A TTF–TCNQ Electrode as a Voltammetric Analogue of an Ion‐Selective Electrode

A TTF‐TCNQ/PVC composite electrode is proposed as a voltammetric cation and anion sensor. The electrode relies on the principle that, during redox processes involving the TCNQ^0/? couple for cations and the TTF^+/0 couple for anions, electrolyte ions are included into lattice sites in the charge neutralization process. This voltammetric ion‐sensor provides results that are similar to those of sensors based on two electrodes (viz. one modified with TCNQ for cations and another modified with TTF for anions) but with some practical advantages over them.     

Hydrogen-Bonding Ionophores for Inorganic Anions and Nucleotides and Their Application in Chemical Sensors

The potential and limits of hydrogen-bonding ionophores and their use in chemical sensors are discussed. Several hydrogen-bonding bis-thiourea ionophores have been found to complex inorganic anions, among them most strongly H2PO4-. Using such ionophores, ion-selective electrodes for chloride and sulfate have been developed. Furthermore, hosts that bind nucleotides with up to five hydrogen bonds have been synthesized. They have been applied in nucleotide selective electrodes, optodes and voltammetric sensors mimicking ion channels.     

Anion-selective interaction and colorimeter by an optical metalloreceptor based on ruthenium(II) 2,2'-biimidazole: hydrogen bonding and proton transfer

A new anion sensor [Ru(bpy)2(H2biim)](PF6)2 (1) (bpy = 2,2'-bipyridine and H2biim = 2,2'-biimidazole) has been developed, in which the Ru(II)-bpy moiety acts as a chromophore and the H2biim ligand as an anion receptor via hydrogen bonding. A systematic investigation shows that 1 is an eligible sensor for various anions. It donates protons for hydrogen bonding to Cl-, Br-, I-, NO3-, HSO4-, H2PO4-, and OAc- anions and further actualizes monoproton transfer to the OAc- anion, changing color from yellow to orange brown. The fluoride ion has a high affinity toward the N-H group of the H2biim ligand for proton transfer, rather than hydrogen bonding, because of the formation of the highly stable HF2- anion, resulting in stepwise deprotonation of the two N-H fragments. These processes are signaled by vivid color changes from yellow to orange brown and then to violet because of second-sphere donor-acceptor interactions between Ru(II)-H2biim and the anions. The significant color changes can be distinguished visually. The processes are not only determined by the basicity of anion but also by the strength of hydrogen bonding and the stability of the anion-receptor complexes. The design strategy and remarkable photophysical properties of sensor 1 help to extend the development of anion sensors.     

Anion detection by aggregation-induced enhanced emission (AIEE) of urea-functionalized tetraphenylethylenes

Substituted tetraphenylethylenes (TPEs) have been prepared that feature four alkyl or aryl urea groups arrayed along the periphery. Exposure of these TPEs to monovalent anions (halide, carboxylate, nitrate, and azide) resulted in enhanced fluorescence emission attributed to aggregation of the TPE molecules via urea-anion hydrogen bonding. Emission enhancement correlated with anion basicity, with fluoride ion eliciting the largest fluorescence response. Increased fluorescence emission could also be detected visually in solutions viewed under UV light. This study demonstrates the feasibility of TPE-based fluorescent anion sensors/detectors, and it is envisioned that additional design modifications may afford anion-selective fluorescent sensors.     

Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution

Ion pair speciation of ionic liquids(ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR(FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic(MD) simulation and nuclear magnetic resonance hydrogen spectroscopy(~1H NMR) to investigate ion pairs of aprotic ILs [Bmim][NO_3], [BuPy][NO_3], [Pyr_(14)][NO_3], [PP_(14)][NO_3] and [Bu-choline][NO_3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory(DFT) calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction(say 0.80 for [BuPy][NO3]). When water content was increased to a critical mole fraction of water(say 0.83 for [BuPy][NO3]), the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions(fully hydrated cations or anions). The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions(fully hydrated ion) were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and ~1H NMR results support the conclusion drawn from FIR spectra investigations.     

Functionalized carbon electrodes for pH determination

The derivatization of carbon materials has allowed electrochemists to develop electrodes for pH measurements that offer distinct advantages compared to other common methods for determining pH in solutions. In this report, an overview on recent work on the different derivatization strategies leading to potentiometric, amperometric, or voltammetric pH sensors is given. The topic is subdivided into five main categories: (1) chemical modification, (2) covalent bonding, (3) physical adsorption, (4) film formation, and (5) composite electrodes.     

Ion transfer voltammetry of amino acids with an all-solid-state ion-selective electrode for non-destructive phenylalanine sensing

Amino acids such as phenylalanine (Phe) are key building blocks of proteins and other biomolecules. Although recent advancements in electrochemical sensors have enabled the rapid detection of Phe, these sensors are often destructive as they irreversibly oxidise Phe. In addition, most of them rely on biorecognition elements, which suffer from limited stability at ambient conditions and sensitivity towards environmental fluctuations. Herein, we report the first example of ion transfer voltammetry of Phe using an all-solid-state ion-selective electrode (ISE). The reversibility of this technique enables both the sensor and the Phe sample to be reused. The optimal voltammetric ISE (VISE) exhibits near Nernstian response (56.8 mV/decade) towards Phe and selectivity against amino acids of all classes (hydrophobic, hydrophilic and charged). Voltammetric interrogation of the ISE significantly enhances sensitivity, linear range, selectivity, and stability as compared to traditional open circuit potential measurements. Phe levels in a commercial nutritional supplement and drinking waters were determined to demonstrate the viability of our sensor in real life applications. This proof-of-concept can be applied to develop VISEs for other amino acids and biological ions for healthcare and nutrition sensing.     

N-硝基苯基吡咯酰胺对阴离子识别研究

合成了2个N-硝基苯基吡咯酰胺阴离子识别主体. 通过X射线单晶衍射确定了间位硝基取代物的结构, 氢键及π-π相互作用在该化合物的组装过程中起到了决定性的作用. 利用UV-Vis光谱研究了这两个主体对常见无机阴离子的识别, 结果表明， 它们不仅对F-和H2PO4-离子有比较强的识别能力, 而且在识别发生时还伴随着显著的颜色变化, 因此这两个化合物都可作为阴离子的比色传感器.     

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.     

目视法检测阴离子用显色剂的研究进展

评述了以超分子化学分子识别为基础发展起来的新型阴离子目视显色剂,内容主要包括显色剂对选择性阴离子的显色属性以及显色属性和显色剂结构的关系.     

Anion-aromatic bonding: a case for anion recognition by pi-acidic rings

The basis for unprecedented noncovalent bonding between anions and the aryl centroid of electron-deficient aromatic rings has been demonstrated by an ab initio study of the interaction between 1,3,5-triazine and the fluoride, chloride, and azide ion at the MP2 level of theory. Minima are also located corresponding to C[bond]H...X(-) hydrogen bonding, reactive complexes for nucleophilic attack on the triazine ring, and pi-stacking interactions (with azide). Trifluoro-1,3,5-triazine also participates in aryl centroid complexation and forms nucleophilic reactive complexes with anions. This novel mode of bonding suggests the development of new cyclophane-type receptors for the recognition of anions.     

Optical sensing based on analyte recognition by enzymes,carriers and molecular interactions

Despite the tremendous variety of methods suitable for sensing applications, we face the fact that chemical sensors displaying sensitivity, selectivity and reversibility are still scarce and are mostly confined to low-molecular-weight species. Obviously, it is not the lack of optical (or other) transduction methods that limit the performance of present day sensor desingns, but rather the insufficient selectivity of the recognition process, particularly in the field of sensors for organic and bioorganic species. The use of enzymes, ion carriers and natural or synthetic receptor/carriers which can under go specific interactions with the species to be recognized (such as through hydrogen bonding or charge-transfer interaction) can result in specific recognition and, consequently, sensing. Examples for optical sensing schemes for clinically or biologically important species including enzyme substrates, metabolites, drugs, alkali and ammonium ions and other will be given. In enzyme-based sensors various options exist: depending on which species is immobilized, assays for substrates (such as glucose, ethanol, lactate or creatine), enzymes (such as esterases) or inhibitors (such as organophosphates) can be designed. In addition, the intrinsic optical properties of certain enzymes, coenzymes or metabolites can be utilized for sensing purposes, a fact that presents an interesting alternative to enzyme sensors with chemical transducers.Notwithstanding the selectivity of biocatalytic sensors, their stability and sensitivity is moderate. Bioorganic synthetic molecules which can recognize and reversibly bind other species offer an attractive alternative, particularly in terms of stability. However, quite a different situation is found in such cases because receptors, in contrast to enzymes, do not “digest” their substrates. Hence, while the steady-state response in enzyme-based sensors is a result of kinetic equilibration, substrate binding in non-metabolizing receptors results in thermodynamic equilibration. However, most existing receptors (except antibodies) lack the unique specificity of enzymes. On the other side, new bioorganic molecules and stable receptor/carriers along with polymer materials of proper permeation selectivity can help to overcome current limitations of protein-based systems. Neutral ion carriers, which may be considered as ion receptors, are a useful example of sometimes highly specific recognition/carrier molecules with excellent stability. Unfortunately, no receptor /carrier molecules of similar specificity do exist yet for most other organic and clinical parameters of interest. There is an obvious need for new and stable molecules suitable for specific recognition of low-molecular weight organic species.We will report on the use of such new receptor/carrier molecules, the respective sensor materials, and how the process of recognition can be coupled to optical transduction. Such receptors/carriers also allow other kinds of discriminations: if, for instance, it is enantio-selective (i.e. preferably binds one species out of a pair of optical isomers), a fairly specific recognition of enantiomers of biogenic amines (such as some drugs and biogenic amines) will become possible. Specific examples will also be given of new types of sensors based on recognition by charge-transfer interaction, through-space interaction and hydrogen bonding, with fair specificity for thiamine, penicilline, nitrate, salicylate and cholic acids. Finally, current problems and the significant challenges for sensors research in the 1990s will be discussed.     

Voltammetric study of the transfer of fluoride ion at the nitrobenzene / water interface assisted by tetraphenylantimony.

The transfer of F- ion assisted by an organometallic complex cation tetraphenylantimony (TPhSb+) across the polarized nitrobenzene / water (NB / W) interface has been studied by means of ion-transfer voltammetry. A well-defined voltammetric wave was observed within the potential window at the NB / W interface when tetraphenylantimony tetrakis(4-chlorophenyl) borate and F- ion were present in NB and W, respectively. The voltammogram can be interpreted as being due to the reversible transfer of F- ion assisted by the formation of the TPhSbF complex through the coordination of F- to Sb atom in NB. The formal formation constant of TPhSbF in NB has been determined to be 10(1.95 +/- 0.2 M(-1). No voltammetric wave due to the TPhSb(+)-assisted transfer of other anions such as Cl-, Br, I-, NO3-, CH3COO- and H2PO4(-) ions has been observed within the potential window.     

Chromogenic anion sensors

Chromogenic sensors for anions generally consist of two parts: anion receptors and chromophores. In this review, 6 types of chromogenic anion sensors are described, namely, NH-based hydrogen bonding, Lewis acid, metal-ion template, transition metal complexes, chromogenic guest displacement and chromoreactands. The first 4 types possess anion receptors attached directly to the chromophores while the guest displacement techniques employ indicators as the ones that were replaced by specific anions. The last type has emerged recently and uses specific reactions between chromogenic hosts or indicators and particular anions to cause dramatic colour changes.     

Thiazole-based chemosensor III: synthesis and fluorescence sensing of CH3CO2 based on inhibition of ESIPT

Novel fluorogenic sensors based on urea derivative of 2-(2′-aminophenyl)-4-phenylthiazole (4 and 5) were prepared and used for recognition of anions with similar basicity and surface charge density. Chemosensor 4 was found to be highly selective to acetate ion over other anions. The selectivity was related to the structure matching between the host and the guest. The evaluation of the chemosensors’ interaction with anions was performed by UV-vis and fluorescence titration. This acetate binding affinity was further tuned by varying the acidity of the N-H proton of the urea moiety in chemosensor 5.     

Novel Dicyanoargentate Polymeric Membrane Sensors for Selective Determination of Cyanide Ions

The construction and general performance characteristics of three novel potentiometric PVC membrane sensors responsive to dicyanoargentate anion are described. The sensors are based on the use of magnesium(II)‐ and iron(II)‐phthalocyanines as neutral ionophores and iron(II)‐bathophenanthroline dicyanoargentate ion‐pair complex as an ion exchanger in plasticized PVC matrices. These sensors exhibit fast, stable and near‐Nernstian response (54–59 mV/decade) for the singly charged dicyanoargentate anion over the concentration range 1×10^?2–5.8×10^?6 M. Potentiometric responses of sensors based on metal phthalocyanines and iron(II)‐bathophenanthroline are stable over the pH ranges 5–7 and 5–12, respectively. The selectivity of the sensors are fairly good over most common anions. Use of the sensors for potentiometric determination of microgram quantities of cyanide ion after conversion into dicyanoargentate anions shows an average recovery of 99.5% and a mean standard deviation of ±0.5%. Determination of cyanide ions in some exhausted electroplating bath samples gives results that compare favourably well with data obtained using the solid‐state cyanide electrode.     

Selective silver ion transfer voltammetry at the polarised liquid/liquid interface

Transfer of silver ions across the water/1,2-dichloroethane interface was studied by cyclic voltammetry (CV). In the absence of added neutral ionophore, Ag+ transferred across the interface when the organic phase contained either tetraphenylborate or tetrakis(4-chloro)phenylborate anions, but this transfer was not possible in the presence of organic phase hexafluorophosphate or perchlorate anions. The ion transfer processes observed were independent of the nature of the organic phase cation. The CV in the presence of tetraphenylborate exhibited a shape consistent with an ion transfer followed by chemical reaction; the rate constant for the following chemical reaction was 0.016 s(-1). In the presence of tetrakis(4-chloro)phenylborate, a return peak equivalent in magnitude to the forward peak was observed, indicative of a simple ion transfer reaction uncomplicated by accompanying chemical reactions. The selectivity of the transfer was assessed with respect to other metal cations: no transfers for copper, cadmium, lead, bismuth, cobalt, nickel, palladium or zinc were observed. The selectivity of the transfer suggests this can form the basis of a selective voltammetric methodology for the determination of silver ions.     

Voltammetric Properties of All‐solid State Ion‐selective Electrodes with Multiwalled Carbon Nanotubes‐poly(3‐octylthiophene‐2,5‐diyl) Nanocomposite Transducer

Voltammetric response of an all‐solid‐state ion‐selective electrode was studied on example of potassium‐selective sensor with poly(vinyl chloride) based membrane and nanocomposite transducer containing poly(3‐octylthiophene‐2,5‐diyl) and multiwalled carbon nanotubes. Factors limiting the rate of the electrochemical process and the response were discussed. The challenge in voltammetric applications of ion‐selective electrodes is thickness of the plastic membrane. It was found that although a relatively thick ion‐selective membrane was applied, as typically used in potentiometric studies, the position of the reduction peak, corresponding to potassium ions incorporation, was dependent on ions concentration in a Nernstian manner. This opens possibility of deviation from the paradigm of ultrathin membranes in voltammetric applications, thus potentially extending the sensors lifetime. The high resistance of the membrane did not affect the voltammetric characteristics, because the resistance was independent of ions concentration in solution. On the other hand, high resistance results in charge trapping effect in the solid contact material, leading to advantageous retention of the oxidized‐conducting state of the solid contact, independently of the applied electrode potential.     

Electrochemical characterisation of novel water-soluble ruthenocene complexes: An anion-dependent response

The synthesis and voltammetric exploration of water-soluble ruthenocene sulfonate is reported. ¹H and ¹³C NMR, mass spectroscopy and elemental analysis data are given to confirm the successful synthesis of this novel compound. Furthermore, it is found that the cyclic voltammetric response is strongly dependent on the size of anion in solution. Sodium toluene sulfonate is found to be capable of forming a charge-transfer complex with the oxidized ruthenocenium ion. In the presence of all other anions, follow-on reactions are observed.     

Calix[4]arenes containing thiourea and amide moieties: neutral receptors towards alpha,omega-dicarboxylate anions

Two-armed neutral anion receptors (4,5), were prepared and examined for their anion-binding ability using UV-vis, fluorescence and 1H NMR spectra in DMSO. The results of non-linear curve fitting indicate that 4 or 5 form 1 : 1 stoichiometric complexes with dicarboxylate anions by multiple hydrogen bonding interactions and the sensitivity for recognition of dicarboxylate depends on the chain length of these dicarboxylate anions. Receptors 4 and 5 have no binding ability with acetate, dihydrogen phosphate and the halogen (Cl-, Br-, I-) anions. This demonstrates that receptors 4 or 5 could be used as chemical sensors for some special dicarboxylate anions.