Anion Recognition and Cation‐Induced Molecular Motion in a Heteroditopic [2]Rotaxane

Abstract

A heteroditopic [2]rotaxane consisting of a calix[4]diquinone-isophthalamide macrocycle and 3,5-bis-amide pyridinium axle components with the capability of switching between two positional isomers in response to barium cation recognition is synthesised. The anion binding properties of the rotaxane's interlocked cavity together with Na(+) , K(+) , NH(4) (+) and Ba(2+) cation recognition capabilities are elucidated by (1) H NMR and UV-visible spectroscopic titration experiments. Upon binding of Ba(2+) , molecular displacement of the axle's positively charged pyridinium group from the rotaxane's macrocyclic cavity occurs, whereas the monovalent cations Na(+) , K(+) and NH(4) (+) are bound without causing significant co-conformational change. The barium cation induced shuttling motion can be reversed on addition of tetrabutylammonium sulfate.

Aggregation of p-Sulfonatocalixarene-Based Amphiphiles and Supra-Amphiphiles

“…In their published works, p -sulfonatocalixarene 4b and 4c were used as hosts, while molecules G3 – G8 were employed as guest [73–76]. In the first report, p -sulfonatocalix [5]arene ( 4c ) and 1-pyrenemethylaminium ( G3 ) were used to construct the vesicular assembly. The aggregation process can be followed by monitoring the polarity-dependent fluorescence spectra of the pyrene moiety.…”

Chloride anion triggered motion in a bis-imidazolium rotaxane

“…We have therefore pursued this line of enquiry, having produced a [2]catenane in which anion coordination acts as a locking mechanism, 14 and a heteroditopic ion-pair [2]rotaxane receptor which displays anion recognition and cation-controlled shuttling. 15 The imidazolium motif is well known as a charge-assisted C-H hydrogen bond donor in acyclic 16 and macrocyclic 16,17 anion receptors, 18 and within this group we have demonstrated its capacity to act as an anion-pair axle in pseudorotaxane formation. 19 In this communication we report the first bis-imidazoliumbased rotaxane, making use of an isophthalamide macrocycle and 2,6-bis-imidazolium-pyridine-cored thread (a system ubiquitous in organometallic chemistry 20 but scarcely examined under the guise of anion coordination 21-24 ), and synthesised by application of anion templated self-assembly.…”

Rotaxanes and pseudorotaxanes with threads containing viologen units

“…25,26 Pseudorotaxanes are also intensively studied, they are prototypes of molecular machines [27][28][29] and serve as building blocks for interlocked supramolecular assemblies, 30 some of them are promising in preparation of molecular sensors 31 and in drug delivery. 32 There should be mentioned here also rotaxanes and pseudorotaxanes containing cyclodextrins, [33][34][35] calixarenes 36,37 or cucurbiturils. 38,39 Today many works concerning viologen-based rotaxanes and pseudorotaxanes appear, [40][41][42][43][44][45] in these systems viologens are components of a thread [45][46][47][48][49] or are present as parts of the tetracationic cyclophane serving as a ring.…”