Electrochemical behavior of p-tert-butyl calix[8]arene in CH2Cl2

The electrochemical behavior of p-tert-butyl calix[8]arene has been investigated by cyclic voltammetry. The result shows that there is an irreversible electrochemical oxidative wave when the potential ranges from −0.3 to 1.6 V versus Ag/0.1 M AgNO₃ in acetonitrile (Ag/Ag⁺). At 25 °C, the peak potential is ca. 1.43 V (versus Ag/Ag⁺) at scan rate of 0.05 V s⁻¹. The number of the electrons transferred in the electrochemical reaction is four. The diffusion coefficient of p-tert-butyl calix[8]arene is 2.8 × 10⁻⁵ cm² s⁻¹. The diffusion activation energy is 12.3 kJ mol⁻¹.     

Selective Extraction of Fe3+ Cation by Calixarene-Based Cyclic Ligands

Abstract

The selective liquid-liquid extraction of Fe³⁺ cation from the aqueous phase to the organic phase was carried out by using p-tert-butylcalix[4]arene [L₁], ca-lix[4]arene [L₂], p-nitro-calix[4]arene [L₃], calix[4]arene p-sulfonic acid [L₄], p-(diethylamino)methylcalixt4]arene [L₅], tetramethyl-p-tert-butylcalix[4]arene tet-raketone [L₆], 25,27-dimethyl-26,28-dihydroxy-p-tert-butylcalix[4]arene diketone [L₇], calix[4]arene-bearing dioxime group on the lower rim [L₈], and a monooxime [L₉]. The effect of varying pH upon the extraction ability of calixarenes substituted with electron-donating and electron-withdrawing groups at their p-position was examined. Observed results were compared with those found for unsubstituted calix[4]arene.     

Synthesis and characterization of novel octa-arm star-block thermoplastic elastomers consisting of poly (p-chlorostyrene-b-isobutylene) arms radiating from a calix[8]arene core

The synthesis and characterization of novel octa-arm star-blocks consisting of poly(p-chlorostyrene-b-isobutylene) (PpClSt-b-PIB) arms radiating from a calix[8]arene (C8) core are described. The synthesis was accomplished by living isobutylene (IB) polymerization induced by a novel octafunctional calix[8]arene derived initiator 1, followed by addition and living polymerization of p-chlorostyrene (pClSt). This sequential block copolymerization method allowed for precise molecular weight control of both polymeric blocks and thus gave rise to star-block thermoplastic elastomers (TPE) with an outstanding combination of mechanical and thermal properties, i.e., high tensile strengths (22 – 27 MPa) and elongations (∼500 %). Differential scanning calorimetry (DSC) indicated microphase separation into glassy PpClSt (T_g= 129°C) and rubbery PIB (T_g=−66°C) domains, and transmission electron microscopy (TEM) indicated that the PpClSt domains are dispersed in the PIB matrix. Received: 1 April 1998/Revised version: 1 June 1998/Accepted: 2 June 1998     

Molecular composites obtained by polyaniline synthesis in the presence of p‐octasulfonated calixarene macrocycle

Polyaniline (PANI) molecular composites were synthesized by chemical oxidative polymerization of the aniline and aniline dimer, N‐phenyl‐1,4‐phenylendiamine, in the presence of a macrocycle, calix[8]arene p‐octasulfonic acid (C8S), using ammonium peroxidisulfate as oxidant. The macrocycle has acted both as acid dopant and surfactant to obtain processable PANI‐ES. The PANI/calix[8]arene p‐octasulfonic acid composite was also obtained by a simple doping of PANI emeraldine base form with calix[8]arene sulfonic acid. The structure of materials was confirmed by Fourier transform infrared, UV–vis and nuclear magnetic resonance spectroscopy. All synthesized composite materials are amorphous and soluble in chloroform, dimethylsulfoxide, NMP, showing excellent solution‐processing properties combined with electrical conductivity. Cyclic voltammetry evidenced a good electroactivity for the composite films. Dielectric properties (dielectric constant and dielectric losses) were determined and are comparable with those of other PANI/ionic acid polymer composites. Preliminary studies have evidenced a high dielectric constant (10⁴ at 100 Hz) and electrical conductivity of 6 × 10^?3 S/cm for PANI composites. From sulfur elemental analysis of the PANI/calixarene, it results that the content in macrocycle is ～30% (weight). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Calixarenes 30. Calixquinones

Chlorine dioxide and thallium trifluoroacetate are shown to be useful reagents for the preparation of calixquinones. p-H-Calix[4]arene( 1a ),p-H-calix[5]arene ( 1b ), and p-H-calix[6]arene ( 1c ) are oxidized in modest yields by ClO₂ to the fully quinonoid compounds calix[4]tetraquinone ( 2a ), calix[5]pentaquinone ( 2b ), and calix[6]hexaquinone ( 2c ), respectively. Although Tl(OCOF₃)₃ is less effective for the oxidation of 1a-c , it proves to be the reagent of choice for converting partially etherified or esterified calixarenes carrying p-tert-butyl groups directly to partially quinonoid calixarenes. Thus, monosubstituted calix[4]arenes yield triquinones; disubstituted calix[4]arenes yield diquinones; trisubstituted calix[4]arenes yield monquinones; and tetrasubstituted calix[6]arenes yield diquinones. The structures of the calixquinones have been established by elemental analysis, ¹H NMR spectroscopy, mass spectroscopy, and in the case of 2c by X-ray crystallography. Since the starting materials are readily accessible, the calixquinones become easily available compounds for further study.     

Synthesis,extraction, and adsorption properties of calix[4]arene‐poly(ethylene‐glycol) crosslinked polymer

Novel calix[4]arene‐poly(ethylene glycol) crosslinked polymer (CCP) has been synthesized by the polycondensation reaction between a p‐tert‐butylcalix[4]arene derivative and dihydroxyl capped poly(ethylene glycol) (DHPEG, M_n = 1000) catalyzed by neodymium tosylate. The hydrogel, consisted of 66.9% water and 33.1% CCP, can selectively extract aromatic organic molecules from aqueous solution according to the diameter of the guest molecules, which infers that the diameter of the calix[4]arene cavity is about 5.4 Å and the conformation of calix[4]arene units altered from cone conformation to 1,3‐alternate conformation during the polycondensation reaction. Furthermore, CCP can also adsorb naphthalene from gas phase, showing much higher capacity than active carbon does, which may have some potential applications in the field of separation and environment protection. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrocatalytic oxidation of glutathione at carbon paste electrode modified with 2,7-<Emphasis Type="Italic">bis</Emphasis> (ferrocenyl ethyl) fluoren-9-one: application as a voltammetric sensor

Electrooxidation of glutathione (GSH) was studied at the surface of 2,7-bis (ferrocenyl ethyl) fluoren-9-one modified carbon paste electrode (2,7-BFEFMCPE). Cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV) were used to investigate the suitability of this ferrocene derivative as a mediator for the electrocatalytic oxidation of GSH in aqueous solutions with various pH. Results showed that pH 7.00 is the most suitable pH for this purpose. At the optimum pH, the oxidation of GSH at the surface of this modified electrode occurs at a potential of about 0.410 V versus Ag|AgCl|KCl_sat. The kinetic parameters such as electron transfer coefficient, α = 0.61, and rate constant for the chemical reaction between GSH and redox site in 2,7-BFEFMCPE, k _h = 1.73 × 10³ cm³ mol⁻¹ s⁻¹, were also determined using electrochemical approaches. Also, the apparent diffusion coefficient, D _app, for GSH was found to be 5.0 × 10⁻⁵ cm² s⁻¹ in aqueous buffered solution. The electrocatalytic oxidation peak current of GSH showed a linear dependence on the glutathione concentration, and linear calibration curves were obtained in the ranges of 5.2 × 10⁻⁵ M to 4.1 × 10⁻³ M and 9.2 × 10⁻⁷ M to 1.1 × 10⁻⁵ M with cyclic voltammetry and differential pulse voltammetry methods, respectively. The detection limits (3σ) were determined as 1.4 × 10⁻⁵ M and 5.1 × 10⁻⁷ M for the CV and DPV methods, respectively. This method was also examined as a selective, simple, and precise new method for voltammetric determination of GSH in real sample such as hemolysed erythrocyte.     

Redox and transport behaviors of Cu(I) ions in TMHA-Tf<Subscript>2</Subscript>N ionic liquid solution

The redox and transport behavior of monovalent copper species in an ammonium imide-type ionic liquid, trimethyl-n-hexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHA-Tf₂N) were examined with a micro-disc electrode to clarify its applicability to, for example, electroplating. It was found that the diffusion coefficient of Cu(I) ions in TMHA-Tf₂N containing 12 mmol dm⁻³ Cu(I) ions was 1.2 × 10⁻⁶ cm² s⁻¹ and the redox potential of Cu(I)/Cu was in the potential range 0.1–0.2 V vs. I ⁻/I ₃⁻ at 50 °C. The diffusion coefficient was one order smaller than that of Cu(II) ions in aqueous solution due to the high viscosity of the ionic liquid. The diffusion coefficient of Cu(I) ion increased with rising temperature and was 1.0 × 10⁻⁵ cm² s⁻¹ at 112 °C, which was comparable to that of Cu(II) ions in aqueous CuSO₄ solutions at ambient temperature. This is accounted for by the drastic decrease in the viscosity of the ionic liquid solution with increasing temperature. The activation energy of diffusion was estimated to be 39 kJ mol⁻¹ in the ionic liquid solution.     

Influence of concentrations of copper,levelling agents and temperature on the diffusion coefficient of cupric ions in industrial electro-refining electrolytes

Few data are available for diffusion coefficients measured in industrial copper electrolytes. In the present work the influence of copper concentration (19.9–58.1 g dm⁻³), temperature (20–60°C) and concentrations levelling agents i.e. animal glue (0–5 mg dm⁻³) and thiourea (0–5 mg dm⁻³) on diffusion coefficients of copper was studied in industrial copper refinery electrolytes. Chronoamperometry at ultramicroelectrodes was used as an electrochemical technique. Apparent bulk diffusion coefficients were calculated on the basis of the theory of electrochemical nucleation on disc-shaped ultramicroelectrodes. Increasing copper concentration decreased the apparent bulk diffusion coefficient of copper and diffusion coefficients followed the Arrhenius temperature relationship. The experimental activation energy was 26.8 kJ mol⁻¹. The influence of levelling agents on diffusion coefficients was not strong in the studied concentration range of animal glue and thiourea.     

A Novel Dinucleating Ligand-Containing Hexabenzimidazoles and Its Dinuclear Zinc Complex Bridged by a Carboxylate Group for the Hydrolysis of 2-Hydroxypropyl-p-nitrophenyl phosphate

A dinuclear zinc(II) complex with the ligand bis{tris[2-(1-methylbenzimidazole-2-yl)ethyl]-methylamine}nitrilotriacetic acid sodium salt, L, was synthesized and characterized. Complex formation of L with Zn²⁺ in aqueous acetone was studied by Zn²⁺ titration using ¹H NMR and UV–vis spectroscopies. Analysis of the titration data indicates the formation of a dizinc complex. The ν_as(COO⁻) and ν_s(COO⁻) stretches were observed at 1572 and 1450 cm⁻¹, respectively. The low separation of the stretches, Δ_exp = 115 cm⁻¹, is an indication of chelating coordination of the carboxylate group between the two zinc(II) ions. The catalytic activity of [LZn₂]³⁺ 1, as a model for phosphatase that catalyze chemical transformation of phosphate ester, in the hydrolysis of the RNA model, 2-hydroxypropyl p-nitrophenyl phosphate, was examined in aqueous acetone buffer solution, pH 7.0–9.5. The mechanism of the catalytic hydrolysis suggests that the rate of acceleration is due to what is called double Lewis acid activation.     

Extraction of Pb2+ with p-tert-butylcalix [4]-, [5]-, [6]Arene Carboxylic Acid Ligands and their Monomeric Counterpart: A Thermodynamic Approach

Studies on extraction equilibrium constants at different temperatures and thermodynamic parameters of solvent extraction of Pb²⁺ ion with carboxylic acid derivatives of different ring size calixarenes and structure related monomeric compound have been carried out. The extraction equilibrium constants corresponding to calix[n]arene (n?=?4, 5, 6) derivatives decrease in the order [5]arene > [6]arene > [4]arene. In all cases, the complexation process is primarily enthalpy driven. The favorable enthalpic contribution for extraction of Pb²⁺ is in the order hexamer ≈ monomer > tetramer > pentamer. However, the unfavorable entropic loss follows the order: monomer > hexamer > tetramer > pentamer. Overall stability of the host-guest complex is the function of entropy-enthalpy compensation and the free energy of complexation is minimum for the pentamer, followed by tetramer ≈ hexamer and monomer. Although the carboxylic acid derivative of calix[4]arene is more preorganized than the calix[5]arene derivative, extraction of Pb²⁺ ion with the tetramer passes through greater entropic loss than that with the pentamer and the degree of preorganization of calix[4]arene derivative is far from perfect for the complexation and extraction of Pb²⁺ ion. As compared to tetrameric and hexameric counterparts, the structural features of the carboxylic acid derivative of calix[5]arene prior to complexation contribute much to interact with the Pb²⁺ ion and form a thermodynamically stable complex. Supplementary materials are available for this article. Go to the publisher's online edition of Solvent Extraction and Ion Exchange to view the supplemental file.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

Scale-up precision synthesis of octa-arm polyisobutylene stars

Summary This paper concerns the scale-up precision synthesis of octa-arm polyisobutylene (PIB) stars. Specifically, we have optimized to the 100–200 g scale the preparation of star polymers consisting of eight PIB arms radiating from a calix[8]arene core. The synthesis strategy involved the use of a calix[8]arene fitted with eight p-C(CH₃)₂OCH₃ groups as the initiator in conjunction with mixed BCl₃/TiCl₄ coinitiators in hexanes/methyl chloride solvent systems at − 80 °C. Various possible side-reactions have been identified and means for their suppression/elimination were developed. Received: 29 December 1999/Revised version: 22 May 2000/Accepted: 22 May 2000     

Selective determination of uric acid in the presence of ascorbic acid at poly(<Emphasis Type="Italic">p</Emphasis>-aminobenzene sulfonic acid)-modified glassy carbon electrode

The electrocatalytic behavior of uric acid has been investigated with a glassy carbon electrode modified with p-aminobenzene sulfonic acid through electrochemical polymerization. This resulting electrode shows an excellent electrocatalytic response to uric acid and ascorbic acid, with a peak-to-peak separation of 0.267 V in a 0.1 mol L⁻¹ phosphate buffer solution (PBS) at pH 7.0. These results indicate that the proposed electrode can eliminate the serious interference of ascorbic acid, which coexists with uric acid in body fluids. Differential pulse voltammetry (DPV) was used for detecting uric acid with selectivity and sensitivity. The anodic peak current of uric acid was proportional to its concentration in the range of 1.2 × 10⁻⁷–8.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁸ mol L⁻¹. The proposed method has been applied with satisfactory results to the determination of uric acid in human urine without any pretreatment.     

The stability of sodium hypochlorite in the presence of surfactants

Studies were made on the stability of NaOCl at 40°C in the presence of sodium alkanesulfonate or alkylarenesulfonate anionic surfactants, and in the presence of a nonionic surfactant,N-octylpyrrolidinone. The results were compared with NaOCl stability in the absence of additives and in the presence of nonsurfactant short-chain sodium alkylbenzenesulfonates. The data indicated that the rate of NaOCl loss is greatly dependent upon the pH of the solution, even at alkaline pHs. At initial pHs below 11, in the absence of additive, there is significant disproportionation of OCl⁻ to ClO ₃ ⁻ , accompanied by decrease in the pH of the solution, within a period of several days. Even at an initial pH of 11.3, in the presence of the surfactants investigated, there is significant disproportionation of OCl⁻ and decrease in the pH of the solution in the first several days. When the initial pH of the solution is 13.5, there is no significant decrease in pH of the solution for at least two months in the presence of the surfactants studied. NaOCl stability in the presence of surfactant decreases in the order: sodium linear alkanesulfonate > sodium linear alkyldiphenylethersulfonate > sodium linear alkylbenzenesulfonate >>N-octylpyrrolidinone. Stability was greater in the presence of linear alkylarenesulfonates than in the presence of branched alkylarenesulfonates. It is suggested that the differences in stability observed are due to the greater ease of oxidation of tertiary carbon atoms compared to primary or secondary atoms.     

New polyisobutylene stars XI. Synthesis and characterization of allyl-telechelic octa-arm polyisobutylene stars

The synthesis and characterization of a novel star comprising eight allyl-terminated polyisobutylene (PIB) arms radiating from a calix[8]arene core is described. The synthesis was accomplished by a core-first method, by inducing the living polymerization of isobutylene (IB) by a suitably functionalized calix[8]arene initiator (1) in conjunction with BCl₃-TiCl₄ coinitiators, and terminating the growth of the living PIB^⊕ arms by allyltrimethylsilane. The relative concentrations of BCl₃ and TiCl₄ are critical for the synthesis of well-defined 8-arm stars. Characterization of the products (which included triple detector GPC studies and ¹H NMR spectroscopy) indicated quantitative allylation. A mechanism which summarizes the experimental observations is proposed. Received: 17 July 1997/Revised version: 11 September 1997/Accepted: 19 September 1997     

Synthesis and characterization of calix[4]arene-based copolyethers and polyurethanes. Ionophoric properties and extraction abilities towards metal cations of polymeric calix[4]arene urethanes

Copolyethers and polyurethanes containing lower and upper rim calix[4]arene units in the fixed cone conformation were prepared in good yield by polycondensation reactions of distal calix[4]arene diols with bisphenol-A/dibromomethane and 2,4-tolylendiisocyanate (TDI), respectively. In a similar way were prepared calix[4]arene-crown-5 and -crown-6 polyurethanes in the fixed 1,3-alternate conformation by condensation of TDI with lower rim calixcrown-5 and calixcrown-6 diols. However, the poor solubility in common organic solvents of the copolyether derivatives (M_w=11,100-11,600 g/mol) hampered further studies on their ionophoric properties. Aiming to obtain model compounds for the investigation of both extraction abilities and ionophoric properties of the polyurethane materials, several bis-urethanes were also synthesized by reaction of the calix[4]arene diols with p-tolylisocyanate (TI). The extraction ability measurements of monomeric and polymeric calix[4]arene urethanes (M_w=12,300-83,500 g/mol) towards alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and Ag⁺showed a remarkable efficiency and selectivity of calixcrown-6 polyurethane toward Rb⁺, Cs⁺and Ag⁺.     

Mixed 8-oxyquinolinecalix[4]arene/phenanthroline receptors as luminescence sensors for zinc(II) ions

The luminescence behavior of bis-(8-oxyquinoline)calix[4]arene is practically centered on the quinoline chromophore, but involves efficient energy transfer from the calix[4]arene moiety. In the presence of Zn²⁺ ions, coordination of the quinoline groups is observed, leading to characteristic changes in the absorption, fluorescence and NMR spectra. Energy transfer from the calix[4]arene moiety is precluded by the coordination of the Zn²⁺ ions. In the resulting complex, a significant decrease in the emission quantum yields takes place. However, by incorporating an additional batho-phenanthroline ligand, a great emission enhancement has been detected, revealing the occurrence of synergistic effects in the bis-(8-oxyquinoline)calix[4]arene(batho-phenanthroline)zinc(II) complex.     

α-Sulfonated fatty acid esters: I. Structural effects of sodium α-sulfonated fatty acid higher alcohol esters on surface-active properties and emulsification ability

The surface-active properties and emulsification ability of sodium α-sulfonated fatty acid esters, C_mH_2m+1CH-(SO₃Na)COOC_nH_2n+1, were studied as a function of the hydrophobic alkyl chainlength in the fatty acid (m=8−16) and the alcohol (n=8−18). As a result, it was discovered that sodium α-sulfonated fatty acid esters have a structural effect on the Krafft point different from that of amphiphiles with short alkyl chains. Moreover, some of the α-sulfonated fatty acid esters have quite low interfacial tensions, as well as non-foaming properties, which depend upon the total (m+n) number of carbon atoms in the alkyl chains.     

Highly selective and sensitive Th<Superscript>4+</Superscript>-PVC-based membrane sensor based on 2-(diphenylphosphorothioyl)-<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-diphenylacetamide

A Th⁴⁺ ion-selective membrane sensor was fabricated from poly (vinyl chloride) (PVC) matrix membrane containing 2-(diphenylphosphorothioyl)-N′,N′-diphenyl acetamide (DPTD) as a neutral carrier, potassium tetrakis (p-chlorophenyl) borate (KTpClPB) as anionic excluder and o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. The effects of the membrane composition, pH and additive anionic influence on the response properties were investigated. The sensor, comprising 30% PVC, 63% solvent mediator, 4% ionophore and 3% anionic additive demonstrates the best potentiometric response characteristics. It displays Nernstian behavior (15.2 ± 0.5 mV per decade) over the concentration range 1.0 × 10⁻²–1.0 × 10⁻⁶ M. The detection limit of the electrode is 6.3 × 10⁻⁷ M (∼140 ng/ml). The response time of the electrode is 30 s .The sensor can be used in the pH range 3.0–9.0 for about 6 weeks. The membrane sensor was used as an indicator electrode in the potentiometric titration of Th⁴⁺ ions with EDTA. It was successfully applied to the determination of thorium ions in binary mixture.