0000000001307148
AUTHOR
Young Lag Cho
Enhanced thermodynamic and kinetic stability of calix[4]arene dimers locked in the cone conformation.
Wide rim tetraurea derivatives (2a,b) have been prepared from a calix[4]arene rigidified in the cone conformation by two diethyleneglycol ether bridges between adjacent oxygens. In comparison to the analogous tetraurea derivatives (3a,b) of a tetrapentoxy calix[4]arene, 2a,b show an increased thermodynamic stability in mixtures of CDCl(3) and DMSO-d(6). Their kinetic stability as expressed by the rate of guest exchange (benzene or cyclohexane against the solvent benzene-d(6)) is also strongly increased by factors of 30-38. Noticeable differences for the inclusion of selected guests are found.
Hydrogen-Bonding Effects in Calix[4]arene Capsules
The synthesis and spectroscopic characterization of self-assembling calix[4]arene based capsules 1a.1a and 1b.1b are described. These compounds feature four urea substituents at the upper rims and four secondary amide fragments at the lower rims that can participate in inter- and intramolecular hydrogen bonding in apolar solution. Communication between the calixarene rims in 1a, b influences the self-assembled cavity's size and shape. Specifically. dimerization results in a perfect cone conformation of the calixarene skeleton in 1a, b and stabilizes a seam of intramolecular amide C=O...H-N hydrogen bonds at the lower rim. This seam is cycloenantiomeric, with either clockwise or counterclock…
CCDC 141173: Experimental Crystal Structure Determination
Related Article: Young Lag Cho, D.M.Rudkevich, A.Shivanyuk, K.Rissanen, J.Rebek Junior|2000|Chem.-Eur.J.|6|3788|doi:10.1002/1521-3765(20001016)6:20<3788::AID-CHEM3788>3.0.CO;2-Y
CCDC 141172: Experimental Crystal Structure Determination
Related Article: Young Lag Cho, D.M.Rudkevich, A.Shivanyuk, K.Rissanen, J.Rebek Junior|2000|Chem.-Eur.J.|6|3788|doi:10.1002/1521-3765(20001016)6:20<3788::AID-CHEM3788>3.0.CO;2-Y