Face-selective [2]- and [3]rotaxanes: kinetic control of the threading direction of cyclodextrins.
New [2]- and [3]pseudorotaxanes containing alpha-cyclodextrin (alpha-CDs) molecules as rotors and alkyl pyridinium derivatives as axles were prepared by a slipping process. The inclusion behavior of these rotaxanes was investigated by using one- and two-dimensional NMR spectroscopy. The methyl group at the 2-position of the pyridinium moiety at the end of each axle molecule was found to control the rates of threading of the alpha-CD onto the axle molecules. alpha-CD can approach axle molecules from a particular direction to form inclusion complexes. Axle molecules that contain a 2-methylpyridinium moiety at one end and a bulky stopper at the other end can regulate the direction of approach to give a [2]pseudorotaxane such as 2 b-alpha-CD. A [3]pseudorotaxane in which two alpha-CD molecules are arranged facing in the same direction at two stations of the tetracationic axle molecule was also obtained. These face-selective behaviors are dominated by kinetic processes rather than thermodynamic processes.
Oshikiri
Tomoya
T
Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Takashima
Yoshinori
Y
Yamaguchi
Hiroyasu
H
Harada
Akira
A
D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D043862:Rotaxanes / Q000737:chemistry*; D013237:Stereoisomerism; D047391:alpha-Cyclodextrins / Q000737:chemistry*
D043862:Rotaxanes; D047391:alpha-Cyclodextrins; C032613:alpha-cyclodextrin