Chloride Anion Templation Research Articles

Anti-Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen-Bonding [2]Rotaxanes.

Exceptionally strong halogen bonding (XB) donor-chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl-functionalised axle components, including a remarkably potent novel 4,6-dinitro-1,3-bis-iodotriazole motif. Halide anion recognition properties in aqueous-organic media, determined via extensive 1 H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl- and Br- , but conversely diminished affinities for hydrophobic I- , relative to their non-interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free-energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti-Hofmeister bias anion selectivity in synthetic receptor design.

Anti‐Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen‐Bonding [2]Rotaxanes

AbstractExceptionally strong halogen bonding (XB) donor‐chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl‐functionalised axle components, including a remarkably potent novel 4,6‐dinitro‐1,3‐bis‐iodotriazole motif. Halide anion recognition properties in aqueous‐organic media, determined via extensive 1H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl− and Br−, but conversely diminished affinities for hydrophobic I−, relative to their non‐interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free‐energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti‐Hofmeister bias anion selectivity in synthetic receptor design.

A Chiral Halogen‐Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate Anions

AbstractThe unprecedented application of a chiral halogen‐bonding [3]rotaxane host system for the discrimination of stereo‐ and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesised by a chloride anion templation strategy, the [3]rotaxane host recognises dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analysed by molecular dynamics simulations, which revealed the critical synergy of halogen and hydrogen bonding interactions in anion discrimination. In addition, the centrally located chiral (S)‐BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.

A Chiral Halogen-Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate Anions.

The unprecedented application of a chiral halogen-bonding [3]rotaxane host system for the discrimination of stereo- and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesised by a chloride anion templation strategy, the [3]rotaxane host recognises dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analysed by molecular dynamics simulations, which revealed the critical synergy of halogen and hydrogen bonding interactions in anion discrimination. In addition, the centrally located chiral (S)-BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response.

Chelated charge assisted halogen bonding enhanced halide recognition by a pyridinium-iodotriazolium axle containing [2]rotaxane.

Four halogen and hydrogen bonding rotaxane host systems featuring pyridinium bis-amide-iodotriazole/prototriazole and pyridinium bis-amide-iodotriazolium/prototriazolium axle components have been synthesized by CuAAC-mediated mono-stoppering chloride anion templation and post-rotaxanation methylation reactions. In competitive 45 : 45 : 10 CDCl3-CD3OD-D2O aqueous solvent media, the dicationic halogen bonding rotaxane displayed a notable enhanced binding affinity and marked selectivity for Br- over other halides and nitrate and dihydrogen phosphate oxoanions in contrast to an all hydrogen bonding counterpart which is attributed to chelated charge assisted halogen bonding interactions.

Chloride-Anion-Templated Synthesis of a Strapped-Porphyrin-Containing Catenane Host System.

The synthesis, structure and anion-recognition properties of a new strapped-porphyrin-containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor–acceptor and coordinative pyridine–zinc interactions. The [2]catenane incorporates a three-dimensional, hydrogen-bond-donating anion-binding pocket; solid-state structural analysis of the catenane⋅chloride complex reveals that the chloride anion is encapsulated within the catenane’s interlocked binding cavity through six convergent CH⋅⋅⋅⋅Cl and NH⋅⋅⋅Cl hydrogen-bonding interactions and solution-phase 1H NMR titration experiments demonstrate that this complementary hydrogen-bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.

Neutral redox-active hydrogen- and halogen-bonding [2]rotaxanes for the electrochemical sensing of chloride.

The first examples of redox-active ferrocene-functionalised neutral [2]rotaxanes have been synthesised via chloride anion templation. (1)H NMR spectroscopic titrations reveal that these [2]rotaxane host systems recognize chloride selectively over other halides and oxoanions in highly-competitive aqueous media. By replacing the hydrogen bonding prototriazole units of the rotaxane axle component with iodotriazole halogen bond-donor groups, the degree of chloride selectivity of the [2]rotaxanes is modulated. Electrochemical voltammetric experiments demonstrate that the rotaxanes can sense chloride via cathodic perturbations of the respective rotaxanes' ferrocene-ferrocenium redox-couple upon anion addition.

Increased Halide Recognition Strength by Enhanced Intercomponent Preorganisation in Triazolium Containing [2]Rotaxanes

Three triazolium-based [2]rotaxanes containing different sized axle and macrocycle components were synthesised in good yields (40-57%) through chloride anion templation. The anion recognition properties of the interlocked receptor systems were investigated using (1)H NMR titration experiments: all three rotaxanes display impressive selectivities for halide anions over the more basic oxoanion acetate. The rotaxanes incorporating shorter, more rigid axle components with aryl-substituted triazolium groups display substantially higher anion binding affinities than those with longer, bis-alkyl-substituted heterocycles, which is attributed to the increased intercomponent preorganisation afforded by the smaller axle component. Computational DFT and molecular dynamics simulations composed of unconstrained and umbrella sampling simulations corroborate the experimental observations.

Iodo-imidazolium salts: halogen bonding in crystals and anion-templated pseudorotaxanes

The 2-iodoimidazolium group is exploited in the anion-templated assembly of pseudorotaxanes with isophthalamide containing macrocycles. Crystallographic and solution-phase studies illustrate that the iodo-imidazolium motif is a potent halogen bond donor, forming the most stable interpenetrated assemblies in solution with the chloride anion template.

Anion Sensing in Aqueous Media by Photo‐active Transition‐Metal Bipyridyl Rotaxanes

A chloride anion templation methodology is utilized in the construction of novel transition-metal rhenium(I) and ruthenium(II) bipyridyl appended [2]rotaxanes. (1)H NMR spectroscopic titrations reveal the ability of the rotaxanes to selectively bind chloride over the more basic oxoanions, with the ruthenium(II) bipyridyl appended rotaxane strongly binding chloride in 30% water. Photophysical investigations demonstrate the ability of the rotaxanes to sense anions in aqueous media, with chloride being selectively complexed, in general agreement with NMR spectroscopy determined anion binding data.

Solution and surface-confined chloride anion templated redox-active ferrocene catenanes

The first examples of ferrocene containing catenanes, in solution and assembled on a surface are described. Chloride anion templation is exploited to synthesize redox-active [2]- and [3]-catenanes via Grubbs' ring closing metathesis, utilizing a novel ferrocene-appended isophthalamide macrocycle. X-ray crystal structures of both catenanes were determined. The ability of the [2]catenane to selectively bind and characteristically sense its chloride anion template is demonstrated by use of 1H NMR and electrochemical voltammetric techniques. Self-assembled monolayers of analogous surface-confined catenanes have been prepared on gold. In addition to being characterized by cyclic voltammetry and ellipsometry, detailed information regarding the structure of the catenane monolayers has been provided by use of angle integrated high resolution X-ray photoelectron spectroscopy.

A catenane host system containing integrated triazole C–H hydrogen bond donors for anion recognition

A 3,5-bis(triazole)-pyridinium motif is integrated into a catenane structural framework via chloride anion templation. The catenane host system displays a high degree of selectivity for halide anions over dihydrogen phosphate.

Anion templated assembly of [2]catenanes capable of chloride anion recognition in aqueous solvent media

An anion templated double cyclization strategy to synthesize [2]catenanes in which two identical acyclic pyridinium receptor motifs interweave around a chloride anion template is described. Ring closing metathesis (RCM) of the preorganized orthogonal precursor chloride complex facilitates the isolation of [2]catenanes in very high yields. X-ray crystal structures provide an insight of the supramolecular forces responsible for chloride anion templated efficacy and recognition. Removal of the chloride anion template generates topologically unique interlocked binding cavities for anions. 1H NMR anion binding investigations demonstrate the catenanes to be highly selective hosts for chloride in preference to more basic monocharged oxoanions. In aqueous solvent media containing 30% water, such catenanes exclusively bind chloride, under which conditions no binding of acetate or dihydrogen phosphate is observed. Molecular dynamic simulations in the solution phase are used to account for the catenanes’ anion recognition properties.

A redox-active [3]rotaxane capable of binding and electrochemically sensing chloride and sulfate anions

A ferrocene functionalised redox-active [3]rotaxane which contains two interlocked anion recognition sites has been prepared by chloride anion templation. With chloride two equivalents of anion are bound, one in each of the interlocked cavities, while sulfate forms a 1:1 stoichimetric sandwich type complex; the rotaxane can also electrochemically sense the two anions in acetonitrile.

A ferrocene functionalized rotaxanehost system capable of the electrochemical recognition of chloride

A ferrocene appended rotaxane is prepared by chloride anion templation and ring closing metathesis. Upon removal of the chloride template, the rotaxane is demonstrated to be selective for chloride over more basic oxoanions by (1)H NMR spectroscopy and electrochemistry, in marked contrast to an acyclic analogue--the first example of a solution based redox-active interlocked host system capable of the electrochemical recognition of anions.

Cation-induced molecular motion of spring-like [2]catenanes

The syntheses and cation recognition studies of two novel heteroditopic [2]catenanes that are capable of reversible rotary motion are described. Prepared by chloride anion templation, both catenanes possess a calixdiquinone unit able to bind Na+, K+, NH4+ and Ba2+ cations. Following characterization of the chloride salts of both catenanes by NMR, mass spectrometry and crystal structure determination, hexafluorophosphate salts were investigated for their behaviour upon addition of cations. Ba2+ complexation caused a partial intra-ring rotation of the two macrocycles in both species, which was reversed upon addition of the sequestering SO42− anion.

Clipping and stoppering anion templated synthesis of a [2]rotaxane host system

A new [2]rotaxane host system containing nitro-isophthalamide macrocycle and polyether functionalised pyridinium axle components is prepared via clipping and stoppering synthetic methodologies using chloride anion templation. After removing the chloride anion template, (1)H NMR titration experiments reveal the unique interlocked host cavity to be highly selective for binding chloride and bromide in preference to basic oxoanions in competitive aqueous solvent mixtures. The rotaxane host system proved to be a superior anion complexant in comparison to the individual macrocycle and axle components. The anion binding affinity of the novel rotaxane is also investigated via molecular dynamics simulations and in general the structural data obtained corroborates the experimental solution anion recognition behaviour.

Synthesis and Characterization of Chloride-incorporated Dodecavanadate from Dicopper Complex of Macrocyclic Octadecavanadate

Abstract A chloride-incorporated dodecavanadate, [V12O32(Cl)]5− (1) has been synthesized from a dicopper macrocyclic complex, [Cu2V8O24]4− (2). By using hydrogen cyanide with a chloride guest anion, two copper cations are removed and the presence of chloride anion template affords a new bowl-shaped dodecavanadate, 1, with chloride anion at the center. The 1:1 mixture of 1 and [V12O32(CH3CN)]4− (3) in acetonitrile shows no 51V NMR signal scrambling at room temperature suggesting the tight binding of the chloride anion inside the anionic bowl molecule. The dissociation of the chloride anion was only observed at higher temperatures.

Calix[4]arene‐Based Rotaxane Host Systems for Anion Recognition

The synthesis, structure and anion binding properties of the first calix[4]arene-based [2]rotaxane anion host systems are described. Rotaxanes 9.Cl and 12.Cl, consisting of a calix[4]arene functionalised macrocycle wheel and different pyridinium axle components, are prepared via adaption of an anion templated synthetic strategy to investigate the effect of preorganisation of the interlocked host's binding cavity on anion binding. Rotaxane 12.Cl contains a conformationally flexible pyridinium axle, whereas rotaxane 9.Cl incorporates a more preorganised pyridinium axle component. The X-ray crystal structure of 9.Cl and solution phase (1)H NMR spectroscopy demonstrate the successful interlocking of the calix[4]arene macrocycle and pyridinium axle components in the rotaxane structures. Following removal of the chloride anion template, anion binding studies on the resulting rotaxanes 9.PF(6) and 12.PF(6) reveal the importance of preorganisation of the host binding cavity on anion binding. The more preorganised rotaxane 9.PF(6) is the superior anion host system. The interlocked host cavity is selective for chloride in 1:1 CDCl(3)/CD(3)OD and remains selective for chloride and bromide in 10 % aqueous media over the more basic oxoanions. Rotaxane 12.PF(6) with a relatively conformationally flexible binding cavity is a less effective and discriminating anion host system although the rotaxane still binds halide anions in preference to oxoanions.

A [2]catenane containing an upper-rim functionalized calix[4]arene for anion recognition

A novel [2]catenane is synthesized in good yield from an upper-rim functionalized calix[4]arene macrobicycle and a nitro-substituted isophthalamide threading component in the presence of a chloride anion template via a ring-closing metathesis (RCM) reaction. After halide anion template removal the resulting catenane host exhibits a high degree of selectivity for chloride in competitive organic solvent mixtures.