomers with bulky O-substituents display a solvent-dependent, slow equilibrium between C3v and Cs cone conformations.
authors.affiliation: Departamento de Quimica Organica, Universidad Autonoma de Madrid, Spain.
authors.initials: JJ
authors.lastname: Gonzalez
authors.initials: R
authors.lastname: Ferdani
authors.initials: E
authors.lastname: Albertini
authors.initials: JM
authors.lastname: Blasco
authors.initials: A
authors.lastname: Arduini
authors.initials: A
authors.lastname: Pochini
authors.initials: P
authors.lastname: Prados
authors.lastname: de Mendoza J