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.     

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 ¹H 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? PF₆ and 12? PF₆ reveal the importance of preorganisation of the host binding cavity on anion binding. The more preorganised rotaxane 9? PF₆ is the superior anion host system. The interlocked host cavity is selective for chloride in 1:1 CDCl₃/CD₃OD and remains selective for chloride and bromide in 10 % aqueous media over the more basic oxoanions. Rotaxane 12? PF₆ 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.     

Anion-templated assembly of interpenetrated and interlocked structures

The rational development of a general anion templation strategy for the construction of a variety of interpenetrated and interlocked molecular structures based upon the coupling of anion recognition with ion-pairing is described. The success of this anion templation methodology is demonstrated with the halide anion directed assembly of a series of novel [2]pseudorotaxanes containing pyridinium, pyridinium nicotinamide, imidazolium, benzimidazolium and guanidinium threading components and anion binding macrocyclic ligands. Interlocked [2]rotaxane and [2]catenane molecular structures are also synthesised using this anion templation protocol. These interlocked structures feature unique topologically defined hydrogen bond donating binding domains that exhibit a high degree of selectivity for chloride, the templating anion. A series of rhenium(I) bipyridyl containing [2]pseudorotaxane assemblies and a [2]rotaxane further highlight the potential this strategic anion templation approach has in future chemical sensor design and fabrication.     

Rational synthesis of multicyclic bis[2]catenanes

Bis-loop tetraurea calix[4]arene 6 has been prepared by acylation of the wide-rim calix[4]arene tetraamine 1 with the activated bis(urethane) 8 under dilution conditions. Similarly the bis(Boc-protected) tetraamine 2 is converted into the mono-loop derivative 3 which after deprotection and acylation gives the bisalkenyl derivative 5. In apolar solvents this tetraurea calix[4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis[2]catenane 10a is formed in 49% by a metathesis reaction followed by hydrogenation. Bis-loop derivative 6 forms no homodimers for steric reasons, but a stoichiometric mixture with the open-chain tetraalkenyl derivative 7a contains exclusively the heterodimer. Metathesis and subsequent hydrogenation now yields 65 % of the pure bis[2]catenane 10a which could not be isolated from the complex reaction mixture obtained from the homodimer 7a.7a. The chirality of 10a (D(2) symmetry) has been verified by optical resolution using HPLC on a chiral stationary phase.     

Anion templated assembly of mechanically interlocked structures

This tutorial review describes the evolution of the field of chemical templation, in particular, emphasising the impact its application has made to the synthesis of mechanically interlocked structures. Recent advances in the use of negatively charged template species for the synthesis of interlocked structures are detailed, with the main focus of this review describing the development of a general anion templation strategy that combines anion recognition with ion-pairing. The versatility of this methodology is demonstrated by the chloride anion templated synthesis of a series of interpenetrated pseudorotaxane, rotaxane and catenane structures. Upon template removal, the mechanically interlocked rotaxanes and catenanes are shown to bind anions within their topologically unique anion binding clefts by virtue of electrostatic and hydrogen bonding interactions, exhibiting a strong selectivity for the chloride halide anion template. The incorporation of the photo-active rhenium(I) bipyridyl signalling group into the rotaxane structural framework highlights the potential of these interlocked systems in future chemical sensor design.     

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.     

Preparation, reactivity and controlled release of SAMs of calix[4,6]arenes and calix[6]arene-based rotaxanes and pseudorotaxanes formed on polycrystalline Cu

Specific and reversible binding of guest molecules from a solution to a surface pre-treated with host molecules is a recent and active field of research. Self-assembled monolayers may result from supramolecular interactions, adding distinct functionalities to the surface. In this frame, the first compared study is given here of the anchoring on the technologically relevant Cu surface of calix[4]arene receptors and calix[6]arene-based rotaxanes and pseudorotaxanes. These molecules, which belong to the most representative classes of compounds in supramolecular chemistry, have been chosen for their synthetic accessibility and versatility, which make them useful building blocks for the synthesis of new advanced supramolecular structures. Covalent functionalisation of calix[4,6]arenes on Cu was reached via a dip-coating procedure, optimizing the various synthetic aspects in order to obtain good coverages and copper passivation. Molecular adhesion has been demonstrated by the presence and relative quantitation of XPS signals from specific elements in the molecules. We have successfully tested the combination of different functionalities by producing a mixed film, prepared by ligand exchange of calix[4]arene with undecanethiol. The availability of the calix[4]arene cavity to reversibly host further species after anchoring on Cu has been demonstrated by a sequence of uptake and release cycles with pyridinium salts. Rotaxane and pseudorotaxane species, composed of a calix[6]arene wheel functionalized with N-phenylurea groups on the upper rim, and a viologen-containing axle, have been anchored on Cu via the SH-termination of the axle. XPS demonstrated the successful self-assembly of fully threaded rotaxanes and pseudorotaxanes from their solutions and the controlled release upon biasing of full rotaxanes and of the pseudorotaxane wheel.     

N-confused calix[4]pyrroles

This is a first review devoted to N-confused calix[4]pyrroles (NCCPs). NCCPs are a relatively recent arrival to the family of the pyrrole-based anion binding macrocycles, being for the first time identified in 1999. Yet, in a relatively short time these calix[4]pyrrole (CP) isomers attracted attention of the community of research groups interested in anion binding and sensing. This is because they are relatively easy to synthesize, but mainly because they posses anion-binding properties that are different from that of regular calix[4]pyrroles. The difference in anion-binding properties stems from a different binding mode between the NCCP and anion. While the regular CPs adopt in the complex an ideal cone-like conformation where all four pyrroles-NHs engage in hydrogen bonding to the anion, the inverted pyrroles do not allow forming the cone. NCCPs bind anions via a confused cone (CC), by three NH hydrogen bonds with an anion and a CH–anion contact. This different binding mode results also in different anion-binding affinity and selectivity compared to regular CPs. Also, the inverted pyrroles offer a unique possibility for selective chemical modification of the receptor. The corresponding colorimetric sensors were tested for anion binding applications. The results of colorimetric assays for anions are presented and potential applications discussed.     

Anion‐binding properties of two calix[4]arene derivatives containing two ferrocene imine or ferrocene amine units at the upper rim

Calix[4]arene derivatives containing ferrocene units at the upper rim have been synthesized and their anion‐binding and sensing investigated towards anions such as chloride, bromide and hydrogen sulfate by cyclic voltammetry. Electrochemical studies show that these redox‐active ligands electrochemically recognize chloride and bromide anions. These compounds have excellent selectivity for chloride and bromide ions, in the comparison with hydrogen sulfate anion. With ferrocenyl Schiff base calix[4]arene 1 an anodic shift as large as 302 mV is observed on addition of four equivalents of Cl⁻ anion. Also electrochemical and UV–vis spectroscopic titrations ferrocenyl calix[4]arene derivatives 1 with chloride and bromide ions and 2 (only with Cl⁻) indicate a 1:1 binding‐stiochiometry. Copyright © 2011 John Wiley & Sons, Ltd.     

Conformational features and anion-binding properties of calix[4]pyrrole: a theoretical study

The conformational preference of calix[4]pyrrole and its fluoride and chloride anion-binding properties have been investigated by density functional theory calculations. Geometries were optimized by the BLYP/3-21G and BLYP/6-31G methods, and energies were evaluated with the BLYP/6-31+G method. To model the effect of medium, the SCIPCM solvent model was also employed. Four typical conformations of the parent substituent-free calix[4]pyrrole were studied. Both in the gas phase and in CH(2)Cl(2) solution, the stability sequence is predicted to be 1,3-alternate > partial cone > 1,2-alternate > cone. The cone conformation is predicted to be about 16.0 and 11.4 kcal/mol less stable in the gas phase and CH(2)Cl(2) solution, respectively. This is mainly due to electrostatic repulsions arising from the all-syn pyrrole/pyrrole/pyrrole/pyrrole arrangement present in this conformer. The existence of possible 1:1 and 1:2 anion-binding modes were explored in the case of fluoride anion, and the factors favoring the 1:1 binding mode are discussed. The calculated binding energy for fluoride anion is about 15 kcal/mol larger than that for chloride anion. The calculated binding energy for chloride anion agrees with the experimental value very well. The presence of meso-alkyl substituents destabilizes the cone conformer with respect to the 1,3-alternate conformer and, therefore, reduces the anion-binding affinity by 3-4 kcal/mol. The strength of N-H- - -anion hydrogen bonds in the various structures subject to study were estimated on the basis of the calculated anion-binding energies and the predicted structural deformation energies of substituent-free calix[4]pyrrole.     

Surface grafting and reactivity of calixarene-based receptors and pseudorotaxanes on Si(100)

The first report is given here on the anchoring on H-Si(100) of calix[4]arenes and calix[6]arene-based pseudorotaxanes, versatile building blocks for molecular devices. Covalent functionalization on Si was reached through a wet chemistry recipe, by making use of an extra-mild photochemical activation via visible light of C=C terminated anchoring arms. Our approach largely preserves the integrity of the molecular substrate, also allowing for a full monolayer of pseudorotaxane to be formed on Si(100). Molecular adhesion has been demonstrated by the presence and quantitation of XPS signals from specific elements in the molecules. AFM measurements performed on Si(100)/calix[4]arenes have revealed structures 2.3 nm high, consistent with the length of the molecule. The availability of the calix[4]arene cavity to host further species after anchoring on Si has been demonstrated by the successful complexation reaction with Cs(+) ions, resulting in a 1:1 calix/Cs(+) ratio, and with N-methyl pyridinium iodide. A pseudorotaxane species, composed of a calix[6]arene wheel derivatised with N-phenylureido groups on the upper rim and a viologen (4,4'-bipyridinium) containing axle, has been anchored on Si(100) via the C=C termination of the axle. We demonstrated the self-assembling of this pseudorotaxane covalently bound by use of XPS.     

Halogen‐ and Hydrogen‐Bonding Catenanes for Halide‐Anion Recognition

Halogen‐bonding (XB) interactions were exploited in the solution‐phase assembly of anion‐templated pseudorotaxanes between an isophthalamide‐containing macrocycle and bromo‐ or iodo‐functionalised pyridinium threading components. ¹H NMR spectroscopic titration investigations demonstrated that such XB interpenetrated assemblies are more stable than analogous hydrogen bonding (HB) pseudorotaxanes. The stability of the anion‐templated halogen‐bonded pseudorotaxane architectures was exploited in the preparation of new halogen‐bonding interlocked catenane species through a Grubbs’ ring‐closing metathesis (RCM) clipping methodology. The catenanes’ anion recognition properties in the competitive CDCl₃/CD₃OD 1:1 solvent mixture revealed selectivity for the heavier halides iodide and bromide over chloride and acetate.     

Induced fit interanion discrimination by binding-induced excimer formation

The synthesis, photophysical, and anion-binding properties of a series of di-, tri-, and tetrapodal anion-binding hosts based on aminopyridinium units with pyrenyl reporter groups are described. The ditopic mesitylene-derived calix[4]arene-based host 4 binds strongly to dicarboxylates, particularly malonate, in a 2:1 anion:host ratio but is essentially nonemissive in the presence of all anions except chloride because of intramolecular quenching by the pyridinium units. Addition of chloride results in a conformational change, giving an initial increase in emission assigned to intramolecular excimer formation. Further chloride addition also results in an increase in the intensity of the pyrenyl monomer emission as chloride binding reduces the acceptor ability of the pyridinium groups. This behavior is not exhibited by control compounds 5 and 6, which lack the ditopic geometry and calixarene spacer unit; however, tripodal 6 forms 1:2 anion:host complexes with a range of anions.     

Specific extraction behavior of amide derivative of calix[4]arene for silver (I) and gold (III) ions from highly acidic chloride media

25,26,27,28-tetrakis(N,N-diethylaminocarbonylmethoxy)-5,11,17,23-tetrakis(1,1,3,3-tetramethylbutyl)calix[4]arene, a macrocyclic extraction reagent, and p-(1,1,3,3-tetra-methylbutyl)phenoxymethyl-N,N-diethylamide, an acyclic extraction reagent corresponding to the former one, were synthesized to investigate their extraction behavior for silver(I), gold(III), palladium(II), and platinum(IV) from highly acidic solution into chloroform. In the extraction of silver and gold from hydrochloric acid solution, a completely different extraction behavior was observed between these two types of the reagents. The extraction behavior was examined in detail for silver and was found to be dependent on whether silver ion was extracted as a cationic species or a anionic species complexed with chloride ion. This was supported by proton nuclear magnetic resonance study of the calix[4]arene derivative. As a result, the extraction of silver ion with calix[4]arene derivative was very peculiar which was attributable to the fitting between cyclic size of calix[4]arene and ionic radius of silver.     

Comparison of pillar[5]arene and calix[4]arene anion receptor ability in aqueous media

Abstract

Recognition ability of both cationic pillar[5]arene and calix[4]arene has been studied in aqueous media. Anion complexation can be evaluated from their ability to complex their counterions as well as an added external organic anion. DOSY NMR experiments and fluorescence quenching show that pillararenes have a larger ability for including their own counterions than calixarenes irrespective of the anion (tetrafluoroborate or chloride or bromide) and the structure of the cationic moiety (trimethylammonium or methylimidazolium). Counterion complexation shows a picture where four to five positive charges of the pillar[5]arene are neutralised, meanwhile only one positive charge of the calixarene is neutralised for a 1 mM solution of the macrocycle. Irrespective of the smaller net positive charge in the pillar[5]arene, its binding ability for organic anions (toluenesulfonate or hydroxybenzoate) is larger than for calix[4]arene allowing a better accommodation of the guest in its cavity. The larger separation between the cationic groups of the receptor and its electron-rich aromatic region improves the anion recognition ability for pillar[5]arene.     

杯芳烃与NO2硝化反应的研究

系统地研究了羟基杯[n]芳烃、甲氧基杯[n]芳烃和对特丁基杯[n]芳烃(n＝4, 6, 8)与NO₂气体的硝化反应, 发现可以成功地得到25,26,27,28-四羟基杯[4]芳烃、37,38,39,40,41,42-六羟基杯[6]芳烃以及25,26,27,28-四甲氧基杯[4]芳烃的对位全硝化产物, 产率分别为90%, 70%和40%; 尤其是25,26,27,28-四羟基杯[4]芳烃与NO₂的反应20 min即可完成. 认为共振式酚氧负离子结构是影响该类硝化反应的关键, 并对反应机理进行了探讨.     

Formation of Self‐Templated 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate

We report the remarkable ability of 2,6‐bis(1,2,3‐triazol‐4‐yl)pyridine ( btp ) compounds 2 with appended olefin amide arms to self‐template the formation of interlocked [2]catenane structures 3 in up to 50 % yield when subjected to olefin ring‐closing metathesis in CH₂Cl₂. X‐ray diffraction crystallography enabled the structural characterization of both the [2]catenane 3 a and the non‐interlocked macrocycle 4 a . These [2]catenanes showed selective triazolyl hydrogen‐bonding interactions with the tetrahedral phosphate anion when screened against a range of ions; 3 a , b are the first examples of selective [2]catenane hosts for phosphate.     

Anion receptors based on ureido-substituted thiacalix[4]arenes and calix[4]arenes

The regioselective nitration of 25,27-dipropoxythiacalix[4]arene was carried out as a key step in the synthesis of thiacalix[4]arene derivative bearing two arylureido functions on the upper rim. The preorganisation of ureido units using the thiacalix[4]arene/calix[4]arene moieties as a molecular scaffold gave novel anion receptors. These compounds, albeit based on hydrogen bonding interactions, show good complexation ability even in highly HB-competitive solvent, such as DMSO. Direct comparison of otherwise identical structures 6a and 7a revealed remarkable dominance of the thiacalix[4]arene derivative over its classical analogue in anion binding.     

新型杯芳烃为载体的铅离子选择电极

报道了5,11,17,23-四（1,1-二甲基乙基）-25,27-二羟基-26,28-二[（2-丙酰胺）乙氧基]杯[4]芳烃1的合成及以此化合物为载体研制了PVC膜铅离子选择电极。研究了不同极性的膜增塑剂和亲脂性阴离子位点对铅离子选择电极响应性能的影响,测定了铅离子选择电极的性能。铅离子选择电极对铅离子表现出优良的能斯特响应和高选择性,能在pH4.0-6.5的范围内使用,该电极可作为电位滴定的指示电极。     

Anionic fullerenes, calixarenes, coronenes, and pyrenes as activators of oligo/polyarginines in model membranes and live cells

We report that the efflux of 5(6)-carboxyfluorescein anions from neutral egg yolk phosphatidylcholine vesicles is mediated by oligo/polyarginines only in the presence of activating amphiphilic anions. Screening of anion activators reveals best synergism for amphiphilic carboxylates (fullerene > calix[4]arene approximately coronene > pyrene > calix[6]arene > alkyl), whereas amphiphilic sulfates show less satisfactory activation despite often lower effective concentrations. The analogous alcohols and one calix[4]arene diphosphate were inactive. These results are discussed in the context of a tentative anion carrier mechanism, where interactions with bilayer (interface-directed translocation) and carrier (arene-templated carboxylate-guanidinium pairing) contribute to activator efficiencies. Applied to HeLa cells, pyrenebutyrate is shown to significantly increase the uptake of a fluorescently labeled octaarginine in a concentration-dependent manner.