Supramolecular daisy chains.

Two series of self-complementary daisy chain monomers, in which a secondary ammonium ion-containing arm is grafted onto a macrocycle with either a [24]- or [25]crown-8 constitution, have been synthesized. In the solid- and 'gas'-phases, the parent [24]crown-8-based monomer forms dimeric superstructures, as revealed by X-ray crystallography and mass spectrometry, respectively. Elucidation of the complicated solution-phase behavior of this compound was facilitated by the synthesis and study of both deuterated, and fluorinated, analogues. These investigations revealed that the cyclic dimeric superstructure also dominates in solution, except when extremes of either concentration (low), temperature (high), or solvent polarity (highly polar, e.g., dimethyl sulfoxide) are employed. Whereas, upon aggregation, the [24]crown-8-based daisy chain monomers have the capacity to form stereoisomeric superstructures further complicating the study of this series of compounds. The assembly of [25]crown-8-based monomers gives only achiral superstructures. The weaker association exhibited between secondary dialkylammonium ions and crown ethers with a [25]crown-8 constitution, however, resulted in limited oligomerization--only dimeric and trimeric superstructures were formed at experimentally attainable concentrations--of [25]crown-8-based daisy chain monomers.

A rotaxane-like complex with controlled-release characteristics.

A rotaxane-like complex, based on a dumbbell-shaped component containing an NH(2)(+) recognition site for a [25]crown-8 ring component and a slippage stopper in the form of a p-(tert-butyl)phenyl group, has been synthesized by a "threading-followed-by-stoppering" approach. The half-life for dissociation of this complex, which is very sensitive to its environment, can be varied from minutes to months by changing the temperature and the polarity of the solvent.

Toward interlocked molecules beyond catenanes and rotaxanes.

A linear bis secondary dialkylammonium ion-containing scaffold-based upon an anthracenyl core-has been synthesized. It has been demonstrated that it is possible to dock either one or two dibenzo[24]crown-8 (DB24C8) macrocycles onto this scaffold to afford either a [2]- or [3]pseudorotaxane, respectively. In solution, the association constants for the formation of each of these species has been quantified by employing (1)H NMR spectroscopy, and both species survive in the "gas phase" as evidenced by FAB mass spectrometry. Additionally, the X-ray crystal superstructure of the [3]pseudorotaxane has been determined.

Ammonium ion binding with pyridine-containing crown ethers.

Dipyrido[24]crown-8 (DP24C8) has been synthesized and shown to form [2]pseudorotaxanes spontaneously with dibenzylammonium ions. These complexes, which have been demonstrated by (1)H NMR spectroscopy to form faster in solution than when the macrocyclic polyether is dibenzo[24]crown-8 (DB24C8), are also stronger than their DB24C8 counterparts. One of the [2]pseudorotaxanes has been used to construct a [2]rotaxane (see above) comprising a dumbbell-shaped component based on a dibenzylammonium ion which is encircled by a DP24C8 macrocycle and terminated by (triphenylphosphonium)methyl stoppers.