Tuning Stopper Size in Multiresponsive [2]Rotaxanes for Fluoride Anion Selective Metastability.

[23]Crown-7-ether incorporated [2]rotaxanes, comprising an anthracene blocker and 4-isopropylphenyl/cyclohexyl end groups, exhibited varying degrees of metastability with a range of chemical (base, halide anions) and physical (solvent, heat) stimuli. Among halides, fluoride, chloride, and bromide anions affected the deslippage of 23-crown-7-ether in 4-isopropylphenyl stoppered [2]rotaxane. Surprisingly, only fluoride anions could selectively induce deslippage in cyclohexyl stoppered [2]rotaxane, whose fluorescence quenching provided an additional tool to selectively detect the fluoride anions down to 2.

BP23C7: high-yield synthesis and application in constructing [3]rotaxanes and responsive pseudo[2]rotaxanes.

A biphenyl-23-crown-7 ether (BP23C7) is synthesized in 86% yield from commercially available starting materials. BP23C7 forms pseudo[2]rotaxane with a dibenzylammonium ion (DBA), exhibiting a good association constant value ( = 1 × 10 M). Subsequently, fluorophoric properties of BP23C7 and anthracene terminated axles are blended to create responsive pseudo[2]rotaxanes.

Rapid and High-Yield Synthesis of [23]Crown Ether: Applied as a Wheel Component in the Formation of Pseudo[2]rotaxane and Synthesis of [2]Catenane with a Dibenzylammonium Dumbbell.

A facile, rapid, and high yield synthesis of [23]crown ether (X23C7) has been developed from commercially available starting materials, in one step with good to excellent yield. The reaction is completed in 6 h under room temperature conditions, with the highest yield being 81%. The X23C7 macrocycle formed pseudo[2]rotaxane with a dibenzylammonium ion (DBA) dumbbell, exhibiting strong association ( = 2.

Carboxylatopillar[n]arenes: a versatile class of water soluble synthetic receptors.

Carboxylatopillar[n]arenes (CP[n]As, n = 5, 6, 7, 9, 10) are water soluble derivatives of pillar[n]arenes. The three-dimensional π-electron-rich cavity and carboxylate groups at the portals, enabled CP[n]A to have strong binding affinity in water, which has been successfully harnessed in fabricating responsive supramolecular assemblies from supra-amphiphiles and developing targeted drug delivery systems (DDSs). CP[n]A based supraamphiphiles have also been used for sensor applications.

Trifluoromethyl acting as stopper in [2]rotaxane.

A modified dumbbell obtained by replacing one of the phenyl groups of the dibenzylammonium with a strong electron-withdrawing trifluoromethyl group templated the synthesis of the smallest [2]rotaxane reported so far. The trifluoromethyl group not only enhances the templating effect of the dumbbell but also acts as the stopper to prevent dethreading of a [20]crown ether macrocycle.

Template-directed synthesis of kinetically and thermodynamically stable molecular necklace using ring closing metathesis.

We report the template-directed synthesis of a well-defined, kinetically stable [5]molecular necklace with dialkylammonium ion (R(2)NH(2)(+)) as recognition site and DB24C8 as macrocycle. A thread containing four dialkylammonium ions with olefin at both ends was first synthesized and then subjected to threading with an excess amount of DB24C8 to form pseudo[5]rotaxane, which in situ undergoes ring closing metathesis at the termini with second generation Grubbs catalyst to yield the desired [5]molecular necklace. The successful synthesis of [5]molecular necklace is mainly attributed to the self-assembly and dynamic covalent chemistry which allows the formation of thermodynamically most stable product.

Synthesis of [n]rotaxanes by template-directed clipping: the role of the dialkylammonium recognition sites.

Linear and rectangular [n]rotaxanes were synthesized by template-directed clipping of heterocrown ether components onto the dumbbell-shaped molecules containing different dialkylammonium recognition sites. The effect of the structure of the dialkylammonium sites on the clipping efficiency was investigated, and selective clipping led to formation of a rectangular [4]rotaxane.