Anion Recognition Properties Research Articles

A counterion displacement assay with a Biginelli product: a ratiometric sensor for Hg2+ and the resultant complex as a sensor for Cl−

Chemosensors are prepared through a one pot, multicomponent organic synthesis and their activities are evaluated in a DMF : H2O (1 : 9, v/v) solvent system. One chemosensor has demonstrated selectivity for Hg2+ by quenching the fluorescence intensity at 394 nm with enhancement at 460 nm. Thus, the sensor offers an interesting opportunity for the ratiometric determination of Hg2+ in a semi aqueous solvent system with a detection limit of 0.2 μM. The resultant mercury complex of the same sensor is evaluated for anion recognition properties. The metal complex is highly selective for the determination of chloride in a semi aqueous medium through a counterion displacement assay.

Kanamycin A: imine formation in aqueous solution

Imine formation in aqueous solution of kanamycin A with pyridoxal 5'-phosphate and other aldehydes was studied by potentiometry, NMR spectroscopy and computational chemistry. It was found that imines are formed with yields near 100 % at pH 7 in equimolar reactant ratio. In order to identify the kanamycin amino groups involved in the reaction, a NMR spectroscopic study was conducted. The structures of possible imines formed between kanamycin and FURAN or PLP were optimized by molecular mechanics with the OPLS-2005 force field. The 1H NMR spectra were calculated at the DFT-GIAO B3LYP/6-31G(d) level of theory for all structures and compared with the experimentally observed spectra. From these results a probable structure of the imines was proposed. The results obtained in this work show that kanamycin has the ability to form imine derivatives in high yields due to its anion recognition properties. Copyright © 2012 John Wiley & Sons, Ltd.

Expanding the Scope of the Anion Templated Synthesis of Interlocked Structures

Nature achieves impressively strong and selective complexation of small molecule anions through the elaborate binding sites of sophisticated proteins. Inspired by these examples, we have developed an anion templation strategy for the synthesis of mechanically interlocked host structures for anion recognition applications. Upon removal of the discrete anionic templating species, such host systems possess unique, three-dimensional, geometrically restrained cavities containing convergent hydrogen bond donor atoms. Such structures exhibit high affinity binding selectivity toward complementary anions. This Account describes recent advances in this anion templation meth odology, demonstrating the versatility and scope of this approach, and progressing to more diverse architectures. Specifically, we have prepared an expansive range of interlocked hosts with enhanced anion recognition properties, such as the ability to operate effectively in competitive aqueous media. We have produced these structures through the utilization of a new anion templated amide condensation synthetic method and through the incorporation of a range of different anion binding motifs, such as groups capable of effective solution-phase halogen bonding interactions. Importantly, direct comparisons between halogen bonding and hydrogen bonding systems reveal impressively magnified anion recognition properties for halogen bonding interlocked host systems. We have also employed the anion templation strategy successfully to construct selective electrochemical and luminescent anion sensors, as well as architectures of increasing complexity, such as a triply interlocked capsule and a handcuff catenane. The synthesis of these latter examples presents greater challenges; however, such molecules offer additional applications in higher order recognition and sensing and in switchable molecular devices. Having established anion templation as a viable synthetic route to interlocked architectures, we have used this strategy to fabricate a multitude of innovative structures. The key principles of this approach are the ability of anionic species to template the association of carefully designed components, and of the resulting molecular framework with its interlocked host cavity to display impressive anion recognition selectivity. Mechanically interlocked structures have numerous potential applications in nanotechnology. Therefore, the continuing development of effective synthetic methods, especially those which yield functional systems, is of great interest in the broad interdisciplinary field of supramolecular chemistry.

Combined Solution‐Phase, Solid‐Phase and Phase‐Interface Anion Binding and Extraction Studies by a Simple Tripodal Thiourea Receptor

AbstractTris(2‐aminoethyl)amine (tren) based 4‐cyanophenyl‐substituted tripodal L, tris{[(4‐cyanophenyl)amino]ethyl}thiourea receptor, was synthesized and explored thoroughly for anion recognition in solution by NMR spectroscopy and isothermal titration calorimetry (ITC) as well as in the solid state by single‐crystal X‐ray diffraction studies. Anion recognition properties of L were further exploited toward the extraction of sulfate as well as fluoride from aqueous media using a liquid–liquid extraction technique. A solution‐state anion binding study using NMR spectroscopy in [D6]DMSO and ITC measurements in dry acetonitrile show a relatively higher association constant of L with halides (F– and Cl–) over oxyanions (H2PO4– and HSO4–). The single‐crystal X‐ray structural analysis of complex 1 reveals a monotopic encapsulation of fluoride in L through six N–H···F– interactions with a distorted trigonal‐prismatic geometry, whereas sulfate and carbonate induce dimeric assemblies of L in complexes 2 and 3, respectively. In the case of sulfate, a tight dimeric capsular assembly of ca. 9.5 Å is observed through 15 N–H···O interactions, whereas carbonate forms a sandwich‐like dimeric molecular aggregation through 14 N–H···O interactions. In the presence of tetrabutylammonium iodide as the phase transfer agent, L has shown ca. 70 % extraction of fluoride (based on L) and ca. 40 % extraction of sulfate (based on L) from aqueous solutions using an anion‐exchange‐based liquid–liquid extraction strategy. Extraction of these anions is unambiguously demonstrated by 1H NMR, 19F NMR and FTIR spectroscopy, PXRD and single‐crystal X‐ray diffraction studies.

Synthesis of 4-Nitrophenylthiosemicarbazone of Salicylaldehyde and its Colorimetric Anion Recognition Properties

An efficient colorimetric anion sensor, N4-nitrophenylthiosemicarbazone of salicylaldehyde, behaves with a good selectivity and sensitivity in the recognition for F- anions by naked eye observations and UV–Vis spectral changes in DMSO. The colour of the solution containing the sensor had an obvious change from colourless to purple only after the addition of F- in DMSO while other anions did not cause obvious colour changes. The sensor reacted with F- to form a stable complex and the association constant Ka is calculated as 1.415×104 M−1.

A simple naphthalene-based colorimetric sensor selective for acetate

A new naphthalene based receptor (L) has been designed and synthesized which shows a remarkable color change from colorless to pink on selective binding with acetate. The anion recognition property of the receptor via hydrogen bonding interactions is monitored by UV–vis, fluorescence, and 1H NMR titrations. It is observed that in each case, the receptor shows a specific selectivity toward the acetate ion over other interfering anions. Thus, a significant bathochromic shift in UV–vis spectrum with a sharp pink color in ‘naked-eye’ makes the receptor suitable for the detection of the acetate ion.

Synthesis and anion recognition properties of shape-persistent binaphthyl-containing chiral macrocyclic amides

We report on the synthesis and characterization of novel shape-persistent, optically active arylamide macrocycles, which can be obtained using a one-pot methodology. Resolved, axially chiral binol scaffolds, which incorporate either methoxy or acetoxy functionalities in the 2,2' positions and carboxylic functionalities in the external 3,3' positions, were used as the source of chirality. Two of these binaphthyls are joined through amidation reactions using rigid diaryl amines of differing shapes, to give homochiral tetraamidic macrocycles. The recognition properties of these supramolecular receptors have been analyzed, and the results indicate a modulation of binding affinities towards dicarboxylate anions, with a drastic change of binding mode depending on the steric and electronic features of the functional groups in the 2,2' positions.

Chalcone derivatives as fluorescence turn-on chemosensors for cyanide anions

Abstract Three o-hydroxy chalcone derivatives 1–3 with carbazolyl (1), pyrene (2) and 4-nitrobenzene (3) as terminal group have been synthesized. Their crystal structures, photophysical properties in CH3CN and recognition properties for cyanide anions have also been examined. The research indicates that the stronger electroaffinity of the chalcone derivative's β-unit is beneficial to Michael reaction and can improve the response rate of the compound to cyanide anions. These compounds are found to be able to recognize cyanide anions with fluorescence turn-on response. Especially, compound 3 with strong electron accepting group exhibits remarkable response to cyanide anions in CH3CN H2O (1:1, v/v) solution with a ca. 40-fold intensity enhancement.

Synthesis and anion recognition studies of novel 5,5-dioxidophenothiazine-1,9-diamides

Novel 5,5-dioxidophenothiazine-1,9-diacetamide and -dibenzamide receptor molecules were prepared starting from commercially available and relatively cheap chemicals. The anion recognition properties of these two diamides were investigated using UV–vis spectroscopy. Chloride formed a simple hydrogen-bonded complex with the diacetamide receptor, while fluoride, acetate and dihydrogen phosphate deprotonated both sensor molecules. Upon titration with fluoride deprotonation occurred via the formation of [HF2]−, and in the case of the diacetamide receptor complexation took place alongside deprotonation.

Anion recognition by a family of quinoline-functionalised bis-amide hosts in solid state and in solution

The interaction between a series of bidentate, amide-functionalised 8-oxyquinoline receptors and coordinating anions is investigated. Anion recognition properties and conformations were studied by solid-state structures, Hartree–Fock calculations and solution-phase 1H NMR investigations. Our findings suggest that the amide-oxyquinoline motif coordinates anions and water with a well-defined, consistent geometry involving multiple hydrogen bonds. Solution studies of the neutral receptors reveal the unprotonated oxyquinoline ring to indirectly contribute to anion binding by the adjacent amide NH groups despite being unable to directly participate through hydrogen bonding.

Investigating the effect of macrocycle size in anion templated imidazolium-based interpenetrated and interlocked assemblies

The effect of varying the size of the macrocycle component on the formation of anion templated imidazolium interpenetrated assemblies is investigated. Two different approaches to reducing the macrocycle size are undertaken and the stabilities of the resulting pseudorotaxanes incorporating substituted imidazolium threading components studied using (1)H NMR spectroscopy. Novel imidazolium axle containing interlocked rotaxane host structures are synthesised using chloride anion templated amide condensation and 'stoppering' methods, and the anion recognition properties of the 'stoppered' rotaxane investigated.

Porphyrin-functionalised rotaxanes for anion recognition

The synthesis and anion-recognition properties of two new porphyrin-functionalised [2]rotaxane host molecules are described. The rotaxane compounds are prepared via a chloride-anion-templated clipping strategy. (1)H NMR titration experiments demonstrate that the rotaxane host systems exhibit high binding affinities and general selectivities for chloride anions in DMSO-d(6) or CDCl(3)/CD(3)OD solvent systems. UV-visible and fluorescence spectroscopy experiments reveal that the rotaxane receptors are ineffective as optical anion sensors. However, both receptors are shown to be capable of detecting chloride anions electrochemically via cathodic shifts in the porphyrin P/P(+) redox couples.

Anion recognition properties of pyridine-2,6-dicarboxamide and isophthalamide derivatives containing l-tryptophan moieties

l-Tryptophan containing anion receptors 1 and 2 have shown interesting features. Receptor 1 behaves as a hetero-ditopic dicompartimental receptor for fluoride and chloride with a certain selectivity for fluoride as supported by 1H NMR titrations and molecular modeling, while receptor 2 forms only 1:1 complexes. Moreover, receptor 1 reveals a certain affinity towards the l enantiomers of amino acids alanine and serine.

Synthesis of molecular Tweezers Based on thiosemi-Carbazide and their Anion Recognition Properties 

Two novel molecular receptors based on thiosemicarbazide,compound 3a(1,3-bis(o-tolueneoxoacetylthio-semicarbazideacyl) benzene) and compound 3b(1,3-bis(p-tolueneoxoacetylthio-semicarbazideacyl)benzene),have been designed and synthesized under solid-liquid phase transfer catalysis conditions.The binding properties for anions such as F-,AcO-,Cl-,Br-and I-in DMSO have been examined by UV-Vis and 1H NMR spectroscopy.The results show a high selectivity for F-and AcO-,however,no obvious interaction was found for Cl-,Br-,and I-.The 1H NMR combined with Job curves indicates that a 1∶1 stoichiometry complex is formed between the receptors and the anions through hydrogen bonding interactions.In view of these results,the influences of the number of NH binding points and steric effect on binding properties were discussed.The receptor compound 3b can form much more hydrogen-bonding interactions due to the presence of many NH binding points,with larger association constant(Ks) than that of thiourea receptor.Compared compound 3a with 3b,large steric effect prevent the combination between compound 3a and anions.In terms of F-and AcO-,association constant of compound 3a and 3b followed the same tendency Ks(F-)Ks(AcO-),owing to the better fit of size and shape between the receptors and F-.

Investigating the Imidazolium-Anion Interaction through the Anion-Templated Construction of Interpenetrated and Interlocked Assemblies

The interaction between imidazolium cations and coordinating anions is investigated through the anion-templated assembly of interpenetrated and interlocked structures. The orientation of the imidazolium motif with respect to anion binding, and hence the hydrogen bond donor arrangement, was varied in acyclic receptors, interpenetrated assemblies, and the first mono-imidazolium interlocked systems. Their anion recognition properties and co-conformations were studied by solution-phase 1H NMR investigations, solid-state structures, molecular dynamics simulations, and density functional theory calculations. Our findings suggest that the imidazolium-anion binding interaction is dominated by electrostatics with hydrogen-bonding contributions having weak orientational dependence.

Thioamide, urea and thiourea bridged rhenium(I) complexes as luminescent anion receptors

Thioamides, urea and thiourea derivatives of 2,6-pyridinedicarbonyl dichloride, isophthaloyl dichloride and terephthaloyl dichloride have been synthesized. These ligands have been incorporated in dinuclear rhenium(I) diimine tricarbonyl complexes and the anion recognition properties of these complexes have been studied by luminescence, UV–Vis and 1H NMR spectroscopic methods. The complexes act as receptors for anions via hydrogen bonding and electrostatic interactions. The anion sensing properties of the complexes are compared to earlier amide-based dinuclear rhenium(I) tricarbonyl complexes.

A Colorimetric Receptor Based on Schiff-Base Bearing Azo-Phenolic Hydroxy Group

A novel N-(2-hydroxy-5-chlorodibenzophenone)-N′-[2-hydroxy-5-azophenyl-benzaldehyde]-1,2-diaminobenzene receptor has been synthesized by simple steps with good yields. The anion recognition properties were studied by ultraviolet-visible spectroscopy. The results showed that the receptor had a higher affinity to F−, AcO−, and H2PO4−, but no evident binding with Cl−, Br−, and I−. Upon addition of the three former anions to the receptors in DMSO, the solution exhibited an obvious color change from colorless to yellow, which could be observed by the naked eye, thus the receptor could act as a fluoride ion sensor even in the presence of other halide ions. The UV-Vis data indicates that a 1:1 stoichiometric complex is formed through hydrogen bonding interactions between receptor and anions.

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.

Anion recognition by 2,2′-binaphthalene derivatives bearing urea and thiourea groups at 8- and 8′-positions by UV–vis and fluorescence spectroscopies

Synthesis and anion recognition properties of 2,2′-binaphthalene derivatives bearing two thiourea ( 1) and urea ( 2) groups at 8- and 8′-positions were studied. The structure of receptor 1 was determined by X-ray crystallography. UV–vis spectra of the receptors showed characteristic changes around 300–400 nm through isosbestic points upon the addition of biologically relevant anions such as acetate, dihydrogenphosphate, and chloride in MeCN and DMSO due to restriction of the rotation around the single bond connecting two naphthyl moieties by cooperative guest binding of two recognition sites. Job’s plots showed 1:1 complexation for guest anions. The fluorescence quantum yields of free form of 1 and 2 in MeCN were determined to be 0.021 and 0.57, respectively. The fluorescence intensities of the receptors diminished upon the addition of anions in MeCN. The association constants of receptors 1 and 2 were one or two orders of magnitude greater than the corresponding monothiourea and urea receptors 3 and 4 indicating cooperative hydrogen bonding with guest anions. The selectivity trends of association of anions were F −>AcO −>H 2PO 4 −>Cl −>>HSO 4 −≈NO 3 −≈Br −≈I − for 1, and F −>AcO −≈Cl −>H 2PO 4 −>Br −>HSO 4 −>I −≈NO 3 − for 2. Receptor 2 showed remarkable Cl − selectivity presumably owing to suitable orientation for effective hydrogen bond formation with Cl −.

Metal ion based chiral fluorescence sensor selective for dihydrogenphosphate

A Cu(II) based conformationally restricted chiral fluorescence sensor (receptor 2) has been designed and synthesized for selective sensing of anions. The anion recognition property of the Cu2+-complex has been studied in acetonitrile by fluorescence methods which show remarkable sensitivity toward dihydrogen phosphate via fluorescence modulation of the Cu2+-complex over the other anions examined.