ROTAXANE OR PSEUDOROTAXANE - THAT IS THE QUESTION

A series of secondary dialkylammonium ions (RCH2)(2)NH2+ have been pre pared, and their binding properties toward the macrocyclic polyether d ibenzo[24]crown-8 (DB24C8) evaluated. By using this information, a rou te to a kinetically stable rotaxane-like entity-stabilized by noncoval ent bonding interactions between the DB24C8 macroring and the ammonium center-was established, in which the crown ether slips over a dialkyl ammonium ion's stopper groups (R). However, we have found that the kin etic stability of this rotaxane-like entity is extremely dependent on the nature of the solvent in which it is dissolved, suggesting that ps eudorotaxanes lie in the fuzzy domain between two sets of extremes, wh erein a beadlike macrocycle and a dumbbell-like component may either ( 1) exist as a rotaxane or (2) be completely disassociated from one ano ther.