A naked-eye detection of fluoride with urea/thiourea receptors which have both a benzophenone group and a nitrophenyl group as a signalling group

Two new colorimetric anion sensors have been synthesised where both a benzophenone group and a nitrophenyl group were used as signalling units and urea/thiourea moieties as binding sites. The receptors, effectively and selectively, recognised fluoride and carboxylate anions from other anions such as chloride, bromide, iodide, perchlorate, hydrogen sulphate and nitrate in DMSO.     

3-Urea-1,8-naphthalimides are good chemosensors: a highly selective dual colorimetric and fluorescent ICT based anion sensor for fluoride

The 1,8-naphthalimide sensor 1 was developed as a colorimetric and fluorescent sensor for anions. Being the first example of such anion sensors, where the 3-position of the naphthalimide ring is used to incorporate the anion recognition moiety, in this case a trifluromethyl derived aryl urea moiety, the sensors gave rise to significant changes in both the absorption and the emission spectra, which were both red shifted upon interacting with anions. The changes were most pronounced for fluoride, and to a lesser extent for acetate and hydrogen phosphate, in DMSO, making 1 a highly selective sensor for F⁻.     

一种三足型比色传感器对阴离子的颜色响应

A thiourea-based tripodal colorimetric anion sensor was synthesized. Its binding abilities with AcO^- and halide anions in DMSO were studied by UV-Vis spectra. The sensor showed different color responses to these anions. The association constants and different stoichiometries were deduced by nonlinear least-square curve fitting or linear fitting.     

Novel Hydrazone‐Based Tripodal Sensors: Single Selective Colorimetric Chemosensor for Acetate in Aqueous Solution

A series of novel tripodal colorimetric anion sensors based on hydrazone CHN NH groups have been synthesized and their recognition behavior with anionic guests has been studied. In DMSO solutions, sensors 1 and 2 show colorimetric responses for F⁻, H₂PO⁻₄ and AcO⁻, while in DMSO/H₂O (9:1, V/V) solutions, sensor 1 shows single selectivity for AcO⁻. ¹H NMR titration confirms that the tripodal sensors could bind anions through the collaboration of three hydrazone groups and anions residing in the central cavity of the sensors.     

Anion recognition using preorganized thiourea functionalized [3]polynorbornane receptors

[structure: see text] A new family of [3]polynorbornane frameworks exhibiting conformationally preorganized aromatic thiourea (cleft-like) receptors have been designed and synthesized for anion recognition. These show excellent affinity for the biologically relevant dihydrogenphosphate (H(2)PO(4)(-)) and dihydrogenpyrophosphate (H(2)P(2)O(7)(2)(-)) anions (among others), which are bound in 1:1 and 2:1 (host:anion) ratio, respectively. Moreover, visually striking color changes accompany guest binding, enabling this family to act as colorimetric anion sensors.     

A Selective Colorimetric Anion Sensor Based on Di（hydroxymethyl） Di-（2-pyrrolyl）methane -TCBQ System

A new class of non-covalent charge-transfer complex for anion sensing, consisting of di(hydroxymethyl) di-(2-pyrrolyl) methane and chloranil (TCBQ) is characterized. The new colorimetric anion sensors can generate visual color change against PO4^3 and HPO4^2- anions in EtOH/H2O (1:1 v/v) mixture solution. The dipyrromethane-quinone aggregations may be used for higher selective detection of PO4^3- than other inorganic anions in water solution.     

高选择性比色识别碘离子的氨基硫脲类阴离子受体

设计合成了一系列基于氨基硫脲的阴离子受体（M1～M4）.此类受体以氨基硫脲基团为识别位点,以硝基苯基为信号报告基团,其中受体M1和M3可在乙腈溶液中高选择性的比色识别碘离子.在受体M1或M3的乙腈溶液中加入I^–时,溶液的颜色由浅红色变成无色,而加入其他离子如F^–,Cl^–,Br^–,AcO^–,HSO4^–,H2PO4^–,ClO4^–等阴离子时,受体溶液不会褪色.通过紫外滴定和核磁滴定等方法研究了受体选择性比色识别碘离子的机理.结果表明,受体通过其氨基硫脲基团上的三个NH质子与碘离子形成的三重氢键选择性的结合碘离子.在此过程中,受体构型发生转变,从而导致了颜色变化,产生了比色识别的效果.此类阴离子受体具有合成方法简便,产率高,识别效果好等优点.     

Urea/thiourea-based colorimetric chemosensors for the biologically important ions: efficient and simple sensors

Some colorimetric anion sensors have been synthesized where 4-nitrophenyl was treated as a signaling unit and urea/thiourea moieties as binding sites. The receptors, effectively and selectively, recognized the biologically important F⁻ and carboxylate anions from other anions such as Cl⁻ and Br⁻ in DMSO.     

Study on the Anion Recognition Properties of Synthesized Receptors （Ⅲ）： Convenient Synthesis and Anion Recognition Property of Bisthiosemicarbazone Derivative

A new series of bisthiosemicarbazone derivative receptors(1,2 and 3)have been synthesized by simple steps ingood yields.Their anion recognition properties were studied by UV-Vis and ~1H NMR spectroscopy.The resultshowed that the receptors 1,2 and 3 all had a better selectivity to F~-,CH_3COO~- and H_2PO_4~-,but no evidentbinding with Cl~-,Br~-,I~-,NO_3~- and HSO_4~-.Upon addition of the three anions to the receptors in DMSO,thesolution acquired a color change from colorless to dark yellow that can be observed by the naked-eyes,thus the re-ceptors can act as fluoride ion sensors even in the presence of other halide ions.The data showed that it was regularthat the three receptors had different binding ability with the three anions.For the same anion,the association con-stants followed the trend:receptor 1>3>2.The UV-Vis data indicates that a 1:1 stoichiometry complex isformed through hydrogen bonding interactions between compound 1,2 or 3 and anions.     

Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors

This review article focuses primarily on the work carried in our laboratories over the last few years using luminescent and colorimetric sensors, where the anion recognition occurs through hydrogen bonding in organic or aqueous solvents. This review begins with the story of the discovery of fluorescent photoinduced electron transfer (PET) sensors for anions using charged neutral urea or thiourea receptors where both fluorescent and NMR spectroscopic methods monitored anion recognition. This work led to the development of dual luminescent and colorimetric anion sensors based on the use of the ICT based naphthalimide chromophore, where ions such as fluoride gave rise to changes in both the fluorescence and the absorption spectra of the sensors, but at different concentrations. Here, the former changes were due to hydrogen bonding interactions, whereas the latter was due to the deprotonation of acidic protons, giving rise to the formation of the bifluoride anion (HF₂⁻). Modification of the 4-amino-l,8-naphthalimide moiety has facilitated the formation of colorimetric anion sensors that work both in organic or aqueous solutions. Such charge neutral receptor motifs have also been incorporated into organic scaffolds with norbomyl and calixarene backbones, which have enabled us to produce anion directed self-assembled structures.     

Anion binding by catechols--an NMR, optical and electrochemical study

The X-ray structure of the ClC chloride channel made it clear that O-H...chloride interactions play a key role in important biological membrane-bound systems, however, surprisingly this type of interaction has only been rarely exploited for the development of synthetic anion receptors. This paper therefore reports the anion binding strengths and selectivities of some simple commercially available bis-phenols. In particular, we compare catechol (1,2-dihydroxybenzene) and resorcinol (1,3-dihydroxybenzene) which show interesting and different selectivities between the halide anions in acetonitrile solution. Catechol binds tetrabutylammononium (TBA) chloride almost 30 times more strongly than TBA bromide, whilst for resorcinol, this difference drops to a factor of ca. 3.5. It is suggested that this is a consequence of the bite angle of the chelating hydrogen bonding groups of catechol being particularly appropriate for effective binding of the smaller anion. The oxidation of catechol to ortho-quinone is perturbed by the addition of chloride anions, as probed via cyclic voltammetry, and this compound can therefore be considered to act as an electrochemical sensor for chloride. Nitrocatechol is able to bind chloride anions more strongly than catechol as a consequence of its enhanced acidity and hence greater hydrogen bond donor character. Furthermore, nitrocatechol senses the bound anion via changes in its UV-visible spectrum. Notably, binding still occurs even in the presence of small amounts of competitive solvents (e.g. water). This observation has biomimetic importance as wet acetonitrile has some similarity in terms of overall polarity and hydrogen bond competition to the solvent shielded interiors of biological macromolecules and membranes--such as the environment within the ClC chloride channel itself. Finally, we report that catechol undergoes a unique colorimetric response on the addition of basic anions, such as fluoride. We can assign this response as being due to oxidative degradation of catechol catalysed by the basic anions (which bind to, and deprotonate, the catechol). This process is somewhat analogous to the well-known metal catalysed oxidation of catechol which can take place in aqueous solution. The speed of response and easily monitored and distinctive colour change induced by fluoride anions indicates this may be a useful mechanism for exploitation in the development of selective fluoride sensors.     

Colorimetric recognition of anions using preorganized tetra-amidourea derived calix[4]arene sensors

The synthesis and the spectroscopic studies of the amidourea based calix[4]arene sensors 1 and 2 are described. The 4-nitrophenyl based sensor 1 was synthesized in two steps from the corresponding calix [4]arene tetraethyl ester and shown to give rise to color changes in the UV-vis spectra in DMSO upon recognition of pyrophosphate and fluoride. Fitting the changes in the absorption spectra using nonlinear regression analysis indicated strong binding of several anions by 1 such as acetate and hydrogen phosphate in 1:1 (Host:Guest) stoichiometry, and at higher concentration in 1:2 stoichiometry. The preorganized calix-cavity was, however, not found to host chlorine while binding of bromide was determined. At high concentrations of these anions, significant colorimetric changes were also observed that were clearly visible to the naked eye for both pyrophosphate and fluoride. The phenyl analogue 2 was made to enable analysis of the anion recognition using 1H NMR titrations and showed that ions such as phosphate were bound in 1:1 stoichiometry, whereas the "urea" protons were shown to be significantly affected upon coordination to the anion.     

A Hybrid Coumarin–Thiazole Fluorescent Sensor for Selective Detection of Bisulfite Anions in Vivo and in Real Samples

A hybrid coumarin–thiazole compound was developed as a novel ratiometric and colorimetric sensor for bisulfite anions. Structure identification of the compound was confirmed by ¹H NMR, ¹³C NMR, ¹H,¹H COSY, heteronuclear single quantum coherence (HSQC), IR, and HRMS spectroscopy. The detection of bisulfite anions was performed through the Michael addition of the bisulfite anion toward the hybrid coumarin–thiazole sensor. The reaction between the sensor and bisulfite anion caused the fluorescence intensity to decrease at 600 nm and to increase at 450 nm and simultaneously yielded a visible color change from purplish red to colorless because the π conjugation between thiazole and coumarin was blocked. The sensor possessed high selectivity and sensitivity for bisulfite with respect to other common anions in aqueous solution. Moreover, the practical value of this sensor was confirmed by its application in the detection of bisulfite anion in human breast adenocarcinoma cells and granulated sugar.     

基于2,4-二硝基苯腙的比色法阴离子探针

本文设计合成了4个双臂2，4-二硝基苯腙衍生物作为F^-和H₂PO₄^-阴离子的比色法检测用探针主体，并得到其中一个主体的单晶结构。4种受体可以通过溶液颜色的变化选择性识别F^-和H₂PO₄^-。UV-Vis和 ¹H NMR光谱研究表明受体与F^-和H₂PO_{4相似文献}   

Conformational changes of functionalised indole receptors upon their interaction with anions

The conformational analysis of four C2-amido and C7-ureido functionalised indole anion receptors was performed by a combination of heteronuclear NMR spectroscopy and ab initio quantum mechanical calculations. NOE experiments showed that anti–anti conformation across C2–C2α and C7–N7α bonds is predominant in acetone solution in the absence of anions. Upon anion binding to receptors, syn–syn conformation becomes predominant. The conformational changes upon anion binding are in good agreement with energetic preferences established by ab initio calculations. Chemical shift changes induced by interaction of anions suggest that binding of chloride and bromide anions occurs primarily to H1 and H7α protons. Nitrate anions favour interaction with H7α and H7γ ureido protons, whereas acetate anions interact strongly with all four available hydrogen bond donor groups.     

The hydrogen sulfate recognition properties of azo-salicylaldehyde schiff base receptors

Azo-salicylaldehyde Schiff base-typed receptors containing an acidic H-bond donor moiety were syn-thesized and characterized. The UV-Vis data indicate that these receptors could act as selective col-orimetric sensors for basic anions and acidic species hydrogen sulfate by different color changes in a water-containing medium. The experiment of Brφnsted acid-base reaction by adding the sodium hy-droxide or perchloric acid revealed that the mechanism of recognition of anions might be deprotona-tion/protonation of the OH fragments by interacting with different anions and that the deprotona-tion/protonation process is fully reversible. The deprotonation/protonation of the receptors is respon-sible for the dramatic color change.     

酰腙类化合物的合成和阴离子识别研究

本文设计合成了3种新型的酰腙类受体分子。利用紫外-可见吸收光谱及 ¹H NMR考察了其与F^-、Cl^-、Br^-、I^-、CH₃COO^-、HSO₄^-、NO₃^-等阴离子的作用。结果表明，该类受体分子能较好地识别阴离子F^-和CH₃COO^-，在DMSO溶液中主客体之间形成氢键加合物。尤其对于受体3(间苯双对硝基苯氧乙酰腙)，加入F^-和CH₃COO^-时，溶液颜色有明显变化，受体3对这两种阴离子可实现裸眼识别。     

Synthesis and photophysical evaluation of charge neutral thiourea or urea based fluorescent PET sensors for bis-carboxylates and pyrophosphate

The synthesis of the fluorescent photoinduced electron transfer (PET) chemosensors 1-3 for bis-anions such as bis-carboxylates and pyrophosphate in organic solvents is described herein. These sensors are based on the receptor-spacer-fluorophore-spacer-receptor motif where the receptors are charge neutral aromatic thiourea or urea receptors and the fluorophore is anthracene. The anion recognition was evaluated using 1H NMR as well as absorption and fluorescence spectroscopy in DMSO. For simple anions such as acetate or fluoride, the recognition was shown to be through hydrogen bonding of the corresponding anion to the receptors. This gave rise to only minor changes in the absorption spectra, but significant changes in the fluorescence emission spectra, which was substantially (70-95%) quenched. Analysis of these recognition events implied a 1 : 2 (sensor : anion) binding and ideal PET behaviour for ions such as AcO- and H2PO4-. For F-, the luminescent quenching indicated a 1 : 1 binding, but we deduced that this was due more to complete quenching of the excited state after the addition of one equivalent of the anion. For all of the anions, the quenching contributed to enhanced efficiency of PET from the receptors to the excited state of the fluorophore. In the case of the bis-anions (ambient), such as di-carboxylates, similar fluorescence quenching was observed. However, here either a 1 : 1 or a 1 : 2 binding was observed depending on the length of the spacer separating the two carboxylate moieties and the nature of the receptor. Whereas both pyrophosphate and malonate gave rise to a 1 : 1 binding, glutarate gave rise to approximately 1 : 2 binding for the thiourea sensors 1 and 2. However, for the urea based sensor 3, the binding was found to be 1 : 1 for all the bis-anions. For such a 1 : 1 binding we propose that the anion most likely bridges the fluorophore moiety. This was also evident from the 1H NMR (DMSO-d6) spectrum where the anthracene resonances were significantly affected. By simply modifying the electronic structure of the receptor, the sensitivity of the recognition process could also be modified; e.g. compound 1, bearing the trifluoromethyl substituent, showed stronger binding to the bis-anions than 2, which possessed a simple phenyl moiety.     

Dipyrrolyl-functionalized bipyridine-based anion receptors for emission-based selective detection of dihydrogen phosphate

New cationic anion receptors, based on the use of pyrrole-substituted bipyridine and coordinated to transition metals, are described. Specifically, polypyridine-ruthenium and -rhodium cores have been functionalized to generate an anion binding site. The design was chosen to probe the influence of the pyrrole-to-pyrrole separation on anion-binding affinities and selectivities; this distance is greater in the new systems of this report (receptors 1 and 2) relative to that present in related dipyrrolyl quinoxaline based receptors 3 and 4. Solution-phase anion-binding studies, carried out by means of (1)H NMR spectroscopic titrations in [D(6)]DMSO and isothermal titration calorimetry (ITC) in DMSO, reveal that 1 and 2 bind most simple anions with substantially higher affinity than either 3 or 4. In the case of chloride anion, structural studies, carried out by means of single-crystal X-ray diffraction analyses, are consistent with the solution-phase results and reveal that receptors 1 and 2 are both able to stabilize complexes with this halide anion in the solid state.     

An Ultrafast Molecular-Rotor-Based Fluorescent Turn-On Sensor for the Perrhenate Anion in Aqueous Solution

Devising sensors for the perrhenate anion in aqueous media is extremely challenging, and has seldom been reported in the literature. Herein, we report a fluorescence turn-on sensor for the perrhenate anion in aqueous media based on the aggregation-induced emission of a popular ultrafast molecular rotor dye, Thioflavin-T. The selective response towards the perrhenate anion has been rationalized in terms of matching water affinity, with the weakly hydrated perrhenate anion spontaneously forming a contact ion pair with the weakly hydrated ultrafast molecule-rotor-based organic cation, Thioflavin-T, which in turn leads to an aggregate assembly that provides a fluorescence turn-on response towards perrhenate. The sensing response of Thioflavin-T has been found to be quite selective towards the perrhenate anion when tested against anions that are ubiquitously present in the environment, such as chloride, nitrate, and sulfate anions. The formation of self-assembled Thioflavin-T aggregates has also been investigated by time-resolved emission and temperature-dependent measurements.