Fluorescent anion chemosensors using 2-aminobenzimidazole receptors

Simple and easy-to-make fluorescent anion chemosensors using 2-aminobenzimidazole moieties as binding subunits showed selective anion-induced fluorescent changes. The receptors effectively recognized fluoride, chloride, bromide, acetate, dihydrogen phosphate ions with a 1:1 stoichiometry.     

含硫脲和酰胺单元的新型杯［4］芳烃中性氟离子受体

Two-armed neutral anion receptors (4,5), calix[4]arenes beating thiourea and amide binding sites, were prepared and examined their anion-binding ability by the UV-vis spectra. The results of non-linear curve fitting and Job plot indicate that 4 or 5 forms 1：1 stoichiometry complex with fluoride by hydrogen bonding interactions. Receptors 4 and 5 have an excellent selectivity for fluoride but have no binding ability with acetate, dihydrogen phosphate and the halogen anions (Cl^-,Br^-,I^-).     

Synthesis and evaluation of fluorimetric and colorimetric chemosensors for anions based on (oligo)thienyl-thiosemicarbazones

A family of heterocyclic thiosemicarbazone dyes (3a–d) containing thienyl groups has been synthesized, characterized, and their chromo-fluorogenic response in acetonitrile in the presence of selected anions was studied. Acetonitrile solutions of 3a–d show absorption bands in the 338–425 nm range, which are modulated by the groups attached to the thiosemicarbazone moiety. The fluoride, chloride, bromide, iodide, dihydrogen phosphate, hydrogen sulfate, nitrate, acetate, and cyanide anions were used in the recognition studies. Only sensing features were observed for fluoride, cyanide, acetate, and dihydrogen phosphate anions. Two different chromogenic responses were found, (i) a small shift of the absorption band due to coordination of the anions with the thiourea protons and (ii) the appearance of a new red-shifted band due to deprotonation of the receptor. For the latter process changes in the color solutions from pale-yellow to orange-red were observed. Fluorescence studies showed a different emission behavior according to the number of thienyl rings in the π-conjugated bridges. Stability constants for the two processes (complex formation+deprotonation) for receptors 3a–d in the presence of fluoride and acetate anions were determined from spectrophotometric titrations using the HypSpec program. The interaction of 3d with fluoride was studied through ¹H NMR titrations. Semiempirical calculations to evaluate the hydrogen-donating ability of the receptors were also performed.     

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.     

Synthesis of a novel tripodand having 3-hydroxy-2-naphthoeic amide groups and its anion recognition ability

A novel tripodand having 3-hydroxy-2-naphthoeic amide groups was prepared by the reaction of 1,3,5-tris(aminomethyl)-2,4,6-trimethylbenzene with 3-allyloxy-2-naphthoeic acid chloride followed by thermal Claisen rearrangement. This tripodand can exhibit the anion binding ability in chloroform solution. In particular, it can bind with acetate, dihydrogen phosphate, and fluoride ions to form 1:1 complexes.     

Anion sensing properties of new colorimetric chemosensors based on macrocyclic ligands bearing three nitrophenylurea groups

Two new colorimetric ligands (1-2) based on macrocyclic structures linked to three nitrophenylurea groups were synthesized in good yields, and their responses toward anions were studied. Anions with different shape, such as of fluoride, chloride, bromide, iodide, hydroxide, nitrate, perclhorate, cyanide, or dihydrogen phosphate in DMSO solution were added and only fluoride, hydroxide, cyanide, and dihydrogen phosphate enhances π delocalization and shifts the π-π^∗ transition in both ligands, leading to the generation of a pleasant orange color.The result is a balance between the acidity of the nitrophenylurea-NH donors modulated by the basic character of the anions. Stability constants for both receptors and the anions fluoride, hydroxide, cyanide, and dihydrogen phosphate were determined spectrophotometrically using the program HYSPEC. ¹H NMR titrations experiments with fluoride were carried out.     

铽配合物Tb(PMIP)3(PhCA)的合成及阴离子识别研究

本文设计合成了稀土铽配合物Tb(PMW)3(PhCA)作为阴离子试剂,利用荧光光谱考察了其与F-、Cl-、Br-、I-、ClO4-、NO3-、AcO-和H2PO-4等阴离子的作用.研究结果表明:不同阴离子的加入能够调控,Tb(PMIP)3(PhCA)的发光行为,当一定量的氟离子(醋酸根离子、磷酸二氢根离子)加入到Tb(PMIP)3(PhCA)的乙腈溶液中后,荧光发射增强;过量的氟离子(醋酸根离子、磷酸二氢根离子)加入后则使其荧光淬灭.而在乙腈和水混合溶液中,Tb(PMIP)3(PhCA)则能选择性识别氟离子和磷酸二氢根离子.     

Molecular structures of 8,8′-dithioureido-2,2′-binaphthalene derivatives and their anions recognition: an ONIOM investigation

The structures of 8,8′-bis(3-phenylthioureidomethyl)-2,2′-binaphthalene (1), 8,8′-bis(3-butylthioureidomethyl)-2,2′-binaphthalene (2) and their complexes with anionic guests such as carboxylate ions (acetate, oxalate, malonate, succinate, glutarate, adipate, pimelate, suberate, and azelate), inorganic oxygen-containing anions (nitrate, sulfate, bicarbonate, hydrogen phosphate, and dihydrogen phosphate), and halide ions (fluoride, chloride, and bromide) were obtained using the ONIOM approach. The binding abilities of receptors 1 and 2 to anionic species in terms of binding energy, thermodynamic properties, and selectivity coefficient were obtained at the ONIOM(B3LYP/6-31G(d):AM1) and BSSE-corrected B3LYP/6-31G(d)//ONIOM(B3LYP/6-31G(d):AM1) levels of theory. The multipoint hydrogen bonding between receptors (either the receptor 1 or 2) and anionic guests were found. The hydrogen phosphate is the most preferable ion to bind with either the receptor 1 or 2.     

The anion recognition properties of Schiff base or its reductive system based on 2,2′-bipyridine derivatives

Two novel artificial receptors, 2,2′-bipyridine derivatives containing phenol group, have been designed and synthesized. The interaction of the receptors containing Schiff base or its reductive system with biologically important anions was determined by UV–vis and ¹H NMR titration experiments. Results indicate that receptors 1 and 2 show the strong binding ability for dihydrogen phosphate (H₂PO₄⁻), fluoride (F⁻), acetate (AcO⁻) and almost no binding ability for chloride (Cl⁻), bromide (Br⁻), iodide (I⁻). At the same time, the strongest binding ability of receptor 1 for H₂PO₄⁻ among studied anions is not influenced by the existence of other anions; as well as receptor 2 for F⁻. In addition, the binding ability of receptor 1 (Schiff base system) with various anions is stronger than that of receptor 2 (the reductive Schiff base system) due to the difference of electronic effect.     

Anion recognition by a novel Fipronil-based receptor: efficient deprotonation or stable intermolecular hydrogen bonding

Strong electron-deficient heterocycles of acetyl Fipronil (F3) was designed and synthesized, its ability for anion recognition was investigated by UV and NMR analyses. This novel Fipronil-based receptor F3 shows strong binding affinity with acetate (?10⁷ M⁻¹), phosphate or fluoride ion through efficient deprotonation. In addition, its interaction with chloride anion or other weak base anions through stable intermolecular H-bonding was also reported.     

A coumarin based ICT probe for fluoride in aqueous medium with its real application

A new coumarin based hydrazone (receptor 1) synthesized by modifying one of our earlier reported receptor detected fluoride ion selectively through naked eye in aq. DMSO (5:95, v/v). It was also able to detect fluoride through naked eye in a toothpaste sample. The addition of 1 equiv. of fluoride as its tetrabutylammonium salt to the 5 × 10⁻⁵ M aq. DMSO solution of the receptor 1 produced red color while the similar addition of acetate produced faint pink color. The dihydrogenphosphate and a variety of other anions were not able to produce any significant color change with receptor 1 under similar experimental conditions. The corresponding UV-vis measurements showed a bathochromic shifting of 455 nm band of receptor 1 to 514 and 484 nm for fluoride and acetate, respectively. The non-linear fittings of corresponding UV-vis titration data in 1:1 binding equation yielded association constants in 10⁵:1 ratio for fluoride and acetate, respectively. The ¹H NMR titrations studies shade further light on their mode of binding with receptor 1. The quantum mechanical calculations through time dependant density functional theory (TD-DFT) using basis set b3lyp/6-311g** supported our experimental findings nicely.     

Anion receptors with viologen molecular scaffold

We have designed and synthesized new anion receptors 1²⁺ and 2²⁺. These receptors interact with anions through hydrogen bonds and charge transfer complex depending on the basicity of anion. Therefore, anions with weak basicity such as chloride, bromide, and hydrogen sulfate bound to the receptors 1²⁺ and 2²⁺ only through hydrogen bonds while anions with strong basicity such as fluoride, acetate and dihydrogen phosphate bound to the receptors 1²⁺ and 2²⁺ only through charge transfer interactions at UV–vis titration condition (20 μM). However, in more concentrated ¹H NMR titration condition (2 mM), 1²⁺ and 2²⁺ decomposed to form the product one of their amide arm is eliminated. As charge transfer complexes showed colorimetric response, they turned out to be efficient naked eye detector for anions with strong basicity such as fluoride, acetate, and dihydrogen phosphate.     

Selective fluorescent sensing of chloride

The urea functionalised phenanthroline sensor 1, which was characterised by several methods, including X-ray crystallography, gives rise to large changes in the fluorescence emission spectra upon interaction with several anions such as acetate, phosphate, fluoride and chloride in CH₃CN. However, only in the presence of Cl⁻ was the emission enhanced, as for the other ions photoinduced electron transfer (PET) quenching was observed. Fitting these fluorescence changes, using non-linear regression analysis, showed that these anions bind to 1 in 1:1 (anion:sensor) stoichiometry, with the exception of Cl⁻, which was shown to give rise to 1:1 as well as 1:2 binding, as a result of coordination of the chloride to two equivalents of 1.     

A quinoline based bis-urea receptor for anions: a selective receptor for hydrogen sulfate

A dipodal bis-urea receptor has been synthesized from the reaction of 8-amino quinoline and 1,4-phenylene diisocyanate in dichloromethane, and the anion binding ability of the receptor has been studied using fluoride, chloride, bromide, iodide, perchlorate, nitrate, dihydrogen phosphate and hydrogen sulfate by UV-Vis titrations in DMSO. The results show that the receptor binds each of the anions with a 1:1 stoichiometry, showing high affinity and moderate selectivity for hydrogen sulfate among the anions studied. Ab initio calculations based on density functional theory (DFT) suggest that an anion (X(-)) is bonded within the cleft formed by the two arms of the receptor through two NH...X(-) and two aromatic CH...X(-) interactions. The results from solution and theoretical studies suggest that binding is predominantly influenced by hydrogen bonding interactions and the basicity of anions.     

Bifunctional maleimide dyes as selective anion sensors

A class of disubstituted maleimide dyes with two symmetrical NH binding sites was found to exhibit distinct color change and fluorescence quenching effect for fluoride, cyanide, and dihydrogen phosphate anions. The intense red emission displayed apparent solvatochromic shift, indicating a strong charge-transfer character. The interactions between the dyes and anions were variable depending on the amine substituents at C(3,4) of the maleimides. For the dyes with two pyrrolyl receptor sites, the NH protons were deprotonated by more basic anions such as fluoride or cyanide. For those with two indolyl receptor sites, formation of a chelate with H₂PO₄⁻ through hydrogen bonds played a major role.     

Thermodynamic Study of Dihydrogen Phosphate Dimerisation and Complexation with Novel Urea‐ and Thiourea‐Based Receptors

Complexation of dihydrogen phosphate by novel thiourea and urea receptors in acetonitrile and dimethyl sulfoxide was studied in detail by an integrated approach by using several methods (isothermal titration calorimetry, ESI‐MS, and ¹H NMR and UV spectroscopy). Thermodynamic investigations into H₂PO₄^? dimerisation, which is a process that has been frequently recognised, but rarely quantitatively described, were carried out as well. The corresponding equilibrium was taken into account in the anion‐binding studies, which enabled reliable determination of the complexation thermodynamic quantities. In both solvents the thiourea derivatives exhibited considerably higher binding affinities with respect to those containing the urea moiety. In acetonitrile, 1:1 and 2:1 (anion/receptor) complexes formed, whereas in dimethyl sulfoxide only the significantly less stable complexes of 1:1 stoichiometry were detected. The solvent effects on the thermodynamic parameters of dihydrogen phosphate dimerisation and complexation reactions are discussed.     

Visible Colorimetric Sensor for Fluoride Ion Based on o-Phenylenediamine

A new chromogenic receptor based on 1,2-phenylene derivative containing thiourea moieties is synthesized and examined for its anion binding ability by UV–Vis and ¹H NMR studies. The results show that the receptor has selective colorimetric sensing of fluoride over all other anions like chloride, bromide, iodide, nitrate, hydrogen sulphate and acetate.     

Controlled Anchoring of (Phenylureido)sulfonamide-Based Receptor Moieties: An Impact of Binding Site Multiplication on Complexation Properties

The repetition of urea-based binding units within the receptor structure does not only lead to monomer properties multiplication. As confirmed by spectroscopic studies, UV-Vis and ¹H-NMR in classical or competitive titration mode, the attachment to a carrier allocates the active moieties to mutual positions predetermining the function of the whole receptor molecule. Bivalent receptors form self-aggregates. Dendritic receptors with low dihydrogen phosphate loadings offer a cooperative complexation mode associated with a positive dendritic effect. In higher dihydrogen phosphate concentrations, the dendritic branches act independently and the binding mode changes to 1:1 anion: complexation site. Despite the anchoring, the dendritic receptors retain the superior efficiency and selectivity of a monomer, paving the way to recyclable receptors, desirable for economic and ecological reasons.     

Preferred Binding of Carboxylates by Chiral Urea Derivatives Containing α‐Phenylethyl Group

An efficient, simple protocol for the synthesis of a new family of chiral ureas 1 – 4 is described. The binding properties of 1 – 4 toward different anion (acetate, benzoate, fluoride, and chloride) have been studied by ¹H‐NMR titration and have been observed in the case of 4 is a selective receptor for acetate. The theoretical calculation M06/6‐311+G(d,p) helped us explain the binding properties observed. The most interesting observation is that this calculated structure is consistent with expected, based on the concept of allylic 1,3‐strain (A^1,3 strain). When chiral caboxylates were studied, urea 1 was the best in discriminating between enantiomers.     

Anion receptor based on thiourea: via hydrogen bonding interaction and efficient deprotonation

A new thiourea-based receptor through Schiff-based condensation of 8-hydroxyqui nolino-7-aldehyde and a phenylthiosemicarbazide was easily obtained. This novel sensor shows strong binding affinity for acetate, fluoride and phosphate ions through efficient deprotonation. We make an in-depth investigation on its anion binding prosperities and deprotonation process through Fluorescence, UV–vis and ¹H NMR titration experiments. Moreover, we propose the anion recognition process by assuming the existence of three-step equilibria.