Dimeric Capsules by the Self-Assembly of Triureidocalix[6]arenes through Hydrogen Bonds

✍ Scribed by Juan J. González; Riccardo Ferdani; Emanuela Albertini; José M. Blasco; Arturo Arduini; Andrea Pochini; Pilar Prados; Javier de Mendoza

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 220 KB
• Volume: 6
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(20000103)6:1<73::aid-chem73>3.0.co;2-#

✦ Synopsis

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 [D 6 ]DMSO-CDCl 3 mixtures. By contrast, N-substituted ureas are monomeric. All urea monomers with bulky O-substituents display a solvent-dependent, slow equilibrium between C 3v and C s cone conformations.