Determination of Tryptophan using a p-Sulfonated Calix [4,6,8]arene Modified Gold Electrode

The ability of p-sulfonated calix[n]arenes (n = 4, 6, 8) to form complexes with tryptophan was studied. The electrochemical properties of these complexes immobilized on gold surfaces were examined by cyclic voltammetry. Parameters affecting the performance of the modified electrodes including the arene concentration, scan rate, applied potential, and pH were optimized. Under the optimal conditions, the method had a linear response to tryptophan between 1 × 10^?7 M and 1 × 10^?5 M with a detection limit of 3 × 10^?8 M. The interaction of the tryptophan–p-sulfonated calix[4]arene complex was more stable than the tryptophan–p-sulfonated calix[6]arene and p-sulfonated calix[8]arene complexes. Molecular modeling calculations indicated that electrostatic interactions and structural matching effects were predominant stabilizing factors. The modified electrodes demonstrated good reproducibility and high selectivity, illustrating their effectiveness for analytical measurements.     

The electrode modified with Langmuir–Blodgett film of p-tert-butylcalix[4]arene derivatives with sulfur-containing functionalities for the determination of silver

A new voltammetric sensor, based on a new p-tert-butylcalix[4]arene derivative (TCAD) modified glassy carbon electrode (GCE) using Langmuir–Blodgett (LB) technique, was designed successfully and used for recognition and determination of Ag⁺. The π?-?A isotherms suggested that the monolayer of TCAD can coordinate with Ag⁺ at the air–water surface. Under the optimum experimental conditions, this voltammetric sensor shows a linear voltammetric response for Ag⁺ in the range of 1.0?×?10^?8?～?6.0?×?10^?6?mol?L^?1 with detection limit 5.0?×?10^?9?mol?L^?1. The high sensitivity, selectivity, and stability of this LB film modified electrode also demonstrate its practical application for a simple, rapid and economical determination of Ag⁺ in water sample.     

Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution

The investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution (I=0.1 mol L^?1 in NaClO₄; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10^?6 to 6×10^?4 mol L^?1 and nitrilotriacetate concentrations were 1×10^?4 and 5×10^?4 mol L^?1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)₂]^3?, mixed ligand complexes [FeOHNTA]^? and [Fe(OH)₂NTA]^2?, showing a one‐electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]^2?, detected above 4×10^?4 mol L^?1 of the added iron(III) ions, showing a one‐electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β₂([Fe(NTA)₂]^3?) from 24 to 27.2, log β₁([FeNTA]^?) from 8.9 to 9.2, log β₂([Fe(NTA)₂]^4?) from 11.89 to 15.7 and log β₂([Fe(OH)₂NTA]^3?) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]^?, such as: transfer coefficient (α), rate constant (k_s) and formal potential (E°') was done using a sampled DC polarography, and found to be 0.46±0.05, 1.0±0.3×10^?3 cm s^?1, and ?0.154±0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.     

Simultaneous Determination of Thallium and Lead on a Chemically Modified Electrode with Langmuir– Blodgett Film of a p‐tert‐Butylcalix[4]arene Derivative

A new voltammetric sensor, Langmuir–Blodgett (LB) film of a p‐tert‐butylcalix[4]arene derivative modified glassy carbon electrode, was designed and successfully used in simultaneous determination of Tl⁺ and Pb²⁺ by square‐wave anodic stripping voltammetry. Under the optimum experimental conditions, this newly developed sensor reveal good linear response for Tl⁺ and Pb²⁺ in the concentration range of 3×10^?8–4×10^?6 mol L^?1 and 2×10^?7–2×10^?5 mol L^?1 respectively. The detect limits are 2×10^?8 mol L^?1 for Tl⁺ and 8×10^?8 mol L^?1 for Pb²⁺. Using proposed method, Tl⁺ and Pb²⁺ in environment samples were determined with satisfactory results.     

Determination of thiabendazole in aqueous solutions using a cucurbituril-enhanced fluorescence method

The complexation of thiabendazole (TBZ) with the cucurbit[6]uril (Q[6]), cucurbit[7]uril (Q[7]) and symmetric tetramethyl-cucurbit[6]uril (TMeQ[6]) in aqueous solution has been investigated using UV–vis and fluorespectrometry. The experimental results show 1:1 host–guest inclusion complexes at pH 6.5 for all three macrocyclic hosts, and the corresponding formation constants by UV and fluorescence methods are (5.37?±?1.05)?×?10⁴?L?mol^?1 and (1.47?±?0.41)?×?10⁴?L?mol^?1 for the Q[6]-TBZ system (7.76?±?0.51)?×?10⁴?L?mol^?1 and (9.36?±?0.22)?×?10⁴?L?mol^?1 for the Q[7]-TBZ system (1.28?±?0.78)?×?10⁴?L?mol^?1 and (2.69?±?0.55)?×?10⁴?L?mol^?1 for the TMeQ[6]-TBZ system, respectively. Based on the enhancement of the fluorescence intensity of TBZ with the addition of Q[n]s in neutral media, a fluorespectrometry method for the determination of TBZ in aqueous solution in the presence of Q[n] was established. In the range of 6.0?×?10^?8?mol?L^?1–8.0?×?10^?6?mol?L^?1 a linear relationship was obtained between fluorescence intensity and TBZ concentration. The detection limit was found to be between 5.51 and 8.85?×?10^?9?mol?L^?1. The interference of coexisting ions was found to be slight. The proposed method has been successfully applied to the determination of TBZ in different aqueous solutions with satisfactory recoveries of 92–103%. The method seems to be suitable for environmental water analysis.     

Aqueous polymerization of acrylonitrile by ascorbic acid–peroxodisulfate redox system

The polymerization of acrylonitrile initiated by an ascorbic acid–peroxodisulfate redox system was studied in an aqueous solution at 35°C in the presence of air. Molecular oxygen was found to have no effect on the polymerization reaction. An increase in ionic strength slightly increased the rate. The overall rate of polymerization, R_p, showed a square dependence on [monomer] and a half-order dependence on [peroxodisulfate]. A first-order dependence on [ascorbic acid] at low concentrations (<3.0 × 10^?3 mol L^?1) followed by a decrease in R_p at higher concentrations of ascorbic acid (>3.0 × 10^?3 mol L^?1) was also noted. R_p remained unchanged up to 40°C and showed a decline thereafter. Addition of catalytic amounts of cupric ions decreased the rate whereas ferric ions were found to increase the rate. Added sulfuric acid in the range (6.0?50.0) × 10^?5 mol L^?1 decreased the R_p.     

基于四丹磺酰胺杯[4]芳烃的汞离子荧光化学传感器

我们方便地合成了上沿修饰四丹磺酰胺基团的杯[4]芳烃衍生物1,发现该化合物在含50％水的乙腈中显示出对汞离子高选择性和灵敏性的识别作用,竞争实验表明多数金属离子对其检测干扰较小。机理研究结果表明荧光萃灭源于由丹磺酰胺基团到汞离子的光致电子转移过程。另外,通过研究1和1-Hg2+的荧光衰减实验,以及对比双丹磺酰胺杯[4]芳烃2和单丹磺酰胺杯[4]芳烃3对汞离子的识别作用,发现化合物1的四丹磺酰胺基团具有很好的预组织和协同作用。化合物1对汞离子的检测限为3.41×10-6 mol·L-1,这可以使1成为一个潜在的汞离子荧光化学传感器。     

ABSORPTIVE IONOPHORES FOR Fe3+ CATION BY PARENT CALIX[n]ARENES

The absorption of Fe³⁺ ion from the aqueous phase to the solid phase was carried out by using p-tert-butyl calix[6]arene (L₁), calix[6]arene (L₂), p-tert-butyl calix[8]arene (L₃), and calix[8]arene (L₄). The effect of varying pH upon the absorption capability of parent calixarenes was examined. It was found that the compounds (L₁, L₂, L₃, and L₄) showed the highest extractability toward Fe³⁺ ion at 4.5–5.4. The calixarene L₂ shows a strong binding ability to Fe³⁺ ion. Based on the continuous variation method, calixarene L₂ formed 1:1 complex with Fe³⁺ ion.     

Novel Polymeric Membrane Sensors Based on Mn(III) Porphyrin and Co(II) Phthalocyanine Ionophores for Batch and Flow Injection Determination of Azide

Two novel potentiometric azide membrane sensors based on the use of manganese(III)porphyrin [Mn(III)P] and cobalt(II)phthalocyanine [Co(II)Pc] ionophores dispersed in plasticized poly(vinyl chloride) PVC matrix membranes are described. Under batch mode of operation, [Mn(III)P] and [Co(II)Pc] based membrane sensors display near‐ and sub‐Nernstian responses of ?56.3 and ?48.5 mV decade^?1 over the concentration ranges 1.0×10^?2?2.2×10^?5 and 1.0×10^?2?5.1×10^?5 mol L^?1 azide and detection limits of 1.5×10^?5 and 2.5×10^?5 mol L^?1, respectively. Incorporation of both membrane sensors in flow‐through tubular cell offers sensitive detectors for flow injection (FIA) determination of azide. The intrinsic characteristics of the [Mn(III)P] and [Co(II)Pc] based detectors in a low dispersion manifold show calibration slopes of ?51.2 and ?33.5 mV decade^?1 for the concentration ranges of 1.0×10^?5?1.0×10^?2 and 1.0×10^?4?1.0×10^?2 mol L^?1 azide and the detection limits are1.0×10^?5 and 3.1×10^?5 mol L^?1, respectively. The detectors are used for determining azide at an input rate of 40–60 samples per hour. The responses of the sensors are stable within ±0.9 mV for at least 8 weeks and are pH independent in the range of 3.9?6.5. No interferences are caused by most common anions normally associated with azide ion.     

Spectroscopy studies on DNA binding of two ruthenium complexes [Ru(MeIm)4(L)]2+ (L = iip and tip)

Two ruthenium(II) complexes [Ru(MeIm)₄(L)]²⁺ (L?=?2-(imidazo-4-group)-1H-imidazo-[4,5-f][1,10]phenanthroline, 2-(thiophene-2-group)-1H-imidazo[4,5-f][1,10]phenanthroline, MeIm?=?1-methylimidazole) have been synthesized according to literature and structurally characterized. The interaction of the complexes with calf thymus DNA has been explored using electronic absorption titration, competitive binding experiment, circular dichroism, thermal denaturation, and viscosity measurements. The results show that both complexes could bind DNA in a intercalation mode and the DNA-binding affinity of [Ru(MeIm)₄(tip)]²⁺ (K _b?=?(7.2?±?0.3)?×?10⁵?(mol?L^?1)^?1) is greater than that of [Ru(MeIm)₄(iip)]²⁺ (K _b?=?(6.1?±?0.2)?×?10⁵?(mol?L^?1)^?1).     

Proparacaine complexation with β‐cyclodextrin and p‐sulfonic acid calix[6]arene,as evaluated by varied 1H‐NMR approaches

This study focused on the use of NMR techniques as a tool for the investigation of complex formation between proparacaine and cyclodextrins (CDs) or p‐sulfonic acid calix[6]arene. The pH dependence of the complexation of proparacaine with β‐CD and p‐sulfonic acid calix[6]arene was studied and binding constants were determined by ¹H NMR spectroscopy [diffusion‐ordered spectroscopy (DOSY)] for the charged and uncharged forms of the local anesthetic in β‐CD and p‐sulfonic acid calix[6]arene. The stoichiometries of the complexes was determined and rotating frame Overhauser enhancement spectroscopy (ROESY) 1D experiments revealed details of the molecular insertion of proparacaine into the β‐CD and p‐sulfonic acid calix[6]arene cavities. The results unambiguously demonstrate that pH is an important factor for the development of supramolecular architectures based on β‐CD and p‐sulfonic acid calix[6]arene as the host molecules. Such host–guest complexes were investigated in view of their potential use as new therapeutic formulations, designed to increase the bioavailability and/or to decrease the systemic toxicity of proparacaine in anesthesia procedures. Copyright © 2009 John Wiley & Sons, Ltd.     

Cavity‐Shaped Ligands: Calix[4]arene‐Based Monophosphanes for Fast Suzuki–Miyaura Cross‐Coupling

Five conical calix[4]arenes that have a PPh₂ group as the sole functional group anchored at their upper rim were assessed in palladium‐catalysed cross‐coupling reactions of phenylboronic acid with aryl halides (dioxane, 100 °C, NaH). With arylbromides, remarkably high activities were obtained with the catalytic systems remaining stable for several days. The performance of the ligands is comparable to a Buchwald‐type triarylphosphane, namely, (2′‐methyl[1,1′‐biphenyl]‐2‐yl)diphenylphosphane, which in contrast to the calixarenyl phosphanes tested may display chelating behaviour in solution. With the fastest ligand, 5‐diphenylphosphanyl‐25,26,27,28‐tetra(p‐methoxy)benzyloxy‐calix[4]arene ( 8 ), the reaction turnover frequency for the arylation of 4‐bromotoluene was 321 000 versus 214 000 mol(ArBr).mol(Pd)^?1. h^?1 for the reference ligand. The calixarene ligands were also efficient in Suzuki cross‐coupling reactions with aryl chlorides. Thus, by using 1 mol % of [Pd(OAc)₂] associated with one of the phosphanes, full conversion of the deactivated arenes 4‐chloroanisole and 4‐chlorotoluene was observed after 16 h. The high performance of the calixarenyl–phosphanes in Suzuki–Miyaura coupling of aryl bromides possibly relies on their ability to stabilise a monoligand [Pd⁰L(ArBr)] species through supramolecular binding of the Pd‐bound arene inside the calixarene cavity.     

Calixarene Complexes of Anion-bridged Oligouranyl Species

The syntheses and structures of uranyl complexes of p-t-Bu-calix[6]arene (calix[6]H₆) and p-t-Bu-calix[9]arene (calix[9]H₉) are reported, further developing the role of calixarenes as 'cluster keepers'. The calix[6]arene complex, formulated as [(HO){UO₂(calix[6]H₄)(dmso)}₃H], is trinuclear and linked symmetrically by the hydroxyl O atom. The calix[9]arene complex is binuclear, with a carbonate atom bridging between the two uranyl cations to give the complex, (HNEt₃)₃[(OCO₂)(UO₂)₃(calix[9]H₄)].     

Chromium(III) Potentiometric Sensor Based on Para‐Tertiary‐Butyl Calix[4]arene

A new chromium(III) PVC membrane sensor incorporating p‐tertiary‐butyl calix[4]arene as ionophore, potassium tetrakis as additive and dibutyl phthalate (DBP) as plasticizer was constructed. The electrode exhibited an excellent potentiometric response over a wide concentration range of 1.0×10^?7–1.0×10^?1 M with a Nernstian slope of 20±0.5 mV per decade. The detection limit was 5.0×10^?8 M. The electrode showed a better performance over a pH range of 3.0–8.0, and had a short response time of about <15 s.The electrode was successfully applied to potentiometric titration of Cr (III) with EDTA and for direct determination of chromium(III) in waste water.     

Anodic Stripping Voltammetric Determination of Mercury(II) in Water Using a 4‐Tert‐Butyl‐1‐(Ethoxycarbonylmethoxy)Thiacalix[4]Arene Modified Glassy Carbon Electrode

A glassy carbon electrode coated the film of 4‐tert‐butyl‐1‐(ethoxycarbonylmethoxy)thiacalix[4]arene is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode, the modified electrode can improve the measuring sensitivity of Hg²⁺. Under the optimum experimental condition, the modified electrode in 0.1 mol L^?1 H₂SO₄ + 0.01 mol L^?1 KCl solution shows a linear voltammetric response in the range of 8.0 × 10^?9 ～ 3.0 × 10^?6 mol L^?1 with detection limit 5.0 × 10^?9 mol L^?1 for Hg²⁺. The high sensitivity, selectivity, and stability of modified electrode also prove its practical application for a simple, rapid and economical determination of Hg²⁺ in water samples.     

5,11,17,23-Tetrakis[(p-carboxyphenyl)azo]-25,26,27,28-tetra-hydroxy Calix[4]arene: Crystal Structure and pH Sensing Properties

Treatment of 5,11,17,23‐tetrakis[(p‐carboxyphenyl)azo]‐25,26,27,28‐tetrahydroxy calix[4]arene ( 2 ) with HCl in DMF or NaOH in MeOH produced 5,11,17,23‐tetrakis[(p‐carboxyphenyl)azo]‐25,26,27,28‐tetrahydroxycalix[4]‐arene·4DMF (2·4DMF) and 5,11,17,23‐tetrakis[(p‐carboxyphenylsodium)azo]‐25,26,27,28‐tetrahydroxycalix[4]‐ arene ( 3 ), respectively, which were characterized by elemental analysis, IR, UV‐vis, ¹H NMR and ¹³C NMR. An X‐ray analysis of 2·4DMF revealed that its calix[4]arene core adopts a flattened cone conformation in which opposed phenyl groups take parallel or sharply inclined positions. The intra‐ and intermolecular hydrogen‐bonding interactions and the π···π interactions form a 2D hydrogen‐bonded wavelike network. Compound 2 had a unique reversible color change in a wide pH range from 1 to 13.5 and showed interesting pH sensing properties.     

Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes

Potentiometric ion sensors have been prepared by galvanostatic electrosynthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-sulfonated calix[4]arene (C[4]S) and p-methylsulfonated calix[4]resorcarenes (R_n[4]S) with alkyl substituents of different chain length (R₁=CH₃; R₂=C₂H₅; R₃=C₆H₁₃). The bowl-shape of these doping ions makes them suitable as ionic recognition sites, and their bulky character is expected to prevent them from leaching out of the conducting polymer membrane. For comparison, sensors based on PEDOT doped with poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS) were also constructed. The resulting GC/PEDOT electrodes were conditioned in 0.01 mol L^–1 AgNO₃ and their performance as Ag⁺ ion-selective electrodes (ISEs) studied. Results reveal that selectivity and lifetime of the electrodes is affected by the doping anion structure, although all electrodes show selectivity towards Ag⁺ ions. Interaction of Ag⁺ with sulfur atoms present in the conducting polymer backbone is considered to be the main reason for this behavior. A second set of electrodes was constructed and conditioned in 0.1 mol L^–1 KCl. These electrodes were tested in chloride solutions of quaternary ammonium cations, showing that C[4]S and R₂[4]S exhibit significant sensitivity towards pyridinium.Dedicated to Professor György Horányi on the occasion of his 70th birthday in recognition of his outstanding contributions to electrochemistry     

Synthesis and electrochemical properties of calix[4]arene derivatives containing ferrocene units in the cone and 1,3-alternate conformation

Two novel calix[4]arene receptors containing ferrocene units in cone (L₁) and 1,3-alternate (L₂) conformations have been synthesized from 25,27-dihydroxy-26,28-bis[(3-aminopropyl)oxy]calix[4]arene 4 or 25,26,27,28-tetra[(3-aminopropyl)oxy]calix[4]arene 6 and ferrocenecarboxaldehyde via condensation, respectively. Their structures have been characterized by ¹H, ¹³C, APT, COSY NMR, FTIR, HSMR, and UV–vis spectral data. The electrochemical behavior of L₁ and L₂ has been investigated in the presence of F^?, Cl^?, Br^?, H₂PO₄^?, CH₃COO^? anions. Electrochemical studies show that these receptors electrochemically recognize CH₃COO^?, H₂PO₄^?, and Cl^?, anions. Using an UV–vis study, the selectivity to these anions in DMSO solution was confirmed.     

Synthesis of （p-Formylphenyl）azo Calix[4]arenes

Five novel azo calix[4]arenes were reported. The p-aminobenzaldehyde was diazotized with sodium nitrite in aqueous hydrochloride solution. Mono-, bis-, tris- and tetrakis(p-formylphenyl)azo calix[4]arenes (including proximal and distal isomers) were obtained respectively by diazo-coupling in different molar ratio to calix[4]arene(1) under pH=7.5--8.5 at 0-5℃. All (p-formylphenyl)azo calix[4]arenes were characterized by ^1H NMR, ^13C NMR, IR, MS (ESIMS) spectroscopies and elemental analysis.     

Synthesis and Rh(I)‐catalyzed polymerization of 1,3‐diphenylyne–calix[4]arene compounds: Novel conjugated,calixarene‐based polymers

The synthesis of two 1,3‐bis(4‐ethynylbenzyloxy)calix[4]arenes, 5,11,17,23‐tetrakis(1,1‐dimethylethyl)‐25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene ( 1 ) and 25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene ( 2 ), was accomplished through Sonogashira coupling of appropriate calixarene derivatives. Methods for the polymerization of these bifunctional building blocks with Rh(I) as a catalyst, leading ultimately to conjugated polymers having calix[4]arene units incorporated into the main chain, were explored. Calixarenes 1 and 2 were efficiently polymerized with rhodium‐based initiators and afforded the conjugated polymers poly{5,11,17,23‐tetrakis(1,1‐dimethylethyl)‐25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene} ( poly 1 ) and poly{25,27‐bis(4‐ethynylbenzyloxy)‐26,28‐dihydroxycalix[4]arene}. Depending on the conditions, high conversions and good yields were obtained. The effects of adding cocatalysts (NHEt₂ and/or PPh₃) were studied in connection with the number‐average molecular weight and the molecular weight distribution of the resultant polymer ( poly 1 ) and tentatively correlated with the formation of low‐molecular‐weight materials. A catalytic system containing triphenylphosphine as the sole additive ([Rh(nbd)Cl]₂; [Rh]/[PPh₃] = 0.5) proved to be the best for the polymerization of p‐tert‐butylcalixarene compound 1 . Linear polymers having high number‐average molecular weights (up to 1.1 × 10⁵ g mol^?1) with low polydispersities were produced under these conditions. For debutylated homologue 2 , its polymerization was best carried out in the absence of any added cocatalyst. A cyclopolymerization route, comprising the intramolecular ring closing of the calix[4]arene pendant ethynyl groups followed by an intermolecular propagation step, is advanced to explain the results. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7054–7070, 2006